Platelet Transfusion Induced Transplant Rejection Across mHA barriers.

描述（由申请人提供）：血小板输注是一种常见的治疗方法，用于治疗多种导致血小板计数低的疾病，血小板计数低可导致出血并发症。由于非恶性造血疾病（骨髓衰竭综合征或造血遗传缺陷），大量输血患者需要血小板，其唯一治疗方法是骨髓移植（BMT）。据观察，输血患者有较高的BMT排斥率，从而限制了利用BMT作为治疗的可行性。对排异率增加的一些解释已被提出，包括免疫效应。我们最近在一个动物模型中报道，血小板输注自身可以免疫移植抗原，从而导致后续的BMT排斥反应。由于BMT在这种情况下是MHC匹配的，这些抗原是次要组织相容性抗原（mHAs）。以前，人们认为输血中的污染白细胞是对次要抗原免疫的主要来源。然而，实施严格的白细胞诱导血液制品（每单位血液白细胞总数少于1x106）并没有降低慢性输血患者的BMT排斥率。基于这些发现，我们假设非白细胞成分负责免疫mha，在这种情况下，血小板本身。为了解决这一假设，并密切模拟人类输血，我们开发了分离和过滤白细胞减少小鼠血小板的程序，使用与人类相同的技术和过滤器。我们的数据表明，严格过滤的白细胞诱导的血小板仍然诱导BMT排斥。为了支持这一概念，我们在本申请中提供的数据表明，输血的血小板上的mHAs交叉呈现到受体抗原呈递细胞（APCs）的MHC I类途径中，导致受体CD8+ T细胞特异性激活和扩增mHAs。通过避免输血来避免免疫接种是不可行的，因为输血的血小板满足治疗的需要；因此，需要制定规避免疫屏障的策略。为了合理开发避免免疫的新方法，需要对血小板输注引起的免疫和随后的移植排斥反应有更详细的机制理解。我们建议通过以下具体目的来研究血小板输注诱导BMT排斥反应的机制。特异性目的1：阐明PLT输注诱导BMT排斥反应的免疫机制。特异性目的2：分析输注血小板携带mHAs对CD4+ T和CD8+ T细胞的免疫作用。特异性目的3：输血中不同细胞亚群的差异免疫原性。总之，提出的目标将提供血小板输注如何诱导后续BMT排斥反应的机制说明。这些研究有可能直接使需要血小板输注和随后的BMT的患者群体受益。

DESCRIPTION (provided by applicant): Platelet transfusions are a common therapeutic maneuver for a variety of diseases that result in low platelet counts, which can lead to bleeding complications. A substantial number of transfused patients require platelets due to non-malignant hematopoietic disorders (either bone marrow failure syndromes or genetic defects in hematopoiesis), the only cure for which is bone marrow transplants (BMT). It has been observed that transfused patients have higher rates of BMT rejection, thus limiting the feasibility of utilizing BMT as a cure. A number of explanations for the increased rejection rates have been suggested, including immunological effects. We have recently reported in an animal model, that platelet transfusions in of themselves immunize against transplantation antigens that can then cause subsequent BMT rejection. Since BMT in this setting is MHC matched, these antigens are minor histocompatibility antigens (mHAs). Previously, it has been assumed that contaminating leukocytes in blood transfusions were the main source of immunization to minor antigens. However, the implementation of stringently leukoreduced blood products (fewer than 1x106 total leukocytes per unit of blood) has not decreased the rate of BMT rejection in chronically transfused patients. Based upon these findings, we hypothesized that non-leukocyte components are responsible for immunization against mHAs, and in this case, the platelets themselves. To address this hypothesis, and to closely model human transfusion, we have developed procedures to isolate and filter leukoreduce murine platelets using the same techniques and filters as are used in humans. Our data demonstrate that stringently filter leukoreduced platelets still induce BMT rejection. In support of this concept, we present data in this application to indicate that mHAs on transfused platelets are crosspresented into the MHC class I pathway of recipient antigen presenting cells (APCs), resulting in activation and expansion of recipient CD8+ T cells specific for the mHAs. Avoiding immunization by avoiding transfusion is not feasible, as the transfused platelets fulfill a therapeutic necessity; thus, generating strategies to circumvent the immune barriers will be required. The rational development of new approaches to avoid immunization requires a more detailed mechanistic understanding of the immunization and subsequent transplant rejection that are caused by platelet transfusion. We propose to study the mechanisms of platelet transfusion induced BMT rejection through the following specific aims. Specific Aim 1: Elucidate the immune mechanisms of PLT transfusion-induced BMT rejection. Specific Aim 2: Analysis of CD4+ T and CD8+ T cell immunization by mHAs carried by transfused PLTs. Specific Aim 3: Differential immunogenicity of distinct cell subsets in transfused blood. Together, the proposed aims will provide a mechanistic elucidation of how platelet transfusion induces subsequent BMT rejection. These studies have the potential to directly benefit patient populations who require platelet transfusions and subsequent BMT.