Axcella Health (AXLA) 10-K 30 Mar 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 28, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
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	840 Memorial Drive
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
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			$ 100,931,832
Entity Common Stock, Shares Outstanding (in shares)		52,521,940
Documents Incorporated by Reference	Part III of this Annual Report on Form 10-K incorporates by reference certain information from the registrant’s definitive proxy statement for its 2022 annual meeting of shareholders, or the Proxy Statement, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2021. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Central Index Key	0001633070

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
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, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 23,574	$ 71,590
Marketable securities	1,598	1,692
Prepaid expenses and other current assets	31,474	35,739
Total current assets	56,646	109,021
Property and equipment, net	870	360
Other assets	211	211
Total assets	57,727	109,592
Current liabilities:
Accounts payable	4,301	2,290
Accrued expenses and other current liabilities	5,849	5,494
Total current liabilities	10,150	7,784
Long-term debt, net of discount	25,070	25,222
Other liabilities	499	1,205
Total liabilities	35,719	34,211
Commitments and contingencies (Note 11)	0	0
Stockholders' equity:
Common stock, $0.001 par value; 150,000,000 shares authorized, 39,605,701 and 38,022,273 shares issued and 39,186,720 and 37,603,292 shares outstanding at December 31, 2021 and 2020, respectively	40	38
Additional paid-in capital	359,261	347,990
Treasury stock, 418,981 shares at cost	0	0
Accumulated other comprehensive loss	(52)	(34)
Accumulated deficit	(337,241)	(272,613)
Total stockholders' equity	22,008	75,381
Total liabilities and stockholders' equity	$ 57,727	$ 109,592

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
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)	39,605,701	38,022,273
Common stock outstanding (in shares)	39,186,720	37,603,292
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, 2021	Dec. 31, 2020
Operating expenses:
Research and development	$ 43,135	$ 37,039
General and administrative	18,711	16,797
Total operating expenses	61,846	53,836
Loss from operations	(61,846)	(53,836)
Other (expense) income:
Interest income	139	306
Interest expense	(2,917)	(3,007)
Other (expense) income, net	(4)	10
Total other (expense) income, net	(2,782)	(2,691)
Net loss	$ (64,628)	$ (56,527)
Net loss per share, basic (USD per share)	$ (1.70)	$ (1.78)
Net loss per share, diluted (USD per share)	$ (1.70)	$ (1.78)
Weighted average common shares outstanding, basic (in shares)	38,110,420	31,747,676
Weighted average common shares outstanding, diluted (in shares)	38,110,420	31,747,676
Comprehensive loss:
Net loss	$ (64,628)	$ (56,527)
Other comprehensive income (loss):
Unrealized losses on marketable securities	(18)	(34)
Comprehensive loss	$ (64,646)	$ (56,561)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (64,628)	$ (56,527)
Adjustment to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	288	419
Stock-based compensation	6,243	6,287
Non-cash interest expense	609	580
Other non-cash items	925	128
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	94	(205)
Accounts payable	2,050	311
Accrued expenses and other current liabilities	198	(764)
Net cash used in operating activities	(54,221)	(49,771)
Cash flows from investing activities:
Purchases of property and equipment	(275)	(239)
Proceeds from the sale of property and equipment	0	40
Purchases of marketable securities	(23,391)	(35,920)
Proceeds from maturities and sales of marketable securities	26,713	0
Net cash provided by (used in) investing activities	3,047	(36,119)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	4,779	65,322
Proceeds from exercise of common stock options and ESPP	236	144
Payment of terminal fee obligation and debt issuance costs	(1,726)	(39)
Payments for capital lease	(131)	0
Net cash provided by financing activities	3,158	65,427
Net decrease in cash and cash equivalents	(48,016)	(20,463)
Cash and cash equivalents, beginning of year	71,590	92,053
Cash and cash equivalents, end of year	23,574	71,590
Supplemental cash flow information:
Cash paid for interest	2,309	2,420
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable	2	13
Offering costs incurred but unpaid at period end	20	35
Property and equipment acquired through capital lease	$ 534	$ 0

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, 2019		23,607,797
Beginning balance at Dec. 31, 2019	$ 60,224	$ 24	$ 276,286	$ 0	$ (216,086)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		3,166
Exercise of common stock options	0
Issuance of common stock, net of issuance costs (in shares)		14,371,267
Issuance of common stock, net of issuance costs	65,287	$ 14	65,273
Issuance of common stock related to ESPP (in shares)		40,043
Issuance of common stock related to ESPP	144		144
Stock-based compensation	6,287		6,287
Unrealized loss on marketable securities	(34)			(34)
Net loss	(56,527)				(56,527)
Ending balance (in shares) at Dec. 31, 2020		38,022,273
Ending 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	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)

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Statement of Stockholders' Equity [Abstract]
Stock issuance costs	$ 349	$ 4,599

