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病原体，其引起一系列感染，包括呼吸道和泌尿道感染、脑膜炎、心内膜炎、伤口感染和菌血症。事实上，A.鲍曼不动杆菌现在是世界上某些地区所有重症监护室感染的20%的原因，其中肺炎是最常见的表现。此外，A.鲍曼不动杆菌是战斗士兵感染的重要原因，并且是从战场上获得的四肢创伤中恢复的最常见的革兰氏阴性杆菌。探讨了A.鲍曼不动杆菌是由这种微生物迅速获得对几乎所有抗生素的耐药性而引起的。综上所述，这些事实已经确立了A。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A.鲍曼不动杆菌。在本申请中，我们描述了我们发现的一种免疫增强生物制剂，其对A.鲍曼不动杆菌肺炎，并能治愈这种感染的小鼠。 我们已经取得了令人兴奋的发现，转座子诱变的A。无论转座子插入的位点如何，鲍曼不动杆菌都严重减弱了其毒力。此外，经历转座子诱变的菌株能够治愈由野生型A引起的感染。在共感染实验中，这种减毒表型不需要转座子诱变的菌株是活的。这种衰减需要暴露在A.鲍曼不动杆菌，并且依赖于宿主中的关键先天免疫信号传导途径。最后，我们发现转座子诱变A。鲍曼不动杆菌导致编码IV型分泌系统（T4 SS）的基因的上调和通过电子显微镜可见的菌毛样表面附属物的丰度增加。基于这些发现，我们提出了一个模型，其中A。当暴露于外源DNA时，鲍曼不动杆菌上调其T4 SS，并且该分泌系统被宿主的先天免疫系统识别以协调入侵病原体的清除。为了测试这个模型，我们提出了一系列的三个综合具体目标。在目标1中，我们将定义由A引起的免疫应答。鲍曼不动杆菌T4 SS高表达。从这些实验中获得的结果可能会导致合理设计的免疫调节疗法治疗细菌性肺炎。在目标2中，我们将阐明转座改变T4 SS表达的机制。在这些实验中，我们将确定T4 SS在暴露于外源DNA时上调的机制，并询问A.鲍曼不动杆菌T4 SS对DNA转移和交换的影响。这些结果将为减少DNA转移和防止该微生物获得抗生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T4 SS的免疫增强生物制剂的广谱功效。A.鲍曼不动杆菌转座子突变体对铜绿假单胞菌引起的肺炎表现出治疗功效，这表明该策略对多种感染因子具有广泛的适用性。除了这一发现的潜在临床益处之外，这些拟议的实验将为我们提供一种研究感染期间宿主-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应答。

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.