Rein Therapeutics (RNTX) 10-Q 8 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 06, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	ALRN
Entity Registrant Name	AILERON THERAPEUTICS INC
Entity Central Index Key	0001420565
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		26,713,617

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 11,272	$ 10,635
Investments	1,998	10,060
Prepaid expenses and other current assets	1,094	1,055
Restricted cash	25	25
Total current assets	14,389	21,775
Operating lease, right-of-use asset	6,543
Property and equipment, net	398	7,290
Restricted cash, non-current	568	568
Other assets	501	679
Total assets	22,399	30,312
Current liabilities:
Accrued expenses and other current liabilities	3,378	3,639
Accounts payable	858	1,731
Operating lease liabilities	387
Total current liabilities	4,623	5,370
Operating lease liabilities, net of current portion	4,929
Construction financing liability		5,342
Total liabilities	9,552	10,712
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized at March 31, 2019 and December 31, 2018, respectively; no shares issued and outstanding at March 31, 2019 and December 31, 2018
Common stock, $0.001 par value; 150,000,000 shares authorized at March 31, 2019 and December 31, 2018; 14,875,035 and 14,748,475 shares issued and outstanding at March 31, 2019 and December 31, 2018, respectively	15	15
Additional paid-in capital	188,811	188,083
Accumulated other comprehensive loss		(5)
Accumulated deficit	(175,979)	(168,493)
Total stockholders’ equity	12,847	19,600
Total liabilities and stockholders’ equity	$ 22,399	$ 30,312

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	14,875,035	14,748,475
Common stock, shares outstanding	14,875,035	14,748,475

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 0	$ 0
Operating expenses:
Research and development	4,174	4,846
General and administrative	3,139	2,917
Total operating expenses	7,313	7,763
Loss from operations	(7,313)	(7,763)
Interest income	100	175
Net loss	$ (7,213)	$ (7,588)
Net loss per share — basic and diluted	$ (0.49)	$ (0.52)
Weighted average common shares outstanding—basic and diluted	14,816,253	14,732,287
Comprehensive loss:
Net loss	$ (7,213)	$ (7,588)
Other comprehensive gain (loss):
Unrealized gain (loss) on investments, net of tax of $0	5	(17)
Total other comprehensive gain (loss)	5	(17)
Total comprehensive loss	$ (7,208)	$ (7,605)

Condensed Statements of Opera_2

Condensed Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Unrealized loss on investments, tax	$ 0	$ 0

Statement of Stockholders' Equi

Statement of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2017	$ 47,797	$ 15	$ 184,761	$ (33)	$ (136,946)
Beginning balance, shares at Dec. 31, 2017		14,723,818
Exercise of stock options	16		16
Exercise of stock options, shares		10,565
Stock-based compensation expense	767		767
Unrealized gain (loss) on investments, net of tax of $0	(17)			(17)
Net loss	(7,588)				(7,588)
Ending balance at Mar. 31, 2018	40,975	$ 15	185,544	(50)	(144,534)
Ending balance, shares at Mar. 31, 2018		14,734,383
Beginning balance at Dec. 31, 2018	$ 19,600	$ 15	188,083	(5)	(168,493)
Beginning balance, shares at Dec. 31, 2018	14,748,475	14,748,475
Exercise of stock options	$ 165		165
Exercise of stock options, shares	126,560	126,560
Stock-based compensation expense	$ 563		563
Adoption of ASC 842, Leases | ASU No. 2016-02 [Member]	(273)				(273)
Unrealized gain (loss) on investments, net of tax of $0	5			$ 5
Net loss	(7,213)				(7,213)
Ending balance at Mar. 31, 2019	$ 12,847	$ 15	$ 188,811		$ (175,979)
Ending balance, shares at Mar. 31, 2019	14,875,035	14,875,035

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (7,213)	$ (7,588)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	31	46
Net amortization of premiums and discounts on investments	(34)	(44)
Stock-based compensation expense	563	767
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(50)	(86)
Other assets	533	11
Accounts payable	(872)	196
Operating lease liabilities	(85)
Accrued expenses and other current liabilities	(374)	(231)
Net cash used in operating activities	(7,501)	(6,929)
Cash flows from investing activities:
Purchases of property and equipment	(127)	(7)
Purchases of investments		(7,548)
Proceeds from sales or maturities of investments	8,100	9,955
Net cash provided by (used in) investing activities	7,973	2,400
Cash flows from financing activities:
Proceeds from exercise of stock options	165	16
Net cash provided by financing activities	165	16
Net decrease in cash, cash equivalents and restricted cash	637	(4,513)
Cash, cash equivalents and restricted cash at beginning of period	11,228	11,951
Cash, cash equivalents and restricted cash at end of period	11,865	$ 7,438
Supplemental disclosure of non-cash financing activities:
Deferred offering costs included in accounts payable and accrued expenses	$ 199

