Probing the Role of TIM-4 in Cross-Presentation of Tumor-Associated Antigens

描述(申请人提供)：癌症是一种循序渐进的疾病，随着异质细胞群体慢慢克服通常阻止细胞无限复制潜力的调节电路。一条这样的调控途径就是免疫监视。现在有来自小鼠模型的良好证据表明，免疫系统对癌症的发展施加了压力，并可以将其维持在一种神秘的状态。细胞溶解T淋巴细胞(CTL)及其效应蛋白已被证明至少是这种效应的部分原因。然而，在肿瘤建立了能够绕过这些压力的免疫抑制环境后，癌症的临床症状就会出现。针对这一途径的治疗方法试图使用病毒载体或通过将肿瘤相关抗原加载到自体树突状细胞(DC)并将其重新注射到患者体内来激活和重振CTL反应。这些疗法已经在一些患者中显示出疗效，证明了这种方案的可行性。尽管可行，但成功率一直令人失望，目前的工作试图将抗原靶向体内相关的DC亚群，以有效地产生抗肿瘤CTL。CD8αDC亚群是一个很有前途的候选细胞，因为它能够获得外源抗原，并将其呈递给CTL，这一过程被称为交叉呈递。这种独特的能力至少在一定程度上归因于它吞噬凋亡细胞的能力。然而，这两个特征很难从机械上联系起来，因为对这种吞噬的分子要求还不清楚。通常认为CD8α树突状细胞表达磷脂酰丝氨酸(PS)受体，这是凋亡细胞的一个显著特征，这可以解释这种现象。我们的初步体外实验表明，T细胞免疫球蛋白结构域和粘蛋白Doman-4(TIM-4)是PS受体，CD8αDC在成熟时优先表达TIM-4，抑制TIM-4功能会导致对凋亡细胞的摄取效率低下，并导致这些细胞相关抗原的交叉提呈缺陷。目的1将确定TIM-4是否以及在多大程度上有助于体内细胞凋亡相关抗原的交叉呈递和随后产生的CTL免疫。目的2将寻求测试TIM-4是否可以用于靶向CD8α树突状细胞的抗原，以有效地交叉呈现和随后的肿瘤排斥反应。如果我们的假设能够被证明是正确的，这些实验将增加我们对免疫监督的分子要求的理解，并为癌症治疗提供可能的基础。

DESCRIPTION (provided by applicant): Cancer is a disease that develops in a stepwise fashion as a heterogeneous population of cells slowly overcomes the regulatory circuits that normally bar cells from limitless replicative potential. One such regulatory pathway is that of immune surveillance. There is now good evidence from mouse models that the immune system places pressure on the development of cancer and can maintain it in an occult state. Cytolytic T lymphocytes (CTLs) and their effector proteins have been shown to be at least partially responsible for this effect. The clinical symptoms of cancer, however, arise after the tumor has established an immunosuppressive environment that is able to circumvent these pressures. Therapies targeting this pathway have sought to prime and reinvigorate CTL responses using viral vectors or by loading autologous dendritic cells (DCs) with tumor-associated antigens and re-injecting them into the patient. These therapies have shown efficacy in some patients, demonstrating the feasibility of such a protocol. Although feasible, success rates have been disappointing and current work seeks to target antigens to the relevant DC subsets in vivo for efficient generation of antitumor CTLs. The CD8alpha DC subset is a promising candidate, given its ability to acquire exogenous antigens for presentation to CTLs, a process termed cross-presentation. This unique ability has, at least in part, been attributed to its ability to endocytose apoptotic cells. These two characteristics, however, have been difficult to mechanistically link since the molecular requirements for this engulfment are not understood. It is generally believed that CD8alpha DCs express a receptor for phosphatidylserine (PS), a prominent feature of apoptotic cells, which could explain this phenomenon. Our preliminary in vitro experiments demonstrate that T cell immunoglobulin domain and mucin doman-4 (TIM-4), a PS receptor, is preferentially expressed by CD8alpha DCs upon maturation and that inhibition of TIM-4 function leads to inefficient uptake of apoptotic cells and defective cross-presentation of these cell-associated antigens. Aim 1 will establish whether and to what extent TIM-4 contributes to cross-presentation of apoptotic cell-associated antigens and subsequent generation of CTL immunity in vivo. Aim 2 will seek to test whether TIM-4 can be used to target antigens to CD8alpha DCs for efficient cross-presentation and subsequent rejection of tumors. If our hypotheses can be proven correct, these experiments will add to our understanding of the molecular requirements for immunosurveillance and provide a possible basis for cancer treatment.