Ovarian and breast cytotoxic T lymphocytes can recognize peptides from theamino enhancer of split protein of the Notch complex

In this study we investigated recognition by ovarian tumor associated lymph ocyte (OVTAL), and breast tumor associated lymphocytes (BRTAL), of peptides corresponding to the sequence 125-135 of the Aminoenhancer of split (AES) protein. Three of these peptides designated as G75:AES1/2 (128-135), G60: A ES1/2 (127-137) and G61: AES1/2 (125-133) correspond to the wildtype AES se quence, while the fourth G76:GPLTPLPV AES1/2 (128-135) corresponds to a var iant sequence of the peptide G75 with the N-terminal Leu substituted to gly cine. These sequences were chosen for study because mass-spectrometric anal ysis (MS) of a CTL active HPLC peptide fraction eluted from immunoaffinity precipitated HLA-A2 molecule, revealed: (a) the presence of an ion with a m ass-to-charge ratio (m/z) Of 793 which was more abundant than other ions of similar masses; (b) the tentatively reconstituted sequence of the ion 793 matched the sequence of peptide G76. We found that AES peptides G75 (128-13 5) and G76 (128-135) (L128G) reconstituted CTL recognition at concentration s ranging between 200-500 nM. These concentrations are lower than concentra tions reported to activate effector function of CTL recognizing other epith elial tumor Ag. Furthermore, analysis with cloned CD8(+) T cells indicated that G75 and G76 were not cross-reactive specificities, suggesting a key ro le for the N-terminal residues of the variant peptide in dictating specific ities. Since the AES proteins are part of a set of transcriptional represso rs encoded by the Enhancer of split [E(spl)] genes, and since these repress ors are activated to suppress cell differentiation in response to Notch rec eptors signalling, the AES peptides may represent a novel class of self-ant igens that deserve further consideration as tumor Ag in epithelial cancers. (C) 1999 Elsevier Science Ltd. All rights reserved.