Characterization of human xenoreactive antibodies in liver failure patients exposed to pig hepatocytes after bioartificial liver treatment - An ex vivo model of pig to human xenotransplantation

Background, There are limited experimental data on the nature of the humora l response elicited in humans against pig antigens, Ttl this study, we have examined the xenoantibody (XAb) response in eight patients with acute Live r failure exposed to pig hepatocytes after treatment with the bioartificial Liver (BAL), Methods. Patients' plasma samples obtained before and after BAL treatment w ere tested for IgM and IgG XAbs, IgG subclasses, and XAb cytotoxicity, usin g enzyme-linked immunosorbent assay and flow-cytometric assays, The charact erization of pig aortic endothelial cell (PAEC) surface xenoantigens was an alyzed by immunoprecipitation, Results. We observed by day 10, a strong anti-pig IgG and IgM XAb response in patients undergoing two or more BAL treatments, with a significant incre ase in all the IgG subclasses; in contrast, XAb titers did not change if th e patients received only one BAL treatment. The majority of the XAbs produc ed to porcine antigens were primarily specific for the alpha Gal epitope, B oth IgG and IgM XAbs were cytotoxic to PAECs, and the cytotoxic activity of IgG was associated with high levels of IgG1 and IgG3 subclasses, known to be efficient on complement activation. The characterization of porcine surf ace antigens demonstrated that IgM human XAbs, before and after BAL exposur e, recognized xenoantigens on PAECs with similar molecular weights, suggest ing that the same population of XAbs were present in the patients before an d after exposure to pig antigens, Conclusions. Repetitive exposure of humans to porcine antigens after BAL tr eatment, results in a strong IgG and IgM XAb responses that are primarily d irected against the alpha Gal epitope, These XAbs are cytotoxic to PAECs an d the IgG toxicity correlates with high IgG1 and IgG3 levels, Our data also suggest that no new XAb specificity emerges after porcine exposure.