Surfaceome CRISPR activation screening uncovers ligands regulating tumor sensitivity to NK cell killing.
Natural killer (NK) cell-based immunotherapies are promising for cancer treatment due to their ability to eliminate cancer cells independently of antigen presentation and "off-the-shelf" utility. However, molecular determinants governing tumor susceptibility to NK cytotoxicity remain incompletely understood. Here we employ CRISPR activation (CRISPRa) screening to identify cancer cell surface regulators of NK killing. Using a surfaceome-focused library, we screen human and murine cancer cell lines co-cultured with NK cells, identifying known and novel ligands modulating NK cytotoxicity. Screens reveal established factors including CD43 and previously uncharacterized regulators CD44, PDPN, and Siglec-1/CD169. Validation with orthogonal approaches confirm that disruption of these factors alters NK killing susceptibility in vitro and in humanized mouse models. Mechanistically, we find that CD43-mediated NK resistance operates independently of its proposed interaction with Siglec-7, and that targeting CD43 on NK cells or CAR T cells substantially enhances cytotoxic activity against leukemia. These results establish gain-of-function surfaceome screening as a powerful tool for identifying therapeutic targets for NK cell-based immunotherapy.