Axcella Health (AXLA) 10-K 30 Mar 23 2022 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2022	Mar. 28, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-38501
Entity Registrant Name	AXCELLA HEALTH INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-3321056
Entity Address, Address Line One	P.O. Box 1270
Entity Address, City or Town	Littleton
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01460
City Area Code	857
Local Phone Number	320-2200
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	AXLA
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
Entity Shell Company	false
Entity Public Float			$ 67,802,542
Entity Common Stock, Shares Outstanding (in shares)		73,683,027
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Central Index Key	0001633070

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2022
Audit Information [Abstract]
Auditor Firm ID	34
Auditor Name	Deloitte & Touche, LLP
Auditor Location	Boston, Massachusetts

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 17,147	$ 23,574
Marketable securities	0	31,474
Prepaid expenses and other current assets	876	1,598
Total current assets	18,023	56,646
Property and equipment, net	693	870
Other assets	211	211
Total assets	18,927	57,727
Current liabilities:
Accounts payable	4,707	4,301
Accrued expenses and other current liabilities	7,849	5,849
Operating lease liability	1,592	0
Total current liabilities	14,148	10,150
Long-term debt, net of discount	0	25,070
Operating lease liability, net of current portion	569	0
Other non-current liabilities	46	499
Total liabilities	14,763	35,719
Commitments and contingencies (Note 11)	0	0
Stockholders' equity:
Common stock, $0.001 par value; 150,000,000 shares authorized, 74,074,201 and 39,605,701 shares issued and 73,655,220 and 39,186,720 shares outstanding at December 31, 2022 and 2021, respectively	74	40
Additional paid-in capital	422,517	359,261
Treasury stock, 418,981 shares at cost	0	0
Accumulated other comprehensive loss	0	(52)
Accumulated deficit	(418,427)	(337,241)
Total stockholders' equity	4,164	22,008
Total liabilities and stockholders' equity	$ 18,927	$ 57,727

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Common stock, par value (USD per share)	$ 0.001	$ 0.001
Common stock authorized (in shares)	150,000,000	150,000,000
Common stock issued (in shares)	74,074,201	39,605,701
Common stock outstanding (in shares)	73,655,220	39,186,720
Treasury stock at cost (in shares)	418,981	418,981

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 56,984	$ 43,135
General and administrative	15,815	18,711
Restructuring and impairment charges	4,189	0
Total operating expenses	76,988	61,846
Loss from operations	(76,988)	(61,846)
Other (expense) income:
Interest income	504	139
Interest expense	(3,021)	(2,917)
Loss on extinguishment of debt	(1,601)	0
Other expense, net	(80)	(4)
Total other (expense) income, net	(4,198)	(2,782)
Net loss	$ (81,186)	$ (64,628)
Net loss per share, basic (USD per share)	$ (1.49)	$ (1.70)
Net loss per share, diluted (USD per share)	$ (1.49)	$ (1.70)
Weighted average common shares outstanding, basic (in shares)	54,355,769	38,110,420
Weighted average common shares outstanding, diluted (in shares)	54,355,769	38,110,420
Comprehensive loss:
Net loss	$ (81,186)	$ (64,628)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	52	(18)
Comprehensive loss	$ (81,134)	$ (64,646)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net loss	$ (81,186)	$ (64,628)
Adjustment to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	412	288
Share-based compensation expense	3,583	6,243
Non-cash interest expense	513	609
Non-cash lease expense	(183)	0
Impairment of operating lease right-of-use assets	2,331	0
Loss on extinguishment of debt	(1,601)	0
Other non-cash items	177	925
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	722	94
Accounts payable	382	2,050
Accrued expenses and other current liabilities	2,060	198
Net cash used in operating activities	(69,588)	(54,221)
Cash flows from investing activities:
Purchases of property and equipment	(426)	(275)
Purchases of marketable securities	0	(23,391)
Proceeds from sales and maturities of marketable securities	31,349	26,713
Net cash provided by investing activities	30,923	3,047
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	53,495	4,779
Proceeds from convertible notes	5,926	0
Proceeds from exercise of common stock options and ESPP	182	236
Principal repayments of debt	(26,000)	0
Payment of terminal fee obligation and debt issuance costs	(1,190)	(1,726)
Repayments of the principal portion of finance lease	(175)	(131)
Net cash provided by financing activities	32,238	3,158
Net decrease in cash and cash equivalents	(6,427)	(48,016)
Cash and cash equivalents, beginning of year	23,574	71,590
Cash and cash equivalents, end of year	17,147	23,574
Supplemental cash flow information:
Cash paid for interest	2,508	2,309
Supplemental disclosure of non-cash investing and financing activities:
Conversion of notes into common stock	6,000	0
Obtaining a right-of-use asset in exchange for an operating lease liability	3,340	0
Purchases of property and equipment included in accounts payable	26	2
Offering costs incurred but unpaid at period end	0	20
Property and equipment acquired through capital lease	$ 0	$ 534

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2020		38,022,273
Beginning balance at Dec. 31, 2020	$ 75,381	$ 38	$ 347,990	$ (34)	$ (272,613)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		111,833
Exercise of common stock options	57	$ 1	56
Issuance of common stock, net of issuance costs (in shares)		1,331,441
Issuance of common stock, net of issuance costs	4,794	$ 1	4,793
Issuance of common stock related to ESPP (in shares)		56,967
Issuance of common stock related to ESPP	$ 179		179
Vesting of restricted stock units (in shares)	83,187
Stock-based compensation	$ 6,243		6,243
Unrealized loss on marketable securities	(18)			(18)
Net loss	(64,628)				(64,628)
Ending balance (in shares) at Dec. 31, 2021		39,605,701
Ending balance at Dec. 31, 2021	$ 22,008	$ 40	359,261	(52)	(337,241)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	8,499	8,499
Exercise of common stock options	$ 6		6
Issuance of common stock, net of issuance costs (in shares)		34,169,490
Issuance of common stock, net of issuance costs	59,525	$ 34	59,491
Issuance of common stock related to ESPP (in shares)		148,416
Issuance of common stock related to ESPP	$ 176		176
Vesting of restricted stock units (in shares)	142,095
Stock-based compensation	$ 3,583		3,583
Unrealized loss on marketable securities	52			52
Net loss	(81,186)				(81,186)
Ending balance (in shares) at Dec. 31, 2022		74,074,201
Ending balance at Dec. 31, 2022	$ 4,164	$ 74	$ 422,517	$ 0	$ (418,427)

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Statement of Stockholders' Equity [Abstract]
Stock issuance costs	$ 71	$ 349

