AnaptysBio has filed a verified complaint in Delaware Chancery Court alleging that Tesaro, now part of GSK, breached a 2014 collaboration and exclusive license for the PD-1 antibody Jemperli (dostarlimab), and that GSK tortiously interfered with the agreement. Tesaro filed its own suit on November 20 seeking injunctive relief and asserting Anaptys breached the contract. The parties have agreed to seek an expedited schedule with trial anticipated in July 2026. Milestone and royalty payments to Anaptys remain due during the proceedings.
Beyond a contract dispute, this case tests how far large pharma can optimize across portfolios without running afoul of legacy exclusivity covenants. Anaptys contends the agreement barred Tesaro from conducting or participating in research, development, manufacturing, or commercialization of any PD-1 antagonist other than those licensed from Anaptys, and required “commercially reasonable efforts” to obtain the optimum commercial return for Jemperli. The complaint points to participation in governed clinical trials with competing PD-1s, including Keytruda, and to a pattern of favoring GSK antibody-drug conjugate development by pairing those ADCs with competitor PD-1s rather than Jemperli. If the court validates a strict reading of exclusivity and a robust interpretation of “commercially reasonable efforts,” it could constrain how companies pair platforms like ADCs with off-portfolio backbones.
The timing matters. Jemperli is approaching a global $1 billion net sales milestone in Q4 2025, which would trigger a $75 million commercial milestone to Anaptys, on top of a steeply tiered royalty that rises up to 25 percent above $2.5 billion in annual sales. At the same time, the standard of care in solid tumors is increasingly defined by PD-1–anchored combinations. For patients and HCPs, the dispute could influence which PD-1s are prioritized in pivotal combos, the pace of evidence generation, and the consistency of data packages across tumor types. For payers, the verdict may affect the availability and pricing strategy of ADC plus PD-1 regimens, where total cost of care and comparative effectiveness are under sharper scrutiny. Competitively, any restriction on GSK’s flexibility in pairing assets could reinforce Merck’s position as the default immuno-oncology backbone, further entrenching Keytruda as the partner of choice in registrational programs.
The financing backdrop is equally relevant. Anaptys previously monetized Jemperli-related receivables to Sagard in a capped, non-recourse structure, with payments continuing until Sagard receives an aggregate $600 million by March 31, 2031, or $675 million thereafter. Anaptys estimates Sagard will have accrued $250 million by year-end 2025 and expects full paydown between Q2 2027 and Q2 2028. That ongoing cash stream, alongside Anaptys’s announced plan to separate its biopharma operations from its royalty assets by year-end 2026, means litigation outcomes could reshape two distinct equity stories: a development-stage immunology company and a royalty vehicle leveraged to Jemperli.
More broadly, the case underscores a friction point in oncology dealmaking: legacy exclusivity around a mechanism of action colliding with today’s combination-first R&D model. As ADCs, radioconjugates, and bispecifics surge, sponsors increasingly rely on external PD-1s to build registrational packages quickly. The industry has leaned on Keytruda as the “universal adapter,” while acquirers push for cross-portfolio synergies. This suit, following a 2020 dispute that ended in higher Jemperli royalties and a Zejula royalty for Anaptys, signals that smaller licensors will aggressively defend value when partners optimize beyond the four corners of old agreements.
The watchlist is clear: how the court defines “commercially reasonable efforts,” what counts as prohibited participation in governed trials with a competing PD-1, and what remedies, if any, recalibrate incentives without derailing patient access. For Commercial and Medical Affairs leaders planning combo strategies through Jemperli’s patent horizon into 2035–2036, the strategic question is whether IO backbones become proprietary chokepoints again—or whether contracting evolves to protect exclusivity while preserving the flexibility modern oncology development now requires.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
