Enhancing immune reconstitution after implantation of postnatal allogeneic thymus

描述(申请人提供)：由于胸腺发育缺陷，DiGeorge畸形患者出现严重的先天性T淋巴细胞减少症。手术植入了出生后的同种异体培养的胸腺片段，试图为这些患者的胸腺生成提供合适的微环境。尽管这种方法取得了一些成功，但外周T细胞数量一直保持在较低水平，自身免疫性疾病是一个常见的问题。在临床环境中，对植入物内发生的胸腺重建的细胞机制的详细分析是不可能的。我们在这项提案中的目标是在免疫缺陷的小鼠模型中使用人类骨髓-胸腺嵌合体来创建一个平台，在这个平台上，我们可以在细胞水平上描绘出人类胸腺植入物中胸腺细胞是如何生成的，以及胸腺的生成可能如何得到改善。为了实现这一目标，我们将汇集我们对正常人类胸腺生成和胸腺血管生态位研究的信息。利用免疫缺陷的小鼠模型，我们注意到，新生儿胸腺为造血干细胞移植后胸腺的快速播种和胸腺生成提供了独特的接受环境。我们的数据表明，新生儿和成人胸腺血管系统之间存在质的差异，这些差异是由高水平的血管内皮生长因子(VEGF)介导的。我们假设，新生胸腺的血管内皮生长因子反应调节快速和强大的胸腺生成。此外，我们认为，在植入的胸腺组织中表达血管内皮生长因子将提高胸腺从宿主造血细胞重建的速度和质量。我们提出了以下具体目标：1.确定人胸腺移植后重建胸腺的细胞机制。2.探讨血管内皮生长因子在人胸腺移植中的表达是否能提高胸腺移植的存活率和胸腺生成。除了这些研究与DiGeorge畸形的治疗直接相关外，这些研究还将提供一种技术上可行的方法，通过体外实验来操纵人类胸腺微环境，并在内源性人类造血的背景下检验这种操纵的生物学。了解血管壁龛在胸腺重建中的作用可能为胸腺细胞间隔内的串扰机制提供新的见解。 与公共卫生相关：靶向人类胸腺分子表达的能力对DiGeorge畸形等原发免疫缺陷和在出生后整个生命过程中发展的获得性胸腺功能不全具有广泛的治疗潜力。

DESCRIPTION (provided by applicant): Severe congenital T lymphopenia occurs in DiGeorge anomaly as a result of a developmental defect of the thymus gland. Surgical implantation of postnatal, allogeneic, cultured thymic fragments has been performed in an attempt to provide an appropriate microenvironment for thymopoiesis in these patients. Despite some success with this approach, peripheral T cell numbers have remained consistently low and autoimmune disease is a frequent problem. Detailed analysis of the cellular mechanisms of thymic reconstitution that occur within the implants is not possible in the clinical setting. Our goal in this proposal is to use a human marrow- thymus chimera in an immune deficient mouse model to create a platform from which we can delineate on a cellular level how thymocytes are generated in the human thymic implants, and how thymopoiesis might be improved. To achieve this goal, we will bring together information from our studies of normal human thymopoiesis, and of the thymic vascular niche. Using immune deficient murine models, we have noted that the neonatal thymus provides a uniquely receptive environment for rapid thymic seeding and thymopoiesis after hematopoietic stem cell transplantation. Our data shows that qualitative differences exist between the neonate and adult thymic vasculature, and that these differences are mediated by high levels of Vascular Endothelial Growth Factor (VEGF). We hypothesize that the VEGF responsive vasculature of the neonatal thymus mediates rapid and robust thymopoiesis. Furthermore, we propose that expression of VEGF in implanted thymic tissue will improve the speed and quality of thymic reconstitution from host hematopoietic cells. We propose the following Specific Aims: 1. To determine the cellular mechanisms by which reconstitution of human thymopoiesis is established after implantation of postnatal cultured thymus. 2. To determine if VEGF expression in human postnatal thymic implants will improve implant survival and thymopoiesis. In addition to the direct relevance of these studies to the treatment of DiGeorge anomaly, these studies will provide a technically feasible approach to manipulate the human thymic microenvironment experimentally ex vivo, and examine the biology of such manipulations in the context of endogenous human hematopoiesis. Understanding the role of the vascular niche in thymic reconstitution may provide novel insight into mechanisms of cross-talk within the cellular compartments of the thymus. PUBLIC HEALTH RELEVANCE: The ability to target expression of molecules specifically to the human thymus has broad therapeutic potential for both primary immune deficiencies like DiGeorge anomaly and for acquired states of thymic insufficiency that develop throughout postnatal life.