Passive Transfer of Immune Sera Induced by a Zika Virus-Like Particle Vaccine Protects AG129 Mice Against Lethal Zika Virus Challenge.

Zika virus (ZIKV) poses a serious public health threat due to its association with birth defects in developing fetuses and Guillain-Barré Syndrome in adults. We are developing a ZIKV vaccine based on virus-like particles (VLPs) generated in transiently transfected HEK293 cells. The genetic construct consists of the prM and envelope structural protein genes of ZIKV placed downstream from a heterologous signal sequence. To better understand the humoral responses and correlates of protection (CoP) induced by the VLP vaccine, we evaluated VLP immunogenicity with and without alum in immune-competent mice (C57Bl/6 x Balb/c) and observed efficient induction of neutralizing antibody as well as a dose-sparing effect of alum. To assess the efficacy of the immune sera, we performed passive transfer experiments in AG129 mice. Mice that received the immune sera prior to ZIKV infection demonstrated significantly reduced viral replication as measured by viral RNA levels in the blood and remained healthy, whereas control mice succumbed to infection. The results underscore the protective effect of the antibody responses elicited by this ZIKV VLP vaccine candidate. These studies will help define optimal vaccine formulations, contribute to translational efforts in developing a vaccine for clinical development, and assist in the definition of immunologic CoP.