Development of a Replicon RNA-based Vaccine against Dengue and Zika

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ABSTRACT The long-term goal of this project is to develop a dengue-Zika vaccine that provides protection against the four serotypes of dengue (DENV1-4) and Zika (ZIKV) viruses with maximal safety and efficacy. To date, flavivirus vaccine development has focused on the induction of neutralizing antibodies (nAbs), as they have been assumed to be the key mechanism for protection against natural infection. However, DENV and perhaps ZIKV are unusual in that weak Ab responses to vaccination or prior infection can induce antibody-dependent enhancement (ADE) of infection and pathogenesis during subsequent reinfections. In fact, DENV disease with severe sequalae has been documented in children given the only currently licensed DENV vaccine. Thus, the primary objective of this application is to develop an effective vaccine against DENV and ZIKV that cannot mediate ADE. We hypothesize that this vaccine will need to elicit both strong nAb responses and strong T cell effector responses that will counterbalance the presence of any ADE-mediating Abs, based on our work investigating the interplay between Ab and T cell responses to DENV and ZIKV. In particular, we have shown that CD8 T cells mediate cross- protection against heterotypic DENV and ZIKV infections, and that DENV vaccine-elicited CD8 T cells can prevent ADE. In addition, our preliminary data show that an RNA replicon-based vaccine expressing ZIKV nonstructural protein 3 elicits only T cell but not nAb responses and confers protection against ZIKV challenge in mice. Thus, we hypothesize that our combinatorial DENV-ZIKV vaccine expressing both Ab- and T cell-targeting proteins of DENV1-4 and ZIKV will produce humoral and cellular immune responses that provide robust, long-term protection against all five viruses. We will test this hypothesis by achieving the following Specific Aims: 1) To evaluate immunogenicity and efficacy of a DENV-ZIKV vaccine. 2) To determine the durability and mechanistic underpinnings of DENV-ZIKV vaccine-induced protective immunity.