L202 is an ionizable lipid designed for mRNA vaccines, featuring a pH-responsive N-methylpiperidine head and a unique branched-tail structure with ester linkages to enable biodegradability. With a pKa of ~6.04–6.29, it facilitates efficient endosomal escape while maintaining stability in physiological conditions. Formulated into lipid nanoparticles (LNPs) of ~103 nm (PDI 0.08), L202 achieves >97% mRNA encapsulation efficiency. Its optimized structure drives robust immunogenicity: in mice, a single 0.1–10 μg dose induced dose-dependent SARS-CoV-2 spike-specific IgG titers, outperforming MC3-based LNPs and protein-alum vaccines. L202-LNPs elicited balanced Th1/Th2 responses (IgG2a/IgG1 ratio) and potent germinal center B cell activation, critical for durable immunity. Lyophilization with 16% sucrose preserved mRNA integrity and immunogenicity after 1-month storage at 5°C or 25°C, addressing cold-chain limitations. In nonhuman primates, two 100-μg doses generated neutralizing antibody titers exceeding convalescent human sera, with broad efficacy against Alpha, Beta, Gamma, and Delta variants. Rapid tissue clearance (72 hours post-injection) and minimal hepatic accumulation, attributed to ester hydrolysis, enhanced safety profiles. Additionally, L202-LNPs functioned as intrinsic adjuvants, amplifying protein vaccine responses. Combined with its lyophilization compatibility, potent cross-variant immunity, and favorable pharmacokinetics, L202 represents a promising platform for next-generation mRNA vaccines.
