title: Human CD55 expression blocks hyperacute rejection and restricts complement activation in Gal knockout cardiac xenografts.
abstract: BACKGROUND
  Transgenic expression of human complement regulatory proteins reduces the frequency of hyperacute rejection (HAR) in Gal-positive cardiac xenotransplantation. In this study, we examined the impact of human CD55 (hCD55) expression on a Gal knockout (GTKO) background using pig-to-primate heterotopic cardiac xenotransplantation.
  
  
  METHODS
  Cardiac xenotransplantation was performed with GTKO (group 1; n=6) and GTKO.hCD55 (group 2; n=5) donor pigs using similar immunosuppression. Cardiac biopsies were obtained 30 min after organ reperfusion. Rejection was characterized by histology and immunohistology. Intragraft gene expression, serum non-Gal antibody, and antibody recovered from rejected hearts were analyzed.
  
  
  RESULTS
  HAR of a GTKO heart was observed. Remaining grafts developed delayed xenograft rejection. Median survival was 21 and 28 days for groups 1 and 2, respectively. Vascular antibody deposition was uniformly detected 30 min after organ reperfusion and at explant. A higher frequency of vascular C5b deposition was seen in GTKO organs at explant. Serum non-Gal antibody, antibody recovered from the graft, and intragraft gene expression were similar between the groups.
  
  
  CONCLUSIONS
  HAR of GTKO hearts without hCD55 may occur. Expression of hCD55 seemed to restrict local complement activation but did not improve graft survival. Chronic vascular antibody deposition with evidence of protracted endothelial cell activation was seen. These observations suggest that non-Gal antibody-induced chronic endothelial cell activation coupled to possible hemostatic incompatibilities may be the primary stimulus for delayed xenograft rejection of GTKO hearts. To avoid possible HAR, future clinical studies should use donors expressing human complement regulatory proteins in the GTKO background.
authors.affiliation: Institute of Cardiovascular Sciences, University College London, London, UK.
authors.forename: Christopher G A
authors.initials: CG
authors.lastname: McGregor
authors.forename: Davide
authors.initials: D
authors.lastname: Ricci
authors.forename: Naoto
authors.initials: N
authors.lastname: Miyagi
authors.forename: Paul G
authors.initials: PG
authors.lastname: Stalboerger
authors.forename: Zeji
authors.initials: Z
authors.lastname: Du
authors.forename: Elise A
authors.initials: EA
authors.lastname: Oehler
authors.forename: Henry D
authors.initials: HD
authors.lastname: Tazelaar
authors.forename: Guerard W
authors.initials: GW
authors.lastname: Byrne
mesh_terms: D000208:Acute Disease; D000818:Animals; D030801:Animals, Genetically Modified; D001706:Biopsy; D018958:CD55 Antigens / Q000235:genetics / Q000378:metabolism*; D003167:Complement Activation / Q000187:drug effects; D004187:Disaccharides / Q000172:deficiency / Q000276:immunology; D005700:Galactosyltransferases / Q000172:deficiency / Q000235:genetics; D055786:Gene Knockout Techniques; D006084:Graft Rejection / Q000235:genetics / Q000276:immunology / Q000473:pathology / Q000517:prevention & control*; D006085:Graft Survival / Q000187:drug effects; D016027:Heart Transplantation / Q000276:immunology*; D006801:Humans; D007150:Immunohistochemistry; D007166:Immunosuppressive Agents / Q000494:pharmacology; D009206:Myocardium / Q000276:immunology* / Q000473:pathology; D010215:Papio; D013552:Swine; D013997:Time Factors; D014183:Transplantation, Heterologous
chemical_list: D018958:CD55 Antigens; D004187:Disaccharides; D007166:Immunosuppressive Agents; C055075:galactosyl-(1-3)galactose; D005700:Galactosyltransferases; C530267:alpha-1,3-galactosyltransferase 1, porcine