CLONAL EVOLUTION OF HEMATOPOIETIC STEM CELLS DURING CHEMOTHERAPY AND TRANSPLANTATION

 描述(由申请人提供)：申请人提出一个五年计划，为候选人提供有指导的研究和职业发展培训。他最近在华盛顿大学医学院完成了血液学/肿瘤学奖学金(和内科科学家培训计划)的正式培训，并被提升为肿瘤科的医学讲师。在他职业生涯的这个关头，他希望得到更多的指导支持，以促进他的科学和职业目标。候选人的最终目标是成为学术医学中心的独立研究员，研究正常和恶性造血，并照顾血液病和癌症患者。本申请中概述的实验旨在了解化疗在促进某些化疗耐药造血克隆的竞争适应优势和随后扩展方面的作用及其潜在的临床后果。拟议的研究将在丹尼尔·林克博士的主要指导下在华盛顿大学进行。林克博士是世界著名的造血领域的领导者。他也是一位经验丰富、备受尊敬的导师，成功地指导了无数学员走向独立。与治疗相关的急性髓系白血病(t-AML)和与治疗相关的骨髓增生异常综合征(t-MDS)是公认的细胞毒性化疗和/或放射治疗的并发症(Godley等人；Semin Oncol2008)。我们研究的长期目标是确定暴露于细胞毒治疗如何有助于白血病的发生。造血干细胞和祖细胞(HSPC)在正常衰老过程中积累体细胞突变，导致健康成年人中的HSPC群体具有遗传异质性(Welch等人；Cell 2012)。在我们的初步数据中，我们使用了一种敏感的纠错下一代测序(NGS)方法来鉴定健康老年人外周血白细胞中非常小的群体中的功能性TP53突变。此外，在几个t-AML/t-MDS病例中，我们发现在诊断时驱动TP53突变的克隆性实际上在化疗开始前的骨髓中出现的频率很低。基于这些数据，我们假设细胞毒治疗提供了一种选择压力，导致了携带某些体细胞突变的HSPC的适合性优势，包括TP53中的那些。为了进一步扩展这一假说，提出了以下具体目标：1)确定携带TP53突变的HSPC在接受自体干细胞移植的复发/难治性淋巴瘤患者中的发生率和克隆性扩展，2)鉴定额外的体细胞突变，使HSPC在细胞毒性化疗和自体移植后具有竞争适应性优势，以及3)表征TP53突变使HSPC在化疗后具有竞争适应性的机制。这些拟议的实验将确定强化化疗对造血干细胞克隆进化的影响程度，并确定TP53(及相关基因)的体细胞突变为某些HSPC提供适合性优势的机制。最终，我们希望开发用于-AML/t-MDS风险分层和早期检测的诊断工具，并潜在地防止这种预后不良的疾病的演变。特别是，更好地理解功能性TP53突变导致化疗后克隆HSPC扩张的机制可能会导致潜在地降低t-AML/t-MDS风险的策略。

 DESCRIPTION (provided by applicant): The applicant proposes a five year plan to provide the candidate with mentored research and career development training. He recently completed his formal training in the Hematology/Oncology fellowship (and Physician Scientist Training Program) at Washington University School of Medicine and was promoted to an Instructor of Medicine in the Division of Oncology. At this juncture of his career, he desires additional mentored support to facilitate his scientific and career goals. The ultimate goal of the candidate is to be an independent investigator in an academic medical center, studying normal and malignant hematopoiesis and taking care of patients with hematologic diseases and cancer. The experiments outlined in this application aim to understand the role of chemotherapy in promoting the competitive fitness advantage and subsequent expansion of certain chemo-resistant hematopoietic clones and its potential clinical ramifications. The proposed studies will be carried out at Washington University under the primary mentorship of Dr. Daniel Link. Dr. Link is a world- renowned leader in the field of hematopoiesis. He is also a highly experienced and well-regarded mentor who has successfully mentored numerous trainees to independence. Therapy-related acute myeloid leukemia (t-AML) and therapy-related myelodysplastic syndrome (t-MDS) are well-recognized complications of cytotoxic chemotherapy and/or radiotherapy (Godley, et al; Semin Oncol 2008). The long-term goal of our research is to determine how exposure to cytotoxic therapy contributes to leukemogenesis. Hematopoietic stem and progenitor cells (HSPCs) accumulate somatic mutations during the normal aging process, resulting in a genetically heterogeneous HSPC population in healthy adult individuals (Welch, et al; Cell 2012). In our preliminary data, we used a sensitive error-corrected next-generation sequencing (NGS) approach to identify functional TP53 mutations in very small populations of peripheral blood leukocytes in healthy elderly individuals. Furthermore, in several cases of t-AML/t-MDS, we found that the driver TP53 mutation clonal at diagnosis was in fact present at low frequencies in the bone marrow prior to the initiation of chemotherapy. Based on these data, we hypothesize that cytotoxic therapy is providing a selective pressure resulting in a fitness advantage to HSPCs harboring certain somatic mutations, including those in TP53. To further expand upon this hypothesis, the following specific aims are proposed: 1) Determine the incidence and assess the clonal expansion of HSPCs harboring TP53 mutations in patients with relapsed/refractory lymphoma undergoing autologous stem cell transplantation, 2) Identify additional somatic mutations providing HSPCs with a competitive fitness advantage after cytotoxic chemotherapy and autologous transplantation, and 3) Characterize the mechanisms by which TP53 mutations confer competitive fitness to HSPCs after chemotherapy. These proposed experiments will define the degree to which intensive chemotherapy influences the clonal evolution of hematopoietic stem cells and define the mechanisms through which somatic mutations in TP53 (and related genes) provide certain HSPCs with a fitness advantage. Ultimately, we hope to develop diagnostic tools for the risk stratification and early detection of -AML/t-MDS and potentially prevent the evolution of this poor prognosis disease. In particular, a better understanding of the mechanisms by which functional TP53 mutations result in clonal HSPC expansion after chemotherapy may lead to strategies to potentially reduce the risk of t-AML/t-MDS.