Replication-Defective West Nile Virus with NS1 Deletion as a New Vaccine Platform for Flavivirus

We previously produced a replication-defective West Nile virus (WNV) lacking NS1 (WNV-Delta NS1) that could propagate at low levels (105 infectious units [IU]/ml) in a 293T cell line expressing wild-type (WT) NS1. This finding indicates the potential of developing WNV-Delta NS1 as a noninfectious vaccine. To explore this idea, we developed an NS1-expressing Vero cell line (Vero(NS1)) that significantly improved the yield of WNV-Delta NS1 (10(8) IU/ml). We evaluated the safety and efficacy of WNV-Delta NS1 in mice. WNV-Delta NS1 appeared to be safe, as no replicative virus was found in naive Vero cells after continuous culturing of WNV-Delta NS1 in Vero(NS1) cells for 15 rounds. WNV-Delta NS1 was noninfectious in mice, even when IFNAR(-/-) mice were administered a high dose of WNV-Delta NS1. Vaccination with a single dose of WNV-Delta NS1 protected mice from a highly lethal challenge with WT WNV. The antibody response against WNV correlated well with the protection of vaccinated mice. Our study demonstrates the potential of the NS1 trans complementation system as a new platform for flavivirus vaccine development. IMPORTANCE Many flaviviruses are significant human pathogens that frequently cause outbreaks and epidemics around the world. Development of novel vaccine platforms against these pathogens is a public health priority. Using WNV as a model, we developed a new vaccine platform for flaviviruses. WNV containing a NS1 deletion (WNV-Delta NS1) could be efficiently trans complemented in Vero cells that constitutively expressed WT NS1 protein. A single-dose immunization with WNV-Delta NS1 elicited robust immune responses in mice. The immunized animals were fully protected against pathogenic WNV infection. No adverse effects related to the WNV-Delta NS1 vaccination were observed. The results have demonstrated the potential of the NS1 complementation system as an alternative platform for flavivirus vaccine development, especially for highly pathogenic flaviviruses.