High efficiency lentiviral gene delivery in non-dividing cells by deoxynucleoside treatment

Gene therapy has recently been advanced by the development of HIV-based vectors that are able to transduce some non-dividing cells. The manipulation of most non-dividing cells remains, however, scarcely efficient. One of the biological mechanisms postulated to prevent powerful transduction of quiescent cells by lentiviral vectors is the paucity of deoxynucleotides (dNTPs). In this study, a novel delivery strategy is developed to improve significantly the efficiency of HIV-based vectors in transducing non-dividing cells. This approach is based on increasing the intracellular availability of dNTPs by incubating target cells with the dNTP precursors, deoxynucleosides (dNSs).

Mature human monocyte-derived macrophages (14-21 days old) were transduced at a low multiplicity of infection (MOI) of HIV vectors carrying a reporter gene. dNSs were added to the medium during transduction (5 mM dNS) and immediately before post-transduction culture (2.5 mM dNS). Macrophages were harvested 2-7 days after transduction and assayed for transgene expression by cytofluorimetry.

The addition of dNS to the medium significantly enhanced the efficiency of transduction of human macrophages by HIV-based vectors. The percentage of cells expressing the transgene rose up to 50% in the presence of dNS, increasing the basal transduction levels up to 35-fold (average=10.8-fold). Furthermore, treatment with dNTP precursors compensated for the wide inter-donor variability, allowing the highest enhancement effects in donors with the lowest basal transduction efficiencies.

This is the first demonstration that a single treatment of non-dividing target cells with exogenous dNS can enhance the efficiency of lentiviral-mediated transduction of cells, allowing for high efficiency gene transfer. The effects of dNTP precursors compensated for both the poor basal levels and the wide inter-donor variability, two major limitations for the transduction of non-dividing cells. Macrophages are a representative model of cells whose permissiveness to gene delivery was increased up to levels suitable for genetic manipulation applications. This simple approach might be transferred to a broader range of quiescent cell types that are scarcely susceptible to lentiviral-based gene delivery due to low dNTP levels.