Structure-guided vaccine design to focus antibody responses to neutralizing epitopes on dengue virus envelope protein

Abstract The four dengue virus (DV) serotypes are mosquito-borne flaviviruses responsible for dengue fever. Live-attenuated DV vaccines that are in human trials have had mixed results with efficacy for just one or two serotypes and an increased dengue risk in some vaccinated populations. DV recombinant envelope (E) proteins as subunit vaccines have had limited success, likely due to DV wild type E protein (WT rE) is mostly monomeric at physiological temperature. Hence, it loses the quaternary structure epitopes recognized by neutralizing human antibodies (Ab) on the native dimer. We previously showed that with targeted amino acid mutations, we can form DV thermostable dimers (SD rE) displaying native quaternary epitopes targeted by strongly neutralizing Ab. Here we report on studies to test if Ab response can be directed to these quaternary epitopes by using SD rE as vaccine antigens. Since fusion loop (FL) Ab can cause antibody dependent enhancement (ADE) that increases disease severity upon heterologous DV infection, we also tested SD rE with mutated FL. Mice were immunized with DV2 WT rE or SD rE variants to compare Ab properties induced by each antigen. We found that SD-vaccinated mice had higher DV2 functional Ab titer compared to WT-vaccinated. To map vaccine responses, we run neutralization assays with chimeric epitope transplant DV and sera depleted of Ab subpopulations. We use ADE assay to determine if stabilized E dimer and mutated FL reduces ADE compared to WT rE. Preliminary results indicate that WT-vaccinated mice neutralizing Ab bind to simple epitopes on rE monomers, while SD-vaccinated mice had mostly dimer-specific neutralizing Ab. Our results demonstrate the promise of structure-guided design for developing dengue subunit vaccines. NIH/NIAID U19 AI109784 R01AI107731 DOD/US Army Medical Research ACQ W81XWH1820034