Defining the specific features of human thymic B cell subsets, their relationship to primary mediastinal B cell lymphoma and nodular sclerosis Hodgkin lymphoma, and pathogenetic mechanisms in these lymphomas

胸腺含有少量成熟的B细胞。在小鼠身上的研究表明，这些细胞在T细胞选择中起着重要作用。然而，人们对它们的具体特征和功能以及它们与人类常规外周血B细胞的关系知之甚少。此外，胸腺B细胞被认为是原发性纵隔B细胞淋巴瘤(PMBCL)的起源细胞，也被认为是青年结节性硬化性霍奇金淋巴瘤(NS-HL)的起源。但是，同样缺乏澄清胸腺B细胞和这两种类型淋巴瘤之间关系的分子研究。我们假设人类胸腺B细胞代表不同的B细胞亚群，具有独特的特征，它们代表了年轻人PMBCL和NS-HL的细胞起源。在准备工作中，我们用流式细胞术鉴定了胸腺B细胞的四个亚群(具有幼稚B细胞表型的细胞、IgM记忆B细胞、类转换B细胞和罕见的CD30+B细胞)。我们的目的是通过对这些胸腺B细胞亚群的B细胞受体谱进行详细的分析，确定它们的分化阶段、克隆组成和亚群间的关系。我们计划通过RNA测序的转录组分析，与传统的幼稚和记忆B细胞进行比较，全面表征它们的特定基因表达模式。通过这一点，我们的目标是深入了解胸腺B细胞的特定免疫学特征。通过比较PMBCL和NS-HL的胸腺B细胞和分离的肿瘤细胞的基因表达谱，我们将确定正常细胞和恶性细胞之间的关系，以此来阐明胸腺B细胞是否是这两种类型淋巴瘤的起源，并确定淋巴瘤细胞中表达下调的基因。我们还将挖掘淋巴瘤的RNA测序数据，以寻找突变和融合转录本，以识别新的遗传病变。对于选定的非调控或突变基因，我们将在淋巴瘤细胞系上进行功能研究，以阐明这些事件的致病作用。总之，我们的目标是首次对仍然神秘的人类胸腺B细胞进行全面的表征，阐明年轻人的PMBCL和NS-HL是否是来自胸腺B细胞，确定这些淋巴瘤中表达的非调控基因，并揭示PMBCL和NS-HL的新的发病机制。

The thymus contains a small population of mature B cells. There is indication from studies in the mouse that these cells have an important role in T cell selection. However, only very little is known about their specific features and functions, and their relationship to conventional peripheral blood B cells in the human. Moreover, thymic B cells are considered as the cell of origin of primary mediastinal B cell lymphoma (PMBCL), and are also discussed as the origin of nodular sclerosis Hodgkin lymphoma (NS-HL) in young adults. But again, molecular studies to clarify the relationship between thymic B cells and the two types of lymphomas are missing. We hypothesize that human thymic B cells represent distinct B cell subsets with unique features and that they represent the cellular origin of PMBCL and NS-HL of young adults. In preparatory work, we identified four subsets of thymic B cells by flow cytometry (cells with the phenotype of naive B cells, IgM memory B cells, class-switched B cells and rare CD30+ B cells). We aim to determine the differentiation stage, clonal composition and intersubset relationship of these thymic B cell subsets by detailed analysis of their B cell receptor repertoire by amplicon next generation sequencing. We plan to comprehensively characterize their specific gene expression pattern in comparison to conventional naive and memory B cells through a transcriptome analysis by RNA sequencing. With this, we aim to obtain insight into the specific immunological features of thymic B cells. By comparison of the gene expression pattern of thymic B cells and isolated tumor cells of PMBCL and NS-HL we will determine the relationship between the normal and malignant cells as a means to clarify whether thymic B cells are the origin of the two types of lymphomas and identify deregulated genes in the lymphoma cells. We will also mine the RNA sequencing data of the lymphomas for mutations and fusion transcripts to identify novel genetic lesions. For selected deregulated or mutated genes we will perform functional studies on lymphoma cell lines to clarify the pathogenetic role of these events. Overall, we aim to perform the first comprehensive characterization of the still enigmatic human thymic B cells, clarify whether PMBCL and NS-HL in young adults are derived from thymic B cells, determine deregulated gene expression in these lymphomas, and reveal novel pathogenetic mechanisms in PMBCL and NS-HL.