Quantification of the CD8⁺ T cell response against a mucin epitope in patients with breast cancer

Introduction: Mucin 1, encoded by the MUC1 gene, is a tumor-associated antigen expressed on the surface of breast cancer cells. It would be of interest to see whether there is a naturally existing T cell immune response against mucin epitopes in cancer patients. Materials and Methods: Using tetramer and interferon-γ assays, the immune response to one MUC1 peptide epitope in the peripheral blood of breast cancer patients was quantified. The data were compared with the clinical course of the patients. Results: CD8⁺ T cells capable of recognizing the HLA-A*0201-restricted STAPPVHNV epitope were detected in 9 of 19 patients with a frequency ranging 0.01-0.082%. No significant difference was found between the occurrence of epitope-specific CD8⁺ T cells of patients with progressive disease and disease-free patients. However, all patients with stable disease showed a specific immune response, including both patients with the highest frequency. Conclusions: The results of this study provide further evidence that a natural specific cellular immune response against this mucin epitope exists in breast cancer patients.