Clinical trials – edible vaccines part 2

The first human clinical trial of an edible vaccine took place in 1997, when volunteers ate raw potatoes genetically engineered against diarrhoea-causing E. coli. Ten of the 11 volunteers who received the vaccine had fourfold rises in serum antibodies.

 a.Diarrhoea

 Researchers from the Boyce Thompson Institute (BTI) at Cornell University conducted a clinical trial of an edible vaccine in 1999. Potatoes containing the Norwalk virus (which causes vomiting and diarrhoea) fed to volunteers elicited an immune response in 19 out of 20 volunteers.

Arntzen and John Clements, of Tulane University Medical School, have also worked with tobacco plants to provide immunity against diarrhoea caused by E. coli.

b. Measles

Measles virus is enveloped with two major surface proteins — the hemagglutinin (H) and fusion proteins. Antibodies raised to the H protein after infection with the wild-type measles virus (MV) have MV-neutralising activity and are associated with immunological protection. The H protein subunit from the attenuated Edmonston vaccine strain was therefore selected as the basis for an edible measles vaccine.

MV-H edible vaccine does not cause atypical measles, which may be occasionally seen with the current vaccine. Thus, chances for eradication of measles may be improved. Transgenic rice, lettuce and baby food against measles are also being developed.

Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Melbourne, Australia have grown a measles-fighting tobacco plant and have begun pilot studies with oral plant-based vaccines for malaria and HIV also.

c. Hepatitis B

The current hepatitis vaccine extracted from yeast requires chemical modification to become active, increasing the cost of the vaccine, which also must be stored under refrigeration. The situation is further complicated by the need for three separate injections of the vaccine at 0, 1, and 6 months of age.

Prodigene and Stauffer Seeds (formerly a division of Novartis) have conducted clinical trials on pigs using an edible vaccine for transmissible gastroenteritis virus (TGEV) expressed in corn, and are developing a Hepatitis B vaccine for humans.

Scientists in Poland working with the US' Thomas Jefferson University have tested a hepatitis B vaccine contained in lettuce on human subjects. Researchers working on an edible hepatitis B vaccine suggest that oral doses may need to be 10-100 times higher than the injectable dose to elicit a comparable immune response. Mice were fed with modified potato, containing an oral vaccine for hepatitis B which passed through the animals' stomachs without being broken down and stimulated the production of antibodies against the disease.

Scientists now say tomatoes and bananas genetically modified to contain such a vaccine may be able to eradicate the virus.

References:

a. http://www.grain.org/seedling/?id=54

b. http://www.mja.com.au/public/issues/176_09_060502/web10753_fm.html

c. http://www.biotech-info.net/hepatitus_vaccine.html

d.http://www.planetark.org/dailynewsstory.cfm/newsid/13265/newsDate/12-Nov-2001/story.htm e. Lal P, Ramachandran VG, Goyal R, Sharma R. Edible vaccines: Current status and future. Indian J Med Microbiol [serial online] 2007 [cited 2008 May 2];25:93-102.

Available from: http://www.ijmm.org/text.asp?2007/25/2/93/32713