Multiplex engineering using microRNA-mediated gene silencing in CAR T cells

Background Multiplex gene-edited chimeric antigen receptor (CAR) T-cell therapies face significant challenges, including potential oncogenic risks associated with double-strand DNA breaks. Targeted microRNAs (miRNAs) may provide a safer, functional, and tunable alternative for gene silencing without the need for DNA editing. Methods As a proof of concept for multiplex gene silencing, we employed an optimized miRNA backbone and gene architecture to silence T-cell receptor (TCR) and major histocompatibility complex class I (MHC-I) in mesothelin-directed CAR (M5CAR) T cells. The efficacy of this approach was compared to CD3ζ and β2-microglobulin (β2M) CRISPR/Cas9 knockout (KO) cells. miRNA-expressing cassettes were incorporated into M5CAR lentiviral vectors, enabling combined gene silencing and CAR expression. Antitumor activity was evaluated using in vitro assays and in vivo pancreatic ductal adenocarcinoma models. Results Silenced (S) M5CAR T cells retained antitumor functionality comparable to, and in some cases exceeding, that of KO cells. In vivo , S M5CAR T cells achieved tumor control with higher persistence and superior metastasis prevention. In vitro assays demonstrated enhanced resistance to alloreactive natural killer (NK) cells and peripheral blood mononuclear cells (PBMCs). Conclusions Titratable multiplex gene silencing via targeted miRNAs offers an alternative to gene editing for CAR T cells, with potential advantages in potency, persistence, metastasis prevention, and immune evasion for allogeneic products. This strategy may overcome tumor-induced immunosuppression while avoiding the risks associated with DNA double-strand breaks.