Climb Bio posts Phase 1b ITP data for budoprutug at EHA 2026
Climb Bio has presented initial Phase 1b data for budoprutug, its anti-CD19 monoclonal antibody, in primary immune thrombocytopenia at the European Hematology Association Congress in Stockholm. The readout, drawn from 15 patients across two dose cohorts, showed encouraging platelet responses, deep B-cell depletion, and a clean safety profile in a population that had exhausted a median of six to seven prior treatment lines.
The Wellesley Hills, Massachusetts company is running a Phase 1b/2a study evaluating three ascending intravenous doses of budoprutug (250 mg, 500 mg, and 1000 mg), administered as two infusions 14 days apart. As of 1 June 2026, six patients had been enrolled in the 250 mg cohort and nine in the 500 mg cohort; enrolment in the 1000 mg cohort is ongoing. Median follow-up at the time of analysis was 38 weeks and 12 weeks for the two cohorts respectively.
Trial data
In the 250 mg cohort, B-cell levels fell by more than 90% on average by week four. Mean platelet count rose by 111,000 platelets per microlitre at week 24, and four of the six patients achieved durable platelet responses. Two patients sustained platelet levels above 100 x 10³/µL for more than 24 weeks. Notably, three of the four patients who had previously received rituximab responded to budoprutug, two with complete and durable responses, a finding the company considers significant given that rituximab failure defines a particularly hard-to-treat subgroup.
At both dose levels, budoprutug was well tolerated. No serious adverse events, treatment discontinuations, or infusion-related reactions were recorded, and all adverse events were Grade 1 or Grade 2.
Edgar D. Charles, Chief Medical Officer of Climb Bio, said the results "highlight the potential to address a high unmet need population where available treatment options remain limited," adding that the data provide proof-of-concept for budoprutug in a non-renal autoimmune indication. The company's more mature dataset for budoprutug is in primary membranous nephropathy, where it holds FDA Orphan Drug and Fast Track designations.
Market context
ITP is estimated to affect around 85,000 patients in the United States, with roughly 20% failing multiple lines of therapy. The existing treatment landscape spans corticosteroids, intravenous immunoglobulin, thrombopoietin receptor agonists such as eltrombopag and romiplostim, and the anti-CD20 antibody rituximab. Fostamatinib, a spleen tyrosine kinase inhibitor, and the neonatal Fc receptor antagonist rozanolixizumab have added further options in recent years, but durable disease modification remains elusive for a meaningful proportion of patients.
The CD19 targeting approach that underpins budoprutug is attracting broader industry interest. Unlike CD20-directed agents, anti-CD19 antibodies and CAR-T constructs can reach plasmablasts and certain plasma cells that lack CD20 expression, offering a potentially deeper depletion of autoantibody-producing cells. Lonigutamab, developed by Zenas BioPharma, and several CAR-T programmes are among the competitors pursuing the same biology in ITP and related autoimmune indications. Climb Bio's differentiator is the monoclonal antibody format, which carries a more tractable manufacturing and administration profile than cell therapy.
Climb Bio also has budoprutug in trials for systemic lupus erythematosus, and a subcutaneous formulation is in development. The company said it expects to report additional ITP data from the study, including the 1000 mg cohort, before the end of 2026. Investors will look for a defined Phase 2a dose selection and an update on the durability of platelet responses as the study matures.