Disclosed is an isolated antibody that specifically binds CD26 wherein the antibody comprises the structure having sequences as defined in the specification. Also disclosed is such an antibody made from the hybridoma cell line deposited at CBA-ICLC of Genoa (Italy) as PD 12002. Also disclosed is the use of the antibody in the treatment of Graft-versus-Host disease and aplastic anaemia; and use of the antibody in promoting engraftment after haematopoietic stem cell transplantation.