By: Suzanne Canada, Ph.D.
Tanager Medical Writing

Vaccines have been used to help control diseases for more than 200 years and are the common practice for children and adults. Childhood vaccination has substantially reduced the morbidity and mortality from infectious diseases in much of the developed world, and influenza vaccinations have reduced the impact of seasonal influenza infections.¹ However, medical researchers are constantly looking for ways to improve the vaccines that are already used, and develop new ones.

Opportunities for improvement of vaccines abound. For example, although much attention is given to child vaccinations, a reservoir of infection could be eliminated through promotion of adult booster shots such as pertussis booster shots for expectant mothers and close family members, to help protect susceptible newborns. In addition, some diseases that have vaccines currently available still flourish in areas of the world where infrastructures for vaccination are poor and are too costly or cannot be delivered in their current forms.¹ Researchers are still trying to develop vaccines for other important diseases, such as HIV/AIDS, malaria and leishmaniasis. Vaccines are also being developed for bacterial pathogens, such as Vibrio cholerae O1 and enterotoxigenic Escherichia coli (ETEC) that are responsible for a high proportion of diarrheal disease and death in adults and children in many countries in Africa and Asia.²

By modifying the factors included in the vaccine, researchers balance the effectiveness of the immune response with the side effects. Previously, whole cell vaccines containing whole organisms that had been chemically inactivated were the norm, but the side effects of fever and discomfort following injections were much more common. Many of the vaccines used today, including those for measles and some influenza vaccines, use live, attenuated viruses. Others use killed forms of viruses, pieces of bacteria (lipopolysaccharides), or inactivated forms of bacterial toxins, known as “toxoids.” Killed viruses, lipopolysaccharides and toxoids can evoke an immune response that protects against future infection.³ Acellular vaccines were introduced in the late 1990’s that contain either three or five key bacterial proteins and have been quite effective in protecting infants and children under four with a much lower rate of side effects.

List Labs offers several virulence factors which are used in vaccine testing.  For testing C. difficile vaccines; available reagents are C. difficile Toxin A (Product #152), C. difficile Toxin B (Product #155), C. difficile Toxoid A (Product #153), C. difficile Toxoid B (Product #154), and both subunits of the Binary Toxin (Products #157 and #158).  Numerous Bordetella pertussis virulence factors are available for use in testing including: Products #179, #180 or #181 Pertussis Toxin, Product #170 FHA, Product #186 Fimbriae, Product #187 Pertactin, Product #188 and #189 Adenylate Cyclase and Product #400 Highly Purified B. pertussis LPS.  Anthrax vaccine testing maybe carried out using Protective Antigen (Product #171) with Lethal Factor (Product #172) in a toxin neutralization assay.  Although these factors are not suitable for testing on humans, they are excellent research tools.

Inactive toxins are quite useful in making antibodies or in capturing antibodies from a vaccinated population on ELISA plates.  Three of our inactivated toxins, which carry mutations in the toxin active site, are B. pertussis Adenylate Cyclase Toxoid, Pertussis Toxin Mutant, Product #184 and CRM197, a non-toxic Mutant Diphtheria Toxin, Product #149.  Toxoids made by formaldehyde treatment of toxins include versions of C difficile Toxins (Products #153 and #154), Diphtheria Toxoid (Product #151), Staphylococcus aureus Enterotoxoid B (Product #123), Tetanus Toxoid (Product #191) and Toxoids of Botulinum Neurotoxins A and B (Product #133 and #139, respectively).

1. Hammond B., Sipics M., Youngdhal K., (2013). From the History of Vaccines, a project of the college of physician of Philadelphia. ISBN: 9780988623101
2. Svennerholm AM., (2011) From Cholera to Enterotoxigenic Escherichia coli (ETEC) vaccine development.  Indian J Med Res. 133(2): 188–194. PMID: 21415493
3. Leitner DR., Feichter S., Schild-Prüfert K., Rechberger GN., Reidl J., Schild S., (2013) Lipopolysaccharide modifications of a cholera vaccine candidate based on outer membrane vesicles reduce endotoxicity and reveal the major protective antigen. Infect Immun 81(7):2379-93. PMID: 23630951