Sublingual targeting of STING with 3′3′-cGAMP promotes systemic and mucosal immunity against anthrax toxins

Abstract

Anthrax is caused by Bacillus anthracis, a zoonotic bacterial pathogen affecting humans and livestock worldwide. The current human anthrax vaccine, anthrax vaccine adsorbed (AVA), is an injected vaccine with a cumbersome administration schedule and fails to promote mucosal immunity. Bacterial enterotoxins, which stimulate production of the cyclic nucleotide cAMP are effective experimental mucosal vaccine adjuvants, but their inherent toxicity has precluded their use in humans. We investigated whether cyclic dinucleotides that target Stimulator of Interferon Gamma Genes (STING) in mammalian cells could represent an alternative to bacterial enterotoxins as adjuvant for sublingual immunization and promotion of mucosal immunity and secretory IgA responses in addition to systemic immunity. We found that sublingual immunization of mice with Bacillus anthracis protective antigen (PA) and the STING ligand 3′3′-cGAMP promotes PA-specific serum IgG Ab responses of the same magnitude as those induced after immunization with PA and the experimental adjuvants cholera toxin (CT). Interestingly, this STING ligand also promoted serum anti-PA IgA and IgA-producing cells in the bone marrow. Furthermore, the saliva of mice immunized with the STING ligand exhibited similar levels of PA-specific IgA Abs as groups immunized with CT as adjuvant. The adjuvant activity of 3′3′-cGAMP was associated with mixed Th1, Th2, and Th17 responses. This STING ligand also induced rapid IFN-β and IL-10 responses in sublingual tissues and cervical lymph nodes, and TGF-β responses in the cervical lymph nodes, which could contribute to promoting IgA responses after sublingual immunization.

The STING ligand cGAMP potentiates the efficacy of vaccine-induced CD8+ T cells

“…Viral replication was also controlled more effectively in mice vaccinated with NP-p24 plus 2′3′-cGAMP relative to mice vaccinated with NP-p24 alone ( Figure 6D). Of note, mucosal and systemic HIV-1 Gag p24-specific IgA and IgG titers were very high in mice vaccinated with NP-p24 plus 2′3′-cGAMP, consistent with recent studies (17,18), but remained undetectable in mice vaccinated with NP-p24 alone (Supplemental Figure 5).…”

Inducing Mucosal IgA: A Challenge for Vaccine Adjuvants and Delivery Systems

“…For example, STING ligands of bacterial origin, including 3′3′-cGAMP, c-di-AMP, and c-di-GMP, have been shown to effectively elicit mucosal and systemic immune responses following intranasal administration (64–66). More recently, targeting STING with 3′3′-cGAMP was found to be an effective strategy for enhancing the magnitude of immune responses and promoting IgA by sublingual immunization (67). It is worth indicating that induction of Th17 responses is a common feature of all the adjuvants mentioned above, which enhance IgA responses by increasing intracellular levels of the cyclic nucleotide cAMP or directly releasing select cyclic nucleotides (i.e., STING ligands) in the cytosol of immune cells.…”

New MoDC-Targeting TNF Fusion Proteins Enhance Cyclic Di-GMP Vaccine Adjuvanticity in Middle-Aged and Aged Mice

“…TNF-Fc fusion protein enhanced the duration (120 days post-immunization) and the magnitude of CDG/PspA antibody production in 1-year-old mice. CDN-adjuvanted protein subunit vaccines protected adult mice from respiratory infections such as influenza (38,39), bacterial pneumonia (40), Mycobacterium tuberculosis (41), and anthrax (42). CDNs were also therapeutic for cancer in adult mice (13,14).…”