Dipeptidyl peptidase 4 (DPP-4) inhibitors block function of DPP-4, a transmembrane glycoprotein receptor identical to the leucocyte surface antigen CD26. DPP-4 is involved in multiple biological processes, including insulin metabolism, bone marrow engraftment, T-cell activation, and leukocyte migration. The receptor is expressed on a variety of cells and circulates in an enzymatically active form in plasma. DPP-4 inhibition is used as anti-diabetic treatment and has also shown to reduce the incidence of acute GvHD.