Fruit and vegetables packed with gene medicines promise inexpensive, easy to administer vaccines for use in developing countries. For several years, researchers have been attempting to develop genetically engineered potatoes as an oral vaccine for protecting individuals against the hepatitis B virus (HBV), a pathogen responsible for millions of cases of a potentially fatal liver disease each year. Now Hugh Mason and his colleagues have shown that an antigen from HBV expressed in potatoes can produce antihepatitis antibodies in the bloodstream of mice after ingestion (Nature Biotechnology, 01 Nov 2000). It had previously not been clear whether an oral vaccine could produce antibodies in the blood.
The researchers set about creating a potato vaccine for hepatitis by linking DNA encoding HBsAg, a highly immunostimulatory hepatitis B surface antigen, to sequences directing expression of the antigen to potato tubers. Plants into which these sequences were introduced then expressed the HBsAg in their spuds. When mice were fed three weekly doses of the transgenic tubers together with a vaccine adjuvant (an immunostimulant), they developed antibodies in their bloodstream, despite the fact that HBsAg would not normally cross the intestine. The antibody response peaked three weeks after the last dose, but a subsequent suboptimal-dose boost by injection with a commercial HBsAg vaccine gave rise to a rapid and enhanced antibody response in the animals.
Although the data are encouraging, the spud vaccine system needs to be refined to produce higher doses of HBsAg to elicit better antibody responses. Additional studies are also needed to resolve such issues as control of antigen dose, requirement of adjuvant, co-expression of HBsAg and adjuvant in the same transgenic plant. Clinical testing of the vaccine is currently underway.
Hugh S. Mason
Boyce Thompson Institute for Plant Research
Ithaca, NY 14853-1801
(News & Views)
Dr. Julian K. Ma
UMDS Guy's Hospital
Department of Oral Medicine and Pathology
Telephone #: 44 +44.171.955.5000x5459
Fax #: +44.171.955.4455
(C) Nature Biotechnology press release.
Message posted by: Trevor M. D'Souza