Antigen presentation by an immature myeloid dendritic cell line does not cause CTL deletion in vivo, but generates CD8+ central memory-like T cells that can be rescued for full effector function.
Immature dendritic cells (DC), in contrast to their mature counterparts, are incapable of mobilizing a CD8+ CTL response, and, instead, have been reported to induce CTL tolerance. We directly addressed the impact of immature vs mature DC on CTL responses by infusing adenovirus peptide-loaded DC (of the D1 cell line) into mice that had received adenovirus-specific naive TCR-transgenic CD8+ T cells. Whereas i.v. injection of mature DC triggered vigorous CTL expansion, immature DC elicited little proliferation involving only a minority of the TCR-transgenic CTL. Even though the latter CTL developed effector functions, including cytolytic activity and proinflammatory cytokine secretion, these cells differed significantly from CTL primed by mature DC in that they did not exhibit down-regulation of CD62L and CCR7, receptors involved in trapping of T cells in the lymphoid organs. Interestingly, adoptive transfer of CTL effector cells harvested after priming by either mature or immature DC into naive recipient mice, followed by exposure to adenovirus, yielded quantitatively and qualitatively indistinguishable CTL memory responses. Therefore, in vivo priming of naive CD8+ T cells by immature DC, although failing to induce a full-blown, systemic CTL response, resulted in the formation of central memory-like T cells that were able to expand and produce IFN-gamma upon secondary antigenic stimulation.