Adjuvant lipidoid-substituted lipid nanoparticles augment the immunogenicity of SARS-CoV-2 mRNA vaccines

Lipid nanoparticle (LNP)-formulated messenger RNA (mRNA) vaccineare a promising platform to prevent infectious diseases as demonstrated by the recent success of SARS-CoV-2 mRNA vaccines. To avoid immune recognition and uncontrolled inflammation, nucleoside-modified mRNA is used. However, such modification largely abrogates the innate immune responses that are critical to orchestrating robust adaptive immunity. Here we develop an LNP component-an adjuvant lipidoid-that can enhance the adjuvanticity of mRNA-LNP vaccines. Our results show that partial substitution of ionizable lipidoid with adjuvant lipidoid not only enhanced mRNA delivery, but also endowed LNPs with Toll-like receptor 7/8-agonistic activity, which significantly increased the innate immunity of the SARS-CoV-2 mRNA-LNP vaccine with good tolerability in mice. Our optimized vaccine elicits potent neutralizing antibodies against multiple SARS-CoV-2 pseudovirus variants, strong Th1-biased cellular immunity, and robust B cell and long-lived plasma cell responses. Importantly, this adjuvant lipidoid substitution strategy works successfully in a clinically relevant mRNA-LNP vaccine, demonstrating its translational potential.