0000950170-24-030478 | 10-K | XBRL Viewer

Stock Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock Options Valuation Assumptions Using a Black-Scholes Option Pricing Model

The assumptions used in the Black-Scholes option pricing model are as follows:


	For the Year ended December 31,
	2023	2022
Expected volatility	69.2% - 69.7%	68.7% - 70.1%
Weighted-average risk-free interest rate	3.45% - 4.22%	1.46% - 4.16%
Expected dividend yield	— %	— %
Expected term (in years)	5.5 - 6.25	5.5 - 6.25
Underlying common stock fair value	$0.92-$1.60	$1.40-$4.17

Summary of Option Activity under Plans

The following table summarizes the Company’s stock option activity during the year ended December 31, 2023:


	Number of Options			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding at January 1, 2023		9,865,734		$	10.96		7.2	$	493
Granted		3,188,150		$	1.53
Exercised		(26,166	)	$	0.61
Cancelled/Forfeited		(3,476,677	)	$	7.05
Outstanding at December 31, 2023		9,551,041		$	9.26		5.2	$	66
Vested and expected to vest at December 31, 2023		9,551,041		$	9.26		5.2	$	66
Exercisable at December 31, 2023		7,061,128		$	11.35		4.3	$	66

Summary of Company's RSU Activity

The following table summarizes the Company's RSU activity for the year ended December 31, 2023:


	Number of Restricted Stock Units			Weighted- Average Grant Date Fair Value

Outstanding at January 1, 2023		543,179		$	6.12
Granted		483,850		$	1.60
Vested		(373,519	)	$	4.86
Forfeited		(312,171	)	$	2.59
Outstanding at December 31, 2023		341,339		$	2.95

Schedule of Stock-Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options, shares purchased under the 2018 ESPP, restricted stock units and stock award modifications as follows:


	For the Year ended December 31,
	2023		2022
	(in thousands)
General and administrative	$	5,952	$	7,867
Research and development		1,372		5,187
	$	7,324	$	13,054

Stockholders' Equity - Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Equity [Abstract]
Common stock, voting rights	Each holder of outstanding shares of common stock are entitled to one vote in respect of each share.
Common stock, shares outstanding	58,017,412	57,483,910
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Net loss	$ 112,961	$ 5,005
Other comprehensive gain (loss):
Change in unrealized gain (loss) on available for sale securities, net	399	(397)
Total other comprehensive gain (loss)	399	(397)
Comprehensive loss	$ (112,562)	$ (5,402)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

5. FAIR VALUE MEASUREMENTS

The Company’s financial instruments consist of cash and cash equivalents, short-term investments, restricted cash and accounts payable. The carrying amount of cash, restricted cash and accounts payable are each considered a reasonable estimate of fair value due to the short-term maturity.

Assets measured at fair value on a recurring basis were as follows:


Description	December 31, 2023		Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Money market mutual funds	$	38,517	$	38,517	$	—	$	—
Total cash equivalents	$	38,517	$	38,517	$	—	$	—
Short-term investments:
US Treasury securities		31,818		—		31,818		—
Corporate debt securities		11,569		—		11,569		—
Total short-term investments	$	43,387	$	—	$	43,387	$	—
Total financial assets	$	81,904	$	38,517	$	43,387	$	—

Description	December 31, 2022		Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Money market mutual funds	$	33,967	$	33,967	$	—	$	—
Total cash equivalents	$	33,967	$	33,967	$	—	$	—
Short-term investments:
Commercial paper	$	57,138	$	—	$	57,138	$	—
US Treasury securities		64,825		—		64,825		—
Corporate debt securities		19,077		—		19,077		—
Total short-term investments	$	141,040	$	—	$	141,040	$	—
Total financial assets	$	175,007	$	33,967	$	141,040	$	—

Short-term securities are valued using models or other valuation methodologies that use Level 2 inputs. These models are primarily industry-standard models that consider various assumptions, including time value, yield curve, volatility factors, default rates, current market and contractual prices for the underlying financial instruments, as well as other relevant economic measures. Substantially all of these assumptions are observable in the marketplace, can be derived from observable data or are supported by observable levels at which transactions are executed in the marketplace.

There were no transfers between fair value measurement levels during the years ended December 31, 2023 and 2022.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Assets Held For Sale (Additional Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment Assets Held-for-Sale Disclosure [Abstract]
Assets Held For Sale	$ 260	$ 0

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Schedule of Assets Measured at Fair Value on Recurring Basis

Assets measured at fair value on a recurring basis were as follows:


Description	December 31, 2023		Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Money market mutual funds	$	38,517	$	38,517	$	—	$	—
Total cash equivalents	$	38,517	$	38,517	$	—	$	—
Short-term investments:
US Treasury securities		31,818		—		31,818		—
Corporate debt securities		11,569		—		11,569		—
Total short-term investments	$	43,387	$	—	$	43,387	$	—
Total financial assets	$	81,904	$	38,517	$	43,387	$	—

Description	December 31, 2022		Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Cash equivalents:
Money market mutual funds	$	33,967	$	33,967	$	—	$	—
Total cash equivalents	$	33,967	$	33,967	$	—	$	—
Short-term investments:
Commercial paper	$	57,138	$	—	$	57,138	$	—
US Treasury securities		64,825		—		64,825		—
Corporate debt securities		19,077		—		19,077		—
Total short-term investments	$	141,040	$	—	$	141,040	$	—
Total financial assets	$	175,007	$	33,967	$	141,040	$	—

Restructuring and Other Charges - Accrued Compensation and Benefits (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Restructuring and Related Activities [Abstract]
Accrued restructuring, Beginning Balance	$ 0
Expenses incurred	10,279
Payments	(5,666)
Accrued restructuring, Ending Balance	$ 4,613

Summary of Significant Accounting Policies - Impact of Adoption of Previously Reported Amounts of Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Right-of-use assets	$ 650	$ 20,563
Operating lease liabilities	1,318
Operating lease liabilities, net of current portion	$ 1,318	$ 1,561

Equity Method Investment (Additional Information) (Details) - USD ($) $ in Thousands		12 Months Ended
	Mar. 10, 2022	Dec. 31, 2023	Dec. 31, 2022	Mar. 11, 2022
Schedule of Equity Method Investments [Line Items]
Equity method investment cash consideration		$ 0	$ 25,814
Equity method investment, temporary impairment		3,800
Gain loss on sale of business	$ 131,249	0	$ 131,249
Carrying value of the equity method investment		0
Maximum
Schedule of Equity Method Investments [Line Items]
Equity method investment cash consideration		74,100
OXB Solutions
Schedule of Equity Method Investments [Line Items]
Transferred units	130,000
Equity method investment, description of principal activities	Homology to sell and transfer to OXB, and (ii) Homology will have an option to cause OXB to purchase from Homology, in each case all of Homology's equity ownership interest in OXB (US) LLC at a price equal to 5.5 times the revenue for the immediately preceding 12-month period (together, the "Options"), subject to a maximum amount of $74.1 million.
Impairment Charge		$ 119,100
Equity method investments, ownership description		The valuation included certain subjective assumptions including discounts for lack of control and marketability given the consideration paid for OXB (US) LLC was for a controlling interest in the entity and the Company owns a noncontrolling interest.
Fair value of investment	$ 31,200
Gain loss on sale of business	$ 131,200
OXB Solutions \| Equity Unit Purchase Agreements
Schedule of Equity Method Investments [Line Items]
Units issued in exchange for transferred assets	175,000
Equity method investment, ownership percentage	100.00%
Contributed cash				$ 50,000
Additional units issued	50,000
Homology \| Equity Unit Purchase Agreements
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	20.00%
Ownership interests, units	45,000
Oxb \| Equity Unit Purchase Agreements
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	80.00%
Transferred units, value	$ 130,000
Ownership interests, units	180,000

Accrued Expenses and Other Liabilities - Schedule of Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued compensation and benefits	$ 5,755	$ 5,953
Accrued research and development expenses	0	9,447
Accrued professional fees	941	1,052
Accrued other	325	2,263
Total accrued expenses and other liabilities	$ 7,021	$ 18,715

Stock Incentive Plans - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Jan. 01, 2024 shares	Mar. 31, 2018 shares	Dec. 31, 2023 USD ($) Employee $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate proceeds from shares issued under the plan \| $			$ 168	$ 595
Stock-based compensation \| $			$ 7,324	$ 13,054
Weighted-average grant date fair value per share for options granted \| $ / shares			$ 1.01	$ 1.68
Total compensation cost reversed \| $			$ 400	$ 100
Compensation cost \| $				800
Incremental compensation cost \| $			$ 100
Incremental compensation cost related to vested awards \| $				$ 400
Number of Employees Terminated \| Employee			86
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total compensation cost reversed \| $			$ 500
Compensation cost \| $			$ 200
Number of stock award and exercise vested option to transferred employees \| shares			1,000,000
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock award and exercise vested option to transferred employees \| shares			6,300,000
OXB Solutions \| Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock award and exercise vested option to transferred employees \| shares			100,000
OXB Solutions \| Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock award and exercise vested option to transferred employees \| shares			1,600,000
2015 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option vesting period			4 years
Stock options expiration period			10 years
Number of additional shares available for future grant \| shares			0
2018 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance \| shares		3,186,205
Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock		4.00%
Maximum shares of common stock may be issued \| shares		20,887,347
Number of shares outstanding available for future grant \| shares	2,320,696		4,978,083
2018 Incentive Award Plan \| Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock	4.00%
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance \| shares		353,980
Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock		1.00%
Number of shares outstanding available for future grant \| shares	580,174		2,693,911
Maximum shares allowed to be issued under ESPP \| shares		4,778,738
Purchase of common stock through payroll deductions expressed in percentage of fair market value			85.00%
Common stock offering period			6 months
Number of shares issued to the plan \| shares			133,817	226,453
Aggregate proceeds from shares issued under the plan \| $			$ 200	$ 600
Stock-based compensation \| $			100	$ 100
Excess of accrued right to purchase stock \| $			25,000
2018 Employee Stock Purchase Plan \| Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Allowed annual percentage increase in shares authorized as percentage of outstanding shares of common stock	1.00%
2015 and 2018 Stock Incentive Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense \| $			$ 13,100
Unrecognized compensation expense estimated to be recognized over period			2 years

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Schedule of Operating Lease Cost and Variable Lease Costs and Sub Lease Income

The following table summarizes operating lease costs and variable lease costs, as well as sublease income:


	For the Year ended December 31,
	2023			2022
	(in thousands)
Operating lease costs	$	4,273		$	3,913
Variable lease costs		1,771			2,142
Sublease income		(2,312	)		(1,979	)
Net lease cost	$	3,732		$	4,076

Schedule of Maturities of Operating Lease Liabilities

The maturities of the Company's operating lease liabilities and minimum lease payments as of December 31, 2023 were as follows:


For the Years Ending December 31,	Amount (in thousands)
2024	$	1,380
Total undiscounted lease payments	$	1,380
Less: imputed interest		(62	)
Present value of operating lease liabilities	$	1,318

Schedule of Lease Term and Discount Rate

The following table summarizes the lease term and discount rate as of December 31, 2023:


	December 31, 2023
Weighted-average remaining lease term (years)
Operating leases		1.0
Weighted-average discount rate
Operating leases		10.5	%

Schedule of Operating Lease Liabilities

The following table summarizes the supplemental cash flow information related to the Company's operating leases:


	For the Year ended December 31,
	2023		2022
	(in thousands)
Cash paid for amounts included in the measurement of lease liabilities	$	3,653	$	3,326
Increase in lease liabilities and right-of-use assets due to lease remeasurements	$	—	$	6,262

Commitments and Contingencies - Schedule of Operating Lease Cost and Variable Lease Costs and Sub Lease Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Operating lease costs	$ 4,273	$ 3,913
Variable lease costs	1,771	2,142
Sublease income	(2,312)	(1,979)
Net lease cost	$ 3,732	$ 4,076

Restructuring and Other Charges (Additional Information) (Details) $ in Millions		1 Months Ended	12 Months Ended
	Jul. 25, 2023 Employee	Nov. 30, 2023 Employee	Dec. 31, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Severance and related Cost			$ 4.6
Merger Agreement
Restructuring Cost and Reserve [Line Items]
Number of Employee Terminated \| Employee		6
Corporate
Restructuring Cost and Reserve [Line Items]
Stock based compensation			$ 1.0
Corporate Restructuring
Restructuring Cost and Reserve [Line Items]
Vest over period			4 years
Corporate Restructuring \| Corporate
Restructuring Cost and Reserve [Line Items]
Reduction in employee \| Employee	80
Reduction in employee pecentage	86.00%
Severance and related Cost			$ 10.3

Property and Equipment - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 0	$ 7,314
Less accumulated depreciation and amortization	0	(6,236)
Property and equipment, net	0	1,078
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	0	6,025
Computers and Purchased Software
Property Plant And Equipment [Line Items]
Property and equipment, at cost	0	644
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 0	$ 645

Equity Method Investment

12 Months Ended

Dec. 31, 2023

Equity Method Investments and Joint Ventures [Abstract]

EQUITY METHOD INVESTMENT

6. EQUITY METHOD INVESTMENT

Summary of Transaction

On March 10, 2022, the Company closed a transaction with OXB (US) LLC, Oxford Biomedica (US), Inc., ("OXB"), and Oxford, pursuant to the Equity Securities Purchase Agreement (the "Purchase Agreement"), dated as of January 28, 2022, by and among Homology, OXB (US) LLC and Oxford, whereby, among other things, Homology and Oxford agreed to collaborate to operate OXB (US) LLC, which provides AAV vector process development and manufacturing services to pharmaceutical and biotechnology companies (the "OXB (US) LLC Transaction").

Pursuant to the terms of the Purchase Agreement and a contribution agreement (the "Contribution Agreement") entered into between Homology and OXB (US) LLC prior to the closing of the OXB (US) LLC Transaction (the "Closing"), Homology contributed its manufacturing team of 125 employees and assigned and transferred to OXB (US) LLC all of its assets that are primarily used in the manufacturing of AAV vectors for use in gene therapy and gene editing products, including its manufacturing facility and equipment and manufacturing-related intellectual property and know-how, but excluding certain assets related to manufacturing or testing of Homology's proprietary AAV vectors (collectively, the "Transferred Assets"), in exchange for 175,000 common equity units in OXB (US) LLC ("Units"), representing 100 percent (100%) of the ownership interest of OXB (US) LLC, and OXB (US) LLC assumed from the Company, and agreed to pay, perform and discharge when due, all of the Company's duties, obligations, liabilities, interests and commitments of any kind under, arising out of or relating to the Transferred Assets.

