The Role of TNFR Family Members GITR and CD30 on CD8 T Cell Responses

GITR and CD30 are T cell costimulatory members of the TNFR superfamily known to regulate T cell responses. Elucidating the mechanisms whereby these receptors modulate T cell responses is crucial for maximizing their potential for immunotherapy. In this thesis, I examine the role of GITR and CD30 on CD8 T cell responses to influenza virus. I show that CD8 T cell intrinsic GITR is required for both maximal primary and secondary CD8 T cell expansion to influenza, while in contrast, CD30 is dispensable for anti-influenza CD8 T cell responses. GITR does not impact on CD8 T cell proliferation or homing, however, it mediates CD8 T cell survival signaling. GITR induces TRAF2/TRAF5 dependent, but TRAF1 independent, NF-κB activation, resulting in the upregulation of the pro-survival molecule Bcl-xL. Furthermore, I show that GITR on CD8 T cells can augment viral clearance and confer protection from death upon severe influenza infection of mice. Similarly, CD30 also elicits protection from death upon severe influenza infection, although the cells responsible for this effect remain to be elucidated. In this thesis, I also show that in unimmunized mice GITR expression is upregulated to higher than basal levels on a population of CD8 memory phenotype cells in the bone marrow. In contrast, CD8 memory phenotype T cells in the spleen and LN have GITR levels similar to that on naïve T cells. The upregulation of GITR in the bone marrow is IL-15 dependent and therefore, GITR serves as a marker for cells that have recently received an IL-15 signal. Furthermore, GITR is required for the persistence, but not for the homeostatic proliferation of CD8 memory phenotype T cells in the bone marrow. Therefore, GITR plays a key role for CD8 T cell intrinsic responses to influenza, as well as for the persistence of CD8 memory phenotype T cells.Ph