Route of immunization and timing for adjuvant delivery : critical factors for efficient T cell cross-priming
CD8+ T cell responses are crucial in the defense against several infectious agents, as well as for the treatment of cancer. Thus, the development of vaccine strategies capable of eliciting robust CD8+ T cell responses is needed. Antigen cross-presentation is known to be an important mechanism for the activation of antigen-specific CD8+ T cells, and multiple parameters contribute to the efficiency of cross-priming. We examined two of them : the route of immunization and the timing of adjuvant delivery. First, we developed the tetramer-based enrichment strategy, which allowed us to study the endogenous CD8+ T cell response. Then, we investigated the impact of the route of immunization on CD8+ T cell cross-priming. We report that local delivery of cell-associated antigen results in delayed cross-priming due to the increased time required for antigen capture and presentation. In comparison, delivery of systemically disseminated antigen resulted in rapid T cell priming. Surprisingly, local injection of cell-associated antigen, while slower to mount a functional response, resulted in the differentiation of a more robust effector T cell population. We were next interested in evaluating the combination of cell-associated antigen with the delivery of poly I:C, an adjuvant known to induce the production of type I interferons (IFN). We observed an immunization-route-specific effect regarding the timing of innate immune stimulation and identified the optimal time window for adjuvant administration in order to maximize the boosting effects on CD8+ T cell cross-priming. We characterized in detail several effects of poly I:C, as well as type I IFN, exerted on immune cells