In vivo studies of immunomodulatory DNA properties - 11th International Symposium on Circulating Nucleic Acids in Plasma and Serum (CNAPS)

Elena Rykova ^1,4 Olga Kolesnikova ² Elena Gavrilova ² Elena Goiman ² Ekaterina Burakova ³ Alesya Fokina ³ Dmitry Stetsenko ³

¹Department of Molecular Medicine, Institute of Chemical Biology and Fundamental Medicine, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
²Department of Experimental Immunology, Institute of Fundamental and Clinical Immunology, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
³Department of Nucleic Acids Chemistry, Novosibirsk State University, Novosibirsk, Russia
⁴Department of Engineer Ecological Problems, Novosibirsk State Technical University, Novosibirsk, Russia

Endogenous cell-free DNA (cfDNA) fragments appear in the blood as complexes and microparticles secreted by living cells along with the cell death remnants. Under specific conditions cfDNA can enter endosomes and activate the innate immune receptor TLR-9 through the recognition of unmethylated CpG-containing motifs with lack of cytosine methylation. Implications of synthetic immunomodulatory CpG ODNs as vaccine adjuvants against infections, cancer and therapies for autoimmune disorders have been intensively studied. CpG ODN analogues with phosphorothioate backbone modification are the most widely used in research for clinical studies, however their application is reduced by a number of drawbacks, as increased toxicity. We studied a CpG-containing isosequential analog of synthetic phosphorothioate ODN CpG 7909 in which the mesyl (methanesulfonyl) phosphoramidate group is substituted for the natural phosphodiester group at each internucleotidic position. CBA mice were treated subcutaneously with either phosphorothioate (P-ODN) or mesyl phosphoramidate ODN (M-ODN) once weekly for 3 weeks at a dose of 1mg/kg. Mice treated with ODNs demonstrated different changes of leukocytes number and redistribution into thymus, spleen and blood compared with control group. Both ODNs – treated groups demonstrated increased levels of spontaneous IL-2 production by spleen lymphocytes in vitro, indicating stimulation of Th1-mediated response. In the imurine chronic graft-versus-host (GVH) induced model of lupus M-ODN showed less influence in Th1/Th2 polarization effect compared with P-ODN. M-ODN led to the lupus development in 57% of mice comparable with the control group (lupus in 50% of mice), while P-ODN led to 78% of lupus development. Our results indicate that mesyl phosphoramidate CpG ODN differ from its phosphorothioate analog in its immunomodulatory properties in vivo probably due to their different potential to activate TLR9 encouraging further studies aimed to develop specifically targeted, non-toxic immunomodulatory DNA-based therapeutics.

This work was supported by RFBR grants No 18-29-09045.