PDCD1 and neoplasm: It has been reported that PD-L1 is up-regulated on CD4+ regulatory T cells in Hodgkin lymphoma tissue and inhibits the function of PD-1 (+) T cells.[16] Therefore, we speculated that a high level of PD-L1 from CD4+ T cells can inhibit the function of the PD-1 (+) T cells by binding with PD-1 on other T cells, to reduce the function of the peripheral blood immune system and promote tumor immune escape.