Researchers from the NIH have conducted a genomewide screen to determine which genes affect sensitivity and resistance of cancer cells to destruction by T cells. Checkpoint blockers, which activate T cells against the immune system, are wildly successful in a minority of patients, and little is known about why some tumors succumb to T-cell boosting immunotherapy, while others shrug it off. In their work, the authors developed a co-culture system consisting of effector T cells and melanoma cells, and used CRISPR to systematically edit the melanoma cells.