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Aileron Therapeutics, Inc. (“Aileron” or the “Company”) is a clinical-stage biopharmaceutical company that is focused on developing and commercializing a novel class of stabilized cell-permeating alpha-helical peptides to address intracellular targets in oncology and other therapeutic areas. The Company’s lead product candidate, ALRN-6924, targets the tumor suppressor p53 for the treatment of a wide variety of cancers. ALRN-6924 is a stabilized cell-permeating peptide that disrupts the interaction of the two primary p53 suppressor proteins, MDM2 and MDMX, with p53, thereby reactivating tumor suppression in wild-type p53 cancers. ALRN-6924 was in multiple clinical trials as of March 31, 2019. The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure, and extensive compliance-reporting capabilities. The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary governmental regulatory approval or that any approved products will be commercially viable. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its key employees and consultants. The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Liquidity In accordance with Accounting Standards Update (“ASU”) No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern The Company’s interim financial statements have been prepared on a going concern basis, which contemplates the continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. Through March 31, 2019, the Company has funded its operations with net proceeds of $50,009 from its IPO, $131,211 from sales of preferred stock and $34,910 from a collaboration agreement. As of March 31, 2019, the Company had cash, cash equivalents and investments of $13,270. The Company has incurred losses and negative cash flows from operations and had an accumulated deficit of $175,979 as of March 31, 2019. The Company expects to continue to generate losses for the foreseeable future. On March 28, 2019, the Company entered into a securities purchase agreement with accredited investors, pursuant to which it agreed to issue and sell to the investors in a private placement an aggregate of (i) 11,838,582 units, consisting of 11,838,582 shares of its common stock and associated warrants, (the “common warrants”), to purchase an aggregate of 11,838,582 shares of common stock, for a combined price of $2.01 per unit and (ii) 1,096,741 units, consisting of pre-funded warrants to purchase 1,096,741 shares of the Company’s common stock and associated common warrants to purchase 1,096,741 shares of common stock, for a combined price of $2.01 per unit. The pre-funded warrants are exercisable at an exercise price of $0.01 per share and have no expiration. The common warrants are exercisable at an exercise price of $2.00 per share and expire five years from the date of issuance. On April 2, 2019, the Company closed the private placement and received aggregate gross proceeds of approximately $26,000, before deducting placement agent fees and offering expenses, and excluding the exercise of any warrants. The Company paid placement agent fees of approximately $1,700. As of May 8, 2019, the date of issuance of these unaudited interim condensed financial statements, the Company expects that its cash, cash equivalents and investments of $13,270 as of March 31, 2019, together with the net proceeds from the private placement of its common stock received on April 2, 2019 will be sufficient to fund its operating expenses and capital expenditure requirements into the fourth quarter of 2020. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. To execute its business plans, the Company will need substantial funding to support its continuing operations and pursue its growth strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through the sale of common stock in public offering and/or private placements, debt financings or other capital sources, including collaborations with other companies or other strategic transactions. The Company may not be able to obtain financing on acceptable terms or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion plans or commercialization efforts, which could adversely affect its business prospects.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of 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 financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of common stock and stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. Unaudited Interim Financial Information The accompanying unaudited condensed financial statements as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 have been prepared by the Company, pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 that was filed with the SEC on March 29, 2019. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2019, the results of its operations for the three months ended March 31, 2019 and 2018 and its cash flows for the three months ended March 31, 2019 and 2018. The financial data and other information disclosed in these notes related to the three months ended March 31, 2019 and 2018 are unaudited. The results for the three months ended March 31, 2019 are not necessarily indicative of results to be expected for the year ending December 31, 2019, any other interim periods, or any future year or period. The accompanying balance sheet as of December 31, 2018 has been derived from the Company’s audited financial statements for the year ended December 31, 2018 previously filed with the SEC. Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, corporate notes and commercial paper, are stated at fair value. Restricted Cash As of March 31, 2019 and December 31, 2018, current restricted cash consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards. As of March 31, 2019 and December 31, 2018, non-current restricted cash consisted of $568 of cash deposited in a separate restricted bank account as a security deposit for Investments The Company classifies its available-for-sale debt security investments as current assets on the balance sheet if they mature within one year from the balance sheet date. The Company classifies all of its investments as available-for-sale securities. The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities or using other inputs that are observable or can be corroborated by observable market data. Unrealized gains and losses on available-for-sale securities are reported as accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit). The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the statements of operations and comprehensive loss. The Company evaluates its investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. 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 and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities. Net Income (Loss) per Share The Company follows the two-class method when computing net income (loss) per share as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options to purchase common stock are considered potential dilutive common shares. Recently Adopted Accounting Pronouncements The Financial Accounting Standards Board (the “FASB”) issued ASU No. 2016-02, Leases The Company adopted the standard effective January 1, 2019. It has implemented the standard using the required modified retrospective approach and has also elected to utilize the package of practical expedients. The expedients used by the Company are as follows: (1) allowing an entity to not reassess the lease classification for any expired or existing leases, (2) allowing an entity to not reassess the treatment of initial direct costs as they related to existing leases, and (3) allowing an entity to not reassess whether expired or existing contracts are or contain leases. In using the modified retrospective approach, the Company is required to recognize and measure leases existing at, or entered into after, the beginning of the earliest comparative period presented. As a result of the adoption of ASU 2016-02, the Company de-recognized $7,079 of the building asset and $81 of accumulated depreciation related to its corporate headquarters at 490 Arsenal Way. Prior to the adoption of ASU 2016-02, the Company classified leasehold improvements associated with the 490 Arsenal Way building as building. Subsequent to the adoption of ASU 2016-02, the leasehold improvements associated with the 490 Arsenal Way building are classified as leasehold improvements. January 1, 2019 prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 as adjusted Operating lease right-of-use assets, net $ — $ 6,697 $ 6,697 Property and equipment, net 7,290 (6,998 ) $ 292 Construction financing liability 5,342 (5,342 ) $ — Other liabilities, current 3,639 (87 ) $ 3,552 Operating lease liabilities, current — 334 $ 334 Operating lease liabilities, net of current portion — 5,067 $ 5,067 Accumulated deficit (168,493 ) (273 ) $ (168,766 ) Recently Issued Accounting Pronouncements The Company does not expect any accounting standards that have been issued or proposed by the FASB or other standards setting bodies that would require adoption on a future date to have a material impact on the Company’s financial statements upon adoption.

Fair Value of Financial Assets

Fair Value of Financial Assets	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets	3. Fair Value of Financial Assets The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of March 31, 2019 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 6,020 $ — $ — $ 6,020 Commercial paper — 1,994 — 1,994 Corporate notes — 2,198 — 2,198 Investments: Commercial paper — 1,998 — 1,998 $ 6,020 $ 6,190 $ — $ 12,210 Fair Value Measurements as of December 31, 2018 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 6,041 $ — $ — $ 6,041 Corporate notes — 998 — 998 Commercial paper — 2,495 — 2,495 Investments: Corporate notes — 3,644 — 3,644 Commercial paper — 6,416 — 6,416 $ 6,041 $ 13,553 $ — $ 19,594 As of March 31, 2019 and December 31, 2018, the Company’s cash equivalents and investments were invested in money market funds, corporate notes and commercial paper and were valued based on Level 1 and Level 2 inputs. In determining the fair value of its corporate notes and commercial paper at each date presented above, the Company relied on quoted prices for similar securities in active markets or using other inputs that are observable or can be corroborated by observable market data. The Company’s cash equivalents have original maturities of less than 90 days from the date of purchase. All available-for-sale investments have contractual maturities of less than one year. During the three months ended March 31, 2019 and the year ended December 31, 2018, there were no transfers between Level 1, Level 2 and Level 3.

