Effector cell recognition of the BKV Tp579 peptide is HLA-A*0201-restricted. BKV Tp579- stimulated PBMC from an HLA A*0201+ healthy individual were stained with the respective tetramer, gating on CD8αβ+ T cells. A small population comprising 2.7% of tetramer-binding CD8+ T cells (panel a, right upper quadrant) was sorted by flow cytometry and propagated in vitro for 2 months. A 97.3% enriched BKV Tp579-specific CTL cell line (panel b, right upper quadrant) could lyse the p579-pulsed T2 cell line, expressing the A*0201 class I molecule only, but not the p579-pulsed M02 BLCL (totally mismatched for HLA class I alleles with the p579 CTL line) (panel c)