Effective as of the Closing, Homology sold to OXB, and OXB purchased from Homology, 130,000 Units, (the "Transferred Units") in exchange for $130.0 million of cash consideration. In connection with the Closing, OXB contributed $50.0 million in cash to OXB (US) LLC in exchange for an additional, newly issued 50,000 Units. Immediately following the Closing, (i) OXB owned 180,000 Units, representing 80 percent (80%) of the fully diluted equity interests in OXB (US) LLC, and (ii) Homology owned 45,000 Units, representing 20 percent (20%) of the fully diluted equity interests in OXB (US) LLC.

Pursuant to the Amended and Restated Limited Liability Company Agreement of OXB (US) LLC (the "OXB (US) LLC Operating Agreement") which was executed in connection with the Closing, at any time following the three-year anniversary of the Closing, (i) OXB will have an option to cause Homology to sell and transfer to OXB, and (ii) Homology will have an option to cause OXB to purchase from Homology, in each case all of Homology's equity ownership interest in OXB (US) LLC at a price equal to 5.5 times the revenue for the immediately preceding 12-month period (together, the "Options"), subject to a maximum amount of $74.1 million. Pursuant to the terms of the OXB (US) LLC Operating Agreement, Homology is entitled to designate one director to the board of directors of OXB (US) LLC, currently Paul Alloway, Homology's President and Chief Operating Officer.

Pursuant to the OXB (US) LLC Transaction, the Company also assigned all of its right, title and interest in, to and under its facility lease to OXB (US) LLC, with Homology subleasing a portion of lab and office space back from OXB (US) LLC. Effective October 1, 2023, the Company was released from being primary obligor under such lease. Therefore, the related right-of-use asset and operating lease liability were derecognized as of October 1, 2023 and a new right-of-use asset and operating lease liability representing the present value of the future sublease payments to be made to OXB (US) LLC was recorded (see Note 10).

Equity Method of Accounting

The Company has significant influence over, but does not control, OXB (US) LLC through its noncontrolling representation on OXB’s board of directors and the Company’s equity interest in OXB (US) LLC. In addition, the Company and OXB (US) LLC have intra-entity transactions through a series of agreements entered into in conjunction with the OXB (US) LLC Transaction, OXB (US) LLC granted certain licenses to the Company, and the Company has representation on the joint steering committee which oversees the activities governed by the Supply Agreement. Accordingly, the Company does not consolidate the financial statements of OXB (US) LLC and accounts for its investment using the equity method of accounting.

The Company recorded its equity method investment in OXB (US) LLC at fair value upon deconsolidation of OXB (US) LLC as of the Closing. The fair value of the equity method investment was determined based on the market approach. This approach estimated the fair value of OXB (US) LLC based on the implied value for the entity using the consideration paid, including the Options, for a controlling interest in OXB (US) LLC at the entity’s formation. As part of its fair value analysis, the Company determined that the Options are embedded in the common equity units because the Options are not legally detachable or separately exercisable. Accordingly, the equity method investment and the Options represent one unit of account and the fair value recorded reflects the value of the equity interest and the Options. The valuation included certain subjective

assumptions including discounts for lack of control and marketability given the consideration paid for OXB (US) LLC was for a controlling interest in the entity and the Company owns a noncontrolling interest.

As of March 10, 2022, the Closing, the fair value of the Company’s investment in OXB (US) LLC was $31.2 million and the Company recorded a gain of $131.2 million on the sale of its manufacturing business in other income in the Company's consolidated statements of operations. The gain was computed as follows:


(in thousands)	March 10, 2022
Cash received	$	130,000
Plus: Fair value of equity method investment		31,223
Less: Carrying value of transferred assets		(29,974	)
Gain on sale of business	$	131,249

During the year ended December 31, 2023, the Company determined that the fair value of its investment in OXB (US) LLC was negatively impacted due to a change in OXB (US) LLC' forecasted performance relative to expected performance when the Company initially invested in OXB (US) LLC. The Company determined that the decline in value was deemed to be other than temporary and recorded an impairment charge of $3.8 million to reduce its equity method investment to fair value. The impairment charge is included in the loss on equity method investment in the Company's consolidated statements of operations.

In addition, the Company records its share of income or losses from OXB (US) LLC on a quarterly basis. For the year ended December 31, 2023, OXB (US) LLC recorded an impairment charge of $119.1 million which significantly increased OXB (US) LLC's net loss for the period. After recording its share of OXB (US) LLC's net loss, the carrying value of the Company's equity method investment was reduced to $0.0 million.

Summarized Financial Information

Summarized financial information for OXB (US) LLC is as follows:


	December 31,
	2023		2022
Balance Sheet Data	(in thousands)
Current assets	$	10,763	$	39,237
Noncurrent assets	$	74,461	$	228,745
Current liabilities	$	6,151	$	12,352
Noncurrent liabilities	$	42,835	$	37,718


	December 31,
	2023		2022
Statement of Operations Data	(in thousands)
Revenues	$	30,699	$	29,380
Net loss	$	167,062	$	29,036

See Note 18 for information regarding the Company's related party transactions with OXB (US) LLC.

Summary of Significant Accounting Policies - Schedule of Estimated Useful Life of Asset (Details)	12 Months Ended
	Dec. 31, 2023
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Estimated useful life of asset	3 years
Laboratory Equipment and Office Furniture
Property Plant And Equipment [Line Items]
Estimated useful life of asset	5 years
Manufacturing Equipment \| Minimum
Property Plant And Equipment [Line Items]
Estimated useful life of asset	5 years
Manufacturing Equipment \| Maximum
Property Plant And Equipment [Line Items]
Estimated useful life of asset	7 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property Plant And Equipment Estimated Useful Lives	Shorter of the lease termor estimated useful life

Stockholder's Equity

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

STOCKHOLDERS' EQUITY

13. STOCKHOLDERS’ EQUITY

Common Stock—Voting, dividend and liquidation rights of the holders of the common stock are subject to and qualified by the rights, powers and preferences of the holders of the preferred stock.

Voting—Each holder of outstanding shares of common stock are entitled to one vote in respect of each share. The holders of outstanding shares of common stock, voting together as a single class, shall be entitled to elect one director. The number of authorized shares of common stock may be increased or decreased by the affirmative vote of a majority of the outstanding shares of common stock and preferred stock voting together as a single class.

Dividends—Subject to the payment in full of any preferential dividends to which the holders of preferred stock are entitled, the holders of common stock shall be entitled to receive dividends out of funds legally available therefore at such times and in such amounts as the Board of Directors may determine in its sole discretion.

Liquidation Rights—In the event of any voluntary or involuntary liquidation, dissolution or winding-up of the Company, after the payment or provision for payment of all debts and liabilities of the Company and any preferential amounts to which the holders of preferred stock are entitled with respect to the distribution of assets in liquidation, the holders of common stock shall be entitled to share ratably in the remaining assets of the Company available for distribution.

There were 58,017,412 and 57,483,910 shares of common stock outstanding at December 31, 2023 and 2022, respectively.

Preferred Stock—As of December 31, 2023 and 2022, there were no shares of preferred stock issued and outstanding.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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-Paragraph 13
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
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-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (112,961)	$ (5,005)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Equity Method Investment - Gain on Sale of Equity Method Investment (Details) - USD ($) $ in Thousands		12 Months Ended
	Mar. 10, 2022	Dec. 31, 2023	Dec. 31, 2022
Equity Method Investments and Joint Ventures [Abstract]
Cash received	$ 130,000
Plus: Fair value of equity method investment	31,223
Less: Carrying value of transferred assets	(29,974)
Gain on sale of business	$ 131,249	$ 0	$ 131,249

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consists of the following:


	December 31,
	2023		2022
	(in thousands)
Laboratory equipment	$	—	$	6,025
Computers and purchased software		—		644
Furniture and fixtures		—		645
Property and equipment, at cost		—		7,314
Less: accumulated depreciation and amortization		—		(6,236	)
Property and equipment, net	$	—	$	1,078

In August 2023, consistent with its decision to stop further development of its programs and explore, review and evaluate a range of potential strategic options available to the Company, the Company committed to a plan to sell its remaining property and equipment and therefore has classified the amount as assets held for sale on the consolidated balance sheet as of December 31, 2023. The assets held for sale were reported at the lower of the carrying amount or fair value with no depreciation expense taken after August 2023. The Company expects to dispose of all assets held for sale during the first quarter of 2024.

Stock Incentive Plans - Schedule of Stock Options Valuation Assumptions Using a Black-Scholes Option Pricing Model (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	69.20%	68.70%
Expected volatility, maximum	69.70%	70.10%
Weighted-average risk-free interest rate, minimum	3.45%	1.46%
Weighted-average risk-free interest rate, maximum	4.22%	4.16%
Expected dividend yield	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months
Underlying common stock fair value	$ 0.92	$ 1.4
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 3 months	6 years 3 months
Underlying common stock fair value	$ 1.6	$ 4.17

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023 shares
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	During the three months ended December 31, 2023, no director or officer of the Company adopted a “Rule 10b5-1 trading arrangement” or “non-Rule 10b5-1 trading arrangement,” as each term is defined in Item 408(a) of Regulation S-K. On November 27, 2023, W. Bradford Smith, former Chief Financial and Business Officer, terminated a Rule 10b5-1 trading arrangement intended to satisfy the affirmative defense of Rule 10b5-1(c) and originally adopted on September 23, 2022 for the sale of up to 89,000 shares of the Company’s common stock until May 23, 2024. On December 5, 2023, Arthur Tzianabos, Chairman of our Board of Directors and former Chief Executive Officer, terminated a Rule 10b5-1 trading arrangement intended to satisfy the affirmative defense of Rule 10b5-1(c) and originally adopted on September 23, 2022 for the sale of up to 539,640 shares of the Company’s common stock until December 31, 2024. On December 5, 2023, Paul Alloway, President and Chief Operating Officer, terminated a Rule 10b5-1 trading arrangement intended to satisfy the affirmative defense of Rule 10b5-1(c) and originally adopted on September 23, 2022 for the sale of up to 24,097 shares of the Company’s common stock until November 23, 2024. As of December 31, 2023, all of the Company’s “Rule 10b5-1 trading arrangements” and “non-Rule 10b5-1 trading arrangements” have been terminated.
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
W. Bradford Smith [Member]
Trading Arrangements, by Individual
Name	W. Bradford Smith
Title	former Chief Financial and Business Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	September 23, 2022
Rule 10b5-1 Arrangement Terminated	true
Termination Date	November 27, 2023
Aggregate Available	89,000
Arthur Tzianabos [Member]
Trading Arrangements, by Individual
Name	Arthur Tzianabos
Title	Chairman of our Board of Directors and former Chief Executive Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	September 23, 2022
Rule 10b5-1 Arrangement Terminated	true
Termination Date	December 5, 2023
Aggregate Available	539,640
Paul Alloway [Member]
Trading Arrangements, by Individual
Name	Paul Alloway
Title	President and Chief Operating Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	September 23, 2022
Rule 10b5-1 Arrangement Terminated	true
Termination Date	December 5, 2023
Aggregate Available	24,097

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Principles of Consolidation—The Company’s consolidated financial statements include the accounts of the Company and its subsidiary, Homology Medicines Securities Corporation, a wholly owned Massachusetts corporation, for the sole purpose of buying, selling, and holding securities on the Company’s behalf. All intercompany balances and transactions have been eliminated in the consolidated financial statements.

Use of Estimates—The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue, and expenses, and the disclosure of contingent assets and liabilities as of and during the reporting period. The Company bases its estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, revenue recognition, accrued research and development expenses and the valuation of the Company's equity method investment. The Company assesses estimates on an ongoing basis; however, actual results could materially differ from those estimates.

Comprehensive Loss —Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. The Company’s only element of other comprehensive income (loss) is unrealized gains and losses on available-for-sale investments.

Cash and Cash Equivalents and Restricted Cash—Cash and cash equivalents consist of standard checking accounts, money market accounts and certain investments. The Company considers all highly liquid investments with original or remaining maturities at the time of purchase of 90 days or less to be cash equivalents.

Short-Term Investments—Short-term investments represent holdings of available-for-sale marketable securities in accordance with the Company’s investment policy and cash management strategy. Short-term investments have maturities of greater than 90 days at the time of purchase and mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses, reported within accumulated other comprehensive income as a separate component of stockholders’ equity until realized or until a determination is made that an other-than-temporary decline in market value has occurred. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the underlying security. Such amortization and accretion, together with interest on securities, are included in interest income in the Company’s consolidated statements of operations. The cost of marketable

securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other income.

Concentrations of Credit Risk—Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents and short-term investments. Periodically, the Company may maintain deposits in financial institutions in excess of government insured limits. The Company believes that it is not exposed to significant credit risk as its deposits are held at financial institutions that management believes to be of high credit quality and the Company has not experienced any losses on these deposits. The Company regularly invest excess cash with major financial institutions in money market funds, U.S. government and corporate debt securities and commercial paper, all of which can be readily purchased and sold using established markets. As of December 31, 2023, the Company’s cash and cash equivalents were held with two financial institutions. The Company believes that the market risk arising from its holdings of these financial instruments is mitigated based on the fact that many of these securities are either government-backed or of high credit rating.

Equity Method Investment—The Company uses the equity method of accounting to account for an investment in an entity that it does not control, but in which it has the ability to exercise significant influence over operating and financial policies. The Company's proportionate share of the net income or loss of the entity is included in consolidated net loss. Judgments regarding the level of influence over the equity method investment include consideration of key factors such as the Company's ownership interest, representation on the board of directors or other management body and participation in policy-making decisions.

Under the equity method of accounting, the Company’s investment is initially recorded at fair value on the consolidated balance sheets. Upon initial investment, the Company evaluates whether there are basis differences between the carrying value and fair value of the Company’s proportionate share of the investee’s underlying net assets. Typically, the Company amortizes basis differences identified on a straight-line basis over the underlying assets’ estimated useful lives when calculating the attributable earnings or losses, excluding the basis differences attributable to in-process research and development that has no alternative future use. If the Company is unable to attribute all of the basis differences to specific assets or liabilities of the investee, the residual excess of the cost of the investment over the proportional fair value of the investee’s assets and liabilities is considered to be equity method goodwill and is recognized within the equity investment balance, which is tracked separately within the Company’s memo accounts. The Company subsequently records in the statements of operations its share of income or loss of the other entity within other income/expense, which results in an increase or decrease to the carrying value of the investment. If the share of losses exceeds the carrying value of the Company’s investment, the Company will suspend recognizing additional losses and will continue to do so unless it commits to providing additional funding; however, if there are intra-entity profits this can cause the investment balance to go negative.

