Pichia pastoris-expressed Zika virus envelope domain III on a virus-like particle platform: design, production and immunological evaluation.

Zika virus (ZIKV) is an arbovirus which shares antigenic similarity and the mosquito vector with dengue viruses (DENVs). ZIKV is a neurotropic virus capable of causing congenital neurodevelopmental birth defects. As ZIKV antibodies (Abs) can potentially enhance infection by DENVs, a preventive ZIKV vaccine must be designed to eliminate antibody dependent enhancement of infection. We developed a Zika Subunit Vaccine (ZSV) consisting of two proteins, ZS and S, in a genetically pre-determined ratio of 1:4, using the methylotrophic yeast Pichia pastoris. ZS is an in-frame fusion of ZIKV envelope domain III with the Hepatitis B virus (HBV) surface antigen, and S is the un-fused HBV surface antigen. Using specific monoclonal Abs we showed the presence of ZS and S in the co-purified material which were found to co-assemble into virus-like particles (VLPs), based on dynamic light scattering and electron microscopic analyses. These VLPs were immunogenic in BALB/c mice, eliciting Abs capable of neutralizing ZIKV reporter virus particles. Further, the VLP-induced Abs did not enhance a sub-lethal DENV-2 challenge in AG129 mice. This important safety feature, coupled to the well-documented advantage of P. pastoris expression system, warrants further exploration of ZSV VLP as a possible vaccine candidate.