The risk of developing GvHD following haematopoetic stem cell transplantation (HSCT) is associated with low numbers of Tregs in the periphery,100 and in vivo expansion of Tregs post-HSCT using low-dose IL-2 has demonstrated efficacy against GvHD.101 102 Studies in mice involving infusion of cultured CD4+CD25+ T cells resulted in a significantly reduced GvHD phenotype,103 and in humans it was found that infusion of freshly isolated donor Tregs given at the same time as haplotype mismatched HSCT prevented the development of GvHD.104. This evidence concerns the gene CD4 and graft versus host disease.