Transduction of thymic epithelial cells with a MuLV-based vector.

(A) In vitro (×40). Pure cultures of thymic epithelium were established from a normal control sheep fetus at 76 days of gestation as described in “Materials and methods.” The thymic epithelial cells were then transduced in vitro with the MuLV-based G1nBgSvNa8.1 supernatant employed in our in utero studies, selected for 1 week in G418, and subjected to x-gal staining. All of the cells present are blue, demonstrating their successful transduction with the MuLV vector. (B) In vivo (×10). Representative in utero–transduced sheep were killed at 21 days postinjection (76 days of gestation) and pure cultures of thymic epithelial cells were grown as described in “Materials and methods.” The thymic epithelial cells were then subjected to x-gal staining. Numerous blue cells are present, demonstrating the successful in vivo transduction of thymic epithelium in the in utero–transduced sheep. We never observed any blue cells in x-gal–stained epithelial cell cultures from control (untransduced) sheep (data not shown).