Comparison of the live-attenuated Japanese encephalitis vaccine SA14 -14-2 strain with its pre-attenuated virulent parent SA14 strain: similarities and differences in vitro and in vivo

Abstract

Japanese encephalitis virus (JEV) is the main cause of acute viral encephalitis, primarily affecting children and young adults in the Asia-Pacific region. JEV is a vaccine-preventable pathogen, with four types of JE vaccine licensed in different regions of the world. To date, the most common JEV strain used in vaccine development and production is SA14-14-2, an attenuated strain derived from its wild-type parental strain SA14. In this study, we directly compared the phenotypic and genotypic characteristics of SA14 and SA14-14-2 to determine the biological and genetic properties associated with their differential virulence. In susceptible BHK-21 cells, SA14-14-2 grew slightly more slowly and formed smaller plaques than SA14, but unlike SA14, it showed almost no expression of the viral protein NS1', the product of a conserved predicted RNA pseudoknot-mediated ribosomal frameshift. In weanling ICR mice, SA14-14-2 was highly attenuated in terms of both neuroinvasiveness and neurovirulence, with its median lethal doses invariably over five logs higher than those of SA14 when inoculated intramuscularly and intracerebrally. Interestingly, the neurovirulence of SA14-14-2 was dependent on mouse age, with the 1- to 7-day-old mice being highly susceptible and the 14- to 21-day-old mice becoming resistant to intracerebral inoculation. At the genome level, SA14-14-2 differed from SA14 by 57 nucleotides, including one silent G-to-A substitution at position 3599 within the predicted RNA pseudoknot for NS1' synthesis; of the 57 differences, 25 resulted in amino acid substitutions. Our data pave the way for the development of new genetically modified JE vaccines.

A live-attenuated Zika virus vaccine candidate induces sterilizing immunity in mouse models

“…The latter safety result is impressive because I.C. inoculation with YFV 17D and JEV SA14–14-2 (two licensed live-attenuated flavivirus vaccines) results in lethal disease in one-day-old newborn mice 21,22 . Although potential homologous recombination between the WT and vaccine ZIKVs might pose a safety liability for the 10-del vaccine candidate, it should be noted that recombination events are rare and could not be detected in cell culture 23–27 .…”

Japanese encephalitis vaccines: Immunogenicity, protective efficacy, effectiveness, and impact on the burden of disease

“…82 Compared to the wild-type SA14 virus, the SA14-14-2 LAV shows a slight growth defect (smaller plaque size, slower kinetics, lower titres) in BHK-21 cells, and is highly attenuated for neuroinvasion and neurovirulence in ICR mice. 83 The LAV fails to replicate in mosquitoes when fed through a blood meal, while it replicates to low titres when inoculated intrathoracically in C. tritaeniorhynchus, but with an inability to be transmitted to suckling mice, 82 suggesting that the SA14-14-2 LAV is transmission-incompetent. The LAV strain has also been shown to be stable upon passage in mosquito or mammalian cells in vitro, or in mice (both intracerebral and intraperitoneal) or mosquitoes.…”

“…A seminal study showed that multiple (at least 4) mutations in the E protein are required for attenuation of neurovirulence, 98 although other studies have shown that a single mutation in the C protein (S66L), or an additional mutation in the E protein (G244E) may also lead to attenuation without loss of immunogenicity in mice. 95,99 Recent studies have also shown that the SA14-14-2 LAV is unable to produce the NS1 0 protein due to the loss of the RNA pseudoknot structure as a result of a single point mutation (G66A) in the NS2A coding region, 83,100 although this does not appear to significantly affect neurovirulence. 101 Despite the excellent safety record of SA14-14-2 LAV vaccine, 102 some issues have been raised about its regulatory compliance.…”

Comparative analysis of neuroinvasion by Japanese encephalitis virulent and vaccine strains in anin cellulomodel of human blood-brain barrier

“…In contrast to virulent JEV strains as RP9, the vaccine strain SA14-14-2 was shown to be essentially non-neuroinvasive and non-neurovirulent in weanling ICR mice, but is still highly neurovirulent in neonates [16]. JEV SA14-14-2 genome displays 57 nucleotide differences positioned along the genome when compared to the parental strain SA14, leading to 25 amino-acid substitutions [16].…”