Processed Antigen Characterization by Mass Spectrometry

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Project Summary Cells in the human body communicate their health status to the immune system by degrading cellular proteins and presenting fragments of each on the cell surface in association class I MHC proteins. Appropriately educated, cytotoxic T-lymphocytes (CTL) (CD8+ T-cells) bind to the class I MHC molecules on the cell surface, sample the protein fragments (peptides) being presented and kill those cells that express new peptides as a result of viral, bacterial and parasitic infection, tissue transplantation and cellular transformation (cancer). Since dysregulation of cell signaling pathways is one of the hallmarks of cancer, we hypothesized that class I MHC phosphopeptides that result from these pathways should be excellent candidates for use in the immunotherapy of cancer. Class I MHC phosphopeptides identified in preliminary work on leukemia, melanoma, and colorectal cancers elicit pre-existing, central-memory, T-cell-recall responses in multiple, healthy blood donors. Central memory recall responses to phosphopeptide antigens is absent in some leukemia patients and correlates with clinical outcome. The response is restored following allogenic stem cell transplantation. These results suggest strongly that class I MHC phosphopeptides are tumor targets of immune surveillance in humans and, therefore, are likely candidates for immunotherapy of cancer. Three of the discovered phosphopeptides will be the subject of a phase I clinical trial on melanoma later this spring. Proposed here is additional research to complete our studies on melanoma, leukemia, and colorectal cancer and to begin an effort to characterize class I MHC phosphopetides presented on esophageal, liver and ovarian cancer. Additional research will be conducted to identify the repertoire of altered class I or class II self-peptides that are induced by prescription drugs or environmental agents and lead to life threatening autoimmune disease. Also proposed is the development novel mass spectrometry technology that will facilitate near complete amino acid sequence coverage of intact therapeutic antibodies and other proteins at the high femtomole level on a chromatographic time scale. This will be accomplished by a combination protein chemical derivatization, changes to existing instrument hardware, enhanced performance of ion-ion chemistry inside the instrument, and modifications to the instrument control software. This approach should accelerate the development of therapeutic antibodies for multiple diseases and also facilitate complete characterization of proteins and protein complexes that contain multiple posttranslational modifications on the same protein molecule.