Ebola survivors' immune responses offer clues for vaccine development

Vaccines against the Ebola virus have been distributed amid several outbreaks. But the immune response to the virus is still not fully understood, which makes improving vaccine design a challenge. Now, scientists in France have found some clues to improving the vaccines by studying survivors from the 2014-2016 outbreak in West Africa.

A team led by the Vaccine Research Institute recently examined blood samples from Ebola survivors two years after the notorious outbreak and characterized responses from memory T cells. They believe their findings could open up the possibility of improving Ebola vaccines.

“Ebola survivors’ immune responses could help to determine which kind of immune responses have to be induced by a vaccine to efficiently fight the virus,” said Aurelie Wiedemann, the lead author of the study, in a statement. The research was presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases in Amsterdam.

B cell and T cell-mediated processes are key in the immune response to viruses. But little is known about T cell responses to Ebola virus. Wiedemann and colleagues examined 35 Ebola survivors from the observational PostEboGui study in Guinea. They analyzed the responses of helper CD4+ T cells and cytotoxic T cells—which destroy virus-infected cells—against Ebola virus glycoprotein.

By stimulating cells from survivors with Ebola antigens in a lab dish, the scientists showed that memory T cells were present and capable of mounting an immune response, indicating that they might be able to control or clear Ebola, according to the researchers. The population Ebola-specific cytotoxic T cells grew 10.5%, as compared to 0.07% growth in Ebola-free conditions, the scientists reported.

Merck & Co.’s rVSV-ZEBOV (V920), an investigational vaccine for Ebola Zaire strain, has been administered to people under emergency use protocols in previous and ongoing outbreaks in Congo. It’s used in “ring” vaccination, where contacts to known Ebola cases are immunized to stop the virus from spreading.

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In a previous ring vaccination study in Guinea, none of the people who received the shot immediately after exposure to the virus became sick. However, the trial design was controversial, as skeptics worried the results did not accurately reflect the vaccine’s true efficacy.

Last November, Merck started a rolling submission for FDA approval of the vaccine. As of April 8, the drugmaker had donated and shipped nearly 145,000 doses in response to the outbreaks in Congo, Merck recently said in a statement.

Meanwhile, scientists are looking at other methods for fighting the potentially deadly virus. Scientists from the U.S. Army Medical Research Institute of Infectious Diseases previously found that a family of natural killer cell receptors help Egyptian fruit bats tolerate infection with Marburg virus, which belongs to the same filovirus family as Ebola does. In another study, a Stanford University-led team found that the cancer drugs Tarceva and Sutent together inhibited the AAK1 and GAK enzymes, which offered some protection against Ebola in mice.

Wiedemann and colleagues believe their study “could provide critical data to develop strategies for mimicking the resilience which some individuals have demonstrated after being infected, and help to better identify a correlate of protection against Ebola virus disease,” she said in a statement.