ORGANIZATION, BASIS OF PRESENTATION, AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying financial statements have been prepared in conformity with the authoritative U.S. generally accepted accounting principles (“GAAP”).
Use of Estimates	Use of Estimates The preparation of the financial statements in accordance with GAAP requires management to make certain estimates and judgments that affect the reported amounts of assets, liabilities, revenue recognition, and expenses. Actual results could differ materially from those estimates.
Revenue Recognition, Licenses and Patents	Revenue Recognition The Company’s sources of revenue in 2019 have been from its licensing agreement with The University of Texas MD Anderson Cancer Center, (“MD Anderson”) and from grants. Prior to 2019, the Company's only source of revenue was from grants. Grant Revenue When grant funds are received after costs have been incurred, the Company records revenue and a corresponding grant receivable. Cash received from grants in advance of incurring qualifying costs is recorded as deferred revenue and recognized as revenue when qualifying costs are incurred. License Revenue The promised services in license agreements consist of license rights to the Company’s intellectual property. When management believes the license to its intellectual property and products has stand-alone value, the Company recognizes revenue attributed to the license upon delivery. The Company recognizes revenue when control of the promised goods or services is transferred to its customers, in an amount that reflects the consideration to which the Company expects to be entitled in exchange for the goods or services. In order to achieve that core principle, a five-step approach is applied: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue allocated to each performance obligation when the Company satisfies the performance obligation. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer, and is the unit of account for revenue recognition. The Company may provide options to additional items in the contracts, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract. License agreements generally include certain milestone payments. The Company utilizes the “most likely amount” method to estimate the amount of variable consideration, to predict the amount of consideration to which it will be entitled for its license agreement. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. Milestone, annual maintenance, and royalty payments that are not within the control of the Company or the licensee, such as those dependent upon receipt of regulatory approval, are not considered to be probable of achievement until the triggering event occurs. At the end of each reporting period, the Company reevaluates the probability of achievement of each and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. To date, the Company has not recognized any development, regulatory or commercial milestones or royalty revenue resulting from its license agreement. Consideration that would be received for optional goods and/or services is excluded from the transaction price at contract inception. License Agreement On January 22, 2019, the Company entered into a licensing and commercialization agreement with MD Anderson (the "MD Anderson License Agreement"). Under the MD Anderson License Agreement, the Company granted MD Anderson non-exclusive rights in certain Caspase-9 and related technologies and use of a small molecule known as rimiducid. During the fourth quarter of 2019, and under the terms of the MD Anderson License Agreement, MD Anderson exercised an option to grant a non-exclusive sublicense of the rights licensed by the Company to MD Anderson under the MD Anderson License Agreement. MD Anderson, as a result of this exercise, granted a sublicense that entitled the Company to receive as consideration an upfront payment of $5.0 million in license fees as well as additional future annual maintenance fees, milestone payments related to the achievement of pre-specified development, regulatory, and commercialization events, and royalties of two percent on net sales of licensed products. During the fourth quarter of 2019, the Company recognized $5.0 million of license fee revenue as delivery of the license occurred and the license to its Caspase-9 intellectual property has stand-alone value. To date, the Company has not received any milestones or royalty revenue resulting from the MD Anderson License Agreement. Cancer Research Grant Contract On August 9, 2017, the Company entered into a Cancer Research Grant Contract (the “CPRIT Agreement”) with the Cancer Prevention Research Institute of Texas (“CPRIT”), pursuant to which CPRIT awarded a grant of approximately $16.9 million to the Company to fund development of rivo-cel for hematologic cancer (the “CPRIT Award”). The CPRIT Award is contingent upon funds being available during the term of the CPRIT Agreement and subject to CPRIT’s ability to perform its obligations under the CPRIT Agreement. The Company and CPRIT will retain joint ownership over any intellectual property developed under the CPRIT Agreement. With respect to non-commercial use of any intellectual property developed under the CPRIT Agreement (the “CPRIT Project Results”), the Company agreed to grant to CPRIT a sublicensable, nonexclusive, irrevocable, royalty-free, perpetual worldwide license to any intellectual property of the Company that is necessary to exploit the CPRIT Project Results. The CPRIT Agreement permits the Company to license any CPRIT Project Results, subject to the Company retaining an exclusive sublicensable license to exploit the CPRIT Project Results for non-commercial purposes. The Company is obligated to make revenue-sharing payments to CPRIT with respect to net sales of any product covered by the CPRIT Agreement, up to a maximum repayment of 400% of the aggregate amount paid to the Company by CPRIT under the CPRIT Agreement. The payments are determined as a percentage of net sales ranging from the low to mid-single digits, which may be reduced if the Company is required to obtain a license from a third party to sell any such product. In addition, upon meeting the foregoing limitation on revenue-sharing payments, the Company agreed to make continued revenue-sharing payments to CPRIT of less than 1% of net sales. During 2017, the Company received $4.2 million in advance funding from CPRIT, which was recorded as deferred revenue. During the years ended December 31, 2019 and 2018, the Company incurred expenses and recognized revenue of $2.1 million and $1.1 million, respectively, for work performed under the CPRIT grant. The CPRIT Agreement was due to expire on February 29, 2020, but was terminated early by the Company on January 31, 2020.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash The Company considers all short-term, highly liquid investments with maturity of three months or less from the date of purchase and that can be liquidated without prior notice or penalty, to be cash equivalents.
