0001739410-24-000035 | 10-K | XBRL Viewer

LEASES - Summary of Company's Operating Lease on the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets:
Operating lease right-of-use assets	$ 346	$ 524
Liabilities:
Operating lease liabilities	219	181
Operating lease liabilities, noncurrent	173	374
Total operating lease liabilities	$ 392	$ 555

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating expenses:
Research and development	$ 53,544	$ 40,689
General and administrative	25,388	27,195
Total operating expenses	78,932	67,884
Loss from operations	(78,932)	(67,884)
Other income:
Interest income	6,147	1,963
Other income	262	342
Total other income, net	6,409	2,305
Loss before equity in losses of joint venture	(72,523)	(65,579)
Loss on investment in joint venture	2,041	1,075
Net loss	$ (74,564)	$ (66,654)
Net loss per common share, basic (in dollars per share)	$ (1.84)	$ (2.09)
Net loss per common share, diluted (in dollars per share)	$ (1.84)	$ (2.09)
Weighted-average common shares outstanding, basic (in shares)	40,447,388	31,821,311
Weighted-average common shares outstanding, diluted (in shares)	40,447,388	31,821,311
Other comprehensive gain (loss):
Net unrealized gain (loss) on marketable securities	$ 229	$ (214)
Other comprehensive gain (loss)	229	(214)
Comprehensive loss	$ (74,335)	$ (66,868)

LEASES

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

LEASES

We have operating leases for approximately nine thousand square feet of corporate office space. The weighted-average remaining lease term as of December 31, 2023 was 1.8 years. The weighted-average discount rate utilized on our operating lease liabilities as of December 31, 2023 was 4.00%.

Operating leases are included in operating lease ROU assets, operating lease liabilities, and operating lease liabilities, noncurrent in our consolidated balance sheets as of December 31, 2023 and 2022.

The following table summarizes the presentation of the Company's operating lease as presented on the consolidated balance sheets:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Assets:
Operating lease right-of-use assets	$	346	$	524
Liabilities:
Operating lease liabilities	$	219	$	181
Operating lease liabilities, noncurrent	173		374
Total operating lease liabilities	$	392	$	555

Future minimum lease payments from December 31, 2023 until the expiration of the operating lease are as follows:


(in thousands)
2024	$	230
2025	176
2026	—
Thereafter	—
Total lease payments	406
Less: imputed discount rate	(14)
Carrying value of operating lease liabilities	$	392

The Company incurred $0.2 million in operating lease rent expense for both the years ended December 31, 2023 and 2022, respectively. Lease payments made were $0.2 million for both the years ended December 31, 2023 and 2022, respectively, with such amounts reflected in the consolidated statements of cash flows in operating activities.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION - Summary of Property and Equipment Estimated Useful Lives (Details)	Dec. 31, 2023
Computer and other equipment
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Capitalized software
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	6 years

STOCKHOLDERS' EQUITY - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		12 Months Ended
	Jan. 01, 2023	Jan. 01, 2022	Nov. 30, 2022	Aug. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Common stock, shares authorized (in shares)					200,000,000	200,000,000
Common stock, shares issued (in shares)					37,829,565	37,837,369
Common stock, shares outstanding (in shares)					37,829,565	37,837,369
Preferred stock, shares authorized (in shares)					50,000,000	50,000,000
Preferred stock, shares outstanding (in shares)					0	0
Weighted average grant date fair value (in dollars per share)					$ 4.93	$ 9.99
Intrinsic value of stock options vested					$ 0	$ 0
Unrecognized share-based compensation expense					$ 16,900
Total unrecognized compensation costs, weighted average period for recognition					2 years 4 months 24 days
Options exercisable, Outstanding, Weighted-Average Contractual Term (in years)					8 years 21 days
Restricted Stock Awards
Class of Stock [Line Items]
Unrecognized share-based compensation expense, restricted stock awards					$ 1,300
Options exercisable, Outstanding, Weighted-Average Contractual Term (in years)					1 year 2 months 12 days
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Total unrecognized compensation costs, weighted average period for recognition					1 year 10 months 24 days
Unrecognized share-based compensation expense, restricted stock units					$ 1,000
2021 Equity Incentive Plan
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)					5,440,344
Percentage of number of shares of common stock outstanding							5.00%
Number of shares increased (in shares)	1,891,868	1,606,549
Shares reserved for future issuance (in shares)					6,775,026
Share-based compensation arrangement by share-based payment award, number of shares available for grant (in shares)					2,284,232
2021 Employee Stock Purchase Plan
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares authorized (in shares)					291,324
Percentage of number of shares of common stock outstanding							1.00%
Number of shares increased (in shares)	378,373	321,309
Share-based compensation arrangement by share-based payment award, number of shares available for grant (in shares)					872,878
Common stock shares outstanding (in shares)					582,648
Shares issued (in shares)					79,283	38,845
Share-based compensation arrangement by share-based payment award, purchase price of common stock, percent					85.00%
Total share based compensation					$ 200	$ 100
Pre-Funded Warrants
Class of Stock [Line Items]
Common stock price per share (in dollars per share)			$ 5.9999
Number of securities called by warrants or rights (in shares)			3,333,388
Pre-funded warrants exercise price (in dollars per share)			$ 0.0001
Total IPO
Class of Stock [Line Items]
Stock issued during the period (in shares)				7,130,000
Common stock price per share (in dollars per share)				$ 13.00
Proceeds from the issuance of common stock from exercise of stock options				$ 92,700
Net proceeds				$ 83,000
Over Allotment on Initial Public Offering
Class of Stock [Line Items]
Stock issued during the period (in shares)				930,000
Follow-on Offering
Class of Stock [Line Items]
Stock issued during the period (in shares)			5,803,655
Common stock price per share (in dollars per share)			$ 6.00
Proceeds from the issuance of common stock from exercise of stock options			$ 54,800
Net proceeds			$ 50,800
Follow-on Offering \| Pre-Funded Warrants
Class of Stock [Line Items]
Number of securities called by warrants or rights (in shares)			3,333,388		3,333,388
Pre-funded warrants exercise price (in dollars per share)			$ 0.0001
Percent excess limit					9.99%
Days of notice					61 days
Percentage of common stock beneficially owned not exceed					19.99%
Over Allotment On Follow-On Offering
Class of Stock [Line Items]
Stock issued during the period (in shares)			803,654

INCOME TAXES - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating Loss Carryforwards [Line Items]
Income tax benefit	$ 0	$ 0
Federal net operating loss carry forwards	135,100,000
State net operating loss carry forwards	134,600,000
Income tax penalties and interest accrued	0	$ 0
Income tax examination, penalties and interest accrued	0
Federal or state and local income tax returns	0
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Deferred tax assets, tax credit carryforwards	17,200,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Deferred tax assets, tax credit carryforwards	$ 500,000

NET LOSS PER COMMON SHARE - Summary of Basic and diluted loss per common share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Net loss	$ (74,564)	$ (66,654)
Weighted-average number of common shares outstanding, basic (in shares)	40,447,388	31,821,311
Weighted-average number of common shares outstanding, diluted (in shares)	40,447,388	31,821,311
Net loss per common share, basic (in dollars per share)	$ (1.84)	$ (2.09)
Net loss per common share, diluted (in dollars per share)	$ (1.84)	$ (2.09)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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+ Details

MARKETABLE SECURITIES - Additional Information (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Aggregate fair value of available-for-sale debt securities in an unrealized loss position	$ 40,000,000	$ 70,000,000
Continuous unrealized loss position for more than twelve months	0	0
Allowance for credit losses	$ 0	$ 0

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References + Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

SUBSEQUENT EVENTS (Details) - Subsequent Event $ in Millions	Feb. 06, 2024 USD ($)
Subsequent Event [Line Items]
Positions eliminated (as a percent)	45.00%
Expected restructuring cost	$ 3.3

INVESTMENT IN JOINT VENTURE (Details) - USD ($)	12 Months Ended
INVESTMENT IN JOINT VENTURE (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Investment in joint venture	$ 2,250,000	$ 300,000
Additional financial support outside of capital contribution	0	0
Allocable share of losses recorded	(2,041,000)	(1,075,000)
Investment in joint venture	$ 239,000	30,000
RE Ventures I, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of interest of joint venture entity	50.00%
Investment in joint venture	$ 2,300,000	300,000
Allocable share of losses recorded	2,000,000	1,100,000
Investment in joint venture	$ 200,000	$ 30,000

BALANCE SHEET COMPONENTS

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

BALANCE SHEET COMPONENTS

Property and Equipment—

Property and equipment consisted of the following as of December 31, 2023 and 2022:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Computer and other equipment	$	191	$	180
Capitalized software	89		89
Furniture and fixtures	151		151
Leasehold improvements	338		338

Less accumulated depreciation	(523)		(373)
Property and equipment—net	$	246	$	385

Depreciation expense totaled $0.1 million and $0.2 million for the years ended December 31, 2023 and 2022, respectively.

Prepaid Expenses and Other Assets—

Prepaid expenses and other assets consisted of the following as of December 31, 2023 and 2022:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Research and development	$	2,067	$	7,904
Insurance	446		933
Other prepaids	293		615
Other assets	2,054		1,050
	$	4,860	$	10,502

Accrued Expenses—

Accrued expenses consisted of the following as of December 31, 2023 and 2022:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Research and development	$	4,123	$	3,582
Compensation and related expenses	3,166		4,703
Professional fees	332		510
Other	447		654
	$	8,068	$	9,449

BALANCE SHEET COMPONENTS - Schedule Of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Research and development	$ 4,123	$ 3,582
Compensation and related expenses	3,166	4,703
Professional fees	332	510
Other	447	654
Accrued expenses	$ 8,068	$ 9,449

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Presentation

Basis of Presentation—The accompanying consolidated financial statements have been prepared with accounting principles generally accepted in the United States of America (“GAAP”), and pursuant to the rules and regulations of the Securities and Exchange Commission (the "SEC"). Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) promulgated by the Financial Accounting Standards Board (“FASB”).