NATURE OF BUSINESS AND BASIS OF

NATURE OF BUSINESS AND BASIS OF PRESENTATION	12 Months Ended
	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS AND BASIS OF PRESENTATION	NATURE OF BUSINESS AND BASIS OF PRESENTATION Company Overview Axcella Health Inc., doing business as “Axcella Therapeutics,” and subsidiaries ("Axcella," the "Company," "we" or "us") is a clinical-stage biotechnology company that was incorporated in Delaware on August 27, 2008 and has a principal place of business in Cambridge, Massachusetts. The Company is focused on pioneering a new approach to treat complex diseases using compositions of endogenous metabolic modulators, or EMMs. The Company's product candidates are comprised of multiple EMMs that are engineered in distinct combinations and ratios with the goal of simultaneously impacting multiple biological pathways. The Company's pipeline includes lead therapeutic candidates for the treatment of Long COVID (also known as Post COVID-19 Condition and Post-Acute Sequelae of COVID-19, or “PASC”) associated fatigue, and for the treatment of non-alcoholic steatohepatitis, or NASH. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, successful development of technology, obtaining additional funding, protection of proprietary technology, compliance with government regulations, risks of failure of preclinical studies, Clinical Studies and Clinical Trials, the need to obtain marketing approval for its product candidates, if required, and successfully market products, fluctuations in operating results, economic pressure impacting therapeutic pricing, dependence on key personnel, risks associated with changes in technologies, development by competitors of technological innovations and the ability to scale manufacturing to large scale production. Product candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and any necessary regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. To date, the Company has primarily financed its operations with proceeds from the sale of preferred and common stock and borrowing of debt. In May 2019, the Company completed its initial public offering pursuant to which the Company issued an aggregate of 3,571,428 shares of its common stock for net proceeds of approximately $64.5 million after deducting the underwriting discounts and commissions and other offering expenses. In May 2020, the Company completed a follow-on public offering pursuant to which the Company issued an aggregate of 12,650,000 shares of its common stock for net proceeds of approximately $55.9 million after deducting the underwriting discounts and commissions and other offering expenses. In June 2020, the Company entered into a sales agreement with SVB Leerink LLC pursuant to which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $35.0 million from time to time through SVB Leerink, acting as its agent (the “ATM Offering”). As of December 31, 2022, the Company sold an aggregate of 3,285,308 shares of common stock under the ATM Offering for net cash proceeds of $14.7 million after deducting commissions and expenses of $0.9 million. During the year ended December 31, 2022, the Company issued 232,600 shares of common stock in a series of sales under the ATM Offering for an aggregate net proceeds of $0.6 million after deducting nominal commissions and expenses. In March 2022, the Company secured $24.8 million in net proceeds after deducting estimated offering expenses through a registered direct offering with certain institutional purchasers and certain directors and officers of the company named therein. In the registered direct offering, the Company sold 13,089,002 shares of common stock, at a purchase price of $1.91 per share. In September 2022, the Company issued convertible notes in an aggregate principal amount of $6.0 million to existing investor Flagship Pioneering. In October 2022, the Company secured $28.1 million in net proceeds after deducting estimated offering expenses through a registered direct offering of common stock. As part of the registered direct offering, the $6.0 million convertible notes held by funds associated with Flagship Pioneering were automatically converted into the Company's common stock. In total, the Company sold 20,847,888 shares of common stock at a purchase price of $1.64 per share. In late 2022, the Company used $27.4 million of its cash and cash equivalents to extinguish its long-term debt and satisfy its obligations under the loan and security agreement with SLR Investment Corp. On December 12, 2022, the Board of Directors approved a reprioritization of the Company's programs and a restructuring of operations to support its streamlined set of priorities. As part of this restructuring, the Board approved a reduction in force of approximately 85% of the Company’s workforce. Since the reorganization, the Company has taken several actions including terminating its EMMPACT Phase 2b clinical trial of AXA1125 for the treatment of NASH to focus on AXA1125 for the treatment of Long COVID associated fatigue, and executing a plan to vacate its facility and to sell its non-leased laboratory equipment. Under Accounting Standards Update (“ASU”) 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 205-40) (“ASC 205-40”), the Company has the responsibility to evaluate whether conditions and/or events raise substantial doubt about its ability to meet its future financial obligations as they become due within one year after the date that the financial statements are issued. As of December 31, 2022, the Company had an accumulated deficit of $418.4 million, and cash and cash equivalents of $17.1 million. For the year ended December 31, 2022, the Company incurred a loss of $81.2 million and used $69.6 million of cash in operations. The Company expects its reorganization will reduce its operating expenses, however the Company will need to raise additional funding to operate to fund operations. Management has assessed the Company’s ability to continue as a going concern in accordance with the requirements of ASC 205-40 based on the need to raise additional capital to finance its future operations, its recurring losses from operations incurred since inception, and expectation of continuing operating losses for the foreseeable future. As of March 30, 2023, the issuance date of the consolidated financial statements for the year ended December 31, 2022, the Company has concluded that there is substantial doubt about its ability to continue as a going concern for a period of one year from the date that these consolidated financial statements are issued. The accompanying consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. The Company's plans to alleviate its financing requirements include, among other things, pursuing the sale of its common stock, a transaction of the Company or its AXA1125 product candidate for Long COVID, and funding through the establishment of a collaboration(s) with a potential partner(s) to further advance its product pipeline, none of which can be guaranteed or are entirely within the Company's control. As of December 15, 2022, the Company was forced to discontinue some of its operations and develop and implement a plan to further extend payables, reduce overhead and scale back its current operating plan until sufficient additional capital is raised to support further operations. These factors individually and collectively raise substantial doubt about the Company's ability to continue as a going concern, and; therefore, it may be more difficult for the Company to attract investors. Unless the Company is able to raise additional capital to finance its operations, its long-term business plan may not be accomplished, and the Company may be forced to cease, further reduce, or further delay operations. However, the Company does not believe it is probable that those plans can be effectively implemented to mitigate the conditions or events that raise substantial doubt. The Company’s consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany accounts and transactions have been eliminated in consolidation.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Principles of Consolidation The accompanying consolidated financial statements include the accounts of Axcella Health Inc. and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the CEO, who is the chief operating decision maker, in making decisions on how to allocate resources and assess performance. The Company operates in one reportable business segment. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements, the reported amounts of expenses during the reporting period, and disclosure of contingent assets and liabilities. On an on-going basis, the Company evaluates its estimates and assumptions, including those related to recoverability of long-lived assets, useful lives used in depreciation and amortization, income taxes and related valuation allowance, accrued expenses and share-based compensation. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates. Cash and Cash Equivalents Cash and cash equivalents include cash held in banks and amounts held in interest-bearing money market accounts. Cash equivalents are carried at cost, which approximates their fair market value. The Company considers all highly liquid investments with a remaining maturity when purchased of three months or less to also be cash equivalents. Marketable Securities The Company’s marketable securities, which consisted of corporate debt obligations, are classified as available-for-sale and are reported at fair value. Unrealized gains and losses on available-for-sale securities are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss. The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the consolidated statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Concentrations of Credit Risk The Company has no off-balance sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. The Company’s cash and cash equivalents consists of bank deposits and money market funds that invest in U.S. treasury securities. Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash equivalents. The Company invests in high-quality financial instruments and its portfolio does not consist of any instrument with a maturity duration in excess of twenty-four months, which we believe limits the Company's credit risk. In addition, the Company's investment policy includes guidelines on the quality of the institutions and financial instruments and defines the allowable investments that the Company believes minimizes the exposure to concentrations of credit risk. The Company has not experienced any credit losses and does not believe that it is subject to significant credit risk. The Company has a banking relationship with SVB. SVB was closed on March 10, 2023 by the California Department of Financial Protection and Innovation, which appointed the FDIC as receiver. On March 12, 2023, the U.S. Treasury, Federal Reserve, and FDIC announced that SVB depositors will have access to all of their money starting March 13, 2023. While the Company has not experienced any losses in such accounts, the recent failure of SVB potentially exposed the Company to significant credit risk prior to the completion by the FDIC of the resolution of SVB in a manner that fully protected all depositors. Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1 — Quoted prices in active markets for identical assets or liabilities. • Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3 — Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above. The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these liabilities. The carrying value of the Company's long-term debt approximates its fair value due to its variable interest rate, which approximates a market interest rate. Long-Lived Assets - Property and Equipment Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets: Estimated useful life Computer equipment and software 3 years Office equipment 3 - 5 years Laboratory equipment 5 years Furniture and fixtures 5 years Leasehold improvements Shorter of the asset’s estimated Upon disposal, retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the results of operations. Expenditures for repairs and maintenance that do not improve or extend the lives of the respective assets are charged to expense as incurred. Long-Lived Asset - Operating Lease In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , as amended by various subsequently issued ASUs. The standard requires lessees to recognize an operating lease with a term greater than one year on their balance sheets as a right-of-use asset and corresponding lease liability, measured at the present value of the lease payments. Under the standard, disclosures are required to enable financial statement users to assess the amount, timing, and uncertainty of cash flows arising from the leases. Companies are also required to recognize and measure leases existing at, or entered into after, the adoption date using a modified retrospective approach, with certain practical expedients available. Comparative periods prior to adoption have not been retrospectively adjusted. Effective January 1, 2022, the Company adopted ASU 2016-02, using the required modified retrospective approach and utilizing January 1, 2022 as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840, Leases (Topic 840). At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. The Company does not have material financing leases. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects an internally developed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. ASC 842 transition practical expedients and application of transition provisions to leases at the transition date The Company elected the following practical expedients, which must be elected as a package and applied consistently to all of its leases at the transition date (including those for which the entity is a lessee or a lessor): i) the Company did not reassess whether any expired or existing contracts are or contain leases; ii) the Company did not reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with ASC 840 are classified as operating leases, and all existing leases that were classified as capital leases in accordance with ASC 840 are classified as finance leases); and iii) the Company did not reassess initial direct costs for any existing leases. For leases that existed prior to the date of initial application of ASC 842 (which were previously classified as operating leases), a lessee may elect to use either the total lease term measured at lease inception under ASC 840 or the remaining lease term as of the date of initial application of ASC 842 in determining the period for which to measure its incremental borrowing rate. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. Application of ASC 842 policy elections to leases post adoption The Company has made certain policy elections to apply to its leases executed post adoption, or subsequent to January 1, 2022, as further described below. In accordance with ASC 842, components of a lease should be split into three categories: lease components, non-lease components, and non-components. The fixed and in-substance fixed contract consideration (including any consideration related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. Entities may elect not to separate lease and non-lease components. Rather, entities would account for each lease component and related non-lease component together as a single lease component. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets and allocate all of the contract consideration to the lease component only. ASC 842 allows for the use of judgment in determining whether the assumed lease term is for a major part of the remaining economic life of the underlying asset and whether the present value of lease payments represents substantially all of the fair value of the underlying asset. The Company applies the bright line thresholds referenced in ASC 842-10-55-2 to assist in evaluating leases for appropriate classification. The aforementioned bright lines are applied consistently to the Company’s leases. Long-Lived Assets Impairment Long-lived assets consist of property and equipment and operating lease, right-of-use asset. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized in loss from operations when estimated undiscounted future cash flows expected to result from the use and eventual disposition of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs, depreciation, third-party license fees, and external costs of outside vendors engaged to conduct preclinical development activities, Clinical Studies and Clinical Trials as well as to manufacture research and development materials. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are deferred and are recognized as an expense as the goods are consumed or the related services are performed. The Company has entered into various research and development related contracts. The Company records accrued liabilities for research costs incurred but not paid. When measuring the accrued liabilities, the Company analyzes progress of the Clinical Studies or Clinical Trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Share-Based Compensation Expense The Company measures the estimated fair value of the stock-based award on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the award. For stock-based awards with service-based vesting conditions, the Company records the expense for these awards using the straight-line method. For stock options with performance-based vesting conditions, the Company records the expense for these awards over the requisite service period using an accelerated attribution method to the extent the achievement of the performance condition is probable. The Company accounts for forfeitures as they occur. The Company classifies stock-based compensation expense in the consolidated statements of operations in the same manner in which the award recipient’s cash compensation costs are classified. Income Taxes Deferred tax assets and liabilities are recognized for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined based on the difference between the consolidated financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. A valuation allowance is provided to reduce the deferred tax asset to an amount, which, more likely than not, will be realized. The Company recognizes the tax benefit from any uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the consolidated financial statements from such a position are measured based on the largest benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement. Interest and penalties associated with uncertain tax positions are recorded as a component of income tax expense. As of December 31, 2022 and 2021, the Company has not identified any uncertain tax positions for which reserves would be required. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the year ended December 31, 2022, the Company’s only element of other comprehensive loss was unrealized gains (losses) on marketable securities.

