Axcella Health (AXLA) 10-K 23 Mar 20 2019 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2019	Mar. 19, 2020	Jun. 28, 2019
Cover page.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
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
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
Entity Shell Company	false
Entity Public Float			$ 107,368,972
Entity Common Stock, Shares Outstanding		23,188,816
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Central Index Key	0001633070
Current Fiscal Year End Date	--12-31
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 2020 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, 2019. 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.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 92,053	$ 79,466
Prepaid expenses and other current assets	1,487	835
Total current assets	93,540	80,301
Property and equipment, net	608	1,076
Security deposits and other assets	211	216
Deferred offering costs	0	251
Total assets	94,359	81,844
Current liabilities:
Accounts payable	1,998	1,612
Accrued expenses and other current liabilities	6,358	5,299
Total current liabilities	8,356	6,911
Long term debt, net of discount	24,897	24,521
Other liabilities	882	1,898
Preferred stock warrant liability	0	425
Total liabilities	34,135	33,755
Commitments and contingencies (Note 9)	0	0
Redeemable convertible preferred stock (Note 7)	0	197,842
Stockholders' equity (deficit):
Preferred stock, $0.001 par value; 10,000,000 shares authorized and no shares issued or outstanding as of December 31, 2019; No shares authorized, issued or outstanding at December 31, 2018	0	0
Common stock, $0.001 par value; 150,000,000 and 47,000,000 shares authorized, 23,607,797 and 5,193,915 shares issued and 23,188,816 and 4,774,934 shares outstanding at December 31, 2019 and 2018, respectively	24	6
Additional paid-in capital	276,286	7,290
Treasury stock, 418,981 shares at cost	0	0
Accumulated deficit	(216,086)	(157,049)
Total stockholders' equity (deficit)	60,224	(149,753)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 94,359	$ 81,844

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development	$ 41,658	$ 25,486
General and administrative	15,781	8,410
Total operating expenses	57,439	33,896
Loss from operations	(57,439)	(33,896)
Other income (expense):
Interest income	1,814	547
Other income	34	79
Change in fair value of preferred stock warrant liability	(51)	(14)
Interest expense	(3,395)	(2,785)
Total other income (expense), net	(1,598)	(2,173)
Net loss	$ (59,037)	$ (36,069)
Net loss per share, basic and diluted (USD per share)	$ (3.55)	$ (7.97)
Weighted average common shares outstanding, basic and diluted (in shares)	16,624,941	4,546,373

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (59,037)	$ (36,069)
Adjustment to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	662	1,071
Stock-based compensation expense	5,824	2,778
Change in fair value of preferred stock warrant liability	51	14
Non-cash interest expense	557	529
Gain on sale of property and equipment	(18)	(36)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(652)	(580)
Other long-term assets	5	0
Accounts payable	366	595
Accrued expenses and other current liabilities	1,280	986
Net cash used in operating activities	(50,962)	(30,712)
Cash flows from investing activities:
Purchases of property and equipment	(136)	(659)
Proceeds from the sale of property and equipment	19	73
Net cash used in investing activities	(117)	(586)
Cash flows from financing activities:
Payment of deferred offering costs	0	(14)
Proceeds from initial public offering, net of issuance costs	64,546	0
Proceeds from issuance of preferred convertible stock, net of issuance costs	0	58,861
Proceeds from issuance of long term debt	0	6,000
Payment of debt issuance costs	0	(945)
Payment of success fee obligation	(1,220)	0
Proceeds from exercise of common stock options	340	45
Net cash provided by financing activities	63,666	63,947
Net increase in cash and cash equivalents	12,587	32,649
Cash and cash equivalents, beginning of year	79,466	46,817
Cash and cash equivalents, end of year	92,053	79,466
Supplemental cash flow information:
Cash paid for interest	2,838	2,255
Deferred offering costs included in accounts payable and accrued expenses	0	237
Purchases of property and equipment included in accounts payable and accrued expenses	59	0
Supplemental disclosure of non-cash investing and financing activities:
Reclassification of warrants to additional paid-in capital	476	0
Conversion of preferred stock to common stock upon closing of the initial public offering	197,888	0
Accretion of preferred stock to redemption value	$ 46	$ 153

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Treasury stock	Accumulated deficit
Redeemable convertible preferred stock, beginning (in shares) at Dec. 31, 2017	21,549,244
Redeemable convertible preferred stock, beginning at Dec. 31, 2017	$ 138,828
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock, net of issuance costs (in shares)	5,282,002
Issuance of redeemable convertible preferred stock, net of issuance costs	$ 58,861
Accretion of preferred stock to redemption value	$ 153
Redeemable convertible preferred stock, ending (in shares) at Dec. 31, 2018	26,831,246
Redeemable convertible preferred stock, ending at Dec. 31, 2018	$ 197,842
Beginning balance (in shares) at Dec. 31, 2017		4,648,078		418,981
Beginning balance at Dec. 31, 2017	(116,354)	$ 5	$ 4,621	$ 0	$ (120,980)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		545,837
Exercise of common stock options	45	$ 1	44
Accretion of preferred stock to redemption value	(153)		(153)
Reclassification of warrants to additional paid-in capital	0
Stock-based compensation	2,778		2,778
Net loss	(36,069)				(36,069)
Ending balance (in shares) at Dec. 31, 2018		5,193,915		418,981
Ending balance at Dec. 31, 2018	(149,753)	$ 6	7,290	$ 0	(157,049)
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of preferred stock to redemption value	$ 46		46
Conversion of preferred stock to common stock upon closing of the IPO (in shares)	(26,831,246)
Conversion of preferred stock to common stock upon closing of the initial public offering	$ (197,888)
Redeemable convertible preferred stock, ending (in shares) at Dec. 31, 2019	0
Redeemable convertible preferred stock, ending at Dec. 31, 2019	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	155,043	155,043
Exercise of common stock options	$ 340		340
Accretion of preferred stock to redemption value	(46)		(46)
Conversion of preferred stock to common stock upon closing of the initial public offering (in shares)		14,641,997
Conversion of preferred stock to common stock upon closing of the initial public offering	197,888	$ 15	197,873
Issuance of common stock, net (in shares)		3,571,428
Issuance of common stock, net of issuance costs of $6,896	64,532	$ 3	64,529
Reclassification of warrants to additional paid-in capital	476		476
Exercise of common stock warrant (in shares)		45,414
Stock-based compensation	5,824		5,824
Net loss	(59,037)				(59,037)
Ending balance (in shares) at Dec. 31, 2019		23,607,797		418,981
Ending balance at Dec. 31, 2019	$ 60,224	$ 24	$ 276,286	$ 0	$ (216,086)

