CD4 and B-cell chronic lymphocytic leukemia: Interestingly, the natural receptor for CD200, CD200R, was found to be mostly expressed on engrafted CD4+T-cells (but not CLL cells) in the spleen of engrafted mice, and the depletion of T-cells with OKT3 mAb in vivo also abrogated CLL engraftment despite the ongoing continuous infusion of sCD200hi CLL serum [23].