Pathfinder: Determining the efficacy of plasmapheresis as a treatment for patients with chronic Pseudomonas infections and inhibitory antibodies

慢性铜绿假单胞菌肺部感染可见于囊性纤维化、非囊性纤维支气管扩张症和慢性阻塞性肺疾病患者。这种感染导致慢性炎症，肺功能恶化，发病率和死亡率增加。一旦确定了定植，用目前的方法几乎不可能根除假单胞菌。方法改善感染对患者的生活质量和寿命有积极影响，抗体对感染具有正常保护作用。然而，最近我们发现，一些慢性假单胞菌肺部感染患者有一种抗体，这种抗体实际上可以保护他们的定植细菌不被免疫系统杀死。这些抑制性抗体被发现可以防止患者的假单胞菌同源菌株的血清和细胞杀伤。这些抑制抗体被鉴定为对脂多糖特异的IgG2，特别是O-抗原成分。我们推测，这些抗体可能通过使补体沉积在细菌膜外，防止膜攻击复合体插入，或通过阻断保护性抗体的访问而发挥其抑制作用。重要的是，我们发现高滴度抑制性抗体的患者比血清杀伤正常的假单胞菌感染患者的肺功能更差。根据我们的数据，我们选择了对一名患有抑制性抗体的危重患者进行根治性治疗。使用血浆置换，我们去除了所有血清蛋白，包括抑制的IgG2，并用IVIg取而代之，我们已经证明IVIg可以介导患者分离的血清杀伤。患者在血浆置换后显著好转，痰中假单胞菌在相当长的一段时间内仍未被检测到。第二名危重患者最近接受了类似的治疗方案，取得了类似的成功。接受这种治疗的患者需要更少的住院天数，更少的治疗干预，如静脉注射抗生素，报告的症状水平大大减轻。令人兴奋的是，这为患有抑制性抗体的危重患者提供了一种新的治疗方法，但许多关键问题仍未得到回答。该项目对于确定抑制性抗体在慢性假单胞菌肺部感染患者中的临床相关性以及确定血浆置换是否是这一新问题的可行治疗方案至关重要。该项目将使用两种方法来实现这一点；第一，通过确定大量患有慢性支气管炎和非慢性支气管扩张症的患者中抑制性抗体的流行率。这将确定问题的规模，并彻底调查抑制性抗体和健康恶化之间的联系。其次，该项目将通过对目前正在接受血浆置换治疗的患者进行纵向研究来调查治疗方案。我们将确定以前的血浆置换治疗是否由于抑制性抗体的去除而成功，或者是否有其他因素在起作用。我们将调查IgG2的增加是否与菌株的复发和疾病的恶化有关。我们还将使用下一代测序来确定菌株替换是否由血浆置换驱动，因为这将支持这样的理论，即抑制抗体的去除对免疫系统控制血浆置换后感染的能力产生了积极影响。最后，该项目旨在优化一种检测抑制性抗体存在的诊断测试。

Chronic Pseudomonas aeruginosa lung infections occur in patients suffering from cystic fibrosis (CF), non-CF bronchiectasis and chronic obstructive pulmonary disorder (COPD). Such infections lead to chronic inflammation, deteriorating lung function and increased morbidity and mortality. Once colonisation is established, Pseudomonas is almost impossible to remove by current methods. Methods to ameliorate infection would positively impact on patient quality of life and longevity.Antibody normally protects against infection. However, recently we identified that some patients with chronic Pseudomonas lung infections had a type of antibody that actually protects their colonising bacteria from killing by the immune system. These inhibitory antibodies were found to prevent both serum and cell killing of patient's Pseudomonas cognate strains. The inhibitory antibodies were identified as IgG2 specific to lipopolysaccharide, specifically the O-antigen component. We hypothesise that these antibodies exert their inhibitory effect either by depositing complement away from the bacterial membrane preventing membrane attack complex insertion or by blocking access of protective antibody. Importantly, we found patients with high titres of inhibitory antibodies had worse lung function than patients infected with Pseudomonas who had normal serum killing. Based on our data, we opted for a radical treatment programme for one critically ill patient who had inhibitory antibodies. Using plasmapheresis we removed all serum protein, including the inhibitory IgG2, and replaced it with IVIg that we had demonstrated could mediate serum killing of the patient's isolate. The patient improved dramatically after plasmapheresis and Pseudomonas remained undetectable in the sputum for a significant period of time. A second critically ill patient has recently undergone a similar treatment regime with similar success. Patients receiving this treatment required fewer days in hospital, fewer treatment interventions such as intravenous antibiotics and reported a much reduced level of symptoms. Excitingly, this offers a novel treatment for critically ill patients with inhibitory antibodies, however many vital questions remain unanswered. This project is vital to determine the clinical relevance of inhibitory antibodies in patients with chronic Pseudomonas lung infections and to identify whether plasma exchange is a viable treatment option for this novel problem. The project will do this using two approaches; first, by determining the prevalence of inhibitory antibodies in a large cohort of patients with both CF and non-CF bronchiectasis. This will determine the scale of the problem as well as thoroughly investigate the link between inhibitory antibodies and health degradation. Secondly, the project will investigate the treatment option by conducting a longitudinal study on patients currently being treated by plasma exchange. We will identify if previous plasma exchange treatments were successful due to removal of inhibitory antibodies alone, or if other factors were at play. We will investigate whether increases in IgG2 correlate with reappearance of the strain and worsening disease. We will also use next-generation sequencing to determine if strain replacement is being driven by plasmapheresis, as this would support the theory that the removal of inhibitory antibody is having a positive impact on the ability of the immune system to control infection post plasma exchange. Finally, this project aims to optimise a diagnostic test for detecting the presence of inhibitory antibodies.