CD4 and graft versus host disease: Zheng et al. (63) found that CD4+CD62L−CD44+CD25− effector memory T cells (CD4+ TEMs), but not naïve T cells (TN), unprimed to recipient cells mediated GVL without causing GVHD, because they retained key cytolytic functions but lacked other features that are pivotal for initiating GVHD.