NATURE OF BUSINESS

NATURE OF BUSINESS	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS	NATURE OF BUSINESS 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 non-alcoholic steatohepatitis, or NASH, 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 reduction in risk of recurrent overt hepatic encephalopathy, or OHE. 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. Going Concern The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. Consequently, management has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within 12 months after the date the annual financial statements herein are issued. Historically, the Company has funded its operations with proceeds from sales of preferred and common stock and borrowings under a loan and security agreement. The Company may never commercialize a product and achieve profitability, and unless and until it does, the Company will need to raise additional capital. The Company has had recurring losses since inception and incurred a loss of $64.6 million during the year ended December 31, 2021 and an accumulated deficit of $337.2 million. Net cash used in operations for the year ended December 31, 2021 was $54.2 million. The Company has spent, and expects to continue to spend, significant funds to continue development of it's current and potential future pipeline candidates and continue to generate operating losses for the foreseeable future. As of December 31, 2021, the Company had cash, cash equivalents and marketable securities of $55.0 million and is required to comply with an unrestricted minimum cash level in accordance with it's Loan and Security Agreement with SLR Investment Corp. until certain clinical trial data conditions are met, and there is a risk that the Company may be unable to remain in compliance with those financial covenants in the future in which case the debt may become immediately due and payable. Accordingly, the foregoing conditions, taken together, raise substantial doubt about the Company’s ability to continue as a going concern for one year from the issuance of these consolidated financial statements. These consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying 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”). 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 the consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, expenses and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the Company’s ability to continue as a going concern. The Company bases its estimates on historical experience, known trends and other market-specific or relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts, and experience. Actual results may differ from those estimates or assumptions. 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. Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company’s cash equivalents and marketable securities consisted of bank deposits, money market funds that invest in U.S. treasury securities, and corporate obligations. 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. 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 long-term debt approximates fair value as evidenced by the recent amendment to the Company's debt facility. 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. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. There were no significant impairments of long‑lived assets for the years ended December 31, 2021 or 2020. 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. Stock-Based Compensation 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, 2021 and 2020, 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, 2021, the Company’s only element of other comprehensive loss was unrealized gains (losses) on marketable securities. Net Loss Per Share Basic 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. Recently Adopted Accounting Pronouncements Effective January 1, 2021, the Company adopted ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, (“ASU 2019-12”) which simplifies the accounting for income taxes by removing certain exceptions to the general principles in ASC 740 and clarifies and amends existing guidance to improve consistent application. ASU 2019-12 requires, among other requirements, the Company to recognize as an income tax the effect of state hybrid taxes that are based on the greater of an income-based tax and a capital-based tax. Adoption of ASU 2019-12 did not have a material impact on the Company’s consolidated financial statements since the Company has no income tax liabilities due to its net operating losses. Additionally, the Company has not recorded any income tax benefits from these losses due to uncertainty of realizing the related tax benefit. Accounting Pronouncements Issued and Not Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), 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. The new standard will become effective for the Company on January 1, 2022. The Company plans to adopt ASU 2016-02, and related amendments, on January 1, 2022 using the modified retrospective approach transition method as of the date of adoption. The Company will also elect a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. Upon adoption of the new standard, the Company expects to recognize a lease liability and related right of-use asset on the consolidated balance sheet of approximately $3.6 million and $3.3 million, respectively. In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326) . The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as available-for-sale. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. The Company is required to adopt this standard effective January 1, 2023 and the Company is evaluating the impact the guidance will have on its consolidated financial statements.

MARKETABLE SECURITIES

MARKETABLE SECURITIES	12 Months Ended
	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
MARKETABLE SECURITIES	MARKETABLE SECURITIES The following table summarizes the Company's marketable securities (in thousands): December 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Corporate obligations $ 31,526 $ — $ (52) $ 31,474 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Corporate obligations $ 35,773 $ 1 $ (35) $ 35,739 The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity. At December 31, 2021 and 2020, the balance in accumulated other comprehensive loss was comprised solely of activity related to marketable securities. There were no realized gains or losses recognized on the sale or maturity of marketable securities for the years ended December 31, 2021 and 2020, and, as a result, the Company did not reclassify any amounts out of accumulated other comprehensive loss during the periods presented. The aggregate fair value of marketable securities by contractual maturity were as follows (in thousands): Contractual Maturities December 31, December 31, Mature in one year or less $ 28,220 $ 17,220 Mature in two years or less 3,254 18,519 Total $ 31,474 $ 35,739 As of December 31, 2021, the Company did not intend to sell, and was more than likely not required to sell, the debt securities in a loss position before recovery of their amortized cost bases. As a result, the Company determined it did not hold any investments with any other-than-temporary impairment at December 31, 2021.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2021
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, 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 Fair value measurements at December 31, 2020 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents Money market funds $ 69,118 $ — $ — $ 69,118 Marketable securities: Corporate obligations — 35,739 — 35,739 Total $ 69,118 $ 35,739 $ — $ 104,857 As of December 31, 2021 and 2020, 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, 2021 and 2020, there were no transfers between Level 1, Level 2 and Level 3.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment consist of the following (in thousands): December 31, 2021 2020 Laboratory equipment $ 3,426 $ 3,022 Leasehold improvements 564 564 Office and computer equipment 148 111 Furniture and fixtures 122 122 Property and equipment, gross 4,260 3,819 Less: accumulated depreciation and amortization (3,390) (3,459) Property and equipment, net $ 870 $ 360

