Question

Compare and contrast the physical characteristics and immunisation properties of three different types of vaccine adjuvants.

Answer 1

An adjuvant is a substance that is formulated as part of a vaccine to enhance its ability to induce protection against infection. It helps to create a stronger immune response in the recepients of that vaccine.

Some common compounds being used as adjuvants are placed under three categories:

* Pathogen components adjuvant

* Particulate adjuvants, and

* Combination adjuvants

Pathogen components-

These adjuvants target various receptors inside or on the surface of innate immune cells which in turn influences adaptive immune responses, which provide long lasting protection against the pathogen that the vaccine targets.

Examoples are- Monophosphoryl lipid A, which is an immune stimulating lipid.

Poly(I:C), which is a synthetic double-stranded RNA. It mimics a molecular pattern of a viral infection and produces immune response.

CpG DNA Adjuvants are short segments of DNA that include sequence motifs commonly found in bacterial DNA. It is present in Hepatitis B vaccine.

Emulsions of oil in water, called MF59 is a commonly used adjuvant in influenza vaccine. It works by recruiting immune cells from the blood to the vaccine injection site.

Particulate adjuvants-

These are very small particles that stimulate the immune system and also help in delivery of antigen to the immune cells.

Examples are- Alum, which is the most commonly used adjuvant and is used in a large number of vaccines. Alum consists of aluminium salts which are not soluble in water.

Virosomes, which are particles that resemble viruses but are non-infectious. These virosomes have antigens and other viral proteins on their surface but cannot cause infection because they do not have a viral genetic material.

Cytokines are used as adjuvants because they serve as chemical messengers of the immune system.

Combination adjuvants -

These adjuvants are able to elicit multiple protective immune responses. In fact, as the name suggests, it is a combination of such adjuvants which produce a more potent response when used together.

An example is ASO4 which is a combination of Monophosphryl Lipid A and alum. It is used in the human papilloma virus vaccine, Cervarix.