PspA: A Potential Pneumococcal Vaccine Component

描述（由申请人提供）：肺炎球菌表面蛋白A （PspA）是预防肺炎链球菌（Sp）感染的主要候选疫苗。该资助解决了定义PspA和抗体（Ab）对PspA的作用机制的关键问题。这一信息对于我们了解Sp的发病机制以及PspA作为普通蛋白疫苗的潜在用途非常重要。拟议的实验构成了PspA重新进行人体试验之前需要的最后一些临床前研究。关于PspA和Ab对PspA的作用机制的新信息和现有信息将用于开发和测试由Ab对PspA介导的体内保护的体外替代试验的相关性。需要相关的替代检测来评估I期和II期人体安全性和免疫原性试验的免疫血清。获得的信息将为决定是否应该进行更昂贵的III期疗效试验提供科学依据。PspA可以抑制C‘的活化和在Sp上的表面沉积。Ab对PspA可以增强C’在Sp上的沉积。我们的研究也应该揭示PspA阻断C'活化的机制。在包括转基因小鼠和KO小鼠在内的研究中，我们将评估Ab对PspA对Sp的吞噬、免疫粘附和血液清除的影响。PspA还通过中和乳铁蛋白及其阳离子肽乳铁蛋白来阻止脱乳铁蛋白杀死Sp。Ab - PspA阻止PspA-乳铁蛋白相互作用，从而增强了乳铁蛋白杀死Sp的能力。我们将使用乳铁蛋白KO小鼠来帮助确定这些作用是否具有体内相关性。我们还将确定PspA是否也可以防止其他阳离子肽的杀伤。我们将使用一组针对PspA的不同结构域和表位的单抗，以及配对的免疫前和免疫后（抗PspA）人类血清，以帮助我们确定哪一种抗体对PspA的保护机制试验最能预测同一单抗被动保护小鼠免受感染的能力。获得的结果将使我们能够确定对体内保护和体外分析至关重要的机制，这些机制将最好地作为PspA抗体介导的体内保护的体外替代品。最后，该建议包括对我们观察到的PspA富含脯氨酸（PR）结构域的免疫可以引起对感染的保护的扩展调查。这一发现可能对使用PspA作为疫苗极为重要，因为先前观察到PspA的保护诱导线圈（CC）结构域的一些Ab可以在室温下与变性肌球蛋白发生反应。尽管没有令人信服的理由相信这一观察结果具有临床相关性，但它已经引起了营利性疫苗公司的紧张。如果正如我们所期望的那样，PR结构域的免疫具有广泛的有效性和交叉保护作用，那么PR结构域将不仅提供一种绕过对CC结构域的理论担忧的手段，而且还将是一种更有效的免疫原。公共卫生相关性：本申请描述了临床前研究，以确定肺炎链球菌蛋白PspA的毒力机制和引发抗体的保护作用。这一信息对于了解PspA在发病机制中的作用以及我们在此开发的体外替代法检测Ab对PspA的体内保护作用至关重要。从I期到III期的临床疫苗试验需要这些替代检测来指导发展。由于多糖-蛋白结合疫苗的高复杂性和高成本，以及肺炎球菌的快速进化以逃避结合疫苗引起的胶囊型特异性保护，针对肺炎链球菌的蛋白质疫苗是重要的。

DESCRIPTION (provided by applicant): Pneumococcal surface protein A (PspA) is a leading vaccine candidate to protect against Streptococcus pneumoniae (Sp) infections. This grant addresses issues critical to defining the mechanisms of action of PspA and antibody (Ab) to PspA. This information is important to our understanding of the pathogenesis of Sp and to the potential use of PspA as a component of a common-protein vaccine. The proposed experiments constitute some of the last pre-clinical studies needed prior to renewed human trials with PspA. New and existing information about the mechanism of action of both PspA and Ab to PspA will be used to develop and test the relevance of in vitro surrogate assays for in vivo protection mediated by Ab to PspA. Relevant surrogate assays are needed to evaluate immune sera from phase I and II human safety and immunogenicity trials. The information gained will provide a scientific basis for decisions about whether the much more expensive phase III efficacy trials should be conducted. PspA can inhibit C' activation and surface deposition on Sp. Ab to PspA can enhance C' deposition on Sp. Our studies should also reveal the mechanism by which PspA blocks C' activation. In studies that will include transgenic and KO mice, we will evaluate the effects of Ab to PspA on phagocytosis, immune adherence, and blood clearance of Sp. PspA also keeps apolactoferrin from killing Sp by neutralizing lactoferrin and its cationic peptide lactoferricin. Ab to PspA prevents the PspA-lactoferrin interaction and, thus, enhances apolactoferrin's ability to kill Sp. We will use a lactoferrin KO mouse to help determine if these effects have in vivo relevance. We will also determine if PspA can also prevent killing by other cationic peptides. We will use a panel of MAb to different domains and epitopes of PspA and paired pre-and post-immune (anti- PspA) human sera to help us determine which of the our mechanistic assays of protection with Ab to PspA are best able to predict the ability of the same MAb to passively protect mice from infection. The results obtained will allow us to identify both those mechanisms that are critical for in vivo protection and in vitro assays that will best serve as in vitro surrogates of in vivo protection mediated by antibodies to PspA. Finally, the proposal includes an expanded investigation of our observation that immunization with the proline-rich (PR) domain of PspA can elicit protection against infection. This finding may turn out to be extremely important to the use of PspA as a vaccine because of a prior observation that some Ab to the protection-eliciting coiled coil (CC) domain of PspA can react with denatured myosin at room temperature. Although there is no compelling reason to believe that this observation has clinical relevance, it has caused nervousness on the part of for-profit vaccine companies. If, as we expect, immunization with the PR domain is broadly efficacious and cross- protective, the PR domain will not only provide a means of circumventing the theoretical worries about the CC domain but will also be a more effective immunogen. PUBLIC HEALTH RELEVANCE: This application describes pre-clinical studies to determine the virulence mechanisms of Streptococcus pneumoniae protein PspA and the protective action of antibody elicited to it. This information is critical to understand the role of PspA in pathogenesis and to our development herein of in vitro surrogate assays of the in vivo protection mediated by Ab to PspA. These surrogate assays are needed to guide the development of clinical vaccine trials from phase I through phase III. A protein vaccine against S. pneumoniae is important because of the high complexity and cost of the polysaccharide-protein conjugate vaccine and the rapid evolution of pneumococci to evade the capsule-type-specific protection elicited by the conjugate vaccine.