DNA vaccines 27/8/02. By Richard Twyman Pathogen genes can be introduced into the body and expressed to make pathogen-specific proteins that stimulate a protective immune response.

The prevention of infectious diseases by vaccination has a long and successful history. Edward Jenner carried out the first vaccination in 1796 by injecting a young boy with cowpox. This conferred protection against a subsequent infection with the deadly smallpox virus. Through concerted worldwide vaccination campaigns, smallpox has now been eliminated.

Most of the vaccines in use today are based on similar principles to Jenner's original vaccine - they are live but attenuated (disabled) bacteria or viruses which cause the body to mount a protective immune response against the target pathogen. Examples include the measles, mumps, rubella and tuberculosis vaccines. Other current vaccines are 'killed vaccines' - the pathogen itself is killed so it is no longer infectious but it can still stimulate the immune system.

Unfortunately, vaccines against all common diseases cannot be made using the above methods and other approaches are needed. One successful strategy is the use of subunit vaccines, where the gene for one specific protein on the pathogen is expressed, and the protein used as the vaccine. The current hepatitis B and influenza vaccines are protein subunits.

Another approach is the use of DNA vaccines. Here, the gene for a pathogen protein is introduced into human cells and is then expressed to produce the protein inside the body. There are many advantages to the DNA vaccination method. For example, it is much cheaper to produce and distribute large amounts of DNA than it is to produce and distribute large amounts of protein. Also, the same strategy can be used to tackle virtually any pathogen, so multiple vaccinations are possible. Technical hurdles that need to be overcome include finding efficient ways of getting the DNA into human cells, making sure the gene is expressed once it is inside the cell, and making sure the DNA does not integrate into the genome and disrupt our own genes. There are many DNA vaccines in clinical and pre-clinical trials, including vaccines for HIV, herpes, hepatitis and influenza.