Elucidating the Immunogenic Mechanisms of Merck's Lipid Nanoparticle (LNP) Adjuvants

Abstract Adjuvants are crucial components of subunit vaccines, as they help induce immune responses to poorly immunogenic antigens. Merck has developed a variety of lipid nanoparticles (LNPs) that contain different cationic lipids, a critical component that is mainly responsible for the reactogenicity induced by the LNP. LNP A that incorporates cationic lipid A results in high antigen expression, robust antigen-specific humoral and cellular responses, and some dose dependent reactogenicity when combined with subunit proteins. In contrast, LNP B, which incorporates cationic lipid B which has a shorter half-life than cationic lipid A, results in high antigen expression, slightly lower immunogenicity, and improved tolerability. Previous studies have shown that mouse TLR2 may be involved in the mechanism of action of LNP A. To determine the human innate signaling pathways triggered by LNP A or LNP B, we stimulated human TLR-expressing HEK-Blue cell lines (Invivogen) with the LNPs followed by measuring SEAP activity. We did not see any activation of the human TLRs despite stimulating with high amounts of LNP. Next, we evaluated whether these LNPs generated different cytokine/chemokine profiles, indicative of differential cellular recruitment in BALB/c mice in vivo. We found that LNP A stimulation results in significant upregulation of monocyte and neutrophil-specific cytokines in the serum and quadricep muscle injection site, while LNP B leads to a lower response. Furthermore, we plan to investigate the recruitment of cells at the injection site and draining LNs by flow cytometry and imaging. Together, these experiments will help mechanistically determine how these fundamentally different LNPs can activate innate immune responses. Supported by Merck & Co.