ACTIVATION OF EPITOPE-SPECIFIC MEMORY CYTOTOXIC T-LYMPHOCYTE RESPONSES BY SYNTHETIC PEPTIDES

Cytotoxic T lymphocytes (CTL) recognize antigens as short peptides sel ected for presentation by their ability to bind to MHC class molecules . Polyclonal Epstein-Barr virus (EBV)-specific memory CTL responses, r eactivated from blood lymphocytes of HLA-A11-positive individuals by s timulation with the autologous EBV-transformed lymphoblastoid cell lin e (LCL), are often dominated by reactivities directed to the peptide e pitope IVTDFSVIK (IVT), corresponding to amino acids 416-424 of EBV nu clear antigen-4 (EBNA4). We now report the selective activation of IVT -specific CTL by stimulation of lymphocytes with the corresponding syn thetic peptide. A more than 10-fold increase in frequency of CTL clone s with this specificity (from 8% to 96%) was obtained when the peptide was presented by HLA-A11-transfected T2 cells (T2/A11). Titration of synthetic peptide in cytotoxic assay demonstrated that clones activate d under these conditions are as efficient as clones activated by conve ntional LCL stimulations. Induction of memory CTL responses required l ow surface density of MHC:peptide complexes, since reactivation was ac hieved by stimulation with T2/A11 cells pulsed with concentrations of peptide that are suboptimal for induction of target cell lysis. This p rotocol of activation revealed the presence of IVT-specific CTL precur sors in a donor that failed to mount an IVT-specific response upon sti mulation with the autologous B95.8 virus-transformed LCL. The results suggest that stimulation with synthetic peptide epitopes can be effici ently used for induction of memory CTL responses, and may be particula rly helpful for the selective expansion of subdominant CTL specificiti es.