Xencor reports early rheumatoid arthritis improvements in Phase 1b plamotamab trial
XNCR•Xencor reported preliminary disease activity improvements and deep B-cell depletion with plamotamab in a Phase 1b rheumatoid arthritis trial. Multiple doses showed greater benefits than single doses, and treatment was well tolerated, with one mild cytokine release syndrome case.
1. Trial findings
Xencor is presenting initial Phase 1b plamotamab results in rheumatoid arthritis at ACR Convergence 2026. Multiple doses showed greater preliminary disease activity benefits than single doses; there was one mild case of cytokine release syndrome and no cases of immune effector cell-associated neurotoxicity syndrome.
2. Separate XmAb657 study
In a Phase 1 study of healthy participants, XmAb657 produced dose-dependent B-cell reductions, and its safety profile supported further dose escalation. Xencor expects another healthy-participant cohort to finish by year-end 2026 and plans to enroll patients with severe autoimmune disease in the first quarter of 2027.
