An ionizable cationic lipid has been used in the generation of lipid nanoparticles for the delivery of mRNA in vitro or in vivo LNPs containing C14-4 and encapsulating mRNA encoding CAR induce CAR expression in primary human T cells ex vivo to the same level as expression induced via electroporation but with reduced cytotoxicity and induce cytotoxicity in Nalm-6 ALL cells in vitro LNPs containing C14-4 and deoxycholic acid and encapsulating mRNA encoding luciferase accumulate in the uterus when intraperitoneally administered and in the lungs and small intestine when intravenously administered in mice