A replication-defective Japanese encephalitis virus (JEV) vaccine candidate with NS1 deletion confers dual protection against JEV and West Nile virus in mice

In our previous study, we have demonstrated in the context of WNV-Delta NS1 vaccine (a replication-defective West Nile virus (WNV) lacking NS1) that the NS1trans-complementation system may offer a promising platform for the development of safe and efficient flavivirus vaccines only requiring one dose. Here, we produced high titer (10(7)IU/ml) replication-defective Japanese encephalitis virus (JEV) with NS1 deletion (JEV-Delta NS1) in the BHK-21 cell line stably expressing NS1 (BHKNS1) using the same strategy. JEV-Delta NS1 appeared safe with a remarkable genetic stability and high degrees of attenuation of in vivo neuroinvasiveness and neurovirulence. Meanwhile, it was demonstrated to be highly immunogenic in mice after a single dose, providing similar degrees of protection to SA14-14-2 vaccine (a most widely used live attenuated JEV vaccine), with healthy condition, undetectable viremia and gradually rising body weight. Importantly, we also found JEV-Delta NS1 induced robust cross-protective immune responses against the challenge of heterologous West Nile virus (WNV), another important member in the same JEV serocomplex, accounting for up to 80% survival rate following a single dose of immunization relative to mock-vaccinated mice. These results not only support the identification of the NS1-deleted flavivirus vaccines with a satisfied balance between safety and efficacy, but also demonstrate the potential of the JEV-Delta NS1 as an alternative vaccine candidate against both JEV and WNV challenge.