Hyperacute rejection of hDAF-transgenic pig organ xenografts in cynomolgus monkeys: influence of pre-existing anti-pig antibodies and prevention by the alpha GAL glycoconjugate GAS914.

BACKGROUND: Our introductory pig-to-cynomolgus monkey heart or kidney transplantation using organs from pigs transgenic for human decay-accelerating factor (hDAF), showed a high incidence of hyperacute rejection (HAR), which was ascribed to extraordinary high levels of anti-pig antibodies. We evaluated the efficacy of GAS914, a Gal alpha 1-3Gal trisaccharide linked to a poly-l-lysine backbone, in inhibition of HAR. METHODS: hDAF transgenic heterotopic heart (n = 15) or life-supporting kidney (n = 8) transplantation included induction with cyclophosphamide or anti-thymocyte globulin, and maintenance with cyclosporine or tacrolimus, steroids and mycophenolate sodium/mofetil. Four doses of GAS914 were given before transplantation. Rejection was confirmed by graft histology, and anti-pig antibody levels were determined in various assays. RESULTS: Four of six heart transplants without GAS914 treatment showed HAR. Nine subsequent transplants with GAS914 pre-treatment, did not show HAR (chi-square, P < 0.05). Two of four kidney transplants without GAS914 treatment ended with HAR. Four subsequent transplants with GAS914 did not show HAR. Animals with HAR showed extremely high antibody levels. Samples just before transplantation showed significantly higher antibody levels in recipients presenting with HAR. In all assays antibody levels were significantly lowered by GAS914 pre-treatment. CONCLUSIONS: HAR of hDAF solid organs could be ascribed to high levels of anti-pig antibodies. It is hypothesized that the hDAF transgene shows a threshold in efficacy, above which an overwhelming attack by antibodies and complement activation cannot be modulated to prevent HAR. HAR does not occur when animals with lower levels are used, or when antibodies are effectively depleted from the circulation by GAS914 treatment.

Anti-pig antibody levels in non-human primates of various origin.

BACKGROUND: Natural anti-porcine antibodies play a major role in hyperacute solid organ xenograft rejection in the pig-to-non-human primate model. Work from other groups and our experience in transplantation experiments has shown that antibody levels are highly variable between non-human primate species, and that extremely high levels can mediate hyperacute rejection even if organs from animals transgenic for human decay-accelerating factor are used. METHODS: Sera were obtained from cynomolgus monkeys wild-caught in Mauritius, captive-bred in the Philippines, captive-bred in Indonesia (Indonesia-Ind), and originating from Indonesia but colony-bred in USA (Indonesia-USA), from baboons wild-caught in Kenya, and from rhesus monkeys originating from India but colony-bred in USA (10 animals in each group). Antibody levels were determined using assays for haemolytic antibody (APA), IgM and IgG class anti-Galalpha1-3Gal antibody, and IgM and IgG class anti-endothelial cell antibody. RESULTS: Cynomolgus monkeys from the Philippines and Indonesia-USA and rhesus monkeys showed median APA and IgM antibody levels in the same range as a pooled human serum standard, and median IgG levels well below the level in this standard. Cynomolgus monkeys from Mauritius and Indonesia-Ind showed extremely high APA levels (median seven to 10 times the human serum standard): IgM class antibodies were also higher, while IgG class antibodies were in the range of the level in the human serum standard. Antibody levels in baboons were in between these two categories. The results of the APA assay showed a highly statistically significant correlation with the assays of IgM antibody, and this was also the case for the IgM antibody assays, indicative of the assessment of the same antibodies in these assays. The same was observed for the assays for IgG antibody. Taking body weight as an indicator for age, there was no relationship between body weight and levels of antibodies. CONCLUSIONS: Natural antibody levels show a significant variation between various groups of non-human primates, with levels in some groups well above those in a human serum standard.