Genetic Disruption of Blimp-1 Drastically Augments the Antitumor Efficacy of BCMA-Targeting CAR-T Cells

• Ablation of Blimp-1 in anti-BCMA CAR-T cells improves efficacy, representing a promising novel therapeutic product for multiple myeloma.

• Transcriptomic analysis revealed novel potential targets to further improve the therapeutic activity of anti-BCMA CAR T-cells.

Chimeric antigen receptor-T (CAR-T) cells directed against B-cell maturation antigen (BCMA) are an effective treatment for multiple myeloma (MM), but short persistence and frequent relapses are challenges for this immunotherapy. This lack of durability has been attributed to the premature terminal differentiation of CAR-T cells which prevents the formation of long-lived memory cells that maintain anti-tumour responses. To improve long-term efficacy, we used CRISPR/Cas9-mediated gene editing to ablate the expression of the transcription factor Blimp-1. Blimp-1 knockout (KO) CAR-T cells displayed a memory-like phenotype compared to control (Mock) CAR-T cells, but had reduced effector function, with a striking loss of granzyme B. However, in a murine model of advanced MM, Blimp-1 KO CAR-T cells effectively slowed or even prevented disease progression, significantly outperforming Mock CAR-T cells in improving survival (p=0.006). To understand this enhanced in vivo effectiveness, Blimp-1 KO CAR-T cells were characterised after being repeatedly challenged with tumour cells in vitro. In this setting, Blimp-1 KO CAR-T cells maintained a highly active state with high expression of memory markers, but crucially, demonstrated enhanced effector function and increased energetic capacity. RNA-sequencing analysis of tumour-exposed Blimp-1 KO CAR-T cells confirmed the presence of a memory-like transcriptomic signature and additionally, revealed enhanced ribosome biogenesis, and repressed CAR-T cell dysfunction as mechanisms that could be contributing to improved anti-tumour activity. Put together, our findings show that dampening Blimp-1 expression altered the phenotype and function of anti-BCMA CAR-T cells, leading to augmented therapeutic efficacy in MM.