Rapid Development of Vaccines for Emerging Viruses

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While the outbreak of ZIKV in the Americas has subsided, there is an ongoing risk of congenital Zika syndrome in babies born to mothers exposed to ZIKV during pregnancy. There is no licensed vaccine or treatment to combat ZIKV infection. Because of the urgent need for a ZIKV vaccine, and a finite time in which efficacy could be demonstrated in the current outbreak, we focused on developing a DNA vaccine which can be rapidly produced and can easily modified using genetic techniques. The first generation DNA vaccines are based on prior success in West Nile Virus. We designed and evaluated two lead DNA vaccine candidates which produce subviral particles (SVP) after transfection. The first candidate (VRC5283) expresses the prM and E proteins from the ZIKV French Polynesia 2014 strain. The other (VRC5288) is a ZIKV/JEV chimera virus and was designed with the final 98 amino acids of (comprising the transmembrane and stem domains from JEV) swapped for the corresponding regions from ZIKV which has been demonstrated to improve SVP secretion for other flaviviruses. Immunization with these constructs generated robust neutralizing antibody responses in mice and rhesus macaques. Two doses of DNA vaccine candidates expressing the prM and E proteins of Zika virus protected 17 out of 18 rhesus macaques from viremia after Zika virus challenge. This protection was correlated with serum neutralizing activity. A single dose of DNA vaccine did not completely prevent infection, but significantly reduced the level of viremia in Zika virus challenged rhesus macaques. Subsequently, we have continued to study the two DNA vaccines by performing dose de-escalation studies to determine the neutralizing antibody threshold of protection, and correlates of protection. Additionally, we have collaborated with multiple groups to help develop alternative ZIKV vaccines, including mRNA-based and live-attenuated vaccines. Nipah Virus (NiV) circulates in animal reservoirs and has caused sporadic outbreaks in humans in India and South East Asia. NiV is transmitted by the respiratory route, but can develop into a highly fatal neurologic disease. There is no licensed vaccine or treatment for NiV, although a G protein vaccine, and mAb from the related Hendra virus are currently being developed for Nipah. We have begun to use structure-based design to stabilize the fusion protein in its prefusion confirmation to use as a vaccine immunogen. Based on the establishment of G antibodies as a correlate of protection for Hendra virus, we also developed oligomeric G protein vaccines and chimeric vaccine that expresses the Pre-F and G protein. These vaccines are highly immunogenic in the protein and mRNA platforms and mRNA vaccines expressing these antigens are currently being evaluated in a ferret challenge model and advancing toward clinical trial testing. We are taking the same approach to develop subunit and gene-based vaccines for other paramyxoviruses (measles and mumps), and are evaluating candidates in animal models. Enterovirus D68 causes biannual respiratory illnesses in pediatric populations, and has been temporally related to outbreaks of acute flacid myelitis (AFM). We have begun efforts to develop a VLP vaccine that expresses the structural proteins of EV-D68. We have demonstrated immunogenicity of B1 subclade VLP and cross-neutralization of B3 and A2 subclade viruses. We are continuing to develop challenge models in immunodeficient AG129 mice, and mouse adapting B3 and A2 subclade viruses to evaluate the efficacy of VLP-elicited immune responses. We aim to apply the knowledge from this project to develop an enterovirus vaccine platform that can be used for vaccines against related enteroviruses.