Notes: PL1 is a multi-tail ionizable cationic phospholipid that has been used in combination with other lipids in the formation of lipid nanoparticles (LNPs) for the delivery of mRNA.{68669} LNPs containing PL1 and encapsulating mRNA encoding the co-stimulatory receptor CD137 or OX40 increase T cell antitumor immunity in various mouse xenograft models.