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DNA Vaccines

By: PetPlace Veterinarians

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Since the advent of the first vaccine in the late 1700s, researchers have continuously tried to improve vaccination and develop better ways to prevent viral infections. One of the latest advances is the development of a vaccine that involves the exciting world of genetic engineering.

Still being researched, these new vaccines are called DNA vaccines, naked-DNA vaccines, plasmid-DNA vaccines or DNA-mediated immunization. This vaccine uses DNA to provide a safer and potentially more effective vaccination. Hopefully, by the end of this decade, at least one DNA vaccine will be available, probably for the prevention of equine influenza.

Viruses

A virus is a packet of genetic material, often DNA, surrounded by a viral envelope or membrane. This virus is quite fragile when outside the body but is very damaging when allowed to thrive inside a body. Once it enters a body, it attaches to certain cells and inserts its DNA into the cell. This DNA takes over the function of the cell and begins to rapidly reproduce itself. In a short time, the cell becomes so full of viral particles that it bursts and releases more viruses throughout the body. Each of these then repeats the process until the body is overwhelmed with virus and illness develops.

As the body undergoes this attack by the virus, the immune system begins to realize there is an invader present. Since the immune system has been basically ambushed and has never seen this invader before, the immune system is not prepared, although it makes a valiant attempt to destroy the virus. In time, the immune system often destroys the virus and the body recovers from the illness. Unfortunately, there are some viruses that never leave the body and ultimately cause death.

In the case of viral infections that result in recovery, the immune system is now prepared and memory cells circulate through the body, waiting for that virus to try to invade again. If and when this occurs, the immune system is ready and the virus is destroyed before it is ever allowed to get a foothold.

Vaccines

This is how typical vaccines work: A modified virus is injected into the body. This altered virus is unable to cause illness but it is recognized by the body as a viral invader. Sometimes, vaccines are made from mutated viruses, sometimes by killed viruses.

Once the modified virus is injected into the body, the immune system responds and mounts an attack. Since the virus is unable to replicate and cause illness, the immune response quickly subsides, although memory cells continue to circulate. If the real live virus is encountered, the immune system is primed and ready for attack. The virus is destroyed before ever causing illness.

DNA Vaccines

Similar to other types of vaccines, DNA vaccines also stimulate the animal's own immune system and prepare it for a possible future attack of the live virus. What makes the DNA vaccine different is how it works. Researchers first isolate the genetic material from the live virus. A specific fragment of the DNA is removed; the fragment that causes the production of the protein that stimulates immunity. This fragment is then added to a ring of DNA called a plasmid. This combined DNA is then injected into the animal as a vaccine. Once inserted into the animal, the DNA vaccine is absorbed into the nucleus of the cells, resulting in a production of certain antigenic proteins. These proteins are harmless to the animal but will stimulate the same response in the immune system as the live virus would stimulate.

The advantage of the DNA vaccine over other types of vaccines is safety and efficiency. The DNA vaccines produce no side effects. Typical vaccines use modified live or killed virus. This can result in side effects and even infection with the virus. DNA vaccines are also being proven to be the most effective in preventing viral diseases, short of surviving an actual infection and developing lifelong immunity.

In addition, DNA vaccines are very stable and do not require special handling. Unfortunately, the one draw back is that they are more difficult to deliver. Most vaccines are given as an injection but DNA vaccines cannot effectively be administered that way. Currently, researchers are looking for ways of administering this new vaccine that is affordable. Today, gene guns are being investigated. These 'guns' are loaded with the DNA vaccine, which is adhered to microscopic gold beads. These beads are small enough that they can painlessly be injected into the skin where they can then be absorbed into the nuclei of cells. This method can also scatter the vaccine over a wide surface area, allowing for a better uptake of the DNA vaccine. Unfortunately, gene guns may be cost-prohibitive so other options are being investigated. One of those is aerosolization, which is being looked at for delivery of an equine influenza DNA vaccine. The DNA vaccine is directly breathed into the horse's respiratory tract.

DNA vaccine will be a wonderful method of preventing a variety of diseases but research and testing can be costly and takes time. So, for now, it is likely that the only DNA vaccines that will be available will be for those diseases that do not respond well to conventional vaccines. Diseases that are easily and efficiently prevented with typical vaccines will likely not need a DNA vaccine. Eventually, combining DNA vaccines with typical vaccines may be the future of disease prevention.

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