Helper and suppressor roles of CD8+ T cells

描述(由申请人提供)：效应CD8+T细胞清除携带抗原的树突状细胞(携带抗原的DC)被认为是限制细胞毒性T淋巴细胞(CTL)反应的机制。然而，在长期暴露于Ag的情况下，如慢性感染或癌症，慢性激活的CD8+T细胞清除DC可能会导致免疫抑制。我们的初步观察表明，在肿瘤裂解液负载的DC中添加与肿瘤无关的(LCMV-gp33)肽可以提高在存在肿瘤特异性免疫的情况下在治疗环境中给药的癌症疫苗的有效性。这种有益的效果依赖于记忆型LCMV-gp33特异性CD8+T细胞的存在，而效应型LCMV-gp33特异性CD8+T细胞则取消了疫苗的效力。提示CD8+T细胞活化的不同时相与CD8+T细胞免疫调节活性的不同有关。因此，我们建议分别描述效应期和记忆期CD8+T细胞抑制和辅助功能的机制。此外，我们将研究如何分别避免或利用这些免疫调节功能来改进癌症免疫疗法。这项建议中概述的工作将遵循三个具体目标-(1)确定效应器CD8+T细胞免疫抑制的机制；(2)确定记忆CD8+T细胞辅助活动的机制；以及(3)比较CD8+帮助和抑制对预防和治疗环境中携带疫苗的DC存活的影响。我们将使用小分子抑制剂、封闭抗体和转基因小鼠进行体外实验，检测效应期CD8+T细胞对DC的杀伤作用，以及记忆期CD8+T细胞对DC成熟和IL-12分泌的诱导作用。利用体内DC迁移实验，我们将使用转基因小鼠来确定在预免疫小鼠中分别参与携带记忆或效应期反应的辅助和抑制功能的途径。最后，这些实验也将在荷瘤小鼠身上进行，以描绘影响基于DC的免疫疗法的途径。相关性：基于DC的治疗性疫苗通常在外围注射，在那里肿瘤特异性效应细胞占主导地位，并可以杀死疫苗。通过确定CD8+T细胞免疫调节功能的机制，我们可以设计出抵抗抑制功能的疫苗，并更有能力接受记忆细胞来源的帮助，从而有望为癌症患者设计有效的治疗性疫苗。

DESCRIPTION (provided by applicant): The clearance of antigen-carrying dendritic cells (Ag-carrying DC) by effector CD8+ T cells has been postulated as a mechanism for limiting cytotoxic T lymphocyte (CTL) responses. However, in situations of prolonged Ag exposure, such as chronic infection or cancer, DC elimination by chronically-activated CD8+ T cells may lead to immune suppression. Our preliminary observations indicate that the addition of a tumor-irrelevant (LCMV-gp33) peptide to tumor-lysate loaded DC can increase the efficacy of cancer vaccines administered in therapeutic settings in the presence of pre-existing tumor-specific immunity. Such beneficial effects of rely on the presence of memory-type LCMV-gp33-specific CD8+ T cells; whereas effector-typeLCMV-gp33-specific CD8+ T cells abolished the efficacy of the vaccine. These data suggest that the sequential phases of CD8+ T cell activation are associated with different immunoregulatory activities of CD8+ T cells. Therefore, we propose to delineate the mechanisms underlying the suppressive and helper functions of effector and memory-stage CD8+ T cells, respectively. Additionally, we will examine how these immunoregulatory functions can be, respectively, avoided or exploited for improved cancer immuno-therapies. The work outlined within this proposal will follow three specific aims- (1) To determine the mechanism of immunosuppression by effector CD8+ T cells; (2) to determine the mechanism of helper activity of memory CD8+ T cells; and (3) compare the impact of CD8+ help versus suppression on the survival of vaccine-carrying DC in preventative vs. therapeutic settings. We will use small molecule inhibitors, blocking antibodies and transgenic mice in in vitro assays examining killing of DC by effector-stage CD8+ T cells and the induction of DC maturation and IL-12 secretion by memory-stage CD8+ T cells. Using a DC migration assay in vivo, we will use transgenic mice to determine the pathways involved in helper and suppressor functions in pre-immunized mice carrying memory or effector stage responses, respectively. Lastly, these experiments will also be performed in tumor-bearing mice to delineate the pathways that effect DC-based immunotherapies. Relevance: Therapeutic DC-based vaccines are typically administered in the periphery, where the tumor-specific effector cells predominate and can kill the vaccine. By determining the mechanisms underlying CD8+ T cell immunoregulatory functions, we can design vaccines that are resistant to the suppressive functions and are more capable of receiving the memory cell-derived help, prospectively allowing us to design effective therapeutic vaccines for cancer patients.