Investments

Investments	3 Months Ended
	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Investments	4. Investments As of March 31, 2019 and December 31, 2018, the fair value of available-for-sale investments by type of security was as follows: March 31, 2019 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial paper $ 1,998 $ — $ — $ 1,998 $ 1,998 $ — $ — $ 1,998 December 31, 2018 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate notes $ 3,646 $ — $ (2 ) $ 3,644 Commercial paper 6,418 — (2 ) 6,416 $ 10,064 $ — $ (4 ) $ 10,060

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: March 31, 2019 December 31, 2018 External research and development services 1,553 1,307 Payroll and payroll-related costs 820 1,473 Professional fees 716 436 Other 289 423 $ 3,378 $ 3,639

Stock-Based Awards

Stock-Based Awards	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	6. Stock-Based Awards 2017 Stock Incentive Plan The Company’s 2017 Stock Incentive Plan (the “2017 Plan”) was approved by the Company’s stockholders on June 16, 2017 and became effective on June 28, 2017. Under the 2017 Plan, the Company may grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2017 Plan; however, incentive stock options may only be granted to employees. The 2017 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The number of shares of common stock covered by options and the date those options become exercisable, type of options to be granted, exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the 2017 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years, although options have been granted with vesting terms of less than four years. The total number of shares of common stock that may be issued under the 2017 Plan was 3,032,188 as of March 31, 2019, of which 1,545,467 shares remained available for grant. The Company initially reserved During the three months ended March 31, 2019, pursuant to the terms of the 2017 Plan, the Company granted options to employees and directors to purchase 100,000 shares of common stock at a weighted average exercise price of $1.47 per share. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards. The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant. 2017 Employee Stock Purchase Plan On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. On December 13, 2018, the Company’s compensation committee of the board of directors determined not to increase the number of shares of common stock that may be issued under the 2017 ESPP. 2016 Stock Incentive Plan The Company’s 2016 Stock Incentive Plan (the “2016 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2016 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the 2016 Plan with service-based vesting conditions vest over four years and expire after ten years. As of the effective date of the 2017 Plan, the board of directors determined to grant no further awards under the 2016 Plan. No stock options or other awards have been made under the 2016 Plan since the adoption of the 2017 Plan. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 Plan. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards under the 2017 Plan. 2006 Stock Incentive Plan The Company’s 2006 Stock Incentive Plan, as amended, (the “2006 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2006 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the 2006 Plan with service-based vesting conditions generally vest over four years and expire after ten years, although options have been granted with vesting terms of less than four years. The 2006 Plan expired in 2016. Since its expiration No further awards have been made under the 2006 Plan. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 Plan. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards under the 2017 Plan. Stock Option Valuation The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the three months ended March 31, 2019 and 2018 were as follows, presented on a weighted average basis: Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Risk-free interest rate 2.53 % 2.67 % Expected term (in years) 6.2 6.2 Expected volatility 76.0 % 76.0 % Expected dividend yield 0 % 0 % Stock Options The following table summarizes the Company’s stock option activity since January 1, 2019: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding at December 31, 2018 2,528,297 $ 6.31 6.7 $ — Granted 100,000 1.47 Exercised (126,560 ) 1.30 Canceled (50,000 ) 5.37 Forfeited (5,250 ) 12.09 Outstanding at March 31, 2019 2,446,487 $ 6.37 6.8 $ 66 Options exercisable at March 31, 2019 1,185,803 $ 6.85 4.4 $ 18 Options vested and expected to vest at March 31, 2019 2,407,749 $ 6.85 4.4 $ 18 Options exercisable at December 31, 2018 1,214,016 $ 6.29 3.9 $ — Options vested and expected to vest at December 31, 2018 2,485,495 $ 6.31 6.6 $ — The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2019 and 2018 was $0.99 and $6.17, respectively. The aggregate fair value of stock options that vested during the three months ended March 31, 2019 and 2018 was $509 and $514, respectively. The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised during the three months ended March 31, 2019 and 2018 was $109 and $83, respectively. Stock-Based Compensation The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations and comprehensive loss: Three Months Ended March 31, 2019 2018 Research and development expenses $ 81 $ 270 General and administrative expenses 482 497 $ 563 $ 767 The Company used an estimated forfeiture rate of 2.43% to calculate its stock compensation expense for each of the three months ended March 31, 2019 and 2018. As of March 31, 2019, the Company had an aggregate of $4,711 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 2.3 years.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Loss per Share	7. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows : Three Months Ended March 31, 2019 2018 Numerator: Net loss $ (7,213 ) $ (7,588 ) Denominator: Weighted average common shares outstanding—basic and diluted. 14,816,253 14,732,287 Net loss per share —basic and diluted $ (0.49 ) $ (0.52 ) The Company’s potential dilutive securities, which include stock options, have been excluded from the computation of diluted net loss per share attributable to common stockholders whenever the effect of including them would be to reduce the net loss per share. In periods where there is a net loss, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2019 2018 Stock options to purchase common stock 2,446,487 2,175,668

