Summary of Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented.
Principles of Consolidation	Principles of Consolidation During 2017, the Company established a wholly-owned subsidiary in Australia. The consolidated financial statements include the Company’s accounts and those of its wholly-owned subsidiary. All intercompany accounts, transactions and balances have been eliminated.
Reverse Stock Split	Reverse Stock Split On March 9, 2018, the Company effected a reverse split of all shares of its common and preferred stock at a ratio of 1-for-3.96 (the Reverse Split). The par values and the authorized shares of the common and preferred stock were not adjusted as a result of the Reverse Split. All references to shares of common stock outstanding, average number of shares outstanding and per share amounts in these consolidated financial statements and notes to the consolidated financial statements have been adjusted within the consolidated financial statements, on a retroactive basis, to reflect the Reverse Split.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, as well as related disclosure of contingent assets and liabilities. Estimates were used to determine the fair value of common stock prior to the IPO and are used to determine stock-based awards and other issuances, accruals for research and development costs, useful lives of long-lived assets, and uncertain tax positions. Actual results could differ materially from the Company’s estimates.
Risks And Uncertainties	Risk and Uncertainties The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential drug candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers. The Company’s product candidates require approvals from the U.S. Food and Drug Administration (FDA) and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company does not obtain approval and does not successfully commercialize any of its product candidates, it would have a materially adverse impact on the Company.
Segments	Segments The Company operates and manages its business as one reportable and operating segment, which is the business of developing and commercializing immunotherapies. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America.
Cash Equivalents, Short-Term and Long-Term Investments	Cash Equivalents, Short-Term and Long-Term Investments Cash equivalents include marketable securities having an original maturity of three months or less at the time of purchase. Short-term investments have maturities of greater than three months at the time of purchase. Long-term investments have maturities greater than 12 months at the time of purchase. Collectively, cash equivalents, short-term and long-term investments are considered available-for-sale and are recorded at fair value. Unrealized gains and losses are recorded in accumulated other comprehensive loss. Realized gains and losses are included in interest and other income, net in the consolidated statements of operations and comprehensive loss. The basis on which the cost of a security sold or amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method.
Restricted Cash	Restricted Cash Restricted cash at December 31, 2018 and 2017 comprises cash balances primarily held as security in connection with the Company’s facility lease agreement and is included in long-term assets in the consolidated balance sheets.
Receivable From a Related Party	Receivable From a Related Party Receivable from a related party is recorded net of any allowances. As of December 31, 2018 and 2017, the outstanding amount is due from PACT Pharma, Inc. (PACT Pharma) for expenses the Company paid for on its behalf. The Company is exposed to credit risk in the event of a default by PACT Pharma. To date, the Company has not experienced any losses related to these receivables (see Note 5) and has not recorded any allowances.
Fair Value Measurements	Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities, including short-term and long-term investments, and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including receivable from a related party, accounts payable and accrued expenses and other current liabilities approximate fair value due to their short-term maturities.
Concentration of Credit Risk	Concentration of Credit Risk Cash equivalents, short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company invests in money market funds, treasury bills and notes, government bonds, commercial paper and corporate notes. The Company limits its credit risk associated with cash equivalents, short-term and long-term investments by placing them with banks and institutions it believes are highly credit worthy and in highly rated investments.
Property and Equipment	Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from one to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive loss.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment charge would be recorded when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is assessed using discounted cash flows or other appropriate measures of fair value. The Company did not recognize any impairment charges for the years ended December 31, 2018 and 2017.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs associated with the Company’s IPO, consisting of legal, accounting, filing and other fees directly related to the IPO, were capitalized. The deferred offering costs, which totaled $3.6 million, were reclassified to additional paid-in capital upon the effectiveness of the IPO in March 2018. As of December 31, 2017, $1.3 million of deferred offering costs were capitalized and included in other long-term assets in the consolidated balance sheet.
Revenue Recognition	Revenue Recognition The Company generates revenue from its option and license agreement for the development and commercialization of its product candidates. Option and license agreements may include non-refundable upfront research and development fees, option fees to obtain development and commercialization licenses for the Company’s products, milestone payments based on achievement of defined development, regulatory and sales targets, and royalties on sales of commercialized products. To date, the Company has not recognized revenue from sales of its product candidates. The Company recognizes revenue when all four of the following criteria have been met: (i) collectability is reasonably assured; (ii) delivery has occurred or services have been rendered; (iii) persuasive evidence of an arrangement exists; and (iv) the fee is fixed or determinable. Revenue under option and license arrangements is recognized based on evaluation of the performance obligations of the contract. Collectability is assessed based on evaluation of payment criteria as stated in the contract as well as the creditworthiness of the customer. Determination of whether delivery has occurred, or services rendered are based on management’s evaluation of the performance obligations as stated in the contract and progress made against those obligations. Evidence of an arrangement