Early Chimeric Antigen Receptor T Cell Expansion Is Associated with Prolonged Progression-Free Survival for Patients with Relapsed/Refractory Multiple Myeloma Treated with Ide-Cel: A Retrospective Monocentric Study

Abstract

The outcomes of patients with relapsed and refractory multiple myeloma (RRMM) previously treated with the 3 main classes of myeloma therapy-immunomodulatory drugs, proteasome inhibitors, and anti-CD38 antibodies-remain poor. Recently, based on the phase II pivotal KarMMa trial showing prolonged overall survival (OS) and progression-free survival (PFS) in heavily treated patients, idecabtagene vicleucel (ide-cel), a B cell maturation antigen (BCMA)-directed chimeric antigen receptor (CAR) T cell therapy (CAR-T) product, was approved in the United States for the treatment of RRMM. In France, since June 2021, an early access program has authorized the use of ide-cel in the setting of RRMM (defined as progressive myeloma after at least 3 previous regimens, including the 3 main antimyeloma therapies). We report the first French experience through this early access program in a retrospective study of 24 consecutive patients treated with ide-cel at our institution. The patients were evaluated according to International Myeloma Working Group criteria and by positron emission tomography computed tomography (PET-CT) at 1, 3, 6, 9, and 12 months after ide-cel infusion. Most patients had adverse cytogenetic abnormalities, and RRMM with triple-refractory drugs were seen in 79%. Bridging therapy was required for 19 of 24 patients. Before CAR-T cell infusion, lymphodepletion with fludarabine and cyclophosphamide was systematically performed. The median follow-up was 15.2 months. At 3 months after ide-cel infusion, 92% of patients achieved at least a partial response, and 50% achieved a complete response or better (≥CR). At 6 months, 70% of patients had a persistent ≥CR. At 3 and 6 months, bone marrow minimal residual disease (10^-6 level) was undetectable in 79% and 75% of patients, respectively. At 6 months, CR as assessed by PET-CT was achieved in 15 of 20 patients (75%). The median PFS was 14.8 months, and median OS was not reached. Notably, an expansion of circulating CAR-T cells to >180/mm³ after infusion was strongly associated with prolonged PFS. Additionally, the level of soluble BCMA measured before infusion was identified as a prognostic factor for PFS, likely correlated to the tumor burden. Grade 1-2 cytokine release syndrome (CRS) occurred in 22 of 24 patients (92%). Only 1 patient (4%) experienced grade ≥3 CRS. The occurrence of neurologic toxicity was infrequent (12.5%) and reversible in all cases. Hematologic toxicity was relatively common, and secondary hypogammaglobulinemia occurred in most patients. Infections (mostly viral) were frequent but most often nonsevere. This study echoes the promising results of the KarMMa trial and identifies possible prognostic indicators in RRMM patients treated with ide-cel, potentially refining treatment strategies and improving outcomes in this challenging context.

Keywords: BCMA; CAR-T cell expansion; Ide-cel; RRMM.