Transcriptional and functional identity of human T follicular helper cells across tissues - Project Summary/Abstract T follicular helper cells (Tfh) are indispensable for the development of memory B cells and plasma cells, facilitating protective antibody responses through a mechanism known as B cell help. The expression of lineage-defining molecules like Bcl6 and CXCR5 enables Tfh cells to migrate to B cell zones of lymphoid follicles, where they provide this essential support. However, examination of Tfh cells in humans is challenging due to their obligate tissue localization. Additionally, T cells with Tfh-like functions, known as peripheral helper T cells (Tph), have been identified in non-lymphoid tissues of mice where they mediate localized B cell responses to provide protection against reinfection. In humans, studies of Tph cells have been limited to samples isolated from autoimmune and chronic inflammatory conditions, where they are implicated in pathology, and it is unclear whether these cells can also play protective roles in healthy mucosal sites in humans. A systematic analysis of human Tfh cells across lymphoid and mucosal tissues is crucial for defining how T cells influence tissue-specific humoral immunity during infection, autoimmunity, and vaccine responses. In the proposed study, we will make use of our novel human tissue resource, from which we have unparalleled access to multiple mucosal and lymphoid tissues from adult and pediatric organ donors. Preliminary analysis of these samples reveals an enrichment of Tfh and Tfh-like populations across mucosal and lymphoid sites of children, necessitating examination in early life to define these populations, their properties, and functionality across different sites. In preliminary studies, we identified Tfh-like cells in the lung, which express certain phenotypes of Tfh cells and produced IL-21 associated with Tfh functional responses. Lung Tfh-like cells also express site-specific signatures including production of multiple effector cytokines while also sharing a set of core genes with Tfh that are associated with B cell help. We hypothesize that human Tfh cells possess a set of core features across diverse lymphoid and mucosal tissues, but exhibit functional adaptations specific to the site in which they reside. We will address this hypothesis in two Aims: (1) Identify a core signature and site- specific adaptations of Tfh cells across diverse human tissues, (2) Determine role of site-specific Tfh cell functions in B cell differentiation. We will dissect the transcriptional mechanisms that specifically, or synergistically, regulate Tfh differentiation, functionality and localization, while interrogating the molecular machinery underlying functional responses for promoting B cell differentiation and antibody secreting cells by Tfh cells isolated from different tissues. This innovative and exploratory study aims to elucidate the cellular and molecular mechanisms behind the essential function of B cell help in various human tissue sites. Understanding these mechanisms could pave the way for tissue targeted approaches that induce localized immune responses after vaccination or dampen these responses in autoimmune conditions, all while preserving the overall integrity of the immune system.