MARKETABLE SECURITIES

MARKETABLE SECURITIES	12 Months Ended
	Dec. 31, 2022
Cash and Cash Equivalents [Abstract]
MARKETABLE SECURITIES	MARKETABLE SECURITIES During the years ended December 31, 2022 and 2021, the Company sold marketable securities worth $15.9 million and $5.9 million, respectively. For the year ended December 31, 2022, the Company recognized realized losses on the sale of those securities of less than $0.1 million, and reclassified amounts out of accumulated other comprehensive loss during the periods. As a result, as of December 31, 2022, the Company did not hold any marketable securities. As of December 31, 2021, marketable securities by security type consisted of the following (in thousands): December 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Corporate obligations $ 31,526 $ — $ (52) $ 31,474 The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity. At December 31, 2021, the balance in accumulated other comprehensive loss was comprised solely of activity related to marketable securities. The aggregate fair value of marketable securities by contractual maturity were as follows (in thousands): Contractual Maturities December 31, Mature in one year or less $ 28,220 Mature in two years or less 3,254 Total $ 31,474

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The following tables present the Company’s assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy (in thousands): Fair value measurements at December 31, 2022 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 14,649 $ — $ — $ 14,649 Total $ 14,649 $ — $ — $ 14,649 Fair value measurements at December 31, 2021 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents Money market funds $ 23,021 $ — $ — $ 23,021 Marketable securities: Corporate obligations — 31,474 — 31,474 Total $ 23,021 $ 31,474 $ — $ 54,495 As of December 31, 2022 and 2021, the Company’s cash equivalents were invested in money market funds and were valued based on Level 1 inputs. The Company’s marketable securities consist of corporate obligations which are adjusted to fair value at each balance sheet date, based on quoted prices, which are considered Level 2 inputs. During the years ended December 31, 2022 and 2021, there were no transfers between Level 1, Level 2 and Level 3.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment consist of the following (in thousands): December 31, 2022 2021 Laboratory equipment $ 3,506 $ 3,426 Leasehold improvements 564 564 Office and computer equipment 303 148 Furniture and fixtures 122 122 Property and equipment, gross 4,495 4,260 Less: accumulated depreciation and amortization (3,802) (3,390) Property and equipment, net $ 693 $ 870 Depreciation and amortization expense for the years ended December 31, 2022 and 2021 was $0.4 million and $0.3 million, respectively. The Company disposed of lab equipment during the year ended December 31, 2021 totaling $0.3 million. The Company recognized an impairment charge of $0.2 million during the year ended December 31, 2022 primarily related to the return of leased laboratory equipment to the lessor in January 2023 (Note 14).

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2022
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2022 2021 Accrued employee compensation and benefits $ 808 $ 3,005 Accrued external research and development expenses 4,791 2,000 Accrued professional fees 824 601 Accrued employee termination benefits 1,221 — Other 205 243 Total accrued expenses and other current liabilities $ 7,849 $ 5,849

DEBT

DEBT	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
DEBT	DEBT Debt consisted of the following (in thousands): December 31, 2022 2021 Principal amount of long-term debt $ — $ 26,000 Debt discount $ — (196) Deferred financing fees $ — (734) Long-term debt, net of discount $ — $ 25,070 In September 2021, the Company entered into a loan and security agreement with SLR Investment Corp., formerly known as Solar Capital Ltd., ("SLR") for term loans in an aggregate principal amount of $26.0 million. The loan and security agreement replaced the prior loan and security agreement between the Company and SLR. The term loans under the loan and security agreement accrued interest at an annual rate equal to 8.60% plus the greater of (a) the thirty (30) day U.S. Dollar LIBOR rate and (b) 0.10%, payable monthly in arrears. The monthly principal payments of $0.6 million were to be paid over a period of 45 months with a final maturity date of September 1, 2026. The interest only period would be extended provided the Company satisfied certain equity related conditions. The term loans were also subject to a prepayment fee of 3.00% if prepayment occurred within the first year subsequent to September 2, 2021 , 2.00% in the second year and 1.00% in the third year through final maturity. The loan and security agreement also contained certain financial covenants, including an unrestricted minimum cash level until certain clinical trial study data conditions are met. As security for its obligations under the loan and security agreement, the Company granted SLR a first priority perfected security interest in all of the Company’s existing and after-acquired assets, including intellectual property. In September 2022, the Company paid SLR approximately $6.4 million, including principal, accrued interest, fees and costs. In October 2022, the Company satisfied an equity related condition under the loan and security agreement that extended the date on which repayment of principal commences from January 2023 to July 2023. On December 15, 2022, the Company entered into a payoff letter with SLR, under which the Company voluntarily accelerated the debt and paid SLR approximately $21.0 million, in full satisfaction of all obligations, including all outstanding principal, accrued interest, fees, costs, expenses and other amounts chargeable, under the loan and security agreement. The Company recognized an extinguishment loss of $1.5 million in the year ended December 31, 2022 representing the difference between the reacquisition price and its net carrying amount. The payoff letter also provided for the termination of all commitments and obligations under the loan and security agreement and release of all liens held by SLR on the Company’s assets. On September 20, 2022, the Company received $6.0 million from existing investor Flagship Pioneering through the issuance of convertible notes. The convertible notes mature one year from the date of issuance and bear interest at the rate of 8.00% per annum payable upon the earlier of (i) voluntary conversion of the notes in accordance with the terms therein and (ii) the maturity date. Upon a change of control, the convertible notes and all accrued and unpaid interest shall be due and payable in full. All principal and accrued interest under the convertible notes will automatically convert at the Company’s next equity financing at a conversion price equal to the lower of: (a) the closing price of the common stock on the conversion date; or (b) the average closing price of the common stock for the five trading days immediately preceding the conversion date. The convertible notes are subordinate and junior in right of payment to the senior secured debt issued pursuant to the New Loan and Security Agreement with SLR Investment Corp. The Company determined that the convertible notes contain cash redemption features and share settled put options which do not result in a variable repayment amount, therefore these features do not require bifurcation from the notes. The Company allocated the full proceeds to the convertible notes. As discussed in Note 1, in October 2022, the Company secured $28.1 million in net proceeds after deducting estimated offering expenses through a registered direct offering of common stock. As part of the registered direct offering, the $6.0 million convertible notes held by funds associated with Flagship Pioneering were automatically converted into the Company's common stock. In total, the Company sold 20,847,888 shares of common stock at a purchase price of 1.64 per share.

CONVERTIBLE NOTES

CONVERTIBLE NOTES	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
DEBT	DEBT Debt consisted of the following (in thousands): December 31, 2022 2021 Principal amount of long-term debt $ — $ 26,000 Debt discount $ — (196) Deferred financing fees $ — (734) Long-term debt, net of discount $ — $ 25,070 In September 2021, the Company entered into a loan and security agreement with SLR Investment Corp., formerly known as Solar Capital Ltd., ("SLR") for term loans in an aggregate principal amount of $26.0 million. The loan and security agreement replaced the prior loan and security agreement between the Company and SLR. The term loans under the loan and security agreement accrued interest at an annual rate equal to 8.60% plus the greater of (a) the thirty (30) day U.S. Dollar LIBOR rate and (b) 0.10%, payable monthly in arrears. The monthly principal payments of $0.6 million were to be paid over a period of 45 months with a final maturity date of September 1, 2026. The interest only period would be extended provided the Company satisfied certain equity related conditions. The term loans were also subject to a prepayment fee of 3.00% if prepayment occurred within the first year subsequent to September 2, 2021 , 2.00% in the second year and 1.00% in the third year through final maturity. The loan and security agreement also contained certain financial covenants, including an unrestricted minimum cash level until certain clinical trial study data conditions are met. As security for its obligations under the loan and security agreement, the Company granted SLR a first priority perfected security interest in all of the Company’s existing and after-acquired assets, including intellectual property. In September 2022, the Company paid SLR approximately $6.4 million, including principal, accrued interest, fees and costs. In October 2022, the Company satisfied an equity related condition under the loan and security agreement that extended the date on which repayment of principal commences from January 2023 to July 2023. On December 15, 2022, the Company entered into a payoff letter with SLR, under which the Company voluntarily accelerated the debt and paid SLR approximately $21.0 million, in full satisfaction of all obligations, including all outstanding principal, accrued interest, fees, costs, expenses and other amounts chargeable, under the loan and security agreement. The Company recognized an extinguishment loss of $1.5 million in the year ended December 31, 2022 representing the difference between the reacquisition price and its net carrying amount. The payoff letter also provided for the termination of all commitments and obligations under the loan and security agreement and release of all liens held by SLR on the Company’s assets. On September 20, 2022, the Company received $6.0 million from existing investor Flagship Pioneering through the issuance of convertible notes. The convertible notes mature one year from the date of issuance and bear interest at the rate of 8.00% per annum payable upon the earlier of (i) voluntary conversion of the notes in accordance with the terms therein and (ii) the maturity date. Upon a change of control, the convertible notes and all accrued and unpaid interest shall be due and payable in full. All principal and accrued interest under the convertible notes will automatically convert at the Company’s next equity financing at a conversion price equal to the lower of: (a) the closing price of the common stock on the conversion date; or (b) the average closing price of the common stock for the five trading days immediately preceding the conversion date. The convertible notes are subordinate and junior in right of payment to the senior secured debt issued pursuant to the New Loan and Security Agreement with SLR Investment Corp. The Company determined that the convertible notes contain cash redemption features and share settled put options which do not result in a variable repayment amount, therefore these features do not require bifurcation from the notes. The Company allocated the full proceeds to the convertible notes. As discussed in Note 1, in October 2022, the Company secured $28.1 million in net proceeds after deducting estimated offering expenses through a registered direct offering of common stock. As part of the registered direct offering, the $6.0 million convertible notes held by funds associated with Flagship Pioneering were automatically converted into the Company's common stock. In total, the Company sold 20,847,888 shares of common stock at a purchase price of 1.64 per share.

