Identification and characterization of effector memory B cell populations that dominate memory responses to subsequent influenza infection and vaccination

季节性流感（流感）感染每年在全世界杀死数十万人，并且当新的大流行性病毒出现时，发病率和死亡率甚至进一步增加。每年的流感疫苗为预防流感感染提供了重要的防线，但有许多记录在案的疫苗疗效不佳的例子，即使在健康的个体中也是如此。因此，存在未满足的改善流感疫苗接种的公共卫生需求。然而，在我们改进疫苗之前，我们必须首先更好地了解对疫苗产生反应的免疫细胞。一种特别重要的细胞类型是记忆B细胞，其在感染和疫苗接种后迅速被召回，并且可以通过分化成产生抗体（Ab）的短寿命抗体分泌细胞（ASC）来有助于抗病毒免疫，所述抗体（Ab）可以中和病毒或促进其快速清除。记忆B细胞也是疫苗驱动的体液免疫反应的种子，可以产生新的长寿ASC和记忆B细胞群，这些细胞将防止未来暴露于流行的流感病毒。尽管记忆B细胞是成年人接种疫苗的直接目标，但我们对这些细胞知之甚少。这种巨大的知识差距至少部分是由于无法分离和表征这些细胞。对人类记忆B细胞的研究甚至更加困难，因为我们通常只能观察血液中的细胞，而许多免疫细胞，包括记忆B细胞，驻留在人类通常无法接近的组织中。我们开发了新的工具来跟踪小鼠和人类中的流感特异性记忆B细胞，现在已经鉴定并表征了小鼠组织中的不同群体，我们认为这些群体可能有助于持久的疫苗诱导的免疫应答。本申请的中心假设是表达转录因子T-bet的流感特异性记忆B细胞亚群在组织如肺中长期维持，并且优先通过疫苗接种被召回。该提议的具体目标是鉴定建立肺驻留T-bet表达记忆B细胞所需的疫苗引发的信号，以确定疫苗接种和感染是否诱导具有不同功能和寿命的不同记忆B细胞群，以鉴定在抗原暴露后哪些记忆B细胞亚群被优先召回，并评估在人组织中发现的表达T-bet的记忆B细胞的库是否富集了对个体可能在生命早期遇到的较老的“历史”流感抗原的反应性。该提案的长期目标是通过开发工具和动物模型系统来填补我们的知识空白，这些工具和动物模型系统将使我们能够系统和全面地研究在淋巴和非淋巴组织中持续存在的流感特异性记忆B细胞的异质群体，并且是成人疫苗接种的直接靶点。我们相信，这一贡献是重要的，因为我们希望提供新的见解复杂和异质性的记忆B区室，这是疫苗诱导的流感反应的关键。

Seasonal influenza (flu) infections kill hundreds of thousands of people throughout the world each year and morbidity and mortality rates increase even further when a new pandemic virus emerges. The annual flu vaccine provides an important line of defense against influenza infections but there are many documented examples of poor vaccine efficacy, even in healthy individuals. Thus, there is an unmet public health need to improve influenza vaccination. However, before we can improve the vaccine, we must first better understand the immune cells that respond to the vaccine. One cell type of particular importance is the memory B cell, which is rapidly recalled following infection and vaccination and can contribute to anti-viral immunity by differentiating into short-lived antibody secreting cells (ASCs) that produce antibodies (Ab) that can either neutralize the virus or facilitate its rapid clearance. Memory B cells also seed the vaccine-driven humoral immune response and can give rise to new cohorts of long-lived ASCs and memory B cells that will protect against future exposures to the circulating flu virus. Despite the fact that memory B cells are the direct targets of vaccination in adults, we know remarkably little about these cells. This substantial knowledge gap is due, at least in part, to an inability to isolate and characterize these cells. Studies of memory B cells in humans have been even more difficult as we can typically only look at the cells in the blood and many immune cells, including the memory B cells, reside in tissues that are usually inaccessible in humans. We developed new tools to track flu-specific memory B cells in both mice and humans and have now identified and characterized distinct populations in the tissues of mice that we believe are likely to contribute to long-lasting vaccine induced immune responses. The central hypothesis of this application is that a flu-specific memory B cell subset that expresses the transcription factor T-bet is maintained long-term in tissues like the lung and is preferentially recalled by vaccination. The specific goals for this proposal are to identify the vaccine-elicited signals required to establish lung-resident T-bet expressing memory B cells, to determine whether vaccination and infection induce distinct populations of memory B cell with differing functions and life- spans, to identify which memory B cell subsets are preferentially recalled following antigen exposure, and to evaluate whether the repertoire of the T-bet expressing memory B cells found in human tissues are enriched for reactivity to older “historic” flu antigens that the individual likely encountered early in life. The long term goal of this proposal is to fill our gap in our knowledge by developing the tools and animal model systems that will allow us to systematically and comprehensively study the heterogeneous populations of flu-specific memory B cells that persist in lymphoid and non-lymphoid tissues and are the direct targets of vaccination in adults. We believe that this contribution is significant as we expect to provide new insight into the complex and heterogeneous memory B compartment that is critical for vaccine-induced responses to flu.