Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461.
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461.
Proc Natl Acad Sci U S A. 2017 May 23;114(21):E4223-E4232. doi: 10.1073/pnas.1617941114. Epub 2017 May 8.
Rational modulation of the immune response with biologics represents one of the most promising and active areas for the realization of new therapeutic strategies. In particular, the use of function blocking monoclonal antibodies targeting checkpoint inhibitors such as CTLA-4 and PD-1 have proven to be highly effective for the systemic activation of the human immune system to treat a wide range of cancers. Ipilimumab is a fully human antibody targeting CTLA-4 that received FDA approval for the treatment of metastatic melanoma in 2011. Ipilimumab is the first-in-class immunotherapeutic for blockade of CTLA-4 and significantly benefits overall survival of patients with metastatic melanoma. Understanding the chemical and physical determinants recognized by these mAbs provides direct insight into the mechanisms of pathway blockade, the organization of the antigen-antibody complexes at the cell surface, and opportunities to further engineer affinity and selectivity. Here, we report the 3.0 Å resolution X-ray crystal structure of the complex formed by ipilimumab with its human CTLA-4 target. This structure reveals that ipilimumab contacts the front β-sheet of CTLA-4 and intersects with the CTLA-4:Β7 recognition surface, indicating that direct steric overlap between ipilimumab and the B7 ligands is a major mechanistic contributor to ipilimumab function. The crystallographically observed binding interface was confirmed by a comprehensive cell-based binding assay against a library of CTLA-4 mutants and by direct biochemical approaches. This structure also highlights determinants responsible for the selectivity exhibited by ipilimumab toward CTLA-4 relative to the homologous and functionally related CD28.
利用生物制剂进行免疫反应的合理调节代表了实现新治疗策略的最有前途和最活跃的领域之一。特别是，使用针对 CTLA-4 和 PD-1 等检查点抑制剂的功能阻断单克隆抗体已被证明对系统性激活人体免疫系统以治疗广泛的癌症非常有效。Ipilimumab 是一种针对 CTLA-4 的全人抗体，于 2011 年获得 FDA 批准用于治疗转移性黑色素瘤。Ipilimumab 是 CTLA-4 阻断的同类首创免疫疗法，可显著改善转移性黑色素瘤患者的总生存期。了解这些 mAb 识别的化学和物理决定因素可直接深入了解途径阻断的机制、细胞表面抗原-抗体复合物的组织以及进一步工程亲和力和选择性的机会。在这里，我们报告了 ipilimumab 与其人类 CTLA-4 靶标形成的复合物的 3.0 Å 分辨率 X 射线晶体结构。该结构表明，Ipilimumab 接触 CTLA-4 的前β-折叠并与 CTLA-4:B7 识别表面交叉，表明 ipilimumab 和 B7 配体之间的直接空间重叠是 ipilimumab 功能的主要机制贡献者。通过针对 CTLA-4 突变体文库的全面基于细胞的结合测定和直接生化方法证实了晶体学观察到的结合界面。该结构还突出了导致 ipilimumab 相对于同源且功能相关的 CD28 对 CTLA-4 表现出选择性的决定因素。