The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that a decline in value has occurred that is other than temporary. Evidence considered in this evaluation includes, but would not necessarily be limited to, the financial condition and near-term prospects of the investee, recent operating trends and forecasted performance of the investee, market conditions in the geographic area or industry in which the investee operates and the Company’s strategic plans for holding the investment in relation to the period of time expected for an anticipated recovery of its carrying value. If the investment is determined to have a decline in value deemed to be other than temporary it is written down to estimated fair value.

At December 31, 2023, the Company accounted for its investment in OXB (US) LLC using the equity method of accounting (see Note 6).

Offering Costs—The Company capitalizes incremental legal, professional accounting and other third-party fees that are directly associated with equity financings as other current assets until the transactions are completed. After equity financings are complete, these costs are recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering.

Leases— The Company determines if an arrangement is a lease at contract inception. The Company’s contracts are determined to contain a lease when all of the following criteria based on the specific circumstances of the arrangement are met: (1) there is an identified asset for which there are no substantive substitution rights; (2) the Company has the right to obtain substantially all of the economic benefits from the identified asset; and (3) the Company has the right to direct the use of the identified asset.

At the commencement date, operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of future lease payments over the expected lease term. The Company’s lease agreements do not provide an implicit rate. As a result, the Company utilizes an estimated incremental borrowing rate to discount lease payments, which is

based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or lease incentives received. Operating lease cost is recognized over the expected term on a straight-line basis. The expected lease term includes noncancelable lease periods and, when applicable, periods covered by an option to extend the lease if the Company is reasonably certain to exercise that option, as well as periods covered by an option to terminate the lease if the Company is reasonably certain not to exercise that option. Variable lease cost is recognized as incurred. Right-of-use assets are periodically evaluated for impairment.

The Company subleases a portion of its headquarters that is now occupied by OXB (US) LLC (see Note 18). Homology assigned all of its right, title and interest in, to and under this lease to OXB (US) LLC and effective October 1, 2023, the Company was released from being the primary obligor under such lease. Therefore, the related right-of-use asset and operating lease liability were derecognized as of October 1, 2023 and a new right-of-use asset and operating lease liability representing the present value of the future sublease payments to be made to OXB (US) LLC was recorded (see Note 10).

Guarantees and Indemnifications—As permitted under Delaware law, the Company indemnifies its officers, directors, consultants and employees for certain events or occurrences that happen by reason of the relationship with, or position held at, the Company. Through December 31, 2023, the Company had not experienced any losses related to these indemnification obligations, and no claims were outstanding. The Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that the fair value of these obligations is negligible, and no related liabilities have been established.

Property and Equipment—Property and equipment are recorded at cost. Expenditures for repairs and maintenance are expensed as incurred. When assets are retired or disposed of, the assets and related accumulated depreciation are derecognized from the accounts, and any resulting gain or loss is included in the determination of net loss. Depreciation is provided using the straight-line method over the estimated useful lives of the related assets. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the asset.


Computer equipment and software		3 years
Laboratory equipment and office furniture		5 years
Manufacturing equipment		5 - 7 years
Leasehold improvements		Shorter of the lease term or estimated useful life

Assets Held for Sale—The Company classifies assets as held for sale when the following conditions are met: (1) management has committed to a plan to sell, (2) the assets are available for immediate sale in their present condition, (3) the Company has initiated an active program to identify a buyer, (4) it is probable that a sale will occur within one year, (5) the assets are actively marketed for sale at a reasonable price in relation to their current fair value, and (6) there is a low likelihood of significant changes to the plan or that the plan will be withdrawn. If all of the criteria are met as of the balance sheet date, the assets are presented separately in the consolidated balance sheet as held for sale at the lower of the carrying amount or fair value less costs to sell. The assets are then no longer depreciated or amortized while classified as held for sale.

Impairment of Long-Lived Assets—The Company evaluates its long-lived assets, which consist primarily of property and equipment and right-of-use assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset exceeds the fair value of the asset. To date, no impairments have been recognized for these assets.

Research and Development Costs—Research and development costs are charged to expense as incurred. Research and development expense consists of expenses incurred in performing research and development activities, including salaries and benefits, materials and supplies, preclinical and clinical expenses, stock-based compensation expense, depreciation of equipment, contract services, and other outside expenses.

Costs for certain development activities are recognized based on an evaluation of the progress to completion of specific tasks using information provided to the Company by its vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid expense or accrued research and development expense.

Income Taxes—The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the Company’s consolidated financial statements and tax returns. Deferred tax assets and liabilities are determined based upon the differences between the financial statement carrying amounts and the tax bases of existing assets and liabilities and for loss and credit carryforwards, using enacted tax rates expected to be in effect in the year in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that these assets may not be realized. The Company determines whether it is more likely than not that a tax position will be sustained upon examination. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes. Since inception, the Company has provided a valuation allowance for the full amount of the net deferred tax assets as the realization of the net deferred tax assets has not been determined to be more likely than not.

Segment Information—Operating segments are identified as components of an enterprise about which separate discrete financial information is made available for evaluation by the chief operating decision maker (“CODM”) in making decisions regarding resource allocation and assessing performance. The CODM is the Company’s President and Chief Operating Officer. The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is dedicated to translating proprietary gene editing and gene therapy technology into novel treatments for patients with rare genetic diseases. All of the Company’s tangible assets are held in the United States.

Revenue Recognition— Revenue is recognized in accordance with FASB Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer.

The promised goods or services in the Company’s arrangements would likely consist of a license, rights to the Company’s intellectual property or research, development and manufacturing services. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract.

The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of consideration to which the Company expects to be entitled to. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period.

The Company’s contracts may include development and regulatory milestone payments that are assessed under the most likely amount method and constrained until it is probable that a significant revenue reversal would not occur. Milestone payments that are not within the Company’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development and regulatory milestones and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenue in the period of adjustment.

For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from the Company’s collaboration arrangement.

The Company allocates the transaction price based on the estimated standalone selling price of each performance obligation. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation.

The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress for its over-time arrangements at each reporting period and, if necessary, updates the measure of progress and revenue recognized.

Stock-based Compensation—The Company recognizes compensation expense for awards to employees and non-employees based on the grant date fair value of stock-based awards on a straight-line basis over the period during which an award holder provides service in exchange for the award. The fair value of options on the date of grant is calculated using the Black-Scholes option pricing model based on key assumptions such as stock price, expected volatility and expected term. The Company’s estimates of these assumptions are primarily based on the trading price of the Company’s stock, historical data, peer company data and judgment regarding future trends and factors. The Company recognizes forfeitures as they occur.

The purchase price of common stock under the Company’s employee stock purchase plan (“ESPP”) is equal to 85% of the lesser of (i) the fair market value per share of the common stock on the first business day of an offering period and (ii) the fair market value per share of the common stock on the purchase date. The fair value of the look-back provision under the ESPP is calculated using the Black-Scholes option pricing model. The fair value of the look-back provision plus the 15% discount is recognized as compensation expense over the 180-day purchase period.

Fair Value Measurements—Certain assets and liabilities are reported on a recurring basis at fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•

Level 1—Quoted prices (unadjusted) in active markets for identical assets or liabilities.

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

Net Loss per Share—Basic net loss per share is computed by dividing net loss by the weighted-average number of common shares outstanding during the period. Diluted net loss per share is computed using the weighted-average number of common shares outstanding during the period and, if dilutive, the weighted-average number of potential shares of common stock. The weighted-average number of common shares included in the computation of diluted net loss gives effect to all potentially dilutive common equivalent shares, including outstanding stock options, restricted stock units and unvested shares of common stock.

Common stock equivalent shares are excluded from the computation of diluted net loss per share if their effect is antidilutive. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share

attributable to common stockholders is generally the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

Recent Accounting Pronouncements—The Jumpstart Our Business Startups Act of 2012 permits an emerging growth company to take advantage of an extended transition period to comply with new or revised accounting standards applicable to public companies until those standards would otherwise apply to private companies. The Company ceased to qualify as an emerging growth company effective December 31, 2023.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”) to improve financial reporting by requiring more timely recording of credit losses on loans and other financial instruments held by financial institutions and other organizations. ASU 2016-13 requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions and reasonable and supportable forecasts. ASU 2016-13 also requires enhanced disclosures to help investors and other financial statement users better understand significant estimates and judgments used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. The Company adopted ASU 2016-13 on January 1, 2023. The adoption of ASU 2016-13 did not have a material impact on the Company's consolidated financial statements and related disclosures.

Pfizer Stock Purchase Agreement

12 Months Ended

Dec. 31, 2023

Pfizer Inc.

PFIZER STOCK PURCHASE AGREEMENT

17. PFIZER STOCK PURCHASE AGREEMENT

On November 9, 2020, the Company entered into a common stock purchase agreement (the “Stock Purchase Agreement”) with Pfizer Inc. (“Pfizer”), pursuant to which the Company agreed to issue and sell to Pfizer 5,000,000 shares of the Company’s common stock through a private placement transaction (the “Private Placement”) at a purchase price of $12.00 per share, for an aggregate purchase price of $60.0 million. The shares of common stock sold to Pfizer were subject to a one-year lock-up from closing, during which time Pfizer was prohibited from selling or otherwise disposing of such shares.

Under the Stock Purchase Agreement, Pfizer was granted an exclusive right of first refusal (the “ROFR”) for a 30-month period (the “ROFR Period”) beginning on the date of the closing of the Private Placement (collectively, the “ROFR Provision”), to negotiate a potential collaboration on the development and commercialization of HMI-102 and HMI-103. The ROFR Period expired on May 9, 2023. In addition to the ROFR, the Stock Purchase Agreement provided for an information sharing committee (the “Information Committee”), comprised of representatives of each company which will serve as a forum for sharing information regarding the development of HMI-102 and HMI-103 during the ROFR Period.

The Company recorded the issuance of common stock at its estimated fair value of $52.0 million, which reflected a discount for the lack of marketability of the shares. The remaining $8.0 million of aggregate purchase price was allocated to the other elements of the Stock Purchase Agreement, which represented a contract with a customer. The Company concluded that the Information Committee represented the only performance obligation under the contract. The ROFR did not provide Pfizer with a material right and was therefore not a performance obligation. As such, the Company allocated the $8.0 million to the Information Committee obligation.

The Company recognized revenue over time as the measure of progress which it believed best depicted the transfer of control to Pfizer. The Information Committee met regularly over the ROFR Period to share information which resulted in recognition of the transaction price over the 30-month ROFR Period.

The Company recognized collaboration revenue of $1.2 million and $3.2 million during the years ended December 31, 2023 and 2022, respectively. There was no deferred revenue related to the Company's obligation to Pfizer as of December 31, 2023. As of December 31, 2022, there was approximately $1.2 million of deferred revenue related to the Company’s obligation to Pfizer.

Equity Method Investment (Tables)

12 Months Ended

Dec. 31, 2023

Equity Method Investments and Joint Ventures [Abstract]

Gain on Sale of Equity Method Investment

The gain was computed as follows:


(in thousands)	March 10, 2022
Cash received	$	130,000
Plus: Fair value of equity method investment		31,223
Less: Carrying value of transferred assets		(29,974	)
Gain on sale of business	$	131,249

Schedule of Summarized Financial Information

Summarized financial information for OXB (US) LLC is as follows:


	December 31,
	2023		2022
Balance Sheet Data	(in thousands)
Current assets	$	10,763	$	39,237
Noncurrent assets	$	74,461	$	228,745
Current liabilities	$	6,151	$	12,352
Noncurrent liabilities	$	42,835	$	37,718


	December 31,
	2023		2022
Statement of Operations Data	(in thousands)
Revenues	$	30,699	$	29,380
Net loss	$	167,062	$	29,036

Net Loss Per Share - Schedule of Anti-dilutive Effect Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	9,892,380	10,408,913
Employee Stock Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	9,551,041	9,865,734
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	341,339	543,179

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets	$ 650	$ 20,563
Operating lease liabilities	1,318
Outstanding claim	0
Impairment of long-lived assets	$ 0
Tax positions, description	The Company determines whether it is more likely than not that a tax position will be sustained upon examination. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount of benefit that is greater than 50% likely of being realized upon ultimate settlement. If it is not more likely than not that a position will be sustained, none of the benefit attributable to the position is recognized.
Employee Stock Purchase Plan
Summary Of Significant Accounting Policies [Line Items]
Purchase of common stock through payroll deductions expressed in percentage of fair market value	85.00%
Share based compensation, discount from market price	15.00%
Share based compensation arrangement by share based payment purchase period	180 days

Accrued Expenses and Other Liabilities

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

ACCRUED EXPENSES AND OTHER LIABILITIES

8. ACCRUED EXPENSES AND OTHER LIABILITIES

Accrued expenses and other liabilities consist of the following:


	December 31,
	2023		2022
	(in thousands)
Accrued compensation and benefits	$	5,755	$	5,953
Accrued research and development expenses		—		9,447
Accrued professional fees		941		1,052
Accrued other		325		2,263
Total accrued expenses and other liabilities	$	7,021	$	18,715

Accrued compensation and benefits includes a restructuring accrual for severance and related costs of approximately $4.6 million (see Note 9).

