Open-label, single-arm phase Ib/II study of immune combination therapy with elotuzumab and belantamab mafodotin in patients with relapsed refractory multiple myeloma.

7559 Background: The B cell maturation antigen (BCMA)-targeted antibody drug conjugate belantamab mafodotin enhances cell-mediated antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis. Elotuzumab, a signaling lymphocytic activation molecule family member 7 (SLAMF7) checkpoint inhibitor, activates NK cells and induces antibody-dependent cellular cytotoxicity. Bela-Elo (NCT05002816) is an ongoing phase Ib/II trial evaluating the safety, tolerability and preliminary efficacy of the unique combination of these two agents in patients with relapsed/refractory myeloma (RRMM). We report data from phase I part of this trial. Methods: This single-arm phase Ib/II study is enrolling patients with triple-class refractory RRMM. Patients with progression after prior BCMA-targeted therapy are eligible. Elotuzumab is administered via intravenous (IV) infusion at an established dose of 10 mg/kg on days 1, 8, 15, 22 every 28 days for cycles 1 and 2; followed by 20mg/kg on day 1 of each 28-day cycle. Belantamab mafodotin is administered via IV infusion with the starting dose of 1.9 mg/kg IV at every 4-week interval, with subsequent dose-reduction based on toxicity. Descriptive statistics were used to summarize patient demographics and safety and efficacy outcomes. Results: As of data cut-off (January 20, 2024) 12 subjects have been enrolled; and 10 subjects received treatment on study. Median age of patients was 66.5 years (range 59-79). The patient population was heavily pretreated with 5 prior median lines of therapy (range 2-8); 40% (4/10) of patients were refractory to prior BCMA-targeted therapy (2 post-BCMA bispecific antibody, 2 post-BCMA chimeric antigen receptor T-cell therapy CART). Phase I part of the study has completed. Median duration of treatment was 4 months (range 2-19). No dose-limiting toxicities were observed. Four severe adverse events were observed possibly related to the study treatment in 3 patients, including grade 3 pulmonary infection (n=1) and lymphopenia (n=3). Ocular keratopathy developed in 40% of patients, all were grades 1-2 and resolved after discontinuation or dose-reduction of belantamab. Preliminary activity is noted with partial responses (PR) in 4/10 (40%) and stable disease (SD) in additional 3/10 (30%) of patients. Among the four patients who were refractory to prior BCMA therapy, 2 (50%) achieved PR, with duration of response (DOR) of 19 months and 9 months, respectively. Conclusions: This novel combination immune therapy with belantamab mafodotin and elotuzumab appears to have an encouraging safety profile and a promising preliminary efficacy in patients with heavily pretreated RRMM, including in those with prior failure of BCMA-targeted therapy. Clinical trial information: NCT05002816 .