Impediments to successful gene transfer to the kidney in the context of transplantation and how to overcome them

Abstract

Manipulation of the graft with immunosuppressive genes represents a novel approach to overcome the toxicity of immunosuppressants currently used to prevent acute rejection. Here we compared the efficiency of a non-viral versus a viral technique of gene transfer to the kidney in the setting of isotransplantation and evaluated whether transfection with adenovirus encoding CTLA4Ig prolonged allograft survival. Donor rat kidneys were perfused with a medium containing the cationic polymer polyethylenimine PEI 25k complexed to a vector coding for the beta-galactosidase (beta-gal) gene or with a replication-deficient adenovirus encoding the beta-gal gene (AdCMVbeta-gal; 1 x 10(9) pfu) before isotransplantation. In another set of experiments, donor kidneys were perfused with an adenovirus encoding the murine CTLA4Ig gene (AdmCTLA4Ig; 1 x 10(9) pfu) before allotransplantation. Perfusion with PEI/DNA complexes resulted in large areas of hypoperfusion, histology showed glomerular and tubular injury, capillary thrombosis, and complement activation. Reperfusion with lower PEI/DNA ratio was possible but no detectable transfection observed. In animals receiving adenovirus, beta-gal activity increased with time and localized mainly in proximal and distal tubular cells as documented by beta-gal histochemistry and in situ hybridization. Adenovirus-mediated transduction of CTLA4Ig, a recombinant fusion protein that blocks T cell activation, resulted in a prolonged allograft survival. The toxic effects observed in kidneys exposed to PEI 25k prevent any future possibility of their use in clinical transplantation. By contrast, adenovirus-mediated gene transfer to the kidney offers exciting perspectives for the future of transplant medicine. Transducing the graft with a gene encoding CTLA4Ig effectively prolongs renal graft survival and induces sustained unresponsiveness to the donor antigens without the need of immunosuppression.