Investigating the role of BCAP in human immunodeficiency and B-cell malignancy

一个功能正常的免疫系统对于应对感染和防止身体在自身免疫或炎症中攻击自身至关重要。原发性免疫缺陷（PID）是由免疫系统功能不良引起的罕见疾病，其特征是感染，通常伴有自身免疫和/或癌症。对于其中一些PID，已经确定了潜在的遗传原因，从而可以进行诊断，支持我们对疾病发生方式的理解，并可以开发新的靶向治疗方法。然而，对于大多数PID，原因尚不清楚。我们最近发现了一个患有PID的个体，并且丢失了一个名为PIK3AP1的基因，该基因通常会产生一种名为“b细胞磷酸肌肽3-激酶适配体”（BCAP）的蛋白质。这种蛋白质已经在动物模型中进行了研究，结果表明BCAP在免疫系统的许多部分都很重要，包括：b细胞的成熟，b细胞产生抗体来对抗细菌感染；t细胞的特化和存活，作为b细胞的助手，在对病毒和癌症的反应中也很重要；和其他免疫细胞，调节对炎症的反应。BCAP引起人类PID的问题以前从未被描述过。然而，BCAP已被证明在某些b细胞血癌中发挥作用，其功能可能异常增加，有助于抵抗某些癌症治疗。该项目旨在了解BCAP缺乏如何导致人类PID。由于完全缺乏b细胞和无法产生抗体是上述个体的主要问题，我们将首先研究BCAP缺乏如何导致人类b细胞数量和抗体产生问题。我们还将研究BCAP缺乏是否会影响人类其他免疫细胞，如t细胞和巨噬细胞。最后，由于BCAP已被证明在某些b细胞血癌中发挥作用，我们将测试BCAP是否可以作为治疗这些或其他疾病的靶点。为此，我们将使用BCAP缺陷和患者细胞的人类细胞系模型来研究BCAP在细胞信号通路中的作用。方法包括使用预期激活bcap相关信号通路的物质刺激bcap缺陷细胞和健康细胞，并使用一系列实验室技术测量该通路中的蛋白质是否被激活。我们还将研究BCAP蛋白如何与免疫细胞中的其他蛋白质相互作用，使用专业的质谱法可以识别与BCAP结合的蛋白质。我们将通过研究BCAP缺陷干细胞在什么阶段不能发育成b细胞来探索BCAP在b细胞发育中的作用，并看看我们是否可以通过恢复BCAP表达来挽救这种情况。最后，对于已知BCAP相关通路受到影响的某些b细胞血癌，我们将使用患者的血液样本检查BCAP功能，其在癌症治疗抗性中的作用，以及BCAP缺乏可能对阻止肿瘤生长的影响。这可能会导致新的血癌治疗方法的发展。该项目是迄今为止对人类BCAP最详细的研究。这将扩大我们对BCAP在人类免疫细胞中的作用和PID的遗传原因的理解，并有助于其他患者的诊断。它对PID以外的其他疾病也有影响，如b细胞癌，其中靶向b细胞功能是一种理想的治疗方法。

A functioning immune system is essential for responding to infection and preventing the body attacking itself in autoimmunity or inflammation. Primary Immunodeficiencies (PID) are rare diseases caused by poor functioning of the immune system and are characterised by infections, often with autoimmunity and/or cancer. For some of these PID, an underlying genetic cause has been identified, which allows diagnosis, supports our understanding of how the disease occurs, and can enable the development of new targeted treatments. However, for the majority of PID, the cause is not known.We recently identified an individual with PID and loss of a gene called PIK3AP1, which normally produces a protein named 'B-cell adaptor for phosphoinositide 3-kinase' (BCAP). This protein has been studied in animal models, which have shown BCAP to be important in many parts of the immune system, including: the maturation of B-cells, which produce antibodies to fight bacterial infections; the specialisation and survival of T-cells, which act as helpers to B-cells and are also important in the response to viruses and cancer; and other immune cells, mediating the response to inflammation. Problems with BCAP causing PID in humans have never been described before. However, BCAP has been shown to play a role in certain B-cell blood cancers, where its function can be abnormally increased, contributing to resistance to certain cancer treatments. This project aims to understand how BCAP deficiency causes PID in humans. As a complete lack of B-cells and inability to produce antibodies was the main issue seen in the individual described above, we will first examine how BCAP deficiency causes problems in B-cell numbers and antibody production in humans. We will also investigate whether BCAP deficiency impacts other immune cells, such as T-cells and macrophages, in humans. Finally, as BCAP has been shown to play a role in certain B-cell blood cancers, we will test whether BCAP could be targeted for treatment of these, or other, diseases. To do this, we will use human cell line models of BCAP deficiency and patient cells, to study the role of BCAP in cell signalling pathways. Methods include stimulating BCAP-deficient and healthy cells with substances that are expected to activate a BCAP-associated signalling pathway and measuring whether proteins in the pathway are activated, using a range of laboratory techniques. We will also look at how BCAP protein interacts with other proteins in immune cells, using specialist mass spectrometry that can identify proteins bound to BCAP. We will explore the role of BCAP in B-cell development by investigating at what stage BCAP-deficient stem cells fail to develop into B-cells, and to see if we can rescue this by restoring BCAP expression. Finally, for certain B-cell blood cancers where BCAP-related pathways are known to be affected, we will examine BCAP function, its role in resistance to cancer treatment, and the impact BCAP deficiency may have on halting tumour growth using blood samples from patients. This could lead to the development of new blood cancer treatments.This project represents the most detailed study of human BCAP to date. It will expand our understanding of the role BCAP plays in human immune cells and the genetic causes of PID, as well as assisting diagnosis for other patients. It has implications beyond PID to other disorders, such as B-cell cancers, where targeting B-cell function is a desirable treatment.