Requirement for B cells or TACI for DC priming in mice. VSV NP 52-59–specific cytolytic activity in mice primed with 2 × 10⁶ mature, BLyS^high bone marrow–derived DCs pulsed with the VSV NP 52-59 peptide after terminal differentiation with TNFα. Three experiments, each containing 2 mice per group, have been averaged (SD ≤ 4 at all the E/T ratios studied). Three recipient mouse strains (wild-type C5BL7/6, and B-cell–deficient and TACI-deficient knockout strains) were used in these experiments, as indicated. To address the importance of TACI signaling in this priming protocol, 2 independent groups of B-cell–deficient mice have been treated either with TACI-Fc administered intraperitoneally 24 hours prior to and 48 hours after CTL priming, or TACI-Fc administered in vitro, the last 48 hours in DC cultures prior to peptide pulsing and in vivo transfer. The results of these experiments, shown with dotted lines, support the need for an ongoing TACI-BlyS signal during priming, as proven by the restored CTL induction in B-cell–deficient mice that received TACI-Fc in vivo but not in vitro (dotted lines).