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)感染每年导致全世界数十万人死亡，当新的大流行病毒出现时，发病率和死亡率甚至会进一步上升。一年一度的流感疫苗为预防流感感染提供了一条重要的防线，但有许多有记录的疫苗效果不佳的例子，即使是在健康的人身上。因此，改善流感疫苗接种是一项尚未得到满足的公共卫生需求。然而，在我们能够改进疫苗之前，我们必须首先更好地了解对疫苗有反应的免疫细胞。一种特别重要的细胞类型是记忆B细胞，它在感染和接种后迅速被召回，并可以通过分化为短暂的抗体分泌细胞(ASCs)来促进抗病毒免疫，这些ASCs产生抗体(Ab)，可以中和病毒或促进其快速清除。记忆B细胞还可以产生疫苗驱动的体液免疫反应，并能产生新的长期存活的ASCs和记忆B细胞，这些细胞将保护人们免受未来接触正在传播的流感病毒的影响。尽管记忆B细胞是成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触到的组织中。我们开发了新的工具来跟踪小鼠和人类的流感特异性记忆B细胞，现在已经确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疫苗诱导的长期免疫反应。这一应用的中心假设是，表达转录因子T-bet的流感特异性记忆B细胞亚群在肺等组织中长期保持，并优先通过接种疫苗被召回。这项建议的具体目标是确定建立表达记忆B细胞的肺常驻T-bet所需的疫苗引发的信号，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群体的记忆B细胞，识别哪些记忆B细胞亚群在抗原暴露后优先被召回，以及评估在人类组织中发现的表达记忆B细胞的T-bet是否丰富了对个体早期可能遇到的较老的“历史”流感抗原的反应能力。这项提议的长期目标是通过开发工具和动物模型系统来填补我们知识的空白，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流感特异性记忆B细胞的不同群体，这些细胞持续存在于淋巴和非淋巴组织中，是成人疫苗接种的直接目标。我们认为，这一贡献是重要的，因为我们希望为复杂和不同种类的记忆B区提供新的见解，记忆B区对于疫苗诱导的流感反应至关重要。

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.