Development and specificity of endogeneous tumor-infiltrating regulatory T cells

描述(由申请人提供)：Foxp3+调节性T细胞(“Treg”)对于调节免疫稳态、器官特异性耐受和炎症至关重要。由于Tregs在免疫调节中的核心作用，以及Tregs在多种人类癌症中的流行，许多新出现的治疗策略将重点放在调节或耗尽Tregs与疫苗注射的同时，以努力激发有效的抗肿瘤免疫反应。然而，对肿瘤浸润性树突状细胞的发育起源、特异性和原位功能知之甚少。到目前为止，对肿瘤相关抗原反应的Foxp3+Tregs的研究一直依赖于模型外源抗原在肿瘤细胞上的异位表达。然而，由于Treg识别的自然抗原是未知的，这些实验系统可能不能正确地概括Treg生物学的几个基本方面。因此，为了了解肿瘤相关Treg的真实性质，开发新的系统来直接分析内源性的抗原特异性Treg群体是至关重要的。在我们正在进行的工作中，我们已经确定了一个自然产生的表达保守TCR的Foxp3+Tregs群体。通过在前列腺癌小鼠中进行抗原驱动的选择，这种特异性的细胞将被称为“RT3”T细胞，并产生了表达这种RT3“Treg TCR”的转基因小鼠，这一点高度丰富。这项建议的总体目标是了解内源性RT3 Treg反应的发育、谱系可塑性和“特异性”。我们的中心假设是，RT3T细胞是在胸腺中发育的“天然”Foxp3+Tregs，这些Tregs对共同的抗原和共同的刺激做出反应，这些Tregs不是前列腺癌所特有的。为了解决这一假设，我们将使用互补的方法：a)分析纯化的TCR转基因细胞在转移到荷瘤宿主后的发育、分化和稳定性，以及b)对规范的RT3 TCR进行量化？用“深度”TCR测序法测定荷瘤小鼠内源性T细胞亚群的转录。我们计划测试我们的中心假设，并通过追求以下三个具体目标来实现此应用程序的目标。在目标1中，我们将验证这样的假设，即在荷瘤小鼠中，由于Foxp3+Treg分化为Foxp3neg细胞，具有相同RT3特异性的Foxp3neg效应T细胞和Foxp3+Tregs同时发育。在目标2中，我们将验证这样的假设：Foxp3+rt3Tregs是在胸腺发育的一群“天然”Tregs，通过抗原驱动的选择在前列腺癌中高度丰富。最后，在目标3中，我们将测试这一假设，即RT3Tregs不是前列腺癌特异性的，而是对共同的抗原和共同的刺激有反应。这些目标的完成将提供对调节性T细胞生物学的基本见解，这将指导旨在通过选择性调节或耗尽肿瘤相关Tregs来诱导癌症消退的治疗策略的发展。

DESCRIPTION (provided by applicant): Foxp3+ regulatory T cels ("Tregs") are critical for the regulation of immune homeostasis, organ-specific tolerance, and inflammation. Because of the central role of Tregs in immune modulation, and the prevalence of Tregs in various human cancers, many emerging therapeutic strategies have focused on the modulation or depletion of Tregs concomitant with vaccine administration, in an effort to stimulate effective anti-tumor immune responses. However, little is known about the developmental origins, specificity, and in situ function of tumor-infiltrating Tregs. To date, studies of Foxp3+ Tregs reactive to tumor-associated antigens have relied on the ectopic expression of model foreign antigens on tumor cells. However, since the natural antigens recognized by Tregs are unknown, these experimental systems may not correctly recapitulate several fundamental aspects of Treg biology. Therefore, in order to understand the true nature of tumor-associated Tregs, it is paramount to develop novel systems by which to directly analyze endogenous, antigen-specific Treg populations. In our ongoing work, we have identified a population of naturally occurring Foxp3+ Tregs expressing a conserved TCR?? that is highly enriched by antigen-driven selection in mice with prostate cancer (hereafter, cells of this specificity will be referred to as "RT3" T cells), and generated transgenic mice expressing this RT3 "Treg TCR". The overall objective of this proposal is to understand the development, lineage plasticity, and "specificity" of the endogenous RT3 Treg response. It is our central hypothesis that RT3 T cells are "natural" Foxp3+ Tregs that develop in the thymus, and that these Tregs are responsive to shared antigens and common stimuli that are not specific to prostate cancer. To address this hypothesis, we will use complementary approaches: a) analysis of the development, differentiation, and stability of purified TCR transgenic cell populations following transfer into tumor-bearing hosts, and b) quantification of canonical RT3 TCR? transcripts in endogenous T cell subsets from tumor-bearing mice using "deep" TCR sequencing. We plan to test our central hypothesis and accomplish the objectives of this application by pursuing the following three specific aims. In Aim 1, we will test the hypothesis that Foxp3neg effector T cells and Foxp3+ Tregs of the same RT3 specificity develop concurrently in tumor-bearing mice, as a result of Foxp3+ Treg differentiation into Foxp3neg cells. In Aim 2, we will test the hypothesis that Foxp3+ RT3 Tregs are a population of "natural" Tregs that develop in the thymus, and are highly enriched in prostate tumors by antigen-driven selection. Finally, in Aim 3, we will test the hypothesis that RT3 Tregs are not prostate cancer-specific, but are instead responsive to shared antigens and common stimuli. Completion of these aims will provide fundamental insight into the biology of regulatory T cells, which will guide the development of therapeutic strategies aimed at the induction of cancer regression through the selective modulation or depletion of tumor-associated Tregs.