CD103, the α chain of the αEβ7 integrin, is a specific marker of mouse and human CD4+ Tregs [44,45], of mouse CD8+ Tregs inhibiting graft-versus-host disease [46] and of human alloantigen-induced CD8+ Tregs [26,47] but also, at the same time, a marker of effector cytotoxic CD8+ T cells, promoting their migration intragraft into epithelial compartment and involved in allograft rejection in a mouse model of islet allograft [48]. The gene discussed is CD8A; the disease is graft versus host disease.