T-CELL RECEPTOR V-ALPHA BIAS CAN BE DETERMINED BY TCR-CONTACT RESIDUES WITHIN AN MHC-BOUND PEPTIDE

Many antigen-specific T cell responses show profound V-region biases i n one or both chains of the TCR alpha beta heterodimer. We have examin ed how changes in residues within an MHC-bound peptide can influence V -region selection. Single-chain TCR transgenic mice were derived using a beta-chain specific for the K-b-restricted peptide from ovalbumin, OVA(257-264). Transgenic T cells were stimulated in vitro using OVA(25 7-264) or a single residue variant having a lysine to aspartic acid su bstitution at determinant position 7 (7D). Recent crystallographic ana lyses have shown that this variant residue is involved in direct conta ct with the TCR. Sequence analysis of the T cell populations showed th at the majority OVA(257-264)-specific T cells used V alpha 10-positive TCR while the majority of the 7D-specific TCR expressed the V alpha 4 element. In both peptide responses we found that some cell lines appe ared to be made up of more than one clone expressing the same V alpha sequence but having limited variation at the V-J junction. These resul ts show that the TCR contact residues within the target peptide can in fluence V-region bias and suggest that the first and second hypervaria ble regions of the TCR are directly or indirectly involved in determin ing peptide specificity.