Consolidated Statements of Re_2

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Statement of Stockholders' Equity [Abstract]
Stock issuance costs	$ 6,896	$ 139

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (USD per share)	$ 0.001	$ 0.001
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Preferred stock issued (in shares)	0	0
Preferred stock outstanding (in shares)	0	0
Common stock, par value (USD per share)	$ 0.001	$ 0.001
Common stock authorized (in shares)	150,000,000	47,000,000
Common stock issued (in shares)	23,607,797	5,193,915
Common stock outstanding (in shares)	23,188,816	4,774,934
Treasury stock at cost (in shares)	418,981	418,981

NATURE OF BUSINESS

NATURE OF BUSINESS	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF BUSINESS	NATURE OF BUSINESS Axcella Health Inc. and subsidiaries ("Axcella," the "Company" or "we") 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 leveraging endogenous metabolic modulators, or EMMs, to pioneer a new approach for treating complex diseases and improving health. 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 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 consumer 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. 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. Through December 31, 2019, the Company has funded its operations primarily with proceeds from the sale of preferred stock, borrowings under a loan and security agreement and the sale of common stock in the Company’s initial public offering (“IPO”), which was completed on May 8, 2019. The Company has incurred recurring losses since its inception, including net losses of $59.0 million and $36.1 million for the years ended December 31, 2019 and 2018, respectively. In addition, as of December 31, 2019, the Company had an accumulated deficit of $216.1 million. The Company expects to continue to generate operating losses for the foreseeable future. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. The Company’s inability to raise capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies. There can be no assurance that the current operating plan will be achieved or that additional funding will be available on terms acceptable to the Company, or at all. The Company believes the cash and cash equivalents on hand as of December 31, 2019 of $92.1 million will be sufficient to fund its operations and capital expenditure requirements through at least the next twelve months following the issuance date of the financial statements.

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2019
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. Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates. Subsequent Events The Company considers events or transactions that occur after the balance sheet date but before the final financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. Cash and Cash Equivalents Cash includes cash in readily available checking accounts. Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. The cash equivalents consisted of money market funds. Concentrations of Credit Risk Financial instruments that subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. The Company’s cash deposits on hand at one financial institution often exceed federally insured limits. The Company places its cash in a financial institution that management believes to be of high credit quality. Deferred Offering Costs The Company capitalized certain legal, professional accounting and other third-party fees that were directly associated with in-process equity financings as deferred issuance costs until such financings were consummated. After consummation of the equity financing, these costs were recorded as a reduction of the proceeds generated as a result of the offering. As of December 31, 2018, the Company recorded deferred issuance costs of $0.3 million related to the IPO within other assets on the consolidated balance sheet. During 2019 and in connection with the IPO, the Company incurred $1.6 million of additional deferred offering costs. All deferred offering costs were reclassified into equity at the closing of the offering. 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 Laboratory equipment 3 - 5 years Furniture and fixtures 3 - 5 years Office and computer equipment 3 - 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. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment losses on long-lived assets during the periods presented. Fair Value Measurements Certain assets and liabilities of the Company were carried at fair value under GAAP (see Note 4). 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. Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision making group, in making decisions on how to allocate resources and assess performance. The Company operates in 1 segment. 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 delivered or the related services are performed or until it is no longer expected that the goods will be delivered or the services rendered. The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research costs. When evaluating the adequacy of 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. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as research and development expenses. 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, 2019 and 2018, the Company has not identified any uncertain tax positions for which reserves would be required. Redeemable Convertible Preferred Stock The Company classified stock that was redeemable in circumstances outside of the Company's control outside of permanent equity. The Company recorded redeemable convertible preferred stock at fair value upon issuance, net of any issuance costs, and the carrying value was increased by periodic accretion to its redemption value at the earliest redemption date, when the events that give rise to redemption are deemed probable of occurrence. These increases were charged to the accumulated deficit. Upon the closing of the IPO, the outstanding shares of redeemable convertible preferred stock were converted to common stock. Stock-Based Compensation For stock-based awards, 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 respective 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 its consolidated statements of operations in the same manner in which the award recipient’s cash compensation costs are classified. Warrant to Purchase Preferred Stock The Company classified the warrant for the purchase of shares of its redeemable convertible preferred stock as a liability on its consolidated balance sheet as the warrant was a free-standing financial instrument that may have required the Company to transfer assets upon exercise. The preferred stock warrant liability was initially recorded at fair value upon the date of issuance and was subsequently remeasured to fair value at each reporting date. Changes in the fair value of the warrant to purchase preferred stock were recognized as a component of other income (expense), net in the consolidated statements of operations. Upon the completion of the IPO, the warrant to purchase preferred stock was converted to a warrant to purchase common stock. The carrying amount of the warrant to purchase preferred stock as of the date of IPO was transferred to additional paid in capital. No further revaluation was needed for the warrant to purchase common stock. The warrant was subsequently net settled in June 2019. 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 years ended December 31, 2019 and 2018, there was no difference between net loss and comprehensive loss in the accompanying consolidated financial statements. Net Income (Loss) Per Share Basic net loss per share attributable to common stockholders is calculated by dividing net loss attributable to common stockholders by the weighted average shares outstanding during the period. The Company allocated no loss to the redeemable convertible preferred stock because those shares had no contractual obligation to share in the losses of the Company. Diluted net income (loss) per share attributable to common stockholders is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock and if-converted methods. All common stock equivalents have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Recently Adopted Accounting Pronouncements Accounting Pronouncements Issued and Not Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less may be accounted for similar to existing guidance for operating leases today. ASU 2016-02 supersedes the previous leases standard, ASC 840, Leases . This standard is effective for the Company beginning January 1, 2021. The Company is evaluating the impact that the adoption of ASU 2016-02 will have on its consolidated financial statements and expects to recognize a lease liability and right-of-use asset related to the Company's leased facilities. See further discussion of the Company's lease obligations in Note 9.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment consist of the following (in thousands): December 31, 2019 2018 Laboratory equipment $ 3,511 $ 3,489 Leasehold improvements 597 564 Office and computer equipment 111 294 Furniture and fixtures 122 122 Property and equipment, gross 4,341 4,469 Less: accumulated depreciation and amortization (3,733) (3,393) Property and equipment, net $ 608 $ 1,076

