Investigating Protein Expression, Immunogenicity, and Protection of Modified mRNA Dengue Vaccine

Dengue virus (DENV) is the most common vector-borne viral disease with nearly 400 million worldwide infections each year concentrated in the tropical and subtropical regions of the world. During secondary infections, humoral immune responses targeting cross-reactive, poorly- neutralizing epitopes can lead to increased infectivity of susceptible cells and more severe disease via antibody-dependent enhancement (ADE) with both infections and vaccinations capable of contributing to ADE. Currently, there are no available therapeutics to combat DENV disease, and there is an urgent need for a safe and efficacious vaccine. We developed a nucleotide- modified mRNA vaccine encoding the membrane and envelope structural proteins from DENV serotype 1 encapsulated into lipid nanoparticles (prM/E mRNA-LNP). Once delivered to cells, prM/E expression results in virus like particle production, as confirmed by electron microscopy. Vaccination of C57BL/6 mice with this DENV1 vaccine elicited robust antiviral immune responses comparable to viral infection with high neutralizing antibody titers and antiviral CD4+ and CD8+ T cells. Immunocompromised AG129 mice vaccinated with the prM/E mRNA-LNP vaccine were protected from a lethal DENV1 challenge. Vaccination with either a wild-type (WT) vaccine or a vaccine with mutations in the immunodominant fusion-loop epitope (DFL) elicited equivalent humoral and cell mediated immune responses. Neutralizing antibodies elicited by the vaccine were sufficient to protect against a lethal challenge after passive transfer of serum antibodies to unvaccinated AG129 mice. Both WT and mutant vaccine constructs demonstrated greatly reduced ADE compared to antibodies elicited from a live DENV1 viral infection. Recently, we optimized both the sequence of a construct coding DENV2 prM/E proteins as well as the production process of the mRNA, itself. Vaccination of C57BL/6 mice with this optimized DENV2 construct resulted in elevated neutralizing antibody response.