A complementary approach has been to xenograft the Mec-1 cell line38 or primary CLL cells into immune-compromised mice.39, 40 Recently, Bagnara et al. reported that peripheral blood mononuclear cells (PBMCs) from CLL patients xenografted into NOD/scid/γc null (NSG) mice localized primarily to the murine spleen. The gene discussed is ATR; the disease is B-cell chronic lymphocytic leukemia.