Agreements	3 Months Ended
Mar. 31, 2022
Agreements
Agreements	C.Agreements Significant Collaborative Agreements Lilly In February 2022, the Company entered into a license agreement with Eli Lilly and Company (Lilly), pursuant to which the Company granted Lilly worldwide exclusive rights to research, develop, and commercialize antibody-drug conjugates based on the Company’s novel camptothecin technology. Under the terms of the license agreement, the Company received a non-refundable upfront payment of $13.0 million, reflecting initial targets selected by Lilly. Lilly may select a pre-specified number of additional targets, with the Company eligible to receive an additional $32.5 million in exercise fees if Lilly licenses the full number of additional targets over the four year period following the effective date of the license agreement, with the potential for up to $1.7 billion in development and sales-based milestone payments if all targets are selected and all milestones are realized. In addition, the Company is entitled to receive tiered royalties, on a product-by-product basis, as a percentage of worldwide annual net sales by Lilly, based on certain net sales thresholds. Lilly is responsible for all costs associated with the research, development, and commercialization of any ensuing products. The Company evaluated the agreement and determined it was within the scope of ASC 606. The Company determined the promised goods and services included an exclusive license to use the Company’s intellectual property and know-how to research, develop, and commercialize products related to each of the initial targets selected by Lilly. Each of these licenses is distinct, as Lilly can derive benefit from each license independent of any other initial target licenses. Accordingly, the license to each of the initial targets selected by Lilly represents a separate performance obligation. Lilly has the right to replace each of the initial licensed targets once during a specified term for no additional consideration. If Lilly fails to advance an initial or replacement target to a specified stage within a specified period from the date the target was selected, Lilly’s rights to the respective target will cease and will revert back to the Company. The Company determined Lilly’s right to a replacement target for each of the initial targets represented a material right. Each material right is therefore a separate performance obligation. Lilly’s right to select additional targets does not represent a material right as the target fee for each additional target is the same and is also consistent with the target fee for each of the initial targets selected by Lilly. Accordingly, each additional target selected by Lilly, if any, will be accounted for as a separate arrangement. The transaction price was determined to consist of the upfront payment of $13.0 million. Future development milestones have been fully constrained. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license granted to Lilly. The transaction price of $13.0 million was allocated to the performance obligations based on their relative stand-alone selling prices. In consideration of each target being at the same stage of development at the time of the initial license or at the time of replacement and each target having approximately the same earnings potential, the Company allocated the $13.0 million transaction price equally across the initial target licenses and the corresponding material rights to obtain licenses to replacement targets, adjusted based on the probability that Lilly would exercise those rights. The Company considered pharmaceutical industry data of the probability of early-stage assets to advance to clinical stage in determining the probability that Lilly would exercise its option to a replacement target. Accordingly, $9.2 million and $3.8 million of the total transaction price was allocated to the initial targets and the material rights to obtain licenses to replacement targets, respectively. The Company re-evaluates the transaction price, including its estimated variable consideration included in the transaction price and all constrained amounts, at each reporting period and as uncertain events are resolved or other changes in circumstances occur. Upon completion of the transfer of intellectual property and know-how to Lilly during the quarter ended March 31, 2022, the Company recognized $9.2 million of license and milestone fee revenue related to the portion of the transaction price allocated to the initial target licenses. The $3.8 million allocated to the material rights to obtain licenses to replacement targets is included in long-term deferred revenue as of March 31, 2022, and will be recognized when the right is either exercised or expires. Roche In 2000, the Company granted Genentech, now a unit of Roche, an exclusive development and commercialization license to use the Company’s maytansinoid ADC technology. Pursuant to this agreement, Roche developed and received marketing approval for its HER2-targeting ADC, KADCYLA, in the U.S., Japan, the European Union, and numerous other countries. In accordance with the Company’s revenue recognition policy, $6.4 million and $15.5 million of non-cash royalties on net sales of KADCYLA were recognized and included in non-cash royalty revenue for the three months ended March 31, 2022 and 2021, respectively. The Company sold its rights to receive royalty payments on the net sales of KADCYLA through two separate transactions in 2015 and 2019. Following the 2019 transaction, OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, is entitled to receive all of these royalties. Huadong In October 2020, the Company entered into a collaboration and license agreement with Huadong. The collaboration and license agreement grants Huadong an exclusive, royalty-bearing, and sublicensable right to develop and commercialize mirvetuximab soravtansine (the Licensed Product) in the People’s Republic of China, Hong Kong, Macau, and Taiwan (collectively, Greater China). The Company retains exclusive rights to the Licensed Product outside of Greater China. Under the terms of the collaboration and license agreement, the Company received a non-refundable upfront payment of $40.0 million with the potential for approximately $265.0 million in development, regulatory, and sales-based milestone payments. In December 2021, the Company received a $5.0 million payment upon achievement of a development milestone. The Company determined that revenue related to the agreement would be recognized as the clinical supply of the Licensed Product is delivered to Huadong, estimated to be completed over approximately two years. Accordingly, based on clinical supply delivered to Huadong in the three months ended March 31, 2022, the Company recorded $21.6 million of the $28.5 million remaining deferred balance as of December 31, 2021 related to the $45.0 million of upfront and development milestone payments previously received. As of March 31, 2022, total deferred revenue related to the Huadong arrangement was $6.9 million and is expected to be recognized during 2022 as additional clinical supply is delivered. Viridian In October 2020, the Company entered into a license agreement with Viridian Therapeutics, Inc. pursuant to which the Company granted Viridian the exclusive right to develop and commercialize an insulin-like growth factor-1 receptor (IGF-1R) antibody for all non-oncology indications that do not use radiopharmaceuticals in exchange for an upfront payment, with the potential to receive up to a total of $143.0 million in development, regulatory, and sales-based milestone payments plus royalties on the commercial sales of any resulting product. In the three months ended December 31, 2021, a $3.0 million development milestone became probable of being achieved, which was allocated to the previously delivered license and recognized as revenue as a component of license and milestone fees for the three months ended December 31, 2021. The development milestone was subsequently achieved in April 2022. For additional information related to these agreements, as well as the Company’s other significant collaborative agreements, please read Note C, “Agreements - Significant Collaborative Agreements,” to the audited financial statements included within the Company’s Annual Report on Form 10-K for the year ended December 31, 2021 filed with the SEC on February 28, 2022.

