Donor natural killer (NK) T cells in hematopoietic cell transplants suppress graft-versus-host disease (GVHD) that is induced by donor CD4⁺ and CD8⁺ conventional T (Tcon) cells. The T-cell antigen receptors (TCR)s of the Tcon cells recognize class I and class II MHC receptors associated with peptides, and the NKT cells recognize CD1d receptors associated with glycolipids on the surface of antigen presenting cells (APCs). Professional illustration by Alice Y. Chen.