Expression of Wild-Type and Noncleavable Fas Ligand by Tetracycline-Regulated Adenoviral Vectors to Limit Intimal Hyperplasia in Vascular Lesions

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Abstract
Proliferation of vascular smooth muscle cells (VSMCs) and the infiltration of T cells and macrophages into vessel wall are considered to be important for intimal lesion formation after balloon angioplasty. Previous studies have shown that Fas ligand (FasL) gene transfer to balloon-injured vessels inhibits lesion formation by killing both proliferating VSMCs and infiltrating inflammatory cells. Here, we describe the construction and utility of a binary, tetracycline-regulated adenovirus system that provides controlled transgene expression in vitro and in vivo. In this system, optimal transgene expression required cotransfection with an adenovirus encoding the tetracycline-dependent trans-activator (rtTA) and induction with doxycycline hydrochloride (DOX), an analog of tetracycline. Using this system, adenovirus constructs were designed that allow regulated expression of wild-type FasL and a noncleavable mutant of FasL (FasL-NC). Transduction of FasL and FasL-NC induced similar extents of apoptosis in proliferating VSMCs in vitro in a manner that was dependent on the doses of the rtTA adenovirus and the presence of DOX in the medium. Furthermore, inhibition of intimal hyperplasia in injured carotid arteries by FasL or FasL-NC transduction was also dependent on cotransfection with the rtTA adenovirus and administration of DOX by subcutaneous injection. In contrast to wild-type FasL, transduction of FasL-NC did not result in the production of soluble (cleaved) FasL in the medium of infected cells in vitro, or in the serum of rats after local gene transfer to carotid arteries. In conclusion, this binary tetracycline-inducible adenovirus system may allow for safer delivery of cytotoxic genes for therapeutic purposes.