The power of treating cancer by engaging patient's own immune defense mechanisms through immunotherapy with antibodies to the co-inhibitory T cell checkpoints, has prompted the question of whether targeting also co-stimulatory immune checkpoints e.g., 4-1BB, OX40, CD40, and GITR can translate into similarly efficacious and perhaps complementary pathways of anti-cancer immunity? The gene discussed is TNFRSF9; the disease is cancer.