is deemed to exist upon execution of the contract. Fees are considered fixed and determinable when the amount payable to the Company is no longer subject to any acceptance, refund rights or other contingencies that would alter the fixed nature of the fees charged for the deliverables. Option and license agreements may contain multiple elements as evaluated under Accounting Standards Codification (ASC) 605-25, Revenue Recognition- Multiple-Element Arrangements, including agreements to provide research and development services, participation in development and/or steering committees, manufacturing services, sharing of know-how and other information, and grants of licenses to develop and commercialize product candidates. Each deliverable under the agreement is evaluated to determine whether it qualifies as a separate unit of accounting based on whether the deliverable has standalone value to the customer. The arrangement’s consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the following hierarchy: (i) vendor-specific objective evidence of the fair value of the deliverable, if it exists; (ii) third-party evidence of selling price, if vendor-specific objective evidence is not available; or (iii) the best estimate of selling price if neither vendor-specific objective evidence or third-party evidence is available. A delivered item or items that do not qualify as a separate unit of accounting within the arrangement are combined with the other applicable undelivered items within the arrangement. The allocation of arrangement consideration and the recognition of revenue is then determined for those combined deliverables as a single unit of accounting. For a combined unit of accounting, non-refundable upfront fees are recognized as performance obligations related to the final deliverable are completed. In the case of research and development services, performance would generally be expected to be ratable over the estimated performance period unless the Company determines there is a discernible pattern of performance other than straight-line, in which case the Company uses a proportionate performance method to recognize the revenue over the estimated performance period. Amounts received in advance of performance are recorded as deferred revenue. If any of the initial deliverables are determined to have standalone value separate from the research and development services, then the allocated consideration is recorded as revenue when those items are delivered. Options to acquire development and commercialization licenses of the Company’s products are evaluated to determine if they are substantive. Fees for substantive options are recognized as revenue when an option is exercised by the collaboration partner and the Company has completed the deliverables that are associated with exercise of such option. Option and license agreements may also contain milestone payments that become due upon the achievement of certain milestones. The Company applies ASC 605-28, Revenue Recognition—Milestone Method. Under the milestone method, payments that are contingent upon achievement of a substantive milestone are recognized in the period in which the milestone is achieved. Milestones are defined as an event that can only be achieved based on the Company’s performance and there is substantive uncertainty about whether the event will be achieved at the inception of the arrangement. Events that are contingent only on the passage of time or only on counterparty performance are not considered milestones subject to this guidance. Further, for the milestone to be considered substantive, the amounts received must relate solely to prior performance, be reasonable relative to all of the deliverables, and the consideration must be commensurate with the Company’s performance to achieve the milestone. Non-substantive milestone payments are recognized as revenue over the estimated period of any remaining performance obligations.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist primarily of personnel costs for the Company’s research and product development employees. Also included are non-personnel costs such as professional fees payable to third parties for preclinical and clinical studies and research services, laboratory supplies and equipment maintenance, product licenses, and other consulting costs. The Company estimates preclinical and clinical study and research expenses based on the services performed, pursuant to contracts with research institutions that conduct and manage preclinical and clinical studies and research services on its behalf. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternative future use are expensed as incurred. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered.
Leases and Rent Expense	Leases and Rent Expense The Company records rent expense on a straight-line basis over the life of the lease. In cases where there is a free rent period or future fixed rent escalations, the Company records a deferred rent liability. Additionally, the receipt of any lease incentives is recorded as a deferred rent liability which is amortized over the lease term as a reduction of rent expense. Any lease incentives that are due from the landlord but have not been collected are recorded as a receivable in Prepaid expenses and other current assets. Building improvements made with the lease incentives or tenant allowances are capitalized as leasehold improvements and included in property and equipment in the consolidated balance sheets.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees in accordance with ASC 718, Stock Compensation. Stock-based awards granted include stock options with time-based vesting. ASC 718 requires the recognition of compensation expense, using a fair value-based method, for costs related to all stock-based payments. The Company’s determination of the fair value of stock options with time-based vesting on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by its common stock price as well as other variables including, but not limited to, expected term that options will remain outstanding, expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends. The fair value of a stock-based award is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period) on a straight-line basis. Stock-based compensation expense is recognized based on the fair value determined on the date of grant and is reduced for forfeitures as they occur. Equity instruments issued to non-employees are accounted for in accordance with ASC 505-50, Equity Based Payments to Non-Employees, and are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The fair value of options granted to consultants is expensed when vested. Non-employee stock-based compensation expense was not material for all periods presented. Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop.
