Expression of the
cancer-testis antigen Taxol resistance-associated gene-3 (TRAG-3)
protein is associated with acquired
paclitaxel (
Taxol) resistance, and is expressed in various
cancer types; e.g.,
breast cancer,
leukemia, and
melanoma. Thus, TRAG-3 represents an attractive target for
immunotherapy of
cancer. To identify
HLA-A*02.01-restricted
epitopes from TRAG-3, we screened
cancer patients for spontaneous cytotoxic T-cell responses against TRAG-3-derived
peptides. The TRAG-3
protein sequence was screened for 9mer and 10mer
peptides possessing
HLA-A*02.01-binding motifs. Of 12 potential binders, 9
peptides were indeed capable of binding to the
HLA-A*02.01 molecule, with binding affinities ranging from strong to weak binders. Subsequently, lymphocytes from
cancer patients (9
breast cancer patients, 12
melanoma patients, and 13 patients with
hematopoietic malignancies) were analyzed for spontaneous reactivity against the panel of
peptides by ELISpot assay. Spontaneous immune responses were detected against 8
epitope candidates in 7 of 9
breast cancer patients, 7 of 12
melanoma patients, and 5 of 13 patients with
hematopoietic malignancies. In several cases, TRAG-3-specific CTL responses were scattered over several
epitopes. Hence, no immunodominance of any single
peptide was observed. Furthermore, single-
peptide responses were detected in 2 of 12 healthy HLA-A2(+) donors, but no responses were detectable in 9 HLA-A2(-) healthy donors or 4 HLA-A2(-)
melanoma patients. The identified
HLA-A*02.01-restricted TRAG-3-derived
epitopes are targets for spontaneous immune responses in
breast cancer, hematopoietic
cancer, and
melanoma patients. Hence, these
epitopes represent potential target structures for future therapeutic vaccinations against
cancer, possibly appropriate for strategies that combine vaccination and
chemotherapy; i.e.,
paclitaxel treatment.