Graft Tolerance with Apoptotic Cells and Dendritic Cells

描述(由申请人提供)：移植排斥的主要原因是受者对供者异基因(Allo)抗原(AGS)的免疫反应。在移植手术后，树突状细胞(DC)是抗原提呈细胞，作为乘客白细胞，将供体同种异体抗原递送给受体T细胞，并引发移植排斥反应。然而，DC也参与了T细胞耐受的诱导。DC的这种耐受特性可能被用来诱导供者特异性T细胞耐受，用于同种异体移植排斥反应或自身免疫性疾病的治疗。有证据表明，细胞在凋亡的早期阶段的吞噬作用向DC传递了一个强有力的抑制信号。内化凋亡细胞的DC下调MHC和共刺激分子的表达，降低其T细胞刺激能力，减少促炎细胞因子的合成，同时保持高水平的转化生长因子-β1。我们建议使用同样的原则来诱导供者特异性耐受，以延长同种异体心脏移植物的存活时间。这项建议将研究早期凋亡细胞对DC产生免疫抑制作用的机制(S)。通过诱导同种异体反应性T细胞的无能/凋亡或产生具有调节功能的同种异体T细胞(Treg细胞)，在细胞凋亡早期给予供者(MHC+)细胞可延长同种异体心脏移植物的存活。我们推测供者特异性T细胞耐受是通过以下机制实现的：i)供者未成熟/半成熟的DC在次级淋巴器官的耐受环境中处理供者的凋亡细胞(间接途径)，ii)供者的凋亡/死亡细胞与受者T细胞的直接相互作用(直接途径)；iii)供者“完整”的MHC分子从供者的凋亡/死亡细胞转移到受者的DC；以及iv)由于缺乏同种异体特异性的CD4+T细胞帮助，同种异体抗体的合成减少。这项建议将确定使用供体凋亡细胞实现心脏移植物长期存活的最佳条件如下：i)通过优化供体凋亡细胞的剂量、动力学、频率和效率；ii)通过同时靶向直接和间接途径；以及iii)通过将供体凋亡细胞与次优水平的免疫抑制相结合。我们建议使用这种方法来诱导同种异体心脏移植受者的供者特异性耐受，作为引起全身免疫抑制和有害副作用的药物治疗的替代方案。所获得的知识将阐明在凋亡的早期阶段将供体细胞用于体内靶向受体DC以促进供体特异性耐受的治疗潜力。我们将致力于以下具体目标：目的1；研究早期凋亡细胞对DC同种异体刺激功能的影响。目的：体内监测同种异体凋亡细胞对同种异体特异性T、B细胞免疫应答的影响。目的：优化供者凋亡细胞对同种异体心脏移植存活的治疗效果。探讨供体凋亡细胞在移植受者体内的作用机制(S)。

DESCRIPTION (provided by applicant): The main cause of transplant rejection is the immune response against donor allogeneic (allo) antigens (Ags) elicited by the recipient. Following transplant surgery, Dendritic cells (DCs) are the Ag-presenting cells that, as passenger leukocytes, present donor alloAgs to recipient T cells and trigger graft rejection. However, DCs also participate in induction of T cell tolerance. This tolerogenic property of DCs may be exploited to induce donor-specific T cell tolerance for treatment of allograft rejection or autoimmune diseases. There is evidence that phagocytosis of cells in early stages of apoptosis delivers a potent inhibitory signal to DCs. DCs that have internalized apoptotic cells downregulate expression of MHC and costimulatory molecules, decrease their T cell stimulatory capacity and reduce the synthesis of pro-inflammatory cytokines while maintaining high levels of TGF-B1. We propose to use the same principle to induce donor-specific tolerance to prolong cardiac allograft survival. This proposal will study the mechanism(s) by which early apoptotic cells exerts immuno-suppressive effects on DCs. It will test the hypothesis that administration of donor (MHC+) cells in early stages of apoptosis prolongs cardiac allograft survival by inducing anergy/apoptosis of alloreactive T cells or generation of allospecific T cells with regulatory function (Treg cells). We hypothesize that donor-specific T cell tolerance will be achieved by the following mechanisms: i) processing of donor apoptotic cells by recipient immature/semi-mature) DCs in the tolerogenic environment of secondary lymphoid organs (indirect pathway), ii) direct interaction of donor apoptotic/dying cells with recipient T cells (direct pathway); iii) transference of donor "intact" MHC molecules from donor apoptotic/dying cells to recipient DCs and iv) reduced synthesis of alloAbs, due to lack of allospecific CD4+ T cell help. This proposal will define the optimal conditions for the use of donor apoptotic cells to achieve long-term cardiac allograft survival as follows: i) by optimizing the dose, kinetics, frequency and efficiency of delivery of donor apoptotic cells; ii) by simultaneous targeting of the direct and indirect pathways and iii) by combination of donor apoptotic cells with suboptimal levels of immunosuppression. We propose to employ this approach to induce donor-specific tolerance in heart allograft recipients as an alternative to pharmacological treatments that induce generalized immunosuppression and harmful side effects. The knowledge gained will clarify the therapeutic potential of administration of donor cells in early stages of apoptosis to target recipient DCs in vivo to promote donor-specific tolerance. We will address the following specific aims: Aim 1; To study the effect that early apoptotic cells exerts on the allostimulatory function of DCs. Aim 2: To monitor in vivo the effect of allogeneic apoptotic cells on allospecific T and B cell immune responses. Aim 3; To optimize the therapeutic effect of donor apoptotic cells on heart allograft survival. To investigate the mechanism(s) of action of donor apoptotic cells in graft recipients.