In line with highly variable treatment outcomes in patients, two studies did not observe changes in tumor-infiltrating Treg frequencies (11, 38), while one study using a combination of anti-PD-1 antibody and CD137 antibody therapies reported an increase in CD8/Treg ratio in tumors of HIS mice xenotransplanted with gastric carcinoma and engrafted with autologous PBMCs from the same donor (55). Here, PDCD1 is linked to neoplasm.