title: CTLA-4 is important in maintaining long-term survival of cardiac allografts.
abstract: BACKGROUND
  CTLA-4 is a negative regulatory molecule upregulated on activated T cells; however, its role in induction and maintenance of transplant tolerance is not well understood.
  
  
  METHODS
  The characteristics and effects of a novel mouse anti-rat CTLA-4 antibody (Ab) (242B58) were examined using fluorescence-activated cell sorter, mixed lymphocyte reaction, enzyme-linked immunospot, signaling studies, and a rat model of cardiac transplant tolerance induced by administration of anti-CD28 Ab and cyclosporine.
  
  
  RESULTS
  The anti-CTLA4 Ab was shown to bind to CTLA-4 but not prevent subsequent binding of B7 to CTLA-4. Binding to CTLA-4 did not result in phosphorylation of early cytoplasmic tyrosine kinases, suggesting that this is not a signaling Ab. However, its in vitro function was compatible with antagonization of the effects of CTLA-4, thereby increasing T-cell proliferation and interferon-gamma production in mixed lymphocyte reaction and enzyme-linked immunospot assays, respectively. Administration of 242B58 to animals treated with anti-CD28 Ab and cyclosporine either at the time of transplantation or various time-points up to 33 days posttransplantation did not result in immediate rejection, but rather caused a delayed severe acute allograft rejection at approximately 45 days posttransplant.
  
  
  CONCLUSIONS
  Our results seem to be a reflection of the unique properties of the 242B58 Ab, which does not antagonize B7 binding to CTLA-4 and affect its ability to out-compete CD28 for B7 binding. It does, however, seem to interfere with CTLA-4 signaling, suggesting that competition for B7 may be important in induction of tolerance, but signaling through CTLA-4 is more important in maintaining a tolerant phenotype.
authors.affiliation: Transplant Research Center, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. achandraker@rics.bwh.harvard.edu
authors.forename: Anil
authors.initials: A
authors.lastname: Chandraker
authors.forename: Volkert
authors.initials: V
authors.lastname: Huurman
authors.forename: Karen
authors.initials: K
authors.lastname: Hallett
authors.forename: Xueli
authors.initials: X
authors.lastname: Yuan
authors.forename: Alfred J
authors.initials: AJ
authors.lastname: Tector
authors.forename: Chul-Hyun
authors.initials: CH
authors.lastname: Park
authors.forename: Ellen
authors.initials: E
authors.lastname: Lu
authors.forename: Nicholas
authors.initials: N
authors.lastname: Zavazava
authors.forename: Martin
authors.initials: M
authors.lastname: Oaks
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000276:immunology / Q000378:metabolism*; D018122:B7-1 Antigen / Q000378:metabolism; D060908:CTLA-4 Antigen; D006084:Graft Rejection / Q000276:immunology; D006085:Graft Survival / Q000276:immunology*; D016027:Heart Transplantation / Q000276:immunology*; D007108:Immune Tolerance / Q000276:immunology*; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D013997:Time Factors
chemical_list: D000906:Antibodies; D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; C556708:Ctla4 protein, rat; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases