Making dendritic cells from the inside out: lentiviral vector-mediated gene delivery of granulocyte-macrophage colony-stimulating factor and interleukin 4 into CD14+ monocytes generates dendritic cells in vitro

We have evaluated a one-hit lentiviral transduction approach to genetically modifying monocytes in order to promote autocrine and paracrine production of factors required for their differentiation into immature dendritic cells (DCs). High-titer third-generation self-inactivating lentiviral vectors expressing granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) efficiently achieved simultaneous and persistent codelivery of the transgenes into purified human CD14+ monocytes. Coexpression of GM-CSF and IL-4 in CD14+ cells was sufficient to induce their differentiation into a DC-like phenotype, as evidenced by their morphology, immature immunophenotypic profile (CD14-, CD1a+, CD80+, CD86+, MHC-I+, MHC-II+), and their ability to further develop into a mature phenotype (CD83+) on further treatment with soluble CD40 ligand. Mixed lymphocyte reactions showed that the T cell-stimulating activity of lentivirus-modified DCs was superior to that of DCs grown by conventional methods. Lentivirus-modified DCs displayed efficient antigen-specific, MHC class I-restricted stimulation of autologous CD8+ T cells, as shown by IFN-gamma production and CTL assays. DCs coexpressing GM-CSF and IL-4 could be kept metabolically active and viable in culture for 14 days in the absence of exogenously added growth factors, unlike conventionally produced DCs. Coexpression of FLT3 ligand did not improve the viability, expansion, or immunologic performance of lentivirus-modified DCs. This article demonstrates the proof-of-concept to genetically convert monocytes to DC-type antigen-presenting cells with lentiviral vectors.