Integrated clinical and single-cell profiling of BCMA CAR-T therapy in relapsed/refractory multiple myeloma

Despite therapeutic advances, multiple myeloma (MM) remains incurable, especially in relapsed/refractory (R/R) disease. B-cell maturation antigen (BCMA)-targeted CAR-T therapy, exemplified by FDA-approved agents like ide-cel and cilta-cel, offers promise, yet accessibility barriers necessitate local production.

This single-arm trial evaluated safety/efficacy of autologous BCMA CAR-T cells in six R/R MM patients.

Cytokine release syndrome (CRS) occurred in 83% (grade 1), managed with tocilizumab without neurotoxicity. Toxicities were transient and resolved. Serum cytokine (IFN-γ, IL-6/8/10) peaked during CRS. Responses included 83% overall response (67% stringent complete response), unaffected by extramedullary disease or high-risk cytogenetics. Median PFS/OS were unreached, with an estimated 12-month OS rate of 83.33% and PFS rate of 66.67%. CAR-T cell persistence, with a median Cmax at 20.5 days, remained detectable in 83% at 1 month and 67% at 6 months. Single-cell RNA sequencing (scRNA-seq) and T-cell receptor sequencing (TCR-seq) demonstrated complementary roles of functionally specialized CD8⁺ Te subsets. Clonal evolution in the sustained responder (patient 2) revealed a shift from a polyclonal infusion product (IP) to oligoclonal dominance, with shared clones exhibiting enhanced cytotoxic and NK-like activity. Transcriptional adaptation of persistent clones over time indicated distinct phases of proliferation, stress response, and long-term persistence, with a concomitant shift in cellular phenotype from IP-derived Tem/circling T cells to a mixed Tem/Te_1/Te_2 population. Comparative analysis of two patients with divergent clinical outcomes (sustained remission vs. transient remission) revealed that early CAR-T exhaustion and increased regulatory T cells (Tregs) were associated with relapse.

Locally produced BCMA CAR-T is safe and effective in heavily pretreated R/R MM, inducing deep responses. scRNA-seq/TCR-seq findings highlight interplay of CAR-T heterogeneity, clonal adaptability, and immune regulation. CD8⁺ subset specialization and clonal persistence matter for durable responses; exhaustion and immunosuppression may cause relapse.