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Operating Lease 490 Arsenal Way On April 4, 2018, the Company entered into a lease agreement for office and laboratory space located in a building (the “Building”) at 490 Arsenal Way, Watertown, Massachusetts (the “490 Arsenal Way Lease”), which is now the Company’s corporate headquarters. Under the terms of the 490 Arsenal Way Lease, starting on August 21, 2018, the Company leases approximately 18,768 square feet of office and laboratory space at $52.55 per square foot per year, or $986 per year in base rent, which is subject to scheduled annual rent increases plus certain operating expenses and taxes. The Company currently maintains a $568 security deposit related to the 490 Arsenal Way Lease. Pursuant to the 490 Arsenal Way Lease, the landlord contributed an aggregate of $2,419 toward the cost of construction and tenant improvements for the Building. The Company has occupied the Building beginning on August 21, 2018 and the 490 Arsenal Way Lease will continue until August 31, 2026. The Company has the option to extend the 490 Arsenal Way Lease for one five-year terms. The Company is accounting for this lease under ASC 842 using its initial eight-year term through August 31, 2026 and will reassess the lease term on a quarterly basis. Due to the Company’s involvement in the construction project, including having responsibility to pay for a portion of the costs of finish work and mechanical, electrical, and plumbing elements of the Building, among other items, the Company was deemed for accounting purposes to be the owner of the Building during the construction period, per ASC 840. Accordingly, under ASC 840, construction costs that were incurred by the landlord directly or indirectly through reimbursement to the Company as part of its tenant improvement allowance were recorded as an asset in Property, plant and equipment, net on the Company’s consolidated balance sheets. The Company evaluated the 490 Arsenal Way Lease upon occupancy on August 21, 2018 and determined that the 490 Arsenal Way Lease did not meet the criteria for “sale-leaseback” treatment under ASC 840. This determination was based on, among other things, the Company's continuing involvement with the property in the form of non-recourse financing to the lessor. Accordingly, upon occupancy, the Company commenced depreciating the portion of the building in service over a useful life of 30 years and incurred interest expense related to the financing obligation. As part of its adoption of ASC 842, the Company de-recognized the building asset and corresponding financing obligation recorded on the Company’s consolidated balance sheets as of January 1, 2019, in accordance with the ASC 842 transition guidance. In applying the ASC 842 transition guidance, the Company classified this lease as an operating lease and recorded a right-of-use asset of $6,697 and lease liability of $5,401 on the effective date. The Company is recognizing rent expense on a straight-line basis throughout the remaining term of the lease. Summary of all lease costs recognized under ASC 842 The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the three months ended March 31, 2019: Three Months Ended March 31, 2019 Lease cost (1) Operating lease cost $ 317 Total lease cost $ 317 Other Information Operating cash flows used for operating leases $ 247 Weighted average remaining lease term (in years) 7.5 Weighted average discount rate 12.0 % (1) Short-term lease costs and variable lease costs incurred by the Company for the three months ended March 31, 2019 were immaterial. As of March 31, 2019, future minimum commitments under ASC 842 under the Company’s operating leases were as follows: As of March 31, 2019 2019 (excluding the three months ended March 31, 2019) $ 750 2020 1,026 2021 1,058 2022 1,089 2023 1,122 2024 and thereafter 3,126 Total lease payments 8,171 Less: imputed interest (2,855 ) Total operating lease liabilities $ 5,316 As of December 31, 2018, future minimum commitments under ASC 840 under the Company’s operating leases were as follows: As of December 31, 2018 2019 $ 997 2020 1,026 2021 1,058 2022 1,089 2023 1,122 2024 and thereafter 3,126 Total lease payments 8,418 Intellectual Property Licenses Harvard and Dana-Farber Agreement In August 2006, the Company entered into an exclusive license agreement with President and Fellows of Harvard College (“Harvard”) and Dana-Farber Cancer Institute (“DFCI”). The agreement granted the Company an exclusive worldwide license, with the right to sublicense, under specified patents and patent applications to develop, obtain regulatory approval for and commercialize specified product candidates based on cell-permeating peptides. Under the agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize one or more licensed products and to achieve specified milestone events by specified dates. In connection with entering into the agreement, the Company paid an upfront license fee and issued to Harvard and DFCI shares of its common stock. In February 2010, the agreement was amended and restated (the “Harvard/DFCI agreement”) under which additional patent rights were added to the scope of the license agreement and the annual license maintenance fees were increased. Under the Harvard/DFCI agreement, the Company is obligated to make aggregate milestones payments of up to $7,700 per licensed therapeutic product upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to such product and up to $700 per licensed diagnostic product upon the Company’s achievement of specified regulatory and sales milestones with respect to such product. In addition, the Company is obligated to pay royalties of low single-digit percentages on annual net sales of licensed products sold by the Company, its affiliates or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis, and may be reduced in specified circumstances. In addition, the agreement obligates the Company to pay a percentage, up to the mid-twenties, of fees received by the Company in connection with its sublicense of the licensed products. In accordance with the terms of the agreement, the Company’s sublicense payment obligations may be subject to specified reductions. The Harvard/DFCI agreement requires the Company to pay annual license maintenance fees of $145 each year. Any payments made in connection with the annual license maintenance fees will be credited against any royalties due. The Company As of March 31, 2019, the Company had not developed a commercial product using the licensed technologies and no royalties under the agreement had been paid or were due. Under the Harvard/DFCI agreement, the Company is responsible for all patent expenses related to the prosecution and maintenance of the licensed patents and applications in-licensed under the agreement as well as cost reimbursement of amounts incurred for all documented patent-related expenses. The agreement will expire on a product-by-product and country-by-country basis upon the last to expire of any valid patent claim pertaining to licensed products covered under the agreement. Umicore Agreement In December 2006, the Company entered into a license agreement with Materia, Inc. (“Materia”), under which it was granted a non-exclusive worldwide license, with the right to sublicense, under specified patent and patent applications to utilize Materia’s catalysts to develop, obtain regulatory approval for and commercialize specified peptides owned or controlled by Materia and the right to manufacture specified compositions owned or controlled by Materia. In February 2017, Materia assigned the license agreement (the “Umicore agreement”) to Umicore Precious Metals Chemistry USA, LLC (“Umicore”), and Umicore agreed to continue to supply the Company under the agreement. Under the Umicore agreement, the Company is obligated to make aggregate milestone payments to Umicore of up to $6,400 upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to each licensed product. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis, and may be reduced in specified circumstances. The Umicore agreement requires the Company to pay annual license fees of $50. The Company incurred license fees of $50 during the three months ended March 31, 2019 and did not incur any license fees during the three months ended March 31, 2018. In addition, the Company did not make any milestone payments during the three months ended March 31, 2019 and 2018. As of March 31, 2019, no additional milestones had been achieved and no liabilities for additional milestone payments had been recorded in the Company’s financial statements. The agreement expires upon the expiration of the Company’s obligation to pay royalties in each territory covered under the agreement. Scripps Agreement In October 2010, the Company entered into a patent license agreement (the “Scripps agreement”) with The Scripps Research Institute (“Scripps”) under which it was granted a license, with the right to sublicense, for the exclusive worldwide rights to utilize Scripps’ “Click” chemistry for therapeutics and non-exclusive worldwide rights for diagnostics with the Company’s stabilized peptide and protein technology platforms. Under the agreement, the Company is obligated to make aggregate milestone payments to Scripps of up to $1,900 for each licensed peptide product and up to $950 for each licensed protein product upon achieving of specified clinical, regulatory and commercial milestones. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis. The Scripps agreement requires the Company to pay annual license fees of $50. The Company did not incur any license fees during the three months ended March 31, 2019 and 2018, respectively. As of March 31, 2019, no milestones had been achieved and no liabilities for milestone payments had been recorded in the Company’s financial statements. As of March 31, 2019, the Company had not developed a commercial product using the licensed technologies and no royalties under the agreement had been paid or were due. The agreement expires upon expiration of the last of any patent rights covered under the agreement. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it had not accrued any liabilities related to such obligations in its financial statements as of March 31, 2019 or December 31, 2018.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company did not provide for any income taxes for the three months ended March 31, 2019 and 2018. The Company has evaluated the positive and negative evidence bearing upon the realizability of its U.S. net deferred tax assets. As required by the provisions of ASC 740, Income Taxes, management has determined that it is more-likely-than-not that the Company will not utilize the benefits of federal and state U.S. net deferred tax assets for financial reporting purposes. Accordingly, the net deferred tax assets are subject to a valuation allowance at March 31, 2019 and December 31, 2018.