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 39,266	$ 33,986

Commitments and Contingencies - Additional Information (Details) $ in Thousands	1 Months Ended			12 Months Ended
	Feb. 28, 2022 USD ($)	Dec. 31, 2017 ft² Phase $ / ft²	Nov. 30, 2017 USD ($) ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Oct. 01, 2023 USD ($)
Commitment And Contingencies [Line Items]
Tenant improvement allowance			$ 6,300
Increase decrease in right-of-use asset	$ 200			$ 10,900
Sublease income				$ 2,312	$ 1,979
Tenant improvement allowances				100.00%
Right-of-use assets				$ 650	20,563
OXB Solutions
Commitment And Contingencies [Line Items]
Increase decrease in right-of-use asset				6,100
Sublease income				2,300	$ 2,000
Lease Release Cash Payment						$ 100
Gain Loss On Derecognization Right-of-use Asset And Operating Lease Liability						8,800
Right-of-use assets						$ 1,600
Maximum
Commitment And Contingencies [Line Items]
Tenant improvement allowance				10,900
Bedford, Massachusetts
Commitment And Contingencies [Line Items]
Operating lease expiration year and month		2027-02	2027-02
Sublease aggregate base rent obligation			$ 1,400	$ 4,700
Office space leased \| ft²		67,000	23,011
Lessee, operating lease, lease not yet commenced, renewal term		5 years
Number of phases \| Phase		2
Initial annual base rent per square foot \| $ / ft²		39.5
Percentage increase in initial annual base rent per square foot.		3.00%	3.00%
Bedford, Massachusetts \| Phase One
Commitment And Contingencies [Line Items]
Office space leased \| ft²		46,000
Rent due date		2018-09
Bedford, Massachusetts \| Phase Two
Commitment And Contingencies [Line Items]
Office space leased \| ft²		21,000
Rent due date		2019-03

Stock Incentive Plans - Summary of Option Activity under Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding at Beginning Balance	9,865,734
Number of Options, Granted	3,188,150
Number of Options, Exercised	(26,166)
Number of Options, Cancelled/Forfeited	(3,476,677)
Number of Options, Outstanding at Ending Balance	9,551,041	9,865,734
Number of Options, Vested and Expected to vest at December 31, 2023	9,551,041
Number of Options, Exercisable at December 31, 2023	7,061,128
Weighted-Average Exercise Price per Share, Outstanding at Beginning Balance	$ 10.96
Weighted-Average Exercise Price per Share, Granted	1.53
Weighted-Average Exercise Price per Share, Exercised	0.61
Weighted-Average Exercise Price per Share, Cancelled/Forfeited	7.05
Weighted-Average Exercise Price per Share, Outstanding at Ending Balance	9.26	$ 10.96
Weighted-Average Exercise Price per Share, Vested and Expected to vest at December 31, 2023	9.26
Weighted-Average Exercise Price Per Share, Exercisable at December 31, 2023	$ 11.35
Weighted Average Remaining Contractual Term, Outstanding	5 years 2 months 12 days	7 years 2 months 12 days
Weighted Average Remaining Contractual Term, Vested and Expected to vest at December 31, 2023	5 years 2 months 12 days
Weighted Average Remaining Contractual Term, Exercisable at December 31, 2023	4 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding Ending Balance	$ 66	$ 493
Aggregate Intrinsic Value, Vested and Expected to vest at December 31, 2023	66
Aggregate Intrinsic Value, Exercisable at December 31, 2023	$ 66

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 39,266	$ 33,986
Short-term investments	43,387	141,040
Assets Held For Sale	260	0
Prepaid expenses and other current assets	1,001	5,989
Total current assets	83,914	181,015
Equity method investment	0	25,814
Property and equipment, net	0	1,078
Right-of-use assets	650	20,563
Total assets	84,564	228,470
Current liabilities:
Accounts payable	3,234	1,144
Accrued expenses and other liabilities	7,021	18,715
Operating Lease Liabilities	1,318	1,561
Deferred revenue	0	1,156
Total current liabilities	11,573	22,576
Non-current liabilities:
Operating lease liabilities, net of current portion	0	27,916
Total liabilities	11,573	50,492
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized; no shares issued and outstanding at December 31, 2023 and 2022	0	0
Common stock, $0.0001 par value; 200,000,000 shares authorized; 58,017,412 and 57,483,910 shares issued and outstanding as of December 31, 2023 and 2022, respectively	6	6
Additional paid-in capital	615,088	607,513
Accumulated other comprehensive gain	(5)	(404)
Accumulated deficit	(542,098)	(429,137)
Total stockholders’ equity	72,991	177,978
Total liabilities and stockholders' equity	$ 84,564	$ 228,470

Restructuring and Other Charges

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

RESTRUCTURING AND OTHER CHARGES

9. RESTRUCTURING AND OTHER CHARGES

On July 25, 2023, the Company's Board of Directors approved a process to explore, review and evaluate a range of potential strategic options available to the Company, including, without limitation, an acquisition, merger, reverse merger, sale of assets, strategic partnerships or other transactions. Therefore, based on cost-reduction initiatives intended to reduce the Company’s ongoing operating expenses and maximize shareholder value as the Company plans to pursue strategic options, the Company's Board of Directors approved a reduction in the Company’s workforce by approximately 80 employees, or 86% of the Company's workforce as of July 2023. Simultaneous with the signing of the Merger Agreement, the Company terminated another 6 employees in November 2023.

In connection with the reduction in force, the Company recorded a restructuring charge for severance and related costs of $10.3 million in the Company's consolidated statements of operations during the year ended December 31, 2023. The Company’s restructuring liability, which was included in accrued compensation and benefits, consisted of the following:


(in thousands)	Employee-Related Costs
Accrued restructuring balance at January 1, 2023	$	—
Expenses incurred		10,279
Payments		(5,666	)
Accrued restructuring balance at December 31, 2023	$	4,613

The Company had previously granted certain of the terminated employees restricted stock units (“RSUs”) that vest in annual installments based on continued service to the Company, as well as options to purchase shares of the Company’s common stock that typically vest over a period of four years. In connection with the reduction in workforce, the Company agreed to accelerate the vesting of a portion of the RSUs that were unvested as of the employees’ termination dates, and also modify the stock options for terminated employees such that subject to the satisfaction of severance conditions, the terminated employees’ vested options will remain outstanding and exercisable until the first anniversary of each employee’s termination date. These equity modifications, described in detail in Note 14, resulted in a net reduction to stock based compensation

expense of approximately $1.0 million reflected within restructuring and other charges in the Company's consolidated statements of operations during the year ended December 31, 2023.

Collaboration and License Agreement - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement revenue recognized	$ 1,156	$ 3,208

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 924
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479941/924-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-40

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
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-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-4

+ Details

Income Taxes - Schedule of provision for income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Federal tax provision:
Current	$ 0	$ 698
Deferred	0	0
Total federal tax provision	0	698
State tax provision:
Current	0	17
Deferred	0	0
Total state tax provision	0	17
Total tax provision	$ 0	$ 715

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Defined Contribution Plan

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

DEFINED CONTRIBUTION PLAN

16. DEFINED CONTRIBUTION PLAN

The Company has a 401(k) defined contribution plan (the “401(k) Plan”) for all of its employees. Eligible employees may make pretax contributions to the 401(k) Plan up to statutory limits, while the Company contributes to the plan at the discretion of the Board of Directors. The Company’s discretionary match made under the 401(k) Plan for the years ended December 31, 2023 and 2022 was $0.4 million and $0.6 million, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
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-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
-Paragraph 1
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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-Paragraph 1
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-Publisher FASB
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Equity Method Investee	ATM	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital Equity Method Investee	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2021	$ 169,651			$ 6	$ 593,784		$ (7)	$ (424,132)
Beginning balance, Shares at Dec. 31, 2021				57,150,274
Issuance of common stock from option exercises	1				1
Issuance of common stock from option exercises, Shares				293
Issuance of common stock pursuant to employee stock purchase plan	595				595
Issuance of common stock pursuant to employee stock purchase plan, Shares				226,453
Issuance of common stock from RSU vesting, Shares				106,890
Stock-based compensation	13,054	$ 79			13,054	$ 79
Other comprehensive loss	(397)						(397)
Net loss	(5,005)							(5,005)
Ending balance at Dec. 31, 2022	177,978			$ 6	607,513		(404)	(429,137)
Ending balance, Shares at Dec. 31, 2022				57,483,910
Issuance of common stock, net of discounts and issuance costs, Shares			0
Issuance of common stock from option exercises	16				16
Issuance of common stock from option exercises, Shares				26,166
Issuance of common stock pursuant to employee stock purchase plan	168				168
Issuance of common stock pursuant to employee stock purchase plan, Shares				133,817
Issuance of common stock from RSU vesting, Shares				373,519
Stock-based compensation	7,324	$ 67			7,324	$ 67
Other comprehensive loss	399						399
Net loss	(112,961)							(112,961)
Ending balance at Dec. 31, 2023	$ 72,991			$ 6	$ 615,088		$ (5)	$ (542,098)
Ending balance, Shares at Dec. 31, 2023				58,017,412

Income Taxes - Schedule of Reconciliation between U.S. Federal Statutory Tax and Effective Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal statutory tax	$ (23,722)	$ (901)
Tax credits	(7,699)	(13,955)
State taxes, net of federal tax benefit	(8,496)	(2,994)
Non-deductible expenses	595	875
Other	(2,351)	1,410
Change in valuation allowance	41,673	16,280
Tax provision	$ 0	$ 715

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Collaboration revenue	$ 1,156	$ 3,208
Operating expenses:
Research and development	62,002	98,351
General and administrative	31,256	38,138
Restructuring and Other Charges	9,327	0
Total operating expenses	102,585	136,489
Loss from operations	(101,429)	(133,281)
Other income:
Gain on sale of business	0	131,249
Gain on lease termination	8,767	0
Interest income	5,582	3,230
Total other income	14,349	134,479
Income (loss) before income taxes	(87,080)	1,198
Provision for income taxes	0	(715)
Loss from equity method investment	(25,881)	(5,488)
Net loss	$ (112,961)	$ (5,005)
Net loss per share-basic	$ (1.95)	$ (0.09)
Net loss per share-diluted	$ (1.95)	$ (0.09)
Weighted average common shares outstanding-basic	57,834,819	57,399,762
Weighted average common shares outstanding-diluted	57,834,819	57,399,762

Accrued Expenses and Other Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Schedule of Accrued Expenses and Other Liabilities

Accrued expenses and other liabilities consist of the following:


	December 31,
	2023		2022
	(in thousands)
Accrued compensation and benefits	$	5,755	$	5,953
Accrued research and development expenses		—		9,447
Accrued professional fees		941		1,052
Accrued other		325		2,263
Total accrued expenses and other liabilities	$	7,021	$	18,715

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

INCOME TAXES

12. INCOME TAXES

Provision for income taxes consists of the following:


	For the Year ended December 31,
	2023		2022
	(in thousands)
Federal tax provision:
Current	$	—	$	698
Deferred		—		—
Total federal tax provision		—		698
State tax provision:
Current		—		17
Deferred		—		—
Total state tax provision		—		17
Total tax provision	$	—	$	715

A reconciliation between the U.S. federal statutory tax and the Company’s tax provision is summarized below.


	For the Year ended December 31,
	2023			2022
	(in thousands)
Federal statutory rate	$	(23,722	)	$	(901	)
Tax credits		(7,699	)		(13,955	)
State taxes, net of federal tax benefit		(8,496	)		(2,994	)
Non-deductible expenses		595			875
Other		(2,351	)		1,410
Change in valuation allowance		41,673			16,280
Tax provision	$	—		$	715

The principal components of the Company’s deferred tax assets and liabilities consist of the following:


	For the Year ended December 31,
	2023			2022
	(in thousands)
Deferred tax assets:
Net operating losses	$	88,552		$	76,735
R&D credits		79,094			66,761
Equity compensation		8,215			7,888
Operating lease liabilities		356			8,003
Accrued expense and other		9,351			1,479
Deferred revenue		—			314
Capitalized R&D costs		35,987			24,477
Total deferred tax assets		221,555			185,657
Deferred tax liabilities:
Right-of-use assets		(176	)		(5,583	)
Depreciation		(54	)		(171	)
Other		—			(251	)
Total deferred tax liabilities		(230	)		(6,005	)
Valuation allowance		(221,325	)		(179,652	)
Net deferred taxes	$	—		$	—

The Company recorded an income tax provision of $0.7 million for the year ended December 31, 2022. This prior year-to-date tax provision predominately resulted from the gain associated with the sale of the Company's manufacturing business due to the transaction with Oxford (see Note 6), offset by available federal and state net operating loss carryforwards and research and development tax credits which are subject to certain limitations as to their utilization. The Company did not record an income tax provision (benefit) for the year ended December 31, 2023.

At December 31, 2023, the Company had $326.2 million and $317.3 million of federal and state net operating loss carryforwards, respectively. Federal net operating loss carryforwards of $0.4 million, generated before 2018, will begin expiring in varying amounts through 2035 unless utilized. The remaining federal net operating loss carryforwards of $325.8 million, generated after 2017, will be carried forward indefinitely. The state net operating losses will begin expiring in varying amounts through 2043 unless utilized. At December 31, 2023, the Company had $65.5 million and $17.2 million of federal and state research and development credit carryforwards, respectively, that expire at various dates through 2043. Included in the $65.5 million of federal research and development credit carryforwards is $50.7 million of orphan drug credit carryforwards.

A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. A roll forward of the valuation allowance is as follows:


(in thousands)	Valuation Allowance
Balance at December 31, 2022	$	(179,652	)
Utilization of net operating losses against taxable income		—
Increase in net deferred taxes		(41,673	)
Balance at December 31, 2023	$	(221,325	)

For all years through December 31, 2023, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards. Since a full valuation allowance has been provided against the Company’s research and development credits, any reduction in the gross deferred tax asset established for the research and development credit carryforwards would not result in any net impact to the Company’s consolidated financial statements.

Realization of the future tax benefits is dependent on many factors, including the Company’s ability to generate taxable income within the net operating loss carryforward period. Under the provisions of the Internal Revenue Code, certain substantial changes in the Company’s ownership, including a sale of the Company or significant changes in ownership due to sales of equity, may have limited, or may limit in the future, the amount of net operating loss carryforwards that could be used annually to offset future taxable income. The Company completed a study to assess ownership changes through December 31,

2021. Based on this analysis, the net operating losses are limited but the Company does not believe that any of its net operating losses or research and development credit carryforwards will expire unutilized due to Section 382 limitations.

The Company files tax returns in the United States, Massachusetts and several other states. All tax years since inception remain open to examination by the major taxing jurisdictions to which the Company is subject, as carryforward attributes generated in years past may still be adjusted upon examination by the Internal Revenue Service (“IRS”) or other authorities if they have or will be used in a future period. The Company is not currently under examination by the IRS or any other jurisdictions for any tax years.

