The Pam3Cys building block with an attached PEG chain is a watersoluble adjuvant and PEG lipid at the same type. It features 3 palmitoyl lipid tails with a cystein core. The hydroxy group on one side of this PEG crosslinker is able to undergo esterification reactions with acids for reversible pegylation. It also enables further derivatization or replacement with other reactive functional groups.