Subsequent Event

Subsequent Event	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Event	10. On March 28, 2019, the Company entered into a securities purchase agreement with accredited investors, pursuant to which it agreed to issue and sell to the investors in a private placement an aggregate of (i) 11,838,582 units, consisting of 11,838,582 shares of its common stock and associated common warrants to purchase an aggregate of 11,838,582 shares of common stock, for a combined price of $2.01 per unit and (ii) 1,096,741 units, consisting of pre-funded warrants to purchase 1,096,741 shares of the Company’s common stock and associated common warrants to purchase 1,096,741 shares of common stock, for a combined price of $2.01 per unit. The pre-funded warrants are exercisable at an exercise price of $0.01 per share and have no expiration. The common warrants are exercisable at an exercise price of $2.00 per share and expire five years from the date of issuance. On April 2, 2019, the Company closed the private placement and received aggregate gross proceeds of approximately $26,000, before deducting placement agent fees and offering expenses, and excluding the exercise of any warrants. The company paid placement agent fees of approximately $1,700.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of 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 financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of common stock and stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying unaudited condensed financial statements as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 have been prepared by the Company, pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 that was filed with the SEC on March 29, 2019. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2019, the results of its operations for the three months ended March 31, 2019 and 2018 and its cash flows for the three months ended March 31, 2019 and 2018. The financial data and other information disclosed in these notes related to the three months ended March 31, 2019 and 2018 are unaudited. The results for the three months ended March 31, 2019 are not necessarily indicative of results to be expected for the year ending December 31, 2019, any other interim periods, or any future year or period. The accompanying balance sheet as of December 31, 2018 has been derived from the Company’s audited financial statements for the year ended December 31, 2018 previously filed with the SEC.
Cash Equivalents	Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, corporate notes and commercial paper, are stated at fair value.
Restricted Cash	Restricted Cash As of March 31, 2019 and December 31, 2018, current restricted cash consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards. As of March 31, 2019 and December 31, 2018, non-current restricted cash consisted of $568 of cash deposited in a separate restricted bank account as a security deposit for
Investments	Investments The Company classifies its available-for-sale debt security investments as current assets on the balance sheet if they mature within one year from the balance sheet date. The Company classifies all of its investments as available-for-sale securities. The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities or using other inputs that are observable or can be corroborated by observable market data. Unrealized gains and losses on available-for-sale securities are reported as accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit). The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the statements of operations and comprehensive loss. The Company evaluates its investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. 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 and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.
Net Income (Loss) per Share	Net Income (Loss) per Share The Company follows the two-class method when computing net income (loss) per share as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options to purchase common stock are considered potential dilutive common shares.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements The Financial Accounting Standards Board (the “FASB”) issued ASU No. 2016-02, Leases The Company adopted the standard effective January 1, 2019. It has implemented the standard using the required modified retrospective approach and has also elected to utilize the package of practical expedients. The expedients used by the Company are as follows: (1) allowing an entity to not reassess the lease classification for any expired or existing leases, (2) allowing an entity to not reassess the treatment of initial direct costs as they related to existing leases, and (3) allowing an entity to not reassess whether expired or existing contracts are or contain leases. In using the modified retrospective approach, the Company is required to recognize and measure leases existing at, or entered into after, the beginning of the earliest comparative period presented. As a result of the adoption of ASU 2016-02, the Company de-recognized $7,079 of the building asset and $81 of accumulated depreciation related to its corporate headquarters at 490 Arsenal Way. Prior to the adoption of ASU 2016-02, the Company classified leasehold improvements associated with the 490 Arsenal Way building as building. Subsequent to the adoption of ASU 2016-02, the leasehold improvements associated with the 490 Arsenal Way building are classified as leasehold improvements. January 1, 2019 prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 as adjusted Operating lease right-of-use assets, net $ — $ 6,697 $ 6,697 Property and equipment, net 7,290 (6,998 ) $ 292 Construction financing liability 5,342 (5,342 ) $ — Other liabilities, current 3,639 (87 ) $ 3,552 Operating lease liabilities, current — 334 $ 334 Operating lease liabilities, net of current portion — 5,067 $ 5,067 Accumulated deficit (168,493 ) (273 ) $ (168,766 )
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements The Company does not expect any accounting standards that have been issued or proposed by the FASB or other standards setting bodies that would require adoption on a future date to have a material impact on the Company’s financial statements upon adoption.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2019
ASU No. 2016-02 [Member]
Schedule of Impact of Adoption of ASC 842	January 1, 2019 prior to ASC 842 Adoption ASC 842 Adjustment January 1, 2019 as adjusted Operating lease right-of-use assets, net $ — $ 6,697 $ 6,697 Property and equipment, net 7,290 (6,998 ) $ 292 Construction financing liability 5,342 (5,342 ) $ — Other liabilities, current 3,639 (87 ) $ 3,552 Operating lease liabilities, current — 334 $ 334 Operating lease liabilities, net of current portion — 5,067 $ 5,067 Accumulated deficit (168,493 ) (273 ) $ (168,766 )

