Revenue Recognition The Company adopted ASC Topic 606 effective January 1, 2018 on a modified retrospective basis. As such, the prior period amounts were not restated and continue to be presented in accordance with ASC Topic 605. For the Companys accounting policy on revenue recognition prior to January 1, 2018, refer to the 2017 Form 10-K filed with the SEC on March 7, 2018. The policy disclosed in this Quarterly Report on Form 10-Q is the Companys policy under ASC Topic 606, which has been applied since January 1, 2018. The Companys revenues are primarily derived through its license, research, development and commercialization agreements. The terms of these types of agreements may include (i) licenses for the Companys technology or programs, (ii) research and development services, and (iii) services or obligations in connection with participation in research or steering committees. Payments to the Company under these arrangements typically include one or more of the following: nonrefundable upfront and license fees, research funding, milestone and other contingent payments to the Company for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products. The Company recognizes revenue when the customer obtains control of the promised goods or services, in an amount that reflects the consideration which the Company has received or expects to receive in exchange for those goods or services. The Company assesses whether the promises in its arrangements with customers are considered distinct performance obligations that should be accounted for separately. Judgment is required to determine whether the license to the Companys intellectual property is distinct from the research and development services or participation on steering committees. The transaction price in each arrangement is allocated to the identified performance obligations based on the standalone selling price (SSP) of each distinct performance obligation, which requires judgment. In instances where SSP is not directly observable, such as when a license or service is not sold separately, SSP is determined using information that may include market conditions and other observable inputs. Due to the early stage of the Companys licensed technology, the license of such technology is typically combined with research and development services and steering committee participation as one performance obligation. In these cases, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Companys collaboration and license agreements may include contingent payments related to specified research, development and regulatory milestones. Such payments are typically payable under the collaborations when the collaboration partner claims or selects a target, or initiates or advances a covered product candidate in preclinical or clinical development, upon submission for marketing approval of a covered product with regulatory authorities, or upon receipt of actual marketing approvals of a covered product or for additional indications. At each reporting date, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price by using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. Once determined, the transaction price is allocated to each performance obligation on a relative SSP basis. At the end of each subsequent reporting period, the Company re-evaluates the probability or achievement of each such milestone and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. The Companys collaboration and license agreements may also include contingent payments related to sales-based milestones. Sales-based milestones are typically payable when annual sales of a covered product reach specified levels. Sales-based milestones are recognized at the later of when the associated performance obligation has been satisfied or when the sales occur. Unlike other contingency payments, such as regulatory milestones, sales-based milestones are not included in the transaction price based on estimates at the inception of the contract, but rather, are included when the sales or usage occur. AbbVie Ireland Unlimited Company (AbbVie), one of the Companys collaboration partners, entered into a license agreement with Seattle Genetics, Inc. (SGEN) to license certain intellectual property rights. As part of the Companys collaboration agreement with AbbVie, the Company pays SGEN sublicense fees. These sublicense fees are treated as reductions to the transaction price and combined with the performance obligation to which they relate. Milestone payments, when considered probable of being reached and when a significant revenue reversal would not be probable of occurring, are also recorded net of the associated sublicense fees and included in the transaction price.