Peking University-Tsinghua University-National Institute of Biological Sciences (PTN) Joint Graduate Program, School of Life Sciences, Peking University, Beijing, China.
National Institute of Biological Sciences (NIBS), Beijing, China.
J Hematol Oncol. 2023 Jan 17;16(1):2. doi: 10.1186/s13045-023-01399-4.
The antiphagocytic molecule CD47 is overexpressed in a wide variety of cancer cells, and antibodies targeting CD47 for cancer therapies are currently under intensive investigation. However, owing to the ubiquitous expression of CD47 on healthy cells, anti-CD47 therapies often achieve only weak therapeutic benefits and can induce severe side effects. Here, we report the generation of a pH-dependent anti-CD47 antibody (BC31M4) which selectively binds to tumors under the acidic solid tumor microenvironment.
BC31M4 was generated using antibody phage display and a pH-dependent selection strategy. The pH-dependent binding and blocking activities of BC31M4 were verified using in vitro assays, and the structural basis of the pH-dependent binding property was characterized. BC31M4's antitumor effect was confirmed by both phagocytosis assays and studies in xenograft models. The tumor selectivity, mechanism of action, PK properties, side effects, and therapeutic efficacy were further evaluated in humanized (hCD47 and its receptor hSIRPα) immunocompetent syngeneic mouse models.
The crystal structure reveals that two histidines locate within the CDRs of the light chain directly contribute to the pH-dependent binding of BC31M4. BC31M4 promotes macrophage phagocytosis of tumor cells more potently at acidic-pH than at physiological-pH. Our hCD47/hSIRPα humanized syngeneic mouse model results demonstrated that BC31M4 selectively accumulates in tumors but not in normal tissues. BC31M4 causes minimal side effects and exhibits superior PK properties as compared to the other examined anti-CD47 antibodies. When combined with adoptive T cell transfer, BC31M4 efficiently promotes adaptive immune responses against tumors and also induces immune memory. Moreover, we show that BC31M4's antitumor effects rely on an Fc that mediates strong effector functions.
Our study illustrates that the development of a tumor-selective, pH-dependent anti-CD47 antibody safely confers strong therapeutic effects against solid tumors, thus providing a promising therapeutic strategy to overcome the challenges of anti-CD47 therapy.
抗吞噬分子 CD47 在多种癌细胞中过表达，针对 CD47 的抗体靶向癌症治疗目前正在深入研究。然而，由于 CD47 在健康细胞上的广泛表达，抗 CD47 疗法通常只能产生微弱的治疗效果，并可能引发严重的副作用。在这里，我们报告了一种 pH 依赖性抗 CD47 抗体（BC31M4）的产生，该抗体在酸性实体瘤微环境下选择性地结合肿瘤。
使用抗体噬菌体展示和 pH 依赖性选择策略生成 BC31M4。使用体外测定法验证了 BC31M4 的 pH 依赖性结合和阻断活性，并对 pH 依赖性结合特性的结构基础进行了表征。通过吞噬测定和异种移植模型研究证实了 BC31M4 的抗肿瘤作用。进一步在人源化（hCD47 及其受体 hSIRPα）免疫活性同基因小鼠模型中评估了肿瘤选择性、作用机制、PK 特性、副作用和治疗效果。
晶体结构表明，两个组氨酸直接位于轻链的 CDR 内，有助于 BC31M4 的 pH 依赖性结合。BC31M4 在酸性 pH 下比在生理 pH 下更有效地促进巨噬细胞吞噬肿瘤细胞。我们的 hCD47/hSIRPα 人源化同基因小鼠模型结果表明，BC31M4 选择性地在肿瘤中积累，而不在正常组织中积累。与其他检查的抗 CD47 抗体相比，BC31M4 引起的副作用最小，PK 特性也更好。当与过继性 T 细胞转移结合使用时，BC31M4 可有效促进针对肿瘤的适应性免疫反应，并诱导免疫记忆。此外，我们表明，BC31M4 的抗肿瘤作用依赖于介导强大效应功能的 Fc。
我们的研究表明，开发一种肿瘤选择性、pH 依赖性的抗 CD47 抗体可以安全地对实体瘤产生强大的治疗效果，从而为克服抗 CD47 治疗的挑战提供了一种有前途的治疗策略。