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of March 31, 2019 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 6,020 $ — $ — $ 6,020 Commercial paper — 1,994 — 1,994 Corporate notes — 2,198 — 2,198 Investments: Commercial paper — 1,998 — 1,998 $ 6,020 $ 6,190 $ — $ 12,210 Fair Value Measurements as of December 31, 2018 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 6,041 $ — $ — $ 6,041 Corporate notes — 998 — 998 Commercial paper — 2,495 — 2,495 Investments: Corporate notes — 3,644 — 3,644 Commercial paper — 6,416 — 6,416 $ 6,041 $ 13,553 $ — $ 19,594

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Fair Value of Available for Sale Investments	As of March 31, 2019 and December 31, 2018, the fair value of available-for-sale investments by type of security was as follows: March 31, 2019 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial paper $ 1,998 $ — $ — $ 1,998 $ 1,998 $ — $ — $ 1,998 December 31, 2018 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate notes $ 3,646 $ — $ (2 ) $ 3,644 Commercial paper 6,418 — (2 ) 6,416 $ 10,064 $ — $ (4 ) $ 10,060

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: March 31, 2019 December 31, 2018 External research and development services 1,553 1,307 Payroll and payroll-related costs 820 1,473 Professional fees 716 436 Other 289 423 $ 3,378 $ 3,639

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Valuation Assumptions of Stock Options Granted	The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the three months ended March 31, 2019 and 2018 were as follows, presented on a weighted average basis: Three Months Ended March 31, 2019 Three Months Ended March 31, 2018 Risk-free interest rate 2.53 % 2.67 % Expected term (in years) 6.2 6.2 Expected volatility 76.0 % 76.0 % Expected dividend yield 0 % 0 %
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity since January 1, 2019: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding at December 31, 2018 2,528,297 $ 6.31 6.7 $ — Granted 100,000 1.47 Exercised (126,560 ) 1.30 Canceled (50,000 ) 5.37 Forfeited (5,250 ) 12.09 Outstanding at March 31, 2019 2,446,487 $ 6.37 6.8 $ 66 Options exercisable at March 31, 2019 1,185,803 $ 6.85 4.4 $ 18 Options vested and expected to vest at March 31, 2019 2,407,749 $ 6.85 4.4 $ 18 Options exercisable at December 31, 2018 1,214,016 $ 6.29 3.9 $ — Options vested and expected to vest at December 31, 2018 2,485,495 $ 6.31 6.6 $ —
Summary of Stock Based Compensation Expense	The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations and comprehensive loss: Three Months Ended March 31, 2019 2018 Research and development expenses $ 81 $ 270 General and administrative expenses 482 497 $ 563 $ 767

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows : Three Months Ended March 31, 2019 2018 Numerator: Net loss $ (7,213 ) $ (7,588 ) Denominator: Weighted average common shares outstanding—basic and diluted. 14,816,253 14,732,287 Net loss per share —basic and diluted $ (0.49 ) $ (0.52 )
Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share	The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2019 2018 Stock options to purchase common stock 2,446,487 2,175,668

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Summary of Lease Costs Recognized Under ASC 842 and Other Information Pertaining to Operating Leases	The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the three months ended March 31, 2019: Three Months Ended March 31, 2019 Lease cost (1) Operating lease cost $ 317 Total lease cost $ 317 Other Information Operating cash flows used for operating leases $ 247 Weighted average remaining lease term (in years) 7.5 Weighted average discount rate 12.0 % (1) Short-term lease costs and variable lease costs incurred by the Company for the three months ended March 31, 2019 were immaterial.
Future Minimum Commitments Under ASC 842 Under Operating Leases	As of March 31, 2019, future minimum commitments under ASC 842 under the Company’s operating leases were as follows: As of March 31, 2019 2019 (excluding the three months ended March 31, 2019) $ 750 2020 1,026 2021 1,058 2022 1,089 2023 1,122 2024 and thereafter 3,126 Total lease payments 8,171 Less: imputed interest (2,855 ) Total operating lease liabilities $ 5,316
Future Minimum Commitments Under ASC 840 Under Operating Leases	As of December 31, 2018, future minimum commitments under ASC 840 under the Company’s operating leases were as follows: As of December 31, 2018 2019 $ 997 2020 1,026 2021 1,058 2022 1,089 2023 1,122 2024 and thereafter 3,126 Total lease payments 8,418

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Apr. 02, 2019	Mar. 28, 2019	Mar. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Proceeds from collaboration agreement			$ 34,910
Cash, cash equivalents and investments			13,270
Accumulated deficit			(175,979)	$ (168,493)
Private Placement [Member]
Class Of Stock [Line Items]
Aggregate gross proceeds from private placement	$ 26,000
Placement agent fees	$ 1,700
Preferred Stock [Member]
Class Of Stock [Line Items]
Proceeds from sales of stock			131,211
Common Stock [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of initial public offering			$ 50,009
Common Stock [Member] | Private Placement [Member] | Purchase Agreement One [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased		11,838,582
Common Stock [Member] | Private Placement [Member] | Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Stock repurchase program, number of shares to be purchased		1,096,741
Stock Units [Member] | Private Placement [Member] | Purchase Agreement One [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares		11,838,582
Sale of stock, combined price per unit		$ 2.01
Stock Units [Member] | Private Placement [Member] | Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Issue and sale of aggregate shares		1,096,741
Sale of stock, combined price per unit		$ 2.01
Common Warrants [Member] | Private Placement [Member] | Purchase Agreement One [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants		11,838,582
Warrants exercisable, exercise price		$ 2
Warrants and Rights Outstanding, Term		5 years
Pre-funded Warrants [Member] | Private Placement [Member] | Purchase Agreement Two [Member]
Class Of Stock [Line Items]
Aggregate shares purchase for warrants		1,096,741
Warrants exercisable, exercise price		$ 0.01

