Abstract 3616: In vivo expansion patterns of anti-BCMA CAR T-cell in relapsed/refractory multiple myeloma: Comparative immunomonitoring of idecabtagene vicleucel and ciltacabtagene autoleucel

Abstract Introduction: Chimeric antigen receptor (CAR) T cell (CAR-T) treatments have revolutionized the treatment of multiple myeloma (MM). Two CAR-T cell products targeting B cell maturation antigen (BCMA) have received approval for the treatment of MM: idecabtagene vicleucel (idecel) and ciltacabtagene autoleucel (ciltacel). A comparative analysis of in vivo CAR-T responses in patients receiving these novel cellular therapies has not been performed, especially not in the real-world setting. Methods: We prospectively enrolled 23 MM patients treated with idecel or ciltacel in our study GCCC2043. Blood samples were obtained at apheresis, pre-lymphodepleting (LD) chemotherapy, on days 0, +7, +14, +21, +28 and at +3 months post CAR-T. Samples were stained using BCMA or control CAR detection reagents, monoclonal antibodies against T cell surface antigens, and analyzed using flow cytometry. Results: Baseline clinical characteristics, pre-apheresis and pre-LD absolute lymphocyte counts were comparable between groups. There were no G3 cytokine release syndrome (CRS) events whereas G1/2 CRS and all-grade Immune Effector Cell-Associated Neurotoxicity Syndrome (ICANS) events were not significantly different between cohorts. The global overall response rate (ORR) was 78.3% (n=18) and 60.9% (n=14) at days 30 and 90, respectively. At +1 month, 72.7% (8/11) of idecel and 83.3% (10/12) of ciltacel cohort had an objective response (p=0.625). There was no statistical ORR difference between idecel and ciltacel cohorts at 3, 6, and 9 months. Two-way ANOVA of CAR-T expansion studies revealed a trend towards an effect of treatment type (p=0.0595). Time to peak CAR-T numbers was significantly shorter for idecel (p=0.0127), however, ciltacel showed a significantly more pronounced CAR-T expansion (p=0.043) and longer persistence. Peak CAR-T expansion was associated with clinical responses across cohorts at +1 (p=0.034) and +3 months (p=0.050). Day +30 responses were indicative of Day +90 and Day +180 responses (p<0.001, p=0.011). There was no difference in CD8+ CAR T cell peak levels, however, CD4+ CAR T cell peak levels were much higher (p=0.019) for ciltacel vs. idecel. Similarly, there were significantly higher (p=0.002) CD4+/CD8+ double-positive CAR-T peak levels in ciltacel vs. idecel patients. There was no significant difference in the distribution of T cell memory subtypes at peak level. Conclusions: We demonstrate here for the first time significant differences in CAR T cell expansion and persistence patterns following infusion of either idacel or ciltacel. Studies are underway at our institution investigating anti-BCMA CAR T cell responses in more detail and larger numbers of patients. Such studies have the potential to identify predictive/prognostic biomarkers and/or lead to further optimization of myeloma-targeting CAR-T. Citation Format: Mehmet Kocoglu, Aaron P. Rapoport, Etse Gebru, Destiny Omili, Daniel Yamoah, Rediet Mulatu, Jean Yared, Nancy M. Hardy, Michael Kallen, Ashraf Z. Badros, Djordje Atanackovic. In vivo expansion patterns of anti-BCMA CAR T-cell in relapsed/refractory multiple myeloma: Comparative immunomonitoring of idecabtagene vicleucel and ciltacabtagene autoleucel [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3616.