HLA-B27/EBV tetramers and use of magnetic beads to enrich for HLA-B27-restricted tetramer-positive CD8+ T cells. In peripheral blood from an HLA-B27+ blood donor, 0.22% EBV EBNA (258–266) peptide-specific T cells were detected with phycoerythrin (PE)-labelled HLA-B27 tetramer (a) and 0.66% of CD8+ T cells by performing intracellular cytokine staining of IFN-γ-secreting cells (b). After magnetic activated cell sorting with anti-PE magnetic beads, antigen-specific T cells were enriched to 41.4% (a). These cells were further purified by fluorescence-activated cell sorting (not shown) and cultured for 4 weeks. After 4 weeks of culturing in the presence of interleukin-2, 95% of the T cell line were antigen-specific as shown by HLA-B27 tetramer staining (a), whereas only 68.3% of antigen-specific T cells could be identified by intracellular cytokine staining (b).