Stress protein complexed multidomain vaccines identify subdominant CD8 T cells with enhanced anti-viral activity.

Abstract

Heat shock proteins (Hsp) of the Hsp70/90 families facilitate cellular immune responses to chaperoned peptides or proteins and have therefore been used as vaccine vehicles. We have developed an expression system in which chimeric proteins with a Hsp-capturing, viral J domain fused to antigen-encoding sequences form stable complexes with eukaryotic stress proteins (Hsp70/73) thus facilitating their expression. In addition to the viral J domain, J domains derived of bacterial and plant origin were able to capture Hsp70/73 and facilitated antigen expression equally well. The tested J domains were also able to bind bacterial Hsp70 (DnaK) thus enabling vaccine production in a large panel of hosts. Purified Hsp/antigen complexes efficiently elicited antigen-specific CD8 T cell responses in mice when delivered as vaccines without adjuvants. The described expression system thus supports the flexible design of multivalent, CD8 T cell-stimulating vaccines. We investigated whether immunodominance hierarchies between CD8 T cell epitopes limit the potential of multivalent, Hsp-binding vaccines. Immunodominance effects were observed analyzing murine H2-Kb-restricted epitopes. Kb/OVA257-264 and Kb/S190-197-specific CD8 T cell responses did not allow priming of a Kb/C93-100-specific CD8 T cell response in mice immunized with multidomain vaccines. However, subdominant Kb/C93-100-specific CD8 T cells were efficiently primed by a HBcAg-encoding vector in 1.4HBV-Smut tg mice (that harbor a replicating HBV genome producing HBV antigens in the liver). Kb/C93-100-specific CD8 T cells accumulated in the liver of vaccinated 1.4HBV-Smut tg mice and suppressed HBV replication. Subdominant epitopes in vaccines can hence prime specific CD8 T cell immunity in a tolerogenic milieu and deliver specific anti-viral effects to HBV-expressing hepatocytes.