Platelet Transfusion Induced Transplant Rejection Across mHA barriers.

血小板输注是导致血小板减少的多种疾病的常见治疗手段。 计数，这可能导致出血并发症。大量输血患者需要血小板 由于非恶性造血系统疾病（骨髓衰竭综合征或遗传缺陷， 造血），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，包括免疫学上的 方面的影响.我们最近在一个动物模型中报告说，血小板输注本身可以免疫 针对移植抗原，然后可能导致随后的BMT排斥反应。由于BMT在此设置中是 MHC匹配，这些抗原是次要组织相容性抗原（mHAs）。此前， 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（少于1x106总白细胞每 单位血液）并没有降低慢性输血患者的骨髓移植排斥率。基于 根据这些发现，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，我们已经开发了程序，以分离和过滤白细胞减少小鼠血小板使用相同的 技术和过滤器在人类中使用。我们的数据表明，严格过滤白细胞减少， 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了数据，以表明 输注血小板上的mHA交叉呈递到受体抗原的MHC I类途径中， 在一些实施方案中，所述方法包括将所述细胞与所述呈递细胞（APC）结合，导致对mHA特异性的受体CD8+ 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，因为输注的血小板实现了治疗作用。 因此，需要制定规避免疫屏障的战略。合理 开发避免免疫接种的新方法需要更详细的机制理解， 血小板输注引起的免疫和随后的移植排斥。我们建议 通过以下几个方面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CD4+ T和CD8+ 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血小板输注如何诱导 随后的BMT拒绝。这些研究有可能直接使需要治疗的患者群体受益。 血小板输注和随后的BMT。

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 has 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 require 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.