Introduction: The causal association of Zika virus (ZIKV) with microcephaly, congenital malformations in infants and Guillain-Barré syndrome in adults highlight the need for effective vaccines. Neutralising antibodies against ZIKV structural (pre-membrane and envelope) proteins can successfully prevent the infection . However, there is a concern that anti-envelope antibodies can enhance infection of dengue virus , which is also endemic in regions where ZIKV circulates. Therefore, we developed novel cytolytic DNA vaccines encoding non-structural proteins (NS2/NS3 and NS4/NS5) of ZIKV. These cytolytic DNA vaccines also encode a truncated form of mouse perforin (PRF), which can more effectively prime T-cell mediated immunity (CMI) in vivo compared to canonical DNA vaccines not encoding PRF .
Method: Cytolytic DNA plasmids encoding ZIKV NS2 and NS3 (pNS2/NS3-PRF) and NS4 and NS5 (pNS4/NS4-PRF) (Brazil-ZKV2015 isolate) were used to prime/boost vaccinate female BALB/c mice. Empty DNA vector (pVAX-PRF) was used as a control. CMI to each vaccine-encoded ZIKV NS protein was evaluated in vivo in vaccinated mice using fluorescent target array (FTA). We have used the FTA to quantify the magnitude and avidity of CMI in vaccinated mice . The assay involves challenging vaccinated mice with fluorescently bar-coded ZIKV peptide-pulsed autologous target cells, which are recognized by effector/memory CD8+ cytotoxic T-lymphocyte (CTL) cells and CD4+ T helper (Th) cells in vivo. T cell responses are assessed 18 hours later by flow cytometry analysis of FTA target cells recovered from the spleen of vaccinated mice.
Results and Conclusion: Vaccination of mice with pNS2/NS3-PRF or pNS4/NS5-PRF elicited significant CD8+ CTL and CD4+ Th responses in vivo that were mainly restricted to ZIKV NS2 and NS3, while NS4 and NS5 were poorly immunogenic. This study suggests that ZIKV NS2 and NS3 can be effective immunogens for the development of T-cell based vaccines against ZIKV. We are currently evaluating the protective efficacy of pNS2/NS3-PRF against ZIKV challenge.