Principles of Consolidation

Principles of Consolidation—The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

Use of Estimates—The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make certain estimates and assumptions that affect the reported amounts and disclosures in the consolidated financial statements. While management believes that estimates and assumptions used in the preparation of the consolidated financial statements are appropriate, actual results could differ from those estimates. The most significant estimates are those used in the determination of the fair value of its common units and incentive units awarded to employees prior to the Company's IPO, for purposes of recording stock-based incentive compensation, the fair value of stock options, as well as contracted research and development expenses incurred.

Liquidity and Ability to Continue as a Going Concern

Liquidity and Ability to Continue as a Going Concern—The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern. Management has evaluated whether there are conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the financial statements are issued. Since its inception, the Company has incurred net losses and negative cash flows from operations.

During the years ended December 31, 2023 and 2022, the Company incurred a net loss of $74.6 million and $66.7 million, respectively. In addition, as of December 31, 2023, the Company had an accumulated deficit of

$235.2 million. The Company expects to continue to generate operating losses and negative cash flows in the foreseeable future.

The Company currently expects that cash, cash equivalents and marketable securities of $109.9 million at December 31, 2023 will be sufficient to fund its operating expenses and capital requirements for more than 12 months from the date the consolidated financial statements are issued. However, we do not anticipate that the current cash, cash equivalents and marketable securities as of December 31, 2023 will be sufficient for us to fund any of our product candidates through regulatory approval, and we will need to raise substantial additional capital to complete the development and commercialization of our product candidates, if approved. We may satisfy our future cash needs through the sale of equity securities, debt financings, working capital lines of credit, corporate collaborations or license agreements, grant funding, interest income earned on invested cash balances or a combination of one or more of these sources.

Collaboration Arrangements

Collaboration Arrangements—The Company considers the nature and contractual terms of an arrangement to assess whether an arrangement involves a joint operating activity that expose two or more parties to significant risks and rewards dependent on the commercial success of the activity. If the Company is an active participant and is exposed to significant risks and rewards dependent on the commercial success of the activity, the Company accounts for such arrangement as a collaborative arrangement under ASC 808, Collaborative Arrangements ("ASC 808"). ASC 808 describes arrangements within its scope and considerations surrounding presentation and disclosure, with recognition matters subjected to other authoritative guidance, in certain cases by analogy.

For arrangements determined to be within the scope of ASC 808 for certain research and development activities where a collaborative partner is not a customer following the guidance of ASC 606, Revenue Recognition ("ASC 606"), the Company accounts for payments due to a collaboration partner as research and development expense and for payments owed to us from our collaboration partner for the reimbursement of research and development costs as a contra-expense in the period such expenses are incurred. The Company classifies payments owed or receivables recorded as other current liabilities and other current assets, respectively, in the Company’s consolidated balance sheets. See Note 3, “License and Collaboration Agreements” for additional details.

Asset Acquisitions

Asset Acquisitions— The Company evaluates acquisitions of assets and other similar transactions to assess whether or not the transaction should be accounted for as a business combination or asset acquisition by first applying a screen test to determine whether substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. If this screen criteria is met, the transaction is accounted for as an asset acquisition. If not, further determination is required as to whether or not the Company has acquired inputs and processes that have the ability to create outputs, which would meet the definition of a business. The Company measures and recognizes asset acquisitions that are not deemed to be business combinations based on the cost to acquire the assets, which includes transaction costs. In an asset acquisition, the cost allocated to acquire in-process research and development ("IPR&D") with no alternative future use is charged to research and development expense at the acquisition date. See Note 3, “License and Collaboration Agreements” for additional details.

Variable Interest Entity

Variable Interest Entity—The Company evaluates its ownership, contractual, and other interests in entities to determine if it has any variable interest in a variable interest entity (“VIE”). These evaluations are complex, involve judgment, and the use of estimates and assumptions based on available historical information, among other factors. If the Company determines that an entity in which it holds a contractual, or ownership, interest is a VIE and that the Company is the primary beneficiary, the Company consolidates such entity in its consolidated financial statements. The primary beneficiary of a VIE is the party that meets both of the following criteria: (i) has the power to make decisions that most significantly affect the economic performance of the VIE; and (ii) has the obligation to absorb losses or the right to receive benefits that in either case could potentially be significant to the VIE. Management performs ongoing reassessments of whether changes in the facts and circumstances regarding the Company’s involvement with a VIE will cause the consolidation conclusion to change. Changes in consolidation status are applied prospectively. The Company evaluated its investment in RE Ventures I, LLC, a limited liability company (“REV-I”), defined in Note 9, and concluded that it represented a VIE and was not deemed the primary beneficiary. If the Company is not deemed to be the primary beneficiary in a VIE, the Company accounts for the investment or other variable interests in a VIE in accordance with the applicable GAAP. See Note 9, “Investment in Joint Venture” for additional details.

Equity Method Investments

Equity Method Investments—The Company accounts for investments for which it does not have a controlling interest in accordance with ASC 323, Investments – Equity Method and Joint Ventures ("ASC 323"). The

Company recognizes its pro-rata share of income and losses in “loss on investment in joint venture” on the consolidated statements of operations and comprehensive loss, with a corresponding change to the investment in joint venture asset on the consolidated balance sheets.

Financial Instruments

Financial Instruments—The Company’s principal financial instruments are comprised of cash, cash equivalents, available for sale marketable securities, accounts payable and accrued liabilities. The carrying value of all financial instruments approximates fair value.

Concentrations of Credit Risk

Concentrations of Credit Risk—Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company invests its excess cash in money market funds and marketable securities in government insured financial institutions that are subject to minimal credit and market risk. Management believes that the Company is not exposed to significant credit risk as the Company’s 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.

Cash and Cash Equivalents

Cash and Cash Equivalents—The Company classifies amounts on deposit in banks and cash invested temporarily in various instruments, primarily money market funds, with original maturities of three months or less at the time of purchase as cash and cash equivalents. The carrying amounts reported in the consolidated balance sheets represent the fair values of cash and cash equivalents.

Marketable Securities

Marketable Securities — We invest our excess cash balances in highly rated United States ("U.S.") government-backed debt securities and treasuries. We classify our marketable securities as available-for-sale and accordingly, record such securities at fair value. Debt securities with original maturities of greater than 90 days are classified as available-for-sale marketable securities and debt securities with original maturities of less than 90 days from the date of purchase are classified as cash equivalents.

Unrealized gains and losses on our marketable debt securities that are deemed temporary are included in accumulated other comprehensive income (loss) as a separate component of stockholders’ equity. If any adjustment to fair value reflects a significant decline in the value of the security, we evaluate the extent to which the decline is determined to be other-than-temporary and would mark the security to market through a charge to our consolidated statements of operations and comprehensive loss. Credit losses are identified when we do not expect to receive cash flows sufficient to recover the amortized cost basis of a security. In the event of a credit loss, only the amount associated with the credit loss is recognized in operating results, with the amount of loss relating to other factors recorded in accumulated other comprehensive income (loss).

Property and Equipment

Property and Equipment—Property and equipment are recorded at cost and consist of computer and other equipment, capitalized software, furniture and fixtures and leasehold improvements. Depreciation is calculated using the straight-line method over the estimated useful lives of the assets, or for leasehold improvements, over the remaining term of the lease, if shorter. The estimated useful life for each major asset classification are as follows:


Asset Classification			Estimated Useful Life
Computer and other equipment			3 years
Capitalized software			3 years
Furniture and fixtures			6 years
Leasehold improvements			lesser of lease life or useful life

Maintenance and repairs which do not extend the lives of the assets are charged directly to expense as incurred. Upon retirement or disposal, cost and related accumulated depreciation are removed from the related accounts, and any resulting gain or loss is recognized as a component of income or loss in the consolidated statements of operations and comprehensive loss.

Impairment of Long-Lived Assets

Impairment of Long-Lived Assets—When indications of potential impairments are present, the Company evaluates the carrying value of long-lived assets. The Company adjusts the carrying value of the long-lived assets if the sum of undiscounted expected future cash flows is less than the carrying value. No such impairments were recorded during the years ended December 31, 2023 or 2022.

Leases

Leases —At the inception of an arrangement, we determine if an arrangement is, or contains, a lease based on the facts and circumstances present in that arrangement. Lease classification, recognition, and measurement are then determined at the lease commencement date. For arrangements that contain a lease we (i) identify lease and non-lease components, (ii) determine the consideration in the contract, (iii) determine whether the

lease is an operating or financing lease; and iv) recognize lease right-of-use ("ROU") assets and liabilities. Lease liabilities and their corresponding ROU assets are recorded based on the present value of fixed, or in substance fixed, lease payments over the expected lease term. When the interest rate implicit in lease contracts is not readily determinable we use our incremental borrowing rate based on the information available at the lease commencement date, which represents an internally developed rate that would be incurred to borrow, on a collateralized basis, over a similar term, an amount equal to the lease payments in a similar economic environment.

