Lokugamage Nandadeva, Ikegami Tetsuro
Department of Pathology, The University of Texas Medical Branch at Galveston, 301 University Blvd. Galveston, Texas 77555 USA.
The Sealy Center for Vaccine Development, The University of Texas Medical Branch at Galveston, 301 University Blvd. Galveston, Texas 77555 USA.
NPJ Vaccines. 2017;2. doi: 10.1038/s41541-017-0021-9. Epub 2017 Jul 17.
Rift Valley fever (RVF) is a mosquito-borne zoonotic disease endemic to Africa which affects both ruminants and humans. RVF causes serious damage to the livestock industry and is also a threat to public health. The Rift Valley fever virus has a segmented negative-stranded RNA genome consisting of Large (L)-, Medium (M)-, and Small (S)-segments. The live-attenuated MP-12 vaccine is immunogenic in livestock and humans, and is conditionally licensed for veterinary use in the U.S. The MP-12 strain encodes 23 mutations (nine amino acid substitutions) and is attenuated through a combination of mutations in the L-, M-, and S-segments. Among them, the M-U795C, M-A3564G, and L-G3104A mutations contribute to viral attenuation through the L- and M-segments. The M-U795C, M-A3564G, L-U533C, and L-G3750A mutations are also independently responsible for temperature-sensitive (ts) phenotype. We hypothesized that a serial passage of the MP-12 vaccine in culture cells causes reversions of the MP-12 genome. The MP-12 vaccine and recombinant rMP12-ΔNSs16/198 were serially passaged 25 times. Droplet digital PCR analysis revealed that the reversion occurred at L-G3750A during passages of MP-12 in Vero or MRC-5 cells. The reversion also occurred at M-A3564G and L-U533C of rMP12-ΔNSs16/198 in Vero cells. Reversion mutations were not found in MP-12 or the variant, rMP12-TOSNSs, in the brains of mice with encephalitis. This study characterized genetic stability of the MP-12 vaccine and the potential risk of reversion mutation at the L-G3750A ts mutation after excessive viral passages in culture cells.
裂谷热（RVF）是一种由蚊子传播的人畜共患病，在非洲流行，会影响反刍动物和人类。裂谷热对畜牧业造成严重损害，也对公共卫生构成威胁。裂谷热病毒具有分段的负链RNA基因组，由大（L）、中（M）和小（S）片段组成。减毒活疫苗MP-12在牲畜和人类中具有免疫原性，在美国有条件地被许可用于兽医用途。MP-12毒株编码23个突变（9个氨基酸替换），并通过L、M和S片段中的突变组合而减毒。其中，M-U795C、M-A3564G和L-G3104A突变通过L和M片段导致病毒减毒。M-U795C、M-A3564G、L-U533C和L-G3750A突变也独立导致温度敏感（ts）表型。我们假设MP-12疫苗在培养细胞中连续传代会导致MP-12基因组的回复突变。MP-12疫苗和重组rMP12-ΔNSs16/198连续传代25次。液滴数字PCR分析显示，MP-12在Vero或MRC-5细胞传代过程中，L-G3750A发生了回复突变。rMP12-ΔNSs16/198在Vero细胞中的M-A3564G和L-U533C也发生了回复突变。在患有脑炎的小鼠大脑中，MP-12或变体rMP12-TOSNSs中未发现回复突变。本研究表征了MP-12疫苗的遗传稳定性以及在培养细胞中病毒过度传代后L-G3750A ts突变处回复突变的潜在风险。
