CD200 and B-cell chronic lymphocytic leukemia: In CLL, the deregulation of key immune checkpoints (ICs), such as PD-1/PD-L1 (programmed cell death protein 1/programmed death-ligand 1), CTLA-4/CD86 (cytotoxic T-lymphocyte-associated protein 4/cluster of differentiation 86), and CD200R/CD200 (cluster of differentiation 200 receptor/ligand), is observed8.