title: Modified AdCTLA-4 vector blocks alloimmune response in vitro.
abstract: BACKGROUND
  Gene transfer of the costimulatory blockade molecule CTLA-4Ig into cold-preserved rat liver allografts results in indefinite allograft survival. Despite local delivery, this mode of immunomodulation is associated with systemic immunosuppression. In an effort to restrict immunosuppression to the graft, we have constructed a novel adenoviral vector, AdCTLA-4ex-TAG, in which the Ig sequence of CTLA-4Ig DNA has been deleted to destabilize the gene product to promote rapid extrahepatic degradation while maintaining its immunosuppressive activity within the graft milieu.
  
  
  METHODS
  (1) Vector construction. CTLA-4 extracellular binding domain (CTLA-4ex) was prepared by PCR-based cloning methods and fused in frame to a genetic element encoding an epitope TAG allowing identification of the transgene product CTLA-4exTAG. CTLA-4exTAG was subcloned into a shuttle vector enabling isolation of AdCTLA-4exTAG. (2) In vitro transfection: AdCTLA-4exTAG was transfected into MH(1)C(1) cells and then supernatant was recovered for Western blot analysis. (3) In vitro alloimmune response was characterized by CFSE proliferation assay. (4) Extrahepatic effect of AdCTLA-4exTAG was characterized by the ability to control tumor growth after implantation of a regressive, immune sensitive cancer cell line (REGb) in the skin of BDIX rats after liver transduction with AdCTLA-4exTAG.
  
  
  RESULTS
  Expression and secretion of the recombinant protein were documented by Western blot after infection of the MH(1)C(1) cell line() with AdCTLA-4exTAG. Addition of infected MH(1)C(1) cell supernatant resulted in abrogation of alloimmune response as shown by markedly diminished division of CD4(+) T cells in a CFSE proliferation assay. Extrahepatic tumor regressed normally after liver transduction with AdCTLA-4exTAG.
  
  
  CONCLUSIONS
  These results show efficient in vitro expression of CTLA-4exTAG after transfection with AdCTLA-4exTAG. The modified protein retains its ability to abrogate in vitro alloimmune response. Efficient control of extrahepatic tumor growth after liver-directed delivery of AdCTLA-4exTAG suggests that the immunosuppressive effect of this vector is restricted to the liver. These results set the ground for the utilization of this novel adenoviral vector in the transplant setting.
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: G
authors.initials: G
authors.lastname: Zamir
authors.forename: A E
authors.initials: AE
authors.lastname: Gelman
authors.forename: F
authors.initials: F
authors.lastname: Debonera
authors.forename: J
authors.initials: J
authors.lastname: Hardwigsen
authors.forename: X
authors.initials: X
authors.lastname: Que
authors.forename: X
authors.initials: X
authors.lastname: Aldeguer
authors.forename: M
authors.initials: M
authors.lastname: Martin
authors.forename: A
authors.initials: A
authors.lastname: Shaked
authors.forename: K M
authors.initials: KM
authors.lastname: Olthoff
mesh_terms: D000069594:Abatacept; D000256:Adenoviridae / Q000235:genetics*; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000235:genetics* / Q000276:immunology; D060908:CTLA-4 Antigen; D002460:Cell Line; D015870:Gene Expression / Q000276:immunology; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D006133:Growth Substances / Q000378:metabolism; D018796:Immunoconjugates; D007136:Immunoglobulins / Q000235:genetics; D007166:Immunosuppressive Agents / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000276:immunology / Q000601:surgery; D016031:Liver Transplantation / Q000276:immunology*; D008297:Male; D019899:Paracrine Communication / Q000276:immunology; D051381:Rats; D011919:Rats, Inbred Strains; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology; D023001:Transplantation Tolerance / Q000276:immunology
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556708:Ctla4 protein, rat; D006133:Growth Substances; D018796:Immunoconjugates; D007136:Immunoglobulins; D007166:Immunosuppressive Agents; D011993:Recombinant Fusion Proteins; D000069594:Abatacept