Nearly 400 million people are infected with dengue virus (DENV) each year through the bite of infected mosquitos concentrated in the tropical and subtropical regions of the world. Symptoms can range from febrile illness to severe dengue that manifests as plasma leakage, sudden loss of blood pressure, organ failure, and shock that can ultimately lead to death. Severe dengue complications are often associated with a secondary heterotypic infection of one of the four circulating serotypes. In this scenario, humoral immune responses targeting cross- reactive, poorly-neutralizing epitopes lead to increased infectivity of susceptible cells via antibody-dependent enhancement (ADE). Additionally, DENV immunity has been implicated in increased susceptibility to Zika virus through ADE. Currently there are no available therapeutics to combat DENV disease. Dengvaxia, the only licensed DENV vaccine, was found to increase hospitalization rates in naïve populations, and thus is not recommended for a large portion of at-risk individuals. There is an urgent need for a safe and efficacious vaccine that elicits a robust, balanced, neutralizing response to all four DENV serotypes. We propose to develop a novel DENV vaccine utilizing an emergent platform: mRNA encoding for viral proteins encapsidated in a lipid nanoparticle (LNP). mRNA-LNP vaccines elicit robust humoral and cell-mediated immune responses in a safe, non-infectious platform. Additionally, we can direct the host immune response towards neutralizing epitopes by mutating the mRNA encoding for the viral protein. We hypothesize that a sequence-engineered tetravalent mRNA-LNP vaccine will induce a balanced, protective immune response against all four serotypes of dengue without the potential of causing immune enhancement and ADE. In Aim 1 of this study we will generate and optimize mRNA constructs encoding for the pre-membrane and envelope viral glycoproteins for all four serotypes of DENV. We will mutate the poorly-neutralizing, cross-reactive epitopes that drive ADE. In Aim 2 we will characterize the immune response to the vaccines in a mouse model. In addition to quantifying humoral and cellular immune responses, we will also measure the immune enhancement capacity of all vaccines. In Aim 3, we will evaluate vaccine efficacy and safety in susceptible mouse models, by challenging vaccinated mice with different DENV serotypes to monitor protection and ADE. We will also determine mechanism of protection via adoptive transfer experiments. Through this study, we will identify DENV vaccines that demonstrate broad protection and lack of immune enhancement for further evaluation as candidate human vaccines.

Dengue virus has a profound impact on human health with 390 million infections and 25,000 deaths annually worldwide. In this study, we will develop and characterize a vaccine against dengue virus utilizing the mRNA platform. With this approach, mRNA encoding for viral proteins is encapsidated in a lipid nanoparticle which will allow us to rapidly generate and screen for vaccines which are efficacious and safe that will be further evaluated as candidate human vaccines.