The galactose-α-1,3-galactose (αGal) carbohydrate epitope is expressed on porcine, but not human cells, and therefore represents a major target for preformed human anti-pig natural Abs (NAb). Based on results from pig-to-primate animal models, NAb binding to porcine endothelial cells will likely induce complement activation, lysis, and hyperacute rejection in pig-to-human xenotransplantation. Human NK cells may also contribute to innate immune responses against xenografts, either by direct recognition of activating molecules on target cells or by FcγRIII-mediated xenogeneic Ab-dependent cellular cytotoxicity (ADCC). The present study addressed the question as to whether the lack of αGal protects porcine endothelial cells from NAb/complement-induced lysis, direct xenogeneic NK lysis, NAb-dependent ADCC, and adhesion of human NK cells under shear stress. Homologous recombination, panning, and limiting dilution cloning were used to generate an αGal-negative porcine endothelial cell line, PED2*3.51. NAb/complement-induced xenog eneic lysis of PED2*3.51 was reduced by an average of 86% compared with the αGal-positive phenotype. PED2*3.51 resisted NK cell-mediated ADCC with a reduction of lysis ranging from 30 to 70%. However, direct xenogeneic lysis of PED2*3.51, mediated either by freshly isolated or IL-2-activated human NK cells or the NK cell line NK92, was not reduced. Furthermore, adhesion of IL-2-activated human NK cells did not rely on αGal expression. In conclusion, removal of αGal leads to a clear reduction in complement-induced lysis and ADCC, but does not resolve adhesion of NK cells and direct anti-porcine NK cytotoxicity, indicating that αGal is not a dominant target for direct human NK cytotoxicity against porcine cells.
Baumann, B. C., Forte, P., Hawley, R. J., Rieben, R., Schneider, M. K. J., & Seebach, J. D. (2014). Lack of Galactose- -1,3-Galactose Expression on Porcine Endothelial Cells Prevents Complement-Induced Lysis but Not Direct Xenogeneic NK Cytotoxicity. The Journal of Immunology, 172(10), 6460–6467. https://doi.org/10.4049/jimmunol.172.10.6460