Characterization of live-attenuated Japanese encephalitis vaccine virus SA14-14-2.
The live attenuated Japanese encephalitis (JE) vaccine SA14-14-2 was licensed decades ago and now approved for clinical use in most JE endemic countries. Large-scale clinical trials demonstrate ideal safety and efficacy profile of this Chinese vaccine. The SA14-14-2 vaccine was derived from a virulent strain SA14 after hundreds of serial passaging in cells and animals, concern about virulence reversion remains exist. In the present study, to study the in vitro and in vivo genetic and attenuation stability of the vaccine virus, SA14-14-2 was serially passaged in Vero cells and mouse brain followed by sequence comparison and attenuation phenotype analysis. The results showed that no significant mutation was acquired after serial passaging in Vero cells except a single Ser66Leu mutation within capsid protein, which had no effect on viral virulence in mice. Importantly, serial passaging of SA14-14-2 in suckling mouse brain resulted in emergence of adaptive mutations and increased virulence in mice. Population and plaque-purified clone consensus sequence analysis showed four adaptive mutations in envelope (E) protein, F107L, K138E, T226R and I270T, sequentially occurred and become predominant during serial passaging in suckling mouse brain. Especially, these adaptive mutations were close related with the enhanced neurovirulence and neuroinvasiveness in mice. Our results provide experimental evidence of highly genetic and attenuation stability of SA14-14-2 following passaging in Vero cells, and reveal the potential virulence reversion during passaging in mouse brain in association with critical adaptive mutations in E protein. These findings are important for quality control and evaluation of live JE vaccines and will help understand the attenuation mechanism of flavivirus vaccine.
College of Veterinary Medicine, Xinjiang Agricultural University, Urumqi 830052, China; Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Dong
D
Yang
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Xiao-Feng
XF
Li
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Qing
Q
Ye
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Hong-Jiang
HJ
Wang
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Yong-Qiang
YQ
Deng
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Shun-Ya
SY
Zhu
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Yu
Y
Zhang
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China.
Shi-Hua
SH
Li
Department of Virology, State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, China. Electronic address: qincf@bmi.ac.cn.
Cheng-Feng
CF
Qin
D000818:Animals; D001921:Brain / Q000821:virology; D002522:Chlorocebus aethiops; D004664:Encephalitis Virus, Japanese / Q000235:genetics* / Q000472:pathogenicity; D016679:Genome, Viral; D022321:Japanese Encephalitis Vaccines / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D012692:Serial Passage; D014613:Vaccines, Attenuated / Q000235:genetics; D014709:Vero Cells; D010948:Viral Plaque Assay; D014774:Virulence / Q000235:genetics*
D022321:Japanese Encephalitis Vaccines; D014613:Vaccines, Attenuated
Genetic stability; Japanese encephalitis virus; Live attenuated vaccine; Serial passaging; Virulence