Vidyya Medical News Service
Volume 6 Issue 47 Published - 14:00 UTC 08:00 EST 16-Feb-2004 Next Update - 14:00 UTC 08:00 EST 17-Feb-2004
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Delayed-release system could help produce more effective vaccines

A delayed-release system could help produce more effective vaccines against a number of diseases, including cancer. Scientists from Massachusetts Institute of Technology encased their "DNA vaccines" in biodegradeable spheres. They do not break down and release the vaccine until they are carried to key locations such as the lymph nodes.

The researchers, writing in the journal Nature Materials, say it should mean a far more powerful vaccine - which might be able to target tumours. DNA vaccines, which instead of a whole virus contain fragments of genetic material from a virus or bacteria.

Doctors see them as a modern alternative to traditional vaccines, possibly working against a wide variety of illnesses with fewer side-effects. It is possible that they could deliver a life-long immunity to certain infections which have a vaccine, but only one which gives a few year's protection.

Instead of giving the patient a dose of dead viruses, or weakened live viruses, in order to train the immune system to tackle the real thing in the event of a genuine infection, the DNA sections are injected into human cells.

They cell's machinery uses this DNA information to start churning out body chemicals specific to the virus - and it is these which are picked up by the immune system. When a real infection happens, the same proteins are produced, and the immune system detects this and launches an attack that should stop the invading organism in its tracks.

However, the machinery of the immune system is complex - and it is important that these DNA fragments make it back to the lymph nodes so that the correct immune cells can be generated. If this does not happen, these proteins may trigger an unwelcome response in immune system cells outside the lymph nodes - and actually make the immune system downgrade the potential threat they pose, meaning the vaccine will not work properly.

The MIT researchers aimed to find a way to delay exposing the immune system to their vaccine-generated proteins until they have been carried back into the lymph nodes. They use a biodegradeable polymer sphere which is just the right size to be picked up by immune cells called dendritic cells, whose role is to grab a potential threat - be it bacterium or virus, then move back to the lymph nodes where it can be used as the basis for a full immune response.

The dendritic cell engulfs the sphere, which does not burst immediately, but gradually breaks down and will release its content for at least 24 hours. The researchers are hoping that this will mean a far more efficient immune response - and believe that this could mean that DNA vaccines targeting cancer could be made to work effectively.

To test this, they developed a DNA vaccine for a particular type of tumour cells in mice. They found that their vaccine was far better at suppressing the growth of tumour cells when it was encased in the polymer sphere.

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