IN-VIVO INDUCTION OF CTL RESPONSES BY RECOMBINANT ADENYLATE-CYCLASE OF BORDETELLA-PERTUSSIS CARRYING VIRAL CD8(+)T CELL EPITOPES

Exogenous Ags enter the endosomal pathway and are presented to CD4(+) T cells in association with class II molecules whereas endogenously sy nthesized Ags, such as viral proteins, are presented to CD8(+) T cells in association with MHC class I molecules. Therefore, most CTL activa tion strategies use live vectors although an alternative possibility c ould be to deliver the epitope into the cytosol by targeting it to an invasive nonreplicative vector. The adenylate cyclase toxin of Bordete lla pertussis is able to invade a large number of eukaryotic cells and to deliver its catalytic domain to the cytosol of the cells. In the p resent study, we have tested the in vivo immunogenicity of recombinant adenylate cyclase toxins expressing CTL epitopes either from the nucl eoprotein of lymphocytic choriomeningitis virus or from the V3 region of HIV-1 gp120. BALB/c mice immunized with these toxins developed high specific CTL responses that were shown to be mediated by class I-rest ricted CD8(+) CTL. The induction of CTL responses by recombinant toxin s did not require CD4(+) T cells and the cytotoxic activity persisted 2 mo after immunization. The activation of CTL responses by the recomb inant adenylate cyclase toxin required the full-length invasive activi ty of the toxin but did not depend upon its catalytic adenylate cyclas e activity as demonstrated with a genetically inactivated recombinant toxin expressing the lymphocytic choriomeningitis virus epitope. This genetically detoxified invasive toxin represents, therefore, an attrac tive new vector for CTL activation.