Plasmid DNA encoding CCR7 ligands compensate for dysfunctional CD8(+) T cell responses by effects on dendritic cells

Lymphotoxin alpha -deficient (LT alpha (-/-)) mice, which lack lymph nodes and possess a disorganized spleen, develop dysfunctional CD8(+) T cells upo n HSV infection and readily succumb to herpes encephalitis. Such mice do de velop apparently normal peptide-specific CD8(+) T cell responses, as measur ed by MHC class I tetramer staining, but the majority of cells fail to beco me cytotoxic or express peptide-induced IFN-gamma production. In the presen t study, we demonstrate that functional defects of CD8(+) T cells in LT alp ha (-/-) mice can be largely rectified by the administration of plasmid DNA encoding CCR7 ligands before HSV infection. Treated mutant mice developed increased peptide-specific cytotoxic responses, enhanced numbers of CD8(+) T cells capable of producing IFN-gamma, as well as improved resistance to H SV challenge. The corrective effect of chemokine treatment appeared to resu lt from improved dendritic cell-mediated Ag presentation. Thus, a major con sequence of the treatment was an increase in splenic dendritic cell number in CCR7 ligand-treated LT alpha (-/-) mice with such splenocyte populations showing improved APC activity in vitro. Our results document that function al defects of CD8(+) T cells can be corrected, and indicate the value of pl asmid vector encoding appropriate chemokines to achieve such immunotherapy.