The role of TLR3- and MyD88-dependent signaling in the development of anti-West Nile virus adaptive immune responses induced by a vaccine candidate, RepliVAX WN.

Recognition of conserved pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs) results in the activation of innate signaling pathways that drive the innate immune response and ultimately shape the adaptive immune response. RepliVAX WN, a single-cycle flavivirus (SCFV) vaccine candidate derived from West Nile virus (WNV), is intrinsically adjuvanted with multiple PAMPs and induces vigorous anti-WNV T and B cell responses. However, the innate mechanisms that link pattern recognition and development of vigorous antigen-specific T and B cell responses are not completely understood. Moreover, the roles of individual PRR signaling pathways in shaping T and B cell responses to this live attenuated SCFV vaccine have not been established. We examined and compared the role of TLR3- and MyD88-dependent signaling in the development of anti-WNV-specific T cell responses by examining the kinetics of WNV-specific IFN-γ secreting CD4+ and CD8+ T cell responses, the functional pattern of primary and secondary effector WNV-specific IFN-γ secreting CD8+ T cells, the development of anti-WNV CD4+ and CD8+ memory T cells and the role of TLR3- and MyD88-dependent signaling in modulating antigen presenting function of myeloid dendritic cells. We examined and compared the role of TLR3- and MyD88-dependent signaling in the development of anti-WNV-specific B cell responses by detecting the kinetics of antibody-secreting cell responses, anti-WNV IgG subclass switch, anti-WNV IgG affinity and neutralizing capacity and memory B cell responses induced by RepliVAX WN. We found that MyD88 deficiency significantly diminished the antigen presenting function of myeloid DCs, T cell proliferation, memory T cell generation, effector cytokine expression by CD8+ T cells, B cell activation, cellularity of germinal centers, and the generation of long-lived plasma cells (LLPCs) and memory B cells (MBCs). In contrast, TLR3 deficiency had more impact on the functional pattern of T cell responses, memory T cell generation and reactivation, the development of LLPCs, whereas differentiation of MBCs was unaffected. Our data suggest that both TLR3- and MyD88-dependent signaling are involved in the intrinsic adjuvanting of RepliVAX WN and differentially contribute to the development of vigorous WNV-specific primary and memory T and B cell responses following immunization with this novel SCFV vaccine.