Identification of HLA-A24-restricted CD8 ⁺ cytotoxic T-cell epitopes derived from mammaglobin-A, a human breast cancer-associated antigen

Human breast cancer-associated antigen, mammaglobin-A (Mam-A), potentially offers a novel therapeutic target as a breast cancer vaccine. In this study, we define the CD8 ⁺ cytotoxic T lymphocyte (CTL) response to Mam-A-derived candidate epitopes presented in the context of HLA-A24 (A*2402). HLA-A24 has a frequency of 72% in Japanese, 27% in Asian Indian, and 18% in Caucasian populations. Using a human leukocyte antigen (HLA)-binding prediction algorithm we identified 7 HLA-A24-restricted Mam-A-derived candidate epitopes (MAA24.1-7). Membrane stabilization studies with TAP-deficient T2 cells transfected with HLA-A2402 (T2.A24) indicated that MAA24.2 (CYAGSGCPL) and MAA24.4 (ETLSNVEVF) have the highest HLA-A24 binding affinity. Further, 2 CD8 ⁺ CTL cell lines generated in vitro against T2.A24 cells individually loaded with Mam-A-derived candidate epitopes demonstrated significant cytotoxic activity against MAA24.2 and MAA24.4. In addition, the same CD8 ⁺ CTL lines lysed the HLA-A24 ⁺/Mam-A ⁺ stable transfected human breast cancer cell lines AU565 and MDA-MB-361. However, these CTLs had no cytotoxicity against HLA-A24 ^-/Mam-A ⁺ and HLA-A24 ⁺/Mam-A ^- breast cancer cell lines. In summary, our results define HLA-A24-restricted, Mam-A-derived, CD8 ⁺ CTL epitopes that can potentially be employed for Mam-A-based breast cancer vaccine therapy to breast cancer patients with HLA-A24 phenotype.