Failure to deplete anti-Galalpha1-3Gal antibodies after pig-to-baboon organ xenotransplantation by immunoaffinity columns containing multiple Galalpha1-3Gal oligosaccharides.

Abstract:  Background:  The impact of anti-Galα1-3Gal (αGal) antibodies on the acute humoral xenograft rejection (AHXR) of pig organs transplanted in baboons is unclear. Methods:  Twenty-three baboons underwent heterotopic pig heart transplantation (Tx). Groups A (n = 5) and B (n = 6) received non-transgenic and human decay accelerating factor (hDAF) pig hearts, respectively, without any treatment. Groups C (n = 5) and D (n = 7) were transplanted with non-transgenic and hDAF organs, respectively, and the exclusive treatment was repeated extracorporeal immunoadsorptions (EIA) before and after Tx with an αGal column containing disaccharide (DI), trisaccharide (TRI) 2 and pentasaccharide (PENTA) oligosaccharides. Results:  In group A, 3 of 5 xenografts underwent hyperacute rejection (HAR). No xenograft from groups B, C and D experienced HAR, most of them failing from AHXR. Immediately after Tx and up to day 2, the level of immunoglobulin (Ig)M and IgG anti-αGal DI, TRI2 and TRI6, and anti-pig hemolytic antibody (APHA) antibodies decreased in all the groups by 80 to 96% compared with the concentration present before Tx. From day 3 to AHXR, a sustained increase of anti-αGal IgM DI, TRI2 and TRI6, and APHA occurred in all groups. EIA depleted anti-αGal IgM and APHA before Tx, but it did not modify the increase of these antibodies after Tx. Baboon serum samples before Tx, pre-incubated in vitro with 1 mg/ml of DI, TRI2 and TRI6, had an average of 93% reduction of anti-αGal IgM antibodies specific against each one of these αGal oligosaccharides. In contrast, at AHXR, the average reduction after in vitro pre-incubation with either 1 or 5 mg/ml of DI, TRI2 and TRI6 was 40%. Conclusions:  The EIA reduces anti-αGal and APHA antibodies, preventing the HAR of non-transgenic pig hearts transplanted in baboons, as does hDAF expression. However, EIA does not modify the level of anti-αGal IgM and APHA antibodies after Tx nor the AHXR of either non-transgenic or hDAF pig organs. The increase in anti-αGal IgM after Tx was similar for the different antibodies of the anti-αGal polymorphism, and was only partially neutralized in vitro with the specific αGal oligosaccharide.