Human TCR-γ/δ alloreactive response to HLA-DR molecules: Comparison with response of TCR-α/β

We have analyzed the human γ/δ T cell alloreactive response to class II HLA-DR molecules and attempted to compare this response with that mediated by the TCR-α/β counterparts. Several γ/δ CTL clones from a healthy individual were generated in mixed lymphocyte reactions against an EBV- transformed B cell line termed E418. Fine specificity and primary TCR structure of 10 representative clones (all CD4^- CD8(±)) were then determined. Functional studies, with the use of B cell lines homozygous for HLA-DR (DR1-10), indicated that all γ/δ T cell clones specifically reacted with HLA-DR2 molecules. In addition, five clones were able to cross-react with subtypes of HLA-DR8. Extended panel target experiments, including lymphoblastoid cells expressing various HLA-DR2 subtypes, showed that the T cell clones displayed distinct fine specificities. Clones with broad (Dw2, Dw12, Dw21, Dw8.1, and Dw8.2) or in contrast, more restricted (DRB1*1501 or DRB1*1503) specificity were identified. Furthermore, amino acid substitutions at predicted peptide binding site position 30 and TCR- interacting position 67 of the DRB*1 β-chain seemed to affect alloresponse of some T cell clones. With respect to TCR-γ/δ structure, diversity in gene segment usage was observed, with the predominance of T cells using a V3- Jγ2/V1-Jδ1⁺ receptor. A smaller fraction of the cells expressed TCR comprising Vγ9 and Vδ1 regions. In contrast, the Vδ3 gene segment was used by a minority of the cells, and the Vδ2 was not expressed by any T cell clone. Together, the present data indicate that similarly to TCR-α/β, human TCR-γ/δ lymphocytes may recognize in a highly specific fashion a particular HLA-DR heterodimer. T cell clones cross-reacting with other HLA-DR molecules were also identified. Despite some degree of heterogeneity, V gene segment use by alloreactive clones seemed to be nonrandom. No obvious correlation between TCR gene use and HLA-DR alloreactivity could be identified. Moreover, our results suggest that similarly to TCR-α/β cells, foreign MHC-bound peptides may contribute to TCR-γ/δ alloreactive response.