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Accrued employee compensation and benefits $ 3,005 $ 2,998 Accrued external research and development expenses 2,000 1,870 Accrued professional fees 601 626 Other 243 — Total accrued expenses and other current liabilities $ 5,849 $ 5,494

DEBT FINANCING

DEBT FINANCING	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
DEBT FINANCING	DEBT FINANCING Long-term debt consisted of the following (in thousands): December 31, 2021 2020 Principal amount of long-term debt $ 26,000 $ 26,000 Debt discount (196) (308) Deferred financing fees (734) (470) Long-term debt, net of discount $ 25,070 $ 25,222 In 2021, the Company entered into a loan and security agreement (the "New Loan and Security Agreement") with SLR Investment Corp., formerly known as Solar Capital Ltd., for term loans in an aggregate principal amount of $26.0 million. The New Loan and Security Agreement replaced prior loan and security agreement between the Company and SLR Investment Corp. (the "Prior Loan and Security Agreement"). The New Loan and Security agreement was accounted for as a debt modification or exchange as the Company determined that the terms of the New Loan and Security Agreement were not substantially different than the terms of the Prior Loan and Security Agreement. Upon entering into the New Loan and Security Agreement, the Company paid a terminal fee obligation and debt issuance costs totaling $1.7 million as required under the terms of the Prior Loan and Security Agreement, of which $1.3 million had been previously accrued. The Company is amortizing additional deferred financing fees of $0.4 million to interest expense along with the existing deferred financing fees and debt discount balances over the term of the New Loan Security Agreement. The Company also agreed to a new terminal fee obligation totaling $1.7 million, which is due and payable on the earliest to occur of (i) the maturity of the New Loan and Security Agreement, (ii) the acceleration of the term loans, and (iii) the prepayment, refinancing, substitution or replacement of the term loans. The obligation is equal to 6.45% of the aggregate principal amount of $26.0 million. The Company is accruing the obligation over the term of the New Loan and Security Agreement. The carrying value of the obligation was $0.1 million as of December 31, 2021. The term loans under the New Loan and Security Agreement will accrue 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 interest rate was 8.70% as of December 31, 2021 . The monthly principal payments of $0.6 million will be paid over a period of 45 months beginning in January 2023 through the final maturity date of September 1, 2026. Per the New Loan and Security Agreement, the date on which repayment of principal commences can be further extended to July 2023 and January 2024, provided we satisfy certain equity related conditions. The term loans are also subject to a prepayment fee of 3.00% if prepayment occurs 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 New Loan and Security Agreement also contains certain financial covenants, including an unrestricted minimum cash level until certain clinical trial study data conditions are met. Customary representations and warranties, as well as certain non-financial covenants, including engaging in any change of control transaction or incurring additional indebtedness or liens are included in the New Loan and Security Agreement as well. As security for its obligations under the New Loan and Security Agreement, the Company granted SLR Investment Corp. a first priority perfected security interest in all of the Company’s existing and after-acquired assets, including intellectual property. The scheduled principal maturity of the long-term debt as of December 31, 2021 is as follows (in thousands): Year Ending December 31, 2022 $ — 2023 6,933 2024 6,933 2025 6,934 2026 5,200 $ 26,000

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY Common Stock On May 18, 2020, the Company completed a 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, commissions, and other offering expenses. On June 5, 2020, the Company entered into a sales agreement with SVB Leerink LLC (“SVB Leerink”) 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”). During the year ended December 31, 2021, the Company sold an aggregate of 1,331,441 shares of its common stock under the ATM Offering for net cash proceeds of $4.8 million, after deducting commissions and expenses of $0.3 million.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION 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 1,040,168 as of December 31, 2021. 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 609,240 as of December 31, 2021. The Company recorded $0.1 million of stock-based compensation expense during the years ended December 31, 2021 and 2020. In connection with all share-based payment awards, total stock-based compensation expense recognized was as follows (in thousands): December 31, 2021 2020 Research and development $ 1,839 $ 2,670 General and administrative 4,404 3,617 Total stock-based compensation expense $ 6,243 $ 6,287 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, 2021 2020 Risk-free interest rate 0.91 % 1.01 % Expected option life (in years) 5.98 5.97 Expected dividend yield — % — % Expected volatility 96 % 79 % The following table summarizes the Company’s stock option activity for the year ended December 31, 2021: Options Weighted Weighted Intrinsic Outstanding as of January 1, 2021 4,919,960 $ 6.37 Granted 2,832,101 5.05 Exercised (111,833) 0.50 Cancelled (1,442,940) 7.06 Outstanding as of December 31, 2021 6,197,288 $ 5.72 7.54 $ 187 Exercisable as of December 31, 2021 3,371,060 $ 6.33 6.22 $ 187 Vested or expected to vest as of December 31, 2021 6,172,288 $ 5.72 7.54 $ 187 The intrinsic value of options exercised during the years ended December 31, 2021 and 2020 was $0.4 million. The weighted-average grant date fair value of the options granted during the years ended December 31, 2021 and 2020, was $3.87 and $3.06 per share, respectively. As of December 31, 2021, there was $8.6 million of unrecognized compensation expense related to unvested stock options that is expected to be recognized over a weighted-average period of approximately 2.6 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, 2021: Number of Shares Weighted Average Grant Date Fair Value per Share Outstanding as of January 1, 2021 347,587 $ 4.04 Granted 120,916 6.41 Vested (83,187) 5.06 Forfeited (109,966) 5.59 Outstanding as of December 31, 2021 275,350 $ 4.15

