title: Persistent strong anti-HLA antibody at high titer is complement binding and associated with increased risk of antibody-mediated rejection in heart transplant recipients.
abstract: BACKGROUND
  Sensitized heart transplant candidates are evaluated for donor-specific anti-HLA IgG antibody (DSA) by Luminex single-antigen bead (SAB) testing (SAB-IgG) to determine donor suitability and help predict a positive complement-dependent cytotoxicity crossmatch (CDC-XM) by virtual crossmatching (VXM). However, SAB testing used for VXM does not correlate perfectly with CDC-XM results and individual transplant programs have center-specific permissible thresholds to predict crossmatch positivity. A novel Luminex SAB-based assay detecting C1q-binding HLA antibodies (SAB-C1q) contributes functional information to SAB testing, but the relationship between SAB strength and complement-binding ability is unclear.
  
  
  METHODS
  In this retrospective study, we identified 15 pediatric and adult heart allograft candidates with calculated panel-reactive antibody (cPRA) >50% by SAB-IgG and compared conventional SAB-IgG results with SAB-C1q testing.
  
  
  RESULTS
  Pre- and post-transplant DSA by SAB-C1q correlated with DSA by SAB-IgG and also with CDC-XM results and early post-transplant endomyocardial biopsy findings. Individual HLA antibodies by SAB-IgG in undiluted sera correlated poorly with SAB-C1q; however, when sera were diluted 1:16, SAB-IgG results were well correlated with SAB-C1q. In some sera, HLA antibodies with low mean fluorescent intensity (MFI) by SAB-IgG exhibited high SAB-C1q MFIs for the same HLA antigens. Diluting or heat-treating these sera increased SAB-IgG MFI, consistent with SAB-C1q results. In 13 recipients, SAB-C1q-positive DSA was associated with positive CDC-XM and with early clinical post-transplant antibody-mediated rejection (cAMR).
  
  
  CONCLUSIONS
  Risk assessment for positive CDC-XM and early cAMR in sensitized heart allograft recipients are correlated with SAB-C1q reactivity.
authors.affiliation: Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA. zeevia@upmc.edu
authors.forename: Adriana
authors.initials: A
authors.lastname: Zeevi
authors.forename: John
authors.initials: J
authors.lastname: Lunz
authors.forename: Brian
authors.initials: B
authors.lastname: Feingold
authors.forename: Michael
authors.initials: M
authors.lastname: Shullo
authors.forename: Christian
authors.initials: C
authors.lastname: Bermudez
authors.forename: Jeffery
authors.initials: J
authors.lastname: Teuteberg
authors.forename: Steven
authors.initials: S
authors.lastname: Webber
mesh_terms: D000293:Adolescent; D000328:Adult; D000906:Antibodies / Q000097:blood / Q000276:immunology*; D002648:Child; D002675:Child, Preschool; D015922:Complement C1q / Q000276:immunology*; D005260:Female; D006084:Graft Rejection / Q000097:blood / Q000276:immunology*; D006680:HLA Antigens / Q000276:immunology*; D016027:Heart Transplantation / Q000276:immunology*; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors
chemical_list: D000906:Antibodies; D006680:HLA Antigens; D015922:Complement C1q