In 1956, Georges Mathé treated four physicists exposed to high-dose radiation following an accident at the nuclear plant at Vinca (then Yugoslavia), with intravenous infusions of allogeneic bone marrow cells harvested from family donors. The men initially developed the donor blood groups but eventually recovered their own initial blood group. In 1963, he treated a patient with leukemia by infusing a mixture of bone marrow and blood obtained from various family members following a preparatory regimen of chemotherapy and radiotherapy. This patient also survived and developed what was described as a “secondary disease” comprising of skin rash, weight loss, and gastro-intestinal problems. This was probably the first recognition of human GvHD. Remarkable for that period, by a series of elegant observations of the major and minor blood groups, he was able to demonstrate that up to eight months following the procedure the patient had the same blood groups as the recipient. This probably was the first report of a full chimerism (see below and “Glossary”). He is also credited with the initial speculation of a graft-versus-leukemia (GvL), also known as graft-versus-tumor (GvT), effect associated with GvHD.