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020 are as follows: December 31, 2021 2020 U.S. federal statutory income tax rate 21.0 % 21.0 % State taxes, net of federal benefit 6.0 % 6.1 % Permanent differences — % (0.1) % Stock compensation (2.2) % (0.4) % Tax credits 3.1 % 2.9 % Other — % 0.1 % Change in valuation allowance (27.9) % (29.6) % Effective income tax rate — % — % Significant components of the Company’s deferred tax asset at December 31, 2021 and 2020 are as follows (in thousands): December 31, 2021 2020 Net operating loss carryforwards $ 82,070 $ 65,911 Research and development tax credit carryforwards 10,892 8,896 Start-up costs 21 28 Capitalized research and development costs — 64 Depreciation 213 304 Accrued expenses 822 1,059 Stock-based compensation 3,316 3,253 Other items 1,366 1,175 Total deferred tax assets 98,700 80,690 Valuation allowance (98,700) (80,690) 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, 2021 and 2020. The valuation allowance increased in 2021 by $18.0 million, primarily as a result of net operating losses generated during the period. As of December 31, 2021, the Company had federal and state net operating loss carryforwards of $302.2 million and $294.3 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 and 2021 can be carried forward indefinitely. As of December 31, 2021, the Company had federal and state research and development tax credit carryforwards of $8.6 million and $2.9 million, respectively. These amounts expire at various dates through 2041. 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. The valuation allowance increased in 2021 by $18.0 million, due to the increase in deferred tax assets by the same amount (primarily due to net operating loss carryforwards) and the Company’s recording of a full valuation allowance. 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, 2021, 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, 2021 and 2020, the Company had no unrecognized tax benefits. Furthermore, as of December 31, 2021 and 2020, 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, 2021, 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 2017, although carryforward attributes that were generated prior to tax year 2017 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, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Leases The Company leases laboratory and office space under a lease agreement that expires on April 30, 2024. The lease agreement and most recent amendment contained escalating rent payments. Rent expense is recorded on a straight-line basis. The Company is obligated to make minimum lease payments under the facility lease as follows (in thousands): Years Ending December 31, 2022 $ 1,672 2023 1,722 2024 580 Total $ 3,974 Rent expense in each of the years ended December 31, 2021 and 2020 was $1.6 million and $1.3 million, respectively. 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, 2021
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, 2021 2020 Numerator: Net loss $ (64,628) $ (56,527) Denominator: Weighted average common shares outstanding, basic and diluted 38,110,420 31,747,676 Net loss per share, basic and diluted $ (1.70) $ (1.78) 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, 2021 2020 Options to purchase common stock 6,197,288 4,919,960 Unvested restricted stock units 275,350 347,587 Shares issuable under employee stock purchase plan 46,520 9,830 6,519,158 5,277,377

401(k) PLAN

401(k) PLAN	12 Months Ended
	Dec. 31, 2021
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 $0.3 million for the years ended December 31, 2021 and 2020.

RELATED-PARTY TRANSACTIONS

RELATED-PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
RELATED-PARTY TRANSACTIONS	RELATED-PARTY TRANSACTIONS In August 2019, the Company entered into a consulting agreement with the chairman of the Company's Board of Directors to provide various consulting services to the Company in exchange for cash and equity compensation. In March 2021, the consulting agreement was modified so that the chairman would no longer receive cash compensation for his consulting services and would instead be compensated solely via equity compensation. The aggregate grant date fair value of the equity awarded to the chairman in 2021 and 2020 for his consulting services was $0.6 million and $0.2 million, respectively. The grant date fair value is calculated in accordance with FASB ASC Topic 718. The total cash paid under the agreement was $0.1 million and was $0.3 million for the year ended December 31, 2021 and 2020, respectively. On March 17, 2022, the chairman and the Company mutually agreed to terminate the consulting agreement, such termination to be effective immediately. The consulting agreement was terminated in connection with a new compensation arrangement for the chairman’s service as the non-executive chairman of the Board.

