CD8+ T cells that infiltrate prostate and melanoma tumors express high levels of PD-1 and have impaired effector functions, moreover, B7-H1/PD-1 forms a molecular shield to prevent destruction by CTLs [85] suggesting that reversal of PD-1 signaling in those cells can have direct effects on the tumor cell killing [86,87]. The gene discussed is CD8A; the disease is neoplasm.