No advantage of cell-penetrating peptides over receptor-specific antibodies in targeting antigen to human dendritic cells for cross-presentation.

Induction of CTL responses by dendritic cell (DC)-based vaccines requires efficient DC-loading strategies for class I Ags. Coupling Ags to cell-penetrating peptides (CPPs) or receptor-specific Abs improves Ag loading of I)Cs. In contrast to CPPs, receptor-specific Abs deliver conjugated Ags to I)Cs with high specificity, which is advantageous for in vivo strategies. It has, however, been speculated that CPPs facilitate uptake and endosomal escape of conjugated Ags, which would potently enhance cross-presentation. In this study, we directly compare the in vitro targeting efficiency of a humanized DI Ab directed against the human DC surface receptor DC-SIGN hD1 to that of three CPPs. The three CPPs colocalized within endosomes when targeted to human monocytederived I)Cs simultaneously, whereas hD1 was present in a different set of endosomes. However, within 75 min after uptake CPPs and hDI colocalized extensively within the lysosomal compartment. Ab-mediated targeting of class I-restricted peptides to DCSIGN enhanced cross-presentation of the peptides, while only one of the CPPs enhanced peptide presentation. This CPP and hDI enhanced cross-presentation with equal efficiencies. Thus, we found no evidence of CPP specifically favoring the delivery of conjugated Ag to the DC class I presentation pathway. Given the specificity with which Abs recognize their targets, this favors the use of DC receptor-specific Abs for in vivo vaccination strategies.