C6mPhE-383 is a top-performing ionizable lipid featuring an aromatic ring and a bioreducible disulfide bond. Formulated into lipid nanoparticles, it preferentially delivers mRNA to lymphoid tissues (lymph nodes/spleen) while minimizing off-target liver accumulation after intramuscular injection. In a SARS-CoV-2 vaccine study, it elicited strong antibody responses, promoted protective effector memory T cells, and exhibited enhanced safety by significantly reducing systemic inflammatory cytokines compared to the standard SM-102 LNP.