Continued production of xenoimmune antibodies 6-8 years after clinical transplantation of fetal pig islet-like cell-clusters

We have monitored the humoral immune responses of 10 type I diabetic patien ts, xenotransplanted with fetal porcine islet-like cell clusters for up to 8 years after xenotransplantation. We investigated the immunoglobulin subcl ass distribution as well as specificity differences of xenoreactive antibod ies. Hemagglutintion tests, using pig erythrocytes, showed that some patien ts maintained higher titers of xenoreactive IgM antibodies during the entir e follow up period, compared with pretransplant levels. In microcytotoxicit y tests all but one patient tested showed higher than pretransplant levels of cytotoxic antibodies against pig peripheral blood mononuclear cells (PBM C) 6-8 years after transplantation. Levels of Gal alpha1,3Gal specific anti bodies, were also high. Antibody dependent cellular cytotoxicity (ADCC) act ivity against a Gal alpha1,3Gal expressing human B cell line was detected i n four patients while ADCC reactivity against adult pig islet cells was det ected in only two patients, 6-8 years after transplantation. Immune sera co llected 30 days and 1 year after transplantation showed positive staining o f adult pig islet cells in fluoromicroscopy whereas sera from later time po ints did not. Western blot experiments showed that some patients had IgG1 antibodies reac tive against epitopes oil pig cells other than Gal alpha1,3Gal, while xenor eactive IgM and IgG2 antibodies mainly reacted with Gal alpha1,3Gal-contain ing epitopes as shown by absorption experiments. These results show that pa tients continue to produce higher than pretransplant levels of IgM and IgG2 xenospecific antibodies against Gal alpha1,3Gal for extended time periods following xenotransplantation. Some patients also produce xenoreactive IgG1 antibodies directed against non-Gal alpha1,3Gal epitopes.