Alloreactivity as a source of high avidity peptide-specific human CTL

PBL from HLA-A2(-) or HLA-A3(-) donors were stimulated with synthetic pepti de libraries fitting HLA-A2 or HLA-AS motifs and presented on HLA-A2 or HLA -A3-expressihg TAP(-) cells. Peptide library-specific allorestricted CTL we re found to constitute up to half the alloreactive CTL response and occurre d at twofold lower frequency than autologous peptide library-specific CTL, This indicates that positive selection by one particular MHC class I molecu le is not absolutely essential for the generation of CTL restricted to the same molecule. However, positive selection increases their frequency. The C TL obtained differed greatly both with respect to peptide dependency and pe ptide specificity. Determination of the peptide avidity for one representat ive CTL clone, 10F4, proved that the method described here allows the stimu lation of high avidity cytotoxic T cells, This approach involving in vitro stimulation of T cells restricted toward a MHC molecule that was not presen t during their negative selection might therefore offer the possibility of isolating CTL against self and foreign peptides with varying avidities. Suc h T cells might indeed be useful for tumor immunotherapy.