Exosomes, Dendritic Cells and Transplant Tolerance

描述（由申请人提供）： 移植物排斥反应的主要原因是受体内引起的同种抗原（Ag）特异性T细胞免疫应答。树突状细胞（Dendritic cells，DC）是专职的抗原提呈细胞（Ag presenting cells，APC），作为“过客白细胞”将供体抗原提呈给初始T细胞并引发移植排斥。除了它们在免疫和移植排斥中的作用之外，具有吞噬凋亡囊泡的DC表现出免疫调节APC的特征，并且似乎参与稳态外周耐受的诱导。然而，凋亡囊泡并不是唯一可能影响DC生物学的细胞外囊泡。DC可以内化细胞外外来体，一群内体来源的小膜囊泡（< 100 nm），富含MHC分子并且在细胞外空间中丰富。DC能够在MHC分子中呈递外泌体衍生的同种异体肽。有证据表明，外泌体，如凋亡囊泡，可能通过与APC相互作用参与外周耐受的诱导。我们建议研究DC-外泌体相互作用，并检验供体来源的MHC +外泌体内化和加工后，受体DC能够产生具有调节功能的同种抗原特异性T细胞的假设。我们预计这种相互作用将产生两个重要影响：i）受体DC将呈递供体MHC +外泌体衍生的同种异体肽+自身MHC，干扰同种异体识别的间接途径，和ii）由于它们的低水平的T细胞共刺激分子，表达供体MHC +外泌体衍生的同种异体肽+自身MHC的受体未成熟DC将指示受体同种异体Ag特异性T细胞变得凋亡、无反应性，或调节性T（Treg）细胞。与大多数报道的用DC诱导移植耐受的技术不同，我们的方法特异性靶向器官排斥反应中同种异体识别的间接途径。我们建议探索这种方法来诱导心脏移植受体的Ag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。所获得的知识将增强对耐受性和排斥反应如何调节的理解，并将阐明DC和外泌体用于移植的治疗潜力。我们提出以下目的：目的1：研究DC与外泌体的相互作用及其对DC生物学的影响。目的2：研究exosomes在体内的转运，并探讨exosomes暴露的DC对T细胞的刺激作用。目标3：研究给予供体MHC +外泌体或暴露于供体MHC +外泌体的受体DC对心脏移植物存活的影响。比较供体-MHC+外泌体与供体-MHC+凋亡细胞的作用。

DESCRIPTION (provided by applicant): The main cause of graft rejection is the allo-antigen (Ag)-specific T cell immune response elicited within the recipient. Dendritic cells (DCs) are the professional Ag-presenting cells (APCs) that as "passenger leukocytes" present donor alloAg to naive T cells and trigger graft rejection. Besides their role in immunity and transplant rejection, DCs that have phagocytosed apoptotic vesicles exhibit characteristics of immunoregulatory APCs and seem to be involved in induction of peripheral tolerance in the steady-state. However, apoptotic vesicles are not the only extracellular vesicles that may affect DC biology. DCs can internalize extracellular exosomes, a population of small membrane vesicles (< 100 nm) of endosomal origin, rich in MHC molecules and abundant in the extracellular space. DCs are able to present exosome-derived allopeptides in MHC molecules. There is evidence that exosomes, like apoptotic vesicles, may participate in induction of peripheral tolerance probably through interaction with APCs. We propose to study the DC-exosome interaction and to test the hypothesis that after internalization and processing of donor-derived MHC + exosomes, recipient DCs are able to generate allo-Ag specific T cells with regulatory function. We expect that this interaction will have two important effects: i) recipient DCs will present the donor MHC + exosome-derived allopeptides + self-MHC interfering with the indirect pathway of allorecognition, and ii) due to their low levels of T cell costimulatory molecules, recipient immature DCs expressing donor MHC + exosome-derived allopeptides + self-MHC will instruct recipient alloAg-specific T cells to become apoptotic, anergic, or regulatory T (Treg) cells. Unlike most of the techniques reported in effort to induce transplant tolerance with DCs, our approach targets specifically the indirect pathway of allorecognition in organ rejection. We propose to explore this approach to induce Ag-specific tolerance in heart allograft recipients as an alternative to pharmacological treatment that induces generalized immunosuppression and harmful side effects. The knowledge gained will enhance understanding of how tolerance and rejection are regulated, and will clarify the therapeutic potential of DCs and exosomes for transplantation. We propose the following aims: AIM 1: To investigate the interaction of DCs with exosomes and its impact on DC biology. AIM 2: To study the trafficking of exosomes in vivo and to characterize the T cell stimnlatory capacity of exosome-exposed DCs. AIM 3: To investigate the effect of administration of donor MHC + exosomes or recipient DCs exposed to donor MHC + exosomes on heart allograft survival. To compare the effects of donor-MHC + exosomes with donor-MHC + apoptotic cells.