Miracle medicine

Bananas that are actually vaccines. Potatoes that kill bacteria. Tobacco plants that fight tooth decay. Medical science has more tricks up its sleeve

Published: Tuesday 15 September 1998

Banana for better health A SINGLE vaccine can save more lives and money than any other form of medication currently available. This is a universal truth.

In the next century, some 15-odd months away, doctors and scientists will strive to develop vaccines far more powerful and effective. Vaccines that will finally put an end to the universally-dreaded diseases such as AIDS and tuber-culosis. Scientists have even reported success in developing plant-based vaccines that can be eaten directly. So in a few years' time, you could be eating an apple not only for the nutrition it provides, but also for its value as a vaccine. But more on that later.

Looking back, the various immunisation programmes have emerged some of the greatest medical triumphs of all times. Poliomyelitis is on its way out, measles has been eliminated in many countries, BCX: and DPT infant immunisation rates are approaching 80 per cent globally, and numerous lives have been saved, not to speak of the millions of children who have been saved from a crippled future by the polio vaccine.

Barry Bloom of the Howard Hughes Medical Institute in New York, USA, and Roy Widdus, coordinator of the Children's Vaccine Initiative, Geneva, Switzerland, have described the global health impacts of vaccines in a recent supplement of Nature Medicine (Vol 4, No 5}.

The commercial value of manufacturing vaccines has improved considerably for pharmaceutical companies, which are now more likely to take on vaccine development than in previous years. New biotechnology methods make them more cost effective to make and sell.

While the traditional enemies have been targeted for final elimination, new challenges have cropped up before us. Diseases such as hepatitis B, yellow fever, childhood meningitis and Haemophilus influenza B are threatening thousands worldwide. The silver lining to the dark cloud of these diseases, however, has been the fantastic progress of basic science in recent years. Today, vaccine development encompasses a variety of technologies that range from century-old approaches of modifying pathogens to advanced genetic manipulations of the immune system itself. All vaccines, however, have the common aim of initiating an immune response designed to prevent or limit infection. Advances in biological knowledge and technology have given medical science new ways to vaccinate people against previously intractable diseases.

In the near future, eating a potato or a banana will really be good for health. The next generation of vegetables and fruits will provide not just the nutrients they are known for, but protection against infectious diseases as well. The first clinical trials of such plant-based vaccines have been encouraging. These are cheap to produce and easy to administer. A patient is vaccinated simply by eating the raw plant tissue. These recent trials have moved plant-based vaccines a step closer to practical application for prevention of infectious diseases in humans (Nature Medicine Vol 4, No 5).

The idea of using plants to generate and deliver vaccines or other immuno-therapies has immense potential since plants can be grown easily and inexpensively. And if the recent reports are to be believed, then this technology is only inches away from application. An effective vaccine might take the form of an antibody - which identifies and attacks an invading pathogen - or an antigen, which encourages our own immune system to make antibodies. Antigens and antibodies are both proteins, and therefore, they are encoded by genes. Recent technological developments have allowed many different foreign genes to be transferred into plants.

Julian Ma of Guy's Hospital in London, UK, and colleagues have managed to produce a transgenic tobacco plant that makes antibodies against Streptococcus mutans bacteria, a common cause of oral bacterial infection that eventually causes tooth decay. The antibody is made up of four separate units, each produced by a different gene. First, the researchers engineered the tobacco plants to make one of the units, and bred these plants until they had a generation of plants which made all four. Amazingly, these plants managed to put all four units together to build a fully functional antibody ready to fight Streptococcus mutans.

Rather than getting their volunteer "patients" to chew the tobacco, the research team extracted the antibody and applied it in solution to their volunteers' teeth, previously sterilised. They found that that the Streptococcus mutans bacteria could recolonise within the mouth for up to four months, thanks to the antibody. Carol Tacket of the Center for Vaccine Development in the University of Maryland School of Medicine in Baltimore, USA, describes a fully edible vaccine against the bacterium Escherichia coli, the leading cause of diarrhoea and food poisoning in infants in the developing world. Targeting the vaccine directly to the intestines, where infection occurs, turns out to be efficient. Eleven subjects ate raw potatoes genetically engineered to produce a part of the toxin released by Escherichia coli. The researchers tested the potato vaccine's ability to stimulate an immune response. They measured antibody-secreting cells (ASC) in the intestine. The strong presence of ASC in the 11 subjects suggested that their intestines were producing an immune response against the bacteria. The transgenic potato might be an effective method of vaccination in the near future, Tacket concluded. The same research group is now investigating the efficacy of bananas as an alternative to potatoes. Bananas are the fourth most common crop in the world and can be eaten without cooking. Thus they are ideal for producing edible vaccines for very young infants. Takeshi Arakawa and William Langridge of the Loma Linda University School of Medicine in California, USA, writing a commentary on these two papers in Nature Medicine found the results extremely promising. "Plant-based immunotherapeutic proteins may soon become economically competitive enough to supplement or even replace more conventional vaccine production systems," they wrote.

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