Platelet Transfusion Induced Transplant Rejection Across mHA barriers.

描述（由申请人提供）：血小板输注是导致血小板计数低的各种疾病的常见治疗方法，可导致出血并发症。大量输血患者由于非恶性造血疾病（骨髓衰竭综合征或造血中的遗传缺陷）而需要血小板，唯一的治愈方法是骨髓移植（BMT）。已经观察到输血患者具有较高的BMT排斥率，因此限制了利用BMT作为治愈的可行性。排斥率增加的原因有很多，包括免疫学效应。我们最近在一个动物模型中报道，血小板输注本身可以免疫移植抗原，然后引起随后的BMT排斥反应。由于这种情况下的BMT是MHC匹配的，因此这些抗原是次要组织相容性抗原（mHA）。以前，人们认为输血中的白细胞污染是次要抗原免疫的主要来源。然而，实施严格的白细胞减少的血液制品（每单位血液的白细胞总数小于1x 106）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针对mHA的免疫，在这种情况下，血小板本身。为了解决这一假设，并密切模拟人输血，我们已经开发了程序，分离和过滤白细胞减少小鼠血小板使用相同的技术和过滤器，用于人类。我们的数据表明，严格过滤去白细胞的血小板仍然诱导BMT排斥反应。为了支持这一概念，我们在本申请中提供的数据表明，输注血小板上的mHA交叉呈递到受体抗原呈递细胞（APC）的MHC I类途径中，导致对mHA特异性的受体CD 8 + T细胞的活化和扩增。通过避免输血来避免免疫接种是不可行的，因为输注的血小板满足了治疗的需要;因此，需要制定规避免疫屏障的策略。避免免疫接种的新方法的合理开发需要对血小板输注引起的免疫接种和随后的移植排斥反应有更详细的机械理解。我们拟通过以下几个方面来研究血小板输注诱导骨髓移植排斥反应的机制。具体目的1：阐明血小板输注诱导骨髓移植排斥反应的免疫机制。具体目的2：分析输注PLT携带的mHA对CD 4 + T和CD 8 + T细胞的免疫作用。具体目标3：输血中不同细胞亚群的差异免疫原性。总之，所提出的目标将提供一个机制阐明如何血小板输注诱导随后的骨髓移植排斥反应。这些研究有可能使需要血小板输注和随后的BMT的患者人群直接受益。

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.