Abstract
BackgroundDuring clinical development of the licensed Japanese encephalitis chimeric virus vaccine (JE-CV), the neutralization capacity of vaccine-induced antibodies was assessed against the vaccine virus and against well characterized wild-type (wt) viruses isolated between 1949–1991. We assessed whether JE-CV-induced antibodies can also neutralize more recent wt Japanese encephalitis virus (JEV) isolates including a genotype 1 isolate.MethodsSera from 12–18 month-old children who received a single dose of JE-CV in a phase III study in Thailand and the Philippines (ClinicalTrials.gov NCT00735644) were randomly selected and pooled according to neutralization titer against JE-CV into eight samples. Neutralization was assessed by plaque reduction neutralization tests (PRNT50) against three recent isolates from JEV genotypes 1 and 3 in addition to four JEV previously tested.ResultsNeutralization titers against the three recent JEV strains were comparable to those observed previously against other strains and the vaccine virus. The observed differences between responses to genotype 1 and 3 viruses were within assay variability for the PRNT50.ConclusionsThe results were consistent with previously generated data on the neutralization of wt JEV isolates, immune responses induced by JE-CV neutralize recently isolated virus from southeast (SE) Asia and India.
Highlights
During clinical development of the licensed Japanese encephalitis chimeric virus vaccine (JE-CV), the neutralization capacity of vaccine-induced antibodies was assessed against the vaccine virus and against well characterized wild-type viruses isolated between 1949–1991
The Japanese encephalitis virus (JEV) neutralizing antibody response is considered to be the correlate of protection for JE vaccines, with a plaque reduction neutralization 50% (PRNT50) titer of 1:10 defining the seroprotective threshold [12,13,14]
We previously demonstrated the ability of serum from adults and children vaccinated with JE-CV to neutralize heterologous wt JEV from genotypes 1–4 isolated between 1949 and 1991 [5,8]
Summary
During clinical development of the licensed Japanese encephalitis chimeric virus vaccine (JE-CV), the neutralization capacity of vaccine-induced antibodies was assessed against the vaccine virus and against well characterized wild-type (wt) viruses isolated between 1949–1991. We assessed whether JE-CV-induced antibodies can neutralize more recent wt Japanese encephalitis virus (JEV) isolates including a genotype 1 isolate. A live, attenuated, JE chimeric virus vaccine (JE-CV), developed by replacing the premembrane and envelope coding sequences from the yellow fever vaccine virus (strain 17D) genome with the JE virus (JEV), a member of the genus Flavivirus, is considered to exist as a single serotype and four main genotypes were identified initially on the basis of sequence within the pre membrane (prM) gene region [9,10]. PRNT50 assays are performed mostly using the vaccine homologous virus [15,16], with neutralization responses against wild-type JEV in general less well characterized, perhaps unsurprising given the difficulty in isolating JEV from clinical infections. Assessing vaccine-induced neutralization responses against circulating heterologous strains of JEV, against JEV genotype 1 which is the dominant genotype across parts of Asia, [17,18,19] provides a deeper understanding of a vaccine’s immunogenicity
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