The Differences between Ide-Cel and Cilta-Cel in Relapsed Myeloma at Single Cell Resolution

Introduction: The two commercially available BCMA-directed CAR T cell therapies idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel) have revolutionized the treatment of relapsed/refractory multiple myeloma (RRMM). Results from clinical trials suggest superior outcome with cilta-cel compared to ide-cel. We conducted a comprehensive longitudinal single-cell multi-omics study in a large real-world cohort of RRMM patients to identify markers associated with response, resistance or side effects after ide-cel or cilta-cel.

Methods: Peripheral blood mononuclear cells (PBMCs) were isolated on the day of leukapheresis (LP), and on days 30 and 100 post infusion. PBMCs were subjected to single cell RNA, TCR, BCR and surface protein analysis. Additionally, peripheral blood samples collected at the day of LP, after lymphodepletion and on days 7, 14, 30 and 100 following CAR T cell therapy were analyzed by flow cytometry to monitor CAR T cell expansion, immune checkpoint and cytotoxicity marker expression and T cell differentiation. Response was evaluated according to IMWG criteria on day 30 after CAR T cell infusion. Progression-free survival (PFS) was analyzed using the Kaplan-Meier method and the log-rank test.

Results: We retrospectively included 62 RRMM patients treated with cilta-cel (n=28) or ide-cel (n=34). We observed a significantly higher overall response rate (93% vs 70%, p<0.05) and complete response rate (75% vs. 35%, p<0.01) in patients treated with cilta-cel vs. ide-cel. At a median follow-up of 10 [95%CI: 8-12] months, this led to a significant improvement in median PFS (not reached (n.r.) in cilta-cel vs. 7 [3-n.r.] months in ide-cel patients, p<0.01). We observed a lower rate of CRS in cilta-cel patients (grade 1 or higher: 52% vs. 79% in ide-cel patients, p<0.05). Four patients who received cilta-cel (15%) and one patient who received ide-cel (3%) experienced ICANS (p=0.16). CAR T cell expansion was initially slower in patients treated with cilta-cel, but reached significantly higher levels on day 14 compared to ide-cel (p<0.01). There was a significantly higher proportion of CD4+ CAR T cells in cilta-cel compared to ide-cel patients (day 14: 35% vs 10%, p<0.01).

More than 500,000 cells from 144 samples collected longitudinally before and after CAR T cell infusion passed quality assessment after single cell sequencing. Cellular composition of peripheral blood between patients with or without CRS was distinct at LP and on days 30 and 100. More CD4+ cells were detected in patients with CRS grade 2 at the time of LP and CD8+ cells on day 30 and 100 after infusion. Fewer classical monocytes were observed at all time points in patients without CRS. We observed a significantly (p<0.05) higher proportion of CD4+ cells with CRS at the time of LP. TCR repertoires showed a higher cytotoxic enrichment score in patients with CRS for the largest CD4+ clones compared to CD8+ clones on day 30. We also observed a significantly (p<0.05) higher proportion of polyfunctional T-cells with increasing CRS on day 30 following infusion.

Increased clonality in TCR repertoires was revealed between non-PD and PD patients at time of leukapheresis and on day 30. TCR diversity analysis of CD4+ T cells showed increased diversity (p<0.05) over day 30 to day 100 and for CD8+ T cells over day 30 in patients with non-PD. In addition, T cell subtypes revealed an increased diversity of cytotoxic CD4+ cells in non-PD compared to PD across all time points.

Conclusion: Patients treated with cilta-cel had significantly improved PFS than patients treated with ide-cel, which was driven by significant expansion of CD4+ CAR T cells. CRS was associated with increased polyfunctional heterogeneity of T cells and occurred less frequently after cilta-cel therapy. ICANS was more common with cilta-cel. Finally, long-term response to CAR T cell therapy was associated with a diversification of the TCR repertoire.