Year: 2021
Type: dissertation
Abstract: Influenza viruses are a serious health burden, with an annual death toll in the hundreds of thousands due to seasonal illness, combined with the additional threat of more severe pandemics emerging. One of the reasons influenza virus remains an ongoing challenge is that the virus presents a moving target, due to mutation and recombination of the surface molecules hemagglutinin (HA) and neuraminidase (NA). Because HA and NA are the major targets of the humoral response invoked by annual vaccination strategies, this presents a challenge in the production of efficacious and long-lasting vaccines. An alternative strategy would be to aim to generate tissue-resident memory CD8 T cells (Trms), which can target conserved proteins and provide strain transcending heterosubtypic immunity to influenza virus. Trms generated in the lung are capable of combating reinfection through rapidly exerting cytolytic function, as well as producing inflammatory cytokines to recruit other immune cells. Influenza-specific Trms are also generated in the lung draining mediastinal lymph node (mLN), though their role in controlling influenza infection is less well defined. At early stages of infection, lower levels of antigen are displayed on the surface of infected cells. Given that the first step in a CD8 T cell response is TCR recognition of cognate antigen in the context of self-MHC, I hypothesized that influenza-specific Trms would have an increased antigen sensitivity, measured by functional avidity, to enable them to rapidly initiate an immune response upon encounter with a newly infected cell. Here, I investigate the IFN production and functional avidity of CD8 T cell subsets generated following infection with influenza A virus (IAV), across tissues and at both effector and memory timepoints; this analysis allows the identification of differences in functional avidity that are either linked to tissue environments or are specific to a CD8 T cell subset such as Trms. In order to perform these comparisons, I have developed a methodology for stimulating CD8 T cells from two tissues within the same well, to identify CD8 T cell intrinsic differences in functional avidity by controlling for the impact of APCs and cell density. Using this strategy, I demonstrate that at an effector timepoint following IAV infection, CD8 T cells that react with intravenous injected antibody (IV+) within the lung vasculature were less functionally avid than IV- lung CD8 T cells or splenic CD8 T cells. This difference was maintained at memory timepoints, though it seemed to diminish in magnitude over time. The most striking difference between memory CD8 T cell populations within the lungs was a loss in IFN production observed in CD8 T cells localized to the airways. By around 40dpi, more than half of IAV-specific airway CD8 T cells were incapable of producing IFN in response to stimulation with cognate antigen. However, those airway cells capable of cytokine production exhibited a similar functional avidity to that of other lung and splenic memory CD8 T cell subsets, indicating that the airway population can be divided into distinct functional and non-cytokine producing populations. Within the mLN CD8 T cell population, functional avidity was not notably different from that of splenic CD8 T cells at an effector timepoint. However, at a memory timepoint, CD103+ mLN Trms were found to be more functionally avid than splenic memory CD8 T cells. This enhanced antigen sensitivity was not seen in CD103- CD8 T cells within the mLN, indicating it is a Trm specific phenotype. I also demonstrate increased TCR expression in mLN Trms, providing a potential mechanism for their enhanced avidity. Together, these data indicate that functional avidity may be uniquely increased in Trm populations, though this is not ubiquitous across tissues. Functional avidity may thus be a phenotype of interest to analyze in other contexts where Trms are key mediators of immunity. Improving our understanding of Trm functional avidity and its regulation could ultimately inform the design of vaccines aimed at generating Trm responses.
DOI: 10.17077/etd.005939
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W4205218700