Rosnilimab failed to improve outcomes over placebo at Week 12 in a 136‑patient Phase 2 ulcerative colitis study, with clinical remission observed in 7% of patients on either 400 mg Q4W or 800 mg Q2W dosing. Endoscopic remission was 5% and 4% on the two regimens, respectively. Despite approximately 90% depletion of PD‑1+ pathogenic T cells in blood and colon tissue sustained through Week 24 and into the treatment‑extension period, the trial missed the primary endpoint of change in modified Mayo Score and key secondary endpoints. Safety was clean, with no treatment‑related SAEs, low rates of injection site reactions, and no malignancies reported.
AnaptysBio will discontinue the UC program for rosnilimab, projecting at least $10 million in cost savings from the shutdown. The company plans to revisit rosnilimab’s path in rheumatoid arthritis with an update in the first half of 2026, funded through strategic or other non‑dilutive capital. In parallel, the pipeline will concentrate on ANB033, a CD122 antagonist advancing through Phase 1b in celiac disease with a second inflammatory indication planned for 2026, and ANB101, a BDCA2 modulator in Phase 1a. Corporate restructuring remains on track: management intends to separate biopharma operations from royalty assets by 2026. Cash is guided to roughly $300 million at 2025 year‑end, inclusive of an expected $75 million milestone from GSK if Jemperli crosses $1 billion in global net sales in Q4 2025.
Strategically, the UC halt underscores a recurring tension in IBD development: compelling pharmacodynamics without corresponding clinical lift. With robust peripheral and tissue depletion of PD‑1+ T cells but no Week 12 benefit—and Week 24 signals falling short of the six‑month target profile—the data argue that PD‑1+ T‑cell depletion is insufficient to drive induction efficacy in moderate‑to‑severe UC under the tested design. In a category where placebo effects, heterogeneity, and induction timing complicate readouts, Anaptys is opting for capital discipline and redeployment toward indications where the mechanism may map more directly to clinical endpoints, while preserving optionality via external funding for RA.
For sites and CROs, near‑term impact is a wind‑down of UC activities and safety follow‑up for extension participants who transitioned to 400 mg Q8W dosing. Gastroenterology networks lose a study but may see reallocation as other IBD programs compete for experienced centers and endoscopy capacity. Rheumatology sites could benefit if rosnilimab advances in RA, though the company’s messaging on non‑dilutive financing suggests partnership‑dependent timelines. Vendors focused on immunophenotyping and tissue biomarker analytics can extract practical learnings from the PD‑efficacy disconnect, informing enrichment strategies and endpoint selection in future T‑cell–modulating approaches. The planned corporate separation also has operational implications: vendor master service agreements, pharmacovigilance infrastructure, and quality systems will need clean partitioning to avoid execution drag across entities.
Key watch items now pivot to three fronts. First, clarity on the RA path in 1H26, including whether Anaptys pursues a partner‑led development plan and which efficacy measures and patient subgroups it targets to sharpen the mechanism’s clinical relevance. Second, readthrough from ANB033’s Phase 1b in celiac disease—proof of activity and tolerability in a well‑defined autoimmune setting could reframe the company’s immunology thesis and capital allocation. Third, execution on the royalty asset separation and associated cash runway assumptions, including the timing of the Jemperli sales milestone. The broader signal for the field: IBD programs targeting T‑cell pathways will face a higher bar to demonstrate rapid induction benefits, pushing sponsors to tighter patient stratification, longer induction windows, or combination logic—each with operational and regulatory costs that demand early, data‑driven conviction.
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.