We have elected to combine lease components with non-lease components on our office real estate asset class. Fixed, or in substance fixed, lease payments on operating leases are recognized over the expected term of the lease on a straight-line basis. Variable lease expenses that are not considered fixed, or in substance fixed, are recognized as incurred. Fixed and variable lease expense on operating leases is recognized within operating expenses within our consolidated statements of operations and comprehensive loss. Some leases include options to extend or terminate the lease and the Company includes these options in the recognition of the Company’s ROU assets and lease liabilities when it is reasonably certain that the Company will exercise such options. We have elected the short-term lease exemption and, therefore, do not recognize a ROU asset or corresponding liability for lease arrangements with an original term of 12 months or less.

Income Taxes

Income Taxes—The Company uses the asset and liability method of accounting for income taxes, as set forth in ASC 740, Accounting for Income Taxes ("ASC 740"). Under this method, deferred tax assets and liabilities are recognized for the expected future tax consequence of temporary differences between the carrying amounts and the tax basis of assets and liabilities and net operating loss carry forwards, all calculated using presently enacted tax rates. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company evaluates whether deferred tax assets are more likely than not of being realized in determining whether a valuation allowance is necessary. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. As of December 31, 2023 and 2022, the Company determined that it is more likely than not that deferred taxes will not be realized and as a result recorded a valuation allowance against its deferred tax assets. The Company files a consolidated U.S. federal income tax return and has elected to include all subsidiaries owned more than 80%.

Research and Development Expenses

Research and Development Expenses—Research and development expenses are comprised of costs incurred in performing research and development activities including personnel salaries, benefits, and equity-based compensation; external research and development expenses incurred under arrangements with third parties, such as contract research organization agreements, investigational sites, and consultants; the cost of developing and manufacturing clinical study materials, program regulatory costs, expenses associated with obligations under asset acquisitions, license agreements and other direct and indirect costs. Costs incurred in connection with research and development activities are expensed as incurred. Costs are considered incurred based on an evaluation of the progress to completion of each contract using information and data provided by the respective vendors, including the Company’s clinical sites. Depending upon the timing of invoicing by the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These prepaid expenses or accrued expenses are based on management’s estimates of the work performed under service agreements, milestones achieved, and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.

Deferred Offering Costs

Deferred Offering Costs— The Company capitalizes incremental legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such equity financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders' equity as a reduction of additional paid-in-capital generated as a result of the offering. Should the planned equity financing no longer be considered probable of being consummated, the offering costs are expensed immediately as a charge to operating expense. Deferred offering costs are included in prepaid expenses and other assets on the consolidated balance sheets. Deferred offering costs as of December 31, 2022 were $0.1 million. There were no deferred offering costs as of December 31, 2023.

Stock Warrants

Stock Warrants — The Company accounts for stock warrants as either equity-classified or liability-classified instruments based on an assessment of the warrant’s specific terms and applicable authoritative guidance included in ASC 480, Distinguishing Liabilities from Equity ("ASC 480") and ASC 815, Derivatives and Hedging ("ASC 815"). The assessment considers whether the warrants are freestanding financial instruments pursuant to ASC 480, whether the warrants meet the definition of a liability pursuant to ASC 480, and whether the warrants meet all of the requirements for equity classification under ASC 815. This assessment, which requires the use of professional judgment, is conducted at the time of warrant issuance and as of each subsequent

quarterly period end date while the warrants are outstanding. Warrants that meet all of the criteria for equity classification are required to be recorded as a component of additional paid-in capital at the time of issuance. For issued or modified warrants that do not meet all the criteria for equity classification, the warrants are required to be recorded at their initial fair value on the date of issuance and remeasured each balance sheet date thereafter.

Share-Based Compensation

Share-Based Compensation—The Company accounts for share-based compensation in accordance with ASC 718, Compensation—Stock Compensation ("ASC 718"). Generally, share-based compensation is measured at the grant date for all equity-based awards made to employees based on the fair value of the awards and is recognized over the requisite service period, which is generally the vesting period. Share-based compensation for awards with performance conditions are recognized over the service period when achievement of the performance condition is probable. The Company has elected to recognize the actual forfeitures by reducing the share-based compensation in the same period as the forfeitures occur. The Company classifies share-based compensation in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipients’ payroll costs are classified.

The Company estimates the fair value of options granted using the Black-Scholes option pricing model ("Black-Scholes") for stock option grants. The fair value of the Company’s common stock is used to determine the fair value of restricted stock awards. Black-Scholes requires inputs based on certain subjective assumptions, including the expected stock price volatility, the expected term of the award, the risk-free interest rate and expected dividends. Due to the lack of a public market for the Company’s common stock and lack of company-specific historical and implied volatility data, the Company has based its computation of expected volatility on the historical volatility of a representative group of public companies with similar characteristics to the Company. The historical volatility is calculated based on a period of time corresponding with expected term assumption. The Company uses the simplified method to calculate the expected term for options granted where the expected term equals the arithmetic average of the vesting term and the original contractual term of the options due to its lack of sufficient historical data. The risk-free interest rate is based on U.S. Treasury securities with a maturity date corresponding with the expected term of the associated award. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock.

Fair Value Measurements

Fair Value Measurements—ASC Topic 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the assets or liabilities and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the price that would be received to sell an asset or paid to transfer a liability, in an orderly transaction between market participants at the measurement date. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tiered value hierarchy that distinguishes between the following:

Level 1—Quoted market prices in active markets for identical assets or liabilities.

Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves.

Level 3—Unobservable inputs for the asset or liability (i.e., supported by little or no market activity). Level 3 inputs include management’s own assumptions about the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk).

To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgement. Accordingly, the degree of judgement exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

In determining fair value, the Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible, as well as considers counterparty credit risk in its assessment of fair value.

Segment Information

Segment Information—Operating segments are defined as components of an enterprise for which discrete financial information is regularly reviewed by the chief operating decision maker in deciding how to allocate

resources and in assessing operating performance. The Company manages its operations as a single segment for the purposes of allocating resources, assessing performance, and making operating decisions. All tangible assets of the Company are held in the U.S.

Basic and Diluted Net Loss Per Share

Basic and Diluted Net Loss Per Share—The Company calculates basic net loss per share by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration of potential dilutive securities. Basic shares outstanding includes the weighted-average effect of the Company's pre-funded warrants to purchase shares of our common stock requiring little consideration upon exercise. Unvested restricted common shares as of December 31, 2023 and 2022 are not considered participating securities and as such are excluded from the weighted-average number of shares used for calculating basic and diluted net loss per share. Diluted net loss per share is computed by dividing the net loss by the sum of the weighted-average number of common shares outstanding during the period plus the dilutive effects of potentially dilutive securities outstanding during the period. Potentially dilutive securities include restricted common shares and stock options. The Company has generated a net loss for all periods presented, therefore diluted net loss per share is the same as basic net loss per share since the inclusion of potentially dilutive securities would be anti-dilutive.

Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements—In June 2016, the FASB issued ASC 2016-13, Financial Instruments - Credit Losses ("ASC 2016-13"), a new standard intended to improve reporting requirements specific to loans, receivables and other financial instruments. The new standard requires that credit losses on financial assets measured at amortized cost be determined using an expected loss model, instead of the current incurred loss model, and requires that credit losses related to available-for-sale debt securities be recorded through an allowance for credit losses and limited to the amount by which carrying value exceeds fair value. We adopted the new standard on January 1, 2022 and have completed our assessment of the standard based on the composition of our portfolio of financial instruments. Our significant financial assets that are within the scope of the new standard consist of available for sale debt securities. There was no impact to our consolidated statements of operations and comprehensive loss or consolidated balance sheets upon adoption. See Note 4 for discussion of unrealized losses on our available for sale marketable securities.

Recently Issued Accounting Pronouncements—In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures ("ASU 2023-07"). This ASU requires disclosures of significant segment expenses and other segment items as well as incremental qualitative disclosures. The amendments in ASU 2023-07 apply to public entities, including those with a single reportable segment. This ASU is effective for all public companies for fiscal years beginning after December 15, 2024, and for interim periods beginning December 15, 2024. The Company may choose to early adopt any new or revised accounting standards whenever such early adoption is permitted. The company has chosen not to early adopt this standard and is currently evaluating the potential impact of adopting this standard on its consolidated financial statements.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures ("ASU 2023-09") which establishes new income tax disclosure requirements in addition to modifying and eliminating certain existing requirements. Public business entities must apply the ASU’s guidance to annual periods beginning after December 15, 2024. The company has chosen not to early adopt this standard and is currently evaluating the potential impact of adopting this standard on its consolidated financial statements.

