Nasal Immunization With Small Molecule Mast Cell Activators Enhance Immunity to Co-Administered Subunit Immunogens

Abstract

Mast cell activators are a novel class of mucosal vaccine adjuvants. The polymeric compound, Compound 48/80 (C48/80), and cationic peptide, Mastoparan 7 (M7) are mast cell activators that provide adjuvant activity when administered by the nasal route. However, small molecule mast cell activators may be a more cost-efficient adjuvant alternative that is easily synthesized with high purity compared to M7 or C48/80. To identify novel mast cell activating compounds that could be evaluated for mucosal vaccine adjuvant activity, we employed high-throughput screening to assess over 55,000 small molecules for mast cell degranulation activity. Fifteen mast cell activating compounds were down-selected to five compounds based on in vitro immune activation activities including cytokine production and cellular cytotoxicity, synthesis feasibility, and selection for functional diversity. These small molecule mast cell activators were evaluated for in vivo adjuvant activity and induction of protective immunity against West Nile Virus infection in BALB/c mice when combined with West Nile Virus envelope domain III (EDIII) protein in a nasal vaccine. We found that three of the five mast cell activators, ST101036, ST048871, and R529877, evoked high levels of EDIII-specific antibody and conferred comparable levels of protection against WNV challenge. The level of protection provided by these small molecule mast cell activators was comparable to the protection evoked by M7 (67%) but markedly higher than the levels seen with mice immunized with EDIII alone (no adjuvant 33%). Thus, novel small molecule mast cell activators identified by high throughput screening are as efficacious as previously described mast cell activators when used as nasal vaccine adjuvants and represent next-generation mast cell activators for evaluation in mucosal vaccine studies.

Mucosal vaccination for SARS-CoV-2 elicits superior systemic T central memory function and cross-neutralizing antibodies against variants of concern

“…Our results here are unique in that we are able to directly compare the responses induced by the same dose of antigen for two routes of immunization since M7 adjuvant is effective as an adjuvant both when injected in the skin and also when administered at mucosal surfaces. However, the limitations of S.C. vaccination were not the result of the adjuvant alone, as M7 has been shown to perform well as an adjuvant when injected S.C. 34,36 , and these differences were also consistently observed when compared to the human-approved adjuvant, Alum. Even so, it is also possible that some of the vaccine induced effects observed here are adjuvant specific, since the adjuvant’s mechanism of mast cell activation (likely with some other beneficial effects on other myeloid cells 70 ) is unique compared to other strategies, and since mast cell phenotypes in these tissues are different 71 .…”

“…Its analogue, mastoparan-7 (M7) has greater cell-activating activity and appears to work in vivo primarily through inducing mast cell degranulation responses through the MrgX2 receptor 35 . M7 is effective in enhancing the titer of antigen-specific antibodies in animal models when delivered in combination with vaccine antigens, both through S.C. injection as well as application to the nasal mucosae 36 . In a haptenated cocaine vaccination strategy, M7 augmented antibody responses that prevented the psychoactive effects of cocaine.…”

Development of Nasal Vaccines and the Associated Challenges

“…Activated mast cells contribute to stimulating inflammatory mediators and releasing immune cells. The mast cell activators named polymeric compound 48/80 (C48/80) and the cationic peptide mastoparan 7 (M7) have been used as adjuvants in nasal mucosal immunization [ 143 ], for example, pneumonia vaccine in combination with C48/80 could combat lethal pneumococcal infection [ 144 ]. Certain small molecule mast cell activators have also exhibited certain mucosal adjuvant effects and may be novel mucosal adjuvants.…”

Mucosal Vaccination: A Promising Alternative Against Flaviviruses

“…Meanwhile, the positive adjuvanticity control was 100%, and EDIII alone showed 33%. The authors used a mucosal subunit vaccine from WNV to demonstrate the induction of a specific and protective immune response when this immunogen was adjuvanted to MCAC ( Johnson-Weaver et al., 2021 ).…”