Flagellin has differential and route-dependent adjuvant effects when encoded in heterologous systemic or mucosal gene-based prime-boost vaccines (VAC4P.1107)

Abstract

Abstract Flagellin has been tested as a protein-based adjuvant, with most studies focused on antibody responses. In this study, we have evaluated the adjuvant activity of flagellin for cellular and humoral immune responses in gene-based immunizations. DNA and adenovirus (Ad) vectors were constructed to encode mycobacterial Ag85B and/or flagellin (FliC) of S. typhimurium. DNA-encoded flagellin given to mice via the IM route enhanced antigen-specific splenic CD4+ and CD8+ T cell responses. Boosting either IM or intranasally (IN) with Ad vectors expressing Ag85B without flagellin enhanced antigen-specific antibody and CD4+ and CD8+ T cell responses in both spleen and pulmonary tissues, correlating with improved protection against pulmonary challenge with Mtb. However, inclusion of flagellin in both DNA prime and Ad boosting vaccines induced localized pulmonary inflammation and transient weight loss, along with route-dependent effects on vaccine-induced T cell immunity. The latter included marked reductions in mucosal CD4+ and CD8+ T cell responses following IM DNA / IN Ad prime-boosting, although antibody responses were not diminished. These findings suggest that flagellin has differential and route-dependent adjuvant activity when included in systemic or mucosal gene-based prime-boost immunization. Adjuvant activity for both T and B cell responses and safety were optimal when flagellin was included only in the DNA vaccine priming phase of systemic or mucosal DNA/Ad prime-boosting.