Genome-wide CRISPR screens decode cancer cell pathways that trigger gamma-delta T cell detection and killing
Gamma-delta T cells are potent anti-cancer effectors with the potential to target tumours broadly, independent of patient-specific neoantigens or HLA background. Gamma-delta T cells can sense conserved cell stress signals prevalent in transformed cells, although the mechanisms behind the targeting of stressed target cells remain poorly characterized. Vg9Vd2 T cells – the most abundant subset of human gamma-delta T cells – recognize a protein complex containing butyrophilin 2A1 (BTN2A1) and BTN3A1, a widely expressed cell surface protein that is activated by phosphoantigens abundantly produced by tumour cells. Here, we layered genome-wide CRISPR screens in target cancer cells to identify pathways that regulate: (1) killing by gamma-delta T cells during co-culture, and (2) BTN3A cell surface expression. In addition to confirming the importance of the phosphoantigen-producing mevalonate pathway, the screens revealed previously unappreciated multilayered regulation of BTN3A abundance on the cell surface and triggering of gamma-delta T cells through transcription, post-translational modifications, membrane trafficking. Notably, IRF1 and ZNF217 were discovered to be positive and negative transcriptional regulators that directly occupy the promoters of BTN3A1/2/3 genes. In addition, diverse genetic perturbations and inhibitors disrupting metabolic pathways in the cancer cells, particularly ATP-producing processes, were found to alter BTN3A levels. This induction of  BTN3A, as well as BTN2A1, during metabolic crises was dependent on AMP-activated protein kinase (AMPK). Finally, small molecule activation of AMPK in a cell line model and in patient-derived tumour organoids led to increased expression of the BTN2A1-BTN3A complex and increased Vg9Vd2 TCR-mediated killing. This AMPK-dependent mechanism of metabolic stress-induced ligand upregulation deepens our understanding of gamma-delta T cell stress surveillance and suggests new avenues to enhance gamma-delta T cell anti-cancer activity. Overall design: CUT&RUN was performed on Daudi-Cas9 cells using IRF1, ZNF217, IgG, and H3K4me3 antibodies. Samples were processed in technical triplicates or duplicates