Investment Securities	Investment Securities Consistent with its investment policy, the Company invests its cash allocated to fund its short-term liquidity requirements with prominent financial institutions in bank depository accounts and institutional money market funds. The Company invests the remainder of its cash in corporate debt securities and municipal bonds rated at least A quality or equivalent, U.S. Treasury notes and bonds and U.S. and state government agency-backed securities. The Company determines the appropriate classification of investment securities based on whether they represent the investment of funds available for current operations. The Company reevaluates its classification as of each balance sheet date. All investment securities owned are classified as available-for-sale. The cost of securities sold is based on the specific identification method. Investment securities are recorded as of each balance sheet date at fair value based on quoted prices in active markets, with unrealized gains and, to the extent deemed temporary, unrealized losses reported as accumulated other comprehensive gain (loss), a separate component of stockholders' (deficit) equity. Interest and dividend income on investment securities, accretion of discounts and amortization of premiums and realized gains and losses are included in interest income in the statements of operations and comprehensive loss. An investment security is considered to be impaired when a decline in fair value below its cost basis is determined to be other than temporary. The Company evaluates whether a decline in fair value of an investment security is below its cost basis is other than temporary using available evidence. In the event that the cost basis of the investment security exceeds its fair value, the Company evaluates, among other factors, the amount and duration of the period that the fair value is less than the cost basis, the financial health of and business outlook for the issuer, including industry and sector performance, and operational and financing cash flow factors, overall market conditions and trends, the Company’s intent to sell the investment security and whether it is more likely than not the Company would be required to sell the investment security before its anticipated recovery. If a decline in fair value is determined to be other than temporary, the Company records an impairment charge in the statement of operations and comprehensive loss and establishes a new cost basis in the investment.
Property and Equipment	Property and Equipment Furniture, equipment and software are recorded at cost and are depreciated using the straight-line method over the estimated useful lives of the related assets, which range from three to five years. Leasehold improvements are amortized over the shorter of the estimated useful life or the remaining lease term.
Intangible Assets	Intangible Assets Non-refundable upfront payments related to a supply agreement with future benefits have been capitalized as an intangible asset, presented in other assets on the accompanying consolidated balance sheets and amortized over the term of the agreement. The amortization of the intangible asset is included in operating expenses in the accompanying consolidated statements of operations and comprehensive loss.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment when events or changes in business conditions indicate that their carrying value may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset exceeds the fair value of the asset.
Debt Issuance Costs	Debt Issuance Costs Costs related to debt issuance are presented in the accompanying consolidated balance sheets as a direct deduction from the carrying amount of the debt liability, consistent with debt discounts and are amortized using the effective interest method. Amortization of debt issuance costs are included in interest expense in the accompanying statements of operations and comprehensive loss.
Warrant Derivatives	Warrant Derivatives Freestanding warrants exercisable for multiple underlying instruments are classified as liabilities in the accompanying consolidated balance sheets. The Company accounts for these warrants at fair value on the date of issuance and are subject to re-measurement to fair value at each balance sheet date. Any change in fair value is recognized as a component of other income (expense) on the accompanying consolidated statements of operations and comprehensive loss. The Company estimates the fair value of these liabilities using the binomial option model, adjusted for the effect of dilution, because it embodies all of the requisite assumptions (including trading volatility, estimated terms, dilution and risk-free rates) necessary to determine the fair value of this instrument. The Company will continue to adjust the liability for changes in fair value until the earlier of the exercise or expiration of the warrants or a change in control, as defined. The warrants are freely exercisable at any time from the issuance date until the expiration date, provided exercise does not cause a warrant holder to exceed a pre-determined beneficial ownership limit.