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The following table sets forth by level, within the fair value hierarchy, the assets and liabilities carried at fair value on a recurring basis (in thousands): Fair value measurements at December 31, 2019 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 91,803 $ — $ — $ 91,803 Total $ 91,803 $ — $ — $ 91,803 Fair value measurements at December 31, 2018 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 79,216 $ — $ — $ 79,216 Total $ 79,216 $ — $ — $ 79,216 Liabilities: Success fee liability $ — $ — $ 1,220 $ 1,220 Preferred stock warrant liability — — 425 425 Total $ — $ — $ 1,645 $ 1,645 Cash equivalents are comprised of funds held in an exchange traded money market fund and the fair value of the cash equivalents is determined based upon quoted market price for that fund. The fair value of the preferred stock warrant was determined using the Black-Scholes option-pricing model with the following assumptions: expected volatility of 65%; risk-free interest rate of 2.49%; weighted-average remaining contractual term of 1.28 years; and expected dividend yield of 0%. The fair value of the success fee liability was determined using a probability weighted present value of cash flows. The Company has projected that 100% of the liability would be paid and that the time value of discounting those cash flows did not have a material impact on the fair value measurement due to the expected term. As a result of the IPO, the preferred stock warrants were converted to warrants to purchase common stock and the fair value of the warrant liability was reclassified to stockholders’ equity and subsequently net settled in June 2019. The success fee liability was also paid. A roll forward of the fair value of the success fee liability and preferred stock warrant liability categorized with Level 3 inputs for the years ended December 31, 2019 and 2018 is as follows (in thousands): Success fee Preferred stock Balance — January 1, 2018 $ 700 $ 411 Increase in success fee included in other liabilities 520 — Increase in warrant fair value included in other expense — 14 Balance — January 1, 2019 1,220 425 Increase in warrant fair value included in other expense — 51 Reclassification to additional paid-in capital in connection with IPO — (476) Payment of success fee (1,220) — Balance — December 31, 2019 $ — $ — There were no transfers among Level 1, Level 2, or Level 3 categories in the periods presented. The carrying value of accounts payable and accrued expenses that are reported on the consolidated balance sheets approximate fair value due to the short-term nature of these assets and liabilities. The carrying value of the long term debt approximates fair value as evidenced by the variable rate and short contractual maturity.

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2019
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other liabilities consisted of the following (in thousands): ​ December 31, 2019 2018 Accrued employee compensation and benefits $ 3,109 $ 1,957 Accrued external research and development expenses 1,799 1,679 Accrued professional fees 985 678 Other 465 985 Total accrued expenses and other current liabilities $ 6,358 $ 5,299

DEBT FINANCING

DEBT FINANCING	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
DEBT FINANCING	DEBT FINANCING Long term debt consisted of the following (in thousands): ​ December 31, 2019 2018 Principal amount of long term debt $ 26,000 $ 26,000 Debt discount (456) (612) Deferred financing fees (647) (867) Long term debt, net of discount $ 24,897 $ 24,521 In January 2018, the Company entered into a secured debt facility (the "2018 Facility") with the existing lender that replaced a prior debt facility. The 2018 Facility increased the funding up to $21.0 million. The Company paid a transaction fee of $0.9 million to the lender in connection with the 2018 Facility, and that fee was recognized as debt discount. The 2018 Facility has an interest rate equal to the LIBOR plus 8.50% per annum (10.20% as of December 31, 2019) payable monthly and a $1.1 million success fee which was payable upon the occurrence of certain events, including an IPO. The Company granted the lender a first priority security interest in all assets of the Company, excluding intellectual property and granted a negative pledge on such intellectual property. In October 2018, the Company amended the 2018 Facility (the "Amended 2018 Facility") to extend the interest only period through July 2020 or January 2021 and the maturity date to July 2022 or January 2023 if certain conditions were met. The Amended 2018 Facility provides additional funding in the amounts of $5.0 million ("Term B Loan") and $4.0 million ("Term C Loan") if certain conditions are met. The Term B Loan of $5.0 million was drawn in December 2018. The success fee increased to $1.2 million. Deferred financing costs of $0.1 million were incurred related to the amendment. The interest rate was not changed through the amendment. Upon completion of the IPO in May 2019, the interest only period was extended through January 2021 and the maturity date was extended to January 2023. Monthly principal payments of $1.1 million are to commence February 2021 for 24 months. The $1.2 million success fee was also paid upon completion of the IPO. Terminal Interest Fee The Company's debt facility includes a terminal interest fee obligation totaling $1.4 million, which is due with the final principal payment of the loan and has been modified from time to time as the facilities were amended. The Company is accruing the terminal fee obligation over the term of the facility. The carrying value of the terminal interest fee was $0.9 million and $0.7 million at December 31, 2019 and 2018, respectively. The scheduled principal maturity of the long term debt as of December 31, 2019 is as follows (in thousands): Year Ending December 31, 2020 $ — 2021 11,917 2022 13,000 2023 1,083 $ 26,000

