Retroviral Gene Transfer into the Intestinal Epithelium

The epithelial cells of the gastrointestinal tract may be attractive targets for somatic gene therapy. In these studies, we have used rats and mice to explore the feasibility of gene transfer into the small intestinal epithelium using retroviral vectors. The first series of experiments was conducted in mature Sprague-Dawley rats using an ecotropic retroviral vector that has bacterial β-galactosidase (β-Gal) as the reporter gene. The vector was introduced into the lumen of ligated segments of terminal ileum. After a 4-hr exposure period, the ligatures were removed. Sham-operated animals were subjected to the same ligation procedure but received only tissue culture medium in the ligated segment. All animals were sacrificed 6 days later, and tissue from both the experimental segment and an upstream control segment was assessed for cytoplasmic β-Gal activity using X-Gal histochemistry. Expression of the reporter gene was observed in the crypt epithelium of tissue exposed to the vector. In the villus epithelium, high background staining precluded accurate assessment of reporter gene expression. To obviate the latter problem, we sought an alternative reporter gene for which there would be no background staining in control animals. We repeated the experiments with β-glucuronidase as the reporter gene in MPS VII mutant mice, which are devoid of this enzyme. In these studies, ileal segments exposed to the vector demonstrated expression of the reporter gene in both the crypt and villus epithelium 4 days after exposure. These results indicate that genes can be transferred into the intestinal epithelium using retroviral vectors introduced luminally. These studies constitute an encouraging first step in the assessment of the intestinal epithelium as a site for somatic gene therapy. There are a number of congenital disorders of the intestinal epithelium that could be amenable to gene therapy (e.g., cystic fibrosis, transporter deficiencies, etc.). In addition, the intestine could be used as an alternative site to correct metabolic disorders, such as phenylketonuria, and secretory disorders, such as hemophilias. This paper presents in vivo studies in both a rat model and a mouse model using retroviral vectors delivered into the intestinal lumen. The results show successful gene transfer into epithelial cells and thus pave the way for future experiments designed to improve the efficiency of this process.