Endogenous DCs but not B cells are required for secondary expansion of CD8⁺ T cells. (A) Lethally irradiated C57BL/6 mice received 5 × 10⁶ bone marrow cells from B^−/− mice plus 1 × 10⁶ bone marrow cells from K^bD^b−/− (B^−/− + K^bD^b−/−) or WT (B^−/− + WT) donors. Mice were primed with Vac-GP33 and boosted with B/VSV-GP33 after complete hematopoietic reconstitution. GP33-specific CD8⁺ T cells were quantified in blood at day 5 post-B/VSV boosting (n = 6/group). (B) CD11c-DTR chimeric mice (CD11c→WT) and their WT controls (WT→WT) were primed with Ad-GP33 and boosted with B/VSV-GP33. One day prior to B/VSV and every other day thereafter, mice received 100 ng of DT (IP) to deplete CD11c⁺ cells. GP33-specific CD8⁺ T cells were quantified in blood at day 5 post-VSV boosting (n = 5/group, *P < .01 compared with DT injection). (C) Negatively selected splenic CD8⁺ T cells from Ad-GP33–immunized congenic mice (Thy1.1) were adoptively transferred into similarly immunized CD11c chimeric recipients (Thy1.2) before B/VSV-GP33 boosting. DT injections were carried out as described previously and GP33-specific Thy1.1⁺CD8⁺ T cells were quantified in blood at day 5 post-VSV boosting (n = 5/group, *P < .01 compared with DT injection).