5. Collaboration and License Agreements and Supply Agreements

The Company has entered into collaboration and license agreements and supply agreements with various pharmaceutical and biotechnology companies. The Company analyzes its agreements to determine whether it should account for the agreements within the scope of ASC 808, and, if so, it analyzes whether it should account for any elements under ASC 606.

The Company’s accounts receivable balances may contain billed and unbilled amounts from upfront payments, milestones and other contingent payments, as well as reimbursable costs from collaboration and license agreements and supply agreements. The Company has not experienced credit loss from its accounts receivable and, therefore, has not recorded a reserve for estimated credit losses as of December 31, 2021.

The Company’s balance of deferred revenue contains a license option payment and the transaction price from collaboration agreements allocated to performance obligations which are partially unsatisfied. The Company expects to recognize approximately $5.5 million of the deferred revenue over the next twelve months.

There have been no material changes to the Company’s agreements during the year ended December 31, 2021, except as described below.

Collaboration with BMS

BMS Agreement

In November 2019, BMS acquired Celgene, and Celgene became a wholly owned subsidiary of BMS. In connection with such acquisition, BMS assumed the rights and obligations of the 2014 Celgene Agreement, 2017 Celgene Agreement and 2018 Celgene Master Services Agreement. Throughout this Annual Report, the Company refers to Celgene as BMS and the Company's agreements with Celgene as the BMS Agreement and the 2018 BMS Master Services Agreement.

In September 2014, the Company signed a Collaboration and License Agreement (the “BMS Agreement”) with BMS to discover and develop bispecific antibodies and/or antibody-drug conjugates (“ADCs”), focused primarily on the field of immuno-oncology, using the Company’s proprietary integrated cell-free protein synthesis platform, XpressCF®. In August 2017, the Company entered into an amended and restated collaboration and license agreement with BMS to refocus the collaboration on four programs that were advancing through preclinical development, including an ADC program targeting B cell maturation antigen (“BCMA ADC”).

In May 2019, the U.S. Food and Drug Administration cleared the investigational new drug (“IND”) application for the BCMA ADC, which was discovered and is being manufactured by the Company and is the first collaboration program IND. BMS has worldwide development and commercialization rights with respect to the BCMA ADC. The Company will continue to be responsible for clinical supply manufacturing and certain development services for the BCMA ADC and is eligible to receive from BMS aggregate development and regulatory contingent payments of up to $275.0 million, if approved in multiple indications, and tiered royalties ranging from mid to high single digit percentages on worldwide sales of any resulting commercial products.

As of December 31, 2021 and 2020, there was no balance of deferred revenue related to payments received by the Company under the BMS Agreement.

2018 BMS Master Services Agreement

In March 2018, the Company entered into a Master Development and Clinical Manufacturing Services Agreement (the “2018 BMS Master Services Agreement”) with BMS, wherein BMS requested the Company to provide development, manufacturing and supply chain management services, including clinical product supply.

As of December 31, 2021 and 2020, there was $0.6 million and $1.2 million, respectively, of deferred revenue under the 2018 BMS Master Services Agreement.

Collaboration with Merck

2018 Merck Agreement

In July 2018, the Company entered into an agreement (the “2018 Merck Agreement”) with Merck for access to the Company’s technology and the identification and preclinical research and development of two target programs, with an option for Merck to engage the Company to continue these activities for a third program, upon the payment of an additional amount, focusing on cytokine derivatives for cancer and autoimmune disorders with an initial transaction price of $60.0 million. The option to expand activities to a third program expired in January 2021.

Under ASC 606, the Company determined there was a financing component associated with the $60.0 million upfront payment and has calculated total interest expense of $7.3 million as of December 31, 2021, on the unearned revenue portion beyond one year from the effective date of the agreement, which amount was recognized as interest expense and revenue over the service period for the first and second target programs.

