Internalization and endosomal degradation of receptor-bound antigens regulate the efficiency of cross presentation by human dendritic cells

Abstract

Dendritic cells (DCs) can capture extracellular antigens and load resultant peptides on to MHC class I molecules, a process termed cross presentation. The mechanisms of cross presentation remain incompletely understood, particularly in primary human DCs. One unknown is the extent to which antigen delivery to distinct endocytic compartments determines cross presentation efficiency, possibly by influencing antigen egress to the cytosol. We addressed the problem directly and quantitatively by comparing the cross presentation of identical antigens conjugated with antibodies against different DC receptors that are targeted to early or late endosomes at distinct efficiencies. In human BDCA1 ؉ and monocyte-derived DCs, CD40 and mannose receptor targeted antibody conjugates to early endosomes, whereas DEC205 targeted antigen primarily to late compartments. Surprisingly, the receptor least efficient at internalization, CD40, was the most efficient at cross presentation. This did not reflect DC activation by CD40, but rather its relatively poor uptake or intraendosomal degradation compared with mannose receptor or DEC205. Thus, although both early and late endosomes appear to support cross presentation in human DCs, internalization efficiency, especially to late compartments, may be a negative predictor of activity when selecting receptors for vaccine development.

Criteria for Dendritic Cell Receptor Selection for Efficient Antibody-Targeted Vaccination

“…Specific trafficking routes that initiate more efficient MHC I or MHC II Ag presentation have not been strictly defined. For example, DEC205 (CD205), a molecule that traffics to late endosomes (4)(5)(6), is considered a superior receptor for MHC I cross-presentation (7)(8)(9)(10). Alternatively, MHC I cross-presentation is efficiently enhanced by receptors that traffic to early, but not late, endosomes (5,6,11,12).…”

“…Furthermore, receptors that traffic to the same intracellular destination can differ in their Ag presentation efficiencies. This is the case for CD40 and mannose receptor that both traffic to early endosomes, yet for unknown reasons CD40 is more efficient at eliciting MHC I cross-presentation (5). Therefore, the emerging view is that receptor trafficking alone is not the sole determinant of the effectiveness of Ag presentation outcomes.…”

Molecular Mechanisms of TLR2-Mediated Antigen Cross-Presentation in Dendritic Cells

“…Other studies have shown that soluble Ags are cross-presented through the TAP-dependent cytosolic pathway (9,10) or the TAPindependent vacuolar pathway (4,10). In particular, Ags conjugated to Abs are targeted to either the early or the late endosome through CD40, the mannose receptor, or DEC205 (11). Efficient cross-presentation is mediated by either prolonged residence of the Ag in the early endosome or decreased degradation in the late endosome (11)(12)(13).…”

“…In particular, Ags conjugated to Abs are targeted to either the early or the late endosome through CD40, the mannose receptor, or DEC205 (11). Efficient cross-presentation is mediated by either prolonged residence of the Ag in the early endosome or decreased degradation in the late endosome (11)(12)(13). Dendritic cell (DC) cross-priming of the TLRmediated CTL response during microbial infection may not only upregulate costimulatory molecules but also regulate this process of cross-presentation (14)(15)(16)(17).…”

Differential uptake and cross‐presentation of soluble and necrotic cell antigen by human DC subsets

“…In humans, MoDCs express high levels of MR whereas CD1c + DCs and CD141 + DCs express little if any MR [21,22], which may account for the lower uptake of soluble protein by CD1c + DCs and CD141 + DCs and suggests that similar uptake mechanisms occur between species. Consistent with their known higher levels of lysosomal proteases [22,23] the proteasome for processing of the pp65 NLV epitope, suggesting preferential use of the vacuolar pathway by MoDCs. This is further corroborated by studies demonstrating preferential use of the vacuolar pathway by mouse MoDCs and their in vitro BM-derived equivalent for cross-presentation of soluble protein [20,24], suggesting conservation of these pathways between species.…”