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

Chimeric antigen receptor-T (CAR-T) cells directed against B-cell maturation antigen (BCMA) are an effective treatment for multiple myeloma, 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 (Prdm1). In a murine model of advanced myeloma, Blimp-1 knockout (KO) CAR-T cells effectively slowed or even prevented disease progression, significantly outperforming control (Mock) CAR-T cells in improving survival. To understand this enhanced in vivo effectiveness, Blimp-1 KO CAR-T cells were characterised after being repeatedly challenged with tumour cells in vitro and subject to gene expression analysis. Overall design: Human T cells transduced with an anti-BCMA CAR gene (ARI0002h) were expanded in vitro and separated into cultures that acted as a control (Mock) or were subject to CRISPR/Cas9 to ablate the expression of Blimp-1 (Blimp-1 KO). Expanded cells were stimulated four times with the multiple myeloma cell line ARP-1, and RNA was isolated from purified CD8+ cells at the end of the co-cultures. Gene expression profiles were assessed by RNA sequencing.