|A Needle or a Banana?|
February, 2000: New York (United States)
A common fruit--the banana--is currently being considered as a potential vehicle for a vaccine against a serious and too-common disease, hepatitis B.
Hepatitis, meaning inflammation of the liver, may be caused by one of five viruses, known as A, B, C, D, and E. Hepatitis B virus (HBV) affects more than 2 billion people worldwide. In 1996, the Roswell Park Cancer Institute (RPCI) estimated that 20,000-25,000 Americans are infected with hepatitis B each year. However, in 1998, the Center for Disease Control and Prevention estimated the number of annual new cases at closer to 200,000.
Hepatitis B is 50 to 100 times more infectious than AIDS. HBV is present in the blood and body fluids of infected individuals and can be transmitted from one person to another through sexual intercourse or shared needles and from mother to child during birth. It can also be transmitted within households among young children. Much of the developing world has a high rate of childhood infection, including parts of Africa, Asia, and the Pacific as well as the Middle East, sections of Europe, and the Amazon region.
HBV infection is characterized by loss of appetite, listlessness, jaundice, diarrhea, vomiting, and pain in the muscles, abdomen, and joints. It often leads to severe liver damage, liver cancer, or death. Although there is no cure for hepatitis B, a vaccine has been available since 1982. The vaccine, which uses recombinant-DNA technology to bioengineer yeast cells, contains a nonliving hepatitis B surface antigen known as [HBsAg].
HBV vaccine has been recommended as a routine infant vaccination worldwide since 1991 and as a routine adolescent vaccination since 1995. Although there are no federal laws requiring the vaccine for day-care and school attendance, the World Health Organization (WHO) recommends that all countries with routine hepatitis B vaccination programs continue that practice, while countries not currently immunizing against HBV infection adopt such programs immediately. The vaccine is delivered in a series of three intramuscular injections over a six-month period. It requires refrigeration, and injections must be administered by a medical professional, with the total cost ranging between $100 and $150 per person. These factors, coupled with transportation and distribution issues, make mass immunization, especially in Third World countries, next to impossible. In 1996, the Rockefeller Foundation provided a three-year grant for oral vaccine research to the Boyce Thompson Institute for Plant Research Inc. (BTI), a private, not-for-profit organization affiliated with Cornell University. The preclinical trials were funded by the National Institute of Allergy and Infectious Diseases, a division of the National Institutes of Health. Clinical trials in 1999 were funded by Axis Genetics of Cambridge, England. These studies not only paved the way for the development of an edible HBV vaccine, but also supported collaborations with researchers in Mexico for a vaccine that would inoculate children against intestinal diseases such as diarrhea and cholera, which result in high rates of infant mortality in Mexico.
BTI researchers announced the beginning of clinical testing of the world's first edible vaccine against HBV in July 1999 at RPCI in Buffalo, New York. The research teams used engineering techniques to introduce the hepatitis B surface antigen into a member of the Solanaceae family, Solanum tuberosum, commonly known as the potato. However, transgenic potatoes may not be the ideal carrier for edible vaccines because few humans eat potatoes raw. Further studies are being done to determine whether cooking will alter or diminish the potency of the vaccine.
Meanwhile, Dr. Yasmin Thanavala of RPCI's department of immunology believes the true breakthrough would be to express the antigen in a food such as the banana, which is consumed worldwide and requires no processing to eat. Thanavala explains that ideally the genetically engineered foods would be grown locally, making transportation issues obsolete. With this technology, the cost of vaccination could be reduced to pennies per person because one banana plant, Musa sp., can produce about 100 pounds of bananas!
Musa is a genus in the Musaceae family, monocots that tend to be tropical. Several species of bananas produce an abundance of seeds. Those with pendent inflorescences are bat-pollinated, so their flowers are open and functional only at night. Musa species with erect inflorescences are self-pollinated, while others are bird-pollinated. In the cultivated Musa sp., the fruit, a true berry, develops without fertilization or seed production and is therefore referred to as parthenocarpic.
Edible vaccine has applications for livestock as well. Instead of giving animals large doses of antibiotics, a controversial issue in itself, feeding them an edible vaccine could provide the necessary disease protection. Many researchers have placed their hopes on edible vaccines as potential eradicators of infectious diseases around the world. Dr. Charles J. Arntzen, president of Boyce Thompson Institute, hopes this research will eventually lead to an edible HIV vaccine.
Edible vaccines will be an attractive prospect not only to Third World Nations, but also to industrialized countries. Which would you rather have: an injection or a piece of fruit?
References, Websites, and Further Reading
Mabberley, D.J. The plant book. New York: Cambridge University Press, 1997.
Stern, Introductory Plant Biology, 8th Edition
Chapter 8: Flowers, Fruits, and Seeds
Chapter 14: Plant Propagation and Biotechnology
Chapter 17: Kingdom Monera and Viruses
Chapter 19: Kingdom Fungi and Lichens
Chapter 23: Flowering Plants
Chapter 24: Flowering Plants and Civilization
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