By Daniela Kenzelmann, Checkbiotech

An increasing number of reports demonstrate that biomedicals like therapeutic antibodies or vaccines can be inexpensively produced in plants. Normally, the production of such a agent requires the generation of a genetically modified plant line, which is a time-consuming process.

Dr. Yuri Gleba and his coworkers have found a shortcut to produce antibodies with a special genetical tool called transient expression system, which allows researchers to introduce desired genetic material into an organism. This means that the genes which encode the antibody to be produced are not inserted into the genome of the plant, but instead viruses are used as vectors to bring the antibody-genes into the plants.

The major problem that the researchers had to solve is that two genes are necessary to build a full antibody, because it is composed of two subunits named the heavy and the light chain. Previous attempts to pack both of these genes together in one virus were unsuccessful in terms of antibody production levels.

Therefore, Dr. Gleba’s group had the idea to use two viruses carrying one of the antibody-subunits each. Normally, two viruses of the same kind would compete, meaning that one cell can only be infected with one virus. For antibody production however, it is required that both viruses are present in the same plant cell. The researchers achieved this by using two different viruses which were known to be non-competing: tobacco mosaic virus and potato virus X.

First, the researchers had to modify the viruses that they would carry one of the antibody genes. Secondly, tobacco leaves were co-infected with the two artificial viruses. The last step involved purification of the antibodies from the leaves and their characterization. Dr. Gleba’s group showed that antibody subunits as well as correctly assembled antibodies accumulate in the leaves in less than 10 days. Equally important is that they showed that the antibodies recognized their target antigen.

To make sure that these modified viruses do not escape and convert normal plants into antibody-plants, the researchers handicapped the viruses in a way that they can only infect plants with the help of a special bacterium. This will prevent them from crossing with other plants and passing on their new genetic material.

Dr. Gleba’s results are a proof of concept that two non-competing viruses can be used to produce therapeutic antibodies in plants without the need to create transgenic plants. The procedure has potential for unlimited scale-up for industrial production of biomedicines and its rapidity and versatility would allow manufacturers to respond to suddenly increasing demands. Additionally it could speed up research, because antibodies are also important tools for scientists.

Future work will be to further improve the antibody production levels, for example to determine the ideal ratios of both viruses for full antibody assembly. Additionally, Dr. Gleba has considered giving cells the ability to produce factors which facilitate the assembly of the antibody. As a next step it will be crucial to prove that antibodies produced by viral infection are equally efficient in treating diseases than conventionally produced antibodies.

Daniela Kenzelmann is a Science Journalist for Checkbiotech and is writing her PhD at the Friedrich Miescher Institute in Basel, Switzerland.

Icon Genetics
Bayer BioScience

Rapid high-yield expression of full-size IgG antibodies in plants coinfected with noncompeting viral vectors
Giritch A, Marillonnet S, Engler C, van Eldik G, Botterman J, Klimyuk V, Gleba Y.
Icon Genetics GmbH, Weinbergweg 22, 06120 Halle, Germany.

ABSTRACT

Plant viral vectors allow expression of heterologous proteins at high yields, but so far, they have been unable to express heterooligomeric proteins efficiently. We describe here a rapid and indefinitely scalable process for high-level expression of functional full-size mAbs of the IgG class in plants. The process relies on synchronous coinfection and coreplication of two viral vectors, each expressing a separate antibody chain. The two vectors are derived from two different plant viruses that were found to be noncompeting. Unlike vectors derived from the same virus, noncompeting vectors effectively coexpress the heavy and light chains in the same cell throughout the plant body, resulting in yields of up to 0.5 g of assembled mAbs per kg of fresh-leaf biomass. This technology allows production of gram quantities of mAbs for research purposes in just several days, and the same protocol can be used on an industrial scale in situations requiring rapid response, such as pandemic or terrorism events.

PMID: 16973752 [PubMed - in process]