Mammaglobin-A (
MGBA), a 10-kD
protein, is over expressed in 80% of primary and metastatic human breast
cancers.
Breast cancer patients demonstrate high frequencies of CD8(+) cytotoxic T lymphocytes (CTL) specific to
MGBA. Defining CD8(+) CTL responses to HLA class I-restricted
MGBA-derived
epitopes assumes significance in the context of our ongoing efforts to clinically translate
vaccine strategies targeting
MGBA for prevention and/or treatment of human breast
cancers. In this study, we define the CD8(+) CTL response to
MGBA-derived candidate
epitopes presented in the context of
HLA-B7, which has a frequency of 17.7% in Caucasian and 15.5% in African American populations. We identified seven
MGBA-derived candidate
epitopes with high predicted binding scores for
HLA-B7 using a computer algorithm. Membrane stabilization studies with TAP-deficient T2 cells transfected with
HLA-B7 indicated that
MGBA B7.3 (VSKTEYKEL), B7.6 (KLLMVLMLA), B7.7 (NPQVSKTEY), and B7.1 (YAGSGCPLL) have the highest
HLA-B7 binding affinities. Further, two CD8(+) CTL cell lines generated in vitro against T2.B7 cells individually loaded with
MGBA-derived candidate
epitopes showed significant cytotoxic activity against
MGBA B7.1, B7.3, B7.6, and B7.7. In addition, the same CD8(+) CTL lines lysed the HLA-B7(+)/
MGBA(+) human
breast cancer cell line DU-4475 but had no significant cytotoxicity against HLA-B7(-) or
MGBA(-)
breast cancer cell lines. Cold-target inhibition studies strongly suggest that
MGBA B7.3 is an
immunodominant epitope. In summary, our results define HLA-B7-restriced,
MGBA-derived, CD8(+) CTL
epitopes with all of the necessary features for developing novel
vaccine strategies against
HLA-B7 expressing
breast cancer patients.