Functional assays

PBMCs were seeded in complete medium at 2 × 10⁶ cells/ml in 96-well V-bottom plates (Corning) with unconjugated anti-CD28 (clone L293) and anti-CD49d (clone L25; each at 3 μl/ml; BD Biosciences), brefeldin A (1 μl/ml; Sigma-Aldrich), monensin (0.7 μl/ml; BD Biosciences), anti-CD107a–PE-CF594 (clone H4A3; BD Biosciences), and the relevant viral peptides (each at a final concentration of 0.5 μg/ml). Unstimulated negative controls were included in each assay. Cells were analyzed by flow cytometry after incubation for 6 hours at 37°C.