STOCKHOLDERS' EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS' EQUITY Redeemable Convertible Preferred Stock As of December 31, 2018, the Company’s redeemable convertible preferred stock (the “Preferred Stock”) consisted of the following (in thousands, except for share data): December 31, 2018 Preferred Preferred Carrying Liquidation Common Series A preferred stock 5,874,334 5,761,539 $ 11,235 $ 11,235 3,127,870 Series B preferred stock 4,737,041 4,737,041 12,250 12,250 2,571,679 Series B-1 preferred stock 1,084,441 1,084,441 2,998 3,000 588,730 Series C preferred stock 6,969,044 6,969,044 70,062 70,248 3,783,401 Series D preferred stock 2,997,179 2,997,179 42,434 42,500 1,702,785 Series E preferred stock 6,266,786 5,282,002 58,863 59,000 2,867,532 27,928,825 26,831,246 $ 197,842 $ 198,233 14,641,997 Upon closing of the IPO, all outstanding Preferred Stock converted into an aggregate of 14,641,997 shares of common stock. The holders of the Company’s Preferred Stock had certain voting, dividend, and redemption rights, as well as liquidation preferences and conversion privileges. All rights, preferences, and privileges associated with the preferred stock were terminated at the time of the Company’s IPO in conjunction with the conversion of all outstanding shares of Preferred Stock into shares of common stock. Common Stock As of December 31, 2018, the Company had authorized 47,000,000 shares of common stock, $0.001 par value. In May 2019, the Company restated its certificate of incorporation, which, among other things: (i) authorized 160,000,000 shares, consisting of (i) 150,000,000 shares of common stock, $0.001 par value per share, and (ii) 10,000,000 shares of undesignated preferred stock, $0.001 par value per share. As of December 31, 2019, no preferred stock was outstanding. Initial Public Offering In May 2019, the Company issued 3,571,428 common shares at a public offering price of $20.00 per share for net proceeds of $64.5 million, after deducting underwriting discounts and commissions and other offering expenses. 2010 Stock Option and Incentive Plan The Company’s 2010 Stock Incentive Plan (the “2010 Plan”) provided for the Company to issue incentive stock options or nonqualified stock options, restricted stock, and other equity awards to employees, directors and consultants of the Company. Upon effectiveness of the 2019 Plan, no future issuances will be made under the 2010 Plan. The awards granted under the 2010 Plan have terms that are the same as those of the 2019 Plan. 2019 Stock Option and Incentive Plan The 2019 Stock Option and Incentive Plan (the "2019 Plan") was approved by our board of directors on April 29, 2019 and became effective upon the IPO. 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. The number of shares initially reserved for issuance under the 2019 Plan is 905,000, which shall be cumulatively increased on January 1, 2020 and 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 36,466 as of December 31, 2019. 2019 Employee Stock Purchase Plan The 2019 Employee Stock Purchase Plan (the "2019 ESPP") was approved by our board of directors on April 29, 2019 and became effective upon the IPO. A total of 237,181 shares of common stock were initially reserved for issuance under this plan, which shall be cumulatively increased on January 1, 2020 and 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 total number of common shares that may be issued under the ESPP is 237,181 shares. As of December 31, 2019, the initial purchase period under the ESPP has not yet commenced. Stock Option Valuation Given the absence of an active market for the Company’s common stock prior to the IPO, the Company and its board of directors (the “Board”), the members of which the Company believes have extensive business, finance, and venture capital experience, were required to estimate the fair value of the Company’s common stock at the time of each grant of a stock-based award. The Company and the Board determined the estimated fair value of the Company’s equity instruments based on a number of factors, including external market conditions affecting the biotechnology industry sector. These estimates and assumptions include a number of objective and subjective factors in determining the value of the Company’s common stock at each grant date, including: (1) prices paid for the Company’s redeemable convertible preferred stock, which the Company had sold to outside investors in arm’s-length transactions, and the rights, preferences, and privileges of the Company’s redeemable convertible preferred stock and common stock; (2) valuations performed by an independent valuation specialist; (3) the Company’s stage of development; (4) the fact that the grants of stock-based awards involved illiquid securities in a private company; and (5) the likelihood of achieving a liquidity event for the common stock underlying the stock-based awards, such as an IPO or sale of the Company, given prevailing market conditions. The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option pricing model. As there was no public market for its common stock prior to May 9, 2019, which was the first day of trading, and as the trading history of the Company’s common stock was limited through December 31, 2019, the Company determined the volatility for awards granted based on an analysis of reported data for a group of guideline companies that issued options with substantially similar terms. The expected volatility has been determined using a weighted-average of the historical volatility measures of this group of guideline companies. The Company expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The Company has not paid, and does not anticipate paying, cash dividends on its common stock; therefore, the expected dividend yield is assumed to be zero. The assumptions that the Company used to determine the grant-date fair value of stock options granted were as follows: Year Ending December 31, 2019 2018 Risk-free interest rate 2.09 % 1.93% - 3.02% Expected option life (in years) 6.16 0.25 - 6.25 Expected dividend yield 0 % 0 % Expected volatility 71 % 65 % The following table summarizes the Company’s stock option activity for the year ended December 31, 2019: Options Weighted Weighted Intrinsic Outstanding as of January 1, 2019 4,039,464 $ 5.67 Granted 1,620,351 11.07 Exercised (155,043) 2.19 Canceled (327,828) 7.66 Outstanding as of December 31, 2019 5,176,944 $ 7.35 7.9 $ 1,490 Exercisable as of December 31, 2019 2,202,669 $ 5.57 6.7 $ 1,268 Vested or expected to vest as of December 31, 2019 5,176,944 $ 7.35 7.9 $ 1,490 The intrinsic value of options exercised during the years ended December 31, 2019 and 2018 was $0.4 million and $0, respectively. The weighted-average grant date fair value of the options granted during the years ended December 31, 2019 and 2018, was $7.21 and $3.63 per share, respectively. Stock-based compensation related to stock options and unvested stock awards are classified as follows (in thousands): December 31, 2019 2018 Research and development $ 2,461 $ 1,088 General and administrative 3,363 1,690 $ 5,824 $ 2,778

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2018
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, 2019 and 2018 are as follows: December 31, 2019 2018 Tax at U.S. statutory rate 21.0 % 21.0 % State taxes, net of federal benefit 6.0 % 6.2 % Permanent differences (1.9) % (1.5) % Tax credits 4.1 % 3.8 % Change in valuation allowance (29.2) % (29.5) % Effective income tax rate 0.0 % 0.0 % Significant components of the Company’s deferred tax asset at December 31, 2019 and 2018 are as follows (in thousands): December 31, 2019 2018 Net operating loss carryforwards $ 52,242 $ 38,337 Research and development tax credit carryforwards 7,917 5,470 Start-up costs 35 43 Capitalized research and development costs 169 277 Depreciation 413 479 Accrued expenses 1,102 811 Stock-based compensation 1,087 600 Other items 971 710 Total deferred tax assets 63,936 46,727 Valuation allowance (63,936) (46,727) Net deferred tax asset $ — $ — As of December 31, 2019, the Company had federal and state net operating loss carryforwards of $192.1 million and $188.3 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 and 2019 can be carried forward indefinitely. As of December 31, 2019, the Company had federal and state research and development tax credit carryforwards of $6.1 million and $2.3 million, respectively. These amounts expire at various dates through 2039. 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 2019 and 2018 by $17.2 million and $10.6 million, respectively, 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, 2019, the Company had not yet completed an analysis of whether its net operating loss and research and development credit carryforwards may be limited.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2019
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 1, 2021. 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, 2020 $ 1,226 2021 415 2022 — Total $ 1,641 Rent expense in each of the years ended December 31, 2019 and 2018 was $1.2 million. 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 noncancelable 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.

RETIREMENT PLAN

RETIREMENT PLAN	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
RETIREMENT PLAN	RETIREMENT 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. As of December 31, 2019, the Company had not made any discretionary contributions.