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY 2019 Stock Option and Incentive Plan The 2019 Stock Option and Incentive Plan (the "2019 Plan") was approved by the Company's board of directors on April 29, 2019. The 2019 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards and cash-based awards to the Company's officers, employees, directors and consultants. Awards under the 2019 plan generally vest ratably over the vesting period (3-4 years) and have a maximum term of 10 years. The number of shares initially reserved for issuance under the 2019 Plan is 905,000, which was increased on January 1, 2020 and will be increased each January 1 thereafter by 4% of the number of shares of the Company's common stock outstanding on the immediately preceding December 31, or such lesser number of shares determined by the Company's board of directors or compensation committee of the board of directors. The number of options available for future grant under the 2019 Plan was 2,317,471 as of December 31, 2022. 2019 Employee Stock Purchase Plan The 2019 Employee Stock Purchase Plan (the "2019 ESPP") was approved by the Company's board of directors on April 29, 2019. A total of 237,181 shares of common stock were initially reserved for issuance under this plan, which was cumulatively increased on January 1, 2020 and will be increased each January 1 thereafter by 1% of the number of shares of the Company's common stock outstanding on the immediately preceding December 31, or such lesser number of shares determined by the Company's board of directors or compensation committee of the board of directors. The number of shares available for future grant was 698,005 as of December 31, 2022. The Company recorded $0.1 million of stock-based compensation expense during the years ended December 31, 2022 and 2021. In connection with all share-based payment awards, total stock-based compensation expense recognized was as follows (in thousands): December 31, 2022 2021 Research and development $ 1,484 $ 1,839 General and administrative 2,099 4,404 Total stock-based compensation expense $ 3,583 $ 6,243 Fair Value of Stock Option Awards The fair value of stock option awards was estimated using the Black-Scholes option-pricing model. The expected term of these awards was determined using the simplified method, which uses the midpoint between the vesting date and the contractual term. The risk-free interest rate was determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining contractual term of the stock awards. The expected dividend was zero as the Company had not paid any dividends on its common stock. Finally, as the Company does not have long-term trading history of its common stock, the expected volatility was derived from the average historical stock volatilities of several public companies within the industry that the Company considers to be comparable to the Company's business over a period equivalent to the expected term of the stock-based awards. The Black-Scholes option pricing model assumptions are included in the table below. Year Ending December 31, 2022 2021 Risk-free interest rate 2.17 % 0.91 % Expected option life (in years) 6.06 5.98 Expected dividend yield — % — % Expected volatility 92 % 96 % The following table summarizes the Company’s stock option activity for the year ended December 31, 2022: Options Weighted Weighted Intrinsic Outstanding as of January 1, 2022 6,197,288 $ 5.72 Granted 2,401,197 1.81 Exercised (8,499) 0.72 Cancelled (2,053,009) 3.30 Outstanding as of December 31, 2022 6,536,977 $ 5.05 5.55 $ — Exercisable as of December 31, 2022 4,496,708 $ 6.00 4.69 $ — Vested or expected to vest as of December 31, 2022 6,302,190 $ 4.99 5.53 $ — The intrinsic value of options exercised during the year ended December 31, 2022 was nominal. The intrinsic value of options exercised during the year ended December 31, 2021 was $0.4 million. The weighted-average grant date fair value of the options granted during the years ended December 31, 2022 and 2021, was $1.09 and $3.87 per share, respectively. As of December 31, 2022, there was $3.3 million of unrecognized compensation expense related to unvested stock options that is expected to be recognized over a weighted-average period of approximately 2.1 years. Restricted Stock Units The fair values of restricted stock units are based on the market value of the Company's common stock on the date of grant. The following table summarizes the Company's restricted stock unit activity for the year ended December 31, 2022: Number of Shares Weighted Average Grant Date Fair Value per Share Outstanding as of January 1, 2022 275,350 $ 4.15 Granted 48,278 1.70 Vested (142,095) 3.59 Forfeited (106,300) 3.16 Outstanding as of December 31, 2022 75,233 $ 5.04

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES There is no provision for income taxes because the Company has historically incurred operating losses and maintains a full valuation allowance against its deferred tax assets. A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations as of December 31, 2022 and 2021 are as follows: December 31, 2022 2021 U.S. federal statutory income tax rate 21.0 % 21.0 % State taxes, net of federal benefit 5.7 % 6.0 % Permanent differences (0.1) % — % Stock compensation (0.6) % (2.2) % Tax credits 2.9 % 3.1 % Other — % — % Change in valuation allowance (28.9) % (27.9) % Effective income tax rate — % — % Significant components of the Company’s deferred tax asset at December 31, 2022 and 2021 are as follows (in thousands): December 31, 2022 2021 Net operating loss carryforwards $ 89,259 $ 82,070 Research and development tax credit carryforwards 13,127 10,892 Start-up costs 14 21 Capitalized research and development costs 13,392 — Operating lease liabilities 577 — Depreciation 237 213 Accrued expenses 212 822 Stock-based compensation 3,688 3,316 Other items 1,619 1,366 Total deferred tax assets 122,125 98,700 Valuation allowance (122,125) (98,700) Net deferred tax asset $ — $ — In assessing the realizability of deferred tax assets, the Company considers all relevant positive and negative evidence in determining whether it is more likely than not that some portion or all deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent on several factors, including the generation of sufficient taxable income prior to the expiration of the net operating loss carryforwards. The Company believes it is more likely than not that the results of future operations will not generate sufficient taxable income to realize the full benefits of its deferred tax assets. As such, there is a full valuation allowance against the net deferred tax assets as of December 31, 2022 and 2021. The valuation allowance increased in 2022 by $23.4 million, primarily as a result of net operating losses generated during the period. As of December 31, 2022, the Company had federal and state net operating loss carryforwards of $329.2 million and $318.3 million, respectively, which may be used to offset future taxable income, if any. These amounts begin to expire in 2030. The federal net operating losses generated in 2018, 2019, 2020, 2021 and 2022 can be carried forward indefinitely. As of December 31, 2022, the Company had federal and state research and development tax credit carryforwards of $10.6 million and $3.2 million, respectively. These amounts expire at various dates through 2042. Due to the degree of uncertainty related to the ultimate use of the deferred tax assets, the Company has fully reserved these tax benefits, as the determination of the realization of the deferred tax benefits was not determined to be more likely than not. In 2022, the valuation allowance increased by $23.4 million which was primarily driven by the current period net operating loss. Utilization of the net operating loss and research and development credit carryforwards may be subject to a substantial annual limitation under Sections 382 and 383 of the Internal Revenue Code of 1986 due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of net operating loss and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. As of December 31, 2022, the Company had not yet completed an analysis of whether its net operating loss and research and development credit carryforwards may be limited. At December 31, 2022 and 2021, the Company had no unrecognized tax benefits. As of December 31, 2022 and 2021, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company's consolidated statements of operations. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. For years through December 31, 2022, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed, and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance. The Company files income tax returns in the U.S. Federal, California, Massachusetts, New Jersey, New York, and Pennsylvania jurisdictions. The statute of limitations for assessment by the Internal Revenue Service, or IRS, and state tax authorities is closed for tax years prior to 2019, although carryforward attributes that were generated prior to tax year 2019 may still be adjusted upon examination by the IRS or state tax authorities if they either have been or will be used in a future period. There are currently no federal or state audits in progress.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Leases The Company leases a facility containing 19,200 square feet of laboratory and office space in Cambridge, Massachusetts. The lease expires in April 2024, subject to an option to extend the lease for an additional three years. The lease agreement and most recent amendment contained escalating rent payments. The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2022 (in thousands, except weighted average figures): Operating leases Year Ended December 31, 2022 Lease cost Operating lease cost $ 1,489 Variable lease cost 711 Total lease cost $ 2,200 Other information Operating cash flows used for operating leases $ 2,383 Weighted average remaining lease term (years) 1.3 Weighted average discount rate (percentage) 9.0 % For the year ended December 31, 2022, the Company incurred $2.2 million and in operating lease expense, and made lease payments of $2.4 million, with such amounts reflected in the consolidated statements of cash flows in operating activities. As the result of adopting ASU 2016-02 using the modified retrospective transition method, the Company did not restate periods prior to the adoption date of January 1, 2022. These periods continue to be presented in accordance with ASC 840. Future minimum lease payments and lease liabilities as of December 31, 2022 were as follows (in thousands): Maturity of lease liabilities December 31, 2023 $ 1,722 2024 580 Total future minimum lease payments $ 2,302 Less: imputed interest (141) Total lease liability $ 2,161 Reported as: Operating lease liability $ 1,592 Operating lease liability, net of current portion 569 Total lease liability $ 2,161 Other Commitments We enter into contracts in the normal course of business with contract research organizations ("CROs"), contract manufacturing organizations ("CMOs") and other third parties for preclinical research studies, Clinical Studies, Clinical Trials, and testing and manufacturing services. These contracts do not contain minimum purchase commitments and are cancelable by upon prior written notice. Payments due upon cancellation consist only of payments for services provided or expenses incurred, including non-cancelable obligations of service providers, up to the date of cancellation. Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to such legal proceedings.

