PDCD1 and melanoma: Similarly, TSTs were present in the population of CD8+ T cells sorted on the basis of CD137 in fresh ovarian cancer tissues, and CD137+CD8+ T cells have been demonstrated to possess specific cell killing ability against autologous tumor cells in vitro and to inhibit the progression of tumors in both melanoma and ovarian cancer NSG mouse models compared with PD-1+ or PD-1−CD137−CD8+ T cells (75).