A Novel Strategy of Cell Targeting Based on Tissue-Specific Expression of the Ecotropic Retrovirus Receptor Gene

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Abstract
Gene transfer into specific tissues or cell types is a key technique in the development of gene therapy. Modification of vector particles such that they selectively bind to the target cells has been attempted, but the limitation 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 tissue-specific promoter, we have engineered a system in which only target cells become susceptible to retrovirus-mediated transduction. In a model experiment, we constructed an adenoviral vector (Ad.AFPEcoRec) containing the ecotropic retrovirus receptor (EcoRec) gene under the control of the α-fetoprotein (AFP) promoter. A binding assay showed that after transduction with AD.AFPEcoRec, EcoRec molecules were efficiently expressed in AFP+HepG2 cells, but not in AFP¯HeLa and AFP¯HLE cells. The EcoRec-expressing HepG2 cells could be stably transduced with ecotropic retroviral vectors, whereas HeLa and HLE cells remained highly resistant to retrovirus-mediated gene transfer. The apparent titer on HepG2 cells was greater than 2 × 105 CFU/ml. Because various tissue-specific promoter/enhancer elements are available, the two-step system could be used as a general strategy for both ex vivo and in vivo targeted gene transfer. Retroviral envelopes have been modified in various ways in order to transduce specific human cells. A general problem, however, has been the low efficiency of gene transfer. In this study, we show that efficient targeted retroviral transduction can be achieved using adenovirus-mediated tissue-specific expression of a retrovirus receptor. Because an unmodified retroviral envelope protein is used in this strategy, transduction efficiency is high. This two-step gene transfer method could be used as a general strategy for targeted gene transfer.