Reactivity against the vaccinia vector. A) IFN-γ and IL-2 secretion by splenocytes isolated 3 weeks following the late boost and stimulated with inactivated vaccinia. * indicates a significant difference (p < 0.05), M = MVA, D = DNA. Error bars show standard deviations of all animals in each group. B) End-point serum dilution for a 50% in vitro neutralization of vaccinia virus at the time of the late boost (black bars) and at the time of sacrifice, 3 weeks after the late boost (white bars).