| 摘要: | 造血作用(Hematopoiesis)是所有血液譜系細胞產生的連續過程，並於個體有生之年持續進行。而血幹細胞則被視為一群有能力經由自我更生、定向分化以及終末分化產生許多不同的成熟血球之細胞。在此過程中，淋巴血球的製造是經由造血幹細胞定向分化轉換成共同淋巴前趨細胞，其再經終末分化而完成。因此淋巴前趨細胞被視為有分化成所以淋巴細胞(包括T 細胞、B 細胞以及自然殺手細胞)之潛能但無分化成骨隨細胞(包括紅血球，血小板，巨噬細胞等)之潛能的特定細胞族群。許多科學家致力於共同淋巴前趨細胞之辨識，但是辨識過程中最大的困難是必須要有一套可以檢測到低數量甚至單一細胞之人類前趨細胞以及多功能幹細胞的系統。儘管我們可以利用外生檢測(xenogenetic assay)分析以及基因標記(gene marking)來測定血液樣品中其細胞之分化能力，但此方法敏感度低，進而影響到檢測之結果。縱使如此，共同淋巴前趨細胞之辨識為現今所迫切需要的知識，因為我們可以從中理解以及探討定向分化以及終末分化的機制。在我們提出的計畫中，我們將嘗試在人類正常骨髓以及周邊血中鑑定出共同淋巴前趨細胞，其有能力分化成T 細胞、B 細胞以及自然殺手細胞卻無能力分化成骨髓細胞。此外，我們也將探討共同淋巴前趨細胞分化成T 細胞、B 細胞以及自然殺手細胞之分化的時序變化，以及探討細胞所存在的利基(niche)環境對於這些共同淋巴前趨細胞分化的影響。最後，我們還將嘗試鑑定這些共同淋巴前趨細胞特殊分化能力的根本分子差異。從計畫中所獲得的實驗結果將有助於我們建立一個更完整對人類造血系統中每一種淋巴細胞之間的等級與發育關係的全貌。我們所辨識出的共同淋巴前趨細胞將可用於移植以及當作基因操作的標靶，針對於淋巴組織生成缺陷患者提供一個替代的治療方法。
Hematopoiesis is a continuum process of blood cell production in all lineages, which lasts the lifespan of the individual. It can also be viewed as a process with distinguishable stages of self-renewal, lineage restriction and terminal differentiation of stem cells as well as their progeny. Hematopoietic stem cells (HSC) are defined as having the ability to generate daughter cells that are still competent to produce all blood cell lineages (self-renewal) and/ or to differentiate irreversibly generating progeny in all hematopoietic lineages (pluripotency). The traditional model of lympho-hematopoietic differentiation from pluripotent stem cells proposes that all lymphopoiesis is derived from a common lymphoid progenitor (CLP). The CLP would therefore be, by definition, a lineage restricted progenitor with full lymphoid potential (T-, B-, and natural killer [NK] cell) but no capacity for myeloid, erythroid, or megakaryocytic differentiation potential. Many efforts have been devoted in the isolation of functionally distinct lineage restricted cell populations. However, the identification of human common lymphoid progenitor has been hampered by the technical inability to measure the myeloid and lymphoid lineage potential of single or low number human progenitors and pluripotent stem cells. Although in vivo xenogeneic assays can be used to measure the lineage potential of whole populations, the lineage potential of individual cells cannot be assessed without the use of inefficient gene marking method. Despite all these difficulties that we may need to overcome, the identification of lymphoid restricted progenitors will facilitate the study of how the earliest and distal events in human lymphoid commitment are regulated. In this study, we will try to Identify a primitive cell population with only lymphoid but no myeloid differentiation potential, that are capable of generating T-, B-, and NK cells, in normal human bone marrow and mobilized peripheral blood. We will also examine the temporal kinetics of T-, B-, and NK progeny outputs from the lymphoid-restricted progenitor identified in normal human mobilized peripheral blood cells at various time points during cultures (bulk + clonal levels) and whether the output kinetics may be altered by niche condition. Finally, we will attempt to characterize the molecular differences that underlying the distinct differentiation potential of the lymphoid -restricted progenitors in normal human mobilized peripheral blood. Data obtained from this study will help to establish a more complete picture on the hierarchal and developmental relationships between each type of lymphoid cells in human hematopoietic system. Identified primitive lymphoid progenitors will useful as transplantation and targets for genetic manipulation, providing an alternative therapeutic treatment in disease that specifically affecting lymphopoiesis. |
