Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, New York, USA.
Center of Excellence in Clinical Virology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
J Virol. 2019 Aug 28;93(18). doi: 10.1128/JVI.00840-19. Print 2019 Sep 15.
Influenza viruses express two surface glycoproteins, the hemagglutinin (HA) and the neuraminidase (NA). Anti-NA antibodies protect from lethal influenza virus challenge in the mouse model and correlate inversely with virus shedding and symptoms in humans. Consequently, the NA is a promising target for influenza virus vaccine design. Current seasonal vaccines, however, poorly induce anti-NA antibodies, partly because of the immunodominance of the HA over the NA when the two glycoproteins are closely associated. To address this issue, here we investigated whether extending the stalk domain of the NA could render it more immunogenic on virus particles. Two recombinant influenza viruses based on the H1N1 strain A/Puerto Rico/8/1934 (PR8) were rescued with NA stalk domains extended by 15 or 30 amino acids. Formalin-inactivated viruses expressing wild-type NA or the stalk-extended NA variants were used to vaccinate mice. The virus with the 30-amino-acid stalk extension induced significantly higher anti-NA IgG responses (characterized by increased antibody-dependent cellular cytotoxicity [ADCC] activity) than the wild-type PR8 virus, while anti-HA IgG levels were unaffected. Similarly, extending the stalk domain of the NA of a recent H3N2 virus enhanced the induction of anti-NA IgGs in mice. On the basis of these results, we hypothesize that the subdominance of the NA can be modulated if the protein is modified such that its height surpasses that of the HA on the viral membrane. Extending the stalk domain of NA may help to enhance its immunogenicity in influenza virus vaccines without compromising antibody responses to HA. The efficacy of influenza virus vaccines could be improved by enhancing the immunogenicity of the NA protein. One of the reasons for its poor immunogenicity is the immunodominance of the HA over the NA in many seasonal influenza virus vaccines. Here we demonstrate that, in the mouse model, extending the stalk domain of the NA protein can enhance its immunogenicity on virus particles and overcome the immunodominance of the HA without affecting antibody responses to the HA. The antibody repertoire is broadened by the extended NA and includes additional ADCC-active antibodies. Our findings may assist in the efforts toward more effective influenza virus vaccines.
流感病毒表达两种表面糖蛋白，血凝素 (HA) 和神经氨酸酶 (NA)。抗 NA 抗体可预防小鼠模型中致命流感病毒的攻击，并且与人类的病毒脱落和症状呈负相关。因此，NA 是流感病毒疫苗设计的有前途的靶标。然而，目前的季节性疫苗不能很好地诱导抗 NA 抗体，部分原因是当两种糖蛋白紧密结合时，HA 对 NA 具有免疫优势。为了解决这个问题，我们研究了是否可以通过延长 NA 的茎部结构使其在病毒颗粒上更具免疫原性。两种基于 H1N1 株 A/Puerto Rico/8/1934 (PR8) 的重组流感病毒被拯救出来，其 NA 茎部结构分别延长了 15 或 30 个氨基酸。用表达野生型 NA 或茎部延伸的 NA 变体的福尔马林灭活病毒对小鼠进行免疫接种。与野生型 PR8 病毒相比，具有 30 个氨基酸茎部延伸的病毒诱导了显著更高的抗 NA IgG 反应（表现为增加的抗体依赖性细胞毒性 [ADCC] 活性），而抗 HA IgG 水平不受影响。同样，延伸最近的 H3N2 病毒的 NA 茎部结构也增强了小鼠中抗 NA IgGs 的诱导。基于这些结果，我们假设如果修饰该蛋白使其高度超过病毒膜上的 HA，则可以调节 NA 的亚优势。延长 NA 的茎部结构可能有助于在流感病毒疫苗中增强其免疫原性，而不会损害对 HA 的抗体反应。通过增强 NA 蛋白的免疫原性可以提高流感病毒疫苗的功效。其免疫原性差的原因之一是在许多季节性流感病毒疫苗中，HA 对 NA 的免疫优势。在这里，我们证明在小鼠模型中，延长 NA 蛋白的茎部结构可以增强其在病毒颗粒上的免疫原性，并克服 HA 的免疫优势，而不影响对 HA 的抗体反应。扩展的 NA 拓宽了抗体谱，包括额外的 ADCC 活性抗体。我们的发现可能有助于更有效的流感病毒疫苗的研发。