Convertible Preferred Stock	Convertible Preferred Stock The Company records all shares of convertible preferred stock at their respective fair values less issuance costs on the dates of issuance. The convertible preferred stock is recorded outside of stockholders’ equity (deficit) because, in the event of certain deemed liquidation events considered not solely within the Company’s control, such as a merger, acquisition and sale of all or substantially all of the Company’s assets, the convertible preferred stock will become redeemable at the option of the holders. In the event of a change of control of the Company, proceeds received from the sale of such shares will be distributed in accordance with the liquidation preferences set forth in the Company’s Amended and Restated Certificate of Incorporation unless the holders of convertible preferred stock have converted their shares of convertible preferred stock into shares of common stock. The Company has determined not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. All of outstanding convertible preferred stock converted into common stock in March 2018 upon the effectiveness of the IPO.
Income Taxes	Income Taxes The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax bases of assets and liabilities and net operating loss and credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. Assessing an uncertain tax position begins with the initial determination of the position’s sustainability and is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit might change as new information becomes available. The Company includes any penalties and interest expense related to income taxes as a component of other expense and interest expense, net, as necessary.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner sources. The Company had unrealized loss from its available-for-sale securities during the years ended December 31, 2018, 2017 and 2016, which meets the criteria as other comprehensive loss and, therefore, the Company has reported comprehensive loss and net loss.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, convertible preferred stock, and common stock options are considered to be potentially dilutive securities. Because the Company reported a net loss for the years ended December 31, 2018, 2017 and 2016, and the inclusion of the potentially dilutive securities would be antidilutive, diluted net loss per share is the same as basic net loss per share for all periods.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the JOBS Act), the Company meets the definition of an emerging growth company, and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. The Company did not adopt any new accounting standards during 2018.
Recently Issued Accounting Standards or Updates Not Yet Effective	Recently Issued Accounting Standards or Updates Not Yet Effective In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09). The FASB issued numerous updates that provide clarification on a number of specific issues as well as requiring additional disclosures. Collectively, the new revenue standards became effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2014-09 will be effective for the Company for the year ended December 31, 2019, and all interim periods thereafter. Early adoption is permitted. ASU 2014-09 also permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). The core principle of ASU 2014-09 is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than required under existing U.S. generally accepted accounting pronouncements. The Company has substantially completed its evaluation related to the adoption of ASU 2014-09, applying the five-step model of the new standard to the option and license agreement with Taiho Pharmaceutical Co., Ltd. (Taiho), the only agreement which will be impacted by the adoption of the new standard, specifically as it pertains to the non-refundable, non-creditable upfront cash payments to the Company totaling $35.0 million, the option exercise payment of $3.0 million and all other future contingent payments the Company may become entitled to. The Company will finalize its accounting assessment and quantitative impact of the adoption during the first quarter of fiscal year 2019, using the modified retrospective method, which will reflect the cumulative effect of the adoption retrospectively as of January 1, 2019, the initial date of adoption. In January 2016, the FASB issued ASU No. 2016-01 (Subtopic 825-10), Financial Instruments (ASU 2016-01). ASU 2016-01 requires management to measure marketable investments at fair value with changes in fair value recognized in net income or loss. ASU 2016-01 will impact the disclosure and presentation of financial assets and liabilities. ASU 2016-01 was effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2016-01 will be effective for the Company as of December 31, 2019, and all interim periods within. Early adoption is not permitted. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases (ASU 2016-02). ASU 2016-02 requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. For public entities, ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2016-02 is effective for the Company for the year ended December 31, 2020, and all interim periods within. Early adoption is permitted. The Company has not yet determined the potential effects of this ASU on its consolidated financial statements. In November 2016, the FASB issued ASU No. 2016-18 (Topic 230), Restricted Cash, Statement of Cash Flows (ASU 2016-18). ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash and, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the consolidated statement of cash flows. ASU 2016-18 was effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2016-18 will be effective for the Company for the year ended December 31, 2019, and all interim periods thereafter. Early adoption is permitted. The amendments in this ASU should be applied using a retrospective transition method to each period presented. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements. In June 2018, the FASB issued ASU No. 2018-07 (Topic 718), Compensation – Stock Compensation (ASU 2018-07). ASU 2018-07 requires an entity to expand the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. For public entities, ASU 2018-07 is effective for fiscal years beginning after December 15, 2018. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2018-07 is effective for the Company for the year ended December 31, 2020, and all interim periods within. Early adoption is permitted. The Company has not yet determined the potential effects of this ASU on its consolidated financial statements. In August 2018, the FASB issued ASU No.2018-13 (Topic 820), Fair Value Measurement. ASU 2018-13 modifies the disclosure requirements on fair value measurement in Topic 820. For public entities, ASU 2018-013 is effective for fiscal years beginning after December 15, 2019. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2018-13 is effective for the Company for the year ended December 31, 2020, and all interim periods within. Early adoption is permitted. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented.

