Cyclic-di-GMP based immune stimulatory formulations as novel vaccine adjuvants and anti-cancer agents

Abstract

Event Abstract Back to Event Cyclic-di-GMP based immune stimulatory formulations as novel vaccine adjuvants and anti-cancer agents Soner Yildiz1*, Esin Alpdundar1, Banu Bayyurt2, Mine Ozcan1, Gozde Gucluler2, Defne Bayik2, Bilgi Gungor1, Ihsan Gursel2 and Mayda Gursel1 1 Middle East Technical University, Department of Biological Sciences, Türkiye 2 Bilkent University, Molecular Biology and Genetics, Türkiye 3´,5´-Cyclic diguanylic acid (c-di-GMP) is a bacterial derived small cyclic dinucleotide that functions as the universal bacterial secondary messenger[1]. To date, studies concerning its immunostimulatory effects revealed that cytosolic sensing of c-di-GMP by the innate immune receptor STING[2], induces a robust type-I interferon production in antigen presenting cells[3], leading to their maturation[4]. However, the chemical structure and the anionic nature of c-di-GMP limit its efficient entry through cellular membranes, requiring its transfection to cytosol. Here, we present a simple molecular complexation strategy that improves the intracellular delivery and boosts the immunostimulatory activity of c-di-GMP. Moreover, we also show that bacteria derived membrane vesicles (MV) can be utilized as vesicular carriers of this cyclic dinucleotide. Vaccination of mice using model antigen OVA adjuvanted with c-di-GMP/nonaarginine peptide complexes or c-di-GMP encapsulated in bacterial MVs, induced significantly higher levels of antigen-specific total IgG when compared to OVA or OVA+free c-di-GMP immunized groups. In contrast to OVA immunized mice, OVA+c-di-GMP/nonaarginine and OVA+c-di-GMP/bacterial MV adjuvanted groups showed complete protection from EG.7 tumor challenge. Consistent with the ability of these formulations to induce anti-tumorimmunity, ex-vivo re-stimulation of spleen cells harvested from immunized mice with the SIINFEKL peptide resulted in 8 to 10 fold increase in IFN-γ production. These findings suggest that c-di-GMP/nonarginine complexes or c-di-GMP/bacterial MVs are effective vaccine adjuvants and can generate tumor-specific CD8 T cell responses.