Retrovirus-mediated transduction of cultured epidermal keratinocytes

Retrovirus-mediated gene transfer is an efficient means of introducing and expressing exogenous gene(s) in many cell types including keratinocytes. However, parameters of transduction and gene expression have not been systematically analyzed for keratinocytes. To carry out such a study we have transduced cultures of newborn foreskin cells with retroviral vectors that encode the genes for neomycin resistance (neor) and for beta-galactosidase (B-gal). The neor gene is a dominant selectable marker and the B-gal gene encodes a histochemically detectable product. Our key findings are the following: 1) all keratinocytes that form colonies can be successfully transduced at a viral titer greater than 5 x 10(6) colony-forming units/ml; 2) transduction is effected by integration of a single copy of retroviral DNA; 3) transduced cells are not at a growth disadvantage and, in fact, single clones of transduced keratinocytes can be expanded to yield over 10(9) cells, suggesting that stem cells are transduced; 4) whereas most transduced colonies exhibit B-gal staining in a high percentage of constituent cells, some colonies had a mosaic or sectored staining pattern; 5) expression of the non-selectable B-gal gene was somewhat greater in differentiated cells of the culture as compared to nondifferentiated precursors. The ability to transduce stem cells at a high efficiency and to follow expression of transduced genes in clonal progeny will allow lineage mapping in stratified epithelial tissues.