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash Flows Used in Operating Activities:
Net loss	$ (74,564)	$ (66,654)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	150	167
Net accretion of discounts/premiums on debt securities	(3,089)	(435)
Stock-based compensation	10,920	9,499
Loss on investment in joint venture	2,041	1,075
Changes in operating assets and liabilities:
Prepaid expenses, right-of-use assets and other assets	5,819	(4,645)
Accounts payable	(99)	487
Accrued expenses and operating lease liabilities	(1,443)	3,222
Net cash used in operating activities	(60,265)	(57,284)
Cash Flows Provided by (Used in) Investing Activities:
Purchases of marketable securities	(108,414)	(201,316)
Proceeds from maturities of marketable securities	138,334	89,500
Purchase of property and equipment	(12)	(54)
Investment in joint venture	(2,250)	(300)
Net cash provided by (used in) investing activities	27,658	(112,170)
Cash Flows Provided by (Used in) Financing Activities:
Proceeds from the issuance of common stock and pre-funded warrants upon the completion of the follow-on offering, net of underwriting discounts and commissions of $3,289	0	51,533
Proceeds from the issuance of common stock from the stock purchase plan	282	217
Proceeds from the issuance of common stock from exercise of stock options	0	21
Payments of offering costs	(139)	(693)
Net cash provided by (used in) financing activities	143	51,078
Net decrease in cash and cash equivalents	(32,464)	(118,376)
Cash and cash equivalents—beginning of year	56,958	175,334
Cash and cash equivalents—end of year	24,494	56,958
Supplemental Disclosures of Noncash Investing and Financing Activities:
Offering costs in accounts payable and accrued expenses	$ 0	$ 139

INCOME TAXES - Schedule of Effective Income Tax Rates (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
U.S. federal statutory tax rate	21.00%	21.00%
State income taxes, net of federal income tax benefit	7.80%	4.40%
Tax credits	9.90%	6.00%
Other	(1.10%)	(2.80%)
Valuation allowance	(37.60%)	(28.60%)
Effective tax rate	0.00%	0.00%

MARKETABLE SECURITIES - Summary of available-for-sale marketable securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 101,948	$ 128,879
Gross Unrealized Holding Gains	79	37
Gross Unrealized Holding Losses	(64)	(251)
Fair Value	101,963	128,665
Level 1 \| Money market funds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	14,538	12,647
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair Value	14,538	12,647
Level 1 \| U.S. treasury securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	35,976	39,372
Gross Unrealized Holding Gains	48	0
Gross Unrealized Holding Losses	(6)	(169)
Fair Value	36,018	39,203
Level 2 \| U.S. government agency securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	51,434	76,860
Gross Unrealized Holding Gains	31	37
Gross Unrealized Holding Losses	(58)	(82)
Fair Value	$ 51,407	$ 76,815

Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Cash Flows Provided by (Used in) Financing Activities:
Follow on offering discounts and commissions	$ 3,289

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION

$235.2 million. The Company expects to continue to generate operating losses and negative cash flows in the foreseeable future.


Asset Classification			Estimated Useful Life
Computer and other equipment			3 years
Capitalized software			3 years
Furniture and fixtures			6 years
Leasehold improvements			lesser of lease life or useful life

Level 1—Quoted market prices in active markets for identical assets or liabilities.

Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves.

BALANCE SHEET COMPONENTS (Tables)

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Schedule of Property and Equipment, Net

Property and equipment consisted of the following as of December 31, 2023 and 2022:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Computer and other equipment	$	191	$	180
Capitalized software	89		89
Furniture and fixtures	151		151
Leasehold improvements	338		338

Less accumulated depreciation	(523)		(373)
Property and equipment—net	$	246	$	385

Schedule of Prepaid Expenses and Other Assets

Prepaid expenses and other assets consisted of the following as of December 31, 2023 and 2022:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Research and development	$	2,067	$	7,904
Insurance	446		933
Other prepaids	293		615
Other assets	2,054		1,050
	$	4,860	$	10,502

Schedule of Accrued Expenses

Accrued expenses consisted of the following as of December 31, 2023 and 2022:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Research and development	$	4,123	$	3,582
Compensation and related expenses	3,166		4,703
Professional fees	332		510
Other	447		654
	$	8,068	$	9,449

LICENSE AND COLLABORATION AGREEMENTS (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
License and Collaboration Agreements [Line Items]
Research and development		$ 53,544	$ 40,689
AbCellera Collaboration
License and Collaboration Agreements [Line Items]
Research and development		900
License Agreement \| Sanofi
License and Collaboration Agreements [Line Items]
Upfront payment	$ 3,000
Aggregate development and regulatory milestone payments		43,000
Obligation to payment upon maximum achievement of certain clinical and commercial milestones		150,000
License Agreement \| License Rights \| Sanofi
License and Collaboration Agreements [Line Items]
Transaction costs associated with asset acquisition			100
License Agreement \| License Rights \| Sanofi \| IPR&D
License and Collaboration Agreements [Line Items]
Research and development		$ 0	$ 3,100

BALANCE SHEET COMPONENTS - Schedule of Prepaid Expenses and Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Research and development	$ 2,067	$ 7,904
Insurance	446	933
Other prepaids	293	615
Other assets	2,054	1,050
Prepaid expenses and other assets	$ 4,860	$ 10,502

INCOME TAXES

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

INCOME TAXES

During each of the years ended December 31, 2023 and 2022 , the Company did not record any income tax benefits.

The Company’s effective income tax rates are different from the federal statutory tax rates in 2023 and 2022 predominantly due to the valuation allowance, tax credits, and state taxes described below:


	2023		2022
U.S. federal statutory tax rate	21.0	%	21.0	%
State income taxes, net of federal income tax benefit	7.8	%	4.4	%
Tax credits	9.9	%	6.0	%
Other	(1.1)	%	(2.8)	%
Valuation allowance	(37.6)	%	(28.6)	%
Effective tax rate	0.0	%	0.0	%

Deferred income taxes represent the tax effect of transactions that are reported in different periods for financial and tax reporting purposes. The combined temporary differences and carryforwards of each tax paying component of the Company that give rise to a significant portion of the deferred income tax benefits and liabilities are as follows at December 31, 2023 and 2022:


	2023		2022
Net operating loss carryforwards	$	37,230	$	26,576
Amortization - non-174 intangibles	2,167		2,306
Section 174 capitalization	17,530		9,895
Research and development credits	17,729		10,242
Stock-based compensation	2,706		616
Other	917		580
Total deferred tax assets	78,279		50,215
Less valuation allowance	(78,279)		(50,215)
Net deferred tax assets	$	—	$	—

At December 31, 2023, the Company has approximately $135.1 million of federal net operating loss carryforwards, which do not expire, and approximately $134.6 million of state net operating loss carryforwards, which begin expiring in 2038.

At December 31, 2023, the Company has approximately $17.2 million of federal research and development tax credit carryforwards, which begin expiring in 2039, and approximately $0.5 million of state research and development tax credit carryforwards, which begin expiring in 2040.

The Company has provided a valuation allowance against the Company’s deferred tax assets, since, in the opinion of management, based upon the history of losses by the Company and insufficient future federal and state taxable income; it is more likely than not that the benefits will not be realized. All or a portion of the remaining valuation allowance may be reduced in future years based on an assessment of earnings sufficient to fully utilize these potential tax benefits.

Effective January 1, 2022, a provision of the Tax Cuts and Jobs Act ("TCJA") changed the treatment of research and experimental ("R&E") expenditures under Section 174 of the Internal Revenue Code ("Code"). Previous to the TCJA being effective, businesses have had the option of deducting Section 174 expenses in the year incurred or capitalizing and amortizing the costs over five years. The new TCJA provision, however, eliminates this option and will require Section 174 expenses associated with research conducted in the U.S to be capitalized and amortized over a five-year period. For expenses associated with research outside of the United States, Section 174 expenses will be capitalized and amortized over a 15-year period.

Utilization of the U.S. federal and state net operating loss carryforwards and research and development tax credit carryforwards may be subject to an annual limitation under Section 382 and Section 383 of the Code, and corresponding provisions of state law, due to ownership changes that may have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income and tax liabilities. In general, an ownership change, as defined by Section 382 of the Code, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 5% over a three-year period.

The Company recently completed a Section 382 study and concluded that we underwent an ownership change as defined by the Code during the year ended December 31, 2021. We do not currently believe that the annual limitation will result in the expiration of any net operating losses or research and development tax credit carryforwards before utilization. Future ownership changes may limit our ability to utilize remaining tax attributes. Any carryforwards that will expire prior to utilization as a result of such additional limitations will be removed from deferred tax assets, with a corresponding reduction of the valuation allowance. Due to the existence of the valuation allowance, limitations created by future ownership changes, if any, will not impact the Company’s effective tax rate.

ASC 740 addresses the determination of whether tax benefits claimed or expected to be claimed on a tax return should be recorded in the financial statements. Under ASC 740, the Company may recognize the tax benefit from an uncertain tax position only if it is more likely that not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The Company has no material uncertain tax positions that qualify for either recognition or disclosure in consolidated financial statements.

It is the Company’s policy to recognize interest and/or penalties related to income tax matters in income tax expense. As of December 31, 2023 and 2022, the Company has accrued no interest and penalties related to uncertain tax positions. The Company does not have any outstanding U.S. federal income tax or material state and local tax matters for periods through December 31, 2023. There are no federal or state and local income tax returns currently under examination. As of December 31, 2023, the statute remains open for returns filed for the tax years ended: December 31, 2018; December 31, 2019; December 31, 2020; June 30, 2021; December 31, 2021; and December 31, 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
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-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
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-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

BALANCE SHEET COMPONENTS - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 0.1	$ 0.2

Audit Information	12 Months Ended
Audit Information	Dec. 31, 2023
Audit Information [Abstract]
Auditor Firm ID	34
Auditor Name	Deloitte & Touche LLP
Auditor Location	Hartford, Connecticut

INVESTMENT IN JOINT VENTURE	12 Months Ended
INVESTMENT IN JOINT VENTURE	Dec. 31, 2023
Equity Method Investments and Joint Ventures [Abstract]
INVESTMENT IN JOINT VENTURE	INVESTMENT IN JOINT VENTURE The Company, through one of its wholly-owned subsidiaries, has a 50% interest of the joint venture entity, REV-I. For the years ended December 31, 2023 and 2022 the Company funded $2.3 million and $0.3 million, respectively, associated with the Company's commitment and its share of REV-I development. The Company did not provide any additional financial support outside of capital contributions to REV-I during the years ended December 31, 2023 and 2022. While the Company held a 50% interest in the joint venture as of December 31, 2023, based on management’s analysis, the Company is not the primary beneficiary of REV-I and accordingly, the entity is not consolidated in the Company's consolidated financial statements. For the years ended December 31, 2023 and 2022, the Company recorded its allocable share of REV-I’s losses, which totaled $2.0 million and $1.1 million, respectively, as a loss on investment in joint venture within the consolidated statements of operations and comprehensive loss. After recognition of its share of losses for the period, the carrying value and maximum exposure to risk of the REV-I investment as of December 31, 2023 and December 31, 2022 was $0.2 million and $30 thousand, respectively, which was recorded in investment in joint venture in the accompanying consolidated balance sheets.

