Myocardial injury-induced fibroblast proliferation facilitates retroviral-mediated gene transfer to the rat heart in vivo

Background Efficient and stable transfer of therapeutic DNA into injured my ocardium would be an initial step towards a genetic treatment aimed at myoc ardial repair after myocardial infarction. Proliferating cardiac fibroblast s in the healing myocardium could be a compelling target for retroviral inf ection. We evaluated the feasibility of direct in vivo gene transfer into i njured myocardium using a high-titer, stable retroviral vector. Methods Using the TE-FLY-A-based MFG retroviral vector harboring nlsLacZ re porter, the gene transfer efficiency was assessed first in vitro in rat car diac fibroblasts, followed by in vivo evaluation in healing rat myocardium after local freeze-chaw injury. A total of 2.5 x 10(7) infectious units of retrovirus were injected into the injured region of a bearing rat heart. Th e transduced cells were identified by X-gal staining and immunohisto-chemis try. Results Highly efficient transduction of cardiac fibroblasts was observed i n vitro with 98% of the cells transduced with single infection. The cell pr oliferation index in the cardiac granulation tissue appeared maximal 3 days after cryoinjury. Retroviral injection into the injured beating heart indu ced gene expression localized to the wound repair region. One week after re trovirus injection, 14% of the cells in the reparative tissue were beta-gal -positive, while 4% were beta-gal-positive after 4 weeks. The transduced ce lls were mostly myofibroblasts. Conclusions Local gene transfer to the healing rat heart: is feasible by re trovirus in vivo. This observation may serve as a useful guide for the deve lopment of gene therapy aimed at myocardial repair after myocardial infarct ion. Copyright (C) 2000 John Wiley & Sons, Ltd.