Allogeneic bone marrow grafting is described in 21 human leukaemic subjects. Failure of the graft occurred in 6 cases and take in 15 cases. In the latter group, all 15 cases were complicated by the secondary syndrome, which was fatal in 11 cases and controlled in 4 cases.
The immunogenetic and immunological factors determining the establishment and evolution of haematological radio‐chimaeras in man are discussed.
The choice of donor in fundamental. Three tests are considered to be effective in donor selection, the indirect histocompatibility test (the so‐called third man test proposed by us), the leucocyte antigen test and the reaction of donor and recipient leucocytes in the dermis of an irradiated hamster. When marrow from several donors is transfused, the recipient spontaneously selects that genetically nearest.
It seems likely there is more chance of finding a suitable donor among genetically related subjects than among those who are unrelated.
The frequency of graft take seems slightly less in recipients who have previously received blood transfusions.
Total bone marrow graft is associated with specific tolerance towards donor tissues. This is paralleled by the production in the chimaera of immunoglobulins produced by the graft.
The secondary syndrome seems, as in animals, to be related essentially to the graft versus host reaction. It is convenient to distinguish between its various manifestations, on the one hand, those lesions which are readily controlled such as hepatitis or erythrodermia associated with infiltration and proliferation of immunologically competent cells from the graft, and on the other hand immune insufficiency with regard to micro organisms, especially viruses and Candida albicans. This latter group, the mechanism of which is complex, still eludes attempts at preventive and curative control.
The use of multiple donors, the administration of cortisone during marrow transfusion and amethopterin and/or cyclophosphamide in the days following transfusions, all seem to have reduced the severity of the secondary syndrome, which however still cannot be satisfactory controlled.
The graft reaction against the leukaemic cells is utilised as an antileukaemic treatment. In the 4 patients who escaped acute secondary syndrome survival has been notably longer, the longest lasted 20 months, when death from zoster encephalitis supervened. There were no clinical signs of leukaemia or histological evidence of this at autopsy.