CD200 and B-cell chronic lymphocytic leukemia: There are also most recent studies showing that CD200 expression controls two other pathways; one is a regulatory T cell expansion and disease progression in acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL); other one is the checkpoint blockade that augments cytotoxicity of cytokine-induced killer cells against human myeloid leukemia blasts [10, 11].