Protection of pig kidney (PK15) cells from the cytotoxic effect of anti-pig antibodies by alpha-galactosyl oligosaccharides.

Anti-pig antibodies in human and baboon serum are believed to be directed against alpha-galactosyl (alpha Gal) epitopes expressed on various pig cells, including vascular endothelia. We have investigated the effect of human sera on the PK15 pig kidney cell line, which abundantly expresses alpha Gal epitopes. To quantitate cell viability, we have used a staining method that differentiates live cells from dead ones. Various carbohydrates (n = 28) were added individually to serum at concentrations of 0.125-50 mg/ml. Unmodified serum caused approximate 100% PK15 cell death within 60 min. Carbohydrates that were not alpha Gal based did not significantly protect PK15 cells. Of the alpha Gal-based carbohydrates, only B disaccharide protected PK15 cells from both human and baboon serum (76% and 93% protection, respectively, at 1 mg/ml). Three alpha Gal oligosaccharides provided approximately 80-90% protection against both human and baboon sera at a concentration of 10 mg/ml. Three other closely related structures protected only against baboon serum (> 80%) at high concentration (50 mg/ml), suggesting a difference in anti-pig antibody affinity between baboon and man. Specific anti-alpha Gal antibody-depleted serum caused < 10% pig cell death, whereas the antibodies eluted from the alpha Gal columns caused > 70% pig cell death. In conclusion, this study provides further evidence that (1) alpha Gal structures are the targets for human and baboon anti-pig antibodies, and (2) there may be a therapeutic role for the infusion of specific alpha Gal carbohydrates, or for antibody removal using alpha Gal immunoaffinity columns, in order to prevent hyperacute rejection of pig organs in man.