Target MIC shedding to revive anti-tumor immunity

 描述（由申请方提供）：在对致癌应激的应答中，人上皮细胞表达MHC-I链相关分子MIC，以通过接合自然杀伤（NK）细胞和效应T细胞上表达的活化免疫受体NKG 2D来警告免疫系统。然而，人类癌细胞广泛采用通过脱落表面MIC以产生可溶性MIC（sMIC）来逃避NKG 2D介导的免疫的策略。已经充分证明，sMIC通过下调NK和效应T细胞上的NKG 2D表达对免疫系统造成全面损伤。血清sMIC水平升高与许多癌症类型的疾病分期相关。这些临床观察表明，sMIC可能是癌症治疗靶点。然而，由于啮齿类动物中不存在人MIC同源物的主要障碍，靶向sMIC的概念直到现在还不能进行临床前测试。为了克服这一限制，我们已经产生并表征了“人源化”MIC/TRAMP双转基因小鼠模型，其中人MIC和癌基因在特定组织前列腺中同时表达。TRAMP/MIC小鼠在病理学和免疫学上与人类癌症患者非常相似，因此为我们提供了有效的临床前工具来评估sMIC是否是治疗靶标。利用TRAMP/MIC小鼠模型，我们还发现了新的sMIC免疫抑制作用，其中sMIC干扰肿瘤宿主中的NK细胞维持。在癌症患者中也发现了sMIC的这种免疫抑制作用。我们进一步发现，sMIC刺激诱导NK细胞上的PD-1表达，并且PD-1通过其配体的连接损害体外NK细胞活力。基于这些初步观察，我们假设PD-1表达的上调显著促进了癌症患者中sMIC介导的NK细胞维持的扰动。重要的是，我们已经开发了一种sMIC中和单克隆抗体，我们已经证明其可以有效地恢复宿主NK细胞并增强抗原特异性CD 8 T细胞抗肿瘤应答。基于这些发现，我们进一步假设靶向sMIC和PD-1阻断的组合疗法可以通过释放免疫“检查点”制动并同时重置NK细胞和T细胞免疫“引擎”以同时修复内源性抗肿瘤应答来产生协同抗肿瘤效应。我们计划用三个具体目的来检验我们的假设：1）确定sMIC诱导NK细胞上PD-1表达的机制; 2）描述PD-1信号传导对sMIC+肿瘤宿主中NK细胞稳态的影响和潜在的分子联系; 3）评估PD-1阻断和靶向sMIC在MIC+肿瘤宿主中的组合治疗功效。我们提出的研究不仅将揭示对NKG 2D和NK细胞生物学的新理解，而且将具有重要的和潜在的直接临床意义。 将NKG 2D肿瘤免疫转化为临床实践。

 DESCRIPTION (provided by applicant): In response to oncogenic stress, human epithelial cells express the MHC-I chain related molecule, MIC, to alert the immune system by engaging the activation immune receptor NKG2D expressed on nature killer (NK) cells and effector T cells. However, human cancer cells broadly adopt a strategy to evade NKG2D-mediated immunity by shedding surface MIC to produce soluble MIC (sMIC). It has been well demonstrated that sMIC poses global insults to the immune system by down-regulating NKG2D expression on NK and effect T cells. Elevated serum levels of sMIC correlates with disease stages in many cancer types. These clinical observations suggested that sMIC may be a cancer therapeutic target. However, due to the major obstacle that no human MIC homolog is present in rodents, the concept of targeting sMIC cannot be tested pre-clinically until now. To overcome this limitation, we have generated and characterized a "humanized" MIC/TRAMP bi- transgenic mouse model in which human MIC and the oncogene concurrently expressed in a specific tissue, the prostate. The TRAMP/MIC mice closely resemble human cancer patients pathologically and immunologically and thus provide us with a valid preclinical tool to evaluate whether sMIC is a therapeutic target. With the TRAMP/MIC mouse model, we also uncovered the novel sMIC immune suppressive effect whereby sMIC perturbs NK cell maintenance in tumor host. This immune suppressive effect of sMIC is also found in cancer patients. We further found that sMIC stimulation induces PD-1 expression on NK cells and that ligation of PD-1 by its ligands impairs NK cell viability in vitro. Based on these preliminary observations, we hypothesize that upregulation of PD-1 expression contributes significantly to sMIC-mediated perturbation of NK cell maintenance in cancer patients. Importantly, we have developed a sMIC-neutralizing monoclonal antibody which we have shown to effectively revive host NK cells and potentiate antigen-specific CD8 T cell anti-tumor responses. Based on these findings, we further hypothesize that a combinatory therapy of targeting sMIC and PD-1 blockade can generate synergistic anti-tumor effect through releasing immune "check-point" brake and simultaneously re-setting the NK cell and T cell immunity "the engine" to concurrently revamp endogenous anti-tumor responses. We plan to test our hypothesis with three Specific Aims: 1) To determine the mechanisms whereby sMIC induces PD-1 expression on NK cells; 2) To delineate the impact of PD-1 signaling on NK cell homeostasis in sMIC+ tumor host and the underlying molecular link; 3) To evaluate the combinatory therapeutic efficacy of PD-1 blockade and targeting sMIC in MIC+ tumor host. Our proposed study will not only uncover novel understandings of NKG2D and NK cell biology, but also will have significant and potentially immediate clinical implications in translating NKG2D tumor immunity into clinical practices.