TLR9 is specifically required in pDCs for capsid-specific CD8⁺T-cell responses. (A) WT or BDCA2-DTR mice were IM injected with AAV2-SIINFEKL, and tetramer-positive cells were quantified over time (n = 4/group). BDCA2-DTR mice received DT intraperitoneally 3×/week. Statistically significant decrease compared with the response in WT mice is indicated. (B) Timeline of WT DC adoptive-transfer experiments. TLR9^−/− mice (n = 4-5/group) were recipients of adoptively transferred WT pDC (3 × 10⁶ cells) or WT cDC (5 × 10⁶ cells), or nothing. On the same day, all mice were IM injected with AAV2-SIINFEKL. WT C57BL/6 mice served as a positive control. (C) Quantification of capsid-specific CD8⁺ T-cell responses over time in TLR9^−/− mice that received either WT pDC, WT cDC, or nothing. The dotted line at 0.1% represents the limit of detection of capsid-specific CD8⁺ T cells using the tetramer. Data points are averages ± SEM. Statistically significant increases compared with responses in TLR9^−/− mice that did not receive cell transfer are indicated. P values: (A) *P =.046; (C) ***P =.0002 for WT vs “TLR9^−/− + WT pDC”; *P =.049 for TLR9^−/− vs TLR9^−/−.