By Katharina Schoebi, Checkbiotech

Scientists now have the know-how to genetically engineer plants to produce pharmacologically active proteins. Taking it one step further, the plants could theoretically be used as a vaccine against viruses or bacteria causing diseases. However, edible plants that act as an edible vaccine do not always effectively stimulate the immune system. Researchers from Poland have now found an orally delivered vaccine protecting mice against two pathogens.

Plant derived vaccines have many advantages over antigens produced by bacteria and mammalian cells. First, plants can modify and assemble proteins in a similar fashion to how human cells carry out this process. Second, plants are able to produce a much higher protein-yield, when compared to pharmaceutical production in yeast, bacteria or human cells. However, probably the most significant advantage of using plant systems to produce an edible vaccine is that unlike mammalian cells, they do not contain human or animal pathogens.

In animal farming, there are some pathogens, that cause contagious, and often, fatal diseases. The Classical Swine Fever Virus (CSFV), also termed Hog Cholera Virus, is one of them. It belongs to the Pestiviridae genus of the flaviviridae familiy. Among other proteins, the Swine Fever Virus contains protein E2, which reacts as an antigen and therefore stimulates the immune system in a very effective way.

Another pathogen causing severe illnesses in farm animals as well as in humans is Fasciola hepatica, the liver fluke. It is the causative agent for fasciolosis, a chronic and worldwide distributed disease, that is a major cause of morbidity and mortality in domestic ruminants, such as cattle, sheep and goats – a severe economic drain.

In developing countries, humans may also become infected by the liver fluke. For its metabolism, F. hepatica needs specific proteins called proteases, which could theoretically be used as a vaccine. Preliminary reports indicate that cystein protheases might be a good source of protective antigens.

For animals, an ideal vaccine would be one that could be fed to animals as an edible vaccine. A Polish research team, lead by Andrezej Legocki from the Institute of Bioorganic Chemistry at the Polish Academy of Sciences in Poznan, has now been able to produce genetically modified plants, that produce antigens from the Classical Swine Fever Virus (CSFV) and the liver worm Fasciola hepatica. They published their work in the journal Vaccine.

In their study, the researchers looked first at which gene from the Swine Fever Virus’ genome is responsible for producing the E2 protein, and which part of the F. hepatica’s genome is responsible for producing the cysteine proteases. Then, Legocki and his team introduced these genes in lettuce (Lactuca sativa) and alfalfa (Medicago sativa) plants. To their satisfaction, the plantlets were able to produce the proteins of interest.

Afterwards, the researchers selected those plants containing the highest amounts of proteins, collected their seeds and planted them. Subsequently, they grew the second generation of these plantlets on a large scale. The antigen levels in the plants were estimated, and then Dr. Legocki’s laboratory fed the alfalfa and lettuce to laboratory mice to test their ability to perform as an edible vaccine and to test if the vaccine was safe. In addition, Legocki and his colleagues immunized the lab mice two times per month. With each immunization, they administered 0.5 microgram of the E2 protein and 2 microgram of the cystein proteases. Afterwards, the researchers collected the mice’s serum and the fecal pellets and determined the levels of IgG and IgA-antibodies.

They found, that after the second immunization, there was a significant increase in antibodies. To their satisfaction, orally administered vaccines in lettuce and alfalfa were capable of effectively inducing an immune response in mice.

However, the researchers have not yet determined, if the immune response was sufficient to provide protection against the pathogens. First, Dr. Legocki wanted to make sure the vaccine was safe and capable of invoking an immune response.

Checkbiotech has learned that Dr. Legocki has just recently received permission to carry out experiments with other animals, including pigs.

“We hope to recognize, if it is possible to induce the immune response in these groups of animals,” Dr. Legocki told Checkbiotech.

Not only lettuce and alfalfa are able to produce vaccines against F. hepatica and/or CSFV. Dr. Legocki noted, “I can assure you that most plants susceptible for regeneration might be suited to this purpose.”

Dr. Legocki’s laboratory has tried to do some experiments with tobacco, however, since the regulations concerning transgenic experiments in Poland are very strict, Dr. Legocki and his colleagues have not carried out any field experiments.

Due to misunderstandings created by some NGOs and the media, people are often hesitant about transgenic developments, such as plant based vaccines. Some individuals could be concerned that genetically modified lettuce might cause human allergies, when incorrectly eaten by people. The Polish researchers are not conducting on any tests with humans, since the edible vaccines are only intended for animals.

“In my opinion, plant-based immunoprotective products cannot be considered as ordinary vegetables,” Dr. Legocki said. “Therefore, the use of the medicinal or veterinary products should be strictly controlled.”

The researchers have obtained patent rights for some of the elaborated methods and technologies. “We decided to apply for an international patent on F. hepatica in collaboration with the Institute of Biotechnology and Antibiotics in Warsaw,” Dr. Legocki told Checkbiotech. This patent will be mainly used in Australia and New Zealand, where the protection against F. hepatica is of great importance.

Katharina Schoebi is a biologist and a Science Writer for Checkbiotech.

Andrzej Legocki et al. Immunoprotective properties of transgenic plants expressing E2 glycoprotein from CSFV and cysteine protesase from Fasciola hepatica. Vaccine, 23 (2003), p. 1844-1846

Contact:
Andrzej B. Legocki
Insitute of Bioorganic Chemistry
Polish Academy of Sciences
Noskowskiego 12/14
61-704 Poznan
Poland
E-mail: legocki@ibch.poznan.pl
Tel.: 0048 61 852 8503
Fax: 0048 61 852 0532
http://www.pan-ol.lublin.pl/biul_10/art_1010.htm