As of December 31, 2023, the Company had no uncertain tax positions. The Company has elected to recognize interest and penalties related to income tax matters as a component of income tax expense, of which no interest or penalties were recorded for the years ended December 31, 2023 and 2022.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating losses	$ 88,552	$ 76,735
R&D credits	79,094	66,761
Equity compensation	8,215	7,888
Operating lease liabilities	356	8,003
Accrued expense and other	9,351	1,479
Deferred revenue	0	314
Capitalized R&D costs	35,987	24,477
Total deferred tax assets	221,555	185,657
Deferred tax liabilities:
Right-of-use assets	(176)	(5,583)
Depreciation	(54)	(171)
Other	0	(251)
Total deferred tax liabilities	(230)	(6,005)
Valuation allowance	(221,325)	(179,652)
Net deferred taxes	$ 0	$ 0

Nature of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

NATURE OF BUSINESS AND BASIS OF PRESENTATION

1. NATURE OF BUSINESS AND BASIS OF PRESENTATION

Nature of Business—Homology Medicines, Inc. (the “Company” or "Homology") is a clinical-stage genetic medicines company historically focused on transforming the lives of patients suffering from rare diseases by addressing the underlying cause of the disease with one-time gene therapy and gene editing treatments. The Company was founded in March 2015 as a Delaware corporation. Its principal offices are in Bedford, Massachusetts.

On July 27, 2023, the Company announced that it had completed a review of its business and the Company's Board of Directors had approved a plan to explore, review and evaluate a range of potential strategic options available to the Company, including, without limitation, an acquisition, merger, reverse merger, sale of assets, strategic partnerships or other transactions. Based on the financing environment and the Company's anticipated clinical development timeline for its lead program, HMI-103, the Company also announced that it was stopping further development of its programs and reduced its workforce by 86% in an effort to significantly reduce its ongoing operating costs as it evaluated strategic alternatives. The workforce reduction was substantially completed in the third quarter of 2023 (see Note 9).

Agreement and Plan of Merger

After a comprehensive review of strategic alternatives, on November 16, 2023, the Company entered into an Agreement and Plan of Merger (the "Merger Agreement"), with Q32 Bio Inc., a Delaware corporation ("Q32"), and Kenobi Merger Sub, Inc., a Delaware corporation and the Company's direct, wholly owned subsidiary ("Merger Sub"), pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, Merger Sub will merge with and into Q32, with Q32 continuing as the Company's wholly owned subsidiary and the surviving corporation of the merger (the "Merger"). The Company's future operations are highly dependent on the success of the Merger and there can be no assurance that the Merger will be successfully consummated. If the Merger is completed, the business of Q32 will continue as the business of the combined company.

Merger Consideration

Subject to the terms and conditions of the Merger Agreement, (i) immediately prior to the effective time of the Merger (the “Effective Time”), all Q32 preferred stock will be converted into Q32 common stock pursuant to the organizational documents of Q32 (the “Q32 Preferred Stock Conversion”), and (ii) at the Effective Time, (a) each outstanding share of Q32 common stock (excluding Q32 common stock issued in the Concurrent Financing, as described below) will be converted into the right to receive a number of shares of the Company’s common stock (“Company Common Stock”), calculated in accordance with the Merger Agreement, (b) each outstanding Q32 stock option and warrant that has not previously been exercised prior to the closing of the Merger will be assumed by the Company and become an option or warrant, as applicable, to purchase a number of shares of Company Common Stock and (c) the Q32 common stock issued in the Concurrent Financing will be converted into the right to receive a number of shares of the Company’s Common Stock calculated in accordance with the Merger Agreement. The shares of Company Common Stock that will be issued to stockholders of Q32 will be calculated using a formula in the Merger Agreement based on the equity value of each of Q32 and the Company. Q32 has been ascribed an aggregate equity value of $195 million and the Company’s equity value is expected to be approximately $80 million subject to adjustment based on the amount of net cash of the Company at closing of the Merger.

Concurrent Financing

Pursuant to the Merger Agreement, immediately prior to the Effective Time, Q32 will consummate a financing through the sale of its common stock for aggregate gross proceeds of $42 million based on the same aggregate equity value of Q32 used in the Merger (the “Concurrent Financing”). On November 16, 2023, Q32 entered into subscription agreements with certain accredited investors (the “Investors”) for the Concurrent Financing with expected gross proceeds to Q32 of $42 million. In connection with the Concurrent Financing, at the closing of the Merger, Q32 will enter into a registration rights agreement with the Investors providing for the registration under the Securities Act of 1933, as amended (the “Securities Act”) of the shares of common stock sold in the Concurrent Financing. The consummation of the transactions contemplated by the subscription agreements is conditioned on the satisfaction or waiver of the conditions set forth in the Merger Agreement and in the subscription agreements. Shares of Q32 common stock issued pursuant to the Concurrent Financing will be converted into shares of Company Common Stock in the Merger in accordance with the Merger Agreement.

Contingent Value Rights Agreement

At the Effective Time, if any Legacy Assets (as defined below) have not been disposed of in a Legacy Asset Disposition (as defined below) or if additional consideration may be payable for the Legacy Assets (as defined below) after closing of the Merger, the Company and Equiniti Trust Company, LLC, a New York limited liability company, as the initial rights agent (“Rights Agent”), will enter into a Contingent Value Rights Agreement (the “CVR Agreement”), pursuant to which the Company’s common stockholders of record as of the close of business on the last business day prior to the day on which the Effective Time occurs will receive one contingent value right (each, a “CVR”) for each outstanding share of Company Common Stock held by such stockholder on such date.

Each CVR will represent the contractual right to receive payments from the Company upon the actual receipt by the Company or its subsidiaries of certain contingent proceeds derived from any cash consideration that is paid to the Company or its subsidiaries as a result of the sale, transfer, license, assignment or other divestiture, disposition or commercialization of any of the Company’s assets, rights and interests relating to the Company’s HMI-103, HMI-204, Capsids and AAVHSC Platform, including any equity interests held directly or indirectly by the Company in Oxford Biomedica Solutions, LLC or its affiliates (“OXB Solutions”) pursuant to that certain Equity Securities Purchase Agreement, dated as of January 28, 2022, by and between the Company and OXB Solutions (the “Legacy Assets” and such disposition, a “Legacy Asset Disposition”), net of certain tax, transaction costs and certain other expenses.

The contingent payments under the CVR Agreement, if they become payable, will become payable to the Rights Agent for subsequent distribution to the holders of the CVRs. There can be no assurance that any holders of CVRs will receive payments with respect thereto. The right to the contingent payments contemplated by the CVR Agreement is a contractual right only and will not be transferable, except in the limited circumstances specified in the CVR Agreement. The CVRs will not be evidenced by a certificate or any other instrument and will not be registered with the Securities and Exchange Commission (the “SEC”). The CVRs will not have any voting or dividend rights and will not represent any equity or ownership interest in the Company or any of its affiliates. No interest will accrue on any amounts payable in respect of the CVRs.

Other Recent Developments

On March 9, 2023, the Company filed a Registration Statement on Form S-3 (File No. 333-270414) (the “Shelf”) with the SEC in relation to the registration of up to an aggregate of $250.0 million of its common stock, preferred stock, debt securities, warrants and/or units of any combination thereof for a period up to three years from the date of the filing. The Shelf became effective on March 17, 2023. The Company also simultaneously entered into a sales agreement with Cowen and Company, LLC (“Cowen”), as sales agent, providing for the offering, issuance and sale by the Company of up to an aggregate of $75.0 million of its common stock from time to time in “at-the-market” offerings under the Shelf (the “ATM”). The Company did not sell any shares of common stock under the ATM during the year ended December 31, 2023. As of December 31, 2023, there remained $75.0 million of common stock available for sale under the ATM.

On March 10, 2022, the Company closed a transaction with Oxford Biomedica (US) LLC ("OXB (US)"), to establish a new adeno-associated virus ("AAV") vector manufacturing company, Oxford Biomedica (US) LLC ("OXB (US) LLC") that provides AAV vector process development and manufacturing services to biotechnology companies. Under the terms of the agreement, the Company contributed its manufacturing team of 125 employees, manufacturing facility and equipment, manufacturing-related intellectual property and know-how and certain other assets. Oxford paid the Company $130.0 million of upfront cash and invested $50.0 million of cash to fund OXB (US) LLC in exchange for an 80 percent ownership interest, while Homology retained a 20 percent ownership interest in the new company and received a put option on this ownership position (see Note 6).

Since its inception and until recently, the Company has devoted substantially all of its resources to recruiting personnel, developing its technology platform and advancing its pipeline of product candidates through discovery, preclinical and clinical trials, developing and implementing manufacturing processes, building out manufacturing and research and development space, and maintaining and building its intellectual property portfolio. The Company is subject to a number of risks similar to those of other companies conducting high-risk, early-stage research and development of product candidates. Principal among these risks are dependency on key individuals and intellectual property, competition from other products and companies, and the technical and regulatory risks associated with the successful research, development and manufacturing of its product candidates.

To date, the Company has not generated any revenue from product sales and does not expect to generate any revenue from the sale of product in the foreseeable future. Through December 31, 2023, the Company has financed its operations primarily through public offerings of its common stock, the issuance of convertible preferred stock, and with proceeds from its transaction with Oxford (see Note 6), its collaboration and license agreement with a former collaboration partner and its private

placement with Pfizer (see Note 17). During the year ended December 31, 2023, the Company incurred a loss from operations of $101.4 million and as of December 31, 2023, had $542.1 million in accumulated deficit.

The Company has incurred and expects to continue to incur costs and expenditures in connection with the process of evaluating strategic alternatives. Though the Company has executed the Merger Agreement with Q32 effective November 16, 2023, there can be no assurance that the Company will be able to successfully consummate the Merger or any other strategic transaction. The process of evaluating strategic options has been and may continue to be costly, time-consuming and complex and the Company may incur significant costs related to this continued evaluation, such as legal, accounting and advisory fees and expenses and other related charges.

Based on current projections, management believes that the Company's cash and cash equivalents and short-term investments as of December 31, 2023 will enable the Company to continue its operations for at least one year from the date of this filing. However, due to the consideration of certain qualitative factors, including the discontinuation of all clinical trials and research activities, as well as the Company's workforce reduction of all but a few custodial employees, management has concluded there is substantial doubt regarding the Company's ability to continue as a going concern for more than twelve months from the date that the consolidated financial statements included in this Annual Report on Form 10-K have been issued. These financial statements do not include any adjustments that might result from the outcome of this uncertainty. Should the Company resume the development of product candidates, it would need to obtain substantial additional funding in connection with continuing operations, particularly if the Company were to resume its preclinical activities and clinical trials for its product candidates. There can be no assurance that the Company will be able to obtain sufficient capital to cover its costs on acceptable terms, if at all.

Basis of Presentation—The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business.

Pfizer Stock Purchase Agreement - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 09, 2020	Dec. 31, 2023	Dec. 31, 2022
Collaboration agreement revenue recognized		$ 1,156	$ 3,208
Pfizer Inc.
Common stock estimated fair value	$ 52,000
Stock purchase agreement remaining allocated value	8,000
Allocated Information Committee obligation	$ 8,000
Pfizer Inc. \| Collaborative Arrangement
Collaboration agreement revenue recognized		$ 1,200	3,200
Deferred revenue			$ 1,200
Private Placement
Issuance of common stock, net of discounts and issuance costs, Shares	5,000,000
Shares issued price per share	$ 12
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs	$ 60,000
Common stock purchase agreement condition	The shares of common stock sold to Pfizer were subject to a one-year lock-up from closing, during which time Pfizer was prohibited from selling or otherwise disposing of such shares.

Commitments and Contingencies - Summary of Cash Paid for Company's Operating Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 3,653	$ 3,326
Increase in lease liabilities and right-of-use assets due to lease remeasurement	$ 0	$ 6,262

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

. COMMITMENTS AND CONTINGENCIES

Operating Leases—In December 2017, the Company entered into a noncancelable operating lease for approximately 67,000 square feet of research and development, manufacturing and general office space in Bedford, Massachusetts. Prior to a subsequent amendment described below, the lease was set to expire in February 2027 with an option for an additional five-year term. Rent became due under the lease in two phases; rent on the first 46,000 square feet started in September 2018 and rent on the remaining 21,000 square feet started in March 2019. The initial annual base rent was $39.50 per square foot and increases by three percent annually. The Company is obligated to pay, on a pro-rata basis, real estate taxes and operating costs related to the premises. The lease agreement allowed for a tenant improvement allowance not to exceed $10.9 million, which the Company received in full, to be applied to the total cost of tenant improvements to the leased premises. The unamortized balance of the tenant improvement allowance was included in deferred rent incentives and recorded as a reduction to operating right-of-use asset upon adoption of the new leasing standards.

In November 2021, the Company entered into an amendment of its December 2017 lease agreement (the “Lease Amendment”) for its corporate headquarters in Bedford, Massachusetts. The Lease Amendment increased the space under lease by approximately 23,011 square feet (the "Expansion Premises") and extended the expiration date of the existing premises under the lease from February 2027 to June 2030. The payment term with respect to the Expansion Premises commenced on May 1, 2022, and continues for a period of ten years and five months. The term of the Expansion Premises and the existing premises are not coterminous. Annual base rent for the existing premise under the Lease Amendment is approximately $4.7 million beginning on March 1, 2027, and increases by three percent annually; annual base rent for the Expansion Premises is approximately $1.4 million per year and increases by three percent annually. The Lease Amendment allows for tenant improvement allowances not to exceed $6.3 million in the aggregate. The Lease Amendment was accounted for as a lease modification and the right-of-use asset and operating lease liability for the existing premises were remeasured at the modification date, which resulted in an increase of $10.9 million to both the right-of-use asset and operating lease liabilities. In February 2022, the Company revised its assumption for when it expected to utilize the tenant improvement allowances. This change in assumption was accounted for as a lease modification and the right-of-use asset and operating lease liability for the existing premises were remeasured at the modification date, which resulted in an increase of $0.2 million to both the right-of-use asset and operating lease liabilities.

In March 2022, in accordance with its transaction with OXB (US) LLC, the Company assigned all of its right, title and interest in, to and under its corporate headquarters lease to OXB (US) LLC and entered into a sublease agreement whereby OXB (US) LLC subleased certain premises in its facility to Homology. However, as the Company remained jointly and severally liable for the payment of rent under this lease, the Company was not released from being the primary obligor and therefore the related right-of-use asset and lease liability were not derecognized and remained on the Company’s balance sheet.

In September 2022, the Company concluded that 100% of the tenant improvement allowances would be utilized by OXB (US) LLC. This change in assumption was accounted for as a lease modification and the right-of-use asset and operating lease liability for the existing premises were remeasured at the modification date, which resulted in an increase of $6.1 million to both the right-of-use asset and operating lease liabilities.

