On the contrary, the memory T cells, including effector memory T cells (TEM, CD62L− CD44+) and central memory T cells (TCM, CD62L+ CD44+) from either untreated or allo-antigen primed donors, do not cause GVHD or cause only minor GVHD after transplantation (3–6). This evidence concerns the gene SELL and graft versus host disease.