In March 2020, Merck exercised its option to extend the research term of the collaboration’s first cytokine-derivative program by one year, which, pursuant to the terms of the 2018 Merck Agreement, triggered a payment of $5.0 million. The $5.0 million was, in prior periods, considered to be a fully constrained variable consideration. Removal of the constraint on this variable consideration resulted in a change to the total transaction price, from

$60.0 million to $65.0 million. The Company allocated the updated transaction price to all identified performance obligations on the same basis as the initial allocation upon inception of the 2018 Merck Agreement, with any adjustments recorded as a cumulative catch-up in the current period.

In the second quarter of 2021, the Company earned a $15.0 million contingent payment for the initiation by Merck of the first IND-enabling toxicology study under the first cytokine-derivative program in the collaboration. The $15.0 million was, in prior periods, considered to be a fully constrained variable consideration. Removal of the constraint on this variable consideration resulted in a change to the total transaction price, from $65.0 million to $80.0 million. The Company allocated the updated transaction price to all identified performance obligations on the same basis as the initial allocation upon inception of the 2018 Merck Agreement, with any adjustments recorded as a cumulative catch-up in the period ended December 31, 2021. As a result of the change in transaction price, the Company recognized substantially all of the $15.0 million contingent payment, with a remaining $0.3 million related to the Joint Steering Committee, ("JSC") performance obligation, as a cumulative catch-up in revenue in the period ended December 31, 2021.

In September 2021, the Company entered into an amendment to the 2018 Merck Agreement (the “2021 Amendment”) to extend the research term for the first program in the 2018 Merck Agreement to discover and develop novel cytokine derivative therapeutics for cancer and autoimmune disorders. Under the terms of the 2021 Amendment, the Company received a payment of $2.5 million and may receive up to an additional $7.5 million upon the achievement of certain developmental milestones. Pursuant to ASC 606, the Company concluded that the 2021 Amendment constitutes a contract modification which is to be accounted for as a separate contract from the 2018 Merck Agreement. From the $2.5 million payment received, $1.9 million was recognized as revenue on a proportion of performance basis in the year ended December 31, 2021, related to the Company’s identified performance obligations under the 2021 Amendment. The additional $7.5 million is considered to be fully constrained variable consideration.

In December 2021, Merck did not extend the research term for the second research program of the collaboration and that research program reverted to the Company. The first program of the collaboration is focused on two distinct cytokine derivative molecules for the treatment of cancer. The Company is also eligible to receive aggregate contingent payments of up to approximately $0.5 billion for the target program selected by Merck, assuming the development and sale of the therapeutic candidate and all possible indications identified under the collaboration. If one or more products from the target program is developed for non-oncology or a single indication, the Company will be eligible for reduced aggregate milestone payments. In addition, the Company is eligible to receive tiered royalties ranging from mid-single digit to low teen percentages on the worldwide sales of any commercial products that may result from the collaboration.

As of December 31, 2021 and 2020, there was a total of $0.9 million and $18.5 million, respectively, of deferred revenue related to the 2018 Merck Agreement and 2021 Amendment.

2020 Merck Master Services Agreement

In August 2020, the Company entered into a Pre-Clinical and Clinical Supply Agreement (the “2020 Merck Master Services Agreement”) with Merck, wherein Merck requested the Company to provide development, manufacturing and supply chain management services, including clinical product supply, upon completion of the research programs under the 2018 Merck Agreement.

As of both December 31, 2021 and 2020, there was no deferred revenue under the 2020 Merck Master Services Agreement.

Collaboration with EMD Serono

EMD Serono Agreements

The Company signed a Collaboration Agreement and a License Agreement with EMD Serono in May 2014 and September 2014, respectively, which were entered into in contemplation of each other and therefore treated as a single agreement for accounting purposes. The Collaboration Agreement was subsumed into the License Agreement (the “MDA Agreement”), which agreement is to develop ADCs for multiple cancer targets. Under the MDA Agreement, a novel bispecific ADC product candidate targeting EGFR and MUC1, known as M1231, is undergoing development.

