title: Prolonged xenograft survival induced by inducible costimulator-Ig is associated with increased forkhead box P3(+) cells.
abstract: BACKGROUND
  Blockade of the inducible costimulator (ICOS) pathway has been shown to prolong allograft survival; however, its utility in xenotransplantation is unknown. We hypothesize that local expression of ICOS-Ig by the xenograft will suppress the T-cell response resulting in significant prolonged graft survival.
  
  
  METHODS
  Pig iliac artery endothelial cells (PIEC) secreting ICOS-Ig were generated and examined for the following: (1) inhibition of allogeneic and xenogeneic proliferation of primed T cells in vitro and (2) prolongation of xenograft survival in vivo. Grafts were examined for Tregs by flow cytometry and cytokine levels determined by quantitative reverse-transcriptase polymerase chain reaction.
  
  
  RESULTS
  Soluble ICOS-Ig markedly decreased allogeneic and xenogeneic primed T-cell proliferation in a dose-dependent manner. PIEC-ICOS-Ig grafts were significantly prolonged compared with wild-type grafts (median survival, 34 and 12 days, respectively) with 20% of PIEC-ICOS-Ig grafts surviving more than 170 days. Histological examination showed a perigraft cellular accumulation of Forkhead box P3 (Foxp3(+)) cells in the PIEC-ICOS-Ig grafts, these were also shown to be CD3(+)CD4(+)CD25(+). Survival of wild-type PIEC grafts in a recipient simultaneously transplanted with PIEC-ICOS-Ig were also prolonged, with a similar accumulation of Foxp3(+) cells at the periphery of the graft demonstrating ICOS-Ig induces systemic graft prolongation. However, this prolongation was specific for the priming xenograft. Intragraft cytokine analysis showed an increase in interleukin-10 levels, suggesting a potential role in induction/function of CD4(+)CD25(+)Foxp3(+) cells.
  
  
  CONCLUSIONS
  This study demonstrates prolonged xenograft survival by local expression of ICOS-Ig, we propose that the accumulation of CD4(+)CD25(+)Foxp3(+) cells at the periphery of the graft and secretion of interleukin-10 is responsible for this novel observation.
authors.affiliation: Department of Surgery, The University of Melbourne, Austin Health/Northern Health, Heidelberg, Victoria, Australia.
authors.forename: Russell
authors.initials: R
authors.lastname: Hodgson
authors.forename: Dale
authors.initials: D
authors.lastname: Christiansen
authors.forename: Andrew
authors.initials: A
authors.lastname: Ziolkowski
authors.forename: Effie
authors.initials: E
authors.lastname: Mouhtouris
authors.forename: Charmaine J
authors.initials: CJ
authors.lastname: Simeonovic
authors.forename: Francesco L
authors.initials: FL
authors.lastname: Ierino
authors.forename: Mauro S
authors.initials: MS
authors.lastname: Sandrin
mesh_terms: D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000235:genetics / Q000276:immunology*; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D042783:Endothelial Cells / Q000276:immunology / Q000637:transplantation*; D005260:Female; D005434:Flow Cytometry; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D005786:Gene Expression Regulation; D006084:Graft Rejection / Q000276:immunology / Q000517:prevention & control*; D006085:Graft Survival; D006801:Humans; D007074:Immunoglobulin G / Q000096:biosynthesis* / Q000276:immunology; D060889:Inducible T-Cell Co-Stimulator Protein; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050378:T-Lymphocytes, Regulatory / Q000276:immunology*; D013997:Time Factors; D014162:Transfection; D014183:Transplantation, Heterologous
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; D016207:Cytokines; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; C556692:ICOS protein, human; C556694:Icos protein, mouse; C508018:Il2ra protein, mouse; D007074:Immunoglobulin G; D060889:Inducible T-Cell Co-Stimulator Protein; D053645:Interleukin-2 Receptor alpha Subunit