When PBMC from the PRV and LV-PRV group were stimulated in vitro with NIA-3 virus, PRV-speci®c killing (i.e. killing of PRV-infected L14 cells and killing of uninfected L14 cells) increased between weeks 3 and 6 after PRV vaccination (up to 30% of PRVinfected target cells were killed compared with up to 15% of uninfected target cells).