By Sharon Begley

NEW YORK, Aug 6 (Reuters) - Drugmakers' use of the tobacco plant as a fast and cheap way to produce novel biotechnology treatments is gaining global attention because of its role in an experimental Ebola therapy.

The treatment, which had been tested only in lab animals before being given to two American medical workers in Liberia, consists of proteins called monoclonal antibodies that bind to and inactivate the Ebola virus.

For decades biotech companies have produced such antibodies by growing genetically engineered mouse cells in enormous metal bioreactors. But in the case of the new Ebola treatment ZMapp, developed by Mapp Pharmaceuticals, the antibodies were produced in tobacco plants at Kentucky Bioprocessing, a unit of tobacco giant Reynolds American.

The tobacco-plant-produced monoclonals have been dubbed "plantibodies."

"Tobacco makes for a good vehicle to express the antibodies because it is inexpensive and it can produce a lot," said Erica Ollmann Saphire, a professor at The Scripps Research Institute and a prominent researcher in viral hemorrhagic fever diseases like Ebola. "It is grown in a greenhouse and you can manufacture kilograms of the materials. It is much less expensive than cell culture."

In the standard method of genetic engineering, DNA is slipped into bacteria, and the microbes produce a protein that can be used to combat a disease.

A competing approach called molecular "pharming" uses a plant instead of bacteria. In the case of the Ebola treatment, Mapp uses the common tobacco plant, Nicotiana benthanmianas.

The process is very similar. A gene is inserted into a virus that is then used to infect the tobacco plant. The virus acts like a micro-Trojan Horse, ferrying the engineered DNA into the plant.

Cells infected with the virus and the gene it is carrying produce the target protein. The tobacco leaves are then harvested and processed to extract the protein, which is purified.

ZMapp's protein is a monoclonal antibody, which resembles ordinary disease-fighting antibodies but has a highly specific affinity for particular cells, including viruses such as Ebola. It attaches itself to the virus cells and inactivates them.

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The drug so far has only been produced in very small quantities, but interest in it is stoking debate over whether it should be made more widely available to the hundreds of people stricken with Ebola in Africa while it remains untested.

"We want to have a huge impact on the Ebola outbreak," Mapp CEO Kevin Whaley said in an interview at company headquarters in San Diego. "We would love to play a bigger role."