TRANSDUCTION OF HUMAN TROPHOBLAST CELLS BY RECOMBINANT ADENOVIRUSES IS DIFFERENTIATION-DEPENDENT

To explore the feasibility of adenoviral (Ad)-mediated gene transfer t o the human placenta, we examined the ability of two recombinant Ad ve ctors to transduce isolated human cytotrophoblast cells and two chorio carcinoma cell lines (BeWo and JEG-3, which have different potentials to undergo morphological differentiation in response to cAMP). Recombi nant Ad efficiently transduced cytotrophoblast cells. However, there w as a marked reduction in the transduction efficiency of these vectors after the terminal differentiation of the mononucleate cytotrophoblast s into multinucleate syncytial trophoblast. BeWo and JEG-3 cells were readily transduced with the recombinant Ad, but a striking reduction i n transduction efficiency of the Ad vector was observed in BeWo cells following cAMP-stimulated cellular differentiation, which includes cel l fusion to form syncytia. In contrast, JEG-3 cells, which are not ind uced to fuse in the presence of cAMP, did not show a reduced transduct ion efficiency when exposed to the cyclic nucleotide. Reporter gene co py number increased with Ad-mediated gene transfer into undifferentiat ed Bewo cells but was low in cells that had been previously exposed to cAMP. In contrast, both undifferentiated and cAMP-treated BeWo cells were capable of expressing a reporter gene when transfected with an Ad -based plasmid. Taken together, these results demonstrate that the red uction in transduction efficiency of the Ad vectors in cAMP-treated Be Wo is the result of reduced infectivity rather than of a reduction in the transcription/translation efficiency of the exogenous genes. Our f indings demonstrate that recombinant Ad vectors will not be useful for the transfer of genes into differentiated trophoblast cells because t hese cells are resistant to Ad infection. This may limit the utility o f Ad-based vectors for placental gene therapy. However, we have docume nted that less-differentiated trophoblast cells are susceptible to Ad- mediated gene transfer. Our observations also suggest a mechanism by w hich differentiated human trophoblast cells resist Ad infection and pr event fetal infection by maternally derived Ad.