With the increasing achievements in the field of immunotherapy, dendritic cells (DC) play an important role as initiators of the adaptive immune response. Induction of the adaptive immune response relies on the recognition of pathogens by DCs via pathogen recognising receptors (PRRs). The conjugation of antigen with immune stimulatory agents is a frequently applied strategy to enhance the immunogenicity of the antigen. Such conjugates have successfully targeted members of the toll-like receptors (TLRs), C-type lectin receptors (CLRs) and NOD-like receptors. Here we describe the synthesis and evaluation of peptide-conjugates that can simultaneous target TLR7 and DC-SIGN and the effect on DC maturation, cytokine profile and antigen (cross-)presentation.
We synthesised and evaluated an array of oligomannose containing clusters that vary in number (ranging from 1-6 copies) and type of mannoside (mono-, di- and tri-mannosides). The affinity of the clusters toward DC-SIGN, and rate of uptake were assessed by SPR and FACS. Based on these studies, a selection was made of the DC-SIGN targeting-constructs to be conjugated to a model epitope (the melanoma tumour antigen GP100). The simultaneous incorporation of a TLR7 agonist allowed us to test for synergistic effects. Our results show that simultaneous targeting of TLR7 with DC-SIGN does not result in synergy and the correlation between affinity of the mannose clusters and antigen presentation of the cluster-conjugates seems to be non-linear. The conjugates that showed the highest affinity for DC-SIGN did not lead to maximal antigen (cross-) presentation and even hampered T cell activation, whereas a moderate binder resulted in enhanced presentation. Our results suggest that targeting antigens towards DCs using DC-SIGN is not just a matter of enhancing the affinity of the carbohydrate ligand-conjugates and our results could contribute to the design of future glycan-based immunotherapeutic drugs.