Zenas BioPharma (NASDAQ:ZBIO) shares plunged about 50% after the company released results from its Phase 3 INDIGO study evaluating obexelimab in Immunoglobulin G4-Related Disease (IgG4-RD).
The company said obexelimab achieved its primary endpoint, cutting the risk of IgG4-RD flares by 56% versus placebo over the 52-week randomized, placebo-controlled period. The treatment also delivered statistically significant outcomes across all four key secondary endpoints.
Despite the headline results, the market reaction was sharply negative. The steep sell-off suggests investors may have been positioned for stronger efficacy data or are uneasy about the regulatory timeline, with Zenas planning to submit its application to the U.S. Food and Drug Administration in the second quarter of 2026.
Zenas reported that obexelimab was generally well tolerated in the trial, noting lower infection rates in patients receiving the drug compared with those on placebo. Management sees obexelimab as a potential first-line treatment for IgG4-RD, emphasizing the convenience of at-home, subcutaneous self-administration.
“We look forward to submitting our Biologics License Application to the FDA in the second quarter of 2026 and our Marketing Authorization Application to the EMA in the second half of this year,” said Lonnie Moulder, Founder and CEO of Zenas.
Beyond IgG4-RD, the company is continuing development of obexelimab in a Phase 2 study for systemic lupus erythematosus, with data expected later this year. Zenas is also advancing orelabrutinib for multiple sclerosis and plans to launch Phase 1 trials for two additional candidates in 2026.