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

在对抗恶性细胞的战斗中，CD8 T细胞处于获得性免疫的前沿。然而，在癌症患者中，CD8T细胞无法清除癌细胞，进入阻止癌症清除的耗尽状态。在这种背景下，激活CD4T细胞的MHC-II类表位在支持CD8T细胞免疫应答和推动CD8T细胞分化为具有强大细胞溶解特性的效应表型方面发挥了重要作用。在没有CD4T细胞的情况下，CD8T细胞的扩增体积变小，并趋向于记忆特性不足的分化状态，称为无助的CD8T细胞。由于抗肿瘤免疫反应的幅度一般较低，因此CD4T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类表位被证明可以促进CD8T细胞的增殖和肉瘤中的肿瘤侵袭。有趣的是，这种作用与肿瘤表面MHC II类分子的表达无关。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摄取，并在树突状细胞的MHC II类分子上呈递给CD4T细胞。然而，CD4T细胞如何将CD8T细胞导向肿瘤并促进肿瘤溶解，在很大程度上仍然难以捉摸。此外，目前还不清楚CD4帮助的这种作用是肉瘤特有的，还是适用于其他肿瘤实体。在我们的研究项目中，我们的目的是阐明CD4T细胞在自发免疫反应和肝细胞癌免疫治疗中的作用。为此，我们小组开发了皮下和自体肝癌模型，定义了一些MHC I和II类表位，并开发了几种有效的细胞疫苗策略。与发表的关于肉瘤的数据相反，我们已经证明了在没有CD4T细胞帮助的情况下，使用单一的MHC I类特异性CD8T细胞表位接种疫苗可以在小鼠中消除肝癌。这些CD8 T细胞反应是由一种获得专利的异种癌症疫苗诱导的，该疫苗使用树突状细胞预置，然后用激动型、共刺激抗体加强免疫。利用建立的Prime-Boost方案，我们将分析CD4T细胞辅助在针对肝癌的自发、适应性免疫反应中的作用以及治疗性T细胞疫苗，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。我们将进一步将我们的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疗法中的作用。最后，利用我们的疫苗接种技术，我们将在CD8T细胞中生成CD4T细胞帮助的转录组图谱，并分析参与CD4T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.