Principles of Consolidation

During 2017, the Company established a wholly-owned subsidiary in Australia. The consolidated financial statements include the Company’s accounts and those of its wholly-owned subsidiary. All intercompany accounts, transactions and balances have been eliminated.

Reverse Stock Split

On March 9, 2018, the Company effected a reverse split of all shares of its common and preferred stock at a ratio of 1-for-3.96 (the Reverse Split). The par values and the authorized shares of the common and preferred stock were not adjusted as a result of the Reverse Split. All references to shares of common stock outstanding, average number of shares outstanding and per share amounts in these consolidated financial statements and notes to the consolidated financial statements have been adjusted within the consolidated financial statements, on a retroactive basis, to reflect the Reverse Split.

Use of Estimates

The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, as well as related disclosure of contingent assets and liabilities. Estimates were used to determine the fair value of common stock prior to the IPO and are used to determine stock-based awards and other issuances, accruals for research and development costs, useful lives of long-lived assets, and uncertain tax positions. Actual results could differ materially from the Company’s estimates.

Risks And Uncertainties

Risk and Uncertainties

The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s potential drug candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers.

The Company’s product candidates require approvals from the U.S. Food and Drug Administration (FDA) and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company does not obtain approval and does not successfully commercialize any of its product candidates, it would have a materially adverse impact on the Company.

Segments

The Company operates and manages its business as one reportable and operating segment, which is the business of developing and commercializing immunotherapies. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America.

Cash Equivalents, Short-Term and Long-Term Investments

Cash equivalents include marketable securities having an original maturity of three months or less at the time of purchase. Short-term investments have maturities of greater than three months at the time of purchase. Long-term investments have maturities greater than 12 months at the time of purchase. Collectively, cash equivalents, short-term and long-term investments are considered available-for-sale and are recorded at fair value. Unrealized gains and losses are recorded in accumulated other comprehensive loss. Realized gains and losses are included in interest and other income, net in the consolidated statements of operations and comprehensive loss. The basis on which the cost of a security sold or amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method.

Restricted Cash

Restricted cash at December 31, 2018 and 2017 comprises cash balances primarily held as security in connection with the Company’s facility lease agreement and is included in long-term assets in the consolidated balance sheets.

