Rabies, HIV, cancer and malaria could all be prevented with pills in the future, if a new technique using specially modified viruses to deliver vaccines is adopted, according to scientists speaking today (Tuesday, 05 April 2005) at the Society for General Microbiology's 156th Meeting at Heriot-Watt University, Edinburgh.
"We can take a special type of virus which only infects bacteria, called a bacteriophage, and replace some of its DNA with vaccine DNA, and then use the phage to deliver vaccines in a highly efficient way," says Dr John March of the Moredun Research Institute, Penicuik, near Edinburgh.
A vaccine packaged in this way is cheap, simple to make, stable, and environmentally safe according to the researchers. Because the phage vaccine can be safely stored at room temperature as a dry powder, it should be possible to turn it into a pill form and deliver it as an oral vaccine. Since the phages can mass produce themselves the system would be very cheap, and easy to store and administer, making it ideal for use in the developing world to protect against diseases such as HIV/AIDS and malaria.
"We have already tested oral delivery of these vaccines, and the data suggest that they work," says Dr March. "We have successful test results from mice, rabbits and sheep - animals in which conventional DNA vaccines do not work - so we are confident that the technique will work for people. Bacteriophages have been used as medicines in eastern Europe since the 1930s to fight bacterial infections, so we have a long history of their safe use in humans, and of large scale manufacturing."
The phage vaccines have several advantages over traditional 'naked' DNA vaccines - they can contain much larger sections of DNA, triggering a more effective immune response. Because the phage vaccine is protected within a virus shell it can be targeted at specific cells in the body, and the shell stops it breaking down and becoming ineffective.
The new vaccines can also be used for diseases where the vaccine material is difficult or expensive to produce using conventional approaches, such as for cancers. The doses needed are much smaller than conventional DNA vaccines, where high doses and multiple injection regimes are often needed. The large cloning capacity of phages means that several vaccines could be delivered simultaneously.
The main applications will be in producing cheap general vaccines for the developing world, and in specialist applications in the developed world in situations where conventional vaccines do not work. In developing countries a pill form of vaccine would do away with the need for scarce and expensive cold storage systems, and also will have no need for a constant supply of clean needles.
"Wildlife use is also ideal since phages are cheap and stable so we can use them in baits or with oral delivery," says Dr March. "This would be ideal for a rabies vaccine, where wildlife programmes will play a major role in disease eradication. The antibody response against the phage is a useful side effect as it gives us a simple marker to tell between vaccinated and naturally infected animals."
"The special phages we are using cannot replicate outside the laboratory, so they are environmentally safe and friendly," explains Dr John March. "The fact that we can make them with the bare minimum of laboratory equipment and expertise only adds to the potential of this exciting new technology."