Identification of human T cell receptor gammadelta-recognized epitopes/proteins via CDR3delta peptide-based immunobiochemical strategy.

Human T lymphocytes, bearing T cell receptor (TCR) gammadelta, play an important role in anti-tumor/microbe immune responses. However, few tumor antigens recognized by TCRgammadelta have been defined so far. To investigate antigenic epitopes/proteins recognized by gammadeltaT cells, we have established a new immunobiochemical strategy that uses complementarity-determining region 3 of TCR delta chain (CDR3delta) peptide-mediated epitope/protein-binding assays. CDR3delta peptides synthesized using the CDR3 region in TCR Vdelta2 chain were validated for their binding specificity to target cells or tissues. These CDR3delta peptides were then employed as probes to pan putative epitopes in a 12-mer random peptide phage-displayed library and to identify putative protein ligands within tumor protein extracts by affinity chromatography and liquid chromatography/electrospray ionization-tandem mass spectrometry analysis. As a result, we have identified nine peptides and two proteins for TCRgammadelta, including human mutS homolog 2 (hMSH2) and heat shock protein (HSP) 60. All nine tested epitope peptides not only bind to gammadeltaT cells but also functionally activate gammadeltaT cells in vitro. Identification of HSP60 confirms the validity of this method as HSP60 is an identified ligand for TCRgammadelta. We show that hMSH2 is expressed on the surface of SKOV3 tumor cells, and cytotoxicity of Vdelta2 gammadeltaT cells to SKOV3 cells was blocked by anti-hMSH2 antibody, suggesting that hMSH2 may be a new ligand for TCRgammadelta. Taken together, our findings provide a novel immunobiochemical strategy to identify epitopes/proteins recognized by gammadeltaT cells.