The efficacy of a 2,4-diaminoquinazoline compound as an intranasal vaccine adjuvant to protect against influenza A virus infection in vivo

Adjuvants are substances added to vaccines to enhance antigen-specific immune responses or to protect antigens from rapid elimination. As pattern recognition receptors, Toll-like receptors 7 (TLR7) and 8 (TLR8) activate the innate immune system by sensing endosomal single-stranded RNA of RNA viruses. Here, we investigated if a 2,4-diaminoquinazoline-based TLR7/8 agonist, (S)-3-((2-amino-8-fluoroquinazolin-4-yl)amino)hexan-1-ol (named compound 31), could be used as an adjuvant to enhance the serological and mucosal immunity of an inactivated influenza A virus vaccine. The compound induced the production of proinflammatory cytokines in macrophages. In a dose-response analysis, intranasal administration of 1 mu g compound 31 together with an inactivated vaccine (0.5 mu g) to mice not only enhanced virus-specific IgG and IgA production but also neutralized influenza A virus with statistical significance. Notably, in a virus-challenge model, the combination of the vaccine and compound 31 alleviated viral infection-mediated loss of body weight and increased survival rates by 40% compared with vaccine only-treated mice. We suggest that compound 31 is a promising lead compound for developing mucosal vaccine adjuvants to protect against respiratory RNA viruses such as influenza viruses and potentially coronaviruses.

Automated summary

This study investigated the use of a TLR7/8 agonist, compound 31, as an adjuvant to enhance the immune response to an inactivated influenza A virus vaccine. The results showed that compound 31 not only increased the production of virus-specific antibodies but also effectively neutralized the influenza A virus. In addition, the combination of compound 31 and the vaccine reduced viral infection-mediated weight loss and improved survival rates in a virus-challenge model. These findings suggest that compound 31 has potential as a mucosal vaccine adjuvant for respiratory RNA viruses.