HLA Class II tetramers reveal tissue-specific regulatory T cells that suppress T-cell responses in breast carcinoma patients.

Regulatory T cells (Tregs) play an important role in controlling antitumor T-cell responses and hence represent a considerable obstacle for cancer immunotherapy. The abundance of specific Treg populations in cancer patients has been poorly analyzed so far. Here, we demonstrate that in breast cancer patients, Tregs often control spontaneous effector memory T-cell responses against mammaglobin, a common breast tissue-associated antigen that is overexpressed by breast carcinoma. Using functional assays, we identified a HLA-DRB1*04:01- and HLA-DRB1*07:01-restricted epitope of mammaglobin (mam34-48) that was frequently recognized by Tregs isolated from breast cancer patients. Using mam34-48-labeled HLA Class II tetramers, we quantified mammaglobin-specific Tregs and CD4+ conventional T (Tcon) cells in breast carcinoma patients as well as in healthy individuals. Both mammaglobin-specific Tregs and Tcon cells were expanded in breast cancer patients, each constituting approximately 0.2% of their respective cell subpopulations. Conversely, mammaglobin-specific Tregs and CD4+ Tcon cells were rare in healthy individuals (0.07%). Thus, we provide here for the first time evidence supporting the expansion of breast tissue-specific Tregs and CD4+ Tcon cells in breast cancer patients. In addition, we substantiate the potential implications of breast tissue-specific Tregs in the suppression of antitumor immune responses in breast cancer patients. The HLA Class II tetramers used in this study may constitute a valuable tool to elucidate the role of antigen-specific Tregs in breast cancer immunity and to monitor breast cancer-specific CD4+ T cells.

Characterization of MHC ligands for peptide based tumor vaccination.

Short peptides derived from cellular proteins may escape complete destruction during protein catabolism and finally serve as a showcase in the immune system. Exposed at the cell surface to scrutiny by T cells, MHC:peptide complexes mediate a highly specific and immediate information transfer from diseased cells to the cellular immune system. Numerous clinical vaccination trials have been carried out employing MHC-presented peptides for T-cell activation with encouraging results but so far without a final breakthrough. In this review, we briefly highlight the molecular basis of MHC-peptide interactions governed by specificity pockets and anchor residues, as summarized in allele-specific peptide motifs. State-of-the-art technology is comprehensively presented and gives an overview of modern mass spectrometric strategies used for qualitative and quantitative analysis of MHC ligands. We describe the details of the HLA-B*3801 peptide motif by comparing features of natural MHC ligands, resulting in a scoring matrix that enables epitope prediction from any viral or tumor antigen. The pronounced individuality in peptide presentation by MHC molecules, as reflected in the highly specific peptide motifs of different MHC allotypes or the tissue-specific MHC ligandomes, represents a current area of interest within this field. Finally, the identification of post-translational modifications--most important phosphorylations--and the promises this holds will be discussed in this chapter.