Induction of molecular chimerism by gene therapy prevents antibody-mediated heart transplant rejection

In order for xenotransplantation to become a clinical reality, and fulfill its promise of overcoming shortages of human organs and tissues, rejection mediated by the host's immune system must first be overcome. In primates, preformed natural antibodies that bind the carbohydrate antigen Galα1-3Galβ1-4GlcNAc-R (αGal), which is synthesized by UDP galactose:β-D-galactosyl-1,4-N-acetyl-D-glucosaminide α(1-3)galactosyltransferase (E.C. 2.4.1.151) or simply αGT, mediate rigorous rejection of transplanted pig organs and tissues. In αGT knockout mice (GT^o mice), which like humans contain in their serum antibodies that bind αGal, expression of a retrovirally transduced αGT in bone marrow-derived cells is sufficient to prevent production of αGal-reactive antibodies. Here, we demonstrate that reconstitution of lethally irradiated GT⁰ mice with αGT-transduced bone marrow cells from GT⁰ littermates prevents antibody-mediated rejection of cardiac transplants from wild-type mice. These data suggest that gene therapy can be used to induce immunological tolerance to defined antigens and thereby overcome transplant rejection.