Phenotypic characterization of tetramer-positive CD3+CD8+ T cells. CMVpp65495/HLA-A*0201 CD8+ T cells were used as a positive control and HLA-A2 null as negative control. (A) Peptide/HLA-A2 tetramer analysis of PBMCs was performed by 6-color flow cytometry in 2 patients. (B) CD45RO and CD27 phenotype of CD3+ CD8+ T-cell gated tetramer-positive lymphocytes on samples from patient 25.