On September 25, 2023, the Company signed and executed a release letter with its lessor related to its corporate headquarters lease. The lessor agreed to release the Company of all obligations under the lease effective October 1, 2023 (the "Release Date") in exchange for a $0.1 million cash payment. On October 1, 2023, the Company derecognized the right-of-use asset and operating lease liability and recorded the difference as a gain of $8.8 million within other income on the consolidated statements of operations. Because the Company’s sublease agreement with OXB (US) LLC remains in effect after termination of the head lease, the Company recorded a new right-of-use asset and an operating lease liability of $1.6 million, which equals the present value of the future sublease payments owed to OXB (US) LLC for the remaining term of the sublease. The Company's sublease expires on December 31, 2024.

During the fourth quarter of fiscal year 2023, the Company significantly reduced active use of its corporate headquarters, with the plan to fully abandon the space in the first quarter of fiscal year 2024. Accordingly, the Company shortened the remaining useful of its right-of-use asset to equal the time remaining until the planned abandonment date. This had no impact on the operating lease liability.

Prior to being released from obligation under the lease, the Company was acting as sublessor to OXB (US) LLC for accounting purposes. For the years ended December 31, 2023 and 2022, the Company received $2.3 million and $2.0 million, respectively, in sublease payments from OXB (US) LLC, which was recorded as a reduction to lease cost.

The following table summarizes operating lease costs and variable lease costs, as well as sublease income:


	For the Year ended December 31,
	2023			2022
	(in thousands)
Operating lease costs	$	4,273		$	3,913
Variable lease costs		1,771			2,142
Sublease income		(2,312	)		(1,979	)
Net lease cost	$	3,732		$	4,076

The maturities of the Company's operating lease liabilities and minimum lease payments as of December 31, 2023 were as follows:


For the Years Ending December 31,	Amount (in thousands)
2024	$	1,380
Total undiscounted lease payments	$	1,380
Less: imputed interest		(62	)
Present value of operating lease liabilities	$	1,318

The following table summarizes the lease term and discount rate as of December 31, 2023:


	December 31, 2023
Weighted-average remaining lease term (years)
Operating leases		1.0
Weighted-average discount rate
Operating leases		10.5	%

The following table summarizes the supplemental cash flow information related to the Company's operating leases:


	For the Year ended December 31,
	2023		2022
	(in thousands)
Cash paid for amounts included in the measurement of lease liabilities	$	3,653	$	3,326
Increase in lease liabilities and right-of-use assets due to lease remeasurements	$	—	$	6,262

Legal Proceedings—On March 25, 2022, the Company and certain of its executives were named as defendants in a putative securities class action lawsuit filed in the United States District Court for the Central District of California; Pizzuto v. Homology Medicines, Inc., No. 2:22–CV–01968 (C.D. Cal 2022). The complaint alleges that the Company failed to disclose certain information regarding efficacy and safety in connection with a Phase I/II HMI-102 clinical trial, and seeks damages in an unspecified amount. The case is in its early stages. The Company believes the claims alleged lack merit and has filed a motion to transfer venue (filed September 2, 2022) and a motion to dismiss (filed October 17, 2022). On April 18, 2023, the court granted the motion to transfer, finding that venue was not proper in the Central District of California and transferring the case to the District of Massachusetts. Following the transfer, the case number changed to 1:23-cv-10858-AK (D. Mass.). On May 9, 2023, the Massachusetts court issued an order permitting the parties to submit updated briefs in connection with the motion to dismiss, which were submitted on June 8, 2023, July 13, 2023, and August 3, 2023. On March 4, 2024, the Massachusetts court held oral argument on the Company’s motion to dismiss, which remains pending. As the outcome is not presently determinable, any loss is neither probable nor reasonably estimable.

On February 22, 2024, a purported stockholder of the Company, Kevin Welsh, filed a putative class action complaint against the Company and its directors related to the Company’s proposed Merger with Q32, alleging violations of Sections 14(a) and 20(a) of the Securities Exchange Act of 1934, as amended. Welsh v. Homology Medicines, Inc., No. 1:24-cv-00242 (D. Del.). The complaint alleges that the Company and its directors filed a proxy statement containing material omissions regarding financial forecasts and their respective analysis, and seeks damages in an unspecified amount. The case is in its early stages. The Company believes the claims alleged lack merit. As the outcome is not presently determinable, any loss is neither probable nor reasonably estimable.

Net Loss Per Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

NET LOSS PER SHARE

15. NET LOSS PER SHARE

The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at December 31, 2023 and 2022, from the

computation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect:


	December 31,
	2023		2022
Stock options to purchase common stock		9,551,041		9,865,734
Restricted stock units		341,339		543,179
Total		9,892,380		10,408,913

Summary of Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 39,266	$ 33,986
Cash
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents	749	19
Money Market Funds
Cash And Cash Equivalents [Line Items]
Total cash and cash equivalents	$ 38,517	$ 33,967

Commitments and Contingencies - Schedule of Maturities of Operating Lease Liabilities (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2024	$ 1,380
Total undiscounted lease payments	1,380
Less: imputed interest	(62)
Present value of operating lease liabilities	$ 1,318

Property and Equipment

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

PROPERTY AND EQUIPMENT

7. PROPERTY AND EQUIPMENT

Property and equipment, net consists of the following:


	December 31,
	2023		2022
	(in thousands)
Laboratory equipment	$	—	$	6,025
Computers and purchased software		—		644
Furniture and fixtures		—		645
Property and equipment, at cost		—		7,314
Less: accumulated depreciation and amortization		—		(6,236	)
Property and equipment, net	$	—	$	1,078

Depreciation expense for the years ended December 31, 2023 and 2022 was approximately $0.6 million and $1.3 million, respectively. The Company disposed of approximately $0.5 million and $0.1 million of property and equipment, net during each of the years ended December 31, 2023 and 2022, respectively.

Stock Incentive Plans - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 7,324	$ 13,054
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	5,952	7,867
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Share-based compensation expense	$ 1,372	$ 5,187

Accrued Expenses and Other Liabilities (Additional Information) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Payables and Accruals [Abstract]
Severance and related costs	$ 4.6

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Line Items]
Tax provision	$ 0	$ 715,000
Net operating loss carryforwards	400,000
Uncertain tax positions	0
Income tax expense, interest or penalties	0	$ 0
Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards	65,500,000
Orphan Drug
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 50,700,000
Tax credit carryforwards expiration year	2043
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 326,200,000
Net operating loss carryforwards indefinitely	$ 325,800,000
Net operating loss carryforwards expiration year	2035
Federal \| Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 65,500,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	317,300,000
State \| Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 17,200,000

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Retirement Benefits [Abstract]
Discretionary match made under the 401(k) Plan by employer	$ 0.4	$ 0.6

Restructuring and Other Charges (Tables)

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Schedule of Restructuring Liability in Accrued Compensation and Benefits

The Company’s restructuring liability, which was included in accrued compensation and benefits, consisted of the following:


(in thousands)	Employee-Related Costs
Accrued restructuring balance at January 1, 2023	$	—
Expenses incurred		10,279
Payments		(5,666	)
Accrued restructuring balance at December 31, 2023	$	4,613

Property and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Depreciation	$ 578	$ 1,293
Disposal of property and equipment	500	100
Property and equipment, net assets held for sale	$ 554	$ 0

Stock Incentive Plans

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

STOCK INCENTIVE PLANS

14. STOCK INCENTIVE PLANS

2015 Stock Incentive Plan

In December 2015, the Company’s Board of Directors adopted the 2015 Stock Incentive Plan (the “2015 Plan”), which provided for the grant of incentive stock options, nonqualified stock options and restricted stock awards to the Company’s employees, officers, directors, advisors, and outside consultants. Stock options granted under the 2015 Plan generally vest over a four-year period and expire ten years from the date of grant. Certain options provide for accelerated vesting if there is a change in control, as defined in the 2015 Plan. At December 31, 2023, there were no additional shares available for future grant under the 2015 Plan.

2018 Incentive Award Plan

In March 2018, the Company’s Board of Directors adopted and the Company’s stockholders approved the Homology Medicines, Inc. 2018 Incentive Award Plan (the “2018 Plan” and, together with the 2015 Plan, the “Plans”), which became effective on the day prior to the first public trading date of the Company’s common stock. Upon effectiveness of the 2018 Plan, the Company ceased granting new awards under the 2015 Plan.

The 2018 Plan provides for the grant of incentive stock options, nonqualified stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock or cash-based awards to employees and consultants of the Company and certain affiliates and directors of the Company. The number of shares of common stock initially available for issuance under the 2018 Plan was 3,186,205 shares of common stock plus the number of shares subject to awards outstanding under the 2015 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company on

or after the effective date of the 2018 Plan. In addition, the number of shares of common stock available for issuance under the 2018 Plan is subject to an annual increase on the first day of each calendar year beginning on January 1, 2019 and ending on and including January 1, 2028 equal to the lesser of (i) 4% of the Company’s outstanding shares of common stock on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as determined by the Company’s Board of Directors, provided that not more than 20,887,347 shares of common stock may be issued under the 2018 Plan upon the exercise of incentive stock options. As of December 31, 2023, there were 4,978,083 shares available for future grant under the 2018 Plan. On January 1, 2024, an additional 2,320,696 shares were added to the 2018 Plan, representing 4% of total common shares outstanding at December 31, 2023.

2018 Employee Stock Purchase Plan

In March 2018, the Company’s Board of Directors adopted, and the Company’s stockholders approved, the Homology Medicines, Inc. 2018 Employee Stock Purchase Plan (the “2018 ESPP”). The 2018 ESPP allows employees to buy Company stock through after-tax payroll deductions at a discount from market value. The 2018 ESPP is intended to qualify as an “employee stock purchase plan” under Section 423 of the Internal Revenue Code. The number of shares of common stock initially available for issuance under the 2018 ESPP was 353,980 shares of common stock plus an annual increase on the first day of each calendar year beginning on January 1, 2019 and ending on and including January 1, 2028 equal to the lesser of (i) 1% of the Company’s outstanding shares of common stock on the final day of the immediately preceding calendar year and (ii) such smaller number of shares of common stock as determined by the Company’s Board of Directors, provided that not more than 4,778,738 shares of common stock may be issued under the 2018 ESPP. As of December 31, 2023, there were 2,693,911 shares available for future grant under the 2018 ESPP. On January 1, 2024, an additional 580,174 shares were added to the 2018 ESPP, representing 1% of total common shares outstanding at December 31, 2023.

Under the 2018 ESPP, employees may purchase common stock through after-tax payroll deductions at a price equal to 85% of the lower of the fair market value on the first trading day of an offering period or the last trading day of an offering period. The 2018 ESPP generally provides for offering periods of six months in duration that end on the final trading day of each February and August. In accordance with the Internal Revenue Code, no employee will be permitted to accrue the right to purchase stock under the 2018 ESPP at a rate in excess of $25,000 worth of shares during any calendar year during which such a purchase right is outstanding (based on the fair market value per share of the Company’s common stock as of the first day of the offering period).

During the year ended December 31, 2023, 133,817 shares were issued under the 2018 ESPP for aggregate proceeds to the Company of $0.2 million. During the year ended December 31, 2022, 226,453 shares were issued under the 2018 ESPP for aggregate proceeds to the Company of $0.6 million. Pursuant to the 2018 ESPP, the Company recorded stock-based compensation of less than $0.1 million for each of the years ended December 31, 2023 and 2022, respectively.

Stock Options

The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model, with the assumptions noted in the table below. Expected volatility for the Company’s common stock was determined based on an average of the historical volatility of a peer group of publicly traded companies that are similar to the Company. The expected term of options was calculated using the simplified method, which represents the average of the contractual term of the option and the weighted-average vesting period of the option. The Company uses the simplified method because it does not have sufficient historical option exercise data to provide a reasonable basis upon which to estimate expected term. The assumed dividend yield is based upon the Company’s expectation of not paying dividends in the foreseeable future. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant for periods commensurate with the expected term of the award. The Company recognizes forfeitures as they occur.

The assumptions used in the Black-Scholes option pricing model are as follows:


	For the Year ended December 31,
	2023	2022
Expected volatility	69.2% - 69.7%	68.7% - 70.1%
Weighted-average risk-free interest rate	3.45% - 4.22%	1.46% - 4.16%
Expected dividend yield	— %	— %
Expected term (in years)	5.5 - 6.25	5.5 - 6.25
Underlying common stock fair value	$0.92-$1.60	$1.40-$4.17

The following table summarizes the Company’s stock option activity during the year ended December 31, 2023:


	Number of Options			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding at January 1, 2023		9,865,734		$	10.96		7.2	$	493
Granted		3,188,150		$	1.53
Exercised		(26,166	)	$	0.61
Cancelled/Forfeited		(3,476,677	)	$	7.05
Outstanding at December 31, 2023		9,551,041		$	9.26		5.2	$	66
Vested and expected to vest at December 31, 2023		9,551,041		$	9.26		5.2	$	66
Exercisable at December 31, 2023		7,061,128		$	11.35		4.3	$	66

The total intrinsic value of options exercised during the year ended December 31, 2023 and 2022 was insignificant for each period. The weighted-average grant date fair value of options granted during the years ended December 31, 2023 and 2022 was $1.01 and $1.68, respectively.

Stock Awards Modifications - Corporate Restructuring

In connection with the Company's reduction in force implemented in July and November of 2023 (see Note 9), the Company terminated approximately 86 employees and modified approximately 6.3 million existing stock options and approximately 1.0 million existing restricted stock units ("RSUs") granted to these terminated employees in prior periods. The modification of the vested stock options to permit terminated employees up to one year following their termination date to exercise their options, rather than the 90-day window for terminated employees, is accounted for as a modification under FASB ASC Topic 718, Compensation—Stock Compensation ("ASC 718"). Accordingly, the Company recognized incremental compensation cost on the modification date in an amount equal to the difference between the fair value of the awards before and after the modification. The fair value of the awards immediately before assumes an expected term equal to 90 days from the termination date, whereas the fair value immediately after assumes an expected term equal to one year from the termination date. Total incremental compensation cost recognized for the year ended December 31, 2023 related to awards that were vested prior to modification was less than $0.1 million. Certain terminated employees’ unvested stock options were also modified such that the stock options will vest in full upon a change of control occurring within 45 days of termination. The remaining unvested stock options were forfeited upon termination and the Company reversed all compensation cost previously recorded on the forfeited awards. Total compensation cost reversed in the year ended December 31, 2023 was approximately $0.4 million.

