Zenas BioPharma’s lead autoimmune asset, obexelimab, met its primary endpoint in a Phase III trial; however, the data has failed to impress investors, sending the company’s stock value down by over 50%.
The B-cell inhibiting monoclonal antibody (mAb) triggered a statistically significant 56% reduction in the risk of Immunoglobulin G4-related disease (IgG4-RD) flare-ups in the INDIGO study (NCT05662241) – meeting its primary endpoint.
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However, the subcutaneous (SC) therapy failed to best its potential market competitor, Amgen’s Uplizna (inebilizumab), which triggered an 87% risk reduction in its respective pivotal trial.
Following the debut of these topline IgG4-RD results, investors have pulled away from Zenas’ stock, causing its value to crash by more than 51.8% from $34.50 at market close on 2 January to $16.61 at market close on 5 January.
Obexelimab also met all of its secondary trial endpoints – reducing the number of flares requiring rescue therapy and the general use of such treatments, while boosting the proportion of patients achieving complete remission.
While Zenas is yet to share detailed information on obexelimab’s safety profile, the biotech did note that patients given the therapy exhibited a lower rate of infections – including those rated Grade 3 – compared with placebo.
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By GlobalDataZenas plans to share further details from the Phase III INDIGO trial at an upcoming, undisclosed medical meeting.
Despite potential waning investor confidence in obexelimab’s future market potential, Zenas will still file for the drug’s US approval, with the company expecting to submit a biologics license application (BLA) for the therapy in IgG4-RD in Q2 2026.
The Massachusetts-based biotech is also eyeing approval for obexelimab on the European market, with Zenas noting its plans to put forward a BLA for the drug to the European Medicines Agency (EMA) in the second half of 2026.
Obexelimab’s IgG4-RD market potential remains unclear
If approved, obexelimab would join Uplizna on the market, which became the first targeted therapy to gain US approval for the treatment of IgG4-RD back in April 2025.
Though obexelimab has failed to demonstrate its superiority to Uplizna in terms of efficacy in IgG4-RD, the therapy does have a dosing edge.
This is because obexelimab can be administered at home, while Uplizna requires intravenous (IV) administration – potentially reducing pressure on both healthcare services and patients.
Obexelimab also works through a different mechanism to Uplizna; it acts by inhibiting B-cells that drive the disease’s progression, rather than eliminating them like the latter drug.
Currently, GlobalData, parent company of Clinical Trials Arena, forecasts that Uplizna will become a blockbuster seller for Amgen, bringing in sales of $1.9bn in 2031, while obexelimab is set to make $663m in the same year, if it gains approval.
