Furthermore, PD-1/PD-L1 axis can promote the development of iTreg (induced regulatory T) cell and increase Foxp3 expression on its surface, induce the differentiation of CD4+CD25+Foxp3+Treg and maintain its immunosuppressive function, thereby indirectly inhibiting T cells proliferation and promoting tumor immune evasion 33. Here, PDCD1 is linked to neoplasm.