Interestingly, STAT3 depletion and anti-PD-1 therapy decreased the percentages of CD8+ and CD4+T cells, leading to an increased CD8/CD4 ratio in STAT3 downregulation and PD-1 blockade combinational treatment in melanoma according to monitoring mice in the PD-1 blockade group (Figures 6A–C). Here, PDCD1 is linked to melanoma.