Immune system stimulation via adjuvant (AS03)

AS03 is an adjuvant system used in vaccines to enhance the immune response. It is an oil-in-water emulsion composed of α-tocopherol (vitamin E), squalene, and polysorbate 80. AS03 stimulates both the innate and adaptive branches of the immune system. It activates local innate immunity at the injection site, increasing antigen uptake and presentation by antigen-presenting cells in draining lymph nodes. The presence of α-tocopherol modulates this process, enhancing immunogenicity. AS03 induces epigenetic reprogramming in innate immune cells, leading to increased expression of antiviral genes. This "turbocharges" the innate immune system for heightened resistance against a broad range of viruses beyond just those targeted by the vaccine. The adjuvant promotes robust memory B cell responses with increased neutralization breadth due to progressive maturation (accumulation of somatic hypermutations) over time. It has been widely used in influenza vaccines, including those for H1N1 and H5N1, and more recently in some COVID-19 vaccine candidates. Enables dose-sparing: lower amounts of viral antigen can be used per dose without compromising efficacy—critical during pandemics when rapid scale-up is needed. While it increases reactogenicity compared to non-adjuvanted formulations (e.g., more frequent mild-to-moderate local reactions), its safety profile remains acceptable for use during public health emergencies or when enhanced immunogenicity is required.

Activates innate immunity locally; enhances adaptive response via improved APC function