Recognition of an octapeptide sequence by multiple Galα(1,3)Gal-binding proteins

Strategies are now being designed to overcome the hyperacute rejection of vascularized pig xenografts by human natural anti-Galα(1,3)Gal antibodies. We now demonstrate that a synthetic octapeptide, Gal pep 1 (DAHWESWL), isolated from a peptide epitope library using the α-galactosyl specific lectin IB4, "mimics" the carbohydrate epitope Galα(1,3)Gal. In vitro studies demonstrated that the binding of the IB4 lectin or human natural antibodies to pig cells could be specifically blocked by Gal pep 1, in several different serological assays: a) the hemagglutnation of pig erythrocytes; b) cytofluorographic analysis of pig lymphocytes and endothelial cells; c) cytotoxicity of human serum against pig endothelial cells; d) an ELISA assay. The relative affinity of the peptide for the IB4 lectin was similar to that of α-galactosyl sugars, although it was bound at a lower affinity by human antibodies. The implications of these observations to xenotransplantation are that peptides could theoretically be used to block hyperacute rejection.