Regulation of Macrophage-Mediated Xenocytotoxicity by Overexpression of Alpha-2,6-sialyltransferase in Swine Endothelial Cells

Macrophages play an important role in xenogenic rejection and therefore may represent a major obstacle in clinical application of xenograft. CD33-related sialic acid–binding immunoglobulin–like lectins (Siglecs) belong to the immunoglobulin superfamily and contain a cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) that is able to inhibit cytokine production. Because human macrophages express various CD33-related Siglecs, we hypothesized that overexpression of α-2,6-sialyltransferase (2,6-ST) in swine endothelial cells (SECs) might prevent the cytotoxicity mediated by macrophages. To confirm our hypothesis, the cytotoxicity of macrophages against 2,6-ST–overexpressing SECs was determined with the use of in vitro–generated macrophages as an effector and naïve or 2,6-ST–overexpressing SECs as a target. The 2,6-ST–overexpressing SECs were established by transfection with the genes for 2,6-ST. Transfection of 2,6-ST led to significant reduction in cytotoxicity compared with naïve SECs. These findings indicate that the sialylated ligands against CD33-related Siglecs may provide an effective therapeutic strategy to inhibit macrophage-mediated xenograft rejection in xenotransplantation.