Dermal dendritic cells sensitized with plasmid DNA encoding immunostimulatory sequence by gene gun efficiently prime murine HIV-1-specific CD8⁺ cytotoxic T lymphocytes

When gold beads coated with plasmid DNA encoding the β-galactosidase (β-gal) gene having a strong immunostimulating sequence (ISS) with CpG-motif were inoculated intradermally by gene gun, blue colored cells producing β-gal could be seen within regional lymph nodes and spleen. Electron microscopic analysis suggested that cells expressing the β-gal gene in the regional lymph nodes look like activated interdigitating dendritic cells (DC). In addition, multiple gold beads were observed in blue colored cells in the regional lymph nodes but not in the spleen where β-gal was actively produced. The DC expressing the β-gal gene may prime directly β-gal epitope peptide (TPHPARIGL)-specific, CD8⁺ cytotoxic T lymphocytes (CTL) without requiring Th1 type of help in this priming step. Moreover, HIV-1 gp120-specific CD8⁺ CTL could be primed when mice were immunized with gold beads coated with gp120 plasmid DNA together with the β-gal plasmid, though gold beads coated with HIV-1 gp120 plasmid alone or a mixture of two distinct gold beads coated with either β-gal or gp120 plasmid could not prime HIV-1-specific CTL. These results suggest that intradermal immature DC, like Langerhans cells, activated by ISS-containing plasmids encoding strong CpG-motif such as β-gal DNA, can efficiently prime CTL specific for not only original β-gal epitope but also the products of another plasmid without encoding ISS when both plasmids are captured simultaneously by the same dermal DC.