Here, they utilized ex vivo RA stimulation to induced CCR9 expression in human PB CD4+Foxp3+ Tregs (176) and demonstrated that the ex vivo induction of CCR9 expression was sufficient to enhance Treg migration to the GI tract and reduce disease severity in a xenogeneic GVHD model (176). This evidence concerns the gene CCR9 and graft versus host disease.