Role of Tspan5 in MHC I antigen presentation and cancer immune evasion

摘要 CD8T淋巴细胞是免疫系统清除癌症和病毒的主要机制 被感染的细胞。CD8T细胞通过识别细胞表面展示的免疫原肽来检测这些异常靶点 MHC I分子。癌症和病毒可以通过抑制MHC I抗原提呈来逃避免疫控制， 使CD8 T淋巴细胞更难检测和杀死这些病理细胞。因此，重要的是要 了解调节抗原提呈的机制以及肿瘤 不规范这些过程--这是这项提案的总体目标。我们的建议是基于我们在 一个Tetraspanin(Tspan5)的无偏正向遗传筛选，它意外地组织MHC I分子在 增强空气刺激CD8 T细胞反应能力的方法。我们的第一个目标将阐明潜在的 这种生物效应的分子机制。这一目标将检验Tspan5组织MHC I的假设 分子进入刺激膜微区，由于大小、MHC I密度和/或掺入 其他关键配体显著提高了抗原呈递的效率。我们的第二个目标将阐明如何、何时 Tspan5-MHC I微区形成的地方。这一目标将检验多肽-MHC I复合体的假设 从多肽负载复合体释放时，被结合到Tspan5免疫刺激微域中 在内质网中，通过与Tspan5和其他Tspan家族成员的特定分子相互作用，然后这些 免疫刺激微区被运输到质膜上并保持在质膜上以供展示。我们的第三个 AIM是基于我们的发现，某些癌症，包括肾细胞癌，显著下调 Tspan 5表达。我们第三个目标背后的假设是，这种Tspan5表达的丧失是 癌症逃脱免疫监视和控制，从而取得进展的途径。这一假设的推论 Tspan5的缺失是影响免疫治疗抵抗的一种机制；因此，Tspan5可能 提供急需的生物标志物，用于识别对免疫治疗无效的患者，还可以 成为潜在的治疗靶点，以恢复对这种治疗的反应。我们的实验方法将使用 临床前模型中等基因Tspan5编辑的肾细胞癌(功能丧失和功能获得) 人源化和野生型小鼠确定Tspan5在肿瘤免疫逃避和对 对人类和小鼠肿瘤进行检查点封锁的免疫治疗。最后，我们将翻译这些 通过研究Tspan5的表达是否是可以预测的生物标记物，在人类癌症患者中的发现 临床课程。我们的假设和拟议实验的可行性得到了强有力的初步支持 数据。综上所述，我们提议的实验将从基本的机械研究出发，这将阐明 潜在的基础和新机制，优化APC刺激T细胞反应的能力，以 临床前和临床研究，这些研究将定义该机制的丧失如何影响癌症的免疫控制 和临床结果。

Abstract CD8 T lymphocytes are the major mechanism by which the immune system eliminates cancers and virally infected cells. CD8 T cells detect these abnormal targets by recognizing immunogenic peptides displayed on MHC I molecules. Cancers and viruses can evade immune control by inhibiting MHC I antigen presentation, making it harder for CD8 T lymphocytes to detect and kill these pathological cells. Therefore, it is important to understand the mechanisms that regulate antigen presentation as well as the mechanisms by which tumors dysregulate these processes - this is the overall goal of this proposal. Our proposal is based on our discovery in an unbiased forward genetic screen of a Tetraspanin (Tspan5) that unexpectedly organizes MHC I molecules in ways that amplify theair ability to stimulate CD8 T cell responses. Our 1st aim will elucidate the underlying molecular mechanisms for this biological effect. This Aim will test the hypothesis that Tspan5 organizes MHC I molecules into stimulatory membrane microdomains that by virtue of size, MHC I density and/or incorporation of other key ligands markedly increases the efficiency of antigen presentation. Our 2nd aim will elucidate how, when and where Tspan5-MHC I microdomains form. This aim will test the hypotheses that peptide-MHC I complexes are incorporated into Tspan5 immunostimulatory microdomains upon release from the peptide-loading complex in the ER, through specific molecular interactions with Tspan5 and other Tspan family members, and then these immunostimulatory microdomains are trafficked to and maintained on the plasma membrane for display. Our 3rd Aim is based on our finding that certain cancers, including renal cell carcinomas, significantly downregulate Tspan 5 expression. The hypothesis underlying our 3rd Aim is that this loss of expression of Tspan5 is one of the ways that cancers escape immune surveillance and control and thereby progress. A corollary of this hypothesis is that the loss of Tspan5 is a mechanism that will influence resistance to immunotherapy; as such, Tspan5 could provide a much-needed biomarker for identifying patients who will not respond to immunotherapy and could also be a potential therapeutic target to restore responses to such therapy. Our experimental approach will use isogenic Tspan5-edited renal cell cancers (loss of function and gain of function) in preclinical models with humanized and wild type mice to define the role of Tspan5 in tumor immune evasion and responsiveness to immunotherapy with checkpoint blockade for both human and mouse tumors. Finally, we will translate these findings into human cancer patients by investigating whether Tspan5 expression is a biomarker that can predict clinical course. Our hypotheses and feasibility of the proposed experiments are supported by strong preliminary data. Taken together, our proposed experiments will go from basic mechanistic studies, which will elucidate a potentially fundamental and novel mechanism for optimizing the ability of APCs to stimulate T cell responses, to preclinical and clinical studies, which will define how loss of this mechanism affects immune control of cancers and clinical outcomes.