A novel strategy of cell targeting based on tissue-specific expression of the ecotropic retrovirus receptor gene

Gene transfer into specific tissues or cell types is a key technique in the development of gene therapy. Modification of vector particles such that th ey selectively bind to the target cells has been attempted, but the limitat ion of this approach is the low transduction efficiency. Here, we show that a two-step gene transfer system can be used for efficient cell targeting, With this strategy, and using a high-titer adenoviral vector containing a t issue-specific promoter, we have engineered a system in which only target c ells become susceptible to retrovirus-mediated transduction. In a model exp eriment, we constructed an adenoviral vector (Ad.AFPEcoRec) containing the ecotropic retrovirus receptor (EcoRec) gene under the control of the cu-fet oprotein (AFP) promoter, A binding assay showed that after transduction wit h AD.AFPEcoRec, EcoRec molecules were efficiently expressed in AFP(+)HepG2 cells, but not in AFP(-)HeLa and AFP(-)HLE cells. The EcoRec-expressing Hep G2 cells could be stably transduced with ecotropic retroviral vectors, wher eas HeLa and HLE cells remained highly resistant to retrovirus-mediated gen e transfer. The apparent titer on HepG2 cells was greater than 2 x 10(5) CF U/ml, Because various tissue-specific promoter/enhancer elements are availa ble, the two-step system could be used as a general strategy for both ex vi vo and in vivo targeted gene transfer.