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTSOn March 16, 2022, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) with certain institutional purchasers and certain directors and officers of the Company named therein. Pursuant to the Purchase Agreement, the Company sold and issued an aggregate of 13,089,002 shares of the Company’s common stock, par value $0.001 per share (the “Common Stock”), at a purchase price of $1.91 per share in a registered direct offering for net proceeds of approximately $24.9 million after deducting estimated offering expenses payable by the Company.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying 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”).
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 the consolidated financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, expenses and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the Company’s ability to continue as a going concern. The Company bases its estimates on historical experience, known trends and other market-specific or relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts, and experience. Actual results may differ from those estimates or assumptions.
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. 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	Concentrations of Credit Risk The Company has no off-balance sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company’s cash equivalents and marketable securities consisted of bank deposits, money market funds that invest in U.S. treasury securities, and corporate obligations. 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.
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.
Property and Equipment	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.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. The Company reviews long-lived assets when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the book values of the assets to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. There were no significant impairments of long‑lived assets for the years ended December 31, 2021 or 2020.
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.
Stock-Based Compensation	Stock-Based Compensation 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, 2021 and 2020, 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, 2021, 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.
Recently Adopted Accounting Pronouncements and Accounting Pronouncements Issued and Not Adopted	Recently Adopted Accounting Pronouncements Effective January 1, 2021, the Company adopted ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, (“ASU 2019-12”) which simplifies the accounting for income taxes by removing certain exceptions to the general principles in ASC 740 and clarifies and amends existing guidance to improve consistent application. ASU 2019-12 requires, among other requirements, the Company to recognize as an income tax the effect of state hybrid taxes that are based on the greater of an income-based tax and a capital-based tax. Adoption of ASU 2019-12 did not have a material impact on the Company’s consolidated financial statements since the Company has no income tax liabilities due to its net operating losses. Additionally, the Company has not recorded any income tax benefits from these losses due to uncertainty of realizing the related tax benefit. Accounting Pronouncements Issued and Not Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), 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. The new standard will become effective for the Company on January 1, 2022. The Company plans to adopt ASU 2016-02, and related amendments, on January 1, 2022 using the modified retrospective approach transition method as of the date of adoption. The Company will also elect a package of practical expedients, under which an entity need not reassess whether any expired or existing contracts are or contain leases, the lease classification for any expired or existing leases, or initial direct costs for any existing leases. Upon adoption of the new standard, the Company expects to recognize a lease liability and related right of-use asset on the consolidated balance sheet of approximately $3.6 million and $3.3 million, respectively. In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326) . The new standard adjusts the accounting for assets held at amortized costs basis, including marketable securities accounted for as available-for-sale. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. The Company is required to adopt this standard effective January 1, 2023 and the Company is evaluating the impact the guidance will have on its consolidated financial statements.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Laboratory equipment $ 3,426 $ 3,022 Leasehold improvements 564 564 Office and computer equipment 148 111 Furniture and fixtures 122 122 Property and equipment, gross 4,260 3,819 Less: accumulated depreciation and amortization (3,390) (3,459) Property and equipment, net $ 870 $ 360

MARKETABLE SECURITIES (Tables)

MARKETABLE SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2021
Cash and Cash Equivalents [Abstract]
Schedule of Cash, Cash Equivalents, and Marketable Securities by Security Type	The following table summarizes the Company's marketable securities (in thousands): December 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Corporate obligations $ 31,526 $ — $ (52) $ 31,474 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Corporate obligations $ 35,773 $ 1 $ (35) $ 35,739
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, December 31, Mature in one year or less $ 28,220 $ 17,220 Mature in two years or less 3,254 18,519 Total $ 31,474 $ 35,739

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2021
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, 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 Fair value measurements at December 31, 2020 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents Money market funds $ 69,118 $ — $ — $ 69,118 Marketable securities: Corporate obligations — 35,739 — 35,739 Total $ 69,118 $ 35,739 $ — $ 104,857

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Laboratory equipment $ 3,426 $ 3,022 Leasehold improvements 564 564 Office and computer equipment 148 111 Furniture and fixtures 122 122 Property and equipment, gross 4,260 3,819 Less: accumulated depreciation and amortization (3,390) (3,459) Property and equipment, net $ 870 $ 360

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Accrued employee compensation and benefits $ 3,005 $ 2,998 Accrued external research and development expenses 2,000 1,870 Accrued professional fees 601 626 Other 243 — Total accrued expenses and other current liabilities $ 5,849 $ 5,494

DEBT FINANCING (Tables)

DEBT FINANCING (Tables)	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Summary of Long-term Debt	Long-term debt consisted of the following (in thousands): December 31, 2021 2020 Principal amount of long-term debt $ 26,000 $ 26,000 Debt discount (196) (308) Deferred financing fees (734) (470) Long-term debt, net of discount $ 25,070 $ 25,222
Schedule of Maturities of Long-term Debt	The scheduled principal maturity of the long-term debt as of December 31, 2021 is as follows (in thousands): Year Ending December 31, 2022 $ — 2023 6,933 2024 6,933 2025 6,934 2026 5,200 $ 26,000

