Anaptys Reports Positive Phase 2b Results For Rosnilimab In Rheumatoid Arthritis, Presented As Late-Breaking Oral At ACR

AnaptysBio, Inc., a clinical-stage biotechnology company developing innovative immunology therapeutics, announced new late-breaking data from its global Phase 2b trial of rosnilimab in rheumatoid arthritis (RA) at the American College of Rheumatology (ACR) Convergence 2025 in Chicago. The study, which included 424 patients, evaluated rosnilimab, a selective and potent pathogenic T cell depleter, and demonstrated that positive outcomes observed at Week 12 continued to improve through Week 28 regardless of prior treatment history. 

The results remained durable for at least three months after discontinuation of therapy. Importantly, rosnilimab was well-tolerated with no treatment-related serious adverse events, no malignancies, and no deaths reported through the end of the 38-week trial follow-up.

Professor Paul Emery, M.D., from the University of Leeds and Leeds Biomedical Research Centre in the U.K., presented the findings and noted several key observations. At Week 12, statistically significant and clinically meaningful improvements were achieved for both the primary endpoint, DAS28-CRP, and for ACR20 across all dosing regimens, including monthly doses. 

By Week 28, additional improvements were recorded in CDAI low disease activity (LDA), CDAI remission, and ACR50/70 response rates, independent of whether patients had previously received anti-TNFα, anti-IL6R, or JAK inhibitor therapies. Similar positive outcomes were seen among patients who had failed two or more classes of biologic or targeted synthetic DMARDs, particularly at the mid (400mg every four weeks) and high (600mg every two weeks) dose levels.

Responses measured at Week 28 across several clinical indicators, including CDAI LDA, mean CDAI, mean DAS28-CRP, and ACR50/70, remained stable for at least three months after the last dose of rosnilimab. The safety profile was favorable throughout the study, with no malignancies or deaths reported and few discontinuations due to adverse effects. 

By Week 6, Tph cells were reduced by more than 90% in the blood at all dose levels and within the synovium at the two highest doses. Moreover, highly significant reductions in T cell and B cell activation were observed in synovial biopsies, with deeper reductions seen in patients achieving CDAI LDA responses, with a p-value of less than 0.0001.

Commenting on the results, Professor Emery emphasized that rosnilimab’s unique mechanism of action provides strong clinical proof-of-concept for the targeted depletion of pathogenic T cells, resulting in meaningful and durable improvements in patients with rheumatoid arthritis. He highlighted that the drug’s favorable safety profile, combined with its robust clinical and translational data, distinguishes it from current treatments such as JAK inhibitors and other biologics, which are often associated with safety concerns. 

With more than half of rheumatoid arthritis patients cycling through multiple therapies due to loss of efficacy or side effects, there remains a pressing need for safer and longer-lasting treatment options. The promising Phase 2b results suggest that rosnilimab has the potential to meet this need by offering sustained disease control and improved outcomes for patients living with this chronic autoimmune condition.