T-Charge™ Manufacturing of the Anti-BCMA CAR-T, Durcabtagene Autoleucel (PHE885), Promotes Expansion and Persistence of CAR-T Cells with High TCR Repertoire Diversity

BCMA targeted CAR-T cells are an effective therapy for patients with relapsed or refractory multiple myeloma (r/r MM). However, autologous CAR-T cell products are highly heterogeneous and the functional roles of various T cell populations within these products have not been established. Stem-like memory T cells (Tscm) are a rare T cell subset which maintain high capacity for self-renewal and multipotency. Previously, we demonstrated that the T-Charge^TM platform, a novel rapid manufacturing process that reduces manufacturing time to <2 days, preserves less differentiated CAR-T cells which exhibit potent anti-tumor activity and robust expansion in preclinical models (Dexiu Bu, ASH 2021). We conducted a phase 1 clinical trial in r/r MM (NCT04318327) of durcabtagene autoleucel (PHE885), a fully human product manufactured using the T-Charge platform. Here we present a detailed analysis of CAR-T cell products and subsequent expansion of CAR-T cells in 32 patients enrolled in this clinical trial at the Dana-Farber Cancer Institute. Apheresis products (APH), final products (FP) and post-infusion peripheral blood mononuclear cells (PBMC) were characterized using flow cytometry, mass cytometry (CyTOF) and TCR sequencing.

We previously reported a 98% overall response rate (ORR) across all dose levels (2.5-20x10⁶ CAR-T cells) and 100% ORR at doses >5x10⁶ cell dose (Sperling, ASCO 2023). CAR-T cells expanded rapidly after infusion reaching median peak levels of 3,118 cells/ul (range 373 to 17,865) with a median 87.4% (range, 46.9-97.8) of CD3+ T cells expressing the CAR at a median of 14 days (range 10 to 27) after infusion. CAR-T cells persisted at high levels with transgene detectable by qPCR in 67% of patients at 6 months. Among 28 evaluable patients, 13 (43%) had >20% CAR positive T cells detectable by flow cytometry at 3 months.

Phenotypic analysis of APH and FP samples showed that less-differentiated T cell subsets, including Tscm and central memory T cells were maintained in FP. CyTOF evaluation of functional markers revealed high expression of proliferation and activation markers in Tscm in FP and subsequently in CAR-T cells at the time of peak expansion in vivo. Subsequently, more differentiated CAR-T cells increased, accompanied by a decline in activation markers, while no significant changes were observed in inhibitory receptors. The proportion of Tscm in the FP positively correlated with early in vivo CAR-T cell expansion.

TCR repertoire diversity and TCR clone tracking were used to characterize product manufacturing and CAR-T cells in peripheral blood after infusion. We sorted naïve/Tscm CD4 T cells, naïve/Tscm CD8 T cells, memory CD4 T cells, and memory CD8 T cells from APH and FP, and isolated CAR-positive CD4 T cells, CAR-positive CD8 T cells, CAR-negative CD4 cells, and CAR-negative CD8 T cells from post-infusion PBMC by fluorescence-activated cell sorting and ran TCR sequence from the extracted gDNA from each T cell subpopulation. Measurement of TCR diversity post-infusion revealed higher TCR repertoire diversity in CAR-T cells than in non-CAR-T cells. Notably, post-infusion CAR-T cells shared significantly more TCR clonotypes with T_SCM than with memory T cells in the FP, suggesting that the highly heterogeneous post-infusion CAR-T clones were preferentially derived from T_SCM clones in the FP. In three evaluable patients with long-term persistence, a highly diverse TCR repertoire in CAR T cells was maintained 1 year after treatment.

Our findings demonstrate that the T-Charge™ manufacturing platform successfully maintains highly heterogeneous transduced Tscm clones with self-renewal potential in durcabtagene autoleucel products. Maintenance of Tscm in manufactured products contributes to robust CAR-T expansion and long-term persistence of CAR-T cells with a highly diverse TCR repertoire after infusion.