The serum level of xenoantibodies, and hDAF or αGAL expression on pig cells, modulate in vitro the protection given by hDAF to primate complement-mediated damage

Abstract

The ability of human complement regulatory molecules to prevent xenograft rejection following pig-to-primate xenotransplantation is limited. We assayed the efficacy of transgenic human decay accelerating factor (hDAF) expressed on porcine cells to inhibit the in vitro complement activity of primate sera. We measured the cytotoxic activity of baboon or human sera against peripheral blood lymphocytes (PBLs) from hDAF or nontransgenic pigs using a flow cytometry complement-mediated cytotoxicity assay (FCCA). We also analyzed the anti–Galα1-3Gal (αGal) antibody titer of the baboon sera by ELISA and the expression of hDAF and αGal on the PBL surface by immunofluorescence. Transgenic hDAF expression was capable of protecting pig cells against injury produced by both baboon and human serum. However, the hDAF molecule was more efficient against human than baboon sera. The humoral cytotoxicity capacity correlated with the level of both IgG and IgM anti-αGal antibodies. In addition, inhibition of complement-mediated cytotoxicity of hDAF pig cells correlated with the expression of hDAF and αGal molecules on target cells. These results confirm in vitro the protective role of hDAF in pig cells to heterologus complement mediated damage, but they also suggest that protection decreases in the presence of high levels of anti-porcine antibodies in serum, low expression of hDAF, or high expression of αGal on pig cells.