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

Background. 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. Methods. Donor rat kidneys were pefused with a medium containing the cationic polymer polyethylenimine PEI 25k complexed to a vector coding for the β-galactosidase (β-gal) gene or with a replication-deficient adenovirus encoding the β-gal gene (AdCMVβ-gal; 1×10⁹ pfu) before isotransplantation. In another set of experiments, donor kidneys were perfused with an adenovirus encoding the murine CTLA4Ig gene (AdmCTLA4Ig; 1×10⁹ pfu) before allotransplantation. Results. 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, β-gal activity increased with time and localized mainly in proximal and distal tubular cells as documented by β-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. Conclusions. 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.