By Rita Rubin
WebMD Health News
Reviewed by Arefa Cassoobhoy, MD, MPH
Aug. 5, 2014 -- An experimental serum grown in specially modified tobacco leaves made headlines this week when it was given to two Americans stricken with Ebola.
The ZMapp treatment had never before been tested in humans. Although both Dr. Kent Brantly and Nancy Writebol, who became ill on aid missions in Liberia, are reportedly improving and have been brought back to the United States, it's unclear how much of a role the serum may be playing in their recovery.
Before the serum could be used on a wider scale, it would have to go through the FDA's drug approval process.
FDA spokeswoman Stephanie Yao says in an e-mail to WebMD that the agency couldn't comment on specific products. But she says the FDA is involved in an inter-agency working group "looking to facilitate and accelerate development of potential investigation treatments for Ebola."
"Currently, there are only experimental Ebola treatments in the earliest stages of development," Yao says. "Even though a drug is not approved right now, the FDA can still provide access to potential products through other [avenues], such as through an emergency Investigational New Drug (IND) application. The FDA stands ready to work with companies and investigators treating these patients who are in dire need of treatment."
Other New Hopes
The companies involved in other treatments and vaccines in the development pipeline say they need funding.
"We've approached big pharma. They don't really view Ebola as a commercial product, so they're not really interested," says John Eldridge, chief scientific officer for Profectus BioSciences in Baltimore. The company has developed a vaccine that, in a single injected dose, works "extremely well" in certain monkeys against Ebola and Marburg viruses, both hemorrhagic fevers, he says.
Still, he says he's instructed his laboratory group to proceed under the assumption "that someone's going to step up to the plate and fund the manufacture of this stuff."
The vaccine uses a weakened version of a type of virus that doesn't make people sick. A molecule from the surface of the Ebola virus is inserted into the weakened virus. After the vaccine is injected, the virus carries the Ebola molecule to cells, triggering an immune response.
Eldridge says the Ebola vaccine has been shown to prevent infection in monkeys, as well as treat them if they've been exposed to Ebola. But he says the tests on monkeys exposed to Ebola used a virus grown in the lab, which becomes less powerful over time. The logical next step would be to test the vaccine in humans, Eldridge says -- but his company needs $3 million to make it according to FDA specifications for human testing.
On the treatment side, an early-stage safety trial of an anti-Ebola therapy developed by Tekmira Pharmaceuticals began in January in healthy volunteers. But the Vancouver company announced in early July that the FDA had put the trial on hold until safety concerns are resolved. The therapy, called TKM-Ebola, is under FDA "fast-track" status. It's been shown to be 100% effective in treating Ebola-infected monkeys.
Tekmira president and CEO Mark Murray, PhD, says in a statement the company is "encouraged" by the progress so far of TKM-Ebola. He emphasized, though, that the treatment "is still in development and remains unapproved for human use."
Another treatment that's been tried but not formally studied in people is using the blood of an infected person. Samaritan's Purse has said Brantly received a unit of blood from a 14-year-old boy, a former patient of his who recovered from Ebola.
The boy's blood would have antibodies against the lethal virus, so giving it to someone battling the disease "makes all the sense in the world," Eldridge says. "There's clear evidence that antibodies will protect against Ebola infection." Because Brantly also received the experimental serum, it will be hard to know which treatment helped or if his health would have improved on its own.
Another path to an Ebola vaccine would be to do studies in animals under the FDA's Animal Rule, a "very long process," says M. Javad Aman, PhD. He's a former research scientist at the U.S. Army Medical Research Institute of Infectious Diseases.
The rule applies to drugs and biological products, such as vaccines, developed to treat or prevent serious or life-threatening conditions caused by exposure to toxic substances. Because it would be unethical to test such drugs or biological products by deliberately exposing people to a toxic substance, the Animal Rule allows the FDA to approve them based on how well they work in animals. The agency applied the Animal Rule in December 2012 to approve raxibacumab injection for treatment and prevention of inhaled anthrax.
Aman is the co-founder of Integrated BioTherapeutics, or IBT, in Gaithersburg, MD. IBT has developed an Ebola vaccine that, like the vaccines against HPV (human papillomavirus), uses "virus-like particles," or VLPs. VLPs are like a sheep in wolf's clothing. They contain proteins found on the surface of a virus, evoking an immune response, but they lack viral genetic material, so they can't make people sick. The IBT vaccine is intended to protect wild gorillas and chimpanzees, for which Ebola is now considered as big a threat as poaching and habitat loss, according to the company.
In May, Aman and his collaborators published the results of a test of their Ebola vaccine in captive chimpanzees. The study found the vaccine triggered an immune response.
While "it's very promising," the vaccine is not ready to be tested in people, Aman says, citing manufacturing challenges. "At this point, we're also looking for funding. We would need additional support to take it to the next level."
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