Immune privilege of the hematopoieitic stem cell niche

项目摘要 尽管干细胞生态位作为调节干细胞功能的部位已被广泛研究， 该利基的免疫学属性在很大程度上仍未得到探索。有趣的是，睾丸和 胎盘是干细胞驻留的器官，众所周知，它是干细胞的免疫学圣地，称为 免疫特权(IP)站点。移植物的存活证明了IP部位的严格免疫抑制 未接受任何外源性免疫抑制治疗的同种或异种移植物。人们对此知之甚少 组织定位的干细胞是否为IP部位，如睾丸和胎盘。总体假设 是最具特色的干细胞利基之一，造血干细胞和祖细胞(HSPC)利基 在骨髓(BM)中，是一个IP部位。利基中的IP可以防止移植的同种异体排斥反应(allo-) HSPC，保护恶性干细胞免受免疫攻击。因此，知识产权可能是一种新的原则， 提供了几种临床环境的机械支撑。我们之前的研究表明，HSPC 利基是一个IP站点。高灵敏的体内显微镜(IVM)能够检测持续存在的异基因HSPC 免疫能力强的小鼠未接受免疫抑制治疗60天以上。此外，FoxP3+ 调节性T细胞(Treg)经常与HSPC形成簇。全身性Treg耗竭导致allo-HSPC 拒绝。数据表明，Tregs赋予了这个利基IP。我们进一步观察到MLL-AF9白血病 干细胞(LSCs)是BM Tregs的家园，这是IP站点的一个标志，这表明IP屏蔽了LSCs。要开发一种 新的治疗方法操纵IP促进allo-HSPC植入或根除BM恶性肿瘤，这是重要的 以获得对知识产权的进一步机械性见解。在目标1中，我们将研究骨髓间充质干细胞的作用。 细胞和CD11b+Gr1+髓系细胞在IP维持和无免疫的allo-HSPC持久性中的作用 压制。为了实现这一目标，我们将采用以下四种方法：a)抑制Treg归巢以 Tregs中CXCR4的条件性缺失所致的骨髓；b)Tregs中CD39的条件性缺失；c)条件性 Lepr+间充质细胞中CXCL12的缺失；以及d)抗Gr1抗体耗尽CD11b+Gr1+细胞 治疗。我们将确定这些方法是否会导致没有移植的异基因HSPC的排斥反应。 免疫抑制，通过活体显微镜、流式细胞术和二次移植试验。在……里面 目的2，我们将测试IP是否保护LSCs免受免疫，并进一步阐明BM树突状细胞的作用。 间充质细胞和CD11b+Gr1+髓系细胞使LSCs逃避免疫。我们将决定 MLL-AF9白血病的排斥反应是否由a)由于Tregs中CXCR4缺失而导致的BM Tregs缺失，b) CD39抑制剂治疗，c)Lepr+间充质细胞CXCL12缺失，d)髓系细胞耗竭。 成功的研究将创造一种新的范式，即HSPC利基是两者的免疫避难所 异基因HSPC和恶性干细胞。此外，这些对知识产权意愿的机械性和系统性的分析 为异基因HSPC移植和恶性肿瘤建立新的治疗策略。

Project Abstract Although the stem cell niche has been extensively studied as a site that regulates stem cell functions, immunological attributes of the niche have remained largely unexplored. Interestingly, the testis and the placenta, organs for residence of stem cells, are known to be immunological sanctuaries for stem cells, termed immune privileged (IP) sites. Rigorous immune suppression in IP sites is evidenced by survival of transplanted allogeneic or xenogeneic grafts without any exogenous immune suppressive therapy. Little is known about whether tissue-committed stem cell niches are IP sites, like the testis and the placenta. The overall hypothesis is that one of the best-characterized stem cell niches, the hematopoietic stem and progenitor cell (HSPC) niche in the bone marrow (BM), is an IP site. IP in the niche may prevent rejection of transplanted allogeneic (allo-) HSPCs, and shield malignant stem cells from immune attack. Therefore, IP may be a novel principle that provides a mechanistic underpinning of several clinical settings. Our previous study indicates that the HSPC niche is an IP site. Highly sensitive in vivo microscopy (IVM) enabled detection of allo-HSPCs persisting in immune competent mice without immune suppressive therapy for more than 60 days. Moreover, FoxP3+ regulatory T cells (Tregs) frequently formed clusters with HSPCs. Systemic Treg depletion led to allo-HSPC rejection. The data suggest that Tregs endow the niche with IP. We further observed that MLL-AF9 leukemia stem cells (LSCs) home to BM Tregs, a hallmark of IP sites, suggesting that IP shields LSCs. To develop a new therapy to manipulate IP to promote allo-HSPC engraftment or eradicate BM malignancies, it is important to obtain further mechanistic insights into IP. In Aim 1, we will investigate the role of BM Tregs, mesenchymal cells, and CD11b+Gr1+ myeloid cells in IP maintenance and allo-HSPC persistence without immune suppression. To achieve this goal, we will employ the following four approaches: a) inhibition of Treg homing to the BM due to conditional deletion of CXCR4 in Tregs; b) conditional deletion of CD39 in Tregs; c) conditional deletion of CXCL12 in lepr+ mesenchymal cells; and d) CD11b+Gr1+ cell depletion by anti-Gr1 antibody treatment. We will determine whether these approaches lead to rejection of allo-HSPCs transplanted without immune suppression, by using in vivo microscopy, flow cytometry, and secondary transplantation assay. In Aim 2, we will test whether IP shields LSCs from immunity, and further elucidate the role of BM Tregs, mesenchymal cells, and CD11b+Gr1+ myeloid cells in allowing LSCs to evade immunity. We will determine whether rejection of MLL-AF9 leukemia is induced by a) lack of BM Tregs due to CXCR4 deletion in Tregs, b) CD39 inhibitor treatment, c) CXCL12 deletion in lepr+ mesenchymal cells, and d) myeloid cell depletion. Successful studies will create a novel paradigm that the HSPC niche is an immunological sanctuary for both allo-HSPCs and malignant stem cells. Furthermore, these mechanistic and systematic analyses of IP will establish novel therapeutic strategies for allo-HSPC transplantation and malignancies.