Vaccines

Vaccines are a product of biotechnology.

The process of vaccination relies on boosting the body’s immune response — its natural defence system.

Most vaccines contain one of the following:

  • low doses of dead pathogenic (disease-causing) microorganisms
  • inactivated toxins from pathogenic bacteria
  • weakened live pathogenic organisms that are unable to cause the severe form of the disease.

The body recognises a vaccine as a foreign substance. The cells of the immune system mount an immune response to destroy it, producing specific antibodies that recognise the foreign substance. The antibodies remain in the body, ready to fight future infections of the naturally-occurring form of the disease.

Read more about the immune system: http://health.howstuffworks.com/immune-system.htm

Producing a vaccine

Vaccines have revolutionised the fight against infectious diseases. They are used to control life-threatening illnesses such as measles, polio, tuberculosis, tetanus, rabies, smallpox, cholera, typhoid fever, diphtheria, pertussis (whooping cough), Japanese encephalitis and yellow fever.

The practice of vaccination began in England in 1796, when Edward Jenner vaccinated an eight-year-old boy against smallpox by using the closely related cow pox virus. Smallpox is an acute, contagious, and sometimes fatal disease causing fever and raised skin rashes. In 1980, after a worldwide vaccination program, smallpox was declared completely eradicated.

A global campaign to eradicate polio is currently underway. Polio is a highly infectious disease that mainly infects children, particularly in developing countries. The polio virus attacks the nervous system and can cause total paralysis in a matter of hours. Those who survive are faced with life-long health problems.

Read more about the polio eradication program: http://www.polioeradication.org/

These days, v accines are researched and developed in a very different way from earlier methods. Genetic modification techniques allows a gene coding for a protein of a disease-causing organism to be isolated and transferred into bacteria.

The GM bacteria then produce large quantities of the protein that can be purified and used as a vaccine. This approach has also been used with GM yeast, which produce hepatitis B vaccine. 

Vaccines in our food?

Imagine if you went to the doctor and instead of an injection, you were handed an apple to eat.

Researchers have been looking at ways to produce edible vaccines, making vaccination programs as easy as eating a piece of fruit or vegetable. They hoped that such foods could be grown and administered in developing countries, providing cheap sources of vaccines without needing costly refrigeration or needle injections.

However, developers decided not to pursue this research, to avoid any possibility of vaccine-laden food straying into shops or markets. If this occurred, it could be unwittingly eaten by consumers, with unpredictable results. Instead, developers are now focusing on making vaccines in edible parts of plants that are not sold as food.

While edible vaccine research has been largely directed at preventing human diseases, the same technology could be valuable for the production of vaccines to add to animal feed.

The first ‘prototype’ edible vaccines were produced in GM potatoes and tobacco leaves. The plants were genetically modified to produce a toxin from the bacterial Escherichia coli strain that causes severe intestinal disease, which can be fatal in developing countries. The GM potatoes and tobacco leaves were fed to laboratory mice. Their immune systems mounted a sufficient response to the toxin to protect their bodies from the bacterium in further experiments.

In similar experiments, the gene for a non-toxic part of the cholera toxin has been inserted in GM alfalfa plants. Mice fed with this alfalfa produced an immune response against the cholera toxin.

GM tomato and lettuce plants have also been produced that contain the gene encoding the hepatitis B surface protein. GM rice and lettuce for use as a measles vaccine, GM tomatoes for rabies and HIV vaccines, and GM tomato and potatoes for respiratory syncytial virus vaccine are also under development.

DNA vaccines

Instead of stimulating the body’s immune system using a dead or weakened form of the pathogen itself, DNA vaccines use the pathogen’s genes.

One or more genes from a pathogen  are copied and multiplied using a common laboratory technique called polymerase chain reaction (PCR). The copied genes are injected into muscle cells of the organism to be vaccinated.

A few muscle cells will take up the genes and  make their protein product. For viral pathogens, this will usually be a virus surface protein. The organism’s immune system recognises the gene product as foreign and remembers it, just as in conventional vaccination.

Some advantages of DNA vaccination are:

  • Purity: because DNA vaccines are made artificially, they  are much purer than if made directly from pathogens.
  • Specificity: the vaccine contains only one of the many genes necessary for pathogen reproduction. The small amount of DNA is enough for the recipient’s immune system to recognise as foreign, but not enough to cause illness.
  • Different genes can be mixed and injected at the same time, making it possible to simultaneously vaccinate against variants of a pathogen or several different pathogens.
  • Cost and ease of storage. Unlike conventional  protein-based vaccines, DNA vaccines are inexpensive to produce, don’t require refrigeration and can be stored for a long time.

DNA vaccination is still an experimental procedure, as very few trials have demonstrated an immune response strong enough to protect against disease. Current studies include avian influenza and West Nile virus DNA vaccines, and a DNA vaccination against multiple sclerosis.