title: Gal-knockout bioprostheses exhibit less immune stimulation compared to standard biological heart valves.
abstract: OBJECTIVE
  Current biological heart valves (BHVs) contain the major xenogeneic antigen Gal. Recipient anti-Gal antibody binding to such an implanted BHV may contribute to valve degeneration. The study aim was to compare, by implantation in non-human primates, the immune consequences of BHVs from Gal-positive wild-type (WT) pigs and those from alpha-galactosyltransferase knockout (GTKO) pigs.
  
  
  METHODS
  Recipients were immunized prior to implant with keyhole limpet hemocyanin (KLH) conjugated to alphaGal to match the anti-Gal levels and isotypes found in humans. Stented glutaraldehyde-fixed BHVs from WT (n = 4) and GTKO (n = 3) pigs were commercially manufactured and implanted in the mitral position in non-human primates. Recipients were treated with enoxaparin (1 mg/kg b.i.d.) for five weeks which was tapered, and then discontinued. Serum antibody levels to Gal and KLH were measured using ELISA.
  
  
  RESULTS
  Overall anti-Gal and anti-KLH antibody levels were decreased in both WT and GTKO BHV recipients after implantation. Serum anti-Gal IgG levels in GTKO BHV recipients fell rapidly within one month, matching the loss of anti-KLH reactivity. There was no significant difference in retention of anti-KLH antibody between the groups. WT BHV recipients retained significantly elevated levels of anti-Gal IgG during the first year post implant. Area under the curve analysis showed that anti-Gal IgG was significantly increased in the WT BHV group compared to GTKO BHV recipients (p < 0.01).
  
  
  CONCLUSIONS
  Persistent and significantly (p < 0.01) elevated levels of anti-Gal IgG were observed in WT but not GTKO BHV non-human primate recipients, and indicated a continuing BHV-specific immune stimulation to the alphaGal antigen. These data support the hypothesis that the clinical use of Gal-positive xenogeneic bioprosthetic materials can induce an anti-Gal antibody response. Bioprosthetic devices prepared from GTKO pig tissue would eliminate immune stimulation to this major xenoreactive antigen, which may reduce the potential of immune-mediated injury and degeneration.
authors.affiliation: Institute of Cardiovascular Sciences, University College London, UK. christopher.mcgregor@uclh.nhs.uk
authors.forename: Christopher G A
authors.initials: CG
authors.lastname: McGregor
authors.forename: Heide
authors.initials: H
authors.lastname: Kogelberg
authors.forename: Michal
authors.initials: M
authors.lastname: Vlasin
authors.forename: Guerard W
authors.initials: GW
authors.lastname: Byrne
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage; D000818:Animals; D015478:Antigens, Heterophile / Q000276:immunology; D001705:Bioprosthesis; D004187:Disaccharides / Q000276:immunology*; D055786:Gene Knockout Techniques; D006350:Heart Valve Prosthesis; D019918:Heart Valve Prosthesis Implantation / Q000009:adverse effects / Q000379:methods; D006433:Hemocyanins / Q000008:administration & dosage; D008943:Mitral Valve / Q000276:immunology / Q000637:transplantation; D023421:Models, Animal; D008955:Models, Cardiovascular; D018448:Models, Immunological; D015166:Monitoring, Immunologic; D010215:Papio; D011183:Postoperative Complications / Q000276:immunology / Q000517:prevention & control; D014312:Trisaccharides / Q000276:immunology*
chemical_list: D000276:Adjuvants, Immunologic; D015478:Antigens, Heterophile; D004187:Disaccharides; D014312:Trisaccharides; C076569:alpha-galactosyl epitope; C055075:galactosyl-(1-3)galactose; D006433:Hemocyanins; C032808:keyhole-limpet hemocyanin