Acetalated Dextran Microparticles for Codelivery of STING and TLR7/8 Agonists

Abstract

Vaccines are the most effective tool for preventing infectious diseases; however, subunit vaccines, considered the safest type, suffer from poor immunogenicity and require adjuvants to create a strong and sustained immune response. As adjuvants, pathogen-associated molecular patterns (PAMPs) offer potent immunostimulatory properties and defined mechanisms of action through their cognate pattern recognition receptors (PRRs). Their activity can be further enhanced through combining two or more PAMPs, particularly those that activate multiple immune signaling pathways. However, the cytosolic localization of many PRRs requires intracellular delivery of PAMPs for optimal biological activity, which is particularly true of the stimulator of interferon genes (STING) PRR. Using acetalated dextran (Ace-DEX) microparticles (MPs) encapsulating STING agonist 3′3′-cyclic GMP-AMP (cGAMP) combined with soluble PAMPS, we screened the effect of codelivery of adjuvants using primary mouse bone marrow derived dendritic cells (BMDCs). We identified that codelivery of cGAMP MPs and soluble Toll-like receptor 7/8 (TLR7/8) agonist resiquimod (R848) elicited the broadest cytokine response. cGAMP and R848 were then coencapsulated within Ace-DEX MPs via electrospray. Using the model antigen ovalbumin, we observed that Ace-DEX MPs coencapsulating cGAMP and R848 (cGAMP/R848 Ace-DEX MPs) induced antigen-specific cellular immunity, and a balanced Th1/Th2 humoral response that was greater than cGAMP Ace-DEX MPs alone and PAMPs delivered in separate MPs. These data indicate that polymeric Ace-DEX MPs loaded with STING and TLR7/8 agonists represent a potent cellular and humoral vaccine adjuvant.

Combination of STING Pathway Agonist With Saponin Is an Effective Adjuvant in Immunosenescent Mice

“…Our data also demonstrate that the cGAMP/Quil-A combination is effective as an adjuvant when co-delivered with the vaccine by either intradermal or systemic routes of administration, which is consistent with recently reported results for 3 ′ 3-cGAMP-loaded microparticles (56). Other adjuvant combinations and delivery vehicles containing STING agonists have been previously reported including use of aluminum hydroxide (57) and encapsulation in lipid nanoparticles (58) or microparticles (59,60). Unlike these formulations, the cGAMP/Quil-A combination that we used is easily added to existing vaccines.…”

Carbohydrate Conjugates in Vaccine Developments

“…For example, cGAMP ES Ac-Dex successfully induced high levels of IFN-β, IL-6, and TNF. With the co-encapsulation of resiquimod (R848) in the same particle, the cGAMP/R848 ES Ac-Dex elicited two more important cytokines for adaptive immune activation, IL-1β, and IL-12p70 (Collier et al, 2018). Co-administration of separate cGAMP ES Ac-Dex and R848 ES Ac-Dex particles was not as efficient as co-encapsulation of the two adjuvants within the same particle based on in vitro cytokine release study.…”

“…An attractive strategy for future vaccine design can be the combination of different adjuvants that activates the immune system through different receptors. Adjuvants are playing crucial roles in vaccine design, and there have been examples indicating that combining adjuvants with different immune activating mechanisms can trigger additive effects and enhance the vaccine efficacy (Collier et al, 2018;Paßlick et al, 2018). However, cautions need to be taken in combining other adjuvants with the "self-adjuvating" carbohydrates.…”

Agonists and inhibitors of the STING pathway: Potential agents for immunotherapy

“…The 2′,3′‐cGAMP‐loaded PC7A NPs efficiently inhibited the replication of HIV RNA and generated a long‐lasting antiretroviral response in human peripheral blood mononuclear cells, with free cGAMP as a control. Other polymers, such as dextran microparticles and poly (beta‐amino ester) (PBAE) NPs, were also employed to deliver CDNs and achieved prominent effects.…”