Soluble DNA circulates in the peripheral blood of healthy subjects, and, at increased concentrations, of pregnant women and patients affected by tumors and vasculitis. Since the discovery of intracellular DNA sensors, inducing inflammatory responses after binding to DNA, DNA has been included among danger signals. However, this view does not explain the presence of abundant circulating DNA in conditions characterized by tolerance (pregnancy) or immunodeficiency (tumor). In order to verify whether DNA mediates also an immunoregulating activity, a 20 base-pair long oligonucleotide (poly-CG) was synthesized and tested for its capacity to: 1) bind MHC class II molecules; 2) exert immunoregulatory activity. The oligo binding to PMJ2-PC macrophages was inhibited by anti-MHC monoclonal antibodies (mAb). The specific binding of DNA to MHC class II molecules was confirmed by western blot analysis. Proliferation of OVA-specific splenocytes was inhibited by incubation with the oligo as well as by circulating DNA from cancer patients; moreover, fluorescent oligo, injected intravenously to NZB/W F1 mice, bound only on MHC class II positive cells (macrophages and B lymphocytes). Finally, nephritic NZB/W F1 mice, administered weekly with the oligo, showed delayed onset of protenuria and improved survival with respect to untreated animals, a phenomenon associated with increased frequencies of Treg. Interestingly, in vitro incubation of PMJ2-PC macrophages with the oligo induced increased CCL22 secretion. These data demonstrate for the first time that free DNA may mediate immunoregulatory activities.

Citation Format: Gilberto Filaci, Francesca Ferrera, Samuele Tardito, Tiziana Altosole, Cinzia Bernardi, Alessia Parodi, Daniela Fenoglio. Free DNA and tolerance [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B127.