Climb Bio Receives FDA Fast Track Designation For Budoprutug, An Investigational Anti-CD19 Antibody For Primary Membranous Nephropathy

Climb Bio, Inc., a clinical-stage biotechnology company focused on developing treatments for immune-mediated diseases, announced that the U.S. Food and Drug Administration has granted Fast Track Designation to budoprutug. Budoprutug is the company’s investigational anti-CD19 monoclonal antibody being developed for primary membranous nephropathy (pMN), a rare kidney disorder with no currently approved FDA therapies.

According to Edgar Charles, M.D., Chief Medical Officer at Climb Bio, the Fast Track Designation acknowledges both the significant need for new treatment options in pMN and the encouraging early clinical results observed with budoprutug. He noted that this designation will allow the company to work more closely with the FDA and may help accelerate the program as budoprutug advances toward later-stage clinical development for this serious immune-mediated kidney disease.

Earlier findings from a completed Phase 1b study in patients with pMN showed strong signals of activity. Treatment with budoprutug led to complete peripheral B-cell depletion in all five treated patients. Among the three participants who could be evaluated for serologic response, all achieved serologic remission. 

Clinical outcomes were also promising, with all five participants experiencing either complete or partial remission by week 48. The safety profile was favorable, with no clinically meaningful treatment-related serious adverse events reported. Long-term follow-up results showed sustained reductions in proteinuria, further supporting budoprutug’s potential as a disease-modifying therapy for pMN.

Budoprutug is now being evaluated in the Phase 2 global open-label dose-range study known as PrisMN. This study aims to assess pharmacodynamic effects including changes in B-cell counts, anti-Phospholipase A2 Receptor (PLA2R) antibody levels, and total immunoglobulin levels as well as preliminary measures of clinical efficacy, such as rates of complete and partial remission. 

The study is enrolling patients with pMN who continue to have significant proteinuria despite optimized renin-angiotensin-aldosterone system (RAAS) inhibition. Findings from PrisMN will also help determine the appropriate dose for Phase 3 clinical development. Climb Bio expects to report initial data from the Phase 2 study in the second half of 2026.