Another study conducted by Kim and collaborators showed that Rapa preconditioning of hASCs increased both mRNA and protein expression of the immunosuppressive cytokines IDO, IL-10, and TGF-β, suppressed T helper 17 (Th17) cells thereby promoting T regulatory cells (Tregs), and prolonged survival in a mouse model of graft-versus-host-disease (GVHD) [29]. Here, IDO1 is linked to graft versus host disease.