While colon cancer patients are not generally responsive to targeting of the programmed death-1 (PD-1)/PD-1 ligand (PD-L1) axis [58, 59], this immunosuppressive pathway has been implicated in blunting CD8+ T cell antitumor immunity in CT26 colorectal cancer [60, 61] and in clinical trials in a subset of colorectal cancer patients with mismatch-repair deficiency [62, 63]. The gene discussed is CD8A; the disease is mismatch repair cancer syndrome 1.