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	$ 25	$ 25
Restricted cash, non-current	568	568
490 Arsenal Way [Member] | Operating Lease Agreements [Member] | ASU No. 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
De-recognized building asset	7,079
De-recognition of accumulated depreciation	81
Security Deposit Related to Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	25	25
Security Deposit Related to Lease Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, non-current	$ 568	$ 568

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Impact of Adoption of ASC 842 (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets, net	$ 6,543
Property and equipment, net	398		$ 7,290
Construction financing liability			5,342
Operating lease liabilities, current	387
Operating lease liabilities, net of current portion	4,929
Accumulated deficit	$ (175,979)		(168,493)
Prior to ASC 842 Adoption [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Property and equipment, net			7,290
Construction financing liability			5,342
Other liabilities, current			3,639
Accumulated deficit			$ (168,493)
ASU No. 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets, net		$ 6,697
Property and equipment, net		292
Other liabilities, current		3,552
Operating lease liabilities, current		334
Operating lease liabilities, net of current portion		5,067
Accumulated deficit		(168,766)
ASU No. 2016-02 [Member] | ASC 842 Adjustment [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Operating lease right-of-use assets, net		6,697
Property and equipment, net		(6,998)
Construction financing liability		(5,342)
Other liabilities, current		(87)
Operating lease liabilities, current		334
Operating lease liabilities, net of current portion		5,067
Accumulated deficit		$ (273)

Fair Value of Financial Asset_2

Fair Value of Financial Assets - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	$ 1,998	$ 10,060
Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,998	6,416
Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,644
Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	12,210	19,594
Recurring [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	6,020	6,041
Recurring [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	6,190	13,553
Recurring [Member] | Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,998	6,416
Recurring [Member] | Commercial Paper [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,998	6,416
Recurring [Member] | Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,644
Recurring [Member] | Corporate Notes [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,644
Recurring [Member] | Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	6,020	6,041
Recurring [Member] | Money Market Funds [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	6,020	6,041
Recurring [Member] | Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	1,994	2,495
Recurring [Member] | Commercial Paper [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	1,994	2,495
Recurring [Member] | Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	2,198	998
Recurring [Member] | Corporate Notes [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	$ 2,198	$ 998

Fair Value of Financial Asset_3

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Available-for-sale investments, maximum contractual maturity period	1 year
Fair value, assets transfers from Level 1 to Level 2	$ 0	$ 0
Fair value, assets transfers from Level 2 to Level 1	0	0
Fair Value, assets transfers into (out of) Level 3	$ 0	$ 0

Investments - Summary of Fair V

Investments - Summary of Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	$ 1,998	$ 10,064
Investments, Gross Unrealized Loss		(4)
Investments, Fair Value	1,998	10,060
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	1,998	6,418
Investments, Gross Unrealized Loss		(2)
Investments, Fair Value	$ 1,998	6,416
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost		3,646
Investments, Gross Unrealized Loss		(2)
Investments, Fair Value		$ 3,644

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
External research and development services	$ 1,553	$ 1,307
Payroll and payroll-related costs	820	1,473
Professional fees	716	436
Other	289	423
Total accrued expenses and other current liabilities	$ 3,378	$ 3,639

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Dec. 13, 2018	Dec. 06, 2017	Jun. 16, 2017	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted				100,000
Common stock, weighted average exercise price per share				$ 1.47
Weighted average grant-date fair value of stock options				$ 0.99	$ 6.17
Aggregate fair value of stock options vested				$ 509	$ 514
Aggregate intrinsic value of stock options exercised				$ 109	$ 83
Share based compensation expense estimated forfeiture rate				2.43%	2.43%
Aggregate unrecognized stock-based compensation expense				$ 4,711
Unrecognized stock-based compensation expense, weighted average period expects for recognition				2 years 3 months 18 days
2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period				4 years
Number of shares, available for grant				3,032,188
Number of shares remained available for grant				1,545,467
Stock reserved for future issuance				1,244,816
Maximum annual increase in common stock reserved for future issuance				1,244,816
Percentage of common stock shares outstanding				4.00%
Increase to shares authorized for issuance	589,939	588,953
Options granted				100,000
Common stock, weighted average exercise price per share				$ 1.47
2016 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period				4 years
Stock option expiration period				10 years
Number of shares issued				0
2016 Stock Incentive Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance				424,601
2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance			150,000			0
Maximum annual increase in common stock reserved for future issuance			622,408
Percentage of common stock shares outstanding			1.00%
Stock incentive plan description				On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. On December 13, 2018, the Company’s compensation committee of the board of directors determined not to increase the number of shares of common stock that may be issued under the 2017 ESPP.
2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period				4 years
Stock option expiration period				10 years
Number of shares issued				0
Stock incentive plan termination year				2016
Maximum [Member] | 2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period				4 years
Stock option expiration period				10 years
Maximum [Member] | 2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period				4 years

Stock-Based Awards - Valuation

Stock-Based Awards - Valuation Assumptions of Stock Options Granted (Detail)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	2.53%	2.67%
Expected term (in years)	6 years 2 months 12 days	6 years 2 months 12 days
Expected volatility	76.00%	76.00%
Expected dividend yield	0.00%	0.00%

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance	2,528,297
Number of Shares, Granted	100,000
Number of Shares, Exercised	(126,560)
Number of Shares, Canceled	(50,000)
Number of Shares, Forfeited	(5,250)
Number of Shares, Ending balance	2,446,487	2,528,297
Number of Shares, Options exercisable	1,185,803	1,214,016
Number of Shares, Options vested and expected to vest	2,407,749	2,485,495
Weighted Average Exercise Price, Beginning balance	$ 6.31
Weighted Average Exercise Price, Granted	1.47
Weighted Average Exercise Price, Exercised	1.30
Weighted Average Exercise Price,Canceled	5.37
Weighted Average Exercise Price, Forfeited	12.09
Weighted Average Exercise Price, Ending balance	6.37	$ 6.31
Weighted Average Exercise Price, Options exercisable	6.85	6.29
Weighted Average Exercise Price, Options vested and expected to vest	$ 6.85	$ 6.31
Weighted-Average Remaining Contractual Term, Outstanding	6 years 9 months 18 days	6 years 8 months 12 days
Weighted Average Remaining Contractual Term, Options exercisable	4 years 4 months 24 days	3 years 10 months 24 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	4 years 4 months 24 days	6 years 7 months 6 days
Aggregate Intrinsic Value	$ 66
Aggregate Intrinsic Value, Options exercisable	18
Aggregate Intrinsic Value, Options vested and expected to vest	$ 18

