AnaptysBio’s Rosnilimab Phase 2 Trial Falls Short But Signals Resilience in Immunology Innovation
San Diego, Nov. 10, 2025 - In a significant update from AnaptysBio, Inc. (Nasdaq: ANAB), a prominent clinical-stage biotechnology company centered on pioneering immunology therapeutics, the much-anticipated results from its Phase 2 trial for rosnilimab in the treatment of moderate-to-severe ulcerative colitis (UC) have been released. The investigational treatment, while showing a strong safety profile, did not achieve the primary efficacy endpoint of mean change from baseline in modified Mayo Score (mMS) nor the key secondary endpoints of clinical response and clinical remission at Week 12. The placebo rates observed were consistent with historical expectations, prompting the company to make the prudent decision to discontinue the UC trial, ultimately leading to cost savings of at least $10 million.
President and CEO of AnaptysBio, Daniel Faga, expressed his disappointment in the trial’s efficacy results yet remained optimistic about the future trajectory of rosnilimab, particularly in rheumatoid arthritis (RA). The company aims to provide new updates in the first half of 2026, exploring potential funding avenues that would enhance their strategic positioning without compromising their lucrative royalties. Moreover, ANB033, their CD122 antagonist currently in Phase 1b development for celiac disease, and plans for further Phase 1b studies in 2026, underscore the company’s commitment to advancing their innovative pipeline.
The comprehensive Phase 2 trial, conducted across multiple centers globally, canvassed 136 patients grappling with moderate-to-severe UC, all of whom had inadequate responses to previous conventional or advanced therapies. Participants were randomized into groups receiving either 400mg SC rosnilimab every four weeks, 800mg SC every two weeks, or placebo. Despite initial hope, rosnilimab did not outperform the placebo, with clinical remission rates strikingly comparable across the board. Although an uptick in remission rates appeared between Weeks 12 and 24, the results still fell short of the company’s six-month target product profile.
Despite these setbacks, the trial yielded compelling evidence regarding the pharmacodynamics of rosnilimab, echoing findings from previous RA studies. A notable ~90% depletion of pathogenic T cells was documented at Week 12, with sustainability observed through Week 24 and Week 50 for those in the treatment extension period transitioning to a 400mg Q8W dose regimen. Furthermore, intra-tissue PD-1+ T cell depletion in colonic samples paralleled those seen in RA synovium studies, affirming the theorized maximum pharmacological effect of the 400mg Q4W induction dose.
On the financial front, AnaptysBio stands resilient, registering a remarkable 102.93% revenue growth in the second quarter of 2025 compared to the previous year. This surge notably surpasses the average revenue growth of 6.62% among its competitors. Nevertheless, this robust sales growth was not mirrored by net income gains, contrasting with a 118.95% income increase seen by most competitors. AnaptysBio’s commitment to optimizing their business strategy is evident, with plans to bifurcate its biopharmaceutical and substantial royalty endeavors by 2026, including notable Jemperli royalties, valued at over $390 million annually, expected to hit peak sales before 2031.
AnaptysBio’s foray into ulcerative colitis may not have yielded the anticipated outcomes; however, the data enrich the existing knowledge base and bolster their position in ongoing immunology research. The company’s unwavering dedication to scientific innovation assures stakeholders of their strategic acumen and long-term vision in the competitive biotech landscape.
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