CD4 and adult T-cell leukemia/lymphoma: It was more recently reported that PD-1 expression in CD4+ and CD8+ T-cells is significantly higher in patients with chronic lymphocytic leukemia (CLL), while the levels of PD-1 expression on both CD4+CD25+ and CD4+CD25- T-cells were increased in adult T-cell leukemia/lymphoma (ATL), but not in CD8+T cells [41-43].