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Research and development $ 1,839 $ 2,670 General and administrative 4,404 3,617 Total stock-based compensation expense $ 6,243 $ 6,287
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, 2021 2020 Risk-free interest rate 0.91 % 1.01 % Expected option life (in years) 5.98 5.97 Expected dividend yield — % — % Expected volatility 96 % 79 %
Schedule of Stock Option Activity	The following table summarizes the Company’s stock option activity for the year ended December 31, 2021: Options Weighted Weighted Intrinsic Outstanding as of January 1, 2021 4,919,960 $ 6.37 Granted 2,832,101 5.05 Exercised (111,833) 0.50 Cancelled (1,442,940) 7.06 Outstanding as of December 31, 2021 6,197,288 $ 5.72 7.54 $ 187 Exercisable as of December 31, 2021 3,371,060 $ 6.33 6.22 $ 187 Vested or expected to vest as of December 31, 2021 6,172,288 $ 5.72 7.54 $ 187
Schedule of Restricted Stock Unit Activity	The following table summarizes the Company's restricted stock unit activity for the year ended December 31, 2021: Number of Shares Weighted Average Grant Date Fair Value per Share Outstanding as of January 1, 2021 347,587 $ 4.04 Granted 120,916 6.41 Vested (83,187) 5.06 Forfeited (109,966) 5.59 Outstanding as of December 31, 2021 275,350 $ 4.15

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 and 2020 are as follows: December 31, 2021 2020 U.S. federal statutory income tax rate 21.0 % 21.0 % State taxes, net of federal benefit 6.0 % 6.1 % Permanent differences — % (0.1) % Stock compensation (2.2) % (0.4) % Tax credits 3.1 % 2.9 % Other — % 0.1 % Change in valuation allowance (27.9) % (29.6) % Effective income tax rate — % — %
Schedule of Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax asset at December 31, 2021 and 2020 are as follows (in thousands): December 31, 2021 2020 Net operating loss carryforwards $ 82,070 $ 65,911 Research and development tax credit carryforwards 10,892 8,896 Start-up costs 21 28 Capitalized research and development costs — 64 Depreciation 213 304 Accrued expenses 822 1,059 Stock-based compensation 3,316 3,253 Other items 1,366 1,175 Total deferred tax assets 98,700 80,690 Valuation allowance (98,700) (80,690) Net deferred tax asset $ — $ —

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments	The Company is obligated to make minimum lease payments under the facility lease as follows (in thousands): Years Ending December 31, 2022 $ 1,672 2023 1,722 2024 580 Total $ 3,974

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2021
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, 2021 2020 Numerator: Net loss $ (64,628) $ (56,527) Denominator: Weighted average common shares outstanding, basic and diluted 38,110,420 31,747,676 Net loss per share, basic and diluted $ (1.70) $ (1.78)
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, 2021 2020 Options to purchase common stock 6,197,288 4,919,960 Unvested restricted stock units 275,350 347,587 Shares issuable under employee stock purchase plan 46,520 9,830 6,519,158 5,277,377

NATURE OF BUSINESS (Details)

NATURE OF BUSINESS (Details) - USD ($) $ in Thousands	Mar. 16, 2022	Dec. 31, 2021	Dec. 31, 2020
Nature Of Business [Line Items]
Net loss		$ (64,628)	$ (56,527)
Accumulated deficit		(337,241)	(272,613)
Net cash used in operations		(54,221)	$ (49,771)
Cash, cash equivalents and marketable securities		$ 55,000
Subsequent Event | Registered Direct Offering
Nature Of Business [Line Items]
Net proceeds on offering	$ 24,900

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021segment	Jan. 01, 2022USD ($)
Accounting Policies [Line Items]
Number of operating segments | segment	1
Forecast | Accounting Standards Update 2016-02
Accounting Policies [Line Items]
Lease liability		$ 3.6
Right of-use asset		$ 3.3

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Property and Equipment Useful Life (Details)	12 Months Ended
	Dec. 31, 2021
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 - Schedul

MARKETABLE SECURITIES - Schedule of Securities by Type (Details) - Corporate obligations - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Line Items]
Amortized Cost	$ 31,526	$ 35,773
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(52)	(35)
Estimated Fair Value	$ 31,474	$ 35,739

MARKETABLE SECURITIES - Sched_2

MARKETABLE SECURITIES - Schedule of Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Abstract]
Mature in one year or less	$ 28,220	$ 17,220
Mature in two years or less	3,254	18,519
Total	$ 31,474	$ 35,739

MARKETABLE SECURITIES - Narrati

MARKETABLE SECURITIES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Abstract]
Sales of marketable securities	$ 5,900,000	$ 0

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets, Fair Value Disclosure [Abstract]
Money market funds	$ 23,021	$ 69,118
Corporate obligations	31,474	35,739
Total	54,495	104,857
Level 1
Assets, Fair Value Disclosure [Abstract]
Money market funds	23,021	69,118
Corporate obligations	0	0
Total	23,021	69,118
Level 2
Assets, Fair Value Disclosure [Abstract]
Money market funds	0	0
Corporate obligations	31,474	35,739
Total	31,474	35,739
Level 3
Assets, Fair Value Disclosure [Abstract]
Money market funds	0	0
Corporate obligations	0	0
Total	$ 0	$ 0