The terminated employees' RSUs were modified to accelerate the vesting of a portion of the RSUs that were unvested as of the employees’ termination dates. The accelerated vesting of certain RSUs is accounted for as a Type III (improbable to probable) modification under ASC 718. Accordingly, the Company reversed all compensation cost previously recorded on the awards that are not expected to vest under the original terms. Certain terminated employees’ unvested RSUs were also modified such that the RSUs will vest in full upon a change of control occurring within 45 days of termination. Total compensation cost reversed in the year ended December 31, 2023 was approximately $0.5 million. Total compensation cost of approximately $0.2 million, equal to the modification date fair value, was recognized over the remaining service period, beginning on the modification date and ending on each employee’s termination date.

Stock Awards Modifications - OXB (US) LLC Transaction

As part of the transaction with OXB (US) LLC (see Note 6), the Company transferred employees to OXB (US) LLC and modified approximately 1.6 million existing stock options and approximately 0.1 million existing restricted stock units granted to these transferred employees in prior periods in order to permit such individuals to continue vesting in their awards and exercise their vested options as long as they are employed by and provide services to OXB (US) LLC. The modification of the unvested stock awards to continue vesting was accounted for as a Type III (improbable to probable) modification under ASC 718. Accordingly, the Company reversed all compensation cost previously recorded on the awards that were not expected to vest under the original terms. Total compensation cost reversed in the year ended December 31, 2022 was less than $0.1 million. Total compensation cost of $0.8 million, equal to the modification date fair value, will be recognized over the

remaining service period. A portion of this total compensation cost will be included as a component of the loss from equity method investment.

The modification of the vested stock awards to permit transferred employees to exercise their options over the remaining life of the award, rather than the 90-day window for terminated employees, was accounted for as a modification under ASC 718. Accordingly, the Company recognized incremental compensation cost on the modification date in an amount equal to the difference between the fair value of the awards before and after modification. The fair value of the awards immediately before modification assumed a 90-day expected term, whereas the fair value immediately after assumed an expected term equal to the remaining life of the modified options. Total incremental compensation cost recognized in the year ended December 31, 2022 related to awards that were vested as of the modification date was $0.4 million.

Restricted Stock Units

The fair value of RSUs is based on the fair market value of the Company's common stock on the date of grant. Each RSU represents a contingent right to receive one share of the Company's common stock upon vesting. In general, RSUs vest annually in two or three equal installments on January 1st of each year after the grant date. The following table summarizes the Company's RSU activity for the year ended December 31, 2023:


	Number of Restricted Stock Units			Weighted- Average Grant Date Fair Value

Outstanding at January 1, 2023		543,179		$	6.12
Granted		483,850		$	1.60
Vested		(373,519	)	$	4.86
Forfeited		(312,171	)	$	2.59
Outstanding at December 31, 2023		341,339		$	2.95

Stock-based Compensation Expense

The Company recognizes compensation expense for awards to employees based on the grant date fair value of stock-based awards on a straight-line basis over the period during which an award holder provides service in exchange for the award, which is generally the vesting period. The Company recorded stock-based compensation expense related to stock options, shares purchased under the 2018 ESPP, restricted stock units and stock award modifications as follows:


	For the Year ended December 31,
	2023		2022
	(in thousands)
General and administrative	$	5,952	$	7,867
Research and development		1,372		5,187
	$	7,324	$	13,054

As of December 31, 2023, there was $13.1 million of unrecognized compensation expense related to unvested employee and non-employee share-based compensation arrangements granted under the Plans. The unrecognized compensation expense is estimated to be recognized over a period of 2.0 years at December 31, 2023.

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	58,017,412	57,483,910
Common stock, shares outstanding	58,017,412	57,483,910

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Mar. 01, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2023
Entity Registrant Name	Homology Medicines, Inc
Entity Central Index Key	0001661998
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Trading Symbol	FIXX
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		58,133,540
Entity Public Float			$ 45.8
Document Financial Statement Error Correction [Flag]	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.0001 par value
Security Exchange Name	NASDAQ
Entity File Number	001-38433
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-3468154
Entity Address, Address Line One	One Patriots Park
Entity Address, City or Town	Bedford
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01730
City Area Code	781
Local Phone Number	301-7277
Document Annual Report	true
Document Transition Report	false
Auditor Firm ID	34
Auditor Name	Deloitte & Touche LLP
Auditor Location	Boston, Massachusetts, USA

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of provision for income taxes

Provision for income taxes consists of the following:


	For the Year ended December 31,
	2023		2022
	(in thousands)
Federal tax provision:
Current	$	—	$	698
Deferred		—		—
Total federal tax provision		—		698
State tax provision:
Current		—		17
Deferred		—		—
Total state tax provision		—		17
Total tax provision	$	—	$	715

Schedule of Reconciliation between U.S. Federal Statutory Tax Rate and Effective Tax Rate

A reconciliation between the U.S. federal statutory tax and the Company’s tax provision is summarized below.


	For the Year ended December 31,
	2023			2022
	(in thousands)
Federal statutory rate	$	(23,722	)	$	(901	)
Tax credits		(7,699	)		(13,955	)
State taxes, net of federal tax benefit		(8,496	)		(2,994	)
Non-deductible expenses		595			875
Other		(2,351	)		1,410
Change in valuation allowance		41,673			16,280
Tax provision	$	—		$	715

Schedule of Deferred Tax Assets and Liabilities

The principal components of the Company’s deferred tax assets and liabilities consist of the following:


	For the Year ended December 31,
	2023			2022
	(in thousands)
Deferred tax assets:
Net operating losses	$	88,552		$	76,735
R&D credits		79,094			66,761
Equity compensation		8,215			7,888
Operating lease liabilities		356			8,003
Accrued expense and other		9,351			1,479
Deferred revenue		—			314
Capitalized R&D costs		35,987			24,477
Total deferred tax assets		221,555			185,657
Deferred tax liabilities:
Right-of-use assets		(176	)		(5,583	)
Depreciation		(54	)		(171	)
Other		—			(251	)
Total deferred tax liabilities		(230	)		(6,005	)
Valuation allowance		(221,325	)		(179,652	)
Net deferred taxes	$	—		$	—

Schedule of valuance allowance

A roll forward of the valuation allowance is as follows:


(in thousands)	Valuation Allowance
Balance at December 31, 2022	$	(179,652	)
Utilization of net operating losses against taxable income		—
Increase in net deferred taxes		(41,673	)
Balance at December 31, 2023	$	(221,325	)

Short-Term Investments

12 Months Ended

Dec. 31, 2023

Investments Disclosure [Abstract]

SHORT-TERM INVESTMENTS

4. SHORT-TERM INVESTMENTS

The Company may invest its excess cash in fixed income instruments denominated and payable in U.S. dollars including U.S. treasury securities, commercial paper, corporate debt securities and asset-backed securities in accordance with the Company’s investment policy that primarily seeks to maintain adequate liquidity and preserve capital.

The following table summarizes the Company’s short-term investments as of December 31, 2023 and December 31, 2022:


As of December 31, 2023	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
US Treasury securities	$	31,817	$	6	$	(5	)	$	31,818
Corporate debt securities		11,575		—		(6	)		11,569
Total	$	43,392	$	6	$	(11	)	$	43,387

As of December 31, 2022	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Commercial paper	$	57,138	$	—	$	—		$	57,138
US Treasury securities		65,160		—		(335	)		64,825
Corporate debt securities		19,146		—		(69	)		19,077
Total	$	141,444	$	—	$	(404	)	$	141,040

The Company utilizes the specific identification method in computing realized gains and losses. The Company had no realized gains and losses on its available-for-sale securities for the years ended December 31, 2023 and 2022. The contractual maturity dates of all of the Company’s investments are less than one year.

Equity Method Investment - Schedule of Summarized Financial Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Current assets	$ 83,914	$ 181,015
Current liabilities	11,573	22,576
Net loss	(112,961)	(5,005)
OXB Solutions [Member]
Schedule of Equity Method Investments [Line Items]
Current assets	10,763	39,237
Noncurrent assets	74,461	228,745
Current liabilities	6,151	12,352
Noncurrent liabilities	42,835	37,718
Revenues	30,699	29,380
Net loss	$ 167,062	$ 29,036

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are expected to be realized in cash, sold, or consumed within one year (or the normal operating cycle, if longer). Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1B

Reference 37: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-2

Reference 38: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-1A

Reference 39: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-1A

+ Details

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

+ Details

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Principles of Consolidation

Use of Estimates

Comprehensive Loss

Cash and Cash Equivalents and Restricted Cash

Short-Term Investments

securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other income.

Concentration of Credit Risk

Equity Method Investment

At December 31, 2023, the Company accounted for its investment in OXB (US) LLC using the equity method of accounting (see Note 6).

Offering Costs

Leases

Guarantees and Indemnifications

Property and Equipment


Computer equipment and software		3 years
Laboratory equipment and office furniture		5 years
Manufacturing equipment		5 - 7 years
Leasehold improvements		Shorter of the lease term or estimated useful life

Assets Held for Sale

Impairment of Long-Lived Assets

Research and Development Costs

Income Taxes

Segment Information

Revenue Recognition

Stock-based Compensation

Fair Value Measurements

•

Level 1—Quoted prices (unadjusted) in active markets for identical assets or liabilities.

•

Net Loss per Share

Recent Accounting Pronouncements

Related Party Transactions (Additional Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Sublease income		$ 2,312	$ 1,979
General and administrative		31,256	38,138
Prepaid expenses and other current assets		1,001	5,989
Oxford Biomedica [Member]
Related Party Transaction [Line Items]
Sublease income		2,300	2,000
Expenses recognized under the transitional services		300	700
Amounts Due To Related Party Current And Noncurrent		300	500
General and administrative		$ 500	1,700
Prepaid expenses and other current assets			300
Oxford Biomedica [Member] \| Vendor
Related Party Transaction [Line Items]
Amounts Paid To Related Party			1,100
Oxford Biomedica [Member] \| Supply Agreement [Member]
Related Party Transaction [Line Items]
Clinical supply requirements		50.00%
Purchase commitment amount		$ 29,700
Purchases of drug substance		21,700	13,900
Amounts Due To Related Party Current And Noncurrent		3,100	5,200
Oxford Biomedica [Member] \| Supply Agreement [Member] \| Process Development Services [Member]
Related Party Transaction [Line Items]
Recorded purchases		7,400	12,500
Oxford Biomedica [Member] \| Supply Agreement [Member] \| Stability and Other Support [Member]
Related Party Transaction [Line Items]
Recorded purchases		$ 1,000	1,800
Oxford Biomedica [Member] \| Transitional Services Agreement [Member]
Related Party Transaction [Line Items]
Amounts Due To Related Party Current And Noncurrent			100
Oxford Biomedica [Member] \| Transitional Services Agreement [Member] \| Vendor
Related Party Transaction [Line Items]
Amounts Due To Related Party Current And Noncurrent			$ 2,000
Oxford Biomedica [Member] \| Forecast [Member] \| Supply Agreement [Member]
Related Party Transaction [Line Items]
Purchase commitment amount	$ 0

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (112,961)	$ (5,005)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	578	1,293
Noncash lease expense	2,065	1,306
Loss from equity method investment	25,881	5,488
Stock-based compensation expense	7,324	13,054
Accretion of discount on short-term investments	(2,948)	(1,947)
Non-cash gain on lease termination	(8,866)	0
(Gain) loss on disposal of property and equipment	(94)	49
Gain on sale of business	0	(131,249)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	4,988	840
Accounts payable	2,090	(981)
Accrued expenses and other liabilities	(11,686)	7,418
Deferred revenue	(1,156)	(3,208)
Operating lease liabilities	(1,445)	(719)
Net cash used in operating activities	(96,230)	(113,661)
Cash flows from investing activities:
Purchases of short-term investments	(73,240)	(157,460)
Maturities of short-term investments	174,240	65,461
Proceeds from sale of business	0	130,000
Proceeds from sale of property and equipment	554	0
Purchases of property and equipment	(228)	(1,285)
Net cash provided by investing activities	101,326	36,716
Cash flows from financing activities:
Proceeds from issuance of common stock pursuant to employee stock purchase plan	168	595
Proceeds from issuance of common stock from option exercises	16	1
Net cash provided by financing activities	184	596
Net change in cash, cash equivalents and restricted cash	5,280	(76,349)
Cash, cash equivalents and restricted cash, beginning of period	33,986	110,335
Cash, cash equivalents and restricted cash, end of period	39,266	33,986
Supplemental disclosures of noncash investing and financing activities:
Lease Liability Settled Through Termination Of Lease	28,338	0
Lease liability obtained in exchange for right-of-use asset	1,625	0
Cash paid for income taxes	0	720
Unrealized gain (loss) on available for sale securities, net	399	(397)
Property and equipment additions included in accrued expenses and other liabilities	$ 0	$ 8

Cash and Cash Equivalents

12 Months Ended

Dec. 31, 2023

Cash and Cash Equivalents [Abstract]

CASH AND CASH EQUIVALENTS

3. CASH AND CASH EQUIVALENTS

From time to time, the Company may have cash balances in financial institutions in excess of federal deposit insurance limits. The Company has never experienced any losses related to these balances. The Company considers only those investments that are highly liquid, readily convertible to cash, and that mature within three months from date of purchase to be cash equivalents.

The following table summarizes the Company’s cash and cash equivalents:


	December 31,
	2023		2022
	(in thousands)
Cash	$	749	$	19
Money market funds		38,517		33,967
Total cash and cash equivalents	$	39,266	$	33,986

Related Party Transactions

12 Months Ended

Dec. 31, 2023

RELATED PARTY TRANSACTIONS

18. RELATED PARTY TRANSACTIONS

Oxford Biomedica (US) LLC

As described in Note 6, the Company has significant influence over, but does not control, OXB (US) LLC through its noncontrolling representation on OXB Solution’s board of directors and the Company’s equity interest in OXB (US) LLC. In March 2022, concurrently with the closing of the transaction with OXB (US) LLC, the Company entered into certain ancillary agreements with OXB (US) LLC including a supply agreement, a lease assignment and assumption agreement, a sublease agreement and a transitional services agreement.