NET LOSS PER SHARE

NET LOSS PER SHARE	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): December 31, 2022 2021 Numerator: Net loss $ (81,186) $ (64,628) Denominator: Weighted average common shares outstanding, basic and diluted 54,355,769 38,110,420 Net loss per share, basic and diluted $ (1.49) $ (1.70) The Company excluded the following potential shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2022 2021 Options to purchase common stock 6,536,977 6,197,288 Unvested restricted stock units 75,233 275,350 Shares issuable under employee stock purchase plan — 46,520 6,612,210 6,519,158

401(k) PLAN

401(k) PLAN	12 Months Ended
	Dec. 31, 2022
Retirement Benefits [Abstract]
401(k) PLAN	401(k) PLANThe Company has a 401(k) retirement and savings plan (the "Plan") covering all qualified employees. The Plan allows each participant to contribute a portion of his or her base wages up to an amount not to exceed an annual statutory maximum. The Company is permitted to make discretionary matching contributions to the Plan. The Company's matching contributions totaled $0.4 million and $0.3 million for the years ended December 31, 2022 and 2021, respectively.

RESTRUCTURING AND IMPAIRMENT CH

RESTRUCTURING AND IMPAIRMENT CHARGES	12 Months Ended
	Dec. 31, 2022
Restructuring and Related Activities [Abstract]
RESTRUCTURING AND IMPAIRMENT CHARGES	RESTRUCTURING AND IMPAIRMENT CHARGESThe Company incurred approximately $4.2 million in restructuring and impairment charges in its consolidated statement of operations and comprehensive loss related to the corporate restructuring, including the reduction in force, as described in Note 1. The actions associated with the reduction in force were completed in December 2022. The following table shows the restructuring and impairment charges as of December 31, 2022 (in thousands): Year Ended December 31, 2022 Employee termination benefits $ 1,858 Impairment of operating lease right-of-use assets 2,116 Impairment of property and equipment 215 Total restructuring and impairment charges $ 4,189 Employee Termination Benefits Employees affected by the reduction in workforce obtained involuntary termination benefits that are provided pursuant to a one-time benefit arrangement. The affected employees have no requirements to provide future service, therefore the Company recognized the liability for the termination benefits in full at fair value in the current period. The following table shows the liability related to employee termination benefits as of December 31, 2022 (in thousands): Employee Termination Benefits Accrued employee termination benefits beginning balance $ — Employee termination benefits charges incurred during the period 1,858 Amounts paid or otherwise settled during the period (637) Accrued employee termination benefits as of December 31, 2022 $ 1,221 Impairment of Operating Lease Right-of-Use Asset The Company leases laboratory and office space in Cambridge, Massachusetts, under a lease agreement that expires on April 30, 2024. On January 1, 2022, the Company adopted ASC 842 and recorded a right-of-use asset of $3.3 million and a lease liability of $3.6 million. The standard did not have a material impact on the statement of operations or statement of cash flows. Additionally, there is no tax impact from the adoption as the net increase in deferred tax assets is fully offset with an increase to the valuation allowance. In December 2022, the Company initiated activities to vacate its corporate offices in Cambridge, Massachusetts, and the activities were completed in January 2023. As a result, the Company performed a recoverability test by comparing the future cash flows attributable to the asset group to the carrying value of the corresponding long-lived, right-of-use asset. Based on this evaluation, the Company determined that the long-lived asset with a carrying value of $2.1 million was no longer recoverable and recorded a right-of-use asset impairment of $2.1 million. The impairment was determined by comparing the fair value of the impacted asset group to their carrying value as of the impairment measurement date, as required under ASC 360, Property, Plant, and Equipment. The impairment is presented in restructuring and impairment charges on the consolidated statements of operations and comprehensive loss. The following table shows the asset and liability as of December 31, 2022 (in thousands): December 31, 2022 Assets Operating lease right-of-use asset $ — Liabilities Operating lease liabilities (current) $ 1,592 Operating lease liabilities (noncurrent) 569 Total lease liabilities $ 2,161 Impairment of Property and Equipment The Company recognized an impairment charge of $0.2 million during the year ended December 31, 2022 primarily related to the return of leased laboratory equipment to the lessor in January 2023. The Company measured the long-lived asset impairment as the amount by which the carrying value of the asset group exceeds its fair value. The impairment is presented in restructuring and impairment charges on the consolidated statements of operations and comprehensive loss.

RELATED-PARTY TRANSACTIONS

RELATED-PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2022
Related Party Transactions [Abstract]
RELATED-PARTY TRANSACTIONS	RELATED-PARTY TRANSACTIONSIn September 2022, the Company issued convertible notes in an aggregate principal amount of $6.0 million to existing investor Flagship Pioneering. Refer to Note 8, Convertible Notes, for further discussion. As discussed in Note 1, in October 2022, the Company sold shares of common stock through a registered direct offering. As part of the registered direct offering, $6.0 million in convertible notes held by funds associated with Flagship Pioneering were converted into common stock.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2022
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTSIn January 2023, the Company sold its non-leased laboratory equipment for $0.5 million in cash and recorded a gain of $0.1 million representing the difference between the carrying amount and the cash proceeds.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Axcella Health Inc. and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Segment Information	Segment InformationOperating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the CEO, who is the chief operating decision maker, in making decisions on how to allocate resources and assess performance. The Company operates in one reportable business segment.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements, the reported amounts of expenses during the reporting period, and disclosure of contingent assets and liabilities. On an on-going basis, the Company evaluates its estimates and assumptions, including those related to recoverability of long-lived assets, useful lives used in depreciation and amortization, income taxes and related valuation allowance, accrued expenses and share-based compensation. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash held in banks and amounts held in interest-bearing money market accounts. Cash equivalents are carried at cost, which approximates their fair market value. The Company considers all highly liquid investments with a remaining maturity when purchased of three months or less to also be cash equivalents.
Marketable Securities	Marketable Securities The Company’s marketable securities, which consisted of corporate debt obligations, are classified as available-for-sale and are reported at fair value. Unrealized gains and losses on available-for-sale securities are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the consolidated statements of operations and comprehensive loss.
Concentrations of Credit Risk	Concentrations of Credit Risk The Company has no off-balance sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. The Company’s cash and cash equivalents consists of bank deposits and money market funds that invest in U.S. treasury securities. Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash equivalents. The Company invests in high-quality financial instruments and its portfolio does not consist of any instrument with a maturity duration in excess of twenty-four months, which we believe limits the Company's credit risk. In addition, the Company's investment policy includes guidelines on the quality of the institutions and financial instruments and defines the allowable investments that the Company believes minimizes the exposure to concentrations of credit risk. The Company has not experienced any credit losses and does not believe that it is subject to significant credit risk. The Company has a banking relationship with SVB. SVB was closed on March 10, 2023 by the California Department of Financial Protection and Innovation, which appointed the FDIC as receiver. On March 12, 2023, the U.S. Treasury, Federal Reserve, and FDIC announced that SVB depositors will have access to all of their money starting March 13, 2023. While the Company has not experienced any losses in such accounts, the recent failure of SVB potentially exposed the Company to significant credit risk prior to the completion by the FDIC of the resolution of SVB in a manner that fully protected all depositors.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1 — Quoted prices in active markets for identical assets or liabilities. • Level 2 — Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3 — Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.
Long-Lived Assets Property and Equipment	Long-Lived Assets - Property and Equipment Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets: Estimated useful life Computer equipment and software 3 years Office equipment 3 - 5 years Laboratory equipment 5 years Furniture and fixtures 5 years Leasehold improvements Shorter of the asset’s estimated Upon disposal, retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in the results of operations. Expenditures for repairs and maintenance that do not improve or extend the lives of the respective assets are charged to expense as incurred.
Long-Lived Asset - Operating Lease	Long-Lived Asset - Operating Lease In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , as amended by various subsequently issued ASUs. The standard requires lessees to recognize an operating lease with a term greater than one year on their balance sheets as a right-of-use asset and corresponding lease liability, measured at the present value of the lease payments. Under the standard, disclosures are required to enable financial statement users to assess the amount, timing, and uncertainty of cash flows arising from the leases. Companies are also required to recognize and measure leases existing at, or entered into after, the adoption date using a modified retrospective approach, with certain practical expedients available. Comparative periods prior to adoption have not been retrospectively adjusted. Effective January 1, 2022, the Company adopted ASU 2016-02, using the required modified retrospective approach and utilizing January 1, 2022 as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840, Leases (Topic 840). At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. The Company does not have material financing leases. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects an internally developed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Prospectively, the Company will adjust the right-of-use assets for straight-line rent expense or any incentives received and remeasure the lease liability at the net present value using the same incremental borrowing rate that was in effect as of the lease commencement or transition date. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. ASC 842 transition practical expedients and application of transition provisions to leases at the transition date The Company elected the following practical expedients, which must be elected as a package and applied consistently to all of its leases at the transition date (including those for which the entity is a lessee or a lessor): i) the Company did not reassess whether any expired or existing contracts are or contain leases; ii) the Company did not reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with ASC 840 are classified as operating leases, and all existing leases that were classified as capital leases in accordance with ASC 840 are classified as finance leases); and iii) the Company did not reassess initial direct costs for any existing leases. For leases that existed prior to the date of initial application of ASC 842 (which were previously classified as operating leases), a lessee may elect to use either the total lease term measured at lease inception under ASC 840 or the remaining lease term as of the date of initial application of ASC 842 in determining the period for which to measure its incremental borrowing rate. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. Application of ASC 842 policy elections to leases post adoption The Company has made certain policy elections to apply to its leases executed post adoption, or subsequent to January 1, 2022, as further described below. In accordance with ASC 842, components of a lease should be split into three categories: lease components, non-lease components, and non-components. The fixed and in-substance fixed contract consideration (including any consideration related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. Entities may elect not to separate lease and non-lease components. Rather, entities would account for each lease component and related non-lease component together as a single lease component. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets and allocate all of the contract consideration to the lease component only. ASC 842 allows for the use of judgment in determining whether the assumed lease term is for a major part of the remaining economic life of the underlying asset and whether the present value of lease payments represents substantially all of the fair value of the underlying asset. The Company applies the bright line thresholds referenced in ASC 842-10-55-2 to assist in evaluating leases for appropriate classification. The aforementioned bright lines are applied consistently to the Company’s leases.
Long-Lived Assets Impairment	Long-Lived Assets Impairment Long-lived assets consist of property and equipment and operating lease, right-of-use asset. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized in loss from operations when estimated undiscounted future cash flows expected to result from the use and eventual disposition of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs, depreciation, third-party license fees, and external costs of outside vendors engaged to conduct preclinical development activities, Clinical Studies and Clinical Trials as well as to manufacture research and development materials. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are deferred and are recognized as an expense as the goods are consumed or the related services are performed. The Company has entered into various research and development related contracts. The Company records accrued liabilities for research costs incurred but not paid. When measuring the accrued liabilities, the Company analyzes progress of the Clinical Studies or Clinical Trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Share-Based Compensation Expense	Share-Based Compensation Expense The Company measures the estimated fair value of the stock-based award on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the award. For stock-based awards with service-based vesting conditions, the Company records the expense for these awards using the straight-line method. For stock options with performance-based vesting conditions, the Company records the expense for these awards over the requisite service period using an accelerated attribution method to the extent the achievement of the performance condition is probable. The Company accounts for forfeitures as they occur. The Company classifies stock-based compensation expense in the consolidated statements of operations in the same manner in which the award recipient’s cash compensation costs are classified.
Income Taxes	Income Taxes Deferred tax assets and liabilities are recognized for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Under this method, deferred tax assets and liabilities are determined based on the difference between the consolidated financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. A valuation allowance is provided to reduce the deferred tax asset to an amount, which, more likely than not, will be realized. The Company recognizes the tax benefit from any uncertain tax positions only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. The tax benefits recognized in the consolidated financial statements from such a position are measured based on the largest benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement. Interest and penalties associated with uncertain tax positions are recorded as a component of income tax expense. As of December 31, 2022 and 2021, the Company has not identified any uncertain tax positions for which reserves would be required.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the year ended December 31, 2022, the Company’s only element of other comprehensive loss was unrealized gains (losses) on marketable securities.
Net Loss Per Share	Net Loss Per ShareBasic net loss per share attributable to common stockholders is calculated by dividing net loss by the weighted average shares outstanding during the period. Diluted net income (loss) per share is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period. All common stock equivalents have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Schedule of Property and Equipment Estimated Useful Lives	Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets: Estimated useful life Computer equipment and software 3 years Office equipment 3 - 5 years Laboratory equipment 5 years Furniture and fixtures 5 years Leasehold improvements Shorter of the asset’s estimated Property and equipment consist of the following (in thousands): December 31, 2022 2021 Laboratory equipment $ 3,506 $ 3,426 Leasehold improvements 564 564 Office and computer equipment 303 148 Furniture and fixtures 122 122 Property and equipment, gross 4,495 4,260 Less: accumulated depreciation and amortization (3,802) (3,390) Property and equipment, net $ 693 $ 870