The Company is eligible to receive up to $52.5 million for M1231 under the MDA Agreement, primarily from pre-commercial contingent payments. Relatedly, the Company earned a $2.0 million contingent payment in the second quarter of 2021 related to a patient enrollment achievement in the Phase 1 dose escalation portion of a study of M1231. In August 2020, the Company earned a $1.0 million clinical supply milestone payment under the MDA Agreement. In September 2019, the Company earned a $1.5 million contingent payment under the MDA Agreement upon designation by EMD Serono of a specific bispecific antibody drug conjugate as a clinical development candidate with their approval to advance it to IND-enabling studies. In addition, the Company is eligible to receive tiered royalties ranging from low-to-mid single digit percentages, along with certain additional one-time royalties, on worldwide sales of any commercial products that may result from the MDA Agreement.

As of both December 31, 2021 and 2020, there was no deferred revenue related to payments received by the Company under the MDA Agreement.

2019 EMD Serono Supply Agreement

In April 2019, the Company entered into an ADC Product Preclinical and Phase I Clinical Supply Agreement (the “2019 EMD Serono Supply Agreement”) with EMD Serono, wherein EMD Serono requested the Company to provide development, manufacturing and supply chain management services, including clinical product supply.

As of December 31, 2021 and 2020, there was zero and $1 million, respectively, of deferred revenue related to payments received by the Company under the 2019 EMD Serono Supply Agreement.

Vaxcyte Supply Agreement

In May 2018, the Company entered into a Supply Agreement (the “Supply Agreement”) with Vaxcyte, wherein Vaxcyte engaged the Company to provide research and development services and to supply extracts and custom reagents, as requested by Vaxcyte. The pricing is based on an agreed upon cost plus arrangement.

During 2020, upon Vaxcyte’s request and their agreement to reimburse the related costs, the Company entered into agreements with third-party contract manufacturers (“CMOs”) to conduct process transfers to allow for such CMOs to manufacture and supply extract and custom reagents for Vaxcyte. For the year ended December 31, 2021 and 2020, the agreed-upon reimbursements by Vaxcyte of the costs associated with such arrangements, principally for pass-through costs from the CMOs, were $8.9 million and $0.5 million, respectively, and were accounted for by the Company as a reduction to research and development expense based on the Company’s conclusion that Vaxcyte was not a customer for such activities and associated payments.

BioNova Option Agreement

In October 2021, the Company entered into an agreement with BioNova to confer BioNova the option to obtain exclusive rights to develop and commercialize STRO-001 in China, Hong Kong, Macau and Taiwan, referred to as Greater China. BioNova will pursue the clinical development, regulatory approval, and commercialization of STRO-001 in multiple indications, including non-Hodgkin's lymphoma, multiple myeloma, and leukemia in the licensed territory. The Company will retain development and commercial rights of STRO-001 globally outside of Greater China, including the United States.

Under the BioNova Option Agreement, BioNova paid the Company an initial licensing option payment of $4.0 million, with potential payments totaling up to $200 million related to option exercise, development, regulatory, and commercial milestones. The Company will provide STRO-001 to BioNova under appropriate clinical and commercial supply service agreements. Upon commercialization, the Company is eligible to receive tiered royalties ranging from low- to mid-teen percentages based on annual net sales of STRO-001 in Greater China for at least ten years following the first commercial sale of STRO-001 in Greater China.

The Company identified a combined performance obligation under the initial license option agreement, which consists of four interrelated promises: generating a recommended dose of STRO-001 for multiple myeloma and Non-Hodgkin’s lymphoma, providing licensed know-how and regulatory filings necessary to prepare an IND; providing initial clinical supply in the People’s Republic of China; and participating in the JSC. These promises are considered to be interdependent and not distinct from each other, representing a combined output. The transaction price at inception included the refundable payment of $4.0 million and was considered constrained at the inception of the agreement since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur. BioNova will have the right to exercise the license option for an additional payment of $12.0 million. As of December 31, 2021, there was $4.0 million of deferred revenue related to the payment received by the Company under the BioNova Option Agreement and BioNova had not yet exercised the license option.

