Immunogenic potential and protective efficacy of formalin inactivated circulating Indian strain of West Nile virus

Comparison of β-Propiolactone and Formalin Inactivation on Antigenicity and Immune Response of West Nile Virus

West Nile Virus (WNV) is a pathogenic arbovirus that belongs to genus Flavivirus under family Flaviviridae. Till now there are no approved vaccines against WNV for human use. In this study, the effect of two alkylating agents, formaldehyde and β-PL, generally used for inactivated vaccine preparation, was assessed on the basis of antigenic and immunogenic potential of the inactivated WNV. Lineage 5 WNV isolates were inactivated by both formalin and β-PL treatments. Inactivation was confirmed by repeated passage in BHK-21 cell line and infant mice. Viruses inactivated by both the treatments showed higher antigenicity. Immune response in mice model showed serum anti-WNV antibody titre was moderately higher in formalin inactivated antigen compared to β-PL inactivated antigen. However, no significant differences were observed in neutralization antibody titre. In conclusion, we can state that both formaldehyde and β-PL inactivation processes were found to be equally efficient for inactivation of WNV. However, they need to be compared with other inactivating agents along with study on cell mediated immune response.

The efficacy of inactivated West Nile vaccine (WN-VAX) in mice and monkeys

Background

West Nile virus (WNV) belonging to the genus Flavivirus of the family Flaviviridae causes nervous system disorder in humans, horses and birds. Licensed WNV vaccines are available for use in horses but not for humans. We previously developed an inactivated West Nile virus vaccine (WN-VAX) using a seed virus from West Nile virus (WNV NY99) that was originally isolated in New York City in 1999. In this study, we report the immunogenicity of WN-VAX in both mice and non-human primates.

Findings

The WN-VAX immunized mice showed protection against lethal infection with WNV NY99. The challenge test performed on mice passively immunized with serum from other mice that were previously immunized with WN-VAX confirmed that the neutralizing antibody titers of more than 1log10 protected the passively immunized mice from WNV lethal infection. Furthermore, monkeys (Macaca fascicularis) immunized three times with 2.5 μg, 5 μg or 10 μg/dose of WN-VAX exhibited neutralizing antibodies in their sera with titers of more than 2log10 after the second immunization.

Conclusions

The WN-VAX was protective in mice both by active and passive immunizations and was immunogenic in monkeys. These results suggest that the vaccine developed in this study may be a potential WNV vaccine candidate for human use.