Pathological B Cells: Novel Strategies to Prevent and Treat Chronic GVHD

 描述(由申请人提供)：我们的目标是调查慢性移植物抗宿主病(CGVHD)的发生机制，以便实施更安全、更有效的异基因造血干细胞移植(HCT)策略。虽然我们和其他人的工作揭示了B细胞是cGVHD发病的关键因素，但导致病理性B细胞激活的免疫机制仍未确定。此外，B细胞如何介导cGVHD仍不清楚。由于免疫重建发生在无处不在的外来抗原的背景下，因此持续清除与受体组织有反应的淋巴细胞是实现或维持免疫耐受的必要条件。在HCT患者中，我们先前发现B细胞生存因子B细胞激活因子(BAFF)水平过高与cGVHD的发生显著相关。给予B细胞特异性抗体利妥昔单抗可改善cGVHD，但前提是幼稚的B细胞室出现强劲恢复，证实了B细胞稳态对cGVHD厌恶的重要性。在cGVHD患者的B细胞中，我们发现BAFF相关的信号通路是结构性信号。慢性GVHD B细胞在体内被激活，并为生存做好准备，这表明BAFF缺失耐受检查点失败。我们的中心假设是B细胞能够在免疫恢复过程中克服免疫耐受机制，介导cGVHD的病理生物学。我们最近的初步数据表明，在cGVHD中，潜在的病理性B细胞具有较低的B细胞受体(BCR)信号阈值。BCR对替代抗原反应性的增强与近端BCR分子水平、B细胞连接蛋白(BLNK)和脾酪氨酸激酶(Syk)水平的增加有关。慢性GVHD B细胞优先被小分子抑制剂阻断，揭示了cGVHD中异常B细胞激活的机制，并为我们拟议的临床试验奠定了基础。数据还支持了我们的推论，即cGVHD患者BCR信号阈值降低可能是由于BAFF过多。在这项提议中，我们将利用小鼠模型和人体化验来检验这一假设。我们还将通过测试BAFF如何驱动这些B细胞以及异常B细胞是否介导T细胞激活来确定具有疾病中介功能的B细胞亚群。具体地说，我们的目标是确定cGVHD中病理性B细胞的发展是否由于：1)过度的BAFF；2)即刻的Ag反应性；以及3)HCT后某些B细胞亚群的免疫调节失败。该提案包括共同研究人员和B细胞免疫学家Thomas Tedder博士，以及共同研究人员Rizzieri和Li博士以及他们的Duke临床试验和统计核心设施。当工作完成时，我们将拥有 确定血细胞移植后BAFF驱动的病理性B细胞如何以及何时出现，以便在患者中有效地实施有针对性的预防性治疗。我们的长期目标是通过安全有效的同种异体血细胞移植来改善血液系统恶性肿瘤和疾病患者的预后。

 DESCRIPTION (provided by applicant): Our goal is to investigate mechanisms responsible for chronic graft versus host disease (cGVHD) development so that strategies for safer, more effective allogeneic hematopoietic stem cell transplantation (HCT) can be implemented. While work by us and others has revealed that B cells are key contributors to cGVHD pathogenesis, the immune mechanisms responsible for pathological B-cell activation remain undetermined. Also, how B cells mediate cGVHD remains unknown. Since immune reconstitution occurs in the setting of ubiquitous foreign antigen, ongoing removal of lymphocytes reactive to recipient tissues is imperative to achieve or maintain immune tolerance. In HCT patients, we previously discovered that excessive levels of a B- cell survival factor, B Cell Activating Factor (BAFF) is significantly associated with cGVHD development. Administration of B-cell specific antibody, rituximab, results in cGVHD amelioration, but only if robust recovery of a naïve B cell compartment occurs, corroborating the importance of B cell homeostasis for cGVHD aversion. In cGVHD patients B cells, we found that BAFF-associated pathways constitutively signal. Chronic GVHD B cells are in vivo activated and primed for survival, suggesting a failure of the BAFF deletional tolerance checkpoint. Our central hypothesis is that B cells, that are able to overcome immune tolerance mechanisms during immune recovery, mediate cGVHD pathobiology. Our more recent preliminary data suggest that in cGVHD, potentially pathological B cells have a lowered B Cell Receptor (BCR) signaling threshold. An increased BCR responsiveness to surrogate antigen was associated with increases in the proximal BCR molecule levels, B-cell linker protein (BLNK) and Spleen tyrosine kinase (Syk). Chronic GVHD B cells were preferentially blocked by a small molecule inhibitor, revealing a mechanism underpinning aberrant B-cell activation in cGVHD and laying the foundation for our proposed clinical trials. Data also forward our corollary hypothesis that a lowered BCR signaling threshold in cGVHD patients may be due to excess BAFF. In this proposal we will utilize both murine models and human assays to test this hypothesis. We will also identify B cell subsets with disease-mediating function by testing how BAFF drives these B cells and whether aberrant B cells mediate T cell activation. Specifically, we aim to determine whether pathological B cells in cGVHD develop because of: 1) excess BAFF; 2) immediate Ag-responsiveness; and 3) failure of immune regulation by certain B cell subsets after HCT. This proposal includes co-investigator and B cell immunologist, Dr. Thomas Tedder, and co-investigators Drs. Rizzieri and Li along and their Duke clinical trial and statistical core facilities. When work is completed, we will have determined how and when BAFF-driven pathological B cells arise after HCT, so that targeted and preventative therapies can be effectively implemented in patients. Our long-term goal is to improve outcomes of patients with hematological malignancies and disorders with safe and effective allogeneic HCT.