Exploring the Biological Role of Kruppel-Like Factor 2 In Cytotoxic T Lymphocytes

Abstract 2783

Kruppel-like factor 2 (KLF2) is a transcription factor which has been shown to be a critical regulator of T lymphocyte quiescence and trafficking. KLF2 is highly expressed in naïve CD8 T cells but its expression is transcriptionally downregulated in effector cytotoxic T lymphocytes (CTL). To understand how KLF2 might co-ordinate biological processes in CTL, we have determined the impact of preventing KLF2 downregulation on the transcriptional program of antigen receptor triggered CD8 T cells. Our data show that CTL which fail to downregulate KLF2 have a strikingly different transcriptional program to normal CTL. Immune activated CD8 T cells that sustain KLF2 expression thus show increased expression of 672 genes and decreased expression of 205 genes compared to normal CTL that have lost KLF2. Previous studies have indicated that high levels of KLF2 correlate with long term T cell survival and the development of memory CD8 T cells. We therefore questioned whether the KLF2 regulated genes identified in our experiments gave any insight as to why increasing levels of KLF2 in immune activated T cells might control T cell memory. In this context, we noted that KLF2 downregulation is necessary for TCR triggering of the CTL mitotic pathway. The molecular basis for this effect includes that KLF2 drives expression of intracellular cell cycle inhibitors. It was equally striking, however, that KLF2 could induce expression of the inhibitory receptor Carcinoembryonic Antigen-related Cell Adhesion Molecule 1 (Ceacam1, CD66a), which can suppress the T cell proliferative response. The present report confirms that KLF2 controls the repertoire of chemokine receptors and adhesion molecules expressed by CTL. Previous studies have identified the adhesion molecule CD62L and the G protein coupled receptor S1P1 as direct gene targets for KLF2. The present data support that KLF2 positively regulates expression of these molecules but also describes a cell autonomous role for KLF2 to negatively regulate the expression of the inflammatory chemokine receptor CXCR3 in antigen primed CTL. The loss of KLF2 is thus essential to allow CTL to traffic to CXCR3 ligands. One other striking observation was that KLF2 expression in CTL upregulates expression of the IL-6 receptor and Serine Protease Inhibitor 6 (Spi6). The latter molecule has a key role in protecting CTL from self injury inflicted by granzymes and is critical for the generation of T cell memory. IL-6 receptor expression is similarly important for memory T cell survival. Collectively, these data identify new KLF2 regulated genes and biological functions in CD8 T cells and provide important insights as to how this transcription factor controls T cell immune responses and might determine the effector/memory fate of a CTL.