Licensed liposomal vaccines and adjuvants in the antigen delivery system

Liposomes (LSs) are promising nanoparticles with unique properties such as controlled nanosize, large surface area, increased reactivity, and ability to undergo modification. Worldwide, licensed liposomal forms of antibiotics, hormones, antioxidants, cytostatics, ophthalmic drugs, etc., are available on the pharmaceutical market. This review focuses on the adjuvant properties of LSs in the production of vaccines (VACs). LS-VACs have the following advantages: antigens with low immunogenicity can become highly immunogenic; LSs can include both hydrophilic and hydrophobic antigens; LSs allow to achieve a prolonged specific action of antibodies; and LSs reduce the toxicity and pyrogenicity of encapsulated antigens and adjuvants. The immune response is influenced by the composition of the liposomal membrane, physicochemical characteristics of lipids, antigen localization in LSs, interaction of LSs with complement, and a number of proteins, which leads to opsonization. The major requirements for adjuvants are their ability to enhance the immune response, biodegradability, and elimination from the organism, and LSs fully meet these requirements. The effectiveness and safety of LSs as carriers in the antigen delivery system have been proven by the long-term clinical use of licensed vaccines against hepatitis A, influenza, herpes zoster, malaria, and COVID-19.