Yasmeen Anila, Ringe Rajesh, Derking Ronald, Cupo Albert, Julien Jean-Philippe, Burton Dennis R, Ward Andrew B, Wilson Ian A, Sanders Rogier W, Moore John P, Klasse Per Johan
Department of Microbiology and Immunology, Weill Cornell Medical College, Cornell University, New York, USA.
Retrovirology. 2014 May 29;11:41. doi: 10.1186/1742-4690-11-41.
The trimeric envelope glycoproteins (Env) on the surface of HIV-1 virions are the targets for neutralizing antibodies (NAbs). No candidate HIV-1 immunogen has yet induced potent, broadly active NAbs (bNAbs). Part of the explanation may be that previously tested Env proteins inadequately mimic the functional, native Env complex. Trimerization and the proteolytic processing of Env precursors into gp120 and gp41 profoundly alter antigenicity, but soluble cleaved trimers are too unstable to serve as immunogens. By introducing stabilizing mutations (SOSIP), we constructed soluble, cleaved Env trimers derived from the HIV-1 subtype A isolate BG505 that resemble native Env spikes on virions both structurally and antigenically.
We used surface plasmon resonance (SPR) to quantify antibody binding to different forms of BG505 Env: the proteolytically cleaved SOSIP.664 trimers, cleaved gp120-gp41ECTO protomers, and gp120 monomers. Non-NAbs to the CD4-binding site bound only marginally to the trimers but equally well to gp120-gp41ECTO protomers and gp120 monomers, whereas the bNAb VRC01, directed to the CD4bs, bound to all three forms. In contrast, bNAbs to V1V2 glycan-dependent epitopes bound preferentially (PG9 and PG16) or exclusively (PGT145) to trimers. We also explored the antigenic consequences of three different features of SOSIP.664 gp140 trimers: the engineered inter-subunit disulfide bond, the trimer-stabilizing I559P change in gp41ECTO, and proteolytic cleavage at the gp120-gp41ECTO junction. Each of these three features incrementally promoted native-like trimer antigenicity. We compared Fab and IgG versions of bNAbs and validated a bivalent model of IgG binding. The NAbs showed widely divergent binding kinetics and degrees of binding to native-like BG505 SOSIP.664. High off-rate constants and low stoichiometric estimates of NAb binding were associated with large amounts of residual infectivity after NAb neutralization of the corresponding BG505.T332N pseudovirus.
The antigenicity and structural integrity of cleaved BG505 SOSIP.664 trimers render these proteins good mimics of functional Env spikes on virions. In contrast, uncleaved gp140s antigenically resemble individual gp120-gp41ECTO protomers and gp120 monomers, but not native trimers. Although NAb binding to functional trimers may thus be both necessary and sufficient for neutralization, the kinetics and stoichiometry of the interaction influence the neutralizing efficacy of individual NAbs.
HIV-1病毒粒子表面的三聚体包膜糖蛋白（Env）是中和抗体（NAbs）的作用靶点。尚无候选的HIV-1免疫原能诱导产生强效、广泛活性的中和抗体（bNAbs）。部分原因可能是先前测试的Env蛋白未能充分模拟功能性天然Env复合物。Env前体的三聚化以及其蛋白水解加工成gp120和gp41会深刻改变抗原性，但可溶性裂解三聚体过于不稳定，无法用作免疫原。通过引入稳定突变（SOSIP），我们构建了源自HIV-1 A亚型分离株BG505的可溶性裂解Env三聚体，其在结构和抗原性上均类似于病毒粒子上的天然Env刺突。
我们使用表面等离子体共振（SPR）来定量抗体与不同形式的BG505 Env的结合：蛋白水解裂解的SOSIP.664三聚体、裂解的gp120-gp41ECTO原聚体和gp120单体。针对CD4结合位点的非中和抗体与三聚体的结合很微弱，但与gp120-gp41ECTO原聚体和gp120单体的结合效果相同，而针对CD4bs的bNAb VRC01与所有三种形式均能结合。相比之下，针对V1V2聚糖依赖性表位的bNAb优先（PG9和PG16）或仅（PGT145）与三聚体结合。我们还探究了SOSIP.664 gp140三聚体三个不同特征的抗原后果：工程化的亚基间二硫键、gp41ECTO中稳定三聚体的I559P变化以及gp120-gp41ECTO连接处的蛋白水解裂解。这三个特征中的每一个都逐步促进了类似天然三聚体的抗原性。我们比较了bNAb的Fab和IgG版本，并验证了IgG结合的二价模型。这些中和抗体表现出广泛不同的结合动力学以及与类似天然的BG505 SOSIP.664的结合程度。高解离速率常数和低中和抗体结合化学计量估计值与相应BG505.T332N假病毒被中和抗体中和后大量的残余感染性相关。
裂解的BG505 SOSIP.664三聚体的抗原性和结构完整性使其成为病毒粒子上功能性Env刺突的良好模拟物。相比之下，未裂解的gp140在抗原性上类似于单个gp120-gp41ECTO原聚体和gp120单体，但不像天然三聚体。因此，尽管中和抗体与功能性三聚体的结合可能对于中和既是必要的也是充分的，但相互作用的动力学和化学计量会影响单个中和抗体的中和效力。
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