The dog-to-pig renal xenograft: a suitable model to study discordant pig-to-human xenografting
Introduction There is a need for readily available large animal models with which to study discordant xenotransplantation. This study evaluated the relevance of the dog-to-pig renal xenograft model with regards to the pig-to-human species combination.
Materials and methods Canine kidneys were transplanted into nephrectomized pigs (n = 6). No immunosuppression was given to the recipients. Rejection was determined by the gross appearance of the organ, cessation of renal artery pulsation and failure of the cut renal surface to bleed. Rejected kidneys were examined by light microscopy and by immunohistochemistry for porcine IgM and IgG. CH50 levels were determined pre and post transplantation to assess complement activation. Cultured canine aortic endothelial cells (CAEC) were labeled with chromium and incubated with 20% porcine serum to determine whether pig serum was directly cytotoxic to canine endothelial cells. The ability of porcine IgM and IgG to bind canine endothelial cells was assessed with an ELISA assay and flow cytometry using CAEC as target antigens. Western Blotting was performed on canine aortic endothelial cell membrane extracts. Porcine serum served as the primary antibody and goat-anti-pig IgM and IgG as the secondary antibodies.
Results Canine renal xenografts survived 56 ± 45 min. CH50 levels decreased to 45 ± 20% of baseline (P < 0.05). Pathological analysis of renal xenografts revealed platelet microthrombi and immunofluorescence revealed binding of IgM and IgG to the glomeruli and vascular endothelium. Chromium release in CAEC incubated with 20% pig serum was 62 ± 4% at 1 h (P < 0.05 vs. dog control serum) indicating that pig serum is directly cytotoxic to canine endothelial cells. ELISA (Fig. 1) and flow cytometry (Figs 2 and 3) results demonstrate that porcine IgM and IgG bind to CAEC, and Western blot analysis revealed that pig IgM and IgG bound to antigens on CAEC with molecular weights of 42, 50, 94, 121, and 203 kDa.
Conclusions The dog-to-pig renal xenograft model is characterized by tissue changes consistent with classical hyperacute rejection. Xenoreactive antibodies bind to specific xenoantigens on canine endothelium. This is a suitable model to study pig-to-human renal xenotransplantation.