Agreements

3 Months Ended

Mar. 31, 2022

C.Agreements

Significant Collaborative Agreements

Lilly

In February 2022, the Company entered into a license agreement with Eli Lilly and Company (Lilly), pursuant to which the Company granted Lilly worldwide exclusive rights to research, develop, and commercialize antibody-drug conjugates based on the Company’s novel camptothecin technology. Under the terms of the license agreement, the Company received a non-refundable upfront payment of $13.0 million, reflecting initial targets selected by Lilly. Lilly may select a pre-specified number of additional targets, with the Company eligible to receive an additional $32.5 million in exercise fees if Lilly licenses the full number of additional targets over the four year period following the effective date of the license agreement, with the potential for up to $1.7 billion in development and sales-based milestone payments if all targets are selected and all milestones are realized. In addition, the Company is entitled to receive tiered royalties, on a product-by-product basis, as a percentage of worldwide annual net sales by Lilly, based on certain net sales thresholds. Lilly is responsible for all costs associated with the research, development, and commercialization of any ensuing products.

The Company evaluated the agreement and determined it was within the scope of ASC 606. The Company determined the promised goods and services included an exclusive license to use the Company’s intellectual property and know-how to research, develop, and commercialize products related to each of the initial targets selected by Lilly. Each of these licenses is distinct, as Lilly can derive benefit from each license independent of any other initial target licenses. Accordingly, the license to each of the initial targets selected by Lilly represents a separate performance obligation. Lilly has the right to replace each of the initial licensed targets once during a specified term for no additional consideration. If Lilly fails to advance an initial or replacement target to a specified stage within a specified period from the date the target was selected, Lilly’s rights to the respective target will cease and will revert back to the Company. The Company determined Lilly’s right to a replacement target for each of the initial targets represented a material right. Each material right is therefore a separate performance obligation.

Lilly’s right to select additional targets does not represent a material right as the target fee for each additional target is the same and is also consistent with the target fee for each of the initial targets selected by Lilly. Accordingly, each additional target selected by Lilly, if any, will be accounted for as a separate arrangement.