NET LOSS PER SHARE

NET LOSS PER SHARE	12 Months Ended
	Dec. 31, 2019
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, 2019 2018 Numerator: Net loss $ (59,037) $ (36,069) Accretion of redeemable convertible preferred stock (46) (153) Net loss attributable to common stockholders $ (59,083) $ (36,222) Denominator: Weighted average common shares outstanding, basic and diluted 16,624,941 4,546,373 Net loss per share, basic and diluted $ (3.55) $ (7.97) The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2019 2018 Redeemable convertible preferred stock (as converted to common stock) — 14,641,997 Warrants to purchase redeemable convertible preferred stock (as converted to common stock) — 61,235 Outstanding stock options 5,176,944 4,039,464 5,176,944 18,742,696

RELATED- PARTY TRANSACTIONS

RELATED- PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
RELATED- PARTY TRANSACTIONS	RELATED-PARTY TRANSACTIONS In April 2013, the Company entered into a services agreement with Flagship Pioneering, Inc. (“Flagship”), an affiliate of one of the Company’s principal stockholders, to provide various strategic consulting services to the Company. The total expense which includes services and reimbursement for travel and entertainment under the agreement for the years ended December 31, 2019 and 2018 was $18,000 and $0, respectively. As of December 31, 2019 and 2018, there was $1,000 and $0, respectively, payable to Flagship for costs related to the services agreement. 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. The total expense under the agreement for the year ended December 31, 2019 was $0.3 million. As of December 31, 2019, there were no amounts payable to the Chairman for costs related to the consulting agreement.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2019
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.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. Changes in estimates are recorded in the period in which they become known. Actual results could differ materially from those estimates.
Subsequent Events	Subsequent Events The Company considers events or transactions that occur after the balance sheet date but before the final financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash includes cash in readily available checking accounts. Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. The cash equivalents consisted of money market funds.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that subject the Company to significant concentrations of credit risk consist primarily of cash and cash equivalents. The Company’s cash deposits on hand at one financial institution often exceed federally insured limits. The Company places its cash in a financial institution that management believes to be of high credit quality.
Deferred Offering Costs	Deferred Offering CostsThe Company capitalized certain legal, professional accounting and other third-party fees that were directly associated with in-process equity financings as deferred issuance costs until such financings were consummated. After consummation of the equity financing, these costs were recorded as a reduction of the proceeds generated as a result of the offering.
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 Laboratory equipment 3 - 5 years Furniture and fixtures 3 - 5 years Office and computer equipment 3 - 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. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment losses on long-lived assets during the periods presented.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities of the Company were carried at fair value under GAAP (see Note 4). 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.
Segment Information	Segment InformationOperating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision making group, in making decisions on how to allocate resources and assess performance. The Company operates in 1 segment.
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 delivered or the related services are performed or until it is no longer expected that the goods will be delivered or the services rendered. The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research costs. When evaluating the adequacy of 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.
Patent Costs	Patent CostsAll patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as research and development expenses.
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.
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock The Company classified stock that was redeemable in circumstances outside of the Company's control outside of permanent equity. The Company recorded redeemable convertible preferred stock at fair value upon issuance, net of any issuance costs, and the carrying value was increased by periodic accretion to its redemption value at the earliest redemption date, when the events that give rise to redemption are deemed probable of occurrence. These increases were charged to the accumulated deficit. Upon the closing of the IPO, the outstanding shares of redeemable convertible preferred stock were converted to common stock.
Stock-Based Compensation	Stock-Based Compensation For stock-based awards, 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 respective 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 its consolidated statements of operations in the same manner in which the award recipient’s cash compensation costs are classified.
Warrant to Purchase Preferred Stock	Warrant to Purchase Preferred Stock The Company classified the warrant for the purchase of shares of its redeemable convertible preferred stock as a liability on its consolidated balance sheet as the warrant was a free-standing financial instrument that may have required the Company to transfer assets upon exercise. The preferred stock warrant liability was initially recorded at fair value upon the date of issuance and was subsequently remeasured to fair value at each reporting date. Changes in the fair value of the warrant to purchase preferred stock were recognized as a component of other income (expense), net in the consolidated statements of operations.
Comprehensive Loss	Comprehensive LossComprehensive 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.
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net loss per share attributable to common stockholders is calculated by dividing net loss attributable to common stockholders by the weighted average shares outstanding during the period. The Company allocated no loss to the redeemable convertible preferred stock because those shares had no contractual obligation to share in the losses of the Company. Diluted net income (loss) per share attributable to common stockholders is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock and if-converted methods. All common stock equivalents have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.
Recently Adopted Accounting Pronouncements and Accounting Pronouncements Issued and Not Adopted	Recently Adopted Accounting Pronouncements Accounting Pronouncements Issued and Not Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less may be accounted for similar to existing guidance for operating leases today. ASU 2016-02 supersedes the previous leases standard, ASC 840, Leases . This standard is effective for the Company beginning January 1, 2021. The Company is evaluating the impact that the adoption of ASU 2016-02 will have on its consolidated financial statements and expects to recognize a lease liability and right-of-use asset related to the Company's leased facilities. See further discussion of the Company's lease obligations in Note 9.

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [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 Laboratory equipment 3 - 5 years Furniture and fixtures 3 - 5 years Office and computer equipment 3 - 5 years Leasehold improvements Shorter of the asset’s estimated Property and equipment consist of the following (in thousands): December 31, 2019 2018 Laboratory equipment $ 3,511 $ 3,489 Leasehold improvements 597 564 Office and computer equipment 111 294 Furniture and fixtures 122 122 Property and equipment, gross 4,341 4,469 Less: accumulated depreciation and amortization (3,733) (3,393) Property and equipment, net $ 608 $ 1,076

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2019
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 Laboratory equipment 3 - 5 years Furniture and fixtures 3 - 5 years Office and computer equipment 3 - 5 years Leasehold improvements Shorter of the asset’s estimated Property and equipment consist of the following (in thousands): December 31, 2019 2018 Laboratory equipment $ 3,511 $ 3,489 Leasehold improvements 597 564 Office and computer equipment 111 294 Furniture and fixtures 122 122 Property and equipment, gross 4,341 4,469 Less: accumulated depreciation and amortization (3,733) (3,393) Property and equipment, net $ 608 $ 1,076

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Fair Value Hierarchy of Assets and Liabilities	The following table sets forth by level, within the fair value hierarchy, the assets and liabilities carried at fair value on a recurring basis (in thousands): Fair value measurements at December 31, 2019 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 91,803 $ — $ — $ 91,803 Total $ 91,803 $ — $ — $ 91,803 Fair value measurements at December 31, 2018 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 79,216 $ — $ — $ 79,216 Total $ 79,216 $ — $ — $ 79,216 Liabilities: Success fee liability $ — $ — $ 1,220 $ 1,220 Preferred stock warrant liability — — 425 425 Total $ — $ — $ 1,645 $ 1,645 Cash equivalents are comprised of funds held in an exchange traded money market fund and the fair value of the cash equivalents is determined based upon quoted market price for that fund.
Rollforward of the Fair Value of the Success Fee Liability and Preferred Stock Warrant Liability	A roll forward of the fair value of the success fee liability and preferred stock warrant liability categorized with Level 3 inputs for the years ended December 31, 2019 and 2018 is as follows (in thousands): Success fee Preferred stock Balance — January 1, 2018 $ 700 $ 411 Increase in success fee included in other liabilities 520 — Increase in warrant fair value included in other expense — 14 Balance — January 1, 2019 1,220 425 Increase in warrant fair value included in other expense — 51 Reclassification to additional paid-in capital in connection with IPO — (476) Payment of success fee (1,220) — Balance — December 31, 2019 $ — $ —

