Immunotherapeutics for the treatment of Acinetobacter baumannii infection

描述(由申请人提供)： 鲍曼不动杆菌是一种重要的医院内致病菌，可引起一系列感染，包括呼吸道和尿路感染、脑膜炎、心内膜炎、伤口感染和菌血症。事实上，鲍曼不动杆菌现在占世界某些地区所有重症监护病房感染的20%，肺炎是最常见的表现。此外，鲍曼不动杆菌是战斗士兵感染的重要原因，也是战场上四肢创伤后发现的最常见的革兰氏阴性杆菌。鲍曼不动杆菌对几乎所有抗生素迅速产生抗药性，这推动了它的临床意义。综上所述，这些事实证明鲍曼不动杆菌是对退伍军人健康的重大威胁。基于此，我们最近启动了一项研究计划，重点是确定针对鲍曼不动杆菌的治疗干预的新靶点。在本申请中，我们描述了我们发现的一种免疫增强生物，它对鲍曼不动杆菌肺炎具有巨大的治疗效果，并可以治愈小鼠的这种感染。我们已经有了一个令人兴奋的发现，无论转座子插入的位置如何，鲍曼不动杆菌的转座子诱变都会严重减弱其毒力。此外，经历了转座子诱变的菌株能够在联合感染实验中治愈鲍曼不动杆菌野生型引起的感染，并且这种减毒表型并不要求转座子诱变的菌株是活的。这种衰减需要暴露在鲍曼不动杆菌表面的DNA-蛋白质复合体，并依赖于宿主中关键的先天免疫信号通路。最后，我们发现，鲍曼不动杆菌转座子突变导致IV型分泌系统(T4SS)编码基因上调，并增加了电子显微镜下可见的毛状表面附属物的数量。基于这些发现，我们提出了鲍曼不动杆菌在暴露于外源DNA时上调其T4SS的模型，该分泌系统被宿主的固有免疫系统识别，以协调对入侵病原体的清除。为了检验这一模型，我们提出了一系列三个综合的具体目标。在目标1中，我们将定义鲍曼不动杆菌T4SS高表达蛋白诱导的免疫反应。这些实验的结果可能会导致合理设计治疗细菌性肺炎的免疫调节疗法。在目标2中，我们将阐明转座改变T4SS表达的机制。在这些实验中，我们将确定T4SS在接触外来DNA时上调的机制，并询问鲍曼不动杆菌T4SS对DNA转移和交换的影响。这些结果将为减少DNA转移和防止这种微生物获得抗菌素耐药决定簇的研究奠定基础。最后，在目标3中，我们将确定基于T4SS的免疫增强生物制品的广谱疗效。鲍曼不动杆菌转座子突变体对铜绿假单胞菌引起的肺炎具有治疗效果，提示该策略对多种感染性病原体具有广泛的适用性。除了这一发现的潜在临床好处外，这些拟议的实验将为我们提供一个研究感染过程中宿主与病原体相互作用的工具，目的是定义对革兰氏阴性病原体引起的肺炎的成功免疫反应。

DESCRIPTION (provided by applicant): Acinetobacter baumannii is an important nosocomial pathogen that causes a range of infections, including respiratory and urinary tract infections, meningitis, endocarditis, wound infections, and bacteremia. In fact, A. baumannii is now responsible for up to 20% of all intensive care unit infections in some regions of the world with pneumonia being the most common presentation. Additionally, A. baumannii is a considerable cause of infection in combat soldiers and is the most common gram-negative bacillus recovered from traumatic injuries to extremities obtained on the battlefield. The clinical significance of A. baumannii has been propelled by this organism's rapid acquisition of resistance to virtually all antibiotics. Taken together, these facts have established A. baumannii as a significant threat to the health of Veterans. Based on this, we have recently initiated a research program focused on identifying novel targets for therapeutic intervention against A. baumannii. In this application, we describe our discovery of an immune enhancing biologic that has tremendous therapeutic efficacy against A. baumannii pneumonia and can cure this infection in mice. We have made the exciting discovery that transposon mutagenesis of A. baumannii severely attenuates its virulence, regardless of the site of transposon insertion. Moreover, strains that have experienced transposon mutagenesis are capable of curing infections caused by wildtype A. baumannii during co-infection experiments, and this attenuating phenotype does not require that the transposon mutagenized strain is viable. This attenuation requires exposure of a DNA-protein complex on the surface of A. baumannii, and relies on key innate immune signaling pathways in the host. Finally, we have found that transposon mutagenesis of A. baumannii leads to up-regulation of genes encoding for the Type IV secretion system (T4SS) and increased abundance of pilus-like surface appendages visible by electron microscopy. Based on these findings, we propose a model whereby A. baumannii up-regulates its T4SS upon exposure to exogenous DNA, and this secretion system is recognized by the innate immune system of the host to coordinate clearance of the invading pathogen. To test this model we propose a series of three integrated Specific Aims. In Aim 1 we will define the immune response elicited by A. baumannii T4SS hyperexpressors. Results obtained from these experiments may lead to the rational design of immunomodulatory therapies for the treatment of bacterial pneumonia. In Aim 2 we will elucidate the mechanism by which transposition alters T4SS expression. In these experiments we will determine the mechanism by which the T4SS is up-regulated upon exposure to foreign DNA and interrogate the impact of the A. baumannii T4SS on DNA transfer and exchange. These results will lay the foundation for studies focused on reducing DNA transfer and preventing the acquisition of antimicrobial resistant determinants by this organism. Finally, in Aim 3 we will determine the broad spectrum efficacy of T4SS-based immune enhancing biologics. A. baumannii transposon mutants exhibit therapeutic efficacy against pneumonia caused by Pseudomonas aeruginosa suggesting that this strategy has broad applicability against a variety of infectious agents. In addition to the potential clinical benefits of this discovery, these proposed experiments will provide us with a tool to study the host-pathogen interaction during infection with the goal of defining a successful immune response to pneumonia caused by Gram negative pathogens.