[Host-graft interactions after allogenic bone marrow transplantation; choice of donor]

The complexity of host-graft interactions after bone marrow transplantation explains the criteria of choice of the donor. Graft rejection, graft-versus-host disease, graft-versus-leukemia, delayed immune reconstitution, often associated or mutually exclusive are observed even with an HLA identical sibling donor. Syngeneic transplants may be complicated by leukemic relapse related to the loss of the graft-versus-leukemia effect. The compilation of files of unrelated donors increases the possibility of finding a matched unrelated donor. Preliminary results suggest that clinical results may be equivalent to those achieved with HLA identical sibling donors. Overall results of HLA mismatched transplants are disappointing because of the increase of immunological complications. Attempts at preventing graft-versus-host disease with T cell depletion led to an increase of immunological complications: rejection and leukemic relapse. Modifications of the conditioning regimen and use of in vivo monoclonal antibodies are currently being investigated. Ethical, legal, and psychological considerations have also to be taken into account in the donor choice especially with the increase of the donor pool.