Immunogenic PEGylated liposomes containing 1 mol% of the Toll-like receptor 4 (TLR4) agonist monophosphoryl lipid A (MPL), which is effective as an immune-stimulating adjuvant. This product is particularly useful in preclinical applications including vaccination, immunotherapy, or other areas of immunology research, especially in situations where a immunologically-active agent is meant to be administered for the purpose of stimulating an immune response. The liposome vehicle is very similar to that of the well-characterized Doxil® formulation in terms of lipid composition, which is desirable for translational purposes.