In 2003, Edinger et al. (52) observed that, in a mouse model, CD4+CD25+ Tregs could suppress the early expansion of alloreactive donor T cells, their IL-2-receptor alpha-chain expression and their capacity to induce GVHD without compomising their GVT effects, mediated primarily by the perforin lysis pathway of T conv cells. Here, CD4 is linked to graft versus host disease.