OGR1在T细胞介导的抗肿瘤免疫中的作用

T-cell immunity plays a critical role in controlling tumor development and CD8+ cytotoxic T lymphocytes (CTLs) are key effector cells in antitumor immunity. Adoptive T-cell therapy has shown promise for cancer therapy. Studies over the last few decades have demonstrated that the extracellular pH of solid tumors is acidic, T cells could be extremely sensitive to pH variations. Low extracellular pH suppresses effective T cell antitumoral immune response. However, there is little knowledge about how acidic microenvironments suppress T-cell immunity. OGR1 (ovarian cancer G protein-coupled receptor) is a proton sensor, OGR1 deficient mice are viable and upon gross-inspection appear normal. Unexpectedly, we have found that prostate and melanoma tumor development is significantly inhibited in OGR1 deficient mice. OGR1 is expressed in T cells and infiltration of CD4+ and CD8+ T cells is significantly increased in tumors from ogr1-/- mice compared with tumors from WT mice. Both CD4+ and CD8+ T cells are involved in tumor rejection in ogr1-/- mice, and function as effector cells in tumor rejection. Thus, we hypothesize that OGR1 may regulate T cell functions and mediate low pH induced T cell suppression in tumors, removing OGR1 unleashes the suppressive effect, resulting in activation of T cells and tumor rejection. Hence, the main goal of this proposal is to determine the cellular and molecular mechanisms underlying the functions of OGR1 in T cells pertinent to its role in antitumor immunity. To test our hypotheses, four specific aims are proposed. 1) We will determine the role of OGR1 in T cell mediated antitumor immunity in vivo employing mice models. 2) We will determine cellular mechanisms underlying OGR1's role in T cell mediated antitumor immunity in vitro using T cell functional assay. 3) We will delineate molecular mechanisms underlying OGR1's role in T cells using biochemical approaches. 4) We will screen specific agonists and antagonists of OGR1 based on Ca2+ flux assays and cAMP assays. Our preliminary studies suggest that OGR1, an un-expected and new player in T cells may represent a novel and significant approach to manipulate T cells. This proposed study will offer new insights into effects of acidic tumor microenvironment on T cells. The information gained from this study will also furnish the bases for the development of effective adoptive T cell therapy for cancer patients by targeting OGR1.

T细胞在肿瘤免疫中起重要作用，过继T细胞治疗是新兴的肿瘤治疗方法。但肿瘤内部的酸性微环境对T细胞的抗肿瘤免疫有抑制作用，我们对于酸性微环境如何影响T细胞功能还知之甚少。OGR1 是感知质子的受体，T细胞高表达OGR1，但OGR1在T细胞中的功能却还未知。我们的前期结果显示OGR1敲除小鼠能抑制肿瘤的生长，这一抑制作用需要T细胞的直接参与。OGR1是潜在的T细胞功能调节者，可能介导了肿瘤酸性微环境中的质子对T细胞的抑制作用。本项目将在现有研究的基础上，利用动物模型、T细胞功能性实验和生化方法，从体内(动物个体)、体外(细胞)和分子机制三个层面深入研究OGR1在T细胞中的功能，特别是OGR1对T细胞抗肿瘤免疫的影响和OGR1在酸性pH对T细胞抑制过程中的作用。在此基础上通过筛选抑制和激活OGR1靶点的小分子，探寻调节OGR1信号通路的途径，为肿瘤的T细胞免疫治疗提供新的思路。

肿瘤的酸性微环境是导致其恶性增殖和治疗失败的重要原因，肿瘤酸性微环境中不同免疫细胞功能及其机制的研究有助于新的治疗靶位点的探索和药物研发。OGR1作为膜表面的质子感受器，对免疫细胞的活性和功能有重要影响。本项目研究显示，OGR1靶向敲除显著抑制了TRAMP-C2小鼠前列腺癌和B16黑色素瘤的生长；通过进一步探究其在不同细胞的表达情况发现，OGR1 在T细胞中有高表达，我们推断其可能通过影响了肿瘤酸性微环境中的T细胞功能进而抑制了肿瘤恶性增殖；通过免疫组化检测实体瘤中T细胞的浸润情况也证实，OGR1功能抑制增加了CD4+和CD8+T细胞在实体瘤灶中的数目；为了进一步探究OGR1对CD4+、CD8+T细胞功能的影响，我们分别构建了CD4+、CD8+T细胞中靶向敲除OGR1的基因敲除小鼠，其均显著抑制了B16黑色素实体瘤的生长；此外，过继回输OGR1-/-T细胞也显著抑制了Rag2-/-小鼠B16黑色素实体瘤的生长；这些结果说明OGR1会影响T细胞的功能，而改变肿瘤的发生发展；为了进一步探究OGR1影响T细胞功能的机制，我们展开了体外实验，其显示OGR1缺失促进了CD4+、CD8+T细胞的增殖，影响了CD8+T细胞的迁移和细胞因子的分泌，其相关分子机制仍在实验过程中；接下来我们以头颈鳞癌为例探寻了OGR1的临床应用价值，结果显示头颈鳞癌组织中OGR1表达显著上调，且其表达情况与患者的性别、年龄、种族和恶性程度紧密相关，且OGR1表达水平的不同直接影响多数相关基因的表达，这说明OGR1作为潜在的肿瘤治疗靶位点有广阔的应用前景。OGR1对肿瘤微环境中T细胞活性和功能影响的研究有助于深入了解其调节机制，为探索新的肿瘤治疗手段有一定的理论和实践意义。