Direct visualisation of hepatitis B virus (HBV)-specific cytotoxic T cells with an human leucocyte antigen (HLA) class I peptide tetrameric complex allows a new insight into their actual frequency. - Maini, M; Ogg, G; Boni, C; Pilli, M; Ferrari, C; Mcmichael, A; Williams, R; Vergani, D; Bertoletti, A (1998)