The selective activation of circulating Tfr and suppression of circulating Tfh provide a mechanism whereby low dose IL-2 therapy can promote both B and T cell tolerance in patients with cGvHD. In summary, these studies suggest a reduction of Tfr correlates with active or chronic GvHD and by boosting numbers of Tfr, either with cell infusion or IL-2, this may prove an effective therapeutic strategy. This evidence concerns the gene IL2 and graft versus host disease.