Tolerance to organ grafts has been achieved by establishing a state of stable mixed-cell chimerism after bone marrow transplantation. Gene therapy has been applied to establish chimerism for cells expressing galactose α 1,3 galactose in α 1,3 galactosyltransferase deficient (gal−/− knockout) mice using retroviral vectors. Limitations to the success of this methodology include short-term expression of the introduced gene and rejection of gal+ hearts transplanted into these animals within a month.Methods.
Autologous bone marrow from gal−/− knockout mice was transduced with a lentiviral vector expressing porcine α 1,3 galactosyltransferase and transplanted into lethally irradiated gal knockout mice. Chimerism was monitored by flow cytometry. Hearts from wild type mice (gal+/+) were transplanted into these animals and palpated daily. Xenoantibodies directed at the gal carbohydrate or porcine xenoantigens were detected by enzyme-linked immunosorbent assay.Results.
Hearts from wild-type gal+/+ donors were permanently accepted in all mice receiving autologous, transduced bone marrow before heart transplantation. Control mice rejected gal+ hearts within 12 to 14 days. Histologic analysis demonstrated classical signs of rejection in controls and normal myocardium with no evidence of rejection in mice chimeric for the gal carbohydrate. Anti-gal xenoantibodies were not produced in gal+ chimeras, but normal antibody responses to other xenoantigens were detected. Specific tolerance for the gal carbohydrate was achieved by this procedure.Conclusions.
These experiments report the first demonstration of permanent survival of gal+ hearts after transplantation with autologous, transduced bone marrow. Transduction with lentiviral vectors results in long-term, stable chimerism at levels sufficient to induce long-term tolerance to heart grafts in mice.