The role of MHC class II epitopes in spontaneous and therapeutic immune responses targeting liver cancer

CD8 T细胞在对抗恶性细胞的适应性免疫中处于最前沿。然而，在癌症患者中，CD8 T细胞不能消灭癌细胞，并进入一种阻止癌症清除的衰竭状态。在这种情况下，激活CD4 T细胞的MHC II类表位在支持CD8 T细胞免疫应答和驱动CD8 T细胞向具有强效细胞溶解特性的效应表型分化中起主要作用。在缺乏CD4 T细胞的情况下，CD8 T细胞的增殖会缩小，并趋于分化状态，缺乏足够的回忆特性，称为“无助的CD8 T细胞”。由于抗肿瘤免疫反应的强度一般较低，CD4 T细胞对CD8反应的贡献比对急性感染的反应更难确定。最近，MHC II类表位已被证明可增强肉瘤中的CD8 T细胞扩增和肿瘤浸润。有趣的是，这种作用与肿瘤的表面MHC II类表达无关。这一事实表明，含有免疫原性MHC II类表位的肿瘤抗原被树突状细胞吸收，并通过树突状细胞的MHC II类分子呈递给CD4 T细胞。然而，CD4 T细胞如何引导CD8 T细胞走向肿瘤并促进肿瘤溶解在很大程度上仍然是难以捉摸的。此外，目前尚不清楚CD4帮助的这种作用是针对肉瘤还是适用于其他肿瘤实体。在我们的研究项目中，我们旨在阐明CD4 T细胞在自发免疫反应和肝细胞癌免疫治疗中的作用。为此，我们的团队开发了皮下和原位肝癌模型，定义了许多MHC I类和II类表位，并开发了几种有效的细胞疫苗接种策略。与发表的关于肉瘤的数据相反，我们已经证明在没有CD4 T细胞帮助的情况下，使用单一MHC类特异性CD8 T细胞表位接种疫苗可以消除小鼠肝癌。这些CD8 T细胞反应是用一种专利的异源癌症疫苗诱导的，该疫苗采用树突状细胞启动，然后用激动性共刺激抗体加强免疫。利用这一已建立的主要-增强方案，我们将分析CD4 T细胞帮助在针对肝癌的自发性适应性免疫应答以及治疗性T细胞疫苗中的作用，并试图解决关于MHC II类表位在肿瘤治疗中的相互矛盾的结果。我们将进一步将研究扩展到其他免疫疗法，并阐明MHC II类表位在肝细胞癌检查点抑制剂治疗中的作用。最后，利用我们的疫苗接种技术，我们将生成CD8 T细胞中CD4 T细胞帮助的转录组图谱，并分析CD4 T细胞帮助的关键分子和途径。

CD8 T cells are at the forefront of adaptive immunity in the battle against malignant cells. In cancer patients, however, CD8 T cells fail to eliminate cancer cells and enter a state of exhaustion that prevents cancer clearance. In this context MHC class II epitopes which activate CD4 T cells play a major role in supporting CD8 T cell immune responses and driving CD8 T cell differentiation towards an effector phenotype with potent cytolytic properties. In the absence of CD4 T cells, CD8 T cell expansion is reduced in size and poised towards a differentiation state with insufficient recall properties, termed "helpless CD8 T cells". Since the magnitude of antitumoral immune responses is in general low, the contribution of CD4 T cells to CD8 responses is harder to determine than in responses to acute infection. Recently, MHC class II epitopes have been shown to enhance CD8 T cell expansion and tumor infiltration in sarcoma. Interestingly, this effect was independent of surface MHC class II expression by the tumor. This fact implies that tumor antigens which harbor immunogenic MHC class II epitopes are taken up by dendritic cells and presented on the dendritic cells' MHC class II molecules to CD4 T cells. How CD4 T cells direct CD8 T cells towards the tumor and favor oncolysis, however, remains largely elusive. Furthermore, it remains unclear whether this role of CD4 help is specific for sarcoma or applicable to other tumor entities as well. In our research project we aim at elucidating the role of CD4 T cell help in spontaneous immune responses and immunotherapy of hepatocellular carcinoma. For this purpose, our group has developed subcutaneous and autochthonous liver cancer models, defined a number of MHC class I and II epitopes and developed several potent cellular vaccination strategies. In contrast to the data published on sarcoma, we have demonstrated elimination of liver cancer in mice using vaccinations with a single, MHC class I-specific CD8 T cell epitope in the absence of CD4 T cell help. These CD8 T cell responses were induced with a patented, heterologous cancer vaccine that employs a dendritic cell priming followed by a booster immunization with agonistic, costimulatory antibodies. Using this established prime-boost regimen we will analyze the role of CD4 T cell help in spontaneous, adaptive immune responses targeting liver cancer as well as therapeutic T cell vaccines and try to resolve the conflicting results regarding MHC class II epitopes in tumor therapy. We will furthermore extend our studies to other immunotherapies and clarify the role of MHC class II epitopes in checkpoint inhibitor therapies of hepatocellular carcinoma. Finally, using our vaccination technology we will generate a transcriptome profile of CD4 T cell help in CD8 T cells and analyze key molecules and pathways involved in CD4 T cell help.