Preferred stock	Preferred Stock Preferred shares issued by the Company that are subject to mandatory redemption are classified as liability instruments in the accompanying consolidated balance sheets and are measured at fair value at the date of issuance. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified within mezzanine equity in the accompanying consolidated balance sheets. At all other times, preferred shares are classified within stockholders’ (deficit) equity.
Operating Leases	Operating Leases At the inception of a contractual arrangement, the Company determines whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. If both criteria are met, upon lease commencement, the Company records a lease liability which represents the Company’s obligation to make lease payments arising from the lease, and a corresponding right-of-use (“ROU”) asset which represents the Company’s right to use an underlying asset during the lease term. Operating leases are recognized as right-of-use, or ROU, assets and operating lease liabilities on the balance sheet based on the present value of the future minimum lease payments over the lease term at commencement date calculated using the Company's incremental borrowing rate applicable to the underlying asset unless the implicit rate is readily determinable. Any lease incentives received are deferred and recorded as a reduction of the ROU asset and amortized over the term of the lease. Rent expense, comprised of amortization of the ROU asset and the implicit interest accreted on the operating lease liability, is recognized on a straight-line basis over the lease term. The Company determines the lease term as the noncancellable period of the lease and may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options. Leases with a term of 12 months or less are not recognized on the balance sheets.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is defined as the exchange price that would be received for an asset or an exit price paid to transfer a liability in an orderly transaction between market participants in a principal market on the measurement date. Accounting standards include disclosure requirements around fair values used for certain financial instruments and establish a fair value hierarchy. The three-tier hierarchy defines a three-tiered valuation hierarchy for disclosures that prioritizes valuation inputs into three levels based on the extent to which inputs used in measuring fair value are observable in the market, as described further in Note 2. Observable inputs reflect readily obtainable data from independent sources, and unobservable inputs reflect the Company’s market assumptions. These inputs are classified into the following hierarchy: Level 1 Inputs - quoted prices (unadjusted) in active markets for identical assets that the reporting entity has the ability to access at the measurement date; Level 2 Inputs - inputs other than quoted prices included within Level 1 that are observable for the asset, either directly or indirectly; and Level 3 Inputs - unobservable inputs for the assets. The categorization of a financial instrument within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Company believes the recorded values of its financial instruments, including cash and cash equivalents, accounts payable, accrued liabilities, and debt approximate their fair values due to the short-term nature of these instruments.
Financial Instruments and Credit Risks	Financial Instruments and Credit Risks Financial instruments that potentially subject the Company to credit risk include cash and cash equivalents, investment securities, and accounts receivable. The Company maintains cash and cash equivalents and investment securities with high credit quality counterparties, regularly monitors the amount of credit exposure to any one issuer and diversifies its investments in order to minimize its credit risk.
Equity Issuance Costs	Equity Issuance Costs Equity issuance costs represent costs paid to third parties in order to obtain equity financing. These costs have been netted against the proceeds of the equity issuances.
Research and Development	Research and Development Research and development expenses consist of expenses incurred in performing research and development activities, including compensation and benefits for research and development employees and consultants, facilities expenses, overhead expenses, cost of laboratory supplies, manufacturing expenses, fees paid to third parties and other outside expenses. Research and development costs are expensed as incurred. Clinical trial and other development costs incurred by third parties are expensed as the contracted work is performed. The Company accrues for costs incurred as the services are being provided by monitoring the status of the clinical trial or project and the invoices received from its external service providers. The Company estimates depend on the timeliness and accuracy of the data provided by the vendors regarding the status of each project and total project spending. The Company adjusts its accrual as actual costs become known. Where contingent milestone payments are due to third parties under research and development arrangements, the milestone payment obligations are expensed when the milestone events are achieved.
Collaboration Agreements	Collaboration Agreements The Company enters into collaboration agreements that include varying arrangements regarding which parties perform and bear the costs of research and development activities. The Company may share the costs of research and development activities with a collaborator, or the Company may be reimbursed for all or a significant portion of the costs of the Company's research and development activities. The Company records its internal and third-party development costs associated with these collaborations as research and development expenses. When the Company is entitled to reimbursement of all or a portion of the research and development expenses that it incurs under a collaboration, the Company records those reimbursable amounts as a deduction to the research and development expenses. If the collaboration is a cost-sharing arrangement in which both the Company and its collaborator perform development work and share costs, the Company also recognizes, as research and development expenses in the period when its collaborator incurs development expenses, the portion of the collaborator's development expenses that the Company is obligated to reimburse.