The transaction price was determined to consist of the upfront payment of $13.0 million. Future development milestones have been fully constrained. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license granted to Lilly. The transaction price of $13.0 million was allocated to the performance obligations based on their relative stand-alone selling prices. In consideration of each target being at the same stage of development at the time of the initial license or at the time of replacement and each target having approximately the same earnings potential, the Company allocated the $13.0 million transaction price equally across the initial target licenses and the corresponding material rights to obtain licenses to replacement targets, adjusted based on the probability that Lilly would exercise those rights. The Company considered pharmaceutical industry data of the probability of early-stage assets to advance to clinical stage in determining the probability that Lilly would exercise its option to a replacement target. Accordingly, $9.2 million and $3.8 million of the total transaction price was allocated to the initial targets and the material rights to obtain licenses to replacement targets, respectively. The Company re-evaluates the transaction price, including its estimated variable

consideration included in the transaction price and all constrained amounts, at each reporting period and as uncertain events are resolved or other changes in circumstances occur.

Upon completion of the transfer of intellectual property and know-how to Lilly during the quarter ended March 31, 2022, the Company recognized $9.2 million of license and milestone fee revenue related to the portion of the transaction price allocated to the initial target licenses. The $3.8 million allocated to the material rights to obtain licenses to replacement targets is included in long-term deferred revenue as of March 31, 2022, and will be recognized when the right is either exercised or expires.

Roche

In 2000, the Company granted Genentech, now a unit of Roche, an exclusive development and commercialization license to use the Company’s maytansinoid ADC technology. Pursuant to this agreement, Roche developed and received marketing approval for its HER2-targeting ADC, KADCYLA, in the U.S., Japan, the European Union, and numerous other countries. In accordance with the Company’s revenue recognition policy, $6.4 million and $15.5 million of non-cash royalties on net sales of KADCYLA were recognized and included in non-cash royalty revenue for the three months ended March 31, 2022 and 2021, respectively. The Company sold its rights to receive royalty payments on the net sales of KADCYLA through two separate transactions in 2015 and 2019. Following the 2019 transaction, OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, is entitled to receive all of these royalties.

Huadong

In October 2020, the Company entered into a collaboration and license agreement with Huadong. The collaboration and license agreement grants Huadong an exclusive, royalty-bearing, and sublicensable right to develop and commercialize mirvetuximab soravtansine (the Licensed Product) in the People’s Republic of China, Hong Kong, Macau, and Taiwan (collectively, Greater China). The Company retains exclusive rights to the Licensed Product outside of Greater China. Under the terms of the collaboration and license agreement, the Company received a non-refundable upfront payment of $40.0 million with the potential for approximately $265.0 million in development, regulatory, and sales-based milestone payments.

In December 2021, the Company received a $5.0 million payment upon achievement of a development milestone. The Company determined that revenue related to the agreement would be recognized as the clinical supply of the Licensed Product is delivered to Huadong, estimated to be completed over approximately two years. Accordingly, based on clinical supply delivered to Huadong in the three months ended March 31, 2022, the Company recorded $21.6 million of the $28.5 million remaining deferred balance as of December 31, 2021 related to the $45.0 million of upfront and development milestone payments previously received. As of March 31, 2022, total deferred revenue related to the Huadong arrangement was $6.9 million and is expected to be recognized during 2022 as additional clinical supply is delivered.

Viridian

In October 2020, the Company entered into a license agreement with Viridian Therapeutics, Inc. pursuant to which the Company granted Viridian the exclusive right to develop and commercialize an insulin-like growth factor-1 receptor (IGF-1R) antibody for all non-oncology indications that do not use radiopharmaceuticals in exchange for an upfront payment, with the potential to receive up to a total of $143.0 million in development, regulatory, and sales-based milestone payments plus royalties on the commercial sales of any resulting product. In the three months ended December 31, 2021, a $3.0 million development milestone became probable of being achieved, which was allocated to the previously delivered license and recognized as revenue as a component of license and milestone fees for the three months ended December 31, 2021. The development milestone was subsequently achieved in April 2022.

For additional information related to these agreements, as well as the Company’s other significant collaborative agreements, please read Note C, “Agreements - Significant Collaborative Agreements,” to the audited financial statements included within the Company’s Annual Report on Form 10-K for the year ended December 31, 2021 filed with the SEC on February 28, 2022.