Characterisation of porcine T follicular helper cells and their response to vaccination and infection

Since they were first discovered in 2000, the function of T follicular helper (Tfh) cells has been a subject of intense and fast-moving research. It is now clear that these cells are critical in orchestrating the B cell/antibody response and they have become a focus in improving targeted cancer immunotherapy and vaccine strategies. In humans and mice, Tfh are characterised by expression of CXC chemokine receptor 5 (CXCR5), inducible T cell costimulatory (ICOS), programmed cell death protein 1 (PD-1), T-cell lymphoma 6 (Bcl-6) and interleukin 21 (IL-21). It is now clear that at least five phenotypes exist across secondary lymphoid tissues and in circulation, each prevalent at different stages of the immune response and each expressing different levels of the archetypal Tfh phenotypic markers. Notably, in both SARS-CoV-2 and HIV infection an increased frequency of circulating Tfh correlates with decreased disease severity and enhanced neutralising antibody responses, respectively.
There are limited studies on Tfh cells in the pig, which is both a major food producing species and an important biomedical model. This project therefore intends to expand our knowledge of the phenotype and function of porcine Tfh cells. We have demonstrated cross-species reactivity of several Tfh markers, including Bcl-6 and ICOS, and in collaboration with the Roslin Institute, developed a reagent for labelling of CXCR5-expressing cells. The first aim of the project is to further
develop and optimise staining panels for both flow cytometry and confocal microscopy applications to identify and characterise porcine Tfh in blood and secondary lymphoid organs. Defined Tfh-like populations will be cell sorted and assessed in functional assays involving assessment of antibody production from co-cultured syngeneic B cells. Sorted cells will be further characterised by RNAseq transcriptomic analysis. Funding permitting, a spatial transcriptomic analysis, whereby the spatial location of each cell is determined and accounted for, may be performed on lymphoid organ sections. Finally, the tools developed will be applied in the context of vaccination and infection. For example, assessing the frequency and phenotype of circulating and tissue resident Tfh during infection with the porcine reproductive and respiratory syndrome virus (PRRSV). Tfh response profiles will be compared to CXCL13, IL-21 and IL-6 levels in serum, virus loads in blood and tissues and neutralising antibody responses to determine whether associations exist.