PDCD1 and ovarian cancer: Recently, a systematic analysis of four biomarkers, PD-1, CD39, CD103 and CD137, in ovarian cancer TILs found that PD-1+, CD39+ and CD103+ TILs all contained a subpopulation of CD137+ T cells and CD137+ TILs highly co-expressed the three previous markers, with the highest expression of major histocompatibility complex (MHC)-dependent IFN-γ and other cellular effector cytokines (78).