Enhanced cytotoxic responses to intravenous exosomal-peptide in CD169^−/−mice. C57BL/6 or CD169^−/− mice were immunized (A) IV or (B) SC with PBS and 100 or 50 µg Exo₂₅₇, respectively, 100 μg Exo_257/323 (IV), 10⁵ DC₂₅₇, or 10⁵ parental B cell₂₅₇. Where stated, mice were supplemented IV with 10⁷ OT-I splenocytes prior to immunization. Seven days after immunization, mice were adoptively transferred with unpulsed (CFSE low) or OVA_257-264-pulsed (CFSE high) target cells. In vivo killing was analyzed 18 hours later by flow cytometry. Results representative of ≥6 mice per group using exosomes purified by ultracentrifugation. Line, mean. One-way ANOVA with Bonferroni postcorrection was performed: ns, not significant; **P < .01; ****P < .0001.