ACCRUED EXPENSES AND OTHER CU_2

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Payables and Accruals (Tables)	12 Months Ended
	Dec. 31, 2019
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consisted of the following (in thousands): ​ December 31, 2019 2018 Accrued employee compensation and benefits $ 3,109 $ 1,957 Accrued external research and development expenses 1,799 1,679 Accrued professional fees 985 678 Other 465 985 Total accrued expenses and other current liabilities $ 6,358 $ 5,299

DEBT FINANCING (Tables)

DEBT FINANCING (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Summary of Long-term Debt	Long term debt consisted of the following (in thousands): ​ December 31, 2019 2018 Principal amount of long term debt $ 26,000 $ 26,000 Debt discount (456) (612) Deferred financing fees (647) (867) Long term debt, net of discount $ 24,897 $ 24,521
Schedule of Maturities of Long-term Debt	The scheduled principal maturity of the long term debt as of December 31, 2019 is as follows (in thousands): Year Ending December 31, 2020 $ — 2021 11,917 2022 13,000 2023 1,083 $ 26,000

STOCKHOLDERS' EQUITY (Tables)

STOCKHOLDERS' EQUITY (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Summary of Preferred Stock	As of December 31, 2018, the Company’s redeemable convertible preferred stock (the “Preferred Stock”) consisted of the following (in thousands, except for share data): December 31, 2018 Preferred Preferred Carrying Liquidation Common Series A preferred stock 5,874,334 5,761,539 $ 11,235 $ 11,235 3,127,870 Series B preferred stock 4,737,041 4,737,041 12,250 12,250 2,571,679 Series B-1 preferred stock 1,084,441 1,084,441 2,998 3,000 588,730 Series C preferred stock 6,969,044 6,969,044 70,062 70,248 3,783,401 Series D preferred stock 2,997,179 2,997,179 42,434 42,500 1,702,785 Series E preferred stock 6,266,786 5,282,002 58,863 59,000 2,867,532 27,928,825 26,831,246 $ 197,842 $ 198,233 14,641,997
Summary of Fair Value Assumptions for Stock Options	The assumptions that the Company used to determine the grant-date fair value of stock options granted were as follows: Year Ending December 31, 2019 2018 Risk-free interest rate 2.09 % 1.93% - 3.02% Expected option life (in years) 6.16 0.25 - 6.25 Expected dividend yield 0 % 0 % Expected volatility 71 % 65 %
Summary of Options Activity	The following table summarizes the Company’s stock option activity for the year ended December 31, 2019: Options Weighted Weighted Intrinsic Outstanding as of January 1, 2019 4,039,464 $ 5.67 Granted 1,620,351 11.07 Exercised (155,043) 2.19 Canceled (327,828) 7.66 Outstanding as of December 31, 2019 5,176,944 $ 7.35 7.9 $ 1,490 Exercisable as of December 31, 2019 2,202,669 $ 5.57 6.7 $ 1,268 Vested or expected to vest as of December 31, 2019 5,176,944 $ 7.35 7.9 $ 1,490
Summary of Stock Based Compensation Expense	Stock-based compensation related to stock options and unvested stock awards are classified as follows (in thousands): December 31, 2019 2018 Research and development $ 2,461 $ 1,088 General and administrative 3,363 1,690 $ 5,824 $ 2,778

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 are as follows: December 31, 2019 2018 Tax at U.S. statutory rate 21.0 % 21.0 % State taxes, net of federal benefit 6.0 % 6.2 % Permanent differences (1.9) % (1.5) % Tax credits 4.1 % 3.8 % Change in valuation allowance (29.2) % (29.5) % Effective income tax rate 0.0 % 0.0 %
Schedule of Deferred Tax Assets and Liabilities	Significant components of the Company’s deferred tax asset at December 31, 2019 and 2018 are as follows (in thousands): December 31, 2019 2018 Net operating loss carryforwards $ 52,242 $ 38,337 Research and development tax credit carryforwards 7,917 5,470 Start-up costs 35 43 Capitalized research and development costs 169 277 Depreciation 413 479 Accrued expenses 1,102 811 Stock-based compensation 1,087 600 Other items 971 710 Total deferred tax assets 63,936 46,727 Valuation allowance (63,936) (46,727) Net deferred tax asset $ — $ —

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2020 $ 1,226 2021 415 2022 — Total $ 1,641

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 2018 Numerator: Net loss $ (59,037) $ (36,069) Accretion of redeemable convertible preferred stock (46) (153) Net loss attributable to common stockholders $ (59,083) $ (36,222) Denominator: Weighted average common shares outstanding, basic and diluted 16,624,941 4,546,373 Net loss per share, basic and diluted $ (3.55) $ (7.97)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: December 31, 2019 2018 Redeemable convertible preferred stock (as converted to common stock) — 14,641,997 Warrants to purchase redeemable convertible preferred stock (as converted to common stock) — 61,235 Outstanding stock options 5,176,944 4,039,464 5,176,944 18,742,696

NATURE OF BUSINESS (Details)

NATURE OF BUSINESS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Net loss	$ (59,037)	$ (36,069)	$ (59,000)
Accumulated deficit	216,086	157,049
Cash and cash equivalents	$ 92,053	$ 79,466	$ 46,817

SUMMARY OF SIGNIFICANT ACCOUN_4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)segment	Dec. 31, 2018USD ($)
Subsidiary, Sale of Stock [Line Items]
Deferred offering costs	$ 0	$ 251
Number of operating segments | segment	1
IPO
Subsidiary, Sale of Stock [Line Items]
Deferred offering costs	$ 1,600	$ 300

SUMMARY OF SIGNIFICANT ACCOUN_5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property and Equipment Useful Life (Details)	12 Months Ended
	Dec. 31, 2019
Laboratory equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Laboratory equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Office and computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Office and computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years

PROPERTY AND EQUIPMENT - Summar

PROPERTY AND EQUIPMENT - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,341	$ 4,469
Less: accumulated depreciation and amortization	(3,733)	(3,393)
Property and equipment, net	608	1,076
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,511	3,489
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	597	564
Office and computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	111	294
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, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 662	$ 1,071