Receivable From a Related Party

Receivable from a related party is recorded net of any allowances. As of December 31, 2018 and 2017, the outstanding amount is due from PACT Pharma, Inc. (PACT Pharma) for expenses the Company paid for on its behalf. The Company is exposed to credit risk in the event of a default by PACT Pharma. To date, the Company has not experienced any losses related to these receivables (see Note 5) and has not recorded any allowances.

Fair Value Measurements

Fair value accounting is applied for all financial assets and liabilities, including short-term and long-term investments, and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including receivable from a related party, accounts payable and accrued expenses and other current liabilities approximate fair value due to their short-term maturities.

Concentration of Credit Risk

Cash equivalents, short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company invests in money market funds, treasury bills and notes, government bonds, commercial paper and corporate notes. The Company limits its credit risk associated with cash equivalents, short-term and long-term investments by placing them with banks and institutions it believes are highly credit worthy and in highly rated investments.

Property and Equipment

Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from one to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive loss.

Impairment of Long-Lived Assets

The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment charge would be recorded when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is assessed using discounted cash flows or other appropriate measures of fair value. The Company did not recognize any impairment charges for the years ended December 31, 2018 and 2017.

Deferred Offering Costs

Deferred offering costs associated with the Company’s IPO, consisting of legal, accounting, filing and other fees directly related to the IPO, were capitalized. The deferred offering costs, which totaled $3.6 million, were reclassified to additional paid-in capital upon the effectiveness of the IPO in March 2018. As of December 31, 2017, $1.3 million of deferred offering costs were capitalized and included in other long-term assets in the consolidated balance sheet.

Revenue Recognition

The Company generates revenue from its option and license agreement for the development and commercialization of its product candidates. Option and license agreements may include non-refundable upfront research and development fees, option fees to obtain development and commercialization licenses for the Company’s products, milestone payments based on achievement of defined development, regulatory and sales targets, and royalties on sales of commercialized products. To date, the Company has not recognized revenue from sales of its product candidates.

The Company recognizes revenue when all four of the following criteria have been met: (i) collectability is reasonably assured; (ii) delivery has occurred or services have been rendered; (iii) persuasive evidence of an arrangement exists; and (iv) the fee is fixed or determinable. Revenue under option and license arrangements is recognized based on evaluation of the performance obligations of the contract. Collectability is assessed based on evaluation of payment criteria as stated in the contract as well as the creditworthiness of the customer. Determination of whether delivery has occurred, or services rendered are based on management’s evaluation of the performance obligations as stated in the contract and progress made against those obligations. Evidence of an arrangement is deemed to exist upon execution of the contract. Fees are considered fixed and determinable when the amount payable to the Company is no longer subject to any acceptance, refund rights or other contingencies that would alter the fixed nature of the fees charged for the deliverables.

Option and license agreements may contain multiple elements as evaluated under Accounting Standards Codification (ASC) 605-25, Revenue Recognition- Multiple-Element Arrangements, including agreements to provide research and development services, participation in development and/or steering committees, manufacturing services, sharing of know-how and other information, and grants of licenses to develop and commercialize product candidates. Each deliverable under the agreement is evaluated to determine whether it qualifies as a separate unit of accounting based on whether the deliverable has standalone value to the customer. The arrangement’s consideration that is fixed or determinable is then allocated to each separate unit of accounting based on the following hierarchy: (i) vendor-specific objective evidence of the fair value of the deliverable, if it exists; (ii) third-party evidence of selling price, if vendor-specific objective evidence is not available; or (iii) the best estimate of selling price if neither vendor-specific objective evidence or third-party evidence is available.

A delivered item or items that do not qualify as a separate unit of accounting within the arrangement are combined with the other applicable undelivered items within the arrangement. The allocation of arrangement consideration and the recognition of revenue is then determined for those combined deliverables as a single unit of accounting. For a combined unit of accounting, non-refundable upfront fees are recognized as performance obligations related to the final deliverable are completed. In the case of research and development services, performance would generally be expected to be ratable over the estimated performance period unless the Company determines there is a discernible pattern of performance other than straight-line, in which case the Company uses a proportionate performance method to recognize the revenue over the estimated performance period. Amounts received in advance of performance are recorded as deferred revenue. If any of the initial deliverables are determined to have standalone value separate from the research and development services, then the allocated consideration is recorded as revenue when those items are delivered.

