The recognition of gamma delta TCR to protein antigen does not depend on the hydrophobic I97 residue of CDR3 delta

The crystal structure analysis demonstrated that the hydrophobic amino acid residue (isolecuine/leucine/valine) at conserved position 97 of V delta 2 TCR plays an important role in recognizing the non-peptide antigen. But its importance to protein antigen remains unclear until now. In the present study, we focus on the role of hydrophobic amino acid residue at conserved position 97 of V delta 2 TCR in complementarity determining region (CDR)3 delta-mediated binding to protein antigen. We employed CDR3 delta peptide and membrane-engineered gamma delta TCR as detecting molecules with mutated 97 hydrophobic amino acid residue in CDR3 delta (nominated as OT10), a V delta 2 CDR3 sequence derived from tumor infiltrating lymphocytes in ovarian epithelial carcinoma (OEC). Binding assays revealed that OT10 peptide and membrane-engineered gamma delta TCR (gamma delta TCR transfected cells with OT10 sequence) could bind specifically ovarian tumor cell line (SKOV3). The mutant analysis indicated that any amino acid substitution at position delta 197 could abolish the response of the transfected cells to isobutylamine, a known non-peptide antigen of gamma delta T cells. But amino acid substitution of isoleucine at position delta 97 did not change the responsiveness of gamma delta TCR transfected cell to protein antigen. Our data suggested that a mechanism other than non-peptide antigen might mediate the recognition of V delta 2 gamma delta T cells for protein antigen. This finding may provide a possibility that gamma delta TCR recognize different ligands in diversity manners.