Nov. 1, 2006 Researchers at the Animal Health Research Centre (CReSA) are developing immunotherapeutical strategies against diseases produced by prion, such as Bovine Spongiform Encephalitis. The most recent results, published in the Journal of Virology, show that important advances have been made in tests using DNA vaccines on animal models, enabling a significant delay in the arrival of symptoms. In the long term, this research could lead to the production of treatment for humans.
The infectious agent responsible for transmissible spongiform encephalopathies, also known as prion diseases, (which include mad cow disease), is a protein known as the infectious prion (PrPi), which has no nucleic acid and which produces contagious neurodegenerative diseases in different species of animals. The PrPi changes shape to that of an existing natural protein in the organism, the cellular prion (PrPc), but does not change its amino acid sequence. In certain circumstances, when the PrPi comes into contact with the original proteins, the proteins take on the shape of the in the infectious protein. Once this accumulates in the central nervous system, it destroys neural mass and makes the brain of affected animals take on a sponge form, which is where the term "spongiform diseases" comes from.
The researchers' work focuses on producing a vaccine that will provide an immune response that is as complete as possible, including both a humoral response (production of antibodies) and a cellular response (eliminating "infected" cells and activating the "memory", enabling the animal cells to continue responding to the infectious agent).
The main obstacle to achieving this objective is that the prions do not produce an immune response since the metabolism of the affected animal identifies it as one of its own antigens. The challenge, therefore, is to overcome the tolerance barrier, that is, that the animal's body produces an immune response to one of its antigens.
The researchers have achieved this objective using a DNA vaccine based on a plasmid (an extrachromosomal DNA molecule) that expresses the prion gene with a small sequence that acts as a transport signal to cellular compartments called lysosomes. Once the vaccination is administered, the prion quickly degrades in the lysosome, allowing a marked improvement in the presentation of the cells of the immune system and inducing a powerful antibody and cellular response.
The results of the research have shown that in vaccinated mice, and only in those vaccinated, there is a significant delay in the appearance of symptoms after the intracerebral infection produced by the infectious prion.
The group is continuing its research to further investigate new administration routes for the vaccine and to eliminate the side effects observed in vaccinated animals.
This work may also enable advances to be made in the development of reactive agents for the diagnosis of diseases produced by the prion that until now could only be achieved post mortem.
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