Endothelial cells derived from pigs lacking Galα(1,3)Gal:: no reduction of human leukocyte adhesion and natural killer cell cytotoxicity

Background. The expression of galactose-alpha (1,3) galactose (Gal) on porcine cells represents a map or barrier to xenotransplantation. The generation of Gal(-/-) pigs to overcome this barrier redirected the focus of research to other rejection mechanisms, including cellular immunity. The present in vitro study investigated (1) the adhesive interactions between human leukocyte subsets and primary endothelial cells derived from inbred Ga-/- and Gal(+/+) pigs, and (2) the susceptibility of such Ga-/- porcine endothelial cells to human natural killer (NK) cell cytotoxicity. Methods. Primary porcine aortic endothelial cells (PAEC) were isolated from Gal(-/-) (PAEC-Gal(-/-)) and Ga+/+ (PAEC-Gal(+/+)) pigs. Human peripheral blood mononuclear cells (PBMC), polymorphonuclear neutrophils (PMN), and NK cells were isolated from healthy volunteers and tested in functional adhesion and cytotoxicity assays. Results. Adhesion of human PBMC, PMN, or purified NK cells on PAEC-Gal(-/-) cells was not different from that on PAEC-Gal(+/+) cells. Comparing the different leukocyte subsets of PBMC, a preferential adhesion of NK and B cells on both PAEC-Gal(-/-) and PAEC-Gal(+/+) was detected. Tumor-necrosis factor-a stimulation of PAEC-Gal(-/-) and PAEC-Gal(+/+) induced an increase of CD62E and CD106 expression and increased cellular adhesion, in particular, of PMN. The lack of Gal expression on PAEC-Gal(-/-) cells did not prevent xenogeneic human NK-cell cytotoxicity mediated by freshly isolated or interleukin-2-activated NK cells. Conclusions. Neither human leukocyte adhesion nor xenogeneic NK-cell cytotoxicity against PAEC are impaired by the lack of Gal, indicating that Gal is not a dominant target of cellular rejection.