Division of Viral Products, Center for Biologics Evaluation and Research, Silver Spring, Maryland, USA
Division of Viral Products, Center for Biologics Evaluation and Research, Silver Spring, Maryland, USA.
J Virol. 2019 Sep 12;93(19). doi: 10.1128/JVI.00570-19. Print 2019 Oct 1.
The potential avian influenza pandemic remains a threat to public health, as the avian-origin influenza A(H7N9) virus has caused more than 1,560 laboratory-confirmed human infections since 2013, with nearly 40% mortality. Development of low-pathogenic candidate vaccine viruses (CVVs) for vaccine production is essential for pandemic preparedness. However, the suboptimal growth of CVVs in mammalian cells and chicken eggs is often a challenge. By introducing a single adaptive substitution, G218E, into the hemagglutinin (HA), we generated reassortant A(H7N9)-G218E CVVs that were characterized by significantly enhanced growth in both cells and eggs. These G218E CVVs retained the original antigenicity, as determined by a hemagglutination inhibition assay, and effectively protected ferrets from lethal challenge with the highly pathogenic parental virus. We found that the suboptimal replication of the parental H7 CVVs was associated with impeded progeny virus release as a result of strong HA receptor binding relative to weak neuraminidase (NA) cleavage of receptors. In contrast, the G218E-mediated growth improvement was attributed to relatively balanced HA and NA functions, resulted from reduced HA binding to both human- and avian-type receptors, and thus facilitated NA-mediated virus release. Our findings revealed that a single amino acid mutation at residue 218 of the HA improved the growth of A(H7N9) influenza virus by balancing HA and NA functions, shedding light on an alternative approach for optimizing certain influenza CVVs. The circulating avian influenza A(H7N9) has caused recurrent epidemic waves with high mortality in China since 2013, in which the alarming fifth wave crossing 2016 and 2017 was highlighted by a large number of human infections and the emergence of highly pathogenic avian influenza (HPAI) A(H7N9) strains in human cases. We generated low-pathogenic reassortant CVVs derived from the emerging A(H7N9) with improved virus replication and protein yield in both MDCK cells and eggs by introducing a single substitution, G218E, into HA, which was associated with reducing HA receptor binding and subsequently balancing HA-NA functions. The and experiments demonstrated comparable antigenicity of the G218E CVVs with that of their wild-type (WT) counterparts, and both the WT and the G218E CVVs fully protected ferrets from parental HPAI virus challenge. With high yield traits and the anticipated antigenicity, the G218E CVVs should benefit preparedness against the threat of an A(H7N9) influenza pandemic.
自 2013 年以来，禽流感 A(H7N9)病毒已导致 1560 多例经实验室确认的人类感染，死亡率接近 40%，因此潜在的禽流感大流行仍然是对公众健康的威胁。开发用于疫苗生产的低致病性候选疫苗病毒 (CVV) 对于大流行的准备至关重要。然而，CVV 在哺乳动物细胞和鸡胚中的生长不佳通常是一个挑战。通过在血凝素 (HA) 中引入单个适应性替换 G218E，我们生成了重组 A(H7N9)-G218E CVV，其在细胞和鸡蛋中的生长明显增强。这些 G218E CVV 保留了原始抗原性，如通过血凝抑制试验确定的，并且有效地保护雪貂免受高致病性亲本病毒的致死性攻击。我们发现，亲本 H7 CVV 的复制不佳与子代病毒释放受阻有关，这是由于 HA 与受体的结合较强，而神经氨酸酶 (NA) 对受体的裂解较弱所致。相比之下，G218E 介导的生长改善归因于 HA 和 NA 功能的相对平衡，这是由于 HA 与人和禽型受体的结合减少，从而促进了 NA 介导的病毒释放。我们的研究结果表明，HA 残基 218 处的单个氨基酸突变通过平衡 HA 和 NA 功能改善了 A(H7N9)流感病毒的生长，为优化某些流感 CVV 提供了一种替代方法。自 2013 年以来，循环的禽流感 A(H7N9)在中国引起了多次高死亡率的流行波，其中引人注目的第五波跨越 2016 年和 2017 年，大量的人类感染和人类病例中出现高致病性禽流感 (HPAI) A(H7N9) 株突出了这一点。我们通过在 HA 中引入单个取代 G218E，从新兴的 A(H7N9) 中生成了低致病性重组 CVV，从而提高了病毒在 MDCK 细胞和鸡胚中的复制和蛋白产量，这与降低 HA 受体结合并随后平衡 HA-NA 功能有关。和 实验表明，G218E CVV 的抗原性与野生型 (WT) 相当，WT 和 G218E CVV 均可完全保护雪貂免受亲本 HPAI 病毒的攻击。具有高产性状和预期的抗原性，G218E CVV 应有助于应对 A(H7N9) 流感大流行的威胁。
