Down-regulation of allogeneic Type 1 T helper (Th1) responses, as measured by decreases in interleukin-2 (IL-2) and interferon-gamma (IFN-γ), was noted following the addition of primary CLL cells to an in vitro mixed lymphocyte reaction, and anti-CD200 antibodies reversed this effect, restoring Th1 responses and suppressing Tregs [14, 16, 22, 23]. The gene discussed is CD200; the disease is B-cell chronic lymphocytic leukemia.