Mapp Biopharmaceutical's experimental Ebola therapy ZMapp shows positive results in non-human primates up to five days post-infection: study

Preclinical study data published in Nature on Friday demonstrated that all 18 rhesus macaques administered Mapp Biopharmaceutical's investigational anti-Ebola drug ZMapp survived lethal doses of the virus, even when treated up to five days after infection. The authors reported that advanced disease "could be reversed, leading to full recovery," adding that "ZMapp exceeds the efficacy of any other therapeutics described so far, and results warrant further development of this cocktail for clinical use."

As part of the study, 21 rhesus monkeys were inoculated with the Kikwit variant of the Ebola virus. Eighteen of the animals received three doses of ZMapp at three-day intervals beginning three, four or five days after infection, with the remaining animals observed without treatment.

Results showed that in addition to surviving, ZMapp-treated animals also displayed undetectable viral loads by 21 days after infection, while untreated animals succumbed to the disease by eight days post-infection. The researchers noted that the Kikwit variant was used because the Guinean strain causing the current Ebola outbreak in West Africa was not available, but results from later cell-culture experiments have since demonstrated that ZMapp inhibited replication of the Guinean strain.

Senior author Gary Kobinger said "the level of improvement was beyond my own expectations," noting that the drug reversed advanced symptoms such as rashes, liver dysfunction and haemorrhaging. However, he cautioned that although the study "strongly supports the concept" that ZMapp would be effective in humans, the findings cannot be taken as proof of the vaccine's effectiveness in people. In August, a World Health Organization panel concluded that it would be ethical under certain conditions to use unproven drugs and vaccines to treat patients infected with the Ebola virus.

Mapp indicated earlier in August that it has exhausted its supply of ZMapp, which is produced from tobacco leaves processed at a Reynolds American plant. Maura Payne, a spokesperson for Reynolds American, said the unit began making more ZMapp "a couple of weeks ago, but the process takes time." She added that the company aims to produce enough product for tests necessary to seek regulatory approval of ZMapp, and that "we plan to begin that testing protocol by year-end." Kobinger said it was his understanding that the production facility can produce 20 to 40 doses of ZMapp per month. He noted that the setup was only designed to make small amounts for use in non-human primate studies and for small-scale human safety trials that could begin in 2015.

Meanwhile, in regards to other experimental Ebola therapies being developed, the FDA recently partially lifted a clinical hold on Tekmira Pharmaceuticals' investigational vaccine, TKM-Ebola, potentially permitting a Phase I study of the therapy to proceed. In addition, GlaxoSmithKline disclosed in late August that enrollment in early-stage studies of its experimental Ebola vaccine will commence shortly.

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