PROTECTIVE CD4(-CELLS AGAINST INFLUENZA-VIRUS INDUCED BY VACCINATION WITH NUCLEOPROTEIN DNA() AND CD8(+) T)

DNA vaccination is an effective means of eliciting both humoral and ce llular immunity, including cytotoxic T lymphocytes (CTL). Using an inf luenza virus model, we previously demonstrated that injection of DNA e ncoding influenza virus nucleoprotein (NP) induced major histocompatib ility complex class I-restricted CTL and cross strain protection from lethal virus challenge in mice (J, B, Ulmer et al., Science 259:1745-1 749, 1993), In the present study, we have characterized in more detail the cellular immune responses induced by NP DNA, which included robus t lymphoproliferation and Th1-type cytokine secretion (high levels of gamma interferon and interleukin-2 [IL-2], with little IL-4 or IL-10) in response to antigen specific restimulation of splenocytes in vitro. These responses were mediated by CD4(+) T cells, as shown by in vitro depletion of T-cell subsets. Taken together, these results indicate t hat immunization with NP DNA primes both cytolytic CD8(+) T cells and cytokine-secreting CD4(+) T cells. Further, we demonstrate by adoptive transfer and in vivo depletion of T-cell subsets that both of these t ypes of T cells act as effecters in protective immunity against influe nza virus challenge conferred by NP DNA.