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2022
Cash and Cash Equivalents [Abstract]
Schedule of Cash, Cash Equivalents, and Marketable Securities by Security Type	As of December 31, 2021, marketable securities by security type consisted of the following (in thousands): December 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Corporate obligations $ 31,526 $ — $ (52) $ 31,474
Schedule of Fair Values of Cash Equivalents and Marketable Securities by Contractual Maturities	The aggregate fair value of marketable securities by contractual maturity were as follows (in thousands): Contractual Maturities December 31, Mature in one year or less $ 28,220 Mature in two years or less 3,254 Total $ 31,474

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Schedule of Assets Measured at Fair Value	The following tables present the Company’s assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy (in thousands): Fair value measurements at December 31, 2022 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 14,649 $ — $ — $ 14,649 Total $ 14,649 $ — $ — $ 14,649 Fair value measurements at December 31, 2021 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents Money market funds $ 23,021 $ — $ — $ 23,021 Marketable securities: Corporate obligations — 31,474 — 31,474 Total $ 23,021 $ 31,474 $ — $ 54,495

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets: Estimated useful life Computer equipment and software 3 years Office equipment 3 - 5 years Laboratory equipment 5 years Furniture and fixtures 5 years Leasehold improvements Shorter of the asset’s estimated Property and equipment consist of the following (in thousands): December 31, 2022 2021 Laboratory equipment $ 3,506 $ 3,426 Leasehold improvements 564 564 Office and computer equipment 303 148 Furniture and fixtures 122 122 Property and equipment, gross 4,495 4,260 Less: accumulated depreciation and amortization (3,802) (3,390) Property and equipment, net $ 693 $ 870

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2022
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2022 2021 Accrued employee compensation and benefits $ 808 $ 3,005 Accrued external research and development expenses 4,791 2,000 Accrued professional fees 824 601 Accrued employee termination benefits 1,221 — Other 205 243 Total accrued expenses and other current liabilities $ 7,849 $ 5,849

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Summary of Long-term Debt	Debt consisted of the following (in thousands): December 31, 2022 2021 Principal amount of long-term debt $ — $ 26,000 Debt discount $ — (196) Deferred financing fees $ — (734) Long-term debt, net of discount $ — $ 25,070

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Schedule of Stock-based Compensation Expense Recognized	In connection with all share-based payment awards, total stock-based compensation expense recognized was as follows (in thousands): December 31, 2022 2021 Research and development $ 1,484 $ 1,839 General and administrative 2,099 4,404 Total stock-based compensation expense $ 3,583 $ 6,243
Schedule of Fair Value Assumptions for Stock Options	The Black-Scholes option pricing model assumptions are included in the table below. Year Ending December 31, 2022 2021 Risk-free interest rate 2.17 % 0.91 % Expected option life (in years) 6.06 5.98 Expected dividend yield — % — % Expected volatility 92 % 96 %
Schedule of Stock Option Activity	The following table summarizes the Company’s stock option activity for the year ended December 31, 2022: Options Weighted Weighted Intrinsic Outstanding as of January 1, 2022 6,197,288 $ 5.72 Granted 2,401,197 1.81 Exercised (8,499) 0.72 Cancelled (2,053,009) 3.30 Outstanding as of December 31, 2022 6,536,977 $ 5.05 5.55 $ — Exercisable as of December 31, 2022 4,496,708 $ 6.00 4.69 $ — Vested or expected to vest as of December 31, 2022 6,302,190 $ 4.99 5.53 $ —
Schedule of Restricted Stock Unit Activity	The following table summarizes the Company's restricted stock unit activity for the year ended December 31, 2022: Number of Shares Weighted Average Grant Date Fair Value per Share Outstanding as of January 1, 2022 275,350 $ 4.15 Granted 48,278 1.70 Vested (142,095) 3.59 Forfeited (106,300) 3.16 Outstanding as of December 31, 2022 75,233 $ 5.04

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations as of December 31, 2022 and 2021 are as follows: December 31, 2022 2021 U.S. federal statutory income tax rate 21.0 % 21.0 % State taxes, net of federal benefit 5.7 % 6.0 % Permanent differences (0.1) % — % Stock compensation (0.6) % (2.2) % Tax credits 2.9 % 3.1 % Other — % — % Change in valuation allowance (28.9) % (27.9) % Effective income tax rate — % — %
Schedule of Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax asset at December 31, 2022 and 2021 are as follows (in thousands): December 31, 2022 2021 Net operating loss carryforwards $ 89,259 $ 82,070 Research and development tax credit carryforwards 13,127 10,892 Start-up costs 14 21 Capitalized research and development costs 13,392 — Operating lease liabilities 577 — Depreciation 237 213 Accrued expenses 212 822 Stock-based compensation 3,688 3,316 Other items 1,619 1,366 Total deferred tax assets 122,125 98,700 Valuation allowance (122,125) (98,700) Net deferred tax asset $ — $ —

