Before even attempting a graft, Mathé wished to first define the best choice of donor at a time when the complete phenotyping of donor cells was unknown. He discovered that after the injection of a pool of bone marrow cells from non-related donors, the recipient favored the graft of one donor only, the closest matching relative, which induced the most tolerable GvH reaction. This “mixed chimerism”, as Mathé referred to it, was until then unheard of and difficult to accept in the scientific community. The controversy was to dampen with the rapidly advancing progresses made in the field, other than simple grafts between twins, towards achieving the goal of characterizing the best donor.
At the time, nobody challenged the dogma of the conditioning necessary by total body irradiation at lethal dose to achieve successful grafting of hematopoietic cells. Yet, this myeloablative conditioning (provoking a total and irreparable destruction of the bone marrow, and thus of all the blood elements present within the organs) induced major immunodeficiency which complicated the rest of the treatment. For this reason, Georges Mathé was considering to transplant bone marrow from “compatible or minimally incompatible” donors after a smaller conditioning (total body irradiation at a dose below 100% lethal), hoping that under these conditions, the GvH reaction would be less intense, that of the GvL preserved, and the post graft immune deficiency reduced. The events that followed made him the first to perform successful bone marrow transplantations on humans that were not identical twins.
At a time when scientists remained largely in the dark in the field of immunology, the bone marrow transplantations they performed were all in animals with nobody daring to attempt one in humans. It was only when confronted with the Yougoslavian radiation victims who had nothing to lose that Georges Mathé dared to be the first to take the plunge. On this occasion, he was contacted in October 1958 by the consultant in radiobiology Doctor Pendic, who worked in the radiocontrol unit of the Vinca Institute of Nuclear Sciences near to Belgrade. On October 15th, the reactor at the centre had suddenly fallen out of control and irradiated six engineers at doses, undoubtedly considering their respective positions and distances from the reactor, that were very high. The dosimetry performed on-site estimated the exposed doses to be between 800 and 1000 rem total body irradiation. Having conducted all the known methods and techniques of microbiological sterilization possible, Pendic asked if Mathé could either come to Belgrade or treat the patients in Paris. He preferred the latter option in view of repeating the dosimetry which Henri Jammet, internationally renowned specialist in radiobiology at the Curie hospital Paris, had committed himself to undertake. Rather than transferring the patients to Professor Jean Bernard’s department in Saint Louis