Background: The immune response to adenoviral vectors used in gene transfer limits the duration of transgene expression and thus poses a potential limitation to their effectiveness for gene therapy. The need for immunosuppression in transplantation may modify this immune response and facilitate prolonged transgene expression. This study hypothesizes that in the setting of heart transplantation, the use of routine immunosuppression will prolong adenoviral-mediated transgene expression. Methods and results: In a model of rat heterotopic abdominal heart transplantation, 350 μl of viral solution (1 x 109 pfu/ml) was infused into the coronary arteries of donor hearts at the time of procurement. The duration of transgene expression was examined following (a) syngeneic transplantation in non-immunosuppressed animals (group A); (b) syngeneic transplantation in immunosuppressed animals (group B); and (c) allogeneic transplantation in immunosuppressed animals (group C). After transplantation donor hearts were studied at: 1, 4, 8 and 12 weeks. Transgene expression was assessed by histochemical staining of tissue cross sections for β-galactosidase activity. In the non-immunosuppressed syngeneic group (group A), transgene expression bad largely disappeared by 4 weeks, whereas in both the immunosuppressed syngeneic (group B) and immunosuppressed allogeneic (group C) animals expression of the reporter gene persisted for the 12 weeks of the study, although the level of expression decreased significantly over time. Conclusions: This study demonstrates that transgene expression using adenoviral vectors is prolonged by immunosuppression in the heart transplantation setting.
Bibliographical noteFunding Information:
The limited duration of transgene expression after adenoviral-mediated gene transfer may be due to immune or non-immune mediated mechanisms . In support of immune mechanisms playing a role, prolonged transgene expression has been reported in immunologically immature neonatal animals , in immunodeficient animals  and with the use of immunosuppression . Furthermore, while some authors report the absence of inflammatory infiltrates in the myocardium after catheter-mediated delivery of adenoviral vectors to both non-transplanted and transplanted hearts [4,18], direct injection has been associated with inflammation around the injection site [19–21]. While some of the inflammation may be due to an effect of the needle, immune-mediated responses to the viral vectors may also be responsible. The latter possibility is supported by our results. In this study, transgene expression was barely detectable in the non-immunosuppressed syngeneic hearts by 4 weeks; but patchy lymphocytic infiltrates consistent with myocarditis were noted in 2 of 6 animals at 4 weeks, 1 of 6 animals at 8 weeks and 2 of 6 animals at 12 weeks. This may indicate an immune response to the vector or transgene even in the absence of detectable transgene expression in these animals. Additionally, we have demonstrated that transgene expression can be prolonged by immunosuppression with cyclosporine after heart transplantation also implying an important role for immunologic factors. It is probable that the broad range of positively staining cells per section is due to the yet unexplained biologic variability of adenoviral-mediated transgene expression.
This work is supported by grants from Mayo Clinic and Foundation. J. Yap is supported by a grant from HN Tjia Education Fund.
- Gene therapy
- Heart transplantation