We performed experiments in preclinical GVHD models using GPRC6A deficient mice; and the Transplant Complications Working Party (TCWP) of the European Society for Blood and Marrow Transplantation (EBMT) performed a prospective, multicenter and non-interventional clinical study following the hypothesis that Ca2+ is correlated to the occurrence of GVHD. This evidence concerns the gene GPRC6A and graft versus host disease.