Protein Interactions Group, Center for Cancer Research Nanobiology Program, National Cancer Institute, National Institutes of Health, Frederick, Maryland 21702, USA.
MAbs. 2009 Jan-Feb;1(1):26-8. doi: 10.4161/mabs.1.1.7480.
Currently, almost all FDA approved therapeutic antibodies (except ReoPro, Lucentis and Cimzia which are Fabs), and the vast majority of those in clinical trials are full-size antibodies mostly in IgG1 format of about 150 kDa size. A fundamental problem for such large molecules is their poor penetration into tissues (e.g., solid tumors) and poor or absent binding to regions on the surface of some molecules (e.g., on the HIV envelope glycoprotein) which are fully accessible only by molecules of smaller size. Therefore, much work especially during the last decade has been aimed at developing novel scaffolds of much smaller size and high stability. Here I briefly describe a proposition to use the immunoglobulin (Ig) constant CH2 domain (CH3 for IgE and IgM) as a scaffold. CH2 is critical for the Ig effector functions. Isolated CH2 is stable monomer in contrast to all other constant domains and most of the variable domains. CH2 and engineered CH2 domains with improved stability can be used as scaffolds for construction of libraries containing diverse binders to various antigens. Such binders based on a CH2 scaffold could also confer some effector functions. Because the CH2 domains are the smallest independently folded antibody domains that can be engineered to contain simultaneously antigen-binding sites and binding sites mediating effector and stability functions, and to distinguish them from domain antibodies which are used to denote engineered VH or VL domains or nanobodies which are used to denote camelid VHH, I termed them nanoantibodies (nAbs).
目前，几乎所有获得美国食品药品监督管理局批准的治疗性抗体（除了 ReoPro、Lucentis 和 Cimzia，它们是 Fab 片段），以及临床试验中绝大多数的抗体都是全尺寸抗体，主要为约 150 kDa 大小的 IgG1 形式。对于这种大型分子来说，一个根本问题是它们在组织中的渗透能力差（例如实体瘤），并且与某些分子表面的区域（例如 HIV 包膜糖蛋白）的结合能力差或不存在，而这些区域只有较小尺寸的分子才能完全进入。因此，在过去十年中，人们进行了大量工作，旨在开发更小尺寸和更高稳定性的新型支架。在这里，我简要描述了一个使用免疫球蛋白（Ig）恒定 CH2 结构域（IgE 和 IgM 的 CH3）作为支架的建议。CH2 对于 Ig 的效应功能至关重要。与所有其他恒定结构域和大多数可变结构域相比，分离的 CH2 是稳定的单体。具有改进稳定性的 CH2 和工程化 CH2 结构域可用作包含针对各种抗原的各种结合物的文库的支架。基于 CH2 支架的这些结合物也可以赋予一些效应功能。由于 CH2 结构域是可以工程化以同时包含抗原结合位点和介导效应和稳定性功能的结合位点的最小独立折叠的抗体结构域，并且可以将它们与用于表示工程化 VH 或 VL 结构域的域抗体以及用于表示骆驼科 VHH 的纳米抗体区分开来，因此我将它们称为纳米抗体（nAbs）。
