Intervention of immune tolerance by small molecules to enhance immune therapy

描述(由申请人提供)：越来越多的证据表明，具有抑制表型的宿主免疫细胞对成功的癌症免疫增强治疗构成了重大障碍。在抑制细胞中，T调节细胞(Tregs)和髓系来源的抑制细胞(MDSCs)在晚期恶性肿瘤患者中显著增加。以前，我们发现各种肿瘤的生长导致荷瘤小鼠的肿瘤、脾和骨髓中的MDSC数量显著增加。更有趣的是，我们已经证明，MDSC可以通过诱导T细胞无能和在体外和荷瘤小鼠中发展Treg来介导肿瘤特异性T细胞反应的抑制。这些结果提供了强有力的证据，证明MDSC在肿瘤特异性耐受的建立和肿瘤宿主Treg的发展中具有体内免疫调节功能。为了获得持久的抗肿瘤免疫，提高免疫调节治疗的疗效，必须克服和研究肿瘤诱导的免疫抑制。我们的初步结果表明，肿瘤细胞表达的cKit配体(干细胞因子)可能是MDSC在荷瘤小鼠体内积累所必需的，阻断cKit配体/cKit受体的相互作用可以防止Treg的发展，并逆转MDSC诱导的耐受。我们假设：1)通过使用小分子抑制剂靶向药物干扰c-kit受体信号转导，可以防止MDSCs的积聚和Treg抑制，从而提高免疫基础治疗的疗效；2)阻断cKit受体酪氨酸激酶激活途径可以刺激晚期恶性肿瘤小鼠的Th1反应，防止T细胞耐受和Th2极化；3)通过阻断cKit的信号通路，可以调节肿瘤微环境中建立免疫耐受所需的白细胞亚群。本研究将致力于三个具体目标：1)研究受体酪氨酸激酶抑制剂对荷瘤小鼠MDSC蓄积、MDSC介导的Treg发育和抑制功能Treg的影响；2)研究在晚期结肠癌模型中，III类受体酪氨酸激酶抑制剂可以破坏免疫耐受的潜在机制和细胞类型；3)研究小分子抑制剂对肿瘤患者MDSC、Treg扩张和免疫耐受的影响。这些研究的成功完成将有助于更好地了解这些小化合物的作用机制和免疫耐受，从而可能为干预肿瘤相关免疫抑制找到新的靶点。这些信息将被用作开发一种新的治疗方式的科学基础，这种治疗方式可以抵消与晚期恶性肿瘤相关的免疫抑制。免疫耐受的消除将显著提高现有基于免疫的治疗晚期转移性结直肠癌的疗效。公共卫生相关性：该项目的目标是1)研究药物抑制肿瘤因子信号转导是否可以防止MDSC聚集并干预MDSC的抑制活动；(2)确定小分子介导的阻断Treg扩增和逆转T细胞耐受所涉及的潜在机制和细胞因子和细胞亚群。将评估通过使用受体酪氨酸激酶抑制剂来调节抑制功能的治疗潜力，以补充现有用于治疗晚期大型肿瘤的基于免疫的策略；(3)研究酪氨酸激酶抑制剂(格列卫和舒坦)对癌症患者MDSC抑制活性和抗肿瘤反应的影响。

DESCRIPTION (provided by applicant): A growing body of evidence suggests that host immune cells with a suppressive phenotype pose a significant hurdle to successful immune enhancing therapy for cancer. Among the suppressor cells, T regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs) have been shown to increase significantly in hosts with advanced malignancies. Previously, we found that the growth of various carcinomas induced a significant increase in the numbers of MDSC in tumor, spleen, and bone marrow of tumor-bearing mice. More interestingly, we have demonstrated that MDSC can mediate the suppression of the tumor-specific T-cell response through the induction of T-cell anergy and the development of Treg in vitro and in tumor-bearing mice. These results provide strong evidence of an in vivo immunoregulatory function of MDSC in the establishment of tumor-specific tolerance and the development of Treg in tumor-bearing hosts. To achieve persistent anti- tumor immunity and to improve the therapeutic effect of immunomodulatory treatments, the tumor-induced immunosuppression must be overcome and investigated. Our preliminary results indicate that ckit ligand (stem cell factor) expressed by tumor cells may be required for MDSC accumulation in tumor bearing mice and that blocking the ckit ligand/ckit receptor interaction can prevent the development of Treg and reverse tolerance induced by MDSC. We hypothesize that: 1) Targeted pharmacological disruption of c-kit receptor signaling by using small molecule inhibitors can prevent the accumulation of MDSCs and Treg suppression, thereby increasing the therapeutic efficacy of immune-based therapy; 2) Disruption of ckit receptor tyrosine kinase activation pathway can stimulate Th1 responses and prevent T-cell tolerance and Th2 polarization in mice with advanced malignancies; 3) Leukocyte subsets required for the establishment of immune tolerance in tumor microenvironment can be modulated by blocking the signaling pathways of ckit. Three specific aims will be pursued: 1) To study the effect of receptor tyrosine kinase inhibitors on MDSC accumulation, MDSC-mediated Treg development, and suppressive function Treg in mice with large tumor burdens; 2) To study the underlying mechanisms and cell types that are involved in the immune tolerance, which can be disrupted by class III receptor tyrosine kinase inhibitors in advanced murine colon tumor models; 3) To study the effect of small molecule inhibitors on the expansion of MDSC, Treg, and immune tolerance in treated cancer patients. Successful completion of these studies will result in a better understanding of the mechanisms of action by these small compounds and immune tolerance, which may lead to the discovery of novel targets for the intervention in tumor-associated immunosuppression. The information will be utilized as the scientific foundation for the development of a novel therapeutic modality that can counteract the immune suppression associated with advanced malignancy. The ablation of immune tolerance should significantly augment the efficacy of existing immune-based therapies for treatment of advanced metastatic colorectal carcinomas. PUBLIC HEALTH RELEVANCE: The goal of this project is 1) To investigate whether pharmacological inhibition of signaling of tumor factors can prevent MDSC accumulation and can intervene with the suppressive activities of MDSC; (2) To identify the underlying mechanisms and cytokines and cell subsets that are involved in small molecule-mediated blockade of Treg expansion and reversion of T-cell tolerance. The therapeutic potential of modulating the suppressive functions through the use of receptor tyrosine kinase inhibitors to complement existing immune based strategies for treating advanced large tumors will be evaluated; (3) To study the effect of tyrosine kinase inhibitors (Gleevec and Sutent) on MDSC suppressive activities and anti-tumor responses in cancer patients.