Identification of MART-1-specific T-Cell Receptors: T Cells Utilizing Distinct T-Cell Receptor Variable and Joining Regions Recognize the Same Tumor Epitope

Abstract

Tumor-specific cytotoxic T lymphocytes (CTLs) can mediate tumor regression in patients with metastatic melanoma and play a central role in the immune response to cancer. The recent identification of shared melanoma antigens has raised the possibility of a limited melanoma-specific T-cell receptor (TCR) repertoire, but subsequent studies have been controversial and difficult to interpret without knowing which tumor-associated antigens (TAAs) are being recognized by specific TCRs. However, the recent cloning of several melanoma TAAs now allows for the identification of the specifically recognized TAA and its epitope. We evaluated the TCR of two clonal CD8⁺ CTL lines, A42 and 1E2, from two HLA-A2⁺ patients with metastatic melanoma. Both CTL lines were MART-1 specific, and both demonstrate reactivity to the same epitope when presented in an HLA-A2.1 context. The TCR genes of the two clones were sequenced. All of the productively rearranged A42 TCR β chain genes were Vβ7/Dβ2.1/Jβ2.7/Cβ2; the TCR α chain genes were Vα21/Jα42/Cα. The 1E2 TCR β chain genes were Vβ3/Dβ1.1/Jβ1.1/Cβ1, and TCR α chains were Vα25/Jα54/Cα. This study is the first report of TCR sequences specific for a melanoma epitope. These TCR clones may be useful for the development of more effective immunotherapies and in studies of the mechanism of T-cell recognition of tumor antigen. They also provide direct evidence that the immune system can provide more than one TCR capable of recognizing a TAA epitope.