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 cl ass I-restricted epitopes leads to the induction of specific CD8(+) cytotox ic T lymphocytes (CTL). The role of in situ transfected antigen-presenting cells (APC) in the priming of specific CTL subsequent to intradermal DNA im munization was investigated using a plasmid (NPV1) expressing the nucleopro tein (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 s itu transfection of MHC class II+ and class II- cells, as revealed by the n uclear 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 a doptive transfer into naive recipients, class II+ migratory cells recovered from the area inoculated with NP-expressing plasmid were significantly sup erior regarding the ability to prime virus-specific CTL as compared to MHC class II- cells. Together, these results are consistent with the role of lo cal dendritic cells loaded with antigen in the priming of CTL by intraderma l DNA immunization.