Adjuvants

Liposome is an excellent vaccine adjuvant, which has the advantages of no immune side effects, less toxic side effects, and non-toxic decomposition in the body. It consists of a hydrophilic part and a hydrophobic part. Antigen molecules can be combined with the hydrophilic part, and the hydrophobic part gathers together on the outside to form a structure similar to a bilayer, which can quickly deliver the antigen to immune cells and activate immune cells in the body. immune system.

Fig. 1. Liposome-based vaccine delivery.

What is Adjuvant?

An adjuvant is a substance that is injected into the animal body prior to or simultaneously with the antigen, and can specifically change or enhance the specific immune response to the antigen and play an auxiliary role. It is generally believed that the role of adjuvants on vaccines is mainly reflected in two aspects: increasing the stability of the vaccine, thereby prolonging the action time of the vaccine; activating the immune system of the body and increasing the action intensity of the vaccine. At present, adjuvants are mainly divided into mineral salt adjuvant, oil emulsion adjuvant, liposome adjuvant, nano adjuvant, cytokine adjuvant and so on.

Liposome Adjuvant

Liposomes are non-immunogenic, non-toxic and biodegradable phospholipids in natural products that can encapsulate antigens. They can be used as antigen delivery adjuvants and as a tool for delivering vaccines. A key advantage of liposomes as a vaccine delivery system is their versatility and plasticity. Taking advantage of their chemical properties, water-soluble antigens (proteins, peptides, nucleic acids, carbohydrates, haptens) are embedded in the aqueous interior space of liposomes, while lipophilic compounds (lipopeptides, antigens, adjuvants, linker molecules) are embedded in the lipid bilayer, while antigens or other adjuvants can be attached to the liposome surface by adsorption or stable chemical linkage. DNA vaccines, for example, are encapsulated in liposomes to more efficiently cross cell membranes for intracellular expression, where the liposomes protect and slow release in the process. In addition, liposomes can be modified with immunostimulatory and targeting molecules. As a multifunctional vaccine adjuvant delivery system involved in the immune process, they can target immune cells and even organelles, produce lysosome escape, and promote the cross-expression of antibodies, thus greatly improving the immune effect of vaccines.

Factors Affecting Liposomal Vaccines

• Effect of particle size: The size of liposomes affects the rate at which they are cleared from the injection site and thus the kinetics of their accumulation in lymph nodes. When the size should be small enough, liposomes are able to migrate through interstitial tissue channels.
• Influence of liposome composition: The lipid composition of the bilayer determines the phase state of the liposome membrane, which in turn significantly affects the fusion process with the plasma membrane and the APC organelle membrane, thereby affecting the presentation mode of the delivered antigen .
• Action of immunostimulatory molecules (PRR ligands): Using specific ligands that activate certain receptors on APCs, it is possible to enhance the adjuvant properties of liposomes or to target one or another type of immune response. A variety of molecular classes can serve as specific ligands for PRRs: DNA, RNA, lipids, carbohydrates, proteins, peptides, and low molecular weight substances.

Monophosphoryl Lipid A

Monophosphoryl lipid A (MPLA) is a lipopolysaccharide (LPS) derivative found in the outer membrane of Gram-negative bacteria. It is a potent immunostimulant and has been extensively studied for its use as a vaccine adjuvant. As a vaccine adjuvant, MPLA enhances the immune response to antigens by activating the innate immune system. It acts as a Toll-like receptor 4 (TLR4) agonist, triggers the release of pro-inflammatory cytokines, and stimulates the maturation and activation of antigen-presenting cells (APCs), such as dendritic cells. MPLA is currently included in a variety of licensed vaccines, including hepatitis B, human papillomavirus (HPV) and influenza. Its use in vaccine adjuvants remains an active area of research, with ongoing research exploring its potential in the development of vaccines against various infectious diseases and cancers.

BOC Sciences, a top provider of lipid reagents, provides a variety of liposomal adjuvants with varying compositions, sizes, and functions. These adjuvants can be modified to meet particular needs, including antigen encapsulation, surface modification, and improved stability. Our staff of skilled scientists is knowledgeable in liposome technology and can offer professional guidance and support in choosing the best adjuvant for a given application.