Climb Bio's budoprutug hits 12-week immunologic remission in pMN trial

Climb Bio has presented the first clinical data from its PrisMN Phase 2 trial of budoprutug in primary membranous nephropathy, reporting encouraging early immunological activity at the lowest dose tested and hinting at deeper effects at higher doses. The data were disclosed in an oral session at the American Society of Nephrology Kidney Week 2026 in Denver.

Budoprutug is an anti-CD19 monoclonal antibody designed to deplete CD19-expressing B cells, including plasmablasts and certain plasma cells, which drive the autoantibody production that underlies pMN. The disease affects an estimated 75,000 people in the United States and currently has no FDA-approved therapy, making it a high-unmet-need setting that has attracted increasing attention from both biotech and larger pharmaceutical developers.

PrisMN Phase 2 readout

In the 200 mg cohort, the mean reduction in PLA2R antibody levels reached 70% at Week 12, and five of 13 patients (38%) achieved immunologic remission. Patients with lower baseline PLA2R antibody titres of under 175 RU/mL showed a mean reduction of 80%. The 200 mg data were consistent with findings from Climb Bio's earlier Phase 1b study across B-cell depletion, PLA2R antibody reduction, and immunologic remission rates, lending credibility to the programme's reproducibility.

Early data from the 600 mg cohort, with follow-up to Week 6 only, suggested greater drug exposure and deeper peripheral B-cell suppression: mean CD20-positive B-cell suppression reached 98% at Week 4 at 600 mg, compared with 74% at the lower dose. A population pharmacokinetic analysis across approximately 120 patients found that those with high proteinuria clear budoprutug at least twice as fast as non-proteinuric individuals, providing the scientific rationale for dose escalation. Enrolment into the 1,000 mg cohort is ongoing; additional data across all three dose levels are expected in 2027.

The safety profile to date appears clean. Most adverse events were Grade 1 or 2, with no treatment-related serious adverse events, no treatment discontinuations due to adverse events, and no deaths reported across either cohort.

Frank Cortazar, Director of the New York Nephrology Vasculitis and Glomerular Center, said early PLA2R antibody reductions are an important surrogate because they correlate with downstream reductions in proteinuria and, ultimately, complete remission. "These data provide further evidence that targeting CD19 with budoprutug may be a compelling approach in the treatment of pMN," he said.

MCD case and broader pipeline implications

A separate case study presented at the conference described a patient with frequently relapsing minimal change disease who received a single 100 mg dose. The patient achieved three-year steroid-free remission and remained in remission for one year after B-cell reconstitution. Climb Bio characterised this as supporting further investigation in MCD, a condition where steroid dependence and frequent relapse are common clinical challenges.

Beyond these two renal indications, budoprutug is in clinical development for immune thrombocytopenia and systemic lupus erythematosus, and the company is advancing a subcutaneous formulation intended to improve patient access. The drug holds both Orphan Drug Designation and Fast Track Designation from the FDA for pMN.

The competitive landscape in B-cell-targeted therapies for glomerular disease is developing rapidly. Anti-CD20 agents such as rituximab are already used off-label in pMN, and a number of companies are pursuing next-generation B-cell depletion approaches, including CD19-targeting strategies. Climb Bio's argument is that budoprutug's enhanced effector function and sub-picomolar affinity may translate into deeper and more durable depletion than CD20-directed therapies, though the clinical evidence to support that differentiation remains early-stage. Full dose-escalation data, including the 1,000 mg cohort readout and longer-term proteinuria and renal function outcomes, will be the key milestones investors and clinicians watch for in 2027.