title: Prolongation of corneal allograft survival by CTLA4-FasL in a murine model.
abstract: BACKGROUND
  To investigate the therapeutic effect of CTLA4-FasL-B7 costimulatory pathway blockage-on graft survival in a murine model of corneal transplantation.
  
  
  METHODS
  Orthotopic penetrating keratoplasty was performed on BALB/c mice. The mice were randomized into four groups: the isograft group, untreated allograft group, cyclosporine A drug delivery system (CsA DDS)-anterior chamber implanted group, and 10 microg/mL CTLA4-FasL-treated group. Allografts were from C57BL/6 mice. Survival time of corneal grafts was evaluated. Immunohistological method and TdT-mediated dUTP Nick End Labeling (TUNEL) were applied for the detection of CD4+ T cells and apoptotic cells in corneal transplants. To assess whether peripheral immune tolerance appeared after the treatment of CTLA4-FasL, CsA DDS-implanted- and CTLA4-FasL-treated BALB/c mice with clear grafts received skin allografts at 4 weeks after keratoplasty, and the status of corneal transplants were observed when skin grafts were rejected.
  
  
  RESULTS
  Allografts in the CTLA4-FasL group (median survival time [MST] = 106 days, p = 0.0042) and the CsA DDS group (MST = 60 days, p = 0.0037) revealed extending survival time, compared with that in the untreated allograft group (MST = 14 days). There were significantly fewer CD4-positive T cells in both the isograft group and the CsA DDS group. In the untreated allograft group, the number of CD4+ T cells gradually increased from day 1 until the final day of observation (day 21). By contrast, it reached a peak on day 7 and then absolutely reduced in the CTLA4-FasL group. Many apoptotic cells were detected on day 7 in the CTLA4-FasL group, but very few were seen in the other groups. Within 30 days of skin-graft rejection, previously healthy and long-standing corneal grafts became rejected in the CsA DDS group but remained clear in the CTLA4-FasL group.
  
  
  CONCLUSIONS
  CTLA4-FasL can prolong the survival time of corneal allografts in mice, exerting a negative regulation on T-cell activation simultaneously by blocking B7 costimulatory signals and inducing Fas-FasL apoptotic pathway. Due to the adjunctive role of FasL, it also appears to be a potential activity of tolerance induction through T-cell apoptotic pathways.
authors.affiliation: State Key Laboratory Cultivation Base, Shandong Provincial Key Laboratory of Ophthalmology, Shandong Eye Institute, Qingdao, China.
authors.forename: Weiyun
authors.initials: W
authors.lastname: Shi
authors.forename: Min
authors.initials: M
authors.lastname: Chen
authors.forename: Lixin
authors.initials: L
authors.lastname: Xie
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000378:metabolism*; D017209:Apoptosis; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D060908:CTLA-4 Antigen; D003315:Cornea / Q000502:physiology*; D016572:Cyclosporine / Q000008:administration & dosage; D004195:Disease Models, Animal; D053222:Fas Ligand Protein / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D006085:Graft Survival / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage; D020287:In Situ Nick-End Labeling; D015948:Keratoplasty, Penetrating / Q000502:physiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D011993:Recombinant Fusion Proteins / Q000627:therapeutic use*; D016038:Skin Transplantation; D014184:Transplantation, Homologous
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C556707:Ctla4 protein, mouse; D053222:Fas Ligand Protein; D007166:Immunosuppressive Agents; D011993:Recombinant Fusion Proteins; D016572:Cyclosporine