[Development of in-vitro and in-vivo assays for dengue vaccine and therapeutics evaluation, and pathogenesis studies].

Antibodies are considered central in the protective immunity to dengue and other flaviviruses. While Japanese encephalitis virus and yellow fever virus vaccines are available for more than half a century, there remains a need for the development of an effective dengue vaccine. An effective dengue vaccine should ideally elicit protective immunity against all four dengue virus serotypes. Cross-reactive antibodies play a competing role in dengue: high levels of neutralizing antibodies are associated with disease protection whereas non-neutralizing cross-reactive antibodies are associated with enhanced clinical presentation. During secondary infection, these cross-reactive, non-neutralizing antibodies are hypothesized to enhance virus infection of the Fcgamma receptor (Fc γ R) bearing cells. In a series of experiments, (1) an in-vitro assay using Fc γ R-expressing BHK cells as assay cells and (2) a non-human primate (NHP) model using marmosets was developed to determine the levels of neutralizing antibodies that contribute to disease pathogenesis and protection. This study has several implications; (1) non-neutralizing, infection-enhancing activity hampers flavivirus neutralizing activity, contributing to an immune profile that fails to offer protection, (2) during secondary flavivirus infection, non-neutralizing antibodies form infectious virus-immune complexes, leading to higher infectivity of virus target cell in vivo, the Fc γ R-bearing cells, and (3) in comparison to conventional neutralizing assays, assays using the Fc γ R-expressing cells may better reflect the biological properties of antibodies in vivo. The results also suggest that common marmosets could be a reliable primate model for the evaluation of candidate vaccines.