Immunomodulatory effects of carbon nanotubes functionalized with a Toll-like receptor 7 agonist on human dendritic cells

The protocols for the preparation of dendritic cells (DCs) as cancer vaccines based on stimulation of Toll-like receptors (TLRs) are very promising. In this study we covalently attached 7-thia-8-oxoguanosine (7-TOG), a selective endosomal TLR7, to previously oxidized multi-walled carbon nanotubes (o-MWCNTs) (mass ratio 1:5.6, respectively), and tested their ability to activate human monocyte-derived (Mo)DCs. Light, confocal and transmission electron microscopy confirmed efficient phagocytosis of 7-TOG-MWCNTs by MoDCs and their efficient delivery to TLR7+ endosomes. The biocompatibility studies showed that 7-TOG-MWCNTs, at concentrations lower than 100 μg/ml, were not cytotoxic for MoDCs. 7-TOG-MWCNTs (50 μg/ml) up-regulated CD86 expression, allostimulatory activity, T helper (Th)1- and Th17-polarizing capability of MoDCs. The same concentration of soluble 7-TOG, alone or in combination with control o-MWCNTs, did not have such effects. It can be hypothesized that the efficacy of 7-TOG-MWCNTs in stimulating MoDCs was a consequence of increased intracellular concentration of 7-TOG after internalization of the nano-complexes, because similar Th-polarizing capability could be induced with 10-times higher concentrations of soluble 7-TOG. In conclusion, our results suggest that functionalized MWCNTs may be a promising system for the delivery of drugs to intracellular targets, in order to improve the immunogenic potential of DCs for therapeutic purposes.