Functional activity of antisera against recombinant Zika virus envelope protein subunits expressed in Escherichia coli

The global Zika virus (ZIKV) outbreak across continents has been drawing research attentions to researchers and healthcare professionals. It highlights the urgent development of ZIKV vaccines that offer rapid, precise and specific protection to those living in the high-risk regions - the tropical and subtropical regions. As a public health priority, there is a progressive development in the discovery of vaccine candidates and design in recent years. Many efforts have been placed in the in vitro development of ZIKV subunits as the vaccine candidate in various protein expression systems, including bacteria, yeast, plant cells, insect cells and mammalian cells. However, due to the lack of knowledge on humoral and cellular immune responses against virus vaccines, a commercialised vaccine against Dengue virus (DENV) has been suspended due to a health scare in Philippines. Moreover, the closely-related DENV and ZIKV has indicated serological cross-reactivity between both viruses. This has led to greater attentions to precautions needed during the design of ZIKV and DENV vaccines. In this study, we pre-selected, synthesised and expressed the domain III of ZIKV envelope protein (namely rEDIII) based on a previously-established report (GenBank: AMC13911.1). The characteristics of purified ZIKV rEDIII was tested using SDS-PAGE, Western blotting and LC-MS/MS. Since the ZIKV rEDIII has been well reported as a potential protein candidate in ZIKV vaccine development, we assessed the possible outcome of preexisting immunity against the rEDIII proteins by conducting dot-blotting assays using mice antisera pre-immunised with ZIKV particles (ZIKV strain: MRS_OPY_Martinique_PaRi_2015, GenBank: KU647676). Surprisingly, the antisera was able to recognise the rEDIII of a different ZIKV strain (GenBank: AMC13911.1). Despite its great antigenicity in eliciting humoral and cellular immunity against ZIKV infection, our finding calls for greater attention to evaluate the details of ZIKV rEDIII as a stand-alone vaccine candidate.