The gene for each antibody is then introduced into the leaves of tobacco plants using a system developed by Icon Genetics, a German company. The leaves then produce the antibody.
In one study published last year, three out of seven monkeys treated with antibodies developed by Mapp survived being infected with Ebola, even though treatment did not start until four days after the infection. Both animals in the control group died. The treatment worked even better in another study when begun earlier after exposure to the virus.
It turns out another tiny company, Defyrus, based in Toronto, was independently developing a similar treatment with the Public Health Agency of Canada.
The companies agreed to combine the best of their antibodies into a single cocktail called ZMapp, which is what the two American aid workers received. The data for ZMapp in monkeys has not been published but is said to be substantially better than for the predecessor drugs.
Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said it was “too early to make any conclusions about how effective this intervention is,” since it was tested in only two people.
Still, there is interest in scaling it up.
Monoclonal antibodies produced by pharmaceutical companies for use in treating cancer or other diseases are typically made in genetically engineered cells of mammals grown in vats. But Mapp chose to use plants instead because large quantities can potentially be produced more quickly and cheaply.
About 15 years ago, it was thought that genetically engineered crops would be widely used to produce human proteins for use as drugs. When Dr. Whaley and Dr. Zeitlin were both researchers at Johns Hopkins University in 1998, they published a paper with Monsanto scientists about a soybean genetically engineered to produce an antibody against genital herpes. But that idea has largely been abandoned, especially when it comes to using food crops, because of concerns that drugs produced in crops might inadvertently get into someone’s cornflakes.
Even so, research has continued, funded by the Defense Department, on quickly producing proteins in tobacco plants that are grown inside buildings.
“You can start making protein within a matter of days,” said Robert L. Erwin, president of iBio, another company that is working on this technology.
Still, it seems that this product will take several months to produce in any quantity. The capacity of the Kentucky facility is small, meant to support only the small scale human safety tests that Mapp had been planning. The tobacco plants have to be grown for about a month before they can be infected with the antibody gene and the proteins have to be harvested and purified.
“Starting from zero and going to 60 is not so easy, but once you’re at sixty you can keep going at that rate,” Dr. Whaley said. He would not say how many doses could be made and how quickly.
Dr. Fauci of the infectious diseases institute said officials had been told it would be a moderate amount even after several months. “You’re not talking about thousands of doses or even hundreds of doses,” he said.
But there are some other companies that can also make drugs in tobacco, including Caliber, which has a larger capacity than the Kentucky facility. So the government is exploring using them to supplement production.
“We told them we have the capacity and are ready,” said Dr. Holtz of Caliber. He said that together Caliber and the Kentucky facility of Reynolds could produce large quantities in six months.
Dr. Michael V. Callahan, an infectious disease specialist at Massachusetts General Hospital who has responded on the ground to Ebola outbreaks, said the use of ZMapp for the two Americans raised some concerns given the limited existing supply. “What was the prioritization that allowed these patients to be treated?” he said.
According to the Department of Health and Human Services, the reason was that Samaritan’s Purse, the organization that employed one of the aid workers, contacted the Centers for Disease Control, which in turn referred them to National Institutes of Health, which in turn referred them to Mapp.
Doing clinical trials in Africa will likely require approvals from authorities there. And treating large numbers of patients with ZMapp, which needs to be given intravenously, could be difficult.