– AA3-DLin is an ionizable cationic amino lipid (pKa = 5.8) that has been used in combination with other lipids in the formation of lipid nanoparticles (LNPs) for the delivery of mRNA.LNPs containing AA3-DLin and encapsulating mRNA for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein induce immunogenicity in mice.