Migration of antigen (Ag)-loaded dendritic cells (DCs) from sites of infection into draining lymphoid tissues is fundamental to the priming of T-cell immune responses. We evaluated monocyte-derived DCs (MoDCs) and peripheral blood DCs (PBDCs) to respond to proinflammatory mediators, CD40L, and intact bacteria. All classes of stimuli induced DC phenotypic maturation. However, for MoDCs, only prostaglandin E 2 (PGE 2 )-containing stimuli induced migratory-type DCs. Thus, immature MoDCs that encountered proinflammatory cytokines or CD40L or intact bacteria in the presence of PGE 2 acquired migratory capacity but secreted low levels of cytokines. Conversely, MoDCs that encountered pathogens or CD40L alone become nonmigratory cytokine-secreting cells (proinflammatory type). Interestingly, both migratoryand proinflammatory-type DCs expressed equivalent levels of chemokine receptors, suggesting that the role of PGE 2 was to switch on migratory function. We demonstrate that PGE 2 induces migration via the E-prostanoid 2/E-prostanoid 4 (EP 2 /EP 4 ) receptors and the cAMP pathway. Finally, migratory-type MoDCs stimulated T-cell proliferation and predominantly IL-2 secretion, whereas proinflammatory-type MoDCs induced IFN-␥ production. In contrast, CD1b/c ؉ PBDC rapidly acquired migratory capacity irrespective of the class of stimulus encountered and secreted low levels of cytokines. This suggests that not all mature stages of DCs are destined to migrate to lymphoid organs and that the sequence in which stimuli are encountered significantly affects which functions are expressed. Thus, certain immature DC subsets recruited from the resting precursor pool may have multiple functional fates that play distinct roles during the induction and effector phases of the immune response. These findings have important implications for the clinical utility

Dendritic cells (DCs) are being evaluated for cancer immunotherapy due to their unique ability to induce tumor-directed T-cell responses. Here we report that the type of human DC, the mode of activation, and the strategy for delivery of antigen are 3 critical factors for efficient stimulation of tumor-specific CD8 ؉ and CD4 ؉ T cells. Only CD1c ؉ blood DCs and monocyte-derived DCs (MoDCs) were capable of presenting epitopes of the full-length tumor antigen NY-ESO-1 on both major histocompatibility complex (MHC) class I (cross-presentation) and MHC II, whereas plasmacytoid DCs were limited to MHC II presentation. Cross-presentation was inefficient for soluble protein, but highly efficient for antigen-antibody immune complexes (NY-ESO-1/IC) and for protein formulated with ISCOMATRIX adjuvant (NY-ESO-1/IMX). DC activation with CD40L further enhanced cross-presentation efficiency. The mode of antigen delivery was found to be a determining factor for cytosolic proteolysis by DCs. Immune complexes (ICs) targeted a slow, proteasomedependent cross-presentation pathway, whereas ISCOMATRIX (IMX) targeted a fast, proteasome-independent pathway. Both cross-presentation pathways resulted in a long-lived, T-cell stimulatory capacity, which was maintained for several days longer than for DCs pulsed with peptide. This may provide DCs with ample opportunities for sensitizing tumorspecific T cells against a broad array of tumor antigen epitopes in lymph nodes. IntroductionTo achieve tumor cell killing by cytotoxic CD8 ϩ T cells (CTLs), cancer vaccines target major histocompatibility complex (MHC) class Irestricted epitopes. CTL responses alone may not be sufficient for effective anticancer immunity, and additional help from CD4 ϩ T cells is required for optimal CTL priming and memory induction. [1][2][3][4] A variety of vaccine strategies are being developed to generate an integrated CD4 ϩ and CD8 ϩ T-cell response. One strategy uses dendritic cells (DCs), which have the unique capacity to not only present exogenous antigen on MHC II, but also to "cross-present" these on MHC I. 5 DC-based clinical trials have demonstrated "proof of concept" using primary DCs isolated directly from peripheral blood or DCs generated in vitro from monocytes (MoDCs) or CD34 ϩ progenitors, pulsed with MHC Irestricted peptides (reviewed in Davis et al 6 ). We and others have previously studied the functional profiles of different DC populations providing valuable insights into their potential clinical utility. [7][8][9] Despite this, the rational design of DC-based cancer vaccines still lacks some critical information. What are the optimal approaches to achieve antigen presentation on both MHC I and MHC II? Which DC population is best suited for this purpose? How should these DCs be matured or activated?We have used the tumor antigen NY-ESO-1 as a model antigen to address these questions. NY-ESO-1 is a 180 amino acid protein, which is absent in normal tissues apart from testis, but is expressed in a variety of common human cancers including melanoma, ...