| Current immunotherapies designed to stimulate specific T cell-mediated immunity have thus far yielded modest objective clinical response rates, despite the increase of tumor-specific T cells have been observed in treated patient blood. Since the majority of tumor antigens being targeted in immunotherapies are non-mutated, "self" antigens, current clinical results may relate, in part, to the low-to-moderate avidity, negatively-selected T cell repertoire in patients that is being asked to regulate tumor progression. In the current thesis, I hypothesized that by conditionally enhancing the proteasomal degradation of tumor antigens, I could generate a "synchronized" pool of derivative peptides that could then be presented in a "wave-like" temporal fashion in MHC class I complexes on the tumor cell surface. For at least a transient period thereafter, I theorized that specific CD8+ T cell recognition and anti-tumor activities would be improved. I selected a family of tumor-associated antigens, receptor tyrosine kinases (RTK) for study, as their overexpression has been linked with poor clinical prognosis in many forms of cancer. In this thesis, I show that EphA2 agonists, as well as, HSP90 inhibitors effectively promote EphA2 degradation via a proteasome-dependent manner, providing the delivery of EphA2 peptides into the classical MHC class I presentation pathway. I also show that specific CD8+ T cell recognition of EphA2 peptides derived from both the extracellular and intracellular domains of this transmembrane protein was improved as a consequence of tumor cell treatment with these agents being in consistent with the use of TAP- and ER-associated degradation. Notably, the combination of both drugs further enhanced anti-EphA2 T cell recognition of tumor cells, suggesting these modalities work via complementary, but not identical mechanisms. Importantly, complete tumor eradication was achieved in vivo (in a Hu-SCID tumor model) using a combinational therapy consisting of agonist administration just prior to the adoptive transfer of human anti-EphA2 CD8+ T cells, where either single modality was minimally beneficial. Preliminary data from additional studies targeting the tumor cell-overexpressed RTKs, Her2/neu and EGFR, suggest that this core treatment paradigm may be generalizable to many (if not all) RTKs. |
