Human antibody responses to HIV type 1 glycoprotein 41 cloned in phage display libraries suggest three major epitopes are recognized and give evidence for conserved antibody motifs in antigen binding

A large panel of human Fab fragments against the gp41 subunit of the HIV-1 envelope glycoprotein was isolated by panning six phage-displayed antibody libraries against recombinant gp41. The libraries were prepared from HIV-1-seropositive donors, Twenty-three Fabs recognizing conformation-dependent determinants on gp41 were isolated, Further selection of libraries against (1) gp41 ligated with Fabs from the initial selection and against (2) a recombinant gp41-containing gp140 protein yielded five additional Fabs, Competition of members of the Fab panel with one another and with previously described antibodies revealed a series of overlapping specificities that were conveniently grouped into three major epitope clusters. The majority of Fabs recognized epitopes involving residues 649-668 (previously known as the cluster II region), numbered using the Los Alamos LAI sequence, A second set of Fabs reacted with an epitope involving residues 584-609 (known as the cluster I region), Another set of Fabs appeared to recognize a third conformational epitope that has been termed the cluster III region. This third Fab epitope group demonstrated some overlap with both clusters I and II in binding assays, None of the Fabs neutralized HIV-1 laboratory strains at biologically significant concentrations, This tends to support the opinion that a vaccine based on the gp41 molecule has the drawback that neutralizing epitopes of gp41 are rare and/or unfavorably presented to the immune system, Analysis of heavy chain sequences revealed common CDR3 motif sequences in several antibodies, which appears to be an interesting consequence of a persistent immune response to conserved antigen structures.

通过用重组gp41对6个噬菌体展示抗体文库进行淘选，分离出了大量针对HIV - 1包膜糖蛋白gp41亚基的人源Fab片段。这些文库是由HIV - 1血清阳性供体制备的。分离出了23种识别gp41上构象依赖性决定簇的Fab。进一步用（1）与初次筛选得到的Fab连接的gp41以及（2）一种含重组gp41的gp140蛋白对文库进行筛选，又得到了5种Fab。Fab组内成员之间以及与先前描述的抗体之间的竞争揭示了一系列重叠的特异性，这些特异性可方便地归为三个主要的表位簇。大多数Fab识别涉及残基649 - 668（先前称为簇II区域，使用洛斯阿拉莫斯LAI序列编号）的表位。第二组Fab与涉及残基584 - 609（称为簇I区域）的表位发生反应。另一组Fab似乎识别第三个构象表位，该表位被称为簇III区域。在结合试验中，这第三组Fab表位与簇I和簇II都有一些重叠。在具有生物学意义的浓度下，没有一种Fab能够中和HIV - 1实验室毒株。这倾向于支持这样一种观点，即基于gp41分子的疫苗存在缺陷，gp41的中和表位很少和/或不利于呈递给免疫系统。对重链序列的分析揭示了几种抗体中常见的CDR3基序序列，这似乎是对保守抗原结构持续免疫应答的一个有趣结果。