FAIR VALUE MEASUREMENTS - Fair

FAIR VALUE MEASUREMENTS - Fair Value Hierarchy (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Liabilities:
Success fee liability expected to be paid (percent)	100.00%
Fair Value, Recurring
Assets:
Cash equivalents	$ 91,803	$ 79,216
Total	91,803	79,216
Liabilities:
Success fee liability		1,220
Preferred stock warrant liability		425
Total		1,645
Fair Value, Recurring | Level 1
Assets:
Cash equivalents	91,803	79,216
Total	91,803	79,216
Liabilities:
Success fee liability		0
Preferred stock warrant liability		0
Total		0
Fair Value, Recurring | Level 2
Assets:
Cash equivalents	0	0
Total	0	0
Liabilities:
Success fee liability		0
Preferred stock warrant liability		0
Total		0
Fair Value, Recurring | Level 3
Assets:
Cash equivalents	0	0
Total	$ 0	0
Liabilities:
Success fee liability		1,220
Preferred stock warrant liability		425
Total		$ 1,645

FAIR VALUE MEASUREMENTS - Narra

FAIR VALUE MEASUREMENTS - Narrative (Details) - Preferred Stock	12 Months Ended
	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	65.00%
Risk-free interest rate	2.49%
Expected option life (in years)	1 year 3 months 10 days
Expected dividend yield	0.00%

FAIR VALUE MEASUREMENTS - Rollf

FAIR VALUE MEASUREMENTS - Rollforward of Fair Value of Success Fee Liability and Preferred Stock Warrant Liability (Details) - Fair Value, Recurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Success fee
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning	$ 1,220	$ 700
Increase in warrant fair value included in other expense		520
Payment of success fee	(1,220)
Balance, ending	0	1,220
Preferred stock warrant liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning	425	411
Increase in warrant fair value included in other expense	51	14
Reclassification to additional paid-in capital in connection with IPO	(476)
Balance, ending	$ 0	$ 425

ACCRUED EXPENSES AND OTHER CU_3

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued employee compensation and benefits	$ 3,109	$ 1,957
Accrued external research and development expenses	1,799	1,679
Accrued professional fees	985	678
Other	465	985
Total accrued expenses and other current liabilities	$ 6,358	$ 5,299

DEBT FINANCING - Summary of Lon

DEBT FINANCING - Summary of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Principal amount of long term debt	$ 26,000	$ 26,000
Debt discount	(456)	(612)
Deferred financing fees	(647)	(867)
Long term debt, net of discount	$ 24,897	$ 24,521

DEBT FINANCING - Narrative (Det

DEBT FINANCING - Narrative (Details) - USD ($)	May 17, 2019	Feb. 28, 2021	Dec. 31, 2018	Oct. 31, 2018	Jan. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Transaction fee						$ 0	$ 945,000
Deferred financing fees			$ 867,000			$ 647,000	867,000
Secured Debt
Line of Credit Facility [Line Items]
Success fee					$ 1,100,000
2018 Facility | Secured Debt
Line of Credit Facility [Line Items]
Funding amount					21,000,000
Transaction fee					$ 900,000
Interest rate at period end						10.20%
2018 Facility | LIBOR | Secured Debt
Line of Credit Facility [Line Items]
Basis spread on interest rate					8.50%
Term Loan B | Line of Credit
Line of Credit Facility [Line Items]
Amounts drawn			5,000,000
Amended 2018 Facility | Line of Credit
Line of Credit Facility [Line Items]
Success fee	$ 1,200,000			$ 1,200,000
Deferred financing fees				100,000
Terminal fee				1,400,000
Terminal fee, at carrying value			$ 700,000			$ 900,000	$ 700,000
Pro Forma | Term Loan B | Line of Credit
Line of Credit Facility [Line Items]
Funding amount				5,000,000
Pro Forma | Term Loan C | Line of Credit
Line of Credit Facility [Line Items]
Funding amount				$ 4,000,000
Forecast | Amended 2018 Facility | Line of Credit
Line of Credit Facility [Line Items]
Monthly principal payments		$ 1,100,000
Term		24 months

DEBT FINANCING - Maturities of

DEBT FINANCING - Maturities of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
2020	$ 0
2021	11,917
2022	13,000
2023	1,083
Principal amount of long-term debt	$ 26,000	$ 26,000

STOCKHOLDERS' EQUITY - Summary

STOCKHOLDERS' EQUITY - Summary of Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)		27,928,825
Preferred Stock Issued (in shares)		26,831,246
Preferred Stock Outstanding (in shares)	0	26,831,246	21,549,244
Carrying Value	$ 0	$ 197,842	$ 138,828
Liquidation Preference		$ 198,233
Common stock issuable upon conversion (in shares)		14,641,997
Series A preferred stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)		5,874,334
Preferred Stock Issued (in shares)		5,761,539
Preferred Stock Outstanding (in shares)		5,761,539
Carrying Value		$ 11,235
Liquidation Preference		$ 11,235
Common stock issuable upon conversion (in shares)		3,127,870
Series B preferred stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)		4,737,041
Preferred Stock Issued (in shares)		4,737,041
Preferred Stock Outstanding (in shares)		4,737,041
Carrying Value		$ 12,250
Liquidation Preference		$ 12,250
Common stock issuable upon conversion (in shares)		2,571,679
Series B-1 preferred stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)		1,084,441
Preferred Stock Issued (in shares)		1,084,441
Preferred Stock Outstanding (in shares)		1,084,441
Carrying Value		$ 2,998
Liquidation Preference		$ 3,000
Common stock issuable upon conversion (in shares)		588,730
Series C preferred stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)		6,969,044
Preferred Stock Issued (in shares)		6,969,044
Preferred Stock Outstanding (in shares)		6,969,044
Carrying Value		$ 70,062
Liquidation Preference		$ 70,248
Common stock issuable upon conversion (in shares)		3,783,401
Series D preferred stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)		2,997,179
Preferred Stock Issued (in shares)		2,997,179
Preferred Stock Outstanding (in shares)		2,997,179
Carrying Value		$ 42,434
Liquidation Preference		$ 42,500
Common stock issuable upon conversion (in shares)		1,702,785
Series E preferred stock
Class of Stock [Line Items]
Preferred Stock Authorized (in shares)		6,266,786
Preferred Stock Issued (in shares)		5,282,002
Preferred Stock Outstanding (in shares)		5,282,002
Carrying Value		$ 58,863
Liquidation Preference		$ 59,000
Common stock issuable upon conversion (in shares)		2,867,532

STOCKHOLDERS' EQUITY - Summar_2

STOCKHOLDERS' EQUITY - Summary of Preferred Stock Narrative (Details)	May 13, 2019shares
IPO
Class of Stock [Line Items]
Conversion of preferred stock to common stock upon closing of the initial public offering (in shares)	14,641,997