LEASES (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Assets And Liabilities, Lessee

The following table summarizes the presentation of the Company's operating lease as presented on the consolidated balance sheets:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Assets:
Operating lease right-of-use assets	$	346	$	524
Liabilities:
Operating lease liabilities	$	219	$	181
Operating lease liabilities, noncurrent	173		374
Total operating lease liabilities	$	392	$	555

Schedule of Future Minimum Annual Lease Payments

Future minimum lease payments from December 31, 2023 until the expiration of the operating lease are as follows:


(in thousands)
2024	$	230
2025	176
2026	—
Thereafter	—
Total lease payments	406
Less: imputed discount rate	(14)
Carrying value of operating lease liabilities	$	392

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Total Follow-On Offering	COMMON	COMMON Total Follow-On Offering	ADDITIONAL PAID-IN CAPITAL	ADDITIONAL PAID-IN CAPITAL Total Follow-On Offering	ACCUMULATED DEFICIT	ACCUMULATED OTHER COMPREHENSIVE GAIN (LOSS)
Beginning Balance (in shares) at Dec. 31, 2021			32,129,970
Beginning Balance at Dec. 31, 2021	$ 175,602		$ 3		$ 269,626		$ (94,027)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued during the period (in shares)				5,803,655
Issuance of common stock and pre-funded warrants upon completion of the follow-on offering, net of underwriting discounts and commissions and offering costs		$ 50,846		$ 1		$ 50,845
Issuance of common stock from the stock purchase plan (in shares)			38,845
Issuance of common stock from the stock purchase plan	217				217
Issuance of common stock from the stock award plan (in shares)			2,000
Issuance of common stock from the stock award plan	0
Issuance of common stock from exercise of stock options (in shares)			2,014
Issuance of common stock from exercise of stock options	21				21
Forfeiture of restricted common stock (in shares)			(139,115)
Forfeiture of restricted common stock	0
Share-based compensation expense	9,499				9,499
Net loss	(66,654)						(66,654)
Other comprehensive gain (loss)	(214)							(214)
Ending Balance (in shares) at Dec. 31, 2022			37,837,369
Ending Balance at Dec. 31, 2022	169,317		$ 4		330,208		(160,681)	(214)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from the stock purchase plan (in shares)			79,283
Issuance of common stock from the stock purchase plan	282				282
Issuance of common stock from the stock award plan (in shares)			11,219
Issuance of common stock from the stock award plan	0
Forfeiture of restricted common stock (in shares)			(98,306)
Forfeiture of restricted common stock	0
Share-based compensation expense	10,920				10,920
Net loss	(74,564)						(74,564)
Other comprehensive gain (loss)	229							229
Ending Balance (in shares) at Dec. 31, 2023			37,829,565
Ending Balance at Dec. 31, 2023	$ 106,184		$ 4		$ 341,410		$ (235,245)	$ 15

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	37,829,565	37,837,369
Common stock, shares outstanding (in shares)	37,829,565	37,837,369
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0

MARKETABLE SECURITIES - Schedule of Available-for-Sale Securities by Balance Sheet Location Classification (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Debt securities, available-for-sale	$ 101,963	$ 128,665
Cash and cash equivalents
Debt Securities, Available-for-Sale [Line Items]
Debt securities, available-for-sale	16,528	16,629
Marketable securities
Debt Securities, Available-for-Sale [Line Items]
Debt securities, available-for-sale	$ 85,435	$ 112,036

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Dec. 31, 2023
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On February 6, 2024, the Company announced a prioritization of its portfolio and a workforce reduction to focus resources on its Phase 2-ready clinical stage programs, RLYB212 and RLYB116. As part of this effort, the Company eliminated approximately 45% of its positions. As a result of these actions, the Company expects to incur charges of approximately $3.3 million, excluding share-based compensation expense. The charges related to the workforce reduction are cash-based expenditures related primarily to one-time severance and benefit payments. The Company expects to recognize substantially all charges related to the workforce reduction in the quarter ending March 31, 2024. These estimates are subject to assumptions and actual results may differ.

BUSINESS	12 Months Ended
BUSINESS	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
BUSINESS	BUSINESS Rallybio Corporation and subsidiaries ("Rallybio", the "Company", "we", "our", or "us") is a clinical-stage biotechnology company comprised of experienced biopharma industry leaders with extensive research, development, and rare disease expertise with a mission to develop and commercialize life-transforming therapies for patients with severe and rare diseases. Since our launch in January 2018, we have built a broad pipeline of promising product candidates aimed at addressing diseases with unmet medical need in the areas of maternal fetal health, complement dysregulation, hematology, and metabolic disorders. Our two most advanced programs are in clinical development: RLYB212, an anti-HPA-1a antibody for the prevention of fetal and neonatal alloimmune thrombocytopenia (“FNAIT”) and RLYB116, an inhibitor of complement component 5 (“C5”), with the potential to treat several diseases of complement dysregulation. Both programs have completed Phase 1 clinical trials, and we currently plan to initiate a Phase 2 clinical trial of RLYB212 in the second half of 2024. In August 2021, the Company completed its initial public offering ("IPO"), pursuant to which it issued and sold 7,130,000 shares of the Company’s common stock, inclusive of 930,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $13.00 per share. The gross proceeds from the IPO, including the exercise of the underwriter's option to purchase additional shares were $92.7 million and the net proceeds were approximately $83.0 million, after deducting underwriting discounts and commissions and other offering costs. In November 2022, the Company completed a follow-on offering of approximately $54.8 million consisting of 5,803,655 shares of common stock, inclusive of 803,654 shares of common stock sold pursuant to the partial exercise of the underwriters' option to purchase additional shares at the price of $6.00 per share and to certain investors in lieu of common stock, pre-funded warrants to purchase up to an aggregate of 3,333,388 shares of common stock at a price of $5.9999, which represents the per share public offering price for the shares less the $0.0001 per share exercise price for each pre-funded warrant. The net proceeds from the November 2022 follow-on offering were approximately $50.8 million, after deducting underwriting discounts and commissions and other offering costs.

COMMITMENTS AND CONTINGENCIES	12 Months Ended
COMMITMENTS AND CONTINGENCIES	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Purchase Commitments—The Company enters contracts in the normal course of business with contract research organizations and other third-party vendors for clinical trials and testing and manufacturing services. These contracts generally do not contain minimum purchase commitments and are cancellable by us upon written notice. Payments that may be due upon cancellation consist of payments for services provided or expenses incurred prior to cancellation. As of December 31, 2023 and 2022 there were no amounts accrued related to termination charges.

MARKETABLE SECURITIES (Tables)

12 Months Ended

Dec. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Summary of Fair Value of Marketable Securities by Type of Marketable Securities

The amortized cost, gross unrealized holding gains, gross unrealized holding losses and fair value of our marketable securities by type of security as of December 31, 2023 and 2022 was as follows:


		DECEMBER 31, 2023
(in thousands)	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
Money market funds	Level 1	$	14,538	$	—	$	—	$	14,538
U.S. treasury securities	Level 1	35,976		48		(6)		36,018
U.S. government agency securities	Level 2	51,434		31		(58)		51,407
		$	101,948	$	79	$	(64)	$	101,963


		DECEMBER 31, 2022
(in thousands)	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
Money market funds	Level 1	$	12,647	$	—	$	—	$	12,647
U.S. treasury securities	Level 1	39,372		—		(169)		39,203
U.S. government agency securities	Level 2	76,860		37		(82)		76,815
		$	128,879	$	37	$	(251)	$	128,665

Schedule of Marketable Securities by Balance Sheet Location Classification

The fair values of marketable securities by classification in the consolidated balance sheets as of December 31, 2023 and 2022 was as follows:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Cash and cash equivalents	$	16,528	$	16,629
Marketable securities	85,435		112,036
	$	101,963	$	128,665

Schedule of Fair Values of Available-for-Sale Debt Securities by Contractual Maturity

The fair values of available-for-sale debt securities as of December 31, 2023 and 2022, by contractual maturity, are summarized as follows:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Due in one year or less	$	98,110	$	127,667
Due after one year through two years	3,853		998
	$	101,963	$	128,665

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 3
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
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-Section 50
-Paragraph 2
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Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
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-Paragraph 2
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Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

STOCKHOLDERS' EQUITY - Summary of Equity-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	$ 10,920	$ 9,499
Research and development
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	4,606	3,542
General and administrative
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation	$ 6,314	$ 5,957

STOCKHOLDERS' EQUITY

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

STOCKHOLDERS' EQUITY

Common Stock

In August 2021, the Company completed its IPO, pursuant to which it issued and sold 7,130,000 shares of the Company’s common stock, inclusive of 930,000 shares sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a public offering price of $13.00 per share. The gross proceeds from the IPO, including the exercise of the underwriter's option to purchase additional shares were $92.7 million and the net proceeds were approximately $83.0 million, after deducting underwriting discounts and commissions and other offering costs.

