Definition of TCR recognition sites on L^d-tum^-complexes

The P911 variant of the P815 mastocytoma was shown by Lurquin et al. (Cell 58:293,1989) to elicit rapid tumor rejection in a syngeneic host. This rejection was mediated by L^d-restricted cytotoxic T lymphocytes (CTL) for which targets could be sensitized by the synthetic peptide designated tum^- (P91A^-.12-24). In a previous study, T cell clones specific for L^d-tum^- complexes displayed very restricted TCR usage and a characteristic TCR motif in the V_α CDR3 region, predicted to interact with peptide. However, in contrast to the majority of L^d peptide Uganda that are nonamers, the tum^- peptide is a 13-mer and its sequence does not fit the Ld binding motif. Thus, to define shorter versions of the tum^- 13-mer and residues involved in TCR recognition, nonamer derivatives were synthesized and compared in several different binding and functional assays. From these comparisons, the peptide TQNHRALDL was found to be the optimal nonamer. CTL recognition of Ala-substituted analogues of this peptide indicated that the Hls and Arg residues at positions 4 and 5 are important for TCR contact We propose that these basic residues of the tum^- peptide interact with the previously defined acidic residues in the CDR3 region of several TCR known to recognize Ld-tum^- complexes.