目的 研制以Vero细胞为生产基质的SA14-14-2乙型脑炎（乙脑）减毒活疫苗候选毒株。方法 将SA14-14-2株原始病毒在Vero上传代并进行空斑克隆，对克隆株病毒进行Vero细胞培养，使用3周龄小鼠及3日龄乳鼠对脑内致病力进行测定，并进行乳鼠脑内回传、弱毒稳定性实验及免疫力实验等。结果 挑选到10个病毒克隆株，通过全面对比后，筛选到1株病毒滴度高（＞6.0 lgPFU/ml）且稳定的毒株SA14-14-2 VC₆。将该株与SA14-14-2原始株进行主要指标对比，结果表明，VC₆株全基因序列与原株相比仅有1个位点发生突变（S66L），对小鼠和乳鼠脑内致病力、弱毒稳定性、免疫原性均与原株相同。结论 筛选到的SA14-14-2 VC₆株符合中国药典乙脑减毒活疫苗生产毒种的要求。各项主要指标不劣于SA14-14-2生产用毒种，是可应用Vero细胞培养生产的乙脑疫苗候选株。

Objective  To develop Vero cell-adapted SA14-14-2 vaccine seed virus candidate for production of Japanese encephalitis (JE) live attenuated vaccine. Methods  SA14-14-2 attenuated virus strain was passaged in Vero cell cultures for 3 generations followed by plaque cloning in Vero cell culture. Neuroattenuation, stability and immunogenicity were detected by infecting 3-week and 3-day mice with different strains of JE viruses. Results  Ten individual plaque colons were picked up for evaluation and detection. One neuroattenuation stable and high titer (＞6.0 lgPFU/ml) clone SA14-14-2 VC₆ was selected after full comparison. The VC₆ clone virus was compared with its parental SA14-14-2 strain on major aspects. The results indicated that the complete gene sequence of VC₆ was similar to SA14-14-2 strain except one single nucleotide mutation (S66L), while the neuroattenuation and stability as well as immunogenicity were all the same as its parental virus SA14-14-2. Conclusion  The selected virus strain SA14-14-2 VC₆ meets requirements for JE live attenuated vaccine in Chinese pharmocopoeia with all major indices non-inferiority to its parental virus SA14-14-2 strain, and is a promising candidate seed virus for development of Vero cell JE vaccine.