Roben P, Moore J P, Thali M, Sodroski J, Barbas C F, Burton D R
Department of Immunology, Scripps Research Institute, La Jolla, California 92037.
J Virol. 1994 Aug;68(8):4821-8. doi: 10.1128/JVI.68.8.4821-4828.1994.
Six recombinant human Fab fragments that were derived from the same human immunodeficiency virus type 1 (HIV-1)-infected individual and are directed against the CD4 binding site (CD4bs) of the gp120 envelope glycoprotein were studied. A range of neutralizing activity against the HIV-1 (HXBc2) isolate was observed, with Fab b12 exhibiting the greatest potency among the Fabs tested. The neutralizing potency of Fab b12 was better than that of monoclonal whole antibodies directed against the third variable (V3) region of gp120. To explore the basis for the efficient neutralizing activity of b12, the recognition of a panel of HIV-1 gp120 mutants by the six Fabs was studied. The patterns of sensitivity to particular gp120 amino acid changes were similar for all six Fabs to those seen for anti-CD4bs monoclonal antibodies derived from HIV-1-infected individuals by conventional means. In addition, recognition by Fab b12 demonstrated an atypical sensitivity to changes in the V1 and V2 variable regions. Next, the binding of the Fabs to monomeric gp120 and to the envelope glycoprotein complex was examined. Neither the binding properties of the b12 Fab to monomeric gp120 nor the ability of the Fab to compete with soluble CD4 for monomeric gp120 binding appeared to account for the greater neutralizing potency. However, both quantitative and qualitative differences between the binding of b12 and that of less potent Fabs to the cell surface envelope glycoprotein complex were observed. Relative to less potently neutralizing Fabs, Fab b12 exhibited a higher affinity for a subpopulation of cell surface envelope glycoproteins, the conformation of which was best approximated by the mature gp120 glycoprotein. Apparently, subtle differences in the gp120 epitope recognized allow some members of the group of anti-CD4bs antibodies to bind to the functionally relevant envelope glycoprotein complex and to neutralize virus more efficiently.
研究了六种重组人Fab片段，它们来自同一例感染了1型人类免疫缺陷病毒（HIV-1）的个体，且针对gp120包膜糖蛋白的CD4结合位点（CD4bs）。观察到了一系列针对HIV-1（HXBc2）分离株的中和活性，在测试的Fab中，Fab b12表现出最强的效力。Fab b12的中和效力优于针对gp120第三可变区（V3）的单克隆全抗体。为了探究b12高效中和活性的基础，研究了这六种Fab对一组HIV-1 gp120突变体的识别情况。所有六种Fab对特定gp120氨基酸变化的敏感模式与通过传统方法从感染HIV-1的个体中获得的抗CD4bs单克隆抗体的敏感模式相似。此外，Fab b12的识别对V1和V2可变区的变化表现出非典型的敏感性。接下来，检测了这些Fab与单体gp120以及包膜糖蛋白复合物的结合情况。b12 Fab与单体gp120的结合特性以及该Fab与可溶性CD4竞争单体gp120结合的能力似乎都不能解释其更强的中和效力。然而，观察到b12与效力较弱的Fab在与细胞表面包膜糖蛋白复合物结合方面存在定量和定性差异。相对于中和效力较弱的Fab，Fab b12对细胞表面包膜糖蛋白亚群表现出更高的亲和力，其构象最接近成熟的gp120糖蛋白。显然，所识别的gp120表位的细微差异使得抗CD4bs抗体组中的一些成员能够结合到功能相关的包膜糖蛋白复合物上，并更有效地中和病毒。