Options to acquire development and commercialization licenses of the Company’s products are evaluated to determine if they are substantive. Fees for substantive options are recognized as revenue when an option is exercised by the collaboration partner and the Company has completed the deliverables that are associated with exercise of such option.

Option and license agreements may also contain milestone payments that become due upon the achievement of certain milestones. The Company applies ASC 605-28, Revenue Recognition—Milestone Method. Under the milestone method, payments that are contingent upon achievement of a substantive milestone are recognized in the period in which the milestone is achieved. Milestones are defined as an event that can only be achieved based on the Company’s performance and there is substantive uncertainty about whether the event will be achieved at the inception of the arrangement. Events that are contingent only on the passage of time or only on counterparty performance are not considered milestones subject to this guidance. Further, for the milestone to be considered substantive, the amounts received must relate solely to prior performance, be reasonable relative to all of the deliverables, and the consideration must be commensurate with the Company’s performance to achieve the milestone. Non-substantive milestone payments are recognized as revenue over the estimated period of any remaining performance obligations.

Research and Development Expenses

Research and development costs are expensed as incurred. Research and development expenses consist primarily of personnel costs for the Company’s research and product development employees. Also included are non-personnel costs such as professional fees payable to third parties for preclinical and clinical studies and research services, laboratory supplies and equipment maintenance, product licenses, and other consulting costs.

The Company estimates preclinical and clinical study and research expenses based on the services performed, pursuant to contracts with research institutions that conduct and manage preclinical and clinical studies and research services on its behalf. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternative future use are expensed as incurred. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered.

Leases and Rent Expense

The Company records rent expense on a straight-line basis over the life of the lease. In cases where there is a free rent period or future fixed rent escalations, the Company records a deferred rent liability. Additionally, the receipt of any lease incentives is recorded as a deferred rent liability which is amortized over the lease term as a reduction of rent expense. Any lease incentives that are due from the landlord but have not been collected are recorded as a receivable in Prepaid expenses and other current assets. Building improvements made with the lease incentives or tenant allowances are capitalized as leasehold improvements and included in property and equipment in the consolidated balance sheets.

Stock-Based Compensation

The Company accounts for stock-based compensation arrangements with employees in accordance with ASC 718, Stock Compensation. Stock-based awards granted include stock options with time-based vesting. ASC 718 requires the recognition of compensation expense, using a fair value-based method, for costs related to all stock-based payments. The Company’s determination of the fair value of stock options with time-based vesting on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by its common stock price as well as other variables including, but not limited to, expected term that options will remain outstanding, expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends.

The fair value of a stock-based award is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period) on a straight-line basis. Stock-based compensation expense is recognized based on the fair value determined on the date of grant and is reduced for forfeitures as they occur.

Equity instruments issued to non-employees are accounted for in accordance with ASC 505-50, Equity Based Payments to Non-Employees, and are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The fair value of options granted to consultants is expensed when vested. Non-employee stock-based compensation expense was not material for all periods presented.

Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop.

Convertible Preferred Stock

The Company records all shares of convertible preferred stock at their respective fair values less issuance costs on the dates of issuance. The convertible preferred stock is recorded outside of stockholders’ equity (deficit) because, in the event of certain deemed liquidation events considered not solely within the Company’s control, such as a merger, acquisition and sale of all or substantially all of the Company’s assets, the convertible preferred stock will become redeemable at the option of the holders. In the event of a change of control of the Company, proceeds received from the sale of such shares will be distributed in accordance with the liquidation preferences set forth in the Company’s Amended and Restated Certificate of Incorporation unless the holders of convertible preferred stock have converted their shares of convertible preferred stock into shares of common stock. The Company has determined not to adjust the carrying values of the convertible preferred stock to the liquidation preferences of such shares because of the uncertainty of whether or when such an event would occur. All of outstanding convertible preferred stock converted into common stock in March 2018 upon the effectiveness of the IPO.

Income Taxes

The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax bases of assets and liabilities and net operating loss and credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized.

The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. Assessing an uncertain tax position begins with the initial determination of the position’s sustainability and is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit might change as new information becomes available.