STOCKHOLDERS' EQUITY - Common S

STOCKHOLDERS' EQUITY - Common Stock and Initial Public Offering Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	May 13, 2019	Dec. 31, 2019	May 31, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Common stock authorized (in shares)		150,000,000	150,000,000	47,000,000
Common stock, par value (USD per share)		$ 0.001	$ 0.001	$ 0.001
Common and preferred stock, shares authorized (in shares)			160,000,000
Preferred stock, authorized (in shares)		10,000,000	10,000,000	10,000,000
Preferred stock, par value (USD per share)		$ 0.001	$ 0.001	$ 0.001
Preferred stock outstanding (in shares)		0		0
IPO
Subsidiary, Sale of Stock [Line Items]
Shares sold	3,571,428
Shares sold, par value (USD per share)	$ 20
Net proceeds on offering	$ 64.5

STOCKHOLDERS' EQUITY - 2019 Sto

STOCKHOLDERS' EQUITY - 2019 Stock Option, Incentive Plan and Employee Stock Purchase Plan Narrative (Details) - shares	Apr. 29, 2019	Dec. 31, 2019
Stock Option And Incentive Plan 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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%
2019 Stock Plan | Outstanding stock options | Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance		36,466
Employee Stock Purchase Plan 2019
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%

STOCKHOLDERS' EQUITY - Stock Op

STOCKHOLDERS' EQUITY - Stock Option Fair Value Measurement Inputs (Details) - 2010 Plan - Stock options	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.09%
Risk-free interest rate, minimum		1.93%
Risk-free interest rate, maximum		3.02%
Expected option life (in years)	6 years 1 month 28 days
Expected dividend yield	0.00%	0.00%
Expected volatility	71.00%	65.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option life (in years)		3 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option life (in years)		6 years 3 months

STOCKHOLDERS' EQUITY - Summar_3

STOCKHOLDERS' EQUITY - Summary of Option Activity (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)$ / sharesshares
Options
Outstanding, beginning balance (in shares) | shares	4,039,464
Granted (in shares) | shares	1,620,351
Exercised (in shares) | shares	(155,043)
Canceled (in shares) | shares	(327,828)
Outstanding, ending balance (in shares) | shares	5,176,944
Options exercisable (in shares) | shares	2,202,669
Options vested or expected to vest (in shares) | shares	5,176,944
Weighted Average Exercise Price
Weighted average exercise price, outstanding, beginning balance (USD per share) | $ / shares	$ 5.67
Weighted-average exercise price, granted (USD per share) | $ / shares	11.07
Weighted-average exercise price, exercised (USD per share) | $ / shares	2.19
Weighted-average exercise price, canceled (USD per share) | $ / shares	7.66
Weighted average exercise price, outstanding, ending balance (USD per share) | $ / shares	7.35
Weighted-average exercise price, options exercisable (USD per share) | $ / shares	5.57
Weighted-average exercise price, options vested or expected to vest (USD per share) | $ / shares	$ 7.35
Weighted Average Remaining Life (in Years)
Weighted Average Remaining Life, Outstanding (in Years)	7 years 10 months 24 days
Intrinsic Value, Outstanding | $	$ 1,490
Weighted Average Remaining Life, Options exercisable (in Years)	6 years 8 months 12 days
Weighted Average Remaining Life, Options vested or expected to vest (in Years)	7 years 10 months 24 days
Intrinsic Value, Options exercisable | $	$ 1,268
Intrinsic Value, Options vested or expected to vest | $	$ 1,490

STOCKHOLDERS' EQUITY - Stock _2

STOCKHOLDERS' EQUITY - Stock Option Valuation Narrative (Details) - Stock options - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value, options exercised	$ 400,000	$ 0
2010 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grand date fair value of options granted in the period (USD per share)	$ 7.21	$ 3.63
Unrecognized compensation expense related to unvested stock options	$ 14,400,000
Unrecognized compensation expense, recognition period	2 years 8 months 12 days

STOCKHOLDERS' EQUITY - Summar_4

STOCKHOLDERS' EQUITY - Summary of Stock Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 5,824	$ 2,778
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	2,461	1,088
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 3,363	$ 1,690

INCOME TAXES - Effective Income

INCOME TAXES - Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax at U.S. statutory rate	21.00%	21.00%
State taxes, net of federal benefit	6.00%	6.20%
Permanent differences	(1.90%)	(1.50%)
Tax credits	4.10%	3.80%
Change in valuation allowance	(29.20%)	(29.50%)
Effective income tax rate	0.00%	0.00%

INCOME TAXES - Net Deferred Tax

INCOME TAXES - Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 52,242	$ 38,337
Research and development tax credit carryforwards	7,917	5,470
Start-up costs	35	43
Capitalized research and development costs	169	277
Depreciation	413	479
Accrued expenses	1,102	811
Stock-based compensation	1,087	600
Other items	971	710
Total deferred tax assets	63,936	46,727
Valuation allowance	(63,936)	(46,727)
Net deferred tax asset	$ 0	$ 0

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Increase (decrease) in valuation allowance	$ 17.2	$ 10.6
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	192.1
Federal | Research And Development Tax Credit Carryforward
Income Taxes [Line Items]
Research and development and other credit carryforwards	6.1
State
Income Taxes [Line Items]
Net operating loss carryforwards	188.3
State | Research And Development Tax Credit Carryforward
Income Taxes [Line Items]
Research and development and other credit carryforwards	$ 2.3

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2019USD ($)
Commitments and Contingencies Disclosure [Abstract]
2020	$ 1,226
2021	415
2022	0
Total	$ 1,641

COMMITMENTS AND CONTINGENCIES_2

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 1.2	$ 1.2

NET LOSS PER SHARE - Calculatio

NET LOSS PER SHARE - Calculation of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss	$ (59,037)	$ (36,069)	$ (59,000)
Accretion of redeemable convertible preferred stock	(46)	(153)
Net loss attributable to common stockholders	$ (59,083)	$ (36,222)
Denominator:
Weighted average common shares outstanding, basic and diluted (in shares)	16,624,941	4,546,373
Net loss per share, basic and diluted (USD per share)	$ (3.55)	$ (7.97)

NET LOSS PER SHARE - Summary of

NET LOSS PER SHARE - Summary of Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share (in shares)	5,176,944	18,742,696
Redeemable convertible preferred stock (as converted to 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)	0	14,641,997
Warrants to purchase redeemable convertible preferred stock (as converted to 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)	0	61,235
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share (in shares)	5,176,944	4,039,464

RELATED-PARTY TRANSACTIONS - Na

RELATED-PARTY TRANSACTIONS - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Related Party Services Agreement | Investor
Related Party Transaction [Line Items]
Related party costs	$ 18,000	$ 0
Related Party Services Agreement | Board of Directors Chairman
Related Party Transaction [Line Items]
Related party costs	300,000
Related Party Consulting Agreement | Investor
Related Party Transaction [Line Items]
Due to related parties	1,000	$ 0
Related Party Consulting Agreement | Board of Directors Chairman
Related Party Transaction [Line Items]
Due to related parties	$ 0