USP22在抗黑色素瘤免疫治疗中的靶向分子机理

Tumor growth and metastasis, despite an intact immune system, were considered prime evidence of the poor immunogenicity of tumor cells, but attempts at immunotherapy to increase anti-tumor responses were largely unsuccessful. A major hurdle in tumor immunotherapy is the immunosuppression mediated by Regulatory T (Treg) cells, which can modulate the immune system by suppressing the function of effector T (Teff) cells. However, current approaches in targeting Treg have only transient efficacy and are highly unspecific. The development of new ways to control Treg functions is essential to improving tumor immunotherapy, and is a central goal of this project. Treg suppressive function is mediated by the transcription factor Forkhehgead Box P3 (FoxP3), also a specific marker for the Treg cell line. Our preliminary data showed that the Ubiquitin-specific peptidase 22 (USP22) was required for proper FoxP3 expression, suggesting a critical role for USP22 in Treg suppressive function and stability. More importantly, targeted deletion of USP22 gene specifically in T cells largely diminished Treg suppressive functions without affecting the immune response of conventional CD4 and CD8 T cell activation, indicating that USP22 is an ideal target to specifically inhibit Treg functions to enhance the antitumor immunity. Indeed, challenging of both WT and mice harboring a USP22 genetic deletion in Tregs (USP22Treg-KO) with EG7 lymphoma showed an increased in anti-tumor response in the USP22Treg-KO background. Based on these preliminary observations, we hypothesis that USP22 is a novel regulator of Treg suppressive functions through modulating FoxP3 expression and a potential therapeutic target to boost the antitumor immunity. This hypothesis will be addressed by studying the role of USP22 on maintaining Treg suppressive function, determining the specific molecular mechanisms by which USP22 controls FoxP3 expression and evaluating the preclinical efficacy of USP22 suppression in antitumor immunity using both xenograft and spontaneous melanoma models. The studies will provide fundamental insights to Treg biology and regulation, and a rationale for USP22 targeting in antitumor immune therapy.

肿瘤细胞低免疫原性是导致恶性肿瘤的发生、生长和转移的一个重要因素，试图增加抗肿瘤应答的免疫治疗虽然近几年取得了一些进展，但大多不成功。调节性T（Treg）细胞介导的免疫抑制是抗肿瘤免疫治疗的主要障碍，其通过抑制效应T（Teff）细胞的功能来调控免疫系统。因此，探究能够特异性抑制Treg细胞功能的新方法对于肿瘤免疫治疗是至关重要的，是该项目的中心目标。前期研究结果显示泛素特异性肽酶22（USP22）基因剔除导致Treg细胞抑制功能丧失，而对Teff细胞功能没有影响，因此USP22是特异性抑制Treg细胞功能以增强抗肿瘤免疫的理想靶标。本课题拟采用细胞免疫学和分子生物学等技术手段探讨USP22调控Treg细胞功能的精细分子机制，并通过不同的黑色素瘤模型探讨USP22抑制对小鼠抗肿瘤免疫反应的促进作用，为恶性肿瘤的发病机制的研究提供新思路，为自主新药研发提供理论基础。

肿瘤免疫微环境在肿瘤发生发展中扮演重要角色，其中Treg细胞介导的肿瘤免疫抑制作用对肿瘤生长转移发挥着重要作用。 Usp22 是一个重要肿瘤干细胞基因，它是 11 个癌死亡标签基因之一，对肿瘤的生长和转移等发挥重要功能。我们前期研究发现在 Treg 细胞中特异性敲除 Usp22 显著抑制 Treg 细胞的功能，增强抗肿瘤免疫反应。本课题围绕 Usp22 在抗免肿瘤疫治疗中的靶向分子机理问题，取得以下研究成果：1、 Usp22 是 FoxP3 特异性去泛素化酶。2、 Usp22 通过抑制组蛋白H2B单泛素化调控FoxP3基因转录。3、 Usp22 对于维持 Treg 抑制功能至关重要，在 Treg 细胞中特异性敲除 Usp22 显著增强抗肿瘤免疫反应抑制肿瘤生长。4、在 Treg 细胞中同时敲除 Usp22 和 Usp21 协同增强抗肿瘤免疫反应。5、缺氧提高 Usp22 和 FoxP3 在 Treg 细胞中的表达，在Treg细胞中敲除 Usp22 ，显著抑制缺氧环境提高 FoxP3 表达。6、低糖环境和氨基酸缺乏环境诱导 Usp22 促进 FoxP3 表达。7、通过通过计算机辅助药物设计结合生物学功能验证，筛选出 Usp22 潜在靶向抑制剂（S02）。小鼠接种肿瘤后给予 S02 ， S02 明显增强抗肿瘤免疫反应，抑制肿瘤生长。