Contract Manufacturing Services	Contract Manufacturing Services Contract manufacturing services are expensed as incurred. Prepaid expenses are capitalized and amortized as services are performed.
Share-Based Compensation	Share-Based Compensation The Company accounts for share-based compensation based on the measurement and recognition of compensation expense for all share-based payment awards made to employees, directors and consultants to be recognized in the financial statements, based on their fair value. The Company calculates the fair value of stock options on the date of grant using the Black-Scholes pricing model, which requires a number of estimates, including the expected life of awards, interest rates, stock volatility and other assumptions. Restricted stock is measured based on the fair market value of the underlying stock on the date of grant. If the awards are classified as liability awards, the fair value is remeasured at each reporting date and the compensation expense is adjusted accordingly. Additionally, the Company applies a forfeiture rate to estimate the number of grants that will ultimately vest, as applicable, and adjust the expense as these awards vest. All of the Company's current equity awards are service based awards and the share-based compensation cost is being recognized over the requisite service period of the awards on a straight-line basis.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. This method also requires the recognition of future tax benefits such as net operating loss and tax credit carry forwards, to the extent that realization of such benefits is more likely than not. A valuation allowance is recorded when the realization of future tax benefits is uncertain. The Company records a valuation allowance for the full amount of deferred tax assets, which would otherwise be recorded for tax benefits relating to the operating loss and tax credit carryforwards, as realization of such deferred tax assets cannot be determined to be more likely than not. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the statement of operations in the period that includes the enactment date. As of December 31, 2019, the Company had recorded a full valuation allowance on its net U.S. and foreign deferred tax assets because the Company expects that it is more likely than not that its deferred tax assets will not be realized in the foreseeable future. Should the actual amounts differ from our estimates, the amount of our valuation allowance could be materially impacted. The Company accounts for uncertain tax positions in accordance with the provisions of the Accounting Standards Codification (ASC) 740, Income Taxes. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2019 and 2018, the Company had no uncertain tax positions and no interest or penalties have been charged for the years ended December 31, 2019 and 2018. The Company is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress. The tax years 2005 through 2019 remain open to examination by the U.S. Internal Revenue Service.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period, from transactions, and other events and circumstances from non-owner sources. Components of other comprehensive loss includes, among other items, unrealized gains and losses on the changes in fair value of investments and unrealized gains and losses on the change in foreign currency exchange rates. These components are added, net of their related tax effect, to the reported net loss to arrive at comprehensive loss.
Net Loss and Net Loss per Share of Common Stock Attributable to Common Stockholders	Net Loss and Net Loss per Share of Common Stock Attributable to Common Stockholders Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period without consideration for common stock equivalents. Diluted earnings per share is based on the treasury stock method and includes the effect from potential issuance of ordinary shares, such as shares issuable pursuant to the conversion of preferred stock to common stock, exercise of warrants to purchase common stock, exercise of stock options, and vesting of restricted stock units. The following outstanding shares of common stock equivalents were excluded from the computations of diluted net loss per shares of common stock attributable to common stockholders for the periods presented as the effect of including such securities would be anti-dilutive.
New Accounting Requirements and Disclosures	New Accounting Requirements and Disclosures Fair Value Measurement In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which modifies fair value disclosures and removes some disclosure requirements for both public and private companies. In addition, public companies are subject to some new disclosure requirements which requires to disclose the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. ASU No. 2018-13 is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not expect the adoption of this standard to have a material effect on its financial statements. Financial Instruments – Credit Losses In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires the measurement of all expected credit losses for financial assets including trade receivables held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts. ASU No. 2016-13 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company does not expect the adoption of this standard to have a material effect on its financial statements. In April 2019, the FASB issued ASU No. 2019-04, Codification Improvements to Topic 326, Financial Instruments-Credit Losses, and Topic 825, Financial Instruments, which provides practical expedients and policy elections related to the presentation and disclosure of accrued interest and the related allowance for credit losses and clarifies how to disclose line-of-credit arrangements that are converted to term loans. ASU No. 2019-04 is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company does not expect the adoption of this standard to have a material effect on its financial statements.