Tang Yong, Lou Jianlong, Alpaugh R Katherine, Robinson Matthew K, Marks James D, Weiner Louis M
Department of Medical Oncology, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
J Immunol. 2007 Sep 1;179(5):2815-23. doi: 10.4049/jimmunol.179.5.2815.
Unconjugated mAbs have emerged as useful cancer therapeutics. Ab-dependent cellular cytotoxicity (ADCC) is believed to be a major antitumor mechanism of some anticancer Abs. However, the factors that regulate the magnitude of ADCC are incompletely understood. In this study, we described the relationship between Ab affinity and ADCC. A series of human IgG1 isotype Abs was created from the anti-HER2/neu (also named c-erbB2) C6.5 single-chain Fv (scFv) and its affinity mutants. The scFv affinities range from 10(-7) to 10(-11) M, and the IgG Abs retain the affinities of the scFv from which they were derived. The apparent affinity of the Abs ranged from nearly 10(-10) M (the lowest affinity variant) to almost 10(-11) M (the other variants). The IgG molecules were tested for their ability to elicit ADCC in vitro against three tumor cell lines with differing levels of HER2/neu expression using unactivated human PBMC from healthy donors as the effector cells. The results demonstrated that both the apparent affinity and intrinsic affinity of the Abs studied regulate ADCC. High-affinity tumor Ag binding by the IgGs led to the most efficient and powerful ADCC. Tumor cells expressing high levels of HER2/neu are more susceptible to the ADCC triggered by Abs than the cells expressing lower amounts of HER2/neu. These findings justify the examination of high affinity Abs for ADCC promotion. Because high affinity may impair in vivo tumor targeting, a careful examination of Ab structure to function relationships is required to develop optimized therapeutic unconjugated Abs.
未偶联的单克隆抗体已成为有用的癌症治疗药物。抗体依赖的细胞毒性（ADCC）被认为是某些抗癌抗体的主要抗肿瘤机制。然而，调节ADCC强度的因素尚未完全明确。在本研究中，我们描述了抗体亲和力与ADCC之间的关系。从抗HER2/neu（也称为c-erbB2）C6.5单链Fv（scFv）及其亲和力突变体中构建了一系列人IgG1同种型抗体。scFv的亲和力范围为10^(-7)至10^(-11) M，IgG抗体保留了其来源的scFv的亲和力。抗体的表观亲和力范围从接近10^(-10) M（最低亲和力变体）到几乎10^(-11) M（其他变体）。使用来自健康供体的未激活人外周血单核细胞（PBMC）作为效应细胞，测试了IgG分子在体外对三种HER2/neu表达水平不同的肿瘤细胞系引发ADCC的能力。结果表明，所研究抗体的表观亲和力和内在亲和力均调节ADCC。IgG与高亲和力肿瘤抗原的结合导致最有效和强大的ADCC。表达高水平HER2/neu的肿瘤细胞比表达较低水平HER2/neu的细胞更容易受到抗体触发的ADCC的影响。这些发现证明了检查高亲和力抗体以促进ADCC的合理性。由于高亲和力可能损害体内肿瘤靶向性，因此需要仔细研究抗体结构与功能的关系，以开发优化的治疗性未偶联抗体。