PROPERTY AND EQUIPMENT - Schedu

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,260	$ 3,819
Less: accumulated depreciation and amortization	(3,390)	(3,459)
Property and equipment, net	870	360
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,426	3,022
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	148	111
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, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 288	$ 419
Property, Plant and Equipment [Line Items]
Depreciation and amortization	288	419
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment disposed of	$ 300	$ 700

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued employee compensation and benefits	$ 3,005	$ 2,998
Accrued external research and development expenses	2,000	1,870
Accrued professional fees	601	626
Other	243	0
Total accrued expenses and other current liabilities	$ 5,849	$ 5,494

DEBT FINANCING - Schedule of Lo

DEBT FINANCING - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Principal amount of long-term debt	$ 26,000	$ 26,000
Debt discount	(196)	(308)
Deferred financing fees	(734)	(470)
Long-term debt, net of discount	$ 25,070	$ 25,222

DEBT FINANCING - Narrative (Det

DEBT FINANCING - Narrative (Details) $ in Thousands	Jan. 01, 2023USD ($)	Sep. 02, 2021USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Sep. 30, 2021
Line of Credit Facility [Line Items]
Principal amount of long-term debt			$ 26,000	$ 26,000
Debt issuance cost and terminal fee			1,726	39
Accrued issuance cost and terminal interest fee			734	$ 470
New Loan and Security Agreement | Line of Credit
Line of Credit Facility [Line Items]
Principal amount of long-term debt		$ 26,000
Debt issuance cost and terminal fee		1,700
Accrued issuance cost and terminal interest fee		1,300
Unamortized debt issuance cost and terminal fee		400
Terminal fee		$ 1,700	$ 100
Terminal fee, percent of principal		0.0645
Basis spread on interest rate		8.60%
Interest rate floor, on which basis spread is added		0.10%
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 | LIBOR
Line of Credit Facility [Line Items]
Interest rate at end of period			8.70%
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

DEBT FINANCING - Schedule of Ma

DEBT FINANCING - Schedule of Maturities of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
2022	$ 0
2023	6,933
2024	6,933
2025	6,934
2026	5,200
Principal amount of long-term debt	$ 26,000	$ 26,000

STOCKHOLDERS' EQUITY (Details)

STOCKHOLDERS' EQUITY (Details) - USD ($) $ in Millions	Jun. 05, 2020	May 18, 2020	Dec. 31, 2021
Class of Stock [Line Items]
Issuance costs			$ 0.3
2020 Follow-on Offering
Class of Stock [Line Items]
Shares sold (in shares)		12,650,000
Net proceeds on offering		$ 55.9
At-the-Market Offering
Class of Stock [Line Items]
Shares sold (in shares)			1,331,441
Net proceeds on offering			$ 4.8
At-the-Market Offering | Maximum
Class of Stock [Line Items]
Net proceeds on offering	$ 35

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) - USD ($)	Apr. 29, 2019	Dec. 31, 2021	Dec. 31, 2020
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	1.00%
Stock-based compensation expense		$ 6,243,000	$ 6,287,000
Intrinsic value, options exercised		$ 400,000	$ 400,000
Weighted-average grand date fair value of options granted in the period (USD per share)		$ 3.87	$ 3.06
Unrecognized compensation expense related to unvested stock options		$ 8,600,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)		609,240
Stock-based compensation expense		$ 100,000	$ 100,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield		0.00%	0.00%
Unrecognized compensation expense, recognition period		2 years 7 months 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		$ 400,000
Unrecognized compensation expense, recognition period		1 year 7 months 6 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	4.00%
Common stock reserved for future issuance (in shares)		1,040,168
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, 2021	Dec. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 6,243	$ 6,287
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	1,839	2,670
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 4,404	$ 3,617

STOCK-BASED COMPENSATION - Sc_2

STOCK-BASED COMPENSATION - Schedule of Fair Value Measurement Inputs (Details) - Stock options	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.91%	1.01%
Expected option life (in years)	5 years 11 months 23 days	5 years 11 months 19 days
Expected dividend yield	0.00%	0.00%
Expected volatility	96.00%	79.00%

