Lack of variation in αgal expression on lymphocytes in miniature swine of different genotypes

Background: Gal alpha l-3Gal epitopes (alpha Gal) have been demonstrated to be present on tissues of all pig breeds tested to-date and are the major target for human anti-alpha galactosyl (alpha Gal) antibodies. We investigated members of an MHC-inbred miniature swine herd to assess whether there was an association between genotype and expression of aGal. Identification of a low expressor genotype would potentially enable selective breeding of pigs that might prove beneficial as donors in clinical xenotransplantation. Methods: we measured alpha Gal expression on various pig cells by use of fluorescent-activate cell sorter (FACS) using (i) purified human anti-alpha Gal antibody and (ii) the isolectin GS-I-B4. Initial studies were on porcine peripheral blood mononuclear cells (PBMCs) and subsequent studies on lymphocytes, platelets, and T cell subsets (CD4 + and CD8 + cells). Results: there was considerable day-to-day variation in alpha Gal expression on PBMCs from the same pig. When only lymphocytes were examined, there was a high degree of reproducibility, and no significant difference in alpha Gal expression was detected between representative pairs of animlas of three different genotypes. Purified anti alpha Gal antibody bound to different sites on the alpha Gal epitope than did Griffonia (Bandeiraea) simplicifolia I-B4 (GS-I-B4). Lectin binding was significantly reduced in the absence of divalent cations. When CD4 + and CD8 + T cells were examined for alpha Gal expression, two distinct populations of each type of cell were observed, with larger cells expressing a higher level of aGal. Conclusions: although the number of pigs of different genotypes studied was small, on the basis of this limited study, pigs of a low aGal expressor genotype that could be selectively bred for use in clinical xenotransplantation were not identified.