Medical Biology - Theses

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Start date: 2000 × Subject: Immunology × Subject: T cells ×

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    Defining the intranodal spatial requirements for the formation and maintenance of long-lived T cell memory
    Duckworth, Brigette Catherine ( 2023-10)
    Immune memory is critical for providing superior protection against infection. Current vaccine strategies exploit immune memory with varying success, with most relying on humoral immunity while failing to elicit and maintain durable CD8+ T cell responses. As such, vaccine outcomes for pathogens which require a strong T cell response are poor. The next generation of vaccines against infectious disease and cancer require robust T cell memory. However, we lack the fundamental understanding of how the longevity of T cell memory is regulated so that we may optimise this strategy. During my PhD, I have made a series of discoveries that offer new insight into this problem. Firstly, I have discovered that memory cell differentiation is imprinted in the centre of draining lymph nodes (LNs). Secondly, I have identified a distinct intranodal location where memory T cells reside long-term. Lastly, I shed light on the changes to this positioning that occur as we age. Following infection, the differentiation of T cells is driven via dynamic interactions with multiple, distinct cellular subsets. I developed and employed a novel platform to quantify cell location in 3D to examine the spatial requirements that instruct T cell fate in intact LNs. Following viral infection, I established that CD8+ effector T cell fate correlates with positioning at the LN periphery, instructed by CXCR3 signalling. In the absence of CXCR3, T cells were retained in the LN paracortex and alternatively formed stem-like memory cell precursors. I also showed that CXCR3 ligands, CXCL9 and CXCL10 are expressed by spatially distinct dendritic and stromal cell subsets. Finally, I demonstrated that T cell location can be tuned, through deficiency in CXCL10 or type I IFN signalling, to promote effector or stem-like memory fates. Increasing evidence suggests that, in the steady-state, CD8+ central memory T cells (TCM) are positioned strategically in LNs; however, the mechanisms that regulate this location remain unknown. I used 3D light-sheet fluorescence microscopy of intact LNs to identify the location of TCM cells following the resolution of viral infection. In steady-state LNs, I showed that a higher density of TCM cells occupy the cortical ridge and interfollicular regions than naive T cells, which primarily reside in the T cell paracortex. This distinct TCM location was observed following various infection challenges and mRNA-LNP vaccination. Furthermore, in the LNs of aged mice, this TCM niche was disrupted and TCM cells relocated to the T cell paracortex. To explore cell-cell contacts regulating TCM location, I employed high-resolution confocal microscopy to identify specific dendritic and stromal cells which interact with TCM within this niche. Together, these findings suggest that TCM occupy a conserved and precise LN memory niche. This provides a platform for further spatial interrogation to determine how this niche promotes cell-specific interactions and sustains long-term TCM maintenance. In identifying the key mechanisms regulating the intranodal TCM niche, my work may contribute to improved vaccine strategies grounded in robust, long-lived T cell memory.
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    Understanding how malaria-induced T-bet expression impacts the development of protective immunity to infection
    Pietrzak, Halina Mary ( 2022)
    Malaria is a globally significant parasitic disease infecting millions of people annually. Clinical immunity to infection takes years of frequent exposure to develop and only partially protects the host against clinical symptoms, with individuals in endemic areas often developing chronic, asymptomatic infections. These observations suggest defects in the generation, maintenance, or effector capacity of immune memory induced in response to infection. Antibody responses are a critical component of clinical immunity to malaria. Recent work from our group demonstrated that inflammatory pathways contributing to the development of clinical malaria episodes play a negative role in the induction of humoral immunity. IFN-g produced in response to acute malaria infection was found to upregulate the expression of transcription factor T-bet in T follicular helper cells (Tfh), the key T cell subset required to provide help to B cells for the induction of protective antibody responses to infection. T-bet expression in Tfh cells impairs their normal differentiation and compromises downstream humoral responses to acute infection. The contribution of T-bet expression to the development of Tfh memory cells in malaria is unknown. To investigate this, the Tfh memory cell compartment was examined using PBMC samples from human P. vivax patients, and a murine model of severe malaria infection. Together, these analyses involving flow cytometry, adoptive transfer, and RNA-sequencing approaches revealed that the T-bet influences the composition and development of the Tfh memory cell compartment in malaria. Specifically, the main results from this investigation revealed that T-bet expression in CD4+ T cells impairs the development of Tfh central memory (TfhCM) cells which are an important compartment that support and bolster long-lived memory responses. This data provides evidence that malaria-induced inflammation negatively impacts the development of memory populations required for an efficient response to malaria, thus restraining a potent immune response to re-infection.