CD1D and graft versus host disease: iNKT cells recognize glycolipid antigen via their invariant T cell receptor (TCR; Vα24Jα18/Vβ11 in humans and Vα14Jα18 with Vbβ, −7, or −8 in mice1,2) when presented by the major histocompatibility complex (MHC)-like protein CD1d.3 As CD1d is monomorphic, iNKT cells are incapable of allorecognition and unable to initiate graft-versus-host disease (GVHD), making them a powerful platform for universal donor cellular therapies.