Antigen-specific immunoregulation by IL-35Ig-transfected dendritic cells

Dendritic cells (DCs) are specialized APCs playing a central role in instructing T lymphocytes to initiate antigen-specific responses, which can be either immunogenic or tolerogenic, depending on DC-intrinsic and DC-extrinsic factors, among which is the cytokine milieu. Belonging in IL-12 family, IL-35 is a potent suppressive heterodimeric cytokine produced by T and B regulatory cells that induces a peculiar regulatory T-cell subset, referred to as iTr35. We transfected immunogenic CD8– DCs purified from murine spleens with a single-chain IL-35-Ig gene construct and we found that IL-35Ig expression abolished the otherwise immunogenic presentation of P815AB antigen by DCs in a skin test assay, triggering the onset of a long-lasting, antigen-specific tolerance to the peptide. To investigate the potential effect of IL-35Ig fusion protein expression on regulatory T-cell subset induction, we attempted a tolerogenic vaccination protocol to prevent allergy in a model of OVA-induced airway inflammation. Ectopic IL-35Ig expression by OVA-presenting DCs effectively prevented allergy onset, as it inhibited Th2 reactivity and fostered the expansion of iTr35, but not Foxp3+, cells. Thus IL-35Ig–transfected DCs, mediating the expansion of iTr35 cells, are suppressive in vivo, an effect that could be exploited in immunotherapeutic antigen-specific tolerization maneuvers.