Target MIC shedding to revive anti-tumor immunity

 描述(申请人提供)：为了应对致癌压力，人类上皮细胞表达MHC-I链相关分子MIC，通过与自然杀伤(NK)细胞和效应器T细胞上表达的激活免疫受体NKG2D结合来警告免疫系统。然而，人类癌细胞普遍采用一种策略来逃避NKG2D介导的免疫，即通过脱落表面MIC来产生可溶性MIC(SMIC)。已有证据表明，中芯国际通过下调NK细胞表面NKG2D的表达，影响T细胞的功能，从而对免疫系统造成全球性的侮辱。在许多癌症类型中，血清SMIC水平升高与疾病分期相关。这些临床观察表明，中芯国际可能是癌症治疗的靶点。然而，由于啮齿动物体内没有人类MIC同源物这一主要障碍，靶向中芯国际的概念直到现在才能在临床前进行测试。为了克服这一局限性，我们建立并鉴定了一种人源化的MIC/TRAMP双转基因小鼠模型，在该模型中，人的MIC和癌基因在特定的组织--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，因此为我们提供了一种有效的临床前工具来评估SMIC是否为治疗靶点。在TRAMP/MIC小鼠模型中，我们还发现了SMIC干扰肿瘤宿主NK细胞维持的新的免疫抑制作用。中芯国际的这种免疫抑制作用也存在于癌症患者身上。我们进一步发现SMIC刺激可诱导NK细胞上PD-1的表达，而PD-1与其配体的连接会在体外损害NK细胞的活性。基于这些初步观察，我们假设PD-1的表达上调在SMIC介导的癌症患者NK细胞维持的扰动中起重要作用。重要的是，我们已经开发了一种SMIC中和单抗，我们已经证明它可以有效地激活宿主NK细胞，并增强抗原特异性的CD8T细胞抗肿瘤反应。基于这些发现，我们进一步假设，靶向中芯国际和PD-1拮抗剂的联合治疗可以通过释放免疫“检查点”刹车，同时重新设置NK细胞和T细胞免疫“引擎”来同时重塑内源性抗肿瘤反应，从而产生协同抗肿瘤效应。我们计划通过三个具体的目标来验证我们的假设：1)确定中芯国际诱导NK细胞表达PD-1的机制；2)描述PD-1信号对中芯国际肿瘤宿主NK细胞稳态的影响及其潜在的分子联系；3)评估PD-1阻断和靶向中芯国际在MIC肿瘤宿主中的联合治疗效果。我们提出的研究不仅将揭示对NKG2D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NKG2D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.