Dendritic cells at a DNA vaccination site express the encoded influenza nucleoprotein and prime MHC class I-restricted cytolytic lymphocytes upon adoptive transfer.

Intradermal inoculation of plasmids expressing antigens that contain MHC class I-restricted epitopes leads to the induction of specific CD8(+) cytotoxic T lymphocytes (CTL). The role of in situ transfected antigen-presenting cells (APC) in the priming of specific CTL subsequent to intradermal DNA immunization was investigated using a plasmid (NPV1) expressing the nucleoprotein (NP) of influenza virus that contains a nuclear targeting signal and a dominant class I/K(d)-restricted epitope. Inoculation of NPV1 leads to in situ transfection of MHC class II(+) and class II(-) cells, as revealed by the nuclear localization of NP. Between 2 and 3% of MHC class II(+) and class II(-) cells with the ability to migrate out of the epidermis expressed NP. Upon adoptive transfer into naive recipients, class II(+) migratory cells recovered from the area inoculated with NP-expressing plasmid were significantly superior regarding the ability to prime virus-specific CTL as compared to MHC class II(-) cells. Together, these results are consistent with the role of local dendritic cells loaded with antigen in the priming of CTL by intradermal DNA immunization.