Zenas BioPharma shares plunge 8.49% following mixed clinical data for obexelimab

Zenas BioPharma’s shares plunged 8.4889% in pre-market trading on January 7, 2026, following a sharp selloff in the prior week as investors reacted to mixed clinical data for its lead candidate, obexelimab. The biotech’s stock had already dropped over 51% from $34.50 to $16.61 between January 2-5, despite obexelimab meeting its primary endpoint in a Phase III trial for IgG4-related disease. The 56% reduction in flare-up risk, while statistically significant, failed to outperform Amgen’s Uplizna, which demonstrated an 87% efficacy in a comparable trial, raising concerns about market competitiveness.

Obexelimab also achieved all secondary endpoints, including reduced flare frequency and higher remission rates, with a favorable safety profile showing lower infection rates compared to placebo. However, the therapy’s subcutaneous administration advantage—enabling at-home use—was insufficient to offset investor skepticism about its ability to challenge Uplizna, which secured U.S. approval in April 2025. Zenas plans to submit a biologics license application for IgG4-RD in Q2 2026 and aims for European approval by mid-2026, though market forecasts suggest Uplizna could dominate with $1.9 billion in 2031 sales, versus $663 million for obexelimab if approved.

The sell-off underscores the challenge of translating positive trial results into market share in a competitive autoimmune therapy landscape. While obexelimab’s mechanism of B-cell inhibition offers a distinct approach to IgG4-RD, its efficacy shortfall against an established rival has shaken investor confidence. Zenas remains focused on advancing the drug through regulatory channels but faces an uphill battle to position obexelimab as a first-line treatment in a market where convenience alone may not drive adoption.