Climb Bio, Inc. (NASDAQ:CLYM), a clinical stage biotechnology company developing therapeutics for patients with immune-mediated diseases, today announced initial data from the ongoing Phase 1b portion of its Phase 1b/2a study evaluating budoprutug, an anti-CD19 monoclonal antibody, in adults with primary immune thrombocytopenia (ITP) demonstrating an encouraging safety and tolerability profile, robust B-cell depletion, and meaningful platelet responses in heavily pretreated patients. The initial data are being presented at the European Hematology Association (EHA) Congress 2026, which is being held on June 11-14, 2026, in Stockholm, Sweden.

The ongoing Phase 1b/2a study is evaluating budoprutug in patients with primary ITP to inform dose and regimen selection and assess safety and the depth and duration of platelet response and B-cell depletion. Initial safety and efficacy data are available from the 250 mg cohort, and initial safety data are available from the 500 mg cohort. Enrollment in the 1000 mg cohort is ongoing.

"Patients with chronic ITP often cycle through multiple therapies without achieving a sustained response," said Edgar D. Charles, M.D., Chief Medical Officer of Climb Bio. "These initial data suggest that targeting CD19 with budoprutug may offer a differentiated approach in ITP, enabling robust B-cell depletion, durable platelet responses, and an acceptable safety and tolerability profile. Importantly, we observed platelet responses in several patients who had been previously treated with rituximab, highlighting the potential to address a high unmet need population where available treatment options remain limited. Taken together, these data demonstrate biological activity of budoprutug in ITP, and importantly, provide proof-of-concept in a non-renal autoimmune indication. We look forward to sharing additional data from this study later in the year."

Study Design and Data Highlights

• The Phase 1b portion of the Phase 1b/2a study (NCT07043946) is evaluating three ascending doses (250 mg, 500 mg and 1000 mg) of intravenous budoprutug, administered in two doses 14 days apart, in adults with primary ITP who have received at least one prior therapy
• As of June 1, 2026, 15 patients had been enrolled across the 250 mg (n=6) and 500 mg (n=9) dose cohorts, median follow-up was 38 weeks and 12 weeks for the 250 mg and 500 mg cohorts respectively.
• Patients enrolled were heavily pretreated, with a median of 6 to 7.5 prior lines of therapy and disease duration ranging from 0.5 to 40 years
• Budoprutug was generally well tolerated at both the 250 mg and 500 mg dose levels, with no serious adverse events, no treatment discontinuations due to adverse events, and no infusion related reactions; all adverse events were Grade 1 to Grade 2
• In the 250 mg dose cohort, B-cell levels were depleted by an average of over 90% by Week 4 and mean platelet count increased by 111,000 platelets/µL at Week 24
• Durable platelet responses were achieved in four out of six patients in the 250 mg dose cohort, with two out of six patients experiencing platelet levels >100 x 103/µL for over 24 weeks
  • Of the four patients who had previously been treated with rituximab, three responded to treatment with budoprutug, two with durable and complete responses
• Results to date support continued clinical evaluation of budoprutug in ITP; enrollment in the 1000 mg cohort is ongoing