CD8A and influenza: Although saturating concentrations of the H-2Db/NP68 tetramer were bound comparably by memory CD8+ T cells isolated 5 days after rVV-NP challenge irrespective of time after influenza priming (Fig. 4A), tetramer decay experiments demonstrated a striking reduction in TCR off-rate for NP-specific CD8+ T cells expanded by rVV-NP challenge 6 months postinfluenza infection compared with the corresponding cells expanded 2 months postinfluenza infection (Fig. 4A).