Tasly License Agreement

In December 2021, the Company entered into a license agreement with Tasly, to grant Tasly an exclusive license to develop and commercialize STRO-002 in Greater China. Tasly will pursue the clinical development, regulatory approval, and commercialization of STRO-002 in multiple indications, including ovarian cancer, non-small cell lung cancer, triple-negative breast cancer, and other indications in Greater China. The Company will retain development and commercial rights of STRO-002 globally outside of Greater China, including the United States.

Under the Tasly License Agreement, Tasly is obligated to make to the Company an initial nonrefundable upfront payment of $40.0 million, with additional potential payments totaling up to $345 million related to development, regulatory and commercialization contingent payments and milestones. The Company will provide STRO-002 to Tasly under appropriate clinical and commercial supply service agreements. Upon commercialization, the Company will receive tiered royalties, ranging from low- to mid-teen percentages based on annual net sales of STRO-002 in Greater China for at least ten years following the first commercial sale of STRO-002 in Greater China.

The Company determined that the Tasly License Agreement falls within the scope of ASC 808, as both parties are active participants in the activities and are exposed to significant risks and rewards dependent on the success of the commercialization of indications for STRO-002 in Greater China. The Company concluded that the Tasly License Agreement contained the following units of account: i) licensed know-how and Sutro patents, license to trademark rights, and initial regulatory data and information necessary to prepare an IND; and ii) collaboration governance and information sharing activities, such as JSC participation and ongoing regulatory and pharmacovigilance support.

The promises related to the licensed know-how and Sutro patents, license to trademark rights, and initial regulatory data and information necessary to prepare an IND are considered to be interdependent and not distinct from each other, representing a combined output. The Company determined that these promises are capable of being distinct from the collaboration governance and information sharing activities discussed below and further determined that this unit of account is a vendor-customer relationship and will account for it in accordance with ASC 606. The transaction price at inception included fixed consideration consisting of the upfront payment of $40.0 million. All potential future milestones and other payments were considered constrained at the inception of the Tasly License Agreement since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur. Since there is only one performance obligation accounted for under ASC 606, no allocation of the transaction price was necessary.

The Company determined that the unit of account consisting of collaboration governance and information sharing activities, such as JSC participation and ongoing regulatory and pharmacovigilance support, do not represent a customer-vendor relationship between the Company and Tasly. These promises are considered to be interdependent and not distinct from each other, representing a combined output. However, the Company determined that these promises are capable of being distinct from the intellectual property and data license promises discussed above. As such, based on the nature of the agreement and collaborative activities, the Company determined that the costs associated with these governance and information sharing activities performed under the agreement will be included in research and development expenses in the statements of operations, with any reimbursement of costs by Tasly reflected as a reduction of such expenses. During the year ended December 31, 2021, the Company did not recognize a reduction of research and development expenses under the Tasly License Agreement.

On December 24, 2021, the effective date of the Tasly License Agreement, the Company satisfied its only performance obligation related to the $40.0 million upfront payment by delivering to Tasly the license, know-how and data required under the Tasly License Agreement. Following the satisfaction of such performance obligation, under the Tasly License Agreement, Tasly is obligated to pay the Company the $40.0 million upfront payment. In February 2022, Tasly indicated to the Company that it would like to discuss and renegotiate the terms of the Tasly License Agreement. As any renegotiation could affect the amount and timing of Tasly’s obligations under the terms of the Tasly License Agreement, including the upfront payment, the Company has concluded that it will not recognize the $40.0 million upfront payment as revenue in December 2021.