Mouse DC-SIGN/CD209a as Target for Antigen Delivery and Adaptive Immunity

The efficacy of vaccination studies aimed at targeting antigens to human DC-SIGN (hDC-SIGN) have been notoriously difficult to study in vivo, as eight dendritic cell-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN) homologs have been described in mice. CD209a/SIGNR5 has been coined as the mouse DC-SIGN (mDC-SIGN) ortholog, based on its expression and location in the genome. Nonetheless, which properties of hDC-SIGN are covered by mDC-SIGN is poorly investigated. One of the most important functions of DC-SIGN is the induction of adaptive immunity. As such, the aim of this study is to determine the capability of mDC-SIGN to induce adaptive immune responses. Here, we show that mDC-SIGN is expressed on GM-CSF cultured bone marrow-derived dendritic cells (BMDCs) and macrophages. However, mDC-SIGN is an internalizing receptor which, unlike hDC-SIGN, quickly resurfaces after internalization. Binding of OVA-coupled anti-mDC-SIGN antibody by BMDCs leads to quick internalization, processing, and presentation to antigen-specific CD8⁺ and CD4⁺ T cells, which can be boosted using the TLR4 ligand, monophosphoryl lipid A. In the homeostatic condition, mDC-SIGN is mostly expressed on myeloid cells in the skin and spleen. A subcutaneous injection of fluorescent anti-mDC-SIGN reveals specific targeting to mDC-SIGN⁺ skin dendritic cells (DCs) and monocyte-derived DCs in situ. A subcutaneous vaccination strategy containing OVA-coupled anti-mDC-SIGN antibody generated antigen-specific polyfunctional CD8⁺ T cell and CD4⁺ T cell responses and a strong isotype-switched OVA-specific antibody response in vivo. We conclude that mDC-SIGN shows partly overlapping similarities to hDC-SIGN and that targeting mDC-SIGN provides a valuable approach to investigate the immunological function of DC-SIGN in vivo.