Adjuvants

Adjuvants are components that enhance the immunogenicity of vaccines when administered with vaccine antigens. Adjuvants can range from synthetic small-molecule compounds to complex natural extracts and particulate materials. Classical human vaccine adjuvants include aluminum adjuvants, MF59, AS01, AS03, AS04, and CpG ODN 1018. These adjuvants have been widely approved for use in various vaccines and are known to increase antibody titers and enhance cellular immune responses. Adjuvants can be classified into immunostimulants and delivery systems based on their mechanisms of action. Immunostimulants work through mechanisms such as targeting Toll-like receptors (TLRs), cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING), and C-type lectin receptors (CLRs). Delivery systems work through mechanisms such as prolonging the bioavailability of antigens, targeting APCs, lymph node trafficking, and antigen cross-presentation. These mechanisms provide a variety of options for the development of vaccines.

Aluminum adjuvants are the most commonly used adjuvants, inducing antibody responses and CD4+ T helper cell responses in humans. They are generally present in vaccines in the form of aluminum hydroxide or amorphous aluminum hydroxyphosphate. These compounds form clustered nanoparticles that can stabilize vaccine antigens.

AS04 is an aluminum salt- and TLR4 agonist-based adjuvant system, consisting of aluminum hydroxide and 3-O-desacyl-4'-monophosphoryl lipid A (MPL). AS04 is a component in two vaccines: the HPV vaccine (Cervarix) and the hepatitis B virus vaccine (Fendrix).

AS01 is a liposome-based adjuvant containing two immunostimulants, MPL and the saponin QS-21. AS01 is a component of Shingrix (recombinant zoster vaccine).

MF59 is an oil-in-water emulsion composed of small droplets of squalene surrounded by a monolayer of nonionic detergents (Span 85 and Tween 80). AS03 is also an oil-in-water emulsion, composed of α-tocopherol, squalene, and polysorbate 80. These two adjuvants have been used in combination with influenza vaccines to boost their immunogenicity.

CpG 1018 is a recently developed adjuvant used in the Heplisav-B vaccine. It is composed of cytosine phosphoguanine (CpG) motifs, a synthetic form of DNA that mimics bacterial and viral genetic material.

Fig. 1 Timeline of major events in the research history of vaccine adjuvants (Zhao, T., et al. 2023)

CD Bioparticles offers a large selection of research-grade adjuvant products for adjuvant formulation, screening, and optimization.

Adjuvants Key Benefits:

• Enhanced immunogenicity
• Improved vaccine efficacy
• Prolonged immunity
• Facilitated vaccine development
• Cost-effectiveness