Abstract
The taxol resistance gene TRAG-3 was initially isolated from cancer cell lines that became resistant to taxol in vitro. TRAG-3 is a cancer germline Ag expressed by tumors of different histological types including the majority of melanoma, breast, and lung cancers. In the present study, we report that patients with stage IV melanoma and breast cancers developed spontaneous IFN-gamma-producing CD4+ T cell responses against a single immunodominant and promiscuous peptide epitope from TRAG-3 presented in the context of multiple HLA-DR molecules. The TRAG-3-specific CD4+ T cells and clones were expanded in vitro and recognized not only peptide pulsed APCs but also autologous dendritic cells (DCs) loaded with the TRAG-3 protein. All stage IV melanoma patients with TRAG-3-expressing tumors developed spontaneous CD4+ T cell responses against TRAG-3, demonstrating its strong immunogenicity. None of these patients had detectable IgG Ab responses against TRAG-3. TCRbeta gene usage studies of TRAG-3-specific CD4+ T cell clones from a melanoma patient and a normal donor suggested a restricted TCR repertoire in patients with TRAG-3-expressing tumors. Altogether, our data define a novel profile of spontaneous immune responses to cancer germline Ag-expressing tumors, showing that spontaneous TRAG-3-specific CD4+ T cells are directed against a single immunodominant epitope and exist independently of Ab responses. Because of its immunodominance, peptide TRAG-3(34-48) is of particular interest for the monitoring of spontaneous immune responses in patients with TRAG-3-expressing tumors and for the development of cancer vaccines.
Highlights
We have synthesized the 15 overlapping peptides and evaluated their binding capacities to 10 different HLA-DR and 2 HLA-DP4 molecules including the 7 molecules encoded by the HLA-DRB1 genes (i.e., HLA-DRB1*0101, HLA-DRB1*0301, HLA-DRB1*0401, HLA-DRB1*0701, HLA-DRB1*1101, HLADRB1*1301, and HLA-DRB1*1501), three molecules encoded by the HLA-DRB3, HLA-DRB4, and HLA-DRB5 genes and the HLADPB1*0401 and -0402 molecules
We investigated the CD4ϩ T cell responses against the cancer germline Ags (CGAs) taxol resistance-associated gene-3 (TRAG-3), commonly expressed by the majority of melanomas, breast cancers, and non-small cell lung carcinoma (NSCLC)
We observed that a single immunodominant epitope, TRAG-334–48, bound to multiple HLA-DR molecules including HLA-DRB1*0101, HLADRB1*0401, HLA-DRB1*0701, HLA-DRB1*1101, HLADRB1*1501, and HLA-DRB5*0101 and stimulated autologous
Summary
CGA, cancer germline Ag; TRAG, taxol resistance gene; UPCI, University of Pittsburgh Cancer Institute; DC, dendritic cells; NSCLC, non-small cell lung carcinoma; IC50, concentration of peptide that prevented binding of 50% of the labeled peptide. In patients with active cancers, CGAs may spontaneously stimulate Abs and circulating CD4ϩ T cells that are most often detectable only after one round of in vitro stimulation with peptide-pulsed APCs [18, 19]. We have investigated the spontaneous CD4ϩ T cell and Ab responses in patients with active solid tumors that commonly expressed the taxol resistance-associated gene-3 (TRAG-3), including melanoma, breast, and lung cancers. All patients with stage IV melanoma and TRAG-3-expressing tumors had detectable TRAG-3-specific CD4ϩ T cells, but no circulating TRAG-3-specific Ab. Our findings add to the diversity of the spontaneous immune responses to CGA-expressing tumors observed in patients with advanced cancers. They provide a good candidate for the monitoring of spontaneous immune responses in patients with TRAG-3-expressing tumors and for the development of TRAG-3-based cancer vaccines
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