Zenas Shares Slide Despite Phase III Success for Obexelimab

Zenas BioPharma’s stock fell by more than 50% after Phase III results for its lead autoimmune drug, obexelimab, failed to meet investor expectations despite achieving its primary endpoint in immunoglobulin G4–related disease (IgG4-RD).

In the Phase III INDIGO trial, obexelimab reduced the risk of disease flares by 56% versus placebo, meeting the study’s main goal. However, the result lagged behind Amgen’s competing therapy Uplizna, which showed an 87% flare-risk reduction in its pivotal trial. Following the data release, Zenas’ share price dropped from $34.50 on January 2 to $16.61 on January 5.

Obexelimab also met all secondary endpoints, including fewer flares requiring rescue treatment and higher remission rates. The company reported lower infection rates compared with placebo, though full safety data are pending.

Despite the sharp market reaction, Zenas plans to seek US approval in 2026 and pursue European authorization later, highlighting the drug’s at-home subcutaneous dosing as a potential competitive advantage.

06-01-2026