Background: Pig islets are considered an attractive alternative treatment for patients with Type 1 diabetes. However, pig islet xenografts, transplanted into non-human primates, are directly rejected by cell-mediated processes. We have previously reported that cell-mediated xenograft-rejections, and especially human CD8+ cytotoxic T lymphocytes (CTL)-mediated cytotoxicity, are highly detrimental to pig xenograft cells. Moreover, we have explored novel strategies for the prevention of CTL killing by overexpression of either human decoy Fas antigen or membrane-bound human FasL in pig endothelial cells. In this study, we assessed the cytoprotective effects of these molecules for pig islets both in vitro and in vivo. Materials and methods: Pig islets were freshly isolated by modified Ricordi's methods. Subsequently, these islets were transfected with an adenoviral expression vector containing the DNA fragments of either membrane-bound human FasL or human decoy Fas. Transfected islets were transplanted into preimmunized diabetic rats under the kidney capsule. Control pig islets (i.e., MOCK), which were transfected with an adenoviral expression vector containing only the enhanced green fluorescent protein gene, were also transplanted. Results: Efficiency of adenoviral expressions of these molecules in pig islets was approximately 80% at a multiplicity of infection of 100. In an in vitro assay, approximately 80% suppression of cytotoxicity was observed in membrane-bound human FasL-expressing pig islets and 60% inhibition of CTL killing was displayed in decoy Fas expression pig islets. In an in vivo transplant model, prolonged survival of pig islets xenografts, expressing either membrane-bound human FasL or human decoy Fas genes, was elicited in comparison with that of control islets xenografts. Conclusion: The extracellular remodeling of either death receptor or death ligand genes by adenoviral expression was effective for the prevention of CTL-mediated xenocytotoxicity in pig islets.
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