AnaptysBio has separately alleged that GSK subsidiary Tesaro breached “certain requirements” under their 2014 license agreement involving a program that would become GSK’s Jemperli.
GSK subsidiary Tesaro has filed a lawsuit against AnaptysBio, alleging that the California biotech is in “material breach” of its existing agreement regarding the PD-1 blocker Jemperli.
In its suit, filed with the Delaware Chancery Court, Tesaro claims that AnaptysBio’s breach of contract means that Tesaro is entitled to terminate the current contract and instead “obtain a perpetual and irrevocable license.” Tesaro, according to a news release on Thursday, would also be allowed to cut its royalties and milestones to AnaptysBio by half.
GSK and Tesaro are firing back at AnaptysBio, which, according to the pharma, has itself claimed that Tesaro “has not fulfilled certain requirements” under their ongoing agreement, without further specification. In lieu of these alleged shortcomings by Tesaro, AnaptysBio has threatened to “revoke” the Jemperli license.
“GSK and TESARO are firmly of the view that these allegations are entirely without merit,” the companies wrote in their Thursday release.
Tesaro and AnaptysBio first teamed up in March 2014. In exchange for an upfront payment of $17 million and the promise to shoulder development costs, AnaptysBio gave Tesaro exclusive rights to a number of antibody programs targeting various cancer markers, including LAG-3, TIM-3 and PD-1. One of these programs would eventually become Jemperli.
Under the 2014 arrangement, Tesaro promised per-program milestone payments of $18 million, payable upon hitting certain R&D events, plus $90 million in conjunction with regulatory submissions and approvals. These obligations got passed on to GSK when it bought Tesaro for $5.1 billion in late 2018.
In 2024, Jemperli earned more than $611 million worldwide, representing a more than 100% year-on-year growth. In 2025 so far, the drug has already exceeded that figure: Over the first nine months of this year, Jemperli surged 93% year-on-year to hit $785.2 million.
For AnaptysBio, the Thursday suit could imperil recent structural changes to its business. Last month, the biotech announced that it would split into two entities: one focused on drug development to advance its clinical pipeline, and another on royalty management. Much of the work of this latter company will be centered on Jemperli.
In the fourth quarter, AnaptysBio could be entitled to a one-time $75 million commercial milestone payment from GSK if Jemperli breaks the $1 billion sales mark, according to its Q3 earnings report. The biotech is also expecting more than $390 million in annualized royalties, payable once Jemperli hits peak sales of around $2.7 billion, which AnaptysBio forecasts to happen before 2031.
First approved in April 2021 for endometrial cancer, Jemperli is a checkpoint inhibitor that specifically targets the PD-1 pathway, in turn stopping tumors from suppressing the immune system. The antibody therapy has since improved its profile in endometrial cancer. Most recently, the FDA in August last year gave Jemperli a broad expansion, allowing its use as a frontline option for all adult patients with primary advanced or recurrent endometrial cancer.
