Department of Pathology, The University of Texas Medical Branch, Galveston, Texas, United States of America.
PLoS Negl Trop Dis. 2013 Apr 18;7(4):e2181. doi: 10.1371/journal.pntd.0002181. Print 2013.
Rift Valley fever virus (RVFV; genus Phlebovirus, family Bunyaviridae) is a mosquito-borne zoonotic pathogen which can cause hemorrhagic fever, neurological disorders or blindness in humans, and a high rate of abortion in ruminants. MP-12 strain, a live-attenuated candidate vaccine, is attenuated in the M- and L-segments, but the S-segment retains the virulent phenotype. MP-12 was manufactured as an Investigational New Drug vaccine by using MRC-5 cells and encodes a functional NSs gene, the major virulence factor of RVFV which 1) induces a shutoff of the host transcription, 2) inhibits interferon (IFN)-β promoter activation, and 3) promotes the degradation of dsRNA-dependent protein kinase (PKR). MP-12 lacks a marker for differentiation of infected from vaccinated animals (DIVA). Although MP-12 lacking NSs works for DIVA, it does not replicate efficiently in type-I IFN-competent MRC-5 cells, while the use of type-I IFN-incompetent cells may negatively affect its genetic stability. To generate modified MP-12 vaccine candidates encoding a DIVA marker, while still replicating efficiently in MRC-5 cells, we generated recombinant MP-12 encoding Punta Toro virus Adames strain NSs (rMP12-PTNSs) or Sandfly fever Sicilian virus NSs (rMP12-SFSNSs) in place of MP-12 NSs. We have demonstrated that those recombinant MP-12 viruses inhibit IFN-β mRNA synthesis, yet do not promote the degradation of PKR. The rMP12-PTNSs, but not rMP12-SFSNSs, replicated more efficiently than recombinant MP-12 lacking NSs in MRC-5 cells. Mice vaccinated with rMP12-PTNSs or rMP12-SFSNSs induced neutralizing antibodies at a level equivalent to those vaccinated with MP-12, and were efficiently protected from wild-type RVFV challenge. The rMP12-PTNSs and rMP12-SFSNSs did not induce antibodies cross-reactive to anti-RVFV NSs antibody and are therefore applicable to DIVA. Thus, rMP12-PTNSs is highly efficacious, replicates efficiently in MRC-5 cells, and encodes a DIVA marker, all of which are important for vaccine development for Rift Valley fever.
裂谷热病毒（RVFV；属布尼亚病毒科，白蛉病毒属）是一种蚊媒传播的人畜共患病病原体，可导致人类出血热、神经紊乱或失明，并导致反刍动物流产率高。MP-12 株是一种减毒活候选疫苗，在 M 和 L 片段中被削弱，但 S 片段保留了强毒表型。MP-12 是作为一种研究性新药疫苗使用 MRC-5 细胞制造的，编码一个功能性 NSs 基因，该基因是 RVFV 的主要毒力因子，1）诱导宿主转录关闭，2）抑制干扰素（IFN）-β启动子激活，3）促进双链 RNA 依赖性蛋白激酶（PKR）的降解。MP-12 缺乏区分感染和接种动物的标记（DIVA）。尽管缺乏 NSs 的 MP-12 可用于 DIVA，但它在 I 型干扰素有效的 MRC-5 细胞中不能有效复制，而使用 I 型干扰素无效的细胞可能会对其遗传稳定性产生负面影响。为了在 MRC-5 细胞中高效复制的同时生成编码 DIVA 标记的改良 MP-12 疫苗候选物，我们用蓬塔托罗病毒 Adames 株 NSs（rMP12-PTNSs）或沙蝇热西西里病毒 NSs（rMP12-SFSNSs）取代了 MP-12 NSs，生成了重组 MP-12。我们已经证明，这些重组 MP-12 病毒抑制 IFN-β mRNA 的合成，但不促进 PKR 的降解。rMP12-PTNSs 比缺乏 NSs 的重组 MP-12 在 MRC-5 细胞中复制更有效，但 rMP12-SFSNSs 则不然。用 rMP12-PTNSs 或 rMP12-SFSNSs 接种的小鼠诱导的中和抗体水平与用 MP-12 接种的小鼠相当，并能有效抵抗野生型 RVFV 攻击。rMP12-PTNSs 和 rMP12-SFSNSs 不诱导与抗 RVFV NSs 抗体交叉反应的抗体，因此适用于 DIVA。因此，rMP12-PTNSs 具有高效性，在 MRC-5 细胞中高效复制，并编码 DIVA 标记，这些都是裂谷热疫苗开发的重要因素。
