Tolerance induction by lentiviral gene therapy with a nonmyeloablative regimen

Antibodies (Abs) directed at the Galα1,3Galβ1,4GlcNAc-R (αGal) carbohydrate epitope initiate xenograft rejection. Previously, we have shown that bone marrow transplantation (BMT) with lentivirus-mediated gene transfer of porcine α1,3 galactosyltransferase (GalT) is able to induce tolerance to αGal-expressing heart grafts following a lethal dose of irradiation. Here we show the first demonstration of permanent survival of αGal+ hearts following transplantation with autologous, lentivirus-transduced BM using a nonmyeloablative regimen. Autologous BM from GalT knockout (GalT–/–) mice was transduced with a lentiviral vector expressing porcine GalT and transplanted into sublethally irradiated (3 Gy) GalT–/– mice. Chimerism in the peripheral blood cells (PBCs) remained low but was higher in the BM, especially within the stromal cell population. Mice reconstituted with GalT did not produce anti-αGal Abs over time. We immunized these mice with αGal-expressing cells and assessed humoral immune responses. Anti-αGal xenoantibodies were not produced in mice reconstituted with GalT, but normal Ab responses to other xenoantigens were detected. Mice reconstituted with GalT accepted αGal+ heart grafts over 100 days. Transduction with lentiviral vectors results in chimerism at levels sufficient to induce long-term tolerance under nonmyeloablative conditions.