title: Anti-CD154 or CTLA4Ig obviates the need for thymic irradiation in a non-myeloablative conditioning regimen for the induction of mixed hematopoietic chimerism and tolerance.
abstract: BACKGROUND
  Thymic irradiation (TI) or repeated administration of T cell-depleting monoclonal antibodies (TCD mAbs) is required in a previously described non-myeloablative regimen allowing allogeneic marrow engraftment with stable mixed chimerism and tolerance. As both treatments might be associated with toxicity in the clinical setting, we evaluated whether T-cell costimulatory blockade could be used to replace them.
  
  
  METHODS
  C57BL/6 mice received depleting anti-CD4 and anti-CD8 mAbs on day -5, 3 Gy whole body irradiation (day 0), and 15x10(6) fully MHC-mismatched, B10.A bone marrow cells. In addition, hosts were injected with an anti-CD154 mAb (day 0) and/or CTLA4Ig (day +2). Chimerism in peripheral blood was followed by flow cytometric (FACS) analysis, and tolerance was assessed by skin grafting, and also by mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML) assays. The frequency of certain Vbeta families was determined by FACS to assess deletion of donor-reactive T cells.
  
  
  RESULTS
  Chimerism was transient and tolerance was not present in animals receiving TCD mAbs on day -5 without costimulatory blockade. The addition of anti-CD154 and CTLA4Ig, alone or in combination, reliably permitted induction of high levels of stable (>6 months) multi-lineage chimerism, with specific tolerance to skin grafts and donor antigens by MLR and CML assays. Long-term chimeras showed deletion of donor-reactive CD4+ peripheral blood lymphocytes, splenocytes, and mature thymocytes. Administration of TCD mAbs only 1 day before bone marrow transplantation plus anti-CD154 also allowed induction of permanent chimerism and tolerance.
  
  
  CONCLUSIONS
  One injection of anti-CD154 or CTLA4Ig overcomes the need for TI or prolonged host TCD in a preclinical model for the induction of mixed chimerism and deletional tolerance and thus further decreases the toxicity of this protocol. Achievement of tolerance with conditioning given over 24 hr suggests applicability to cadaveric organ transplantation.
authors.affiliation: Transplantation Biology Research Center, Massachusetts General Hospital/Harvard Medical School, Boston 02129, USA.
authors.forename: T
authors.initials: T
authors.lastname: Wekerle
authors.forename: M H
authors.initials: MH
authors.lastname: Sayegh
authors.forename: H
authors.initials: H
authors.lastname: Ito
authors.forename: J
authors.initials: J
authors.lastname: Hill
authors.forename: A
authors.initials: A
authors.lastname: Chandraker
authors.forename: D A
authors.initials: DA
authors.lastname: Pearson
authors.forename: K G
authors.initials: KG
authors.lastname: Swenson
authors.forename: G
authors.initials: G
authors.lastname: Zhao
authors.forename: M
authors.initials: M
authors.lastname: Sykes
mesh_terms: D000069594:Abatacept; D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000627:therapeutic use*; D023201:CD40 Ligand; D060908:CTLA-4 Antigen; D002678:Chimera; D005260:Female; D006085:Graft Survival; D006410:Hematopoiesis; D007108:Immune Tolerance; D018796:Immunoconjugates; D007166:Immunosuppressive Agents / Q000627:therapeutic use*; D007959:Lymphocyte Culture Test, Mixed; D008562:Membrane Glycoproteins / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D016038:Skin Transplantation / Q000276:immunology; D013950:Thymus Gland / Q000528:radiation effects; D019172:Transplantation Conditioning
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D007166:Immunosuppressive Agents; D008562:Membrane Glycoproteins; D023201:CD40 Ligand; D000069594:Abatacept