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Summary of Lease Costs	The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2022 (in thousands, except weighted average figures): Operating leases Year Ended December 31, 2022 Lease cost Operating lease cost $ 1,489 Variable lease cost 711 Total lease cost $ 2,200 Other information Operating cash flows used for operating leases $ 2,383 Weighted average remaining lease term (years) 1.3 Weighted average discount rate (percentage) 9.0 %
Schedule of Future Minimum Lease Payments	These periods continue to be presented in accordance with ASC 840. Future minimum lease payments and lease liabilities as of December 31, 2022 were as follows (in thousands): Maturity of lease liabilities December 31, 2023 $ 1,722 2024 580 Total future minimum lease payments $ 2,302 Less: imputed interest (141) Total lease liability $ 2,161 Reported as: Operating lease liability $ 1,592 Operating lease liability, net of current portion 569 Total lease liability $ 2,161

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2022
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): December 31, 2022 2021 Numerator: Net loss $ (81,186) $ (64,628) Denominator: Weighted average common shares outstanding, basic and diluted 54,355,769 38,110,420 Net loss per share, basic and diluted $ (1.49) $ (1.70)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The Company excluded the following potential shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2022 2021 Options to purchase common stock 6,536,977 6,197,288 Unvested restricted stock units 75,233 275,350 Shares issuable under employee stock purchase plan — 46,520 6,612,210 6,519,158

RESTRUCTURING AND IMPAIRMENT _2

RESTRUCTURING AND IMPAIRMENT CHARGES (Tables)	12 Months Ended
	Dec. 31, 2022
Restructuring and Related Activities [Abstract]
Schedule of Restructuring and Impairment Costs	Year Ended December 31, 2022 Employee termination benefits $ 1,858 Impairment of operating lease right-of-use assets 2,116 Impairment of property and equipment 215 Total restructuring and impairment charges $ 4,189
Schedule of Liability Related to Employee Termination Benefits	The following table shows the liability related to employee termination benefits as of December 31, 2022 (in thousands): Employee Termination Benefits Accrued employee termination benefits beginning balance $ — Employee termination benefits charges incurred during the period 1,858 Amounts paid or otherwise settled during the period (637) Accrued employee termination benefits as of December 31, 2022 $ 1,221
Schedule of Operating Lease	December 31, 2022 Assets Operating lease right-of-use asset $ — Liabilities Operating lease liabilities (current) $ 1,592 Operating lease liabilities (noncurrent) 569 Total lease liabilities $ 2,161

NATURE OF BUSINESS AND BASIS _2

NATURE OF BUSINESS AND BASIS OF PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended						3 Months Ended	12 Months Ended		31 Months Ended
	Dec. 31, 2022	Oct. 31, 2022	Mar. 31, 2022	Jun. 30, 2020	May 31, 2020	May 31, 2019	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Sep. 30, 2022
Nature Of Business [Line Items]
Commissions and expenses										$ 900
Conversion of notes into common stock	$ 6,000						$ 6,000	$ 6,000	$ 0	6,000
Extinguishment of debt							27,400
Positions eliminated, percentage	85%
Accumulated deficit	$ (418,427)						(418,427)	(418,427)	(337,241)	(418,427)
Cash and cash equivalents	$ 17,147						$ 17,147	17,147	23,574	$ 17,147
Net loss								(81,186)	(64,628)
Net cash used in operations								$ (69,588)	$ (54,221)
Convertible Debt
Nature Of Business [Line Items]
Conversion of notes into common stock		$ 6,000									$ 6,000
IPO
Nature Of Business [Line Items]
Shares sold (in shares)						3,571,428
Net proceeds on offering						$ 64,500
2020 Follow-on Offering
Nature Of Business [Line Items]
Shares sold (in shares)					12,650,000
Net proceeds on offering					$ 55,900
Registered Direct Offering
Nature Of Business [Line Items]
Shares sold (in shares)		20,847,888	13,089,002
Net proceeds on offering		$ 28,100	$ 24,800
Offering price per share (in USD per share)		$ 1.64	$ 1.91
At-the-Market Offering
Nature Of Business [Line Items]
Shares sold (in shares)								232,600		3,285,308
Net proceeds on offering								$ 600		$ 14,700
At-the-Market Offering | Maximum
Nature Of Business [Line Items]
Net proceeds on offering				$ 35,000

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) segment	Jan. 01, 2022 USD ($)
Accounting Policies [Line Items]
Number of operating segments | segment	1
Total lease liability | $	$ 2,161	$ 3,600

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Property and Equipment Useful Life (Details)	12 Months Ended
	Dec. 31, 2022
Computer equipment and software
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Office equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Office equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Laboratory equipment
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years

MARKETABLE SECURITIES - Narrati

MARKETABLE SECURITIES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
Sales of marketable securities	$ 15.9	$ 5.9
Realized loss on sale of securities	$ 0.1

MARKETABLE SECURITIES - Schedul

MARKETABLE SECURITIES - Schedule of Securities by Type (Details) - Corporate obligations $ in Thousands	Dec. 31, 2021 USD ($)
Cash and Cash Equivalents [Line Items]
Amortized Cost	$ 31,526
Gross Unrealized Gains	0
Gross Unrealized Losses	(52)
Estimated Fair Value	$ 31,474

MARKETABLE SECURITIES - Sched_2

MARKETABLE SECURITIES - Schedule of Securities by Contractual Maturity (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Cash and Cash Equivalents [Abstract]
Mature in one year or less	$ 28,220
Mature in two years or less	3,254
Total	$ 31,474

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Assets:
Money market funds	$ 14,649	$ 23,021
Corporate obligations		31,474
Total	14,649	54,495
Level 1
Assets:
Money market funds	14,649	23,021
Corporate obligations		0
Total	14,649	23,021
Level 2
Assets:
Money market funds	0	0
Corporate obligations		31,474
Total	0	31,474
Level 3
Assets:
Money market funds	0	0
Corporate obligations		0
Total	$ 0	$ 0

PROPERTY AND EQUIPMENT - Schedu

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,495	$ 4,260
Less: accumulated depreciation and amortization	(3,802)	(3,390)
Property and equipment, net	693	870
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,506	3,426
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	564	564
Office and computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	303	148
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 122	$ 122

PROPERTY AND EQUIPMENT - Narrat

PROPERTY AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 412	$ 288
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 412	288
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment disposed of		$ 300

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued employee compensation and benefits	$ 808	$ 3,005
Accrued external research and development expenses	4,791	2,000
Accrued professional fees	824	601
Accrued employee termination benefits	1,221	0
Other	205	243
Total accrued expenses and other current liabilities	$ 7,849	$ 5,849

DEBT - Schedule of Long-term De

DEBT - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
Principal amount of long-term debt	$ 0	$ 26,000
Debt discount	0	(196)
Deferred financing fees	0	(734)
Long-term debt, net of discount	$ 0	$ 25,070

DEBT FINANCING - Narrative (Det

DEBT FINANCING - Narrative (Details) $ in Thousands				1 Months Ended	12 Months Ended
	Jan. 01, 2023 USD ($)	Dec. 15, 2022 USD ($)	Sep. 02, 2021 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Line of Credit Facility [Line Items]
Principal amount of long-term debt					$ 0	$ 26,000
Principal repayments of debt					26,000	0
Debt issuance cost and terminal fee					1,190	1,726
Loss on extinguishment of debt					1,601	$ 0
New Loan and Security Agreement | Line of Credit
Line of Credit Facility [Line Items]
Principal amount of long-term debt			$ 26,000
Basis spread on interest rate			8.60%
Interest rate floor, on which basis spread is added			0.10%
Debt instrument prepayment				$ 6,400
Principal repayments of debt		$ 21,000
Loss on extinguishment of debt					$ 1,500
New Loan and Security Agreement | Line of Credit | Forecast
Line of Credit Facility [Line Items]
Principal periodic payments	$ 600
Period of payment	45 months
New Loan and Security Agreement | Line of Credit | Debt Instrument, Redemption, Period One
Line of Credit Facility [Line Items]
Prepayment fee, percent of principal				0.0300
New Loan and Security Agreement | Line of Credit | Debt Instrument, Redemption, Period Two
Line of Credit Facility [Line Items]
Prepayment fee, percent of principal				0.0200
New Loan and Security Agreement | Line of Credit | Debt Instrument, Redemption, Period Three
Line of Credit Facility [Line Items]
Prepayment fee, percent of principal				0.0100

CONVERTIBLE NOTES (Details)

CONVERTIBLE NOTES (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		12 Months Ended
	Sep. 20, 2022	Oct. 31, 2022	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2022
Class of Stock [Line Items]
Conversion of notes into common stock				$ 6,000	$ 0
Loss on extinguishment of debt				1,601	$ 0
Convertible Debt
Class of Stock [Line Items]
Convertible notes maturity term	1 year
Convertible notes interest rate	8%
Conversion of notes into common stock		$ 6,000				$ 6,000
Convertible Notes Issued To Investors | Convertible Debt | Flagship Pioneering
Class of Stock [Line Items]
Debt instrument, face amount	$ 6,000					$ 6,000
Registered Direct Offering
Class of Stock [Line Items]
Net proceeds on offering		$ 28,100	$ 24,800
Shares sold (in shares)		20,847,888	13,089,002
Offering price per share (in USD per share)		$ 1.64	$ 1.91
Loss on extinguishment of debt				$ 100

STOCKHOLDERS' EQUITY - Narrativ

STOCKHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Apr. 29, 2019	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares initially reserved for future issuance (in shares)	237,181
Annual percent increase in authorized shares available for issuance under share based payment arrangements	1%
Stock-based compensation expense		$ 3,583	$ 6,243
Intrinsic value, options exercised		$ 0	$ 400
Weighted-average grand date fair value of options granted in the period (USD per share)		$ 1.09	$ 3.87
Unrecognized compensation expense related to unvested stock options		$ 3,300
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)		698,005
Stock-based compensation expense		$ 100	$ 100
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield		0%	0%
Unrecognized compensation expense, recognition period		2 years 1 month 6 days
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested stock options		$ 200
Unrecognized compensation expense, recognition period		1 year 2 months 12 days
Stock Option And Incentive Plan 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum award term		10 years
Number of shares initially reserved for future issuance (in shares)	905,000
Annual percent increase in authorized shares available for issuance under share based payment arrangements	4%
Common stock reserved for future issuance (in shares)		2,317,471
Stock Option And Incentive Plan 2019 | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		3 years
Stock Option And Incentive Plan 2019 | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		4 years

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Stock Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 3,583	$ 6,243
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	1,484	1,839
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 2,099	$ 4,404

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Fair Value Measurement Inputs (Details) - Stock options	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.17%	0.91%
Expected option life (in years)	6 years 21 days	5 years 11 months 23 days
Expected dividend yield	0%	0%
Expected volatility	92%	96%

STOCK-BASED COMPENSATION - Sc_3

STOCK-BASED COMPENSATION - Schedule of Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares
Options
Outstanding, beginning balance (in shares) | shares	6,197,288
Granted (in shares) | shares	2,401,197
Exercised (in shares) | shares	(8,499)
Canceled (in shares) | shares	(2,053,009)
Outstanding, ending balance (in shares) | shares	6,536,977
Options exercisable (in shares) | shares	4,496,708
Options vested or expected to vest (in shares) | shares	6,302,190
Weighted Average Exercise Price
Weighted average exercise price, outstanding, beginning balance (USD per share) | $ / shares	$ 5.72
Weighted-average exercise price, granted (USD per share) | $ / shares	1.81
Weighted-average exercise price, exercised (USD per share) | $ / shares	0.72
Weighted-average exercise price, canceled (USD per share) | $ / shares	3.30
Weighted average exercise price, outstanding, ending balance (USD per share) | $ / shares	5.05
Weighted-average exercise price, options exercisable (USD per share) | $ / shares	6
Weighted-average exercise price, options vested or expected to vest (USD per share) | $ / shares	$ 4.99
Weighted Average Remaining Life (in Years)
Weighted average remaining life of shares outstanding	5 years 6 months 18 days
Weighted average remaining life of shares exercisable	4 years 8 months 8 days
Weighted average remaining life of shares vested or expected to vest	5 years 6 months 10 days
Intrinsic value of shares outstanding | $	$ 0
Intrinsic value of shares exercisable | $	0
Intrinsic value of shares vested or expected to vest | $	$ 0

STOCK-BASED COMPENSATION - Sc_4

STOCK-BASED COMPENSATION - Schedule of Restricted Stock Units (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2022 $ / shares shares
Number of Shares
Outstanding, beginning balance (in shares) | shares	275,350
Granted (in shares) | shares	48,278
Vested (in shares) | shares	(142,095)
Forfeited (in shares) | shares	(106,300)
Outstanding, ending balance (in shares) | shares	75,233
Weighted Average Grant Date Fair Value per Share
Weighted average exercise price, outstanding, beginning balance (USD per share) | $ / shares	$ 4.15
Weighted-average exercise price, granted (USD per share) | $ / shares	1.70
Weighted-average exercise price, vested (USD per share) | $ / shares	3.59
Weighted-average exercise price, forfeited (USD per share) | $ / shares	3.16
Weighted average exercise price, outstanding, ending balance (USD per share) | $ / shares	$ 5.04

INCOME TAXES - Schedule of Effe

INCOME TAXES - Schedule of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	21%	21%
State taxes, net of federal benefit	5.70%	6%
Permanent differences	(0.10%)	0%
Stock compensation	(0.60%)	(2.20%)
Tax credits	2.90%	3.10%
Other	0%	0%
Change in valuation allowance	(28.90%)	(27.90%)
Effective income tax rate	0%	0%

INCOME TAXES - Schedule of Net

INCOME TAXES - Schedule of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 89,259	$ 82,070
Research and development tax credit carryforwards	13,127	10,892
Start-up costs	14	21
Capitalized research and development costs	13,392	0
Operating lease liabilities	577	0
Depreciation	237	213
Accrued expenses	212	822
Stock-based compensation	3,688	3,316
Other items	1,619	1,366
Total deferred tax assets	122,125	98,700
Valuation allowance	(122,125)	(98,700)
Net deferred tax asset	$ 0	$ 0

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Increase (decrease) in valuation allowance	$ 23,400,000
Unrecognized tax benefits	0	$ 0
Income tax penalties and interest accrued	0	0
Interest or penalties recognized	0	$ 0
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	329,200,000
Federal | Research And Development Tax Credit Carryforward
Income Taxes [Line Items]
Research and development and other credit carryforwards	10,600,000
State
Income Taxes [Line Items]
Net operating loss carryforwards	318,300,000
State | Research And Development Tax Credit Carryforward
Income Taxes [Line Items]
Research and development and other credit carryforwards	$ 3,200,000

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) ft²
Commitments and Contingencies Disclosure [Abstract]
Lease facility square footage | ft²	19,200
Option to extend lease	3 years
Total lease cost	$ 2,200
Operating cash flows used for operating leases	$ 2,383

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Summary of Lease Cost (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Lease cost
Operating lease cost	$ 1,489
Variable lease cost	711
Total lease cost	2,200
Other information
Operating cash flows used for operating leases	$ 2,383
Weighted average remaining lease term (years)	1 year 3 months 18 days
Weighted average discount rate (percentage)	9%

COMMITMENTS AND CONTINGENCIES_3

COMMITMENTS AND CONTINGENCIES - Schedule of Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Jan. 01, 2022	Dec. 31, 2021
Maturity of lease liabilities
2023	$ 1,722
2024	580
Total future minimum lease payments	2,302
Less: imputed interest	(141)
Total lease liability	2,161	$ 3,600
Liabilities
Operating lease liability	1,592		$ 0
Operating lease liability, net of current portion	569		$ 0
Total lease liability	$ 2,161	$ 3,600

NET LOSS PER SHARE - Schedule o

NET LOSS PER SHARE - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net loss	$ (81,186)	$ (64,628)
Denominator:
Weighted average common shares outstanding, basic (in shares)	54,355,769	38,110,420
Weighted average common shares outstanding, diluted (in shares)	54,355,769	38,110,420
Net loss per share, basic (USD per share)	$ (1.49)	$ (1.70)
Net loss per share, diluted (USD per share)	$ (1.49)	$ (1.70)

NET LOSS PER SHARE - Schedule_2

NET LOSS PER SHARE - Schedule of Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share (in shares)	6,612,210	6,519,158
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share (in shares)	6,536,977	6,197,288
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share (in shares)	75,233	275,350
Shares issuable under employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share (in shares)	0	46,520

401(k) PLAN (Details)

401(k) PLAN (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Company's matching contribution	$ 0.4	$ 0.3

RESTRUCTURING AND IMPAIRMENT _3

RESTRUCTURING AND IMPAIRMENT CHARGES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2022
Restructuring Cost and Reserve [Line Items]
Restructuring and impairment charges	$ 4,189	$ 0
Total lease liability	2,161		$ 3,600
Impairment of operating lease right-of-use assets	2,116
Impairment of property and equipment	215
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-02
Restructuring Cost and Reserve [Line Items]
Operating lease right-of-use asset	2,100		$ 3,300
Laboratory equipment
Restructuring Cost and Reserve [Line Items]
Impairment of property and equipment	$ 200

RESTRUCTURING AND IMPAIRMENT _4

RESTRUCTURING AND IMPAIRMENT CHARGES - Schedule of Restructuring and Impairment Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Restructuring and Related Activities [Abstract]
Employee termination benefits	$ 1,858
Impairment of operating lease right-of-use assets	2,116
Impairment of property and equipment	215
Restructuring and impairment charges	$ 4,189	$ 0

RESTRUCTURING CHARGES - Schedul

RESTRUCTURING CHARGES - Schedule of Changes in Employee Termination Liability (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Restructuring Reserve [Roll Forward]
Accrued employee termination benefits, beginning balance	$ 0
Employee termination benefits	1,858
Amounts paid or otherwise settled during the period	(637)
Accrued employee termination benefits, ending balance	$ 1,221

RESTRUCTURING AND IMPAIRMENT _5

RESTRUCTURING AND IMPAIRMENT CHARGES - Schedule of Operating Lease (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Jan. 01, 2022	Dec. 31, 2021
Liabilities
Operating lease liability	$ 1,592		$ 0
Operating lease liability, net of current portion	569		$ 0
Total lease liability	$ 2,161	$ 3,600

RELATED-PARTY TRANSACTIONS (Det

RELATED-PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Oct. 31, 2022	Sep. 30, 2022	Sep. 20, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Conversion of notes into common stock	$ 6,000				$ 0
Convertible Debt
Related Party Transaction [Line Items]
Conversion of notes into common stock		$ 6,000	$ 6,000
Convertible Notes Issued To Investors | Flagship Pioneering | Convertible Debt
Related Party Transaction [Line Items]
Debt instrument, face amount			$ 6,000	$ 6,000

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - Subsequent Event - Laboratory equipment $ in Millions	1 Months Ended
	Jan. 31, 2023 USD ($)
Subsequent Event [Line Items]
Proceeds from the sale of property and equipment	$ 0.5
Gain on sale of assets	$ 0.1