Park et al. [22] reported that human-derived cord blood (CB)-MDSCs present a potent immunosuppressive function on T cell-mediated chronic inflammation in a mouse graft-versus-host disease (GvHD) model through immunosuppressive molecules, including iNOS, Arg-1, and indoleamine 2,3-dioxygenase (IDO). Here, IDO2 is linked to graft versus host disease.