Despite the potency of dendritic cells (DCs) as a vaccine carrier, they are short-lived and sensitive to CTL-mediated elimination. Thus, it is believed that the longevity of Ag presentation by peptide-pulsed DC is limited in vivo. Surprisingly, however, we found that although the majority of injected DCs disappeared from the draining lymph nodes within 7 days, Ag presentation persisted for at least 14 days following DC immunization. This prolonged Ag presentation was not mediated by the remaining injected DCs or through Ag transfer to endogenous APCs. We provide evidence that exosomes released by DCs might be responsible for the persistence of Ag presentation. Functional exosomes could be recovered from the draining lymph nodes of C57BL/6 mice following DC vaccination and, in contrast to DCs, T cell stimulation by exosomes in vivo was not affected by the presence of CTL. Our findings demonstrate that Ag presentation following delivery of DC vaccines persists for longer than expected and indicate that the exosome may play a previously unrecognized role in Ag presentation following DC vaccination. Furthermore, our study reinforces the application of exosomes as a vaccination platform and suggests that exosome-based vaccines may be advantageous for booster immunizations due to their resistance to CTL.