Supply Agreement

Pursuant to the terms of the Manufacturing and Supply Agreement with OXB (US) LLC entered into in March 2022 (the "Supply Agreement"), the Company agreed to purchase from OXB (US) LLC at least 50% of its clinical supply requirements of AAV-based products during the initial term of the supply agreement. The Supply Agreement provides for an initial term of three years, which may be extended for an additional one-year term. Under the Supply Agreement, the Company was committed to purchase a minimum number of batches of drug substance and drug product, as well as process development services, for a total commitment of approximately $29.7 million in 2023. As of December 31, 2023, the Company had no remaining purchase obligations to OXB (US) LLC pursuant to the Supply Agreement; there are no minimum purchase commitments in 2024 (year three) of the Supply Agreement. After the initial term, the Company will have the right to terminate the Supply Agreement for convenience or other reasons specified in the Supply Agreement upon prior written notice. Either party may terminate the Supply Agreement upon an uncured material breach by the other party or upon the bankruptcy or insolvency of the other party.

During the years ended December 31, 2023 and 2022, the Company recorded purchases of drug substance from OXB (US) LLC related to the Supply Agreement of approximately $21.7 million and $13.9 million, respectively, purchases of process development services of approximately $7.4 million and $12.5 million, respectively, and stability and other support of approximately $1.0 million and $1.8 million, respectively. These amounts are included within research and development expenses on the Company's consolidated statements of operations. The amounts due to OXB (US) LLC under the Supply Agreement were $3.1 million and $5.2 million as of December 31, 2023 and 2022, respectively, and were included in accounts payable and accrued expenses and other liabilities on the Company's consolidated balance sheets.

Lease Assignment and Sublease Agreement

As described in Note 10, the Company leases space for research and development, manufacturing and general office space in Bedford, Massachusetts. In March 2022, the Company and OXB (US) LLC entered into a lease assignment and assumption agreement pursuant to which Homology assigned all of its right, title and interest in, to and under this lease to OXB (US) LLC and a sublease agreement whereby OXB (US) LLC subleased certain premises in its facility to Homology. However, as the Company remained jointly and severally liable for the payment of rent under this lease, the Company was not released from being the primary obligor under such lease and therefore the related right-of-use asset and operating lease liability were not derecognized and the Company recorded sublease income from OXB (US) LLC as if it were subleasing the space to OXB (US) LLC. See Note 10 for details.

During the years ended December 31, 2023 and 2022, the Company recorded sublease income of $2.3 million and $2.0 million, respectively, related to the sublease agreement with OXB (US) LLC. This amount was recognized as a reduction to lease expense in the Company's consolidated statements of operations.

During 2023, OXB (US) LLC assumed responsibility for paying the landlord for invoices related to the leased property and, as such, the Company began making direct payments to OXB (US) LLC for amounts due to OXB (US) LLC under the sublease. Therefore, as of December 31, 2023, the amount of sublease income payable to OXB (US) LLC was $0.3 million and was included in accrued expenses on the Company's consolidated balance sheets. As of December 31, 2022, the amount of sublease income receivable from OXB (US) LLC was $0.5 million and was included in prepaid expenses and other current assets on the Company's consolidated balance sheets.

Transitional Services Agreement

Under the transitional services agreement with OXB (US) LLC (the “Services Agreement”), the Company is performing certain services for the benefit of OXB (US) LLC and OXB (US) LLC is performing certain services for the benefit of the Company. The term of the Services Agreement will not exceed eighteen months and lasts until the earlier of termination for convenience, termination for cause in the event of an uncured material breach, termination as a result of bankruptcy of either party, and expiration or termination of the only remaining outstanding service as set forth in the Services Agreement. Each company is fully reimbursing the other for these services. As of December 31, 2023, the Services Agreement was substantially complete.

Expenses incurred by the Company for services provided by OXB (US) LLC recognized under the Services Agreement totaled approximately $0.3 million and $0.7 million for the years ended December 31, 2023 and 2022, respectively, and are presented within research and development expenses in the consolidated statements of operations as the services related to facilities support within the Company's research and development labs. The Company did not have a payable balance to OXB (US) LLC under the Services Agreement as of December 31, 2023. As of December 31, 2022, the amount due to OXB (US) LLC under the Services Agreement was $0.1 million and was included in accrued expenses and other liabilities on the Company's consolidated balance sheets.

The Company provided finance, human resources, IT and legal services to OXB (US) LLC under the Services Agreement and recognized $0.5 million and $1.7 million for the years ended December 31, 2023 and 2022, respectively, for amounts reimbursed by OXB (US) LLC as a reduction to general and administrative expense in the Company's consolidated statements of operations. The Company did not provide reimbursable services to OXB (US) LLC under the Services Agreement during the second half of 2023 and did not have a receivable balance from OXB (US) LLC as of December 31, 2023. As of December 31, 2022, the Company had a receivable balance of $0.3 million from OXB (US) LLC which was recorded as a component of prepaid expenses and other current assets in the Company's condensed consolidated balance sheets. Pursuant to the Services Agreement, the Company had been paying vendors on OXB (US) LLC's behalf; this process was fully transitioned to OXB (US) LLC in 2023. As of December 31, 2022, the amount receivable from OXB (US) LLC for amounts paid to vendors on their behalf was $1.1 million and was included in prepaid expenses and other current assets on the Company's consolidated balance sheets. In addition, as of December 31, 2022, the Company had an amount due to OXB (US) LLC of $2.0 million as a result of a year-end reconciliation between the two companies related to vendor invoicing.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Income Taxes - Schedule of valuance allowance (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Income Tax Disclosure [Abstract]
Balance at December 31, 2022	$ (179,652)
Utilization of net operating losses against taxable income	0
Increase in net deferred taxes	(41,673)
Balance at December 31, 2023	$ (221,325)

Commitments and Contingencies - Schedule of Lease Term and Discount Rate (Details)	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Weighted-average remaining lease term (years), Operating leases	1 year
Weighted-average discount rate, Operating leases	10.50%

Short-Term Investments - Summary of Short Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	$ 43,392	$ 141,444
Cash equivalents and short-term investments, Unrealized Gains	6	0
Cash equivalents and short-term investments, Unrealized Losses	(11)	(404)
Cash equivalents and short-term investments, Fair Value	43,387	141,040
Commercial Paper
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost		57,138
Cash equivalents and short-term investments, Unrealized Gains		0
Cash equivalents and short-term investments, Unrealized Losses		0
Cash equivalents and short-term investments, Fair Value		57,138
U.S Treasury Securities
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	31,817	65,160
Cash equivalents and short-term investments, Unrealized Gains	6	0
Cash equivalents and short-term investments, Unrealized Losses	(5)	(335)
Cash equivalents and short-term investments, Fair Value	31,818	64,825
Corporate Debt Securities
Schedule Of Cash Cash Equivalents And Available For Sale Securities [Line Items]
Cash equivalents and short-term investments, Amortized Cost	11,575	19,146
Cash equivalents and short-term investments, Unrealized Gains	0	0
Cash equivalents and short-term investments, Unrealized Losses	(6)	(69)
Cash equivalents and short-term investments, Fair Value	$ 11,569	$ 19,077

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Schedule of Estimated Useful Life of Asset


Computer equipment and software		3 years
Laboratory equipment and office furniture		5 years
Manufacturing equipment		5 - 7 years
Leasehold improvements		Shorter of the lease term or estimated useful life

License Agreements

12 Months Ended

Dec. 31, 2023

License Agreement [Abstract]

LICENSE AGREEMENTS

11. LICENSE AGREEMENTS

City of Hope

In April 2016, the Company entered into an exclusive license agreement with City of Hope, or COH, an academic research and medical center. COH granted the Company an exclusive, sublicensable, worldwide license, or the COH License, to certain AAV vector-related patents and know-how owned by COH to develop, manufacture, use and commercialize products and services covered by such patents and know-how in any and all fields.

The Company is required to pay an annual license fee of $25,000, reimburse COH for patent costs incurred, pay amounts up to $3.2 million upon the achievement of certain development and commercialization milestones for each product under the license, pay royalties on future sales in the low single-digits and royalties on sublicense revenue in the low double-digits, if any. Other than the annual license fee, there were no payments to COH in 2022. In January 2023, the Company paid $50,000 to COH upon dosing the first patient in the pheEDIT Phase 1 clinical trial.

On August 6, 2021, the Company received notice from COH that it did not accomplish at least one of the partnering milestones by the applicable deadline, as set forth in the COH License. This notice does not affect the Company's exclusive license in the field of mammalian therapeutics, including all human therapeutics, associated diagnostics, and target validation, or the Mammalian Therapeutic Field, where the Company retains exclusive rights. Instead, the notice served as written notice that the exclusive license granted pursuant to the COH License in all fields except the Mammalian Therapeutic Field converted from exclusive to non-exclusive effective as of September 20, 2021, which was forty-five days from the receipt of notice. In connection with the conversion, any royalty obligations and sublicensee fees relating to fields outside of the Mammalian Therapeutic Field shall be reduced by a certain percentage. This change to the Company's exclusive worldwide license with COH does not impact any of its product candidates, including HMI-102, HMI-103, HMI-104, HMI-203 and HMI-204.

Short-Term Investments - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash Cash Equivalents And Available For Sale Securities [Abstract]
Realized gains and losses on available-for-sale securities	$ 0	$ 0
Contractual maturity date of investments	less than one year	less than one year

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Transfers between fair value measure levels	$ 0	$ 0

Cash and Cash Equivalents (Tables)

12 Months Ended

Dec. 31, 2023

Cash and Cash Equivalents [Abstract]

Summary of Cash and Cash Equivalents

The following table summarizes the Company’s cash and cash equivalents:


	December 31,
	2023		2022
	(in thousands)
Cash	$	749	$	19
Money market funds		38,517		33,967
Total cash and cash equivalents	$	39,266	$	33,986

Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended
	Nov. 16, 2023	Mar. 09, 2023	Mar. 10, 2022	Nov. 09, 2020	Dec. 31, 2023	Dec. 31, 2022	Jul. 31, 2023
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Reduction in workforce							86.00%
Proceeds from Sale of Equity Method Investments			$ 130,000
Net loss					$ 112,961	$ 5,005
Loss from operations					101,429	133,281
Accumulated deficit					$ 542,098	$ 429,137
Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs		$ 250,000
Oxford Biomedica plc
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from Sale of Equity Method Investments			50,000
Upfront Payment Received			$ 130,000
ATM
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Issuance of common stock, net of discounts and issuance costs, Shares					0
Proceeds through future financings					$ 75,000
ATM \| Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds through future financings		$ 75,000
ATM \| Oxford Biomedica plc
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Sale of Stock, Percentage of Ownership after Transaction			80.00%
ATM \| Homology
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Sale of Stock, Percentage of Ownership after Transaction			20.00%
Private Placement
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Issuance of common stock, net of discounts and issuance costs, Shares				5,000,000
Shares issued price per share				$ 12
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs				$ 60,000
Merger Agreement \| Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds through future financings	$ 80,000
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs	195,000
Concurrent Financing
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds from issuance of common stock in follow-on public offering, net of discounts and issuance costs	42,000
Concurrent Financing \| Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Proceeds through future financings	$ 42,000

Short-Term Investments (Tables)

12 Months Ended

Dec. 31, 2023

Investments Disclosure [Abstract]

Summary of Short Term Investments

The following table summarizes the Company’s short-term investments as of December 31, 2023 and December 31, 2022:


As of December 31, 2023	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
US Treasury securities	$	31,817	$	6	$	(5	)	$	31,818
Corporate debt securities		11,575		—		(6	)		11,569
Total	$	43,392	$	6	$	(11	)	$	43,387

As of December 31, 2022	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Commercial paper	$	57,138	$	—	$	—		$	57,138
US Treasury securities		65,160		—		(335	)		64,825
Corporate debt securities		19,146		—		(69	)		19,077
Total	$	141,444	$	—	$	(404	)	$	141,040

Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 43,387	$ 141,040
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	38,517	33,967
Financial assets, fair value	81,904	175,007
Repurchase agreements	38,517	33,967
Short-term investments	43,387	141,040
Fair Value, Measurements, Recurring \| Money Market Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	38,517	33,967
Repurchase agreements	38,517	33,967
Fair Value, Measurements, Recurring \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		57,138
Fair Value, Measurements, Recurring \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	11,569	19,077
Fair Value, Measurements, Recurring \| U.S Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	31,818	64,825
Fair Value, Measurements, Recurring \| Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	38,517	33,967
Financial assets, fair value	38,517	33,967
Repurchase agreements	38,517	33,967
Fair Value, Measurements, Recurring \| Quoted Prices (Unadjusted) in Active Markets for Identical Assets (Level 1) \| Money Market Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents, fair value	38,517	33,967
Repurchase agreements	38,517	33,967
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets, fair value	43,387	141,040
Short-term investments	43,387	141,040
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments		57,138
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	11,569	19,077
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| U.S Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 31,818	$ 64,825

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Schedule of Anti-dilutive Effect Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders

computation of diluted net loss per share attributable to common stockholders because including them would have had an anti-dilutive effect:


	December 31,
	2023		2022
Stock options to purchase common stock		9,551,041		9,865,734
Restricted stock units		341,339		543,179
Total		9,892,380		10,408,913

License Agreements - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
License Agreement [Line Items]
Collaboration agreement revenue recognized	$ 1,156	$ 3,208
Research and development	$ 62,002	$ 98,351
Common stock, shares issued	58,017,412	57,483,910
City of Hope
License Agreement [Line Items]
Annual license fee	$ 25,000
City of Hope \| Maximum
License Agreement [Line Items]
Development and commercialization milestone payment	3,200
City of Hope \| January 2023
License Agreement [Line Items]
Amount paid to related party upon dosing the first patient	$ 50,000

Stock Incentive Plans - Summary of RSU Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of Options, Outstanding at Beginning Balance	9,865,734
RSU Granted	3,188,150
Number of Options, Outstanding at Ending Balance	9,551,041	9,865,734
Weighted-Average Grant Date Fair Value, Granted	$ 1.01	$ 1.68
RSU Member
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of Options, Outstanding at Beginning Balance	543,179
RSU Granted	483,850
RSU Vested	(373,519)
RSU Forfeited	(312,171)
Number of Options, Outstanding at Ending Balance	341,339	543,179
Weighted-Average Grant Date Fair Value, Outstanding, Beginning Balance	$ 6.12
Weighted-Average Grant Date Fair Value, Granted	1.6
Weighted-Average Grant Date Fair Value, Vested	4.86
Weighted-Average Grant Date Fair Value, Forfeited	2.59
Weighted-Average Grant Date Fair Value, Outstanding, Ending Balance	$ 2.95	$ 6.12