In November 2022, the Company completed a follow-on offering of approximately $54.8 million consisting of 5,803,655 shares of common stock, inclusive of 803,654 shares of common stock sold pursuant to the partial exercise of the underwriters' option to purchase additional shares at the price of $6.00 per share and to certain investors in lieu of common stock, pre-funded warrants to purchase up to an aggregate of 3,333,388 shares of common stock at a price of $5.9999, which represents the per share public offering price for the shares less the $0.0001 per share exercise price for each pre-funded warrant. The net proceeds from the November 2022 follow-on offering were approximately $50.8 million, after deducting underwriting discounts and commissions and other offering costs.

The Company had 200,000,000 shares of common stock authorized as of December 31, 2023 and 2022, respectively, of which 37,829,565 and 37,837,369 shares were issued and outstanding as of December 31, 2023 and 2022, respectively.

Preferred Stock

The Company had 50,000,000 shares of preferred stock authorized as of December 31, 2023 and 2022, respectively, of which no shares were outstanding as of December 31, 2023 and 2022, respectively.

Pre-Funded Warrants

In connection with the November 2022 follow-on offering, the Company entered into an agreement with certain investors for pre-funded warrants in lieu of common stock to purchase up to an aggregate of 3,333,388 shares of common stock at a price of $5.9999, which represents the per share public offering price at the November 2022 follow-on offering for common stock less a $0.0001 per share exercise price for each pre-funded warrant.

The Company may not effect the exercise of any pre-funded warrant, and a holder will not be entitled to exercise any portion of any pre-funded warrant if, upon giving effect to such exercise, the aggregate number of shares of common stock beneficially owned by the holder (together with its affiliates) would exceed 9.99% of the number of shares of common stock outstanding immediately after giving effect to the exercise, which

percentage may be increased or decreased at the holder’s election upon 61 days’ notice to the Company subject to the terms of such pre-funded warrants, provided that such percentage may in no event exceed 19.99%.

The Company's pre-funded warrant is a freestanding instrument that does not meet the definition of a liability pursuant to ASC 480 and does not meet the definition of a derivative pursuant to ASC 815. The pre-funded warrant is indexed to the Company’s common stock and meets all other conditions for equity classification under ASC 480 and ASC 815. Accordingly, the pre-funded warrant was classified as equity and accounted for as a component of additional paid-in capital at the time of issuance. All of the pre-funded warrants related to our November 2022 follow-on offering remain outstanding and unexercised as of December 31, 2023.

Share-based Compensation

Share-based compensation which comprised of stock options, restricted stock awards, restricted stock units and the employee stock purchase plan is classified in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2023 and 2022 and was as follows:


	FOR THE YEAR ENDED DECEMBER 31,
(in thousands)	2023		2022
Research and development	$	4,606	$	3,542
General and administrative	6,314		5,957
	$	10,920	$	9,499

2021 Equity Incentive Plan

In 2021, the board of directors adopted the Rallybio Corporation 2021 Equity Incentive Plan (the "2021 Plan"). The 2021 Plan reserves 5,440,344 for shares of the Company's common stock that have been issued in respect of outstanding equity awards granted prior to the registrant’s IPO and for future issuances of shares to employees, directors and consultants in the form of stock options, SARs, restricted and unrestricted stock and stock units, performance awards and other awards that are convertible into or otherwise based on the Company's common stock. Dividend equivalents may also be provided in connection with awards under the 2021 Plan. The share pool will automatically increase on January 1st of each year from 2022 to 2031 by the lesser of (i) five percent of the number of shares of the Company's common stock outstanding as of such date and (ii) the number of shares of the Company's common stock determined by the board of directors on or prior to such date. On January 1, 2023 and January 1, 2022, the 2021 Plan share pool was automatically increased by 1,891,868 and 1,606,549 shares, respectively. As of December 31, 2023, the total number of shares of the Company's common stock that were issuable under the 2021 Plan was 6,775,026 shares, of which 2,284,232 shares remained available for future issuance.

The following table summarizes stock option activity for the year ended December 31, 2023:


Stock Options	Number of Option Shares	Weighted-Average Exercise Price		Weighted-Average Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022	2,609,314	$	13.01	8.8	$	—
Granted	2,017,183	$	6.51
Forfeited	(230,484)	$	12.16
Expired	(125,469)	$	13.15
Exercised	—	$	—
Outstanding at December 31, 2023	4,270,544	$	9.98	8.45	$	—
Options exercisable at December 31, 2023	1,590,886	$	11.59	8.06	$	—

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company's common stock. Options outstanding and exercisable with an exercise price above the closing price as of December 31, 2023 are considered to have no intrinsic value. Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the years ended December 31, 2023 and 2022 was $4.93 per share and $9.99 per share, respectively. Options vested during the years ended December 31, 2023 and 2022 with an exercise price above

the closing price are considered to have no intrinsic value. As of December 31, 2023, there was unrecognized share-based compensation expense related to unvested stock options of $16.9 million, which the Company expects to recognize over a weighted-average period of approximately 2.4 years.

The fair value of the stock options granted during the years ended December 31, 2023 and 2022 was determined using the Black-Scholes option pricing model with the following assumptions:


	FOR THE YEAR ENDED DECEMBER 31,
	2023	2022
Expected volatility	88.38% - 92.27%	89.31% - 91.62%
Expected term (years)	5.50- 6.08	5.50- 6.08
Risk free interest rate	3.58% - 4.52%	1.42% - 2.94%
Expected dividend yield	—	—
Exercise price	$5.38 - $7.83	$7.54 - $15.04

A summary of the status of the Company's nonvested restricted common stock awards at December 31, 2023 and changes during the year ended December 31, 2023 was as follows:


Restricted Stock Awards	Shares	Weighted-Average Grant Date Fair Value Per Share
Nonvested restricted stock awards at December 31, 2022	1,006,368	$	3.48
Granted	—	$	—
Vested	(553,668)	$	3.20
Forfeited	(98,306)	$	2.78
Outstanding nonvested restricted stock awards at December 31, 2023	354,394	$	4.10

As of December 31, 2023, there was unrecognized share-based compensation expense related to unvested restricted stock awards of $1.3 million, which the Company expects to recognize over a weighted-average period of approximately 1.2 years.

A summary of the status of the Company's nonvested restricted common stock units at December 31, 2023 and changes during the year ended December 31, 2023 was as follows:


Restricted Stock Units	Shares	Weighted-Average Grant Date Fair Value Per Share
Nonvested restricted stock units at December 31, 2022	128,600	$	11.12
Granted	110,075	$	5.61
Forfeited	(6,500)	$	9.11
Vested	(11,925)	$	8.88
Outstanding nonvested restricted stock units at December 31, 2023	220,250	$	8.55

As of December 31, 2023, there was unrecognized share-based compensation expense related to unvested restricted stock units of $1.0 million, which the Company expects to recognize over a weighted-average period of approximately 1.9 years.

2021 Employee Stock Purchase Plan

In connection with the Company's IPO, the board of directors adopted the Rallybio Corporation 2021 Employee Stock Purchase Plan (the "2021 ESPP"), which reserves 291,324 shares of the Company's common stock for future issuances under this plan. The share pool will automatically increase on January 1st of each year from 2022 to 2031 by the lesser of (i) one percent of the number of shares of the Company's common stock outstanding as of such date (ii) 582,648 shares of the Company's common stock, and (iii) the number of shares of the Company's common stock determined by the board of directors on or prior to such date. On January 1, 2023 and January 1, 2022, the 2021 ESPP share pool was automatically increased by 378,373 and 321,309 shares, respectively. As of December 31, 2023, the total number of shares of the Company's common stock that

were available for future issuance under the 2021 ESPP was 872,878 shares. During the years ended December 31, 2023 and 2022, the Company issued 79,283 and 38,845 shares, respectively, of the Company's common stock under the 2021 ESPP.

The 2021 ESPP allows eligible participants to purchase shares of our common stock through authorized payroll deductions. The purchase price of the shares will be not less than 85% of the lower of the fair market value of our common stock on the first day of an offering or on the date of purchase.

