What Do Chaotrope-Based Avidity Assays for Antibodies to HIV-1 Envelope Glycoproteins Measure?
What Do Chaotrope-Based Avidity Assays for Antibodies to HIV-1 Envelope Glycoproteins Measure?
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DOI：
10.1128/jvi.00320-15
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发表时间：
2015-06-01
影响因子：
5.4
通讯作者：
Klasse, Per Johan
中科院分区：
文献类型：
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作者：
Alexander, Marina R.;Ringe, Rajesh;Klasse, Per Johan
当在人类和其他物种中测试包含可溶性包膜糖蛋白（Env）的HIV-1候选疫苗时，对Env产生的抗体应答进行筛选，以确定保护或风险的相关性。一种常用的测定法通过添加离液剂（例如硫氰酸盐）来测量抗体与Env抗原结合的减少。基于该测定，设计了一种亲合力指数，用于评估多克隆血清中未知浓度抗体的亲和力成熟。由于高亲合力指数与HIV-1感染动物模型中的保护作用有关，因此它已成为评价对候选疫苗的抗体应答的标准。但是这种检测方法测量的是什么，亲合力指数又意味着什么呢？在这里，我们使用了一组针对Env上明确定义的表位（gp 120、gp 41和SOSIP）的单克隆抗体。664三聚体）以探索离液剂如何起作用。我们的结论是，离液剂的抗体结合Env的敏感性取决于几个属性的表位（连续性与三级和四级结构的依赖性），并且抗体的亲和力指数没有简单的关系功能Env尖峰病毒粒子上的抗体亲和力。我们表明，广泛中和抗体对四级结构表位的结合是特别敏感的离液剂治疗，而抗体结合可变环中的表位和gp 41中的非中和表位通常是耐药的。由于这种偏差，亲合力指数可能充其量只是一个不确定的抗体或其他免疫反应，弱相关的保护。重要一个有效的HIV-1疫苗是一个重要的目标。这种疫苗可能需要诱导抗体来中和HIV-1的典型传播变体，防止它们感染靶细胞。到目前为止，候选疫苗未能诱导这种抗体反应，尽管有些疫苗确实对动物（可能还有人类）的感染有微弱的保护作用。在寻找与保护相关的反应时，通常使用基于化学破坏的亲合力测定来测量抗体结合的强度。我们已经从机理上分析了该测定，发现抗体的表位特异性对结果的影响大于其亲和力。因此，亲合力测定偏向于检测某些抗体特异性，而不利于其他抗体特异性。我们的结论是，该试验可能产生的只是间接的相关性与弱保护，特别是当Env疫苗接种未能诱导广泛的中和反应。
When HIV-1 vaccine candidates that include soluble envelope glycoproteins (Env) are tested in humans and other species, the resulting antibody responses to Env are sifted for correlates of protection or risk. One frequently used assay measures the reduction in antibody binding to Env antigens by an added chaotrope (such as thiocyanate). Based on that assay, an avidity index was devised for assessing the affinity maturation of antibodies of unknown concentration in polyclonal sera. Since a high avidity index was linked to protection in animal models of HIV-1 infection, it has become a criterion for evaluating antibody responses to vaccine candidates. But what does the assay measure and what does an avidity index mean? Here, we have used a panel of monoclonal antibodies to well-defined epitopes on Env (gp120, gp41, and SOSIP. 664 trimers) to explore how the chaotrope acts. We conclude that the chaotrope sensitivity of antibody binding to Env depends on several properties of the epitopes (continuity versus tertiary-and quaternary-structural dependence) and that the avidity index has no simple relationship to antibody affinity for functional Env spikes on virions. We show that the binding of broadly neutralizing antibodies against quaternary-structural epitopes is particularly sensitive to chaotrope treatment, whereas antibody binding to epitopes in variable loops and to nonneutralization epitopes in gp41 is generally resistant. As a result of such biases, the avidity index may at best be a mere surrogate for undefined antibody or other immune responses that correlate weakly with protection.IMPORTANCEAn effective HIV-1 vaccine is an important goal. Such a vaccine will probably need to induce antibodies that neutralize typically transmitted variants of HIV-1, preventing them from infecting target cells. Vaccine candidates have so far failed to induce such antibody responses, although some do protect weakly against infection in animals and, possibly, humans. In the search for responses associated with protection, an avidity assay based on chemical disruption is often used to measure the strength of antibody binding. We have analyzed this assay mechanistically and found that the epitope specificity of an antibody has a greater influence on the outcome than does its affinity. As a result, the avidity assay is biased toward the detection of some antibody specificities while disfavoring others. We conclude that the assay may yield merely indirect correlations with weak protection, specifically when Env vaccination has failed to induce broad neutralizing responses.