FDA Grants Fast Track Designation to Climb Bio’s Rare Kidney Disease Drug

Rare Daily Staff

The U.S. Food and Drug Administration has granted Fast Track designation to Climb Bio’s experimental therapy budoprutug for the treatment of primary membranous nephropathy, a rare autoimmune kidney disease with no approved therapies.

Fast Track designation is intended to speed the development and review of drugs that address serious conditions and unmet medical needs, allowing for more frequent interactions with the FDA and potential eligibility for accelerated approval pathways.

Primary membranous nephropathy is driven by autoantibodies that damage the kidney’s filtering units, leading to heavy proteinuria, nephrotic syndrome, and a gradual loss of renal function. If untreated, the disease can progress to chronic kidney disease or end-stage kidney failure requiring dialysis or transplantation.

Budoprutug is an experimental anti-CD19 monoclonal antibody designed to deplete B cells, including plasmablasts and some plasma cells that produce harmful autoantibodies. The drug has shown the ability to induce deep and sustained B-cell depletion, reduce autoantibody levels, and drive clinical remission in early studies.

The company said results from a phase 1b study demonstrated complete peripheral B-cell depletion in all five treated patients, along with serologic remission in all evaluable participants and clinical remission in all patients by week 48. No treatment-related serious adverse events were reported.

Budoprutug is currently being evaluated in a global phase 2 open-label trial, known as PrisMN, which is enrolling patients with persistent proteinuria despite standard therapy. Climb Bio said it expects initial data from the study in the second half of 2026.