The Sir William Dunn School of Pathology, The University of Oxford, Oxford, United Kingdom.
Department of Integrative Structural and Computational Biology, IAVI Neutralizing Antibody Center, Collaboration for AIDS Vaccine Discovery and Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, California, United States of America.
PLoS Pathog. 2018 May 10;14(5):e1006986. doi: 10.1371/journal.ppat.1006986. eCollection 2018 May.
Inducing broad spectrum neutralizing antibodies against challenging pathogens such as HIV-1 is a major vaccine design goal, but may be hindered by conformational instability within viral envelope glycoproteins (Env). Chemical cross-linking is widely used for vaccine antigen stabilization, but how this process affects structure, antigenicity and immunogenicity is poorly understood and its use remains entirely empirical. We have solved the first cryo-EM structure of a cross-linked vaccine antigen. The 4.2 Å structure of HIV-1 BG505 SOSIP soluble recombinant Env in complex with a CD4 binding site-specific broadly neutralizing antibody (bNAb) Fab fragment reveals how cross-linking affects key properties of the trimer. We observed density corresponding to highly specific glutaraldehyde (GLA) cross-links between gp120 monomers at the trimer apex and between gp120 and gp41 at the trimer interface that had strikingly little impact on overall trimer conformation, but critically enhanced trimer stability and improved Env antigenicity. Cross-links were also observed within gp120 at sites associated with the N241/N289 glycan hole that locally modified trimer antigenicity. In immunogenicity studies, the neutralizing antibody response to cross-linked trimers showed modest but significantly greater breadth against a global panel of difficult-to-neutralize Tier-2 heterologous viruses. Moreover, the specificity of autologous Tier-2 neutralization was modified away from the N241/N289 glycan hole, implying a novel specificity. Finally, we have investigated for the first time T helper cell responses to next-generation soluble trimers, and report on vaccine-relevant immunodominant responses to epitopes within BG505 that are modified by cross-linking. Elucidation of the structural correlates of a cross-linked viral glycoprotein will allow more rational use of this methodology for vaccine design, and reveals a strategy with promise for eliciting neutralizing antibodies needed for an effective HIV-1 vaccine.
诱导针对具有挑战性的病原体（如 HIV-1）的广谱中和抗体是疫苗设计的主要目标，但可能会受到病毒包膜糖蛋白（Env）构象不稳定的阻碍。化学交联广泛用于疫苗抗原稳定化，但人们对该过程如何影响结构、抗原性和免疫原性知之甚少，其应用仍然完全是经验性的。我们已经解决了交联疫苗抗原的第一个冷冻电镜结构。在与 CD4 结合位点特异性广谱中和抗体（bNAb）Fab 片段复合物中，HIV-1 BG505 SOSIP 可溶性重组 Env 的 4.2 Å 结构揭示了交联如何影响三聚体的关键特性。我们观察到在三聚体顶端的 gp120 单体之间以及三聚体界面处的 gp120 和 gp41 之间存在对应于高度特异性戊二醛（GLA）交联的密度，这些交联对整体三聚体构象几乎没有影响，但对三聚体稳定性和提高 Env 抗原性至关重要。在 gp120 内也观察到与 N241/N289 聚糖孔相关的位点的交联，这些交联局部改变了三聚体的抗原性。在免疫原性研究中，交联三聚体的中和抗体反应对全球困难中和的 Tier-2 异源病毒的广谱性略有增加，但具有显著意义。此外，自体 Tier-2 中和的特异性从 N241/N289 聚糖孔改变，暗示了一种新的特异性。最后，我们首次研究了下一代可溶性三聚体的 T 辅助细胞反应，并报告了交联修饰的 BG505 内与疫苗相关的免疫显性反应。阐明交联病毒糖蛋白的结构相关性将允许更合理地使用该方法进行疫苗设计，并揭示了一种有前途的策略，可诱导中和抗体，从而有效预防 HIV-1。
