USE OF GENE-THERAPY TO INDUCE HUMAN-MOUSE XENOGENEIC CHIMERISM

Background. Bone marrow transplantation (BMT) has been used in the lab oratory to overcome the immunologic barriers to xenotransplantation an d results in chimerism and specific tolerance to donor antigens in let hally irradiated mice. Clinically, BMT carries the considerable risks of graft-versus-host disease and graft failure. Retrovirus-mediated ge ne transfer could provide a means of introducing foreign major histoco mpatibility (MHC) genes into host bone marrow cells (BMC) and thus acc omplish the immunologic goals of BMT, without the associated risks. Me thods. Using a Moloney virus-based vector, a replication defective ret rovirus was constructed that contained a compleMentary DNA encoding th e human MHC antigen HLA-A2. Three million C57BL/6 mouse BMC were cocul tured for 48 hours with 1 X 10(6) HLA-A2 virus ''producer'' cells in t he presence of 15% WEHI supernatant (interleukin-3) and 200 units/ml i nterleukin-6. Putatively infected BMC were then used at 2 to 3 X 10(6) BMC/animal to reconstitute lethally irradiated syngeneic mice. Result s. Twelve days after reconstitution, spleen colonies were found to hav e integrated the full-length retroviral sequences. Thirty days after B MT, the introduced DNA could be found in the bone marrow, thymus, and spleen, and approximately 5% of T cells in the spleen expressed the HL A-A2 surface antigen. Conclusions. These data show that xenogeneic MHC genes can be introduced and expressed in mouse hematopoietic cells in vivo and indicate that gene therapy potentially may be used in the fu ture to manipulate the immune system to induce transplantation toleran ce.