Mesenchymal stem cells for therapeutic application in corneal transplantation
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Although corneal transplantation success rates are high within the first year, the prognosis is much less favourable 5 years post-transplantation with immune-mediated rejection the primary cause of allograft failure. For this reason, on-going preventive and therapeutic measures are needed. Mesenchymal stem cells (MSCs) are being studied extensively in a wide range of diseases/disorders and more recently in solid organ transplantation, due to their ability to suppress or dampen host immune responses. However, reports on the therapeutic efficacy of MSC therapy have been mixed and the genetic modification of MSCs using viral vectors is one option to improve their therapeutic potential. Consequently, the focus of this research work was twofold. Firstly, to investigate if the genetic modification of MSCs using recombinant adenovirus alters the syngeneic host immune response and secondly, to investigate the therapeutic efficacy of MSCs in the promotion of corneal allograft survival. The results from the first part of this work showed that Ad-transduction of MSCs does not lead to up-regulation of major histocompatibility complex class I and II and co-stimulatory molecule expression. Moreover, Ad-transduction caused no significant changes in terms of pro-inflammatory cytokine expression, chemokine and chemokine receptor and Toll-like receptor expression. Ad-modification of MSCs also had no effect on their ability to suppress T cell proliferation in vitro. In vivo injection of Ad-transduced MSCs did not change the frequency of various immune cell populations either in the blood or in tissues. Overall, the results indicate that Ad-modification has no major influence on the immunological properties of MSCs and therefore can be considered as a suitable gene vector for therapeutic applications of MSCs. In the second part of this work the results showed that, in contrast to syngeneic MSC treatment which failed to significantly prolong survival, corneal allograft survival was significantly prolonged in approximately 90% of allogeneic MSC and 80% of 3rd party MSC treated recipients. Flow cytometric analysis showed lower percentages of infiltrating natural killer (NK) T cells in corneas of both allogeneic and 3rd party MSC treated animals, coupled with a significantly higher frequency of splenic regulatory T cells, compared to controls. Thus, allogeneic and 3rd party MSC treatment prolongs corneal allograft survival by suppressing peripheral immune responses and promoting an intragraft immunoregulatory milieu.