Minor antigens identified by tandem mass spectrometry

The immune system functions to protect the body against disease and cancer. One way this occurs is through the recognition of antigens on the surface of diseased, mutated, or foreign cells by CTL. These antigens are peptides derived from cellular proteins that are presented on the cell surface in association with MHC class I molecules. By combining microcapillary liquid chromatography-electrospray ionization mass spectrometry with T cell epitope reconstitution assays, we can identify a single immunologically relevant antigen in a complex mixture of over 10,000 peptides extracted from the surface of cells.; Minor Histocompatibility antigens can induce transplant rejection and GVHD in a host, even when the MHC molecules are entirely matched between host and donor. In general, minor antigens fail to induce B cell responses and are characterized by MHC-restricted T cell responses. Mismatch between host and donor for one such minor antigen, HA-1, is highly correlated with the development of GVHD. HA-1 was identified by mass spectrometry as a 9-residue peptide. This identification makes it possible to type for HA-1 prior to transplantation to identify HLA-A2.1 positive BMT recipients who are at high risk for GVHD.; There is a subset of minor antigens known as the male specific antigen H-Y that can lead to rejection of male organ and bone marrow grafts by female recipients. However, the origin and function of H-Y antigens has eluded researchers for 40 years. The first human H-Y antigen presented by HLA-B7 was identified by mass spectrometry as an 11-residue peptide derived from SMCY, an evolutionarily conserved protein encoded by the Y chromosome. This peptide is a candidate for immunomodulatory approaches in bone marrow transplantation.; Another H-Y antigen presented by HLA-A2.1 was identified as a 9-residue peptide also derived from SMCY. In naturally processed peptides, T cells only recognize post-translationally altered forms of this peptide that have undergone modification of a cysteine residue. One of these modifications involves the attachment of a second cysteine residue via a disulfide bond. This modification has profound effects on T cell recognition, and also occurs in other class I MHC associated peptides, supporting its general importance as an immunological determinant.