Results of clinical islet transplantation remain disappointing despite sporadic reports of short-term insulin independence. Failure of a large proportion of islet grafts to function has been ascribed to poor islet recovery from cadaveric pancreas, lack of adequate islet vascularization following transplantation and nonspecific immune mediated islet destruction or allogenic rejection. To overcome the problem of primary nonfunction, our laboratory has developed procedures to improve viability of isolated islets including novel culture techniques. In addition, we developed a NOD-SCID mouse model that allows viability testing of islets in vivo prior to transplantation. Furthermore, we embarked on a gene immunotherapy approach to improve human islet survival in vivo. We hypothesized that transfection of human islets with TGFbeta1 will prevent structural and immune mediated destruction of islets. Reconstitution of the NOD-SCID mouse with human CD34+ cells in the presence or absence of thymic fragments, will allow us to test the impact of the genetic manipulation in a clinically relevant model.
Our specific aims are to test the hypothesis that: l) transient, low level of TGFbeta1 expression by human islets transduced with Ad-RSV-TGFbeta1 vector will improve and prolong in vivo function; 2) transient TGFbeta1 expression by human islets will promote their implantation by enhancing extracellular matrix formation and neovascularization, resulting in preservation or improvement of in vivo function; 3) expression of TGFbeta1 by human islets will protect against nonspecific inflammatory destruction in vivo; and 4) expression of TGFbeta1 by human islets will protect against allogenic immune destruction. The proposed work emphasizes the utilization of human islets for genetic modification and should provide clinically relevant data regarding the structural and immunological requirement for successful engraftment. The long-term goal of this multidisciplinary research is to develop an effective gene therapy approach that could be clinically utilized to achieve successful human islet transplantation. Future experiments based on the findings of this research would allow us to examine the utility of other gene candidates or other vectors that could complement our gene therapy program in islet transplantation.
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