CD200 and neoplasm: In an in vitro study, blockade of CD200 expression in CLL (by anti-CD200 antibody or siRNAs) decreased the number of CD4+CD25+Foxp3+Treg, enhanced production of the proinflammatory cytokines IFN-γ and TNFα by effector PBMCs, and augmented effective killing of tumor cells by CD8+ CTL [81,84].