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

Abstract

There is an urgent need to improve protective responses to influenza vaccination in the elderly population, which is at especially high risk for adverse outcomes from influenza infection. Currently available inactivated vaccines provide limited protection, even when a 4-fold higher dose of the vaccine is administered. Adjuvants are often added to vaccines to boost protective efficacy. Here we describe a novel combination of an activator of the STING pathway, 2 ′ ,3 ′ -cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) with a saponin adjuvant, that we found to be highly effective in boosting protective immunity from vaccination in an aged mouse model. Using this combination with a subunit influenza vaccine, we observed that survival of vaccinated 20 month-old mice after lethal challenge increased from 0 to 20% with unadjuvanted vaccine to 80-100%, depending on the vaccination route. Compared to unadjuvanted vaccine, the levels of vaccine-specific IgG and IgG2a increased by almost two orders of magnitude as early as 2 weeks after a single immunization with the adjuvanted formulation. By analyzing phosphorylation of interferon regulatory factor 3 (IRF3) in cell culture, we provide evidence that the saponin component increases access of exogenous cGAMP to the intracellular STING pathway. Our findings suggest that combining a STING activator with a saponin-based adjuvant increases the effectiveness of influenza vaccine in aged hosts, without having to increase dose or perform additional vaccinations. This study reports a novel adjuvant combination that (a) is more effective than current methods of boosting vaccine efficacy, (b) can be used to enhance efficacy of licensed influenza vaccines, and (c) results in effective protection using a single vaccine dose.

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

“…In comparison, 75% of aged mice immunized with Quil-A, a saponin adjuvant, with HA antigen immunization (i.d.) survived from influenza infection (33). Our observations here are in line with this latest result.…”

“…They immunized mice [subcutaneously (s.c.)] with 50 µg OVA antigen and 20 µg CDNs (32), a rather high dose of CDNs. In late December 2019, Vassilieva et al (33) showed that 2 ′ 3 ′ -cGAMP (5 (33). In comparison, 75% of aged mice immunized with Quil-A, a saponin adjuvant, with HA antigen immunization (i.d.)…”

“…They immunized mice [subcutaneously (s.c.)] with 50 μg OVA antigen and 20 μg CDNs ( 32 ), a rather high dose of CDNs. In late December 2019, Vassilieva et al ( 33 ) showed that 2′3′-cGAMP (5 μg) adjuvanted with 1 μg of hemagglutinin (HA) [intradermally (i.d.)] did not induce antibodies or protective immunity in the 19-month-old female BALB/c mice.…”

“…And 100% aged mice immunized (i.d.) with 2′3′-cGAMP/HA died subsequently from influenza infection ( 33 ). In comparison, 75% of aged mice immunized with Quil-A, a saponin adjuvant, with HA antigen immunization (i.d.)…”

The Age of Cyclic Dinucleotide Vaccine Adjuvants

“…In late December 2019, Compans and R et al showed that cGAMP (5 µg) adjuvanted with 1 μg of hemagglutinin (HA) ( i.d. ) did not induce antibodies or protective immunity in the 19-month-old female BALB/c mice [ 94 ]. One hundred percent aged mice immunized ( i.d. )…”