Supra-agonist peptides enhance the reactivation of memory CTL responses

Single amino acid substitutions at TCR contacts may transform a natural pep tide Ag in CTL ligands with partial agonist, antagonist, or null activity. We obtained peptide variants by changing nonanchor amino acid residues invo lved in MHC class I binding. These peptides were derived from a subdominant HLA-A2-presented, latent membrane protein 2-derived epitope expressed in E BV-infected cells and in EBV-associated tumors. We found that small structu ral changes produced ligands with vastly different activities. In particula r, the variants that associated more stably to HLA-A2/molecules did not act ivate any CTL function, behaving as null ligands, Interestingly, T cell sti mulations performed with the combination of null ligands and the natural ep itope produced significantly higher specific CTL reactivation than reactiva tion of CTLs induced by the wild-type epitope alone, In addition, these par ticular variants activated memory CTL responses in the presence of concentr ations of natural epitope that per se did not induce T cell, responses. We show here that null ligands increased ZAP-70 tyrosine kinase activation ind uced by the natural epitope, Our results demonstrate for the first time tha t particular peptide variants, apparently behaving as null ligands, interac t with the TCR, showing a supra-agonist activity. These variant peptides di d not affect the effector T cell functions activated by the natural epitope . Supra-agonist peptides represent the counterpart of antagonists and may h ave important applications in the development of therapeutic peptides.