STOCK-BASED COMPENSATION - Sc_3

STOCK-BASED COMPENSATION - Schedule of Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)$ / sharesshares
Options
Outstanding, beginning balance (in shares) | shares	4,919,960
Granted (in shares) | shares	2,832,101
Exercised (in shares) | shares	(111,833)
Canceled (in shares) | shares	(1,442,940)
Outstanding, ending balance (in shares) | shares	6,197,288
Options exercisable (in shares) | shares	3,371,060
Options vested or expected to vest (in shares) | shares	6,172,288
Weighted Average Exercise Price
Weighted average exercise price, outstanding, beginning balance (USD per share) | $ / shares	$ 6.37
Weighted-average exercise price, granted (USD per share) | $ / shares	5.05
Weighted-average exercise price, exercised (USD per share) | $ / shares	0.50
Weighted-average exercise price, canceled (USD per share) | $ / shares	7.06
Weighted average exercise price, outstanding, ending balance (USD per share) | $ / shares	5.72
Weighted-average exercise price, options exercisable (USD per share) | $ / shares	6.33
Weighted-average exercise price, options vested or expected to vest (USD per share) | $ / shares	$ 5.72
Weighted Average Remaining Life (in Years)
Weighted average remaining life of shares outstanding	7 years 6 months 14 days
Weighted average remaining life of shares exercisable	6 years 2 months 19 days
Weighted average remaining life of shares vested or expected to vest	7 years 6 months 14 days
Intrinsic value of shares outstanding | $	$ 187,000
Intrinsic value of shares exercisable | $	187,000
Intrinsic value of shares vested or expected to vest | $	$ 187,000

STOCK-BASED COMPENSATION - Sc_4

STOCK-BASED COMPENSATION - Schedule of Restricted Stock Units (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2021$ / sharesshares
Number of Shares
Outstanding, beginning balance (in shares) | shares	347,587
Granted (in shares) | shares	120,916
Vested (in shares) | shares	(83,187)
Forfeited (in shares) | shares	(109,966)
Outstanding, ending balance (in shares) | shares	275,350
Weighted Average Grant Date Fair Value per Share
Weighted average exercise price, outstanding, beginning balance (USD per share) | $ / shares	$ 4.04
Weighted-average exercise price, granted (USD per share) | $ / shares	6.41
Weighted-average exercise price, vested (USD per share) | $ / shares	5.06
Weighted-average exercise price, forfeited (USD per share) | $ / shares	5.59
Weighted average exercise price, outstanding, ending balance (USD per share) | $ / shares	$ 4.15

INCOME TAXES - Schedule of Effe

INCOME TAXES - Schedule of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	21.00%	21.00%
State taxes, net of federal benefit	6.00%	6.10%
Permanent differences	0.00%	(0.10%)
Stock compensation	(2.20%)	(0.40%)
Tax credits	3.10%	2.90%
Other	0.00%	0.10%
Change in valuation allowance	(27.90%)	(29.60%)
Effective income tax rate	0.00%	0.00%

INCOME TAXES - Schedule of Net

INCOME TAXES - Schedule of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 82,070	$ 65,911
Research and development tax credit carryforwards	10,892	8,896
Start-up costs	21	28
Capitalized research and development costs	0	64
Depreciation	213	304
Accrued expenses	822	1,059
Stock-based compensation	3,316	3,253
Other items	1,366	1,175
Total deferred tax assets	98,700	80,690
Valuation allowance	(98,700)	(80,690)
Net deferred tax asset	$ 0	$ 0

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Increase (decrease) in valuation allowance	$ 18,000,000
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	302,200,000
Federal | Research And Development Tax Credit Carryforward
Income Taxes [Line Items]
Research and development and other credit carryforwards	8,600,000
State
Income Taxes [Line Items]
Net operating loss carryforwards	294,300,000
State | Research And Development Tax Credit Carryforward
Income Taxes [Line Items]
Research and development and other credit carryforwards	$ 2,900,000

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2021USD ($)
Commitments and Contingencies Disclosure [Abstract]
2022	$ 1,672
2023	1,722
2024	580
Total	$ 3,974

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 1.6	$ 1.3

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, 2021	Dec. 31, 2020
Numerator:
Net loss	$ (64,628)	$ (56,527)
Denominator:
Weighted average common shares outstanding, basic (in shares)	38,110,420	31,747,676
Weighted average common shares outstanding, diluted (in shares)	38,110,420	31,747,676
Net loss per share, basic (USD per share)	$ (1.70)	$ (1.78)
Net loss per share, diluted (USD per share)	$ (1.70)	$ (1.78)

NET LOSS PER SHARE - Schedule_2

NET LOSS PER SHARE - Schedule of Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share (in shares)	6,519,158	5,277,377
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)	6,197,288	4,919,960
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)	275,350	347,587
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)	46,520	9,830

401(k) PLAN (Details)

401(k) PLAN (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Retirement Benefits [Abstract]
Company's matching contribution	$ 0.3	$ 0.3

RELATED-PARTY TRANSACTIONS (Det

RELATED-PARTY TRANSACTIONS (Details) - Related Party Consulting Agreement - Board of Directors Chairman - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Grant date fair value of equity awarded	$ 0.6	$ 0.2
Related party costs	$ 0.1	$ 0.3

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 16, 2022	Dec. 31, 2021	Dec. 31, 2020
Subsequent Event [Line Items]
Common stock, par value (USD per share)		$ 0.001	$ 0.001
Subsequent Event
Subsequent Event [Line Items]
Common stock, par value (USD per share)	$ 0.001
Subsequent Event | Registered Direct Offering
Subsequent Event [Line Items]
Shares issued and sold (in shares)	13,089,002
Offering price per share (USD per share)	$ 1.91
Expected net proceeds from offering	$ 24.9