Zenas BioPharma shares plunge 51.86% as obexelimab trial results fall short vs. Amgen's Uplizna efficacy

Zenas BioPharma’s shares plummeted 51.8551% in pre-market trading on January 6, 2026, following the release of Phase III trial results for its lead autoimmune drug, obexelimab, in IgG4-related disease. Despite meeting primary endpoints—showing a 56% reduction in flare-up risk—investors reacted negatively to the data, which fell short of outperforming Amgen’s Uplizna, a rival therapy with an 87% efficacy rate in a comparable trial.

The subcutaneous administration of obexelimab, which offers a dosing advantage over Uplizna’s intravenous delivery, failed to offset concerns over its competitive edge. While the drug met secondary endpoints and demonstrated a favorable safety profile with reduced infection rates, its efficacy gap against Uplizna likely dampened market confidence. Zenas plans to present full trial data at an upcoming medical conference and aims to file for U.S. and European approvals in 2026, though the stock’s sharp decline reflects lingering skepticism about its commercial potential.

Industry analysts have remained cautious about Zenas BioPharma’s market position due to the high unmet need in IgG4-related disease treatment. Uplizna, having already secured regulatory approval and a strong safety record, continues to dominate the market. However, obexelimab’s subcutaneous formulation could appeal to patients seeking more convenient treatment options. Regulatory approval timelines remain a key uncertainty, with Zenas expected to engage in detailed discussions with the FDA and EMA in the coming months.

Zenas BioPharma’s future success will depend heavily on its ability to differentiate obexelimab in the market and convince clinicians and payers of its value proposition. The company also plans to expand its pipeline into other autoimmune diseases, leveraging the platform it has built for monoclonal antibody development. Investors are likely to remain watchful until the full data package is available and regulatory decisions become clearer.