Conjugate vaccine

History

The idea of a conjugate vaccine first appeared in experiments involving rabbits in 1927, when the immune response to the Streptococcus pneumoniae type 3 polysaccharide antigen was increased by combining the polysaccharide antigen with a protein carrier. The first conjugate vaccine used in humans became available in 1987. Soon after the vaccine was made available the rates of Hib infection dropped, with a decrease of 90.7% between 1987 and 1991. Infection rates diminished even more once the vaccine was made available for infants.

Technique

Vaccines evoke an immune response to an antigen, and the immune system reacts by producing T cells and antibodies. By conjugating the polysaccharide to a protein carrier, a T cell response can be induced. Normally, polysaccharides by themselves cannot be loaded onto the major histocompatibility complex (MHC) of antigen presenting cells (APC) because MHC can only bind peptides. In the case of a conjugate vaccine, the carrier peptide linked to the polysaccharide target antigen is able to be presented on the MHC molecule and the T cell can be activated. This improves the vaccine as T cells stimulate a more vigorous immune response and also promote a more rapid and long-lasting immunologic memory. The conjugation of polysaccharide target antigen to the carrier protein also increases efficiency of the vaccine, as a non conjugated vaccine against the polysaccharide antigen is not effective in young children.

Approved conjugate vaccines

The most commonly used conjugate vaccine is the Hib conjugate vaccine. Other pathogens that are combined in a conjugate vaccine to increase an immune response are Streptococcus pneumoniae (see pneumococcal conjugate vaccine) and Neisseria meningitidis (see meningococcal vaccine), both of which are conjugated to protein carriers like those used in the Hib conjugate vaccine. Both Streptococcus pneumoniae and Neisseria meningitidis are similar to Hib in that infection can lead to meningitis.

In 2018, World Health Organization recommended the use of the typhoid conjugate vaccine which may be more effective and prevents typhoid fever in many children under the age of five years.

In 2021, Soberana 02, a conjugate COVID-19 vaccine developed in Cuba, was given emergency use authorisation in Cuba and Iran.

Select list of other conjugate vaccines

• Various immunocontraception vaccines for animal use, including GonaCon (GnRH linked to keyhole limpet hemocyanin)
• NicVAX, which aims to vaccinate against nicotine using a chemically modified hapten version linked to exotoxin A
• TA-CD, cocaine linked to inactivated cholera toxin
• TA-NIC, nicotine linked to inactivated cholera toxin

References

References

1. (2018-10-18). "Understanding How Vaccines Work {{!}} CDC".
2. (2011). "Vaccine design : innovative approaches and novel strategies". Caister Academic.
3. "Immunization: You Call the Shots".
4. (1929). "Chemo-immunological studies on conjugated carbohydrate-proteins: II. Immunological specificity of synthetic sugar-protein antigens". Journal of Experimental Medicine.
5. Goldblatt, D.. (January 2000). "Conjugate vaccines". Clinical and Experimental Immunology.
6. (March 1999). "Conjugated Polysaccharide Vaccines". Infectious Disease Clinics of North America.
7. (2002). "Polysaccharide Vaccines for Prevention of Encapsulated Bacterial Infections: Part 1". Infect. Med..
8. (January 2022). "An overview of progress from empirical to rational design in modern vaccine development, with an emphasis on computational tools and immunoinformatics approaches". Comput Biol Med.
9. (4 April 2018). "Typhoid vaccines: WHO position paper – March 2018". Weekly Epidemiological Record.
10. (26 April 2001). "The efficacy of a Salmonella typhi Vi conjugate vaccine in two-to-five-year-old children.". The New England Journal of Medicine.
11. (21 August 2021). "Cuba grants emergency approval to second homegrown COVID-19 vaccine". GMA News.
12. (1 July 2021). "Autorizo de emergencia SOBERANA 02 en Irán". Instituto Finlay de Vacunas.