GENE-TRANSFER INTO FETAL-RAT INTESTINE

To assess the fetal intestine as a site for gene therapy, we have expl ored a xenograft model in which fetal rat intestine is grafted subcuta neously into nu/nu mice, Prior to grafting, the tissue was exposed to a replication-deficient retroviral vector bearing the neo gene, Transd uction efficiency was assessed by quantitative polymerase chain reacti on (PCR) of neo in DNA recovered from the grafts, Three methods of inf ection were employed: (i) simple flushing of the fetal intestine with the vector; (ii) incubation with the vector for 2 hr; rand (iii) a com bination of both, The first method gave the highest transduction effic iencies in terms of both the proportion of samples that were neo-posit ive and the number of neo-positive cells per sample, Using this approa ch, the time course of persistence of neo-positive cells was analyzed by collecting grafts at 1 versus 3 weeks post-infection, The results s howed approximately five-fold more positive cells at the earlier time point than at the later, suggesting loss of transduced cells due to ce ll turnover, Nevertheless, the persistence of a portion of the positiv e cells for at least 3 weeks is encouraging for future studies with fe tal intestine.