Department of First Viral Vaccine, National Institute for the Control of Pharmaceutical and Biological Products, Tiantan Xili 2# Chongwen Qu, Beijing 100050, China.
Vaccine. 2010 May 7;28(21):3635-41. doi: 10.1016/j.vaccine.2010.02.105. Epub 2010 Mar 11.
A novel Japanese encephalitis (JE) attenuated live vaccine virus SA14-14-2 was licensed for commercial application in China in 1989. Since then this vaccine has been widely used in China and other countries in Asia, and no vaccine associated encephalitis case was reported. The neurovirulence of the SA14-14-2 was tested in JE susceptible laboratory animals, such as mice, monkeys, hamsters and athymic nude mice. The results showed that the attenuated virus strain was avirulent to these animals by intracerebral inoculation (i.c.) or intraperitoneal inoculation (i.p.). Studies on the neuroattenuation stability revealed that no reversion after 17 times tissue culture passages or one i.c. sucking mice passage. Mosquito infection studies indicated that after one mosquito intrathoracical passage, the progeny viruses in the infected mosquitoes were unable to cause sucking mice or weanling mice disease. Molecules characteristics' studies of the SA14-14-2 virus strain showed that there are 57-61 nucleotide changes and 24-31 amino acid substitutions, eight substitutions in the E protein gene are the critical amino acid related to the virus attenuation. The E gene sequence studies have showed that the 8 critical amino acids were not changed after 22 passages in tissue cultures or one passage in mosquitoes. Comparison of the full-length sequence to the parental SA14 virus has revealed that after 22 passages in the tissue cultures, only 8 nucleotides changed leading to 4 amino acid substitutions. However they were not the reverse mutation and none of the 8 critical residues changed. The homology of the nucleotide and amino acid between the virus of passage 22 and the primary seed virus in Genbank was 99.93% and 99.88% respectively. The above results demonstrated that the SA14-14-2 virus is highly attenuated for the various JE susceptible animals. The attenuated phenotypes and the genetic characteristics of the SA14-14-2 strain are highly stable after multiple in vitro passages or mosquitoes infection. Therefore the safety of the live JE vaccine is due to a high degree of neuroattenuation and a number of stable phenotypically and genetically characteristics, suggesting that reversion to neurovirulence of the vaccine strain would be highly unlikely.
一种新型的乙型脑炎（JE）减毒活疫苗病毒 SA14-14-2 于 1989 年在中国获得商业应用许可。自那时以来，该疫苗已在中国和亚洲其他国家广泛使用，并且没有报告与疫苗相关的脑炎病例。SA14-14-2 的神经毒力已在 JE 易感的实验动物（如小鼠、猴子、仓鼠和无胸腺裸鼠）中进行了测试。结果表明，通过脑内接种（i.c.）或腹腔接种（i.p.），减毒病毒株对这些动物无毒。神经减毒稳定性研究表明，经过 17 次组织培养传代或一次 i.c.感染吸痰小鼠传代后没有回复。蚊虫感染研究表明，经过一次蚊虫胸内传代后，感染蚊虫中的后代病毒无法引起吸痰小鼠或断奶小鼠发病。对 SA14-14-2 病毒株的分子特征研究表明，存在 57-61 个核苷酸变化和 24-31 个氨基酸取代，E 蛋白基因中的 8 个取代是与病毒减毒相关的关键氨基酸。E 基因序列研究表明，在组织培养中传代 22 次或在蚊虫中传代一次后，8 个关键氨基酸没有变化。比较全长序列与亲本 SA14 病毒发现，在组织培养中传代 22 次后，只有 8 个核苷酸发生变化，导致 4 个氨基酸取代。但是它们不是回复突变，并且 8 个关键残基没有改变。在 Genbank 中，传代 22 次的病毒与原始种子病毒的核苷酸和氨基酸同源性分别为 99.93%和 99.88%。上述结果表明，SA14-14-2 病毒对各种 JE 易感动物高度减毒。SA14-14-2 株的减毒表型和遗传特征在多次体外传代或蚊虫感染后高度稳定。因此，活乙型脑炎疫苗的安全性是由于高度神经减毒和许多稳定的表型和遗传特征，表明疫苗株向神经毒力的回复突变极不可能。