For the years ended December 31, 2023 and 2022, the total share-based compensation for the 2021 ESPP was $0.2 million and $0.1 million, respectively.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
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-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//505/tableOfContent

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+ Details

NET LOSS PER COMMON SHARE - Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Nov. 30, 2022
Stock options and unvested restricted stock awards and units
Antidilutive Units
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	4,800,000	3,700,000
Pre-Funded Warrants
Antidilutive Units
Number of securities called by warrants or rights (in shares)			3,333,388
Pre-Funded Warrants \| Follow-on Offering
Antidilutive Units
Number of securities called by warrants or rights (in shares)	3,333,388		3,333,388

MARKETABLE SECURITIES - Schedule of Fair Values of Available-For-Sale Debt Securities By Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Due in one year or less	$ 98,110	$ 127,667
Due after one year through two years	3,853	998
Total available-for-sale debt securities by contractual maturity	$ 101,963	$ 128,665

COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Termination charges	$ 0	$ 0

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Property and Equipment Estimated Useful Lives

The estimated useful life for each major asset classification are as follows:


Asset Classification			Estimated Useful Life
Computer and other equipment			3 years
Capitalized software			3 years
Furniture and fixtures			6 years
Leasehold improvements			lesser of lease life or useful life

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 24,494	$ 56,958
Marketable securities	85,435	112,036
Prepaid expenses and other assets	4,860	10,502
Total current assets	114,789	179,496
Property and equipment, net	246	385
Operating lease right-of-use assets	346	524
Investment in joint venture	239	30
Total assets	115,620	180,435
Current liabilities:
Accounts payable	976	1,114
Accrued expenses	8,068	9,449
Operating lease liabilities	219	181
Total current liabilities	9,263	10,744
Operating lease liabilities, noncurrent	173	374
Total liabilities	9,436	11,118
Commitments and contingencies (Note 10)
Stockholders' equity
Common stock, $0.0001 par value per share; 200,000,000 shares authorized as of December 31, 2023 and 2022, respectively; and 37,829,565 and 37,837,369 shares issued and outstanding as of December 31, 2023 and 2022, respectively	4	4
Preferred stock, $0.0001 par value per share; 50,000,000 shares authorized as of December 31, 2023 and 2022, respectively; no shares issued or outstanding as of December 31, 2023 and 2022, respectively	0	0
Additional paid-in capital	341,410	330,208
Accumulated other comprehensive gain (loss)	15	(214)
Accumulated deficit	(235,245)	(160,681)
Total stockholders' equity	106,184	169,317
Total liabilities and stockholders' equity	$ 115,620	$ 180,435

Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Dec. 31, 2023	Mar. 07, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-40693
Entity Registrant Name	RALLYBIO CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-1083789
Entity Address, Address Line One	234 Church Street
Entity Address, Address Line Two	Suite 1020
Entity Address, City or Town	New Haven
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06510
City Area Code	203
Local Phone Number	859-3820
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	RLYB
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 134.4
Entity Common Stock, Shares Outstanding (in shares)		37,811,970
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s Definitive Proxy Statement for its 2024 Annual Meeting of Stockholders scheduled to be held on May 15, 2024, which Definitive Proxy will be filed with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2023 are incorporated by reference into Part II and Part III of this Annual Report on Form 10-K.
Entity Central Index Key	0001739410
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

LEASES - Additional Information (Details) $ in Thousands	12 Months Ended
LEASES - Additional Information (Details) $ in Thousands	Dec. 31, 2023 USD ($) ft²	Dec. 31, 2022 USD ($)
Operating Leased Assets [Line Items]
Operating lease, weighted average remaining lease term	1 year 9 months 18 days
Office
Operating Leased Assets [Line Items]
Area of real estate property \| ft²	9,000
Operating lease, weighted average discount percent	4.00%
Operating lease, expense	$ 200	$ 200
Lease payments	$ 200	$ 200

MARKETABLE SECURITIES

12 Months Ended

Dec. 31, 2023

Investments, Debt and Equity Securities [Abstract]

MARKETABLE SECURITIES

The amortized cost, gross unrealized holding gains, gross unrealized holding losses and fair value of our marketable securities by type of security as of December 31, 2023 and 2022 was as follows:


		DECEMBER 31, 2023
(in thousands)	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
Money market funds	Level 1	$	14,538	$	—	$	—	$	14,538
U.S. treasury securities	Level 1	35,976		48		(6)		36,018
U.S. government agency securities	Level 2	51,434		31		(58)		51,407
		$	101,948	$	79	$	(64)	$	101,963


		DECEMBER 31, 2022
(in thousands)	Fair Value Hierarchy Level	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
Money market funds	Level 1	$	12,647	$	—	$	—	$	12,647
U.S. treasury securities	Level 1	39,372		—		(169)		39,203
U.S. government agency securities	Level 2	76,860		37		(82)		76,815
		$	128,879	$	37	$	(251)	$	128,665

The fair values of marketable securities by classification in the consolidated balance sheets as of December 31, 2023 and 2022 was as follows:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Cash and cash equivalents	$	16,528	$	16,629
Marketable securities	85,435		112,036
	$	101,963	$	128,665

The fair values of available-for-sale debt securities as of December 31, 2023 and 2022, by contractual maturity, are summarized as follows:


(in thousands)	DECEMBER 31, 2023		DECEMBER 31, 2022
Due in one year or less	$	98,110	$	127,667
Due after one year through two years	3,853		998
	$	101,963	$	128,665

The aggregate fair value of available-for-sale debt securities in an unrealized loss position as of December 31, 2023 and 2022 was $40.0 million and $70.0 million, respectively. As of December 31, 2023 and 2022, we did not have any investments in a continuous unrealized loss position for more than twelve months. As of December 31, 2023, we believe that the cost basis of our available-for-sale debt securities is recoverable. No allowance for credit losses was recorded as of December 31, 2023 and 2022.

INCOME TAXES - Schedule of Deferred Income Tax Benefits and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 37,230	$ 26,576
Amortization - non-174 intangibles	2,167	2,306
Section 174 capitalization	17,530	9,895
Research and development credits	17,729	10,242
Stock-based compensation	2,706	616
Other	917	580
Total deferred tax assets	78,279	50,215
Less valuation allowance	(78,279)	(50,215)
Net deferred tax assets	$ 0	$ 0

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rates


	2023		2022
U.S. federal statutory tax rate	21.0	%	21.0	%
State income taxes, net of federal income tax benefit	7.8	%	4.4	%
Tax credits	9.9	%	6.0	%
Other	(1.1)	%	(2.8)	%
Valuation allowance	(37.6)	%	(28.6)	%
Effective tax rate	0.0	%	0.0	%

Schedule of Deferred Income Tax Benefits and Liabilities

The combined temporary differences and carryforwards of each tax paying component of the Company that give rise to a significant portion of the deferred income tax benefits and liabilities are as follows at December 31, 2023 and 2022:


	2023		2022
Net operating loss carryforwards	$	37,230	$	26,576
Amortization - non-174 intangibles	2,167		2,306
Section 174 capitalization	17,530		9,895
Research and development credits	17,729		10,242
Stock-based compensation	2,706		616
Other	917		580
Total deferred tax assets	78,279		50,215
Less valuation allowance	(78,279)		(50,215)
Net deferred tax assets	$	—	$	—

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Total Follow-On Offering
Offering costs	$ 3,976

LICENSE AND COLLABORATION AGREEMENTS	12 Months Ended
LICENSE AND COLLABORATION AGREEMENTS	Dec. 31, 2023
License and collaboration agreements [Abstract]
LICENSE AND COLLABORATION AGREEMENTS	LICENSE AND COLLABORATION AGREEMENTS Asset Acquisition In May 2022, we obtained worldwide exclusive rights to RLYB331, with Kymab Limited ("Sanofi") a preclinical antibody. We believe RLYB331 has the potential to address a significant unmet need for patients with severe anemias with ineffective erythropoiesis and iron overload, including beta thalassemia and a subset of lower risk myelodysplastic syndromes. Under the terms of the license agreement, we made an upfront payment to Sanofi of $3.0 million in the second quarter of 2022 for the exclusive license to KY1066. We could also be required to pay up to an aggregate of $43.0 million in development and regulatory milestones and up to an aggregate of $150.0 million in commercial milestones for a product in its first indication, plus tiered low-to-mid double digit percentages of such milestone amounts for up to three additional indications, and mid to high single digit royalties on net sales. The license was accounted for as an asset acquisition as substantially all of the fair value of the asset acquired was concentrated in a single asset and thus the acquisition was deemed not to be a business combination. The acquired license rights represent an IPR&D asset that was determined to have no alternative future use. Accordingly, the Company recorded an IPR&D charge of $3.1 million to research and development expense, including transaction costs associated with this asset acquisition of $0.1 million, in the accompanying consolidated statements of operations and comprehensive loss for the year ended December 31, 2022. The Company did not record an IPR&D charge for the year ended December 31, 2023. AbCellera Collaboration In December 2022, the Company entered into a multi-year, multi-target collaboration with AbCellera to discover, develop, and commercialize novel antibody-based therapeutics for rare diseases. Under the terms of the agreement, AbCellera and Rallybio will co-develop and share the development costs of up to five rare disease therapeutic targets, which will be chosen together by both companies. At the point one party in the collaboration opts-out of future co-development cost sharing, that party will be entitled to a share of future profit sharing from commercialization of the collaboration target, dependent on the proportion of their co-development contributions compared to the total development costs of a target as defined within the agreement. The agreement also has defined profit sharing floors that correspond to the stage of development at the time a collaboration party opts-out of co-developing a target. The Company concluded that the agreement with AbCellera will be accounted under the scope of ASC 808 as both parties will actively participate in joint operating activities and are exposed to significant risks and rewards that depend on the commercial success of those activities. Under ASC 808, certain transactions between collaborative arrangement participants should follow the accounting for revenue under ASC 606 when the collaborative arrangement participant is a customer. The Company determined that co-development arrangement as defined in our agreement with AbCellera does not meet the definition of a customer as defined by ASC 606. As a result, these activities will be accounted for as research and development costs. Payments due because of the co-development will be recorded as research and development expense in the period such expenses are incurred and for payments owed to us from our collaboration partner for the reimbursement of research and development costs will be recorded as a contra-research and development expense in the period such expenses are incurred. Costs related to the AbCellera collaboration were $0.9 million for the year ended December 31, 2023. Costs related to the AbCellera collaboration were not material for the year ended December 31, 2022.