The Company includes any penalties and interest expense related to income taxes as a component of other expense and interest expense, net, as necessary.

Comprehensive Loss

Comprehensive loss is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner sources. The Company had unrealized loss from its available-for-sale securities during the years ended December 31, 2018, 2017 and 2016, which meets the criteria as other comprehensive loss and, therefore, the Company has reported comprehensive loss and net loss.

Net Loss per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, convertible preferred stock, and common stock options are considered to be potentially dilutive securities. Because the Company reported a net loss for the years ended December 31, 2018, 2017 and 2016, and the inclusion of the potentially dilutive securities would be antidilutive, diluted net loss per share is the same as basic net loss per share for all periods.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s consolidated financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended (the JOBS Act), the Company meets the definition of an emerging growth company, and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. The Company did not adopt any new accounting standards during 2018.

Recently Issued Accounting Standards or Updates Not Yet Effective

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09). The FASB issued numerous updates that provide clarification on a number of specific issues as well as requiring additional disclosures. Collectively, the new revenue standards became effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2014-09 will be effective for the Company for the year ended December 31, 2019, and all interim periods thereafter. Early adoption is permitted. ASU 2014-09 also permits two methods of adoption: retrospectively to each prior reporting period presented (full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method).

The core principle of ASU 2014-09 is that an entity should recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than required under existing U.S. generally accepted accounting pronouncements. The Company has substantially completed its evaluation related to the adoption of ASU 2014-09, applying the five-step model of the new standard to the option and license agreement with Taiho Pharmaceutical Co., Ltd. (Taiho), the only agreement which will be impacted by the adoption of the new standard, specifically as it pertains to the non-refundable, non-creditable upfront cash payments to the Company totaling $35.0 million, the option exercise payment of $3.0 million and all other future contingent payments the Company may become entitled to. The Company will finalize its accounting assessment and quantitative impact of the adoption during the first quarter of fiscal year 2019, using the modified retrospective method, which will reflect the cumulative effect of the adoption retrospectively as of January 1, 2019, the initial date of adoption.

In January 2016, the FASB issued ASU No. 2016-01 (Subtopic 825-10), Financial Instruments (ASU 2016-01). ASU 2016-01 requires management to measure marketable investments at fair value with changes in fair value recognized in net income or loss. ASU 2016-01 will impact the disclosure and presentation of financial assets and liabilities. ASU 2016-01 was effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2016-01 will be effective for the Company as of December 31, 2019, and all interim periods within. Early adoption is not permitted. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.

In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases (ASU 2016-02). ASU 2016-02 requires an entity to recognize assets and liabilities arising from a lease for both financing and operating leases. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. For public entities, ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2016-02 is effective for the Company for the year ended December 31, 2020, and all interim periods within. Early adoption is permitted. The Company has not yet determined the potential effects of this ASU on its consolidated financial statements.

In November 2016, the FASB issued ASU No. 2016-18 (Topic 230), Restricted Cash, Statement of Cash Flows (ASU 2016-18). ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash and, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the consolidated statement of cash flows. ASU 2016-18 was effective for public business entities for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2016-18 will be effective for the Company for the year ended December 31, 2019, and all interim periods thereafter. Early adoption is permitted. The amendments in this ASU should be applied using a retrospective transition method to each period presented. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.

In June 2018, the FASB issued ASU No. 2018-07 (Topic 718), Compensation – Stock Compensation (ASU 2018-07). ASU 2018-07 requires an entity to expand the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. For public entities, ASU 2018-07 is effective for fiscal years beginning after December 15, 2018. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2018-07 is effective for the Company for the year ended December 31, 2020, and all interim periods within. Early adoption is permitted. The Company has not yet determined the potential effects of this ASU on its consolidated financial statements.

In August 2018, the FASB issued ASU No.2018-13 (Topic 820), Fair Value Measurement. ASU 2018-13 modifies the disclosure requirements on fair value measurement in Topic 820. For public entities, ASU 2018-013 is effective for fiscal years beginning after December 15, 2019. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2018-13 is effective for the Company for the year ended December 31, 2020, and all interim periods within. Early adoption is permitted. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.