ALC-0159 is a polyethylene glycol (PEG) lipid conjugate used primarily in lipid nanoparticle (LNP) formulations for delivering nucleic acid-based therapeutics. It functions as a PEGylated lipid that helps stabilize the nanoparticle structure, prolong circulation time in the bloodstream, and reduce immune recognition. This compound is especially important in mRNA vaccine platforms, where it contributes to the efficient delivery of mRNA into cells by enhancing particle integrity and preventing premature degradation. Its inclusion in LNP systems improves overall transfection efficiency and plays a key role in the success of advanced vaccine and gene therapy technologies.