STOCKHOLDERS' EQUITY (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Summary of Share-based Compensation


	FOR THE YEAR ENDED DECEMBER 31,
(in thousands)	2023		2022
Research and development	$	4,606	$	3,542
General and administrative	6,314		5,957
	$	10,920	$	9,499

Summary of Stock Option Activity

The following table summarizes stock option activity for the year ended December 31, 2023:


Stock Options	Number of Option Shares	Weighted-Average Exercise Price		Weighted-Average Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022	2,609,314	$	13.01	8.8	$	—
Granted	2,017,183	$	6.51
Forfeited	(230,484)	$	12.16
Expired	(125,469)	$	13.15
Exercised	—	$	—
Outstanding at December 31, 2023	4,270,544	$	9.98	8.45	$	—
Options exercisable at December 31, 2023	1,590,886	$	11.59	8.06	$	—

Summary of Assumptions of Fair Value of Option Pricing Granted

The fair value of the stock options granted during the years ended December 31, 2023 and 2022 was determined using the Black-Scholes option pricing model with the following assumptions:


	FOR THE YEAR ENDED DECEMBER 31,
	2023	2022
Expected volatility	88.38% - 92.27%	89.31% - 91.62%
Expected term (years)	5.50- 6.08	5.50- 6.08
Risk free interest rate	3.58% - 4.52%	1.42% - 2.94%
Expected dividend yield	—	—
Exercise price	$5.38 - $7.83	$7.54 - $15.04

Summary of Unvested Restricted Common Stock Awards

A summary of the status of the Company's nonvested restricted common stock awards at December 31, 2023 and changes during the year ended December 31, 2023 was as follows:


Restricted Stock Awards	Shares	Weighted-Average Grant Date Fair Value Per Share
Nonvested restricted stock awards at December 31, 2022	1,006,368	$	3.48
Granted	—	$	—
Vested	(553,668)	$	3.20
Forfeited	(98,306)	$	2.78
Outstanding nonvested restricted stock awards at December 31, 2023	354,394	$	4.10

Summary of Unvested Restricted Common Stock Units

A summary of the status of the Company's nonvested restricted common stock units at December 31, 2023 and changes during the year ended December 31, 2023 was as follows:


Restricted Stock Units	Shares	Weighted-Average Grant Date Fair Value Per Share
Nonvested restricted stock units at December 31, 2022	128,600	$	11.12
Granted	110,075	$	5.61
Forfeited	(6,500)	$	9.11
Vested	(11,925)	$	8.88
Outstanding nonvested restricted stock units at December 31, 2023	220,250	$	8.55

STOCKHOLDERS' EQUITY - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Option Shares
Outstanding at beginning of period (in shares)	2,609,314
Granted (in shares)	2,017,183
Forfeited (in shares)	(230,484)
Expired (in shares)	(125,469)
Exercised (in shares)	0
Outstanding at ending of period (in shares)	4,270,544	2,609,314
Options exercisable at ending of period (in shares)	1,590,886
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 13.01
Granted (in dollars per share)	6.51
Forfeited (in dollars per share)	12.16
Expired (in dollars per share)	13.15
Exercised (in dollars per share)	0
Outstanding at ending of period (in dollars per share)	9.98	$ 13.01
Options exercisable at ending of period (in dollars per share)	$ 11.59
Weighted-Average Contractual Term (in years) and Aggregate Intrinsic Value (in thousand)
Outstanding, Weighted-Average Contractual Term (in years)	8 years 5 months 12 days	8 years 9 months 18 days
Options exercisable, Outstanding, Weighted-Average Contractual Term (in years)	8 years 21 days
Outstanding, Aggregate Intrinsic Value	$ 0	$ 0
Options exercisable, Aggregate Intrinsic Value	$ 0

NET LOSS PER COMMON SHARE (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Summary of Basic and Diluted Loss Per Common Share

Basic and diluted loss per common share were calculated as follows:


	FOR THE YEAR ENDED DECEMBER 31,
(in thousands except share and per share amounts)	2023		2022
Net loss	$	(74,564)	$	(66,654)
Weighted-average number of common shares outstanding, basic and diluted	40,447,388		31,821,311
Net loss per common share, basic and diluted	$	(1.84)	$	(2.09)

NET LOSS PER COMMON SHARE

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

NET LOSS PER COMMON SHARE

Basic and diluted loss per common share were calculated as follows:


	FOR THE YEAR ENDED DECEMBER 31,
(in thousands except share and per share amounts)	2023		2022
Net loss	$	(74,564)	$	(66,654)
Weighted-average number of common shares outstanding, basic and diluted	40,447,388		31,821,311
Net loss per common share, basic and diluted	$	(1.84)	$	(2.09)

Basic net loss per share of common stock is based on the weighted-average number of shares of common stock outstanding during the period. Pre-funded warrants to purchase 3,333,388 shares of common stock that were issued in connection with the November 2022 follow-on offering were included in the weighted-average number of common shares outstanding for the years ended December 31, 2023 and 2022, respectively. The weighted-average number of common shares outstanding diluted for the years ended December 31, 2023 and 2022 excludes approximately 4.8 million and 3.7 million stock options and unvested restricted stock awards and units, respectively, which were not dilutive.

STOCKHOLDERS' EQUITY - Summary of Assumptions of Fair Value of Option Pricing Granted (Details) - Employee Stock Options - 2021 Equity Incentive Plan - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected volatility, minimum	88.38%	89.31%
Expected volatility, maximum	92.27%	91.62%
Risk-free interest rate, minimum	3.58%	1.42%
Risk-free interest rate, maximum	4.52%	2.94%
Expected dividend yield	0.00%	0.00%
Minimum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	5 years 6 months
Exercise price (in dollars per share)	$ 5.38	$ 7.54
Maximum
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (years)	6 years 29 days	6 years 29 days
Exercise price (in dollars per share)	$ 7.83	$ 15.04

STOCKHOLDERS' EQUITY - Summary of Unvested Restricted Common Stock Units (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Shares
Outstanding, beginning balance (in shares) \| shares	128,600
Granted (in shares) \| shares	110,075
Forfeited (in shares) \| shares	(6,500)
Vested (in shares) \| shares	(11,925)
Outstanding, ending balance (in shares) \| shares	220,250
Weighted-Average Grant Date Fair Value Per Share
Outstanding, beginning balance (in dollars per share) \| $ / shares	$ 11.12
Weighted average grant date fair value, shares granted \| $ / shares	5.61
Forfeited (in dollars per share) \| $ / shares	9.11
Vested (in dollars per share) \| $ / shares	8.88
Outstanding, ending balance (in dollars per share) \| $ / shares	$ 8.55

BUSINESS (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Nov. 30, 2022	Aug. 31, 2021	Dec. 31, 2023
Pre-Funded Warrants
Class of Stock [Line Items]
Common stock price per share (in dollars per share)	$ 5.9999
Number of securities called by warrants or rights (in shares)	3,333,388
Pre-funded warrants exercise price (in dollars per share)	$ 0.0001
Total IPO
Class of Stock [Line Items]
Stock issued during period, shares, new issues		7,130,000
Common stock price per share (in dollars per share)		$ 13.00
Proceeds from the issuance of common stock from exercise of stock options		$ 92.7
Net proceeds		$ 83.0
Over Allotment on Initial Public Offering
Class of Stock [Line Items]
Stock issued during period, shares, new issues		930,000
Follow-on Offering
Class of Stock [Line Items]
Stock issued during period, shares, new issues	5,803,655
Common stock price per share (in dollars per share)	$ 6.00
Proceeds from the issuance of common stock from exercise of stock options	$ 54.8
Net proceeds	$ 50.8
Follow-on Offering \| Pre-Funded Warrants
Class of Stock [Line Items]
Number of securities called by warrants or rights (in shares)	3,333,388		3,333,388
Pre-funded warrants exercise price (in dollars per share)	$ 0.0001
Over Allotment On Follow-On Offering
Class of Stock [Line Items]
Stock issued during period, shares, new issues	803,654

BALANCE SHEET COMPONENTS - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Less accumulated depreciation	$ (523)	$ (373)
Property and equipment—net	246	385
Computer and other equipment
Property, Plant and Equipment [Line Items]
Property and equipment gross	191	180
Capitalized software
Property, Plant and Equipment [Line Items]
Property and equipment gross	89	89
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment gross	151	151
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 338	$ 338

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES BASIS OF PRESENTATION AND PRINCIPLES OF CONSOLIDATION - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Net income (loss)	$ 74,564	$ 66,654
Retained earnings (accumulated deficit)	235,245	160,681
Cash, cash equivalents and marketable securities	109,900
Impairment of long-lived assets	$ 0	0
Subsidiaries, ownership percentage	80.00%
Deferred offering costs	$ 0	100
Operating lease right-of-use assets	346	524
Carrying value of operating lease liabilities	$ 392	$ 555

- Definition

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

+ References

+ Details

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

STOCKHOLDERS' EQUITY - Summary of NonVested Restricted Common Stock Awards (Details) - Restricted Stock Awards	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Shares
Outstanding, beginning balance (in shares) \| shares	1,006,368
Granted (in shares) \| shares	0
Vested (in shares) \| shares	(553,668)
Forfeited (in shares) \| shares	(98,306)
Outstanding, ending balance (in shares) \| shares	354,394
Weighted-Average Grant Date Fair Value Per Share
Outstanding, beginning balance (in dollars per share) \| $ / shares	$ 3.48
Granted (in dollars per share) \| $ / shares	0
Vested (in dollars per share) \| $ / shares	3.20
Forfeited (in dollars per share) \| $ / shares	2.78
Outstanding, ending balance (in dollars per share) \| $ / shares	$ 4.10

LEASES - Schedule of Future Minimum Annual Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 230
2025	176
2026	0
Thereafter	0
Total lease payments	406
Less: imputed discount rate	(14)
Carrying value of operating lease liabilities	$ 392	$ 555