Promoting immunity against acute myeloid leukemia through Fc effector-optimized antibody inhibitory of MICA/B shedding

摘要 急性髓系白血病(AML)是一种克隆性的造血干/祖细胞恶性肿瘤，其特征是 临床结果不佳。恶性转化触发表面蛋白的表达，这些蛋白起到了“危险”的作用 信号“，如MICA和MICB(MICA/B)，通常由白血病细胞表达 细胞应激途径。自然杀伤细胞和细胞毒T淋巴细胞识别MICA/B的NKG2D 受体，进而诱导对白血病细胞的细胞毒作用。然而，他们经常逃脱 通过一种有趣的翻译后修饰，称为蛋白质分解切割，脱落MICA/B进行识别。在……里面 在之前的革命性研究中，我们开发了一系列针对MICA/B的单抗，可以抑制 MICA/B通过二硫键异构酶阻断经历解折叠的胞外结构域而脱落， 这使得随后可以被金属蛋白水解酶切割。其中一个被进一步表征，它 通过NKG2D和Fc受体的双重信号转导促进NK细胞介导的实体瘤免疫。 最近，我们发现，在AML模型中，该抗体还通过以下方式促进巨噬细胞驱动的免疫 使血液和骨髓中的白血病细胞能够依靠抗体吞噬。在这种情况下， MICA/B作为Fc受体驱动免疫的“白血病抗原”，尽管NKG2D、NK 细胞和T细胞也检测到。现在我们开发了这种抗体的新版本，有三个点 Fc结构域突变以增加与所有三种Fc激活受体的结合亲和力，同时保持 对Fc抑制受体亲和力低。这种新的版本是人源化的，可以诱导出强大的NK细胞效应器 与人源化野生型版本相比，它具有抗人类AML细胞的功能。我们还建立了小鼠 人Fc受体生物学模型及小鼠和人AML模型的建立及其抗白血病作用 我们现在增强的分子在体内的活性。此外，我们提出了一种机制驱动的药物组合 组蛋白脱乙酰酶抑制剂(罗米非辛)诱导人白血病细胞表达MICA/B的方案 然后被翻译成MICA/B蛋白的mRNA，随后通过以下方式稳定在细胞表面 我们的抗体可以抑制脱落。我们认为急性髓系白血病的免疫治疗可以通过这种药物来实现。 联合，增加白血病细胞的天然免疫原性。出于这些原因，我们的研究将 生成有关如何诱导对AML的保护性免疫的重要信息。抗体介导 抑制MICA/B脱落是我们开创的一种新的免疫治疗机会，现已得到验证 由多家制药公司独立进行，其中一家最近已开始I期临床试验 在晚期实体肿瘤患者身上测试一种与我们类似的抗体，但是野生型。因此， 我们的研究将产生令人信服的理由，在AML试验中通过药物测试MICA/B靶向抗体 公司、我们自己在学术界，或者两者都通过合作来实现。

SUMMARY Acute myeloid leukemia (AML) is a clonal hematopoietic stem and progenitor cell malignancy characterized by poor clinical outcomes. Malignant transformation triggers expression of surface proteins that serve as “danger signals”, such as MICA and MICB (MICA/B) that are commonly expressed by leukemia cells in response to cellular stress pathways. Natural killer (NK) cells and cytotoxic T lymphocytes recognize MICA/B with the NKG2D receptor, which in turn induces cytotoxic functions against leukemia cells. However, they often escape recognition by shedding MICA/B via an intriguing post-translational modification called proteolytic cleavage. In previous and revolutionary study, we developed a series of MICA/B-targeted monoclonal antibodies that inhibit the shedding of MICA/B by blocking the extracellular domain that undergoes an unfolding by disulfide isomerase, which enables subsequent cleavage by metalloproteases. One of them was further characterized, and it promotes NK cell-mediated immunity against solid tumors by dual signaling of NKG2D and Fc receptors. Recently, we discovered that the antibody also promotes macrophage-driven immunity in AML models, by enabling antibody-dependent phagocytosis of leukemia cells in the blood and bone marrow. In this setting, MICA/B serve as “leukemia antigens” for Fc receptor-driven immunity, although contributions by NKG2D, NK cells, and T cells were also detected. Now we developed a new version of this antibody, with three point mutations in the Fc domain to increase the binding affinity to all three Fc activating receptors while maintaining low affinity to the Fc inhibitory receptor. This new version is humanized and induces potent NK cell effector functions against human AML cells, compared to the humanized wild type version. We also established mouse models of human Fc receptor biology and both murine and human AML models, to establish the anti-leukemia activity of our now enhanced molecule in vivo. Furthermore, we propose a mechanism-driven drug combination regimen, whereby a histone deacetylase inhibitor (romidepsin) induces human leukemia cells to express MICA/B mRNAs that are then translated to MICA/B proteins, which are followed by stabilization on cellular surface by our antibody that inhibits the shedding. We propose that immunotherapy for AML can be achieved via this drug combination, which increases the innate immunogenicity of leukemia cells. For these reasons, our studies will generate important information about how to induce protective immunity against AML. Antibody-mediated inhibition of MICA/B shedding is a new immunotherapeutic opportunity pioneered by us and now validated independently by multiple pharmaceutical companies, one of which has recently began phase-I clinical trial testing an antibody analog to ours, but the wild type version, in patients with advanced solid tumors. Therefore, our studies will generate compelling rationale to test MICA/B-targeted antibodies in AML trials, by pharmaceutical companies, ourselves in academia, or both by working in collaboration.