RETROVIRAL GENE-TRANSFER INTO THE INTESTINAL EPITHELIUM

The epithelial cells of the gastrointestinal tract may be attractive t argets for somatic gene therapy. In these studies, we have used rats a nd mice to explore the feasibility of gene transfer into the small int estinal epithelium using retroviral vectors. The first series of exper iments was conducted in mature Sprague-Dawley rats using an ecotropic retroviral vector that has bacterial beta-galactosidase (beta-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 ligatur es were removed. Sham-operated animals were subjected to the same liga tion procedure but received only tissue culture medium in the ligated segment. All animals were sacrificed 6 days later, and tissue from bot h the experimental segment and an upstream control segment was assesse d for cytoplasmic beta-Gal activity using X-Gal histochemistry. Expres sion of the reporter gene was observed in the crypt epithelium of tiss ue exposed to the vector. In the villus epithelium, high background st aining precluded accurate assessment of reporter gene expression. To o bviate the latter problem, we sought an alternative reporter gene for which there would be no background staining in control animals. We rep eated the experiments with beta-glucuronidase as the reporter gene in MPS VII mutant mice, which are devoid of this enzyme. In these studies , heal segments exposed to the vector demonstrated expression of the r eporter gene in both the crypt and villus epithelium 4 days after expo sure. These results indicate that genes can be transferred into the in testinal epithelium using retroviral vectors introduced luminally. The se studies constitute an encouraging first step in the assessment of t he intestinal epithelium as a site for somatic gene therapy.