PRDM1 is a key regulator of the natural killer T–cell central memory program and effector function

Natural killer T cells (NKTs) are a promising platform for cancer immunotherapy, but few genes involved in the regulation of NKT therapeutic activity have been identified. To find regulators of NKT functional fitness, we developed a CRISPR/Cas9-based mutagenesis screen that uses a guide RNA (gRNA) library targeting 1,118 immune-related genes. Unmodified NKTs and NKTs expressing a GD2-specific chimeric antigen receptor (GD2.CAR) were transduced with the gRNA library and exposed to CD1d+ leukemia or CD1d−GD2+ neuroblastoma cells, respectively, over six challenge cycles in vitro. Quantification of gRNA abundance revealed enrichment of PRDM1-specific gRNAs in both NKTs and GD2.CAR NKTs, a result that was validated through targeted PRDM1 knockout. Transcriptional, phenotypic, and functional analyses demonstrated that CAR NKTs with PRDM1 knockout underwent central memory–like differentiation and resisted exhaustion. However, these cells downregulated the cytotoxic mediator granzyme B and showed reduced in vitro cytotoxicity and only moderate in vivo antitumor activity in a xenogeneic neuroblastoma model. In contrast, short hairpin RNA-mediated PRDM1 knockdown preserved effector function while promoting central memory differentiation, resulting in GD2.CAR NKTs with potent in vivo antitumor activity. Thus, we have identified PRDM1 as a regulator of NKT memory differentiation and effector function that can be exploited to improve the efficacy of NKT-based cancer immunotherapies.