Graft Tolerance with Apoptotic Cells and Dendritic Cells

描述（申请人提供）：移植排斥反应的主要原因是受体引发的针对供体同种（allo）抗原（Ags）的免疫反应。在移植手术后，树突状细胞（DC）是Ag呈递细胞，其作为过客白细胞将供体alloAg呈递给受体T细胞并触发移植物排斥。然而，DC也参与T细胞耐受的诱导。DC的这种致耐受性特性可用于诱导供者特异性T细胞耐受，用于治疗同种异体移植排斥或自身免疫性疾病。有证据表明，在细胞凋亡的早期阶段，细胞的吞噬作用向DC传递了有效的抑制信号。具有内化凋亡细胞的DC下调MHC和共刺激分子的表达，降低其T细胞刺激能力，并减少促炎细胞因子的合成，同时维持高水平的TGF-β 1。我们建议使用相同的原理来诱导供体特异性耐受以延长心脏移植物的存活。本研究将探讨早期凋亡细胞对树突状细胞产生免疫抑制作用的机制。它将测试的假设，供体（MHC+）细胞在凋亡的早期阶段的管理，通过诱导无反应性/同种异体反应性T细胞的凋亡或具有调节功能的同种异体特异性T细胞（Treg细胞）的产生，提高心脏同种异体移植物的存活率。我们假设供体特异性T细胞耐受将通过以下机制实现：i）受体未成熟/半成熟DC在次级淋巴器官的致耐受性环境中处理供体凋亡细胞ii）供体凋亡/死亡细胞与受体T细胞的直接相互作用（直接途径）; iii）供体“完整”MHC分子从供体凋亡/死亡细胞转移至受体DC和iv）由于缺乏同种特异性CD 4 + T细胞帮助，同种抗体的合成减少。该提案将定义使用供体凋亡细胞实现长期心脏同种异体移植物存活的最佳条件，如下：i）通过优化供体凋亡细胞的递送剂量、动力学、频率和效率; ii）通过同时靶向直接和间接途径; iii）通过将供体凋亡细胞与次优水平的免疫抑制相结合。我们建议采用这种方法来诱导心脏移植受体的供体特异性耐受，作为诱导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细胞凋亡的早期阶段将供体细胞施用到体内靶向受体DC以促进供体特异性耐受的治疗潜力。本研究的具体目的如下：目的1：研究早期凋亡细胞对树突状细胞同种异体刺激功能的影响。目的2：观察同种异体凋亡细胞对同种异体T、B细胞免疫应答的影响。目的3：优化供者凋亡细胞对心脏移植存活的治疗作用。探讨供者凋亡细胞在移植受体中的作用机制。

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.