Angela Zarling, PhD
Manipulation of phosphopeptide display on cancer cells
Malignant transformation often leads to alterations in the protein kinase pathways regulating cell growth, differentiation, and cell death. Class I Major histocompatibility complex (MHC) molecules are cell surface proteins that bind and display a broad repertoire of peptides produced by degradation of cellular proteins to CD8+ T lymphocytes. This allows the immune system to detect subtle changes in peptide display which are the result of either infected cells that are expressing newly synthesized viral proteins or cells undergoing malignant transformation that may express new antigens that are formed from either aberrantly expressed proteins or from epitopes derived from mutated proteins. Tumor immunotherapy has centered around the identification of antigens expressed on the tumors with limited to no expression on normal adult tissues. We have recently extended this paradigm by demonstrating that altered signal transduction pathways in cancer cells can generate novel phosphopeptides that are capable of eliciting tumor-specific CD8 + T lymphocytes (Zarling et al., PNAS, 2006). Research within the Zarling laboratory focuses on two offshoots of these findings. The first area investigates how phosphopeptide presentation by class I MHC on the surface of cancer cells is altered following chemotherapeutic treatments or signaling through growth factor receptors. The second research area investigates the utility of phosphopeptide-specific T cell receptors (TCR)-expressing cells to mediate tumor regression.
We previously identified a phosphopeptide derived from insulin receptor substrate-2 (IRS2) which was presented by HLA-A*0201 on a number of cancer cell lines by mass spectrometry and which could be utilized to elicit phosphopeptide-specific CD8 + T lymphocytes (Zarling et al., PNAS, 2006). IRS2 has been suggested to be strongly linked to transformation, motility and metastasis but little information is known about what causes phosphorylation at residue Ser 1100 in IRS2 or what modulates the presentation of IRS2-derived phosphopeptides by class I MHC. Therefore, we are investigating the role of Ser 1100 in IRS2 phosphorylation and degradation and whether we can utilize this information to enhance phosphopeptide presentation on the surface of breast cancer cells. This information will lead to a better understanding of the generation of these post-translationally modified peptides while also evaluating the feasibility of manipulating phosphopeptide display on breast cancer cells for enhanced removal by phosphopeptide-specific CD8+ T lymphocytes.
Even with the identification of tumor-associated antigens (TAA), a major obstacle remains in our ability to generate TAA-specific T cells in tumor-bearing hosts. Adoptive transfer of T cells with anti-tumor activity has been utilized to treat cancer patients to circumvent problems in generating anti-tumor immune responses in vivo. TCR gene therapy may permit the generation of a large population of TAA-specific T cells that are not present naturally and allow for a mechanism to bypass the limitations of the endogenous T cell repertoire in cancer patients. Our intention is to investigate the ability of TCRs, cloned from murine T cells specific for the phosphopeptides we have identified that are presented by HLA-A*0201 on both melanoma and ovarian carcinoma, to efficiently reconstitute human peripheral blood lymphocytes (PBL) so that they can recognize and kill cancer cells. We will then validate these potential therapeutics in a pre-clinical model system where adoptively transferred phosphopeptide-specific murine TCR-electroporated human PBL are evaluated for their ability to prevent growth of human tumors that has been engrafted into non-obese mice with severe combined immunodeficiency (NOD/SCID). This research will allow for a complete evaluation of the ability of phosphopeptide-specific T cells to mediate tumor regression in a more clinically-relevant setting and validate their transition to the clinic.