In a follow-up study, we pre-treated mice with a CD8-depleting antibody before vaccination with P2Iio/anti-CD200-coated cells, and showed that protection from CLL growth was abolished, implying a role for the blockade of CD200 expression on CLL cells as a component of a tumor vaccination strategy, which involved the induction of protection afforded by CD8 cytotoxic cells [15]. This evidence concerns the gene CD200 and B-cell chronic lymphocytic leukemia.