Platelet Transfusion Induced Transplant Rejection Across mHA barriers.

描述(申请人提供)：血小板输注是一种常见的治疗各种疾病的手法，这些疾病会导致低血小板计数，这可能会导致出血并发症。相当多的输血患者由于非恶性造血疾病(骨髓衰竭综合征或造血遗传缺陷)而需要血小板，唯一的治疗方法是骨髓移植(BMT)。已经观察到，输血患者的骨髓移植排斥反应发生率较高，因此限制了利用骨髓移植作为治疗方法的可行性。对于排斥率的增加，人们提出了许多解释，包括免疫效应。我们最近在一个动物模型中报道，血小板输注本身就能对移植抗原产生免疫，从而导致随后的骨髓移植排斥反应。由于这种情况下的骨髓移植是MHC相合的，这些抗原是次要组织相容抗原(MHAS)。以前，人们认为输血中污染的白细胞是对次要抗原免疫的主要来源。然而，实施严格的去白细胞血液产品(每单位血中总白细胞少于1x106)并没有降低长期输血患者的骨髓移植排斥反应的发生率。基于这些发现，我们假设非白细胞成分负责对MHA的免疫，在这种情况下，是血小板本身。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，严格过滤去白细胞的血小板仍然会诱导骨髓移植排斥反应。为了支持这一概念，我们在本申请中提供的数据表明，输注的血小板上的MHA交叉进入受体抗原提呈细胞(APC)的MHC I类途径，导致MHA特异性的受体CD8+T细胞的激活和扩增。通过避免输血来避免免疫是不可行的，因为输注的血小板满足了治疗的需要；因此，需要产生绕过免疫屏障的策略。合理开发避免免疫的新方法需要对免疫和随后的移植排斥反应有更详细的机械理解，这些都是由于输注血小板引起的。我们建议通过以下特定的目的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PLT输注诱导骨髓移植排斥反应的免疫机制。特异性目的2：分析输注的PLT携带的mHAS对CD4+T细胞和CD8+T细胞的免疫效果。具体目标3：输血中不同细胞亚群的不同免疫原性。总之，拟议的AIMS将为血小板输注如何导致随后的骨髓移植排斥反应提供一个机制阐明。这些研究有可能直接造福于需要血小板输注和随后的骨髓移植的患者群体。 与公共卫生相关：骨髓移植代表着一种治疗多种疾病的方法，包括再生障碍性贫血、镰状细胞性贫血、β-地中海贫血、钻石布莱克凡贫血、范科尼贫血、骨髓增生异常综合征等。然而，在接受输血作为治疗的一部分的患者中，使用骨髓移植的治愈率会降低，而输血是上述大多数疾病所必需的。这项拨款建议研究输注血小板导致骨髓移植排斥反应的机制；了解这些机制将为提高骨髓移植的治愈率提供合理的基础，从而使所有患有上述和相关疾病的人受益。

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. PUBLIC HEALTH RELEVANCE: Bone marrow transplantation represents a cure for a wide variety of diseases, including aplastic anemia, sickle cell anemia, beta-thalassemia, Diamond Blackfan anemia, Fanconi anemia, myelodysplastic syndromes, and others. However, the cure rate using bone marrow transplant is decreased in patients who have received transfusions as part of their therapy, which is required for most of the above diseases. This grant proposes to study the mechanisms by which transfusion of platelets induces rejection of bone marrow transplantation; understanding these mechanisms will provide a rational basis to increasing cure rates using bone marrow transplantation, and thus stands to benefit all individuals with the listed and related diseases.