Crooks Ema T, Tong Tommy, Chakrabarti Bimal, Narayan Kristin, Georgiev Ivelin S, Menis Sergey, Huang Xiaoxing, Kulp Daniel, Osawa Keiko, Muranaka Janelle, Stewart-Jones Guillaume, Destefano Joanne, O'Dell Sijy, LaBranche Celia, Robinson James E, Montefiori David C, McKee Krisha, Du Sean X, Doria-Rose Nicole, Kwong Peter D, Mascola John R, Zhu Ping, Schief William R, Wyatt Richard T, Whalen Robert G, Binley James M
San Diego Biomedical Research Institute, San Diego, California, United States of America.
International AIDS Vaccine Initiative (IAVI) Neutralizing Antibody Center at The Scripps Research Institute, Department of Immunology and Microbial Science, La Jolla, California, United States of America.
PLoS Pathog. 2015 May 29;11(5):e1004932. doi: 10.1371/journal.ppat.1004932. eCollection 2015 May.
Eliciting broad tier 2 neutralizing antibodies (nAbs) is a major goal of HIV-1 vaccine research. Here we investigated the ability of native, membrane-expressed JR-FL Env trimers to elicit nAbs. Unusually potent nAb titers developed in 2 of 8 rabbits immunized with virus-like particles (VLPs) expressing trimers (trimer VLP sera) and in 1 of 20 rabbits immunized with DNA expressing native Env trimer, followed by a protein boost (DNA trimer sera). All 3 sera neutralized via quaternary epitopes and exploited natural gaps in the glycan defenses of the second conserved region of JR-FL gp120. Specifically, trimer VLP sera took advantage of the unusual absence of a glycan at residue 197 (present in 98.7% of Envs). Intriguingly, removing the N197 glycan (with no loss of tier 2 phenotype) rendered 50% or 16.7% (n = 18) of clade B tier 2 isolates sensitive to the two trimer VLP sera, showing broad neutralization via the surface masked by the N197 glycan. Neutralizing sera targeted epitopes that overlap with the CD4 binding site, consistent with the role of the N197 glycan in a putative "glycan fence" that limits access to this region. A bioinformatics analysis suggested shared features of one of the trimer VLP sera and monoclonal antibody PG9, consistent with its trimer-dependency. The neutralizing DNA trimer serum took advantage of the absence of a glycan at residue 230, also proximal to the CD4 binding site and suggesting an epitope similar to that of monoclonal antibody 8ANC195, albeit lacking tier 2 breadth. Taken together, our data show for the first time that strain-specific holes in the glycan fence can allow the development of tier 2 neutralizing antibodies to native spikes. Moreover, cross-neutralization can occur in the absence of protecting glycan. Overall, our observations provide new insights that may inform the future development of a neutralizing antibody vaccine.
诱导产生广泛的二级中和抗体（nAbs）是HIV-1疫苗研究的主要目标。在此，我们研究了天然的、膜表达的JR-FL Env三聚体诱导产生nAbs的能力。在用表达三聚体的病毒样颗粒（VLPs）免疫的8只兔子中有2只以及在用表达天然Env三聚体的DNA免疫并随后进行蛋白加强免疫（DNA三聚体血清）的20只兔子中有1只产生了异常强效的nAb滴度。所有这3种血清均通过四级表位进行中和，并利用了JR-FL gp120第二个保守区域聚糖防御中的天然间隙。具体而言，三聚体VLP血清利用了197位残基处异常缺失聚糖的情况（98.7%的Env中存在该聚糖）。有趣的是，去除N197聚糖（二级表型无损失）使50%或16.7%（n = 18）的B亚型二级分离株对这两种三聚体VLP血清敏感，显示出通过被N197聚糖掩盖的表面进行广泛中和。中和血清靶向与CD4结合位点重叠的表位，这与N197聚糖在假定的“聚糖屏障”中限制对该区域的 access 的作用一致。一项生物信息学分析表明，一种三聚体VLP血清与单克隆抗体PG9具有共同特征，这与其三聚体依赖性一致。中和性DNA三聚体血清利用了230位残基处聚糖缺失的情况，该残基也靠近CD4结合位点，提示存在一个与单克隆抗体8ANC195类似的表位，尽管缺乏二级广度。综上所述，我们的数据首次表明，聚糖屏障中的菌株特异性漏洞可使针对天然刺突产生二级中和抗体。此外，在没有保护性聚糖的情况下也可发生交叉中和。总体而言，我们的观察结果提供了新的见解，可能为中和抗体疫苗的未来发展提供参考。
