DEFINITION OF TCR RECOGNITION SITES ON L(D)-TUM(-) COMPLEXES

The P911 variant of the P815 mastocytoma was shown by Lurquin al al. ( Cell 58:293, 1989) to elicit rapid tumor rejection in a syngeneic host . This rejection was mediated by L(d)-restricted cytotoxic T lymphocyt es (CTL) for which targets could be sensitized by the synthetic peptid e designated tum(-)(P91A(-).12-24). In a previous study, T cell clones specific for L(d)-tum(-) complexes displayed very restricted TCR usag e and a characteristic TCR motif in the V-a CDR3 region, predicted to interact with peptide. However, in contrast to the majority of Ld pept ide ligands that are nonamers, the tum(-)peptide is a 13-mer and its s equence does not fit the Ld binding motif. Thus, to define shorter ver sions of the tum(-)13-mer and residues involved in TCR recognition, no namer derivatives were synthesized and compared in several different b inding and functional assays. From these comparisons, the peptide TQNH RALDL was found to be the optimal nonamer. CTL recognition of Ala-subs tituted analogues of this peptide indicated that the His and Arg resid ues at positions 4 and 5 are important for TCR contact. We propose tha t these basic residues of the tum(-) peptide interact with the previou sly defined acidic residues in the CDR3 region of several TCR known to recognize L(d)-tum(-) complexes.