Characterization of the interaction between dendritic cells and the Venezuelan Equine Encephalitis replicon particle vector system

As exceptionally potent antigen-presenting cells, dendritic cells (DCs) are the focus of extensive study and incorporation into a variety of immunotherapeutic strategies. The diversity of DC subsets imposes a substantial challenge to the successful development of DC-based therapies, requiring the characterization of the involved subset(s) and the potential role each contributes to elicit immunologic responses. The Venezuelan Equine Encephalitis (VEE) replicon particle (VRP) vector system is currently being utilized to target infectious and neoplastic diseases. VRP-based immunotherapies have been demonstrated to induce robust antigen-specific immune responses. This has been attributed to the tropism of VRP toward DCs, however the interaction is poorly understood. Efforts to optimize VRP-based strategies will be facilitated by characterizing the specific human DC subset(s) involved. Using fresh human peripheral blood DCs, mononuclear cells, monocyte-derived macrophages, and monocyte-derived DCs (M-DCs), we demonstrated here the VRP has restricted tropism for a subset of human immature DCs. VRP transduced immature DCs retain intact functional capacity, e.g., the ability to resist the cytopathic effects of VRP transduction and the capacity to acquire the mature phenotype. A novel technique was developed to isolate the subset of VRP receptive DCs within the M-DC population for further characterization. Comparison of mRNA expression between VRP receptive and non-receptive DC subsets by microarray analysis revealed 652 genes significantly differentially expressed (p≤0.001, PPDE≥0.99) between these cellular subsets. Gene expression analysis using RT-PCR confirmed the presence of the pro-inflammatory cytokine interleukin (IL)-32 as a distinguishing characteristic of VRP receptive DCs. IL-32 transcript was also accompanied by IL-32 protein expression. Together, these data provide the initial characterization of a subset of human DCs receptive to the VRP, allowing the explicit study of the mechanisms employed by this exceptionally potent immunotherapeutic vector system.