Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Proc Natl Acad Sci U S A. 2010 Oct 19;107(42):17880-7. doi: 10.1073/pnas.1004728107. Epub 2010 Sep 27.
Elicitation of antibodies against targets that are immunorecessive, cryptic, or transient in their native context has been a challenge for vaccine design. Here we demonstrate the elicitation of structure-specific antibodies against the HIV-1 gp41 epitope of the broadly neutralizing antibody 2F5. This conformationally flexible region of gp41 assumes mostly helical conformations but adopts a kinked, extended structure when bound by antibody 2F5. Computational techniques were employed to transplant the 2F5 epitope into select acceptor scaffolds. The resultant "2F5-epitope scaffolds" possessed nanomolar affinity for antibody 2F5 and a range of epitope flexibilities and antigenic specificities. Crystallographic characterization of the epitope scaffold with highest affinity and antigenic discrimination confirmed good to near perfect attainment of the target conformation for the gp41 molecular graft in free and 2F5-bound states, respectively. Animals immunized with 2F5-epitope scaffolds showed levels of graft-specific immune responses that correlated with graft flexibility (p < 0.04), while antibody responses against the graft-as dissected residue-by-residue with alanine substitutions-resembled more closely those of 2F5 than sera elicited with flexible or cyclized peptides, a resemblance heightened by heterologous prime-boost. Lastly, crystal structures of a gp41 peptide in complex with monoclonal antibodies elicited by the 2F5-epitope scaffolds revealed that the elicited antibodies induce gp41 to assume its 2F5-recognized shape. Epitope scaffolds thus provide a means to elicit antibodies that recognize a predetermined target shape and sequence, even if that shape is transient in nature, and a means by which to dissect factors influencing such elicitation.
针对在天然环境中免疫原性低、隐匿或短暂的靶标产生抗体一直是疫苗设计的挑战。在这里，我们展示了针对广泛中和抗体 2F5 的 HIV-1 gp41 表位产生结构特异性抗体的方法。gp41 的这个构象灵活区域主要呈现为螺旋构象，但当与抗体 2F5 结合时，它会采取扭曲、伸展的结构。我们采用计算技术将 2F5 表位移植到特定的受体支架上。所得的“2F5 表位支架”对抗体 2F5 具有纳摩尔亲和力，并具有一系列表位柔韧性和抗原特异性。对具有最高亲和力和抗原区分度的表位支架的晶体学表征证实，在游离和 2F5 结合状态下，gp41 分子嫁接体分别很好地接近甚至完美地达到了目标构象。用 2F5 表位支架免疫的动物显示出与嫁接体柔韧性相关的（p < 0.04）的嫁接体特异性免疫反应水平，而针对嫁接体的逐个残基用丙氨酸取代进行分析的抗体反应更类似于 2F5，而不是用柔性或环化肽引发的血清反应，这种相似性通过异源初免-加强得到增强。最后，与由 2F5 表位支架引发的单克隆抗体结合的 gp41 肽的晶体结构揭示了所诱导的抗体使 gp41 采取其被 2F5 识别的形状。因此，表位支架提供了一种产生识别预定靶标形状和序列的抗体的方法，即使该形状在天然环境中是短暂的，并且提供了一种分析影响这种诱导的因素的方法。
