Functional fitness of CAR-T cells in the bone marrow following anti-BCMA durcabtagene autoleucel (PHE885) therapy correlate with prolonged PFS in RRMM

Abstract There have been significant advances in therapy for multiple myeloma (MM). The development of chimeric antigen receptor (CAR) engineered T cells have shown incredible responses by harnessing anti-tumor activity of T cells. However, most CAR-T therapies targeting BCMA involve long manufacturing and expansion times impacting its utility as well as outcome. In a phase 1 clinical trial (NCT04318327) of dose escalation study, we treated 55 RRMM patients, using the next-generation T-charge platform to generate anti-BCMA CAR-T cells in less than 2 days by reducing ex-vivo processing and enhancing in-vivo expansion and preserving T-cell stemness. As we reported earlier, the overall response rate was 98%, and the complete response rate was 55% (Sperling et al ASCO, 2023). Our earlier reports also showed that T-cell stemness is preserved, with CAR T cells expanding robustly in peripheral blood of patients with high clone diversity (Shuntaro et al ASH, 2024). To identify CAR related features that can predict for longer-term response, we performed the immune-monitoring study, evaluating the CAR-T cell-activation and functional activity in bone marrow (BM) microenvironment at 3 months following infusion of PHE885 using CyTOF analysis for 74 markers from 32 patients. We specifically evaluated the association of functional fitness of CAR-T cells in patients with sCR > 2 years (N=8, 27%) compared to patients who progressed (PD, N=24) within 2 years. We observed significant reduction in percentages of regulatory T cell population in CAR+ T cells in BM of sCR patients compared with PD patients (8% vs 18% respectively; p<0.05). We also observed significantly higher expressions of activation markers CD38 (69% vs 31%), CD28 (58% vs 32%) and CD27 (68% vs 48%) on CAR+ T cells in sCR patients compared to PD patients (p<0.05). Interestingly, we observed significantly higher expression of TIM-4 in CAR+ T cells in sCR patients (38% vs 8%; p<0.05), indicating that CAR-T cells in sCR patients have reduced apoptosis. Furthermore, sCR patients have significantly higher population of CAR+ T cells producing IL-2 (46% vs 16%) and granzyme-B (59% vs 28%) and higher frequency of IL-10-producing cells (43% vs 10%) compared with PD patients (p<0.05), suggesting higher proliferative and killing capacity as well as enhanced mitochondrial fitness. In summary, our results suggest that higher expression of activation markers and cytotoxic/proliferating cytokines in CAR-T cells is associated with sustained sCR of > 2 years. Interestingly, these CAR-T cells show less susceptibility to apoptosis and exhibit better mitochondrial fitness. Taken together, we conclude that these functional phenotypes of CAR-T cells in bone marrow might potentially be contributing to sustained outcomes following therapy.