Inhibiting HPK1 kinase function by knocking in the kinase-dead mutant of HPK1, M46, in which the ATP-binding lysine-46 residue is mutated to methionine, increases T cell receptor signaling, cytokine secretion, and CD8+ T cell function, and inhibits tumor growth in M46-transgenic mice (20, 21). The gene discussed is MAP4K1; the disease is neoplasm.