Immunological importance of chimerism in transplantation: New conditioningprotocol in BMT and the development of chimeric state

Chimerism is an exceptional immunogenetic state, characterized by the survi val and collaboration of cell populations originated from two different ind ividuals. The prerequisits to induce chimerism are immunosuppression, myelo ablation, or severe immunodeficiency of the recipients on the one side and donor originated immuno-hematopoietic cells in the graft on the other. The pathologic or special immunogenetic conditions to establish chimerism are c ombined with bone marrow transplantation, transfusion, and various kinds of solid organ grafting. Different types of chimerism are known including com plete, mixed and mosaic, or split chimerism. There are various methods used to detect the type of chimera state, depending on the immunogenetic differ ences between the donor and recipient. The induction of complete or mixed c himerism is first determinated by the effect of myeloablative therapy. The chimera state seems to be one of the leading factors to influence the cours e of the post-transplant period, the frequency and severity of GVHD, and th e rate of relapse. However, the most important contribution of the chimeric state is in development of graft versus leukemia effect. A new conditionin g protocol (DBM/Ara-C/Cy) for allogeneic BMT in CML patients and its conseq uence on chimera state and GVL effect is demonstrated. Human Immunology 61, 101-110 (2000). (C) American Society for Histocompatibility and Immunogene tics, 2000. Published by Elsevier Science Inc.