Phase 1b study of the anti-CD38 antibody mezagitamab in patients with relapsed/refractory multiple myeloma

•In a phase 1b study of relapsed/refractory myeloma, the anti-CD38 antibody mezagitamab was well tolerated and showed preliminary activity.•At the recommended phase 2 dose of 600 mg, the overall response rate was 47%, and the median duration of response was 22.1 months. [Display omitted] This phase 1b trial aimed to determine the safety, tolerability, and preliminary efficacy of mezagitamab, a subcutaneously administered anti-CD38 monoclonal antibody, in patients with relapsed/refractory multiple myeloma (RRMM). Eligible patients had received ≥3 prior lines of treatment, including an immunomodulatory drug (IMiD), a proteasome inhibitor (PI), and a steroid, or ≥2 prior lines in which 1 included a PI + IMiD, and were refractory or intolerant to ≥1 IMiD and ≥1 PI. Fifty patients were enrolled: 44 received mezagitamab monotherapy (dose-escalating cohorts at 45-1200 mg) and 6 received mezagitamab 300 mg in combination with pomalidomide plus dexamethasone. Patients received mezagitamab weekly for 8 doses, every other week for 8 doses, and monthly thereafter. No dose-limiting toxicities were reported with single-agent mezagitamab, and the recommended phase 2 dose was determined as 600 mg. The most common drug-related treatment-emergent adverse events (TEAEs) were fatigue in the monotherapy cohort (9/44 patients) and neutropenia in the combination cohort (4/6 patients); neutropenia was the only drug-related grade ≥3 TEAE to occur in >1 patient. No infusion reactions occurred, and 4 injection-site reactions were reported. Three patients discontinued treatment due to TEAEs. Among the 22 patients receiving 600 mg mezagitamab, the overall response rate was 47%, and the median duration of response was 22.1 months. Mezagitamab outcomes were comparable to those reported with other anti-CD38 therapies in patients with advanced RRMM. Further development of mezagitamab in myeloma is not planned, but studies are underway in autoimmune conditions. This trial was registered at www.ClinicalTrials.gov as #NCT03439280.