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 563	$ 767
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	81	270
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 482	$ 497

Net Loss per Share - Basic and

Net Loss per Share - Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net loss	$ (7,213)	$ (7,588)
Denominator:
Weighted average common shares outstanding—basic and diluted	14,816,253	14,732,287
Net loss per share —basic and diluted	$ (0.49)	$ (0.52)

Net Loss per Share - Summary of

Net Loss per Share - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	2,446,487	2,175,668

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Apr. 04, 2018USD ($)ft²$ / ft²	Oct. 31, 2010USD ($)	Feb. 28, 2010USD ($)	Mar. 31, 2019USD ($)OptionMilestone	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2006USD ($)
Other Commitments [Line Items]
Operating lease, right-of-use asset				$ 6,543,000
Operating lease, liability				$ 5,316,000
ASU No. 2016-02 [Member]
Other Commitments [Line Items]
Operating lease, right-of-use asset							$ 6,697,000
Operating lease, liability							$ 5,401,000
Operating Lease Agreements [Member] | Building [Member]
Other Commitments [Line Items]
Lessee, Operating Lease, Existence of Option to Extend [true false]				true
Lessee Operating Lease Option To Extend				The Company has the option to extend the 490 Arsenal Way Lease for one five-year terms.
Harvard and Dana-Farber Agreement [Member]
Other Commitments [Line Items]
Milestone payments				$ 0	$ 0
Milestones achieved | Milestone				0
Additional liabilities for milestone payments				$ 0
Non-refundable cash payment				4,718,000		$ 4,573,000
Payments for royalties				0
Harvard and Dana-Farber Agreement [Member] | Therapeutic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments			$ 7,700,000
Harvard and Dana-Farber Agreement [Member] | Diagnostic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments			700,000
Harvard and Dana-Farber Agreement [Member] | License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees			$ 145,000
Harvard and Dana-Farber Agreement [Member] | License [Member]
Other Commitments [Line Items]
Annual license maintenance fees				145,000	145,000
Umicore Agreement [Member]
Other Commitments [Line Items]
Aggregate milestones payments								$ 6,400,000
Milestone payments				$ 0	0
Milestones achieved | Milestone				0
Additional liabilities for milestone payments				$ 0
Umicore Agreement [Member] | License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees				50,000
Umicore Agreement [Member] | License [Member]
Other Commitments [Line Items]
Annual license maintenance fees				$ 50,000	0
Scripps Agreement [Member]
Other Commitments [Line Items]
Milestones achieved | Milestone				0
Additional liabilities for milestone payments				$ 0
Payments for royalties				0
Scripps Agreement [Member] | License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees		$ 50,000
Scripps Agreement [Member] | License [Member]
Other Commitments [Line Items]
Annual license maintenance fees				$ 0	$ 0
Scripps Agreement [Member] | Peptide Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments		1,900,000
Scripps Agreement [Member] | Protein Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments		$ 950,000
Watertown, Massachusetts [Member] | Operating Lease Agreements [Member] | 490 Arsenal Way [Member] | Building [Member]
Other Commitments [Line Items]
Area of Land | ft²	18,768
Operating lease price per square foot per year | $ / ft²	52.55
Base rent per year	$ 986,000
Security deposit	568,000
Cost of construction and tenant improvements	$ 2,419,000
Period of contract				Aug. 31, 2026
Number of option to extend | Option				1
Lease initial term				8 years
Lease extension term				5 years
Building in service over a useful life				30 years

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Lease Costs Recognized Under ASC 842 and Other Information Pertaining to Operating Leases (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Lease cost
Operating lease cost	$ 317	[1]
Total lease cost	317	[1]
Other Information
Operating cash flows used for operating leases	$ 247
Weighted average remaining lease term (in years)	7 years 6 months
Weighted average discount rate	12.00%
[1]	Short-term lease costs and variable lease costs incurred by the Company for the three months ended March 31, 2019 were immaterial.

Commitments and Contingencies_3

Commitments and Contingencies - Future Minimum Commitments Under ASC 842 Under Operating Leases (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019 (excluding the three months ended March 31, 2019)	$ 750
2020	1,026
2021	1,058
2022	1,089
2023	1,122
2024 and thereafter	3,126
Total lease payments	8,171
Less: imputed interest	(2,855)
Total operating lease liabilities	$ 5,316

Commitments and Contingencies_4

Commitments and Contingencies - Future Minimum Commitments Under ASC 840 Under Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 997
2020	1,026
2021	1,058
2022	1,089
2023	1,122
2024 and thereafter	3,126
Total lease payments	$ 8,418

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Private Placement [Member] - USD ($) $ / shares in Units, $ in Thousands	Apr. 02, 2019	Mar. 28, 2019
Subsequent Event [Line Items]
Aggregate gross proceeds from private placement	$ 26,000
Placement agent fees	$ 1,700
Stock Units [Member] | Purchase Agreement One [Member]
Subsequent Event [Line Items]
Issue and sale of aggregate shares		11,838,582
Sale of stock, combined price per unit		$ 2.01
Stock Units [Member] | Purchase Agreement Two [Member]
Subsequent Event [Line Items]
Issue and sale of aggregate shares		1,096,741
Sale of stock, combined price per unit		$ 2.01
Common Warrants [Member] | Purchase Agreement One [Member]
Subsequent Event [Line Items]
Aggregate shares purchase for warrants		11,838,582
Warrants exercisable, exercise price		$ 2
Warrants and Rights Outstanding, Term		5 years
Common Stock [Member] | Purchase Agreement One [Member]
Subsequent Event [Line Items]
Stock repurchase program, number of shares to be purchased		11,838,582
Common Stock [Member] | Purchase Agreement Two [Member]
Subsequent Event [Line Items]
Stock repurchase program, number of shares to be purchased		1,096,741
Pre-funded Warrants [Member] | Purchase Agreement Two [Member]
Subsequent Event [Line Items]
Aggregate shares purchase for warrants		1,096,741
Warrants exercisable, exercise price		$ 0.01