Functional characterisation of human CD4+CD25+ regulatory T cells and the transcriptional regulator, FOXP3

Naturally occurring CD4+CD25+ regulatory T cells are thought to play an essential role in the maintenance of immunological self-tolerance by actively suppressing auto reactive T lymphocytes. Exploitation of these cells could provide novel and effective therapies for the treatment of various clinical diseases, including autoimmune diseases and cancer. However the biology surrounding these cells is complex and there are many unresolved issues, including a lack of specific markers for these cells and an incomplete understanding of the mechanism of action of these cells. The initial experiments described in this thesis attempted to identify cell surface markers that were specific to the human CD4+CD25+ regulatory T cell population. Functional assays were conducted in parallel in an attempt to identify cell surface molecules and cytokines that might be responsible for the cell-mediated suppression. The lack of identification of a specific molecule responsible for the suppressor phenotype highlights the complexity of this cell population. As these studies progressed, a new marker of CD4+CD25+ regulatory T cells was reported called FOXP3. Subsequent experiments described in these studies focussed on investigating the effects of overexpressing human FOXP3 in human T cells. A novel cotransfection system was devised whereby the gene encoding FOXP3 was cotransfected with DNA encoding a specific receptor involved in T-cell activation (chimeric receptor). The data generated showed that overexpression of FOXP3 in resting human CD4+ and CD8+ T cells resulted in a significant inhibition of subsequent T cell activation. Splice variant forms of the FOXP3 protein were also investigated and were shown to possess potent repressor activity