Protein Interactions Group, Center for Cancer Research Nanobiology Program, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA.
Viruses. 2009 Dec;1(3):802-17. doi: 10.3390/v1030802. Epub 2009 Nov 6.
Several human monoclonal antibodies (hmAbs) and antibody fragments, including the best characterized in terms of structure-function b12 and Fab X5, exhibit relatively potent and broad HIV-1 neutralizing activity. However, the elicitation of b12 or b12-like antibodies in vivo by vaccine immunogens based on the HIV-1 envelope glycoprotein (Env) has not been successful. B12 is highly divergent from the closest corresponding germline antibody while X5 is less divergent. We have hypothesized that the relatively high degree of specific somatic hypermutations may preclude binding of the HIV-1 envelope glycoprotein (Env) to closest germline antibodies, and that identifying antibodies that are intermediates in the pathways to maturation could help design novel vaccine immunogens to guide the immune system for their enhanced elicitation. In support of this hypothesis we have previously found that a germline-like b12 (monovalent and bivalent scFv as an Fc fusion protein or IgG) lacks measurable binding to an Env as measured by ELISA with a sensitivity in the μM range [1]; here we present evidence confirming and expanding these findings for a panel of Envs. In contrast, a germline-like scFv X5 bound Env with high (nM) affinity. To begin to explore the maturation pathways of these antibodies we identified several possible b12 intermediate antibodies and tested their neutralizing activity. These intermediate antibodies neutralized only some HIV-1 isolates and with relatively weak potency. In contrast, germline-like scFv X5 neutralized a subset of the tested HIV-1 isolates with comparable efficiencies to that of the mature X5. These results could help explain the relatively high immunogenicity of the coreceptor binding site on gp120 and the abundance of CD4-induced (CD4i) antibodies in HIV-1-infected patients (X5 is a CD4i antibody) as well as the maturation pathway of X5. They also can help identify antigens that can bind specifically to b12 germline and intermediate antibodies that together with Envs could be used as a conceptually novel type of candidate vaccines. Such candidate vaccines based on two or more immunogens could help guiding the immune system through complex maturation pathways for elicitation of antibodies that are similar or identical to antibodies with known properties.
几种人源单克隆抗体（hmAbs）和抗体片段，包括结构功能方面研究最充分的 b12 和 Fab X5，表现出相对较强和广泛的 HIV-1 中和活性。然而，基于 HIV-1 包膜糖蛋白（Env）的疫苗免疫原在体内诱导 b12 或 b12 样抗体尚未成功。B12 与最接近的相应 germline 抗体高度不同，而 X5 则不同。我们假设，相对较高程度的特异性体细胞超突变可能会阻止 HIV-1 包膜糖蛋白（Env）与最接近的 germline 抗体结合，并且鉴定处于成熟途径中的中间体抗体可以帮助设计新型疫苗免疫原，以指导免疫系统增强其诱导。为了支持这一假设，我们之前发现，一种类似 germline 的 b12（单价和二价 scFv 作为 Fc 融合蛋白或 IgG）在 ELISA 中缺乏可测量的与 Env 的结合，其灵敏度在μM 范围内[1]；在这里，我们提供了证据，证实并扩展了这些发现，涉及一组 Envs。相比之下，一种类似 germline 的 scFv X5 与 Env 具有高（nM）亲和力结合。为了开始探索这些抗体的成熟途径，我们鉴定了几种可能的 b12 中间体抗体，并测试了它们的中和活性。这些中间抗体仅中和了一些 HIV-1 分离株，并且中和活性相对较弱。相比之下，类似 germline 的 scFv X5 以与成熟 X5 相当的效率中和了一部分测试的 HIV-1 分离株。这些结果可以帮助解释 gp120 上的共受体结合位点和 HIV-1 感染患者中 CD4 诱导（CD4i）抗体的相对高免疫原性（X5 是一种 CD4i 抗体）以及 X5 的成熟途径。它们还可以帮助鉴定能够特异性结合 b12 germline 和中间体抗体的抗原，这些抗体与 Envs 一起可作为一种新型候选疫苗。这种基于两种或更多免疫原的候选疫苗可以帮助引导免疫系统通过复杂的成熟途径，诱导具有已知特性的类似或相同的抗体。
