Vaccines of a "Garden Variety"

Scientists from Novosibirsk are engaged in the development of an unusual vaccine which, apart from being less expensive to produce, safe and painless to administer, is also edible. The research is being accomplished in the framework of the ISTC Partner Project #2176, which is funded by the Agricultural Research Service of the U.S. Department of Agriculture, and so far the project team has managed to introduce a HIV antigen protein gene into tomatoes.

Usually, vaccines are injected, but some – like the polio vaccine – can be ingested or eaten. Thus, a number of years ago plant genetic engineers started producing vaccine proteins in plants to test their effectiveness, which started a whole new area of plant derived edible vaccines. This approach has already been used to test vaccines for hepatitis viruses and some bacterial pathogens, but Dr. Sergey Shchelkunov at SRC of Virology and Biotechnology “Vector” wondered if an edible vaccine for HIV AIDS could be produced.

Dr. Shchelkunov’s laboratory teamed up with other Russian scientists from both the Novosibirsk Institute of Biological Chemistry and Basic Medicine, and the Siberian Institute of Plant Physiology and Biochemistry in Irkutsk, Russia. A functional vaccine from their work is still to be tested, but as a result of project 2176 the researchers were able to insert into the chromosome of tomato plants a gene from HIV. Furthermore, they were able to show that the corresponding protein product from the HIV gene was expressed in different parts of the transgenic tomato plant including ripe fruit. And, because this is a vaccine based on a single protein from HIV, there is no risk of acquiring an HIV infection from eating the tomato fruit.

The choice of tomatoes for these experiments was well planned, because previous researchers have done similar work in tobacco and potato plants. But, of course tobacco cannot be eaten and potatoes must be cooked before consumption, which in most cases destroys the medicinal properties of the vaccine. Edible vaccines have also been produced in bananas, which can be eaten fresh, but bananas can only be grown under tropical conditions. Thus tomatoes were a wise choice because they can grow in many different climate zones and conditions, and their fruit can be eaten fresh.

To introduce the HIV gene into tomatoes, the Russian scientists took advantage of a naturally occurring bacteria which has been harnessed by plant genetic engineers to introduce foreign pieces of DNA into many different plant genomes including tomatoes. All of this was done in tissue culture in the laboratory, but when whole plants were regenerated in test tubes they were moved to special greenhouses where the transgenic tomato plants grew like usual tomato plants. Scientists then applied PCR (polymerase chain reaction) technology to confirm the presence of the HIV gene in the transgenic plants. Other techniques were also used to confirm that the correct HIV protein was being made in different parts of the transgenic plants including and most importantly the ripe fruit of the tomato plants.

However, this was only the beginning of the scientist’s work. For example, the researchers had to check whether the HIV gene was inherited by subsequent generations of plants. To do this they took seeds from transgenic tomatoes, let them germinate and grew a second generation of transgenic tomatoes, which also proved to contain the HIV gene and antigen protein just as the their parent plants had.

Of course, there remains many avenues of research to explore regarding edible HIV vaccines (e.g., efficacy, mechanisms of action, etc.), but in the words of the Russian scientists “The resultant transgenic tomatoes present significant interest as a basis for the creation of edible vaccines against HIV/AIDS and hepatitis B.” Thus, although a useable edible vaccine against AIDS may be years away, the results from ISTC project #2176, the potential convenience, safety and low cost of edible vaccines and the hope that AIDS and other deadly diseases may someday be controlled makes the efforts worthwhile.