The Role of Somatic Mutations in Aplastic Anemia

 描述(由申请人提供)：再生障碍性贫血(AA)发病机制的概念框架的关键方面与可触发针对造血祖细胞和干细胞的免疫攻击的事件有关。在再生障碍性贫血的各种类型的自我定向免疫反应中，已经提出了对出现的克隆性产物的免疫肿瘤监视反应，这些反应具有交叉反应和对干细胞室的附带损害。这种可能性符合再障与克隆性骨髓增生异常综合征(MDS)密切的病理生理联系。后者是再生障碍性贫血的一种常见的晚期并发症，由于缺乏足够的细胞进行细胞形态或细胞遗传学评估，它以低细胞形式构成了误诊再生障碍性贫血的替代诊断。另一种解释再生障碍性贫血与克隆性造血疾病的病理生理学关系的理论与干细胞耗竭引起的寡克隆性可能导致有缺陷的干细胞招募的可能性有关。新的分子技术，包括高密度SNP阵列和下一代测序(NGS)，为研究再生障碍性贫血的分子发病机制创造了机会。这些新技术允许对涉及基因组主要部分的突变进行无偏见的筛查。它们还允许对克隆体系结构进行高灵敏度和分析。我们的初步结果表明，克隆性事件可能在再生障碍性贫血发病时就被检测到，或者发生在病程的早期。虽然体细胞突变的存在并不一定在所有情况下都会导致MDS，但如果随后发生MDS，很可能会在这些损害的基础上发生。在这一建议中，我们假设在部分AA患者的初始表现中可以检测到克隆事件，某些克隆事件是允许的，并通过获得继发性事件导致后期克隆进化和进展，而其他克隆事件可能被免疫系统根除。本项目的目的是评估AA患者存在体细胞克隆性损害的比例，并从免疫抑制和克隆性进化的反应方面确定此类基因缺陷的预后意义和诊断价值。此外，我们希望确定这些患者的祖先事件，以确定哪些继发事件会导致MDS。我们将筛查AA和AA后克隆性进化的患者队列，包括MDS和PNH，以确定他们病程中是否存在体细胞克隆性损害。通过系列和横截面分析，我们将研究由体细胞突变和染色体分析组成的等级克隆结构。最后，我们将建立临床相关性和这些克隆体细胞事件对预后的影响。将进行临床分析，以确定体细胞突变对进化风险与亚克隆性持久性、对免疫抑制的反应/耐受性的影响，以及PNH持久性或进化的速度和动力学。我们推测，在再生障碍性贫血中解决这些重要问题可能会导致对这种疾病的理解发生范式转变。

 DESCRIPTION (provided by applicant): The key aspect of the conceptual framework in the pathogenesis of aplastic anemia (AA) relates to the events that can trigger immune attacks directed against hematopoietic progenitor and stem cells. Immune tumor surveillance reactions to emerging clonal outgrowth with a cross-reactivity and collateral damage to the stem cell compartment have been proposed among various types of self-directed immune responses in AA. This possibility fits with the close pathophysiologic association of AA with clonal myelodysplastic syndromes (MDS). The latter is a common late-stage complication of AA and constitutes, in its hypocellular form, an alternative diagnosis in misdiagnosed AA because of the lack of sufficient cells for cytomorphologic or cytogenetic evaluation. An alternative theory explaining the pathophysiological relationship of AA to clonal diseases of hematopoiesis relates to the possibility that oligoclonality due to stem cell depletion may lead to a higher probability f recruitment of defective stem cells. New molecular technologies, including high-density SNP arrays and next generation sequencing (NGS), have created opportunities for study of the molecular pathogenesis of AA. These new technologies allow for unbiased screens for mutations involving major portions of the genome. They also allow for high sensitivity and analysis of clonal architecture. Our preliminary results suggest that clonal events may be detected in AA at presentation or occur very early in the course of the disease. While the presence of somatic mutations may not necessarily result in MDS in every instance, it is likely that if subsequent MDS develops it happens on the basis of these lesions. In this proposal we hypothesize that clonal events may be detected at initial presentation in a proportion of AA patients, and that certain clonal events are permissive and lead to late clonal evolution and progression through acquisition of secondary events, while others may be eradicated by the immune system. The objectives of this project are to assess the proportion of AA patients harboring somatic clonal lesions and determine the prognostic significance and diagnostic utility of such genetic defects in terms of response to immunosuppression and clonal evolution. In addition we hope to identify ancestral events in these patients that determine which secondary events lead to MDS. We will screen cohorts of patients with AA as well as post-AA clonal evolution, including MDS and PNH, for the presence of somatic clonal lesions during the course of their disease. By serial and cross-sectional analysis we will investigate hierarchical clonal architecture consisting of somatic mutations and chromosomal analysis. Finally, we will establish clinical correlations and the prognostic impact of these clonal somatic events. Clinical analyses will be performed to determine the impact of somatic mutations on risk of evolution vs. sub clonal persistence, response/refractoriness to immunosuppression, and the speed and dynamics of PNH persistence or evolution. We postulate that addressing these important questions in AA may lead to paradigm-shifting concepts in the understanding of this disease.