Rosnilimab's Phase 2b Success in RA: Insights from ACR Convergence 2025

AnaptysBio's rosnilimab Phase 2b trial in rheumatoid arthritis presented at ACR Convergence 2025 showed robust, durable efficacy and a favorable safety profile through 38 weeks, with no treatment-related serious adverse events reported; the company highlighted durable ACR responses that improved through Week 28 and were sustained to Week 38.This finding could influence treatment sequencing and guideline discussions as clinicians evaluate options for patients with inadequate responses to existing therapies.

The randomized Phase 2b tested multiple dosing arms and reported clinically meaningful ACR responses that emerged by Week 12, continued to improve through Week 28, and remained durable to Week 38; the trial population was a multi-arm cohort enrolled irrespective of prior biologic exposure. The company described a JAK-like efficacy profile through six months with persistence off drug for at least three months, and mechanistic data point to selective depletion of pathogenic T cells as a plausible driver of the effect.

No treatment-related serious adverse events were reported and rosnilimab was described as well tolerated through the 38-week follow-up; there were no malignancies and no deaths observed in the dataset. Tolerability appeared favorable relative to general expectations for biologics and JAK inhibitors—particularly regarding infection risk and laboratory-monitoring burdens. The absence of opportunistic infections or cytopenias in this readout is reassuring, but confirmation in larger, longer Phase 3 programs will be required before asserting comparative safety advantages.

These outcomes could prompt guideline committees and clinicians to consider rosnilimab as a potential new option for patients with inadequate response to conventional DMARDs or biologics, given a novel mechanism coupled with durable efficacy and a favorable short-term safety signal. Regulatory filings and Phase 3 confirmatory data will determine timing for guideline integration; real-world safety surveillance and clearer patient-selection criteria (for example, prior biologic exposure or relevant comorbidities) will be critical operational factors. Rheumatologists are likely to watch forthcoming Phase 3 readouts and label details to understand likely positioning, dosing, and monitoring requirements if rosnilimab proceeds to approval.