Immunologists reported recently that the drug rapamycin, normally used to restrain the immune system after organ transplant, has the unexpected ability to broaden the activity of a flu vaccine.
The results, published in Nature Immunology, indicate that rapamycin steers immune cells away from producing antibodies that strongly target a particular flu strain, in favor of those that block a wide variety of strains. The results could help in the effort to develop a universal flu vaccine.
The finding is just the latest surprise from rapamycin, says immunologist Rafi Ahmed of Emory University in Atlanta, author of the 2009 Nature study that inspired the work. Discovered from a soil sample taken from Rapa Nui, the Polynesian name of Easter Island, rapamycin http://www.raybani.com/ was first developed as an antifungal agent and later found to have immune suppressant and antitumor properties. Then a 2009 study showed that rapamycin also increased lifespan in mice. Ahmed says that he initially studied the drug to see whether long-term use in transplant patients might damage the immune system. “We really wanted to look at whether rapamycin might be screwing up established immunologic memory,” he says. “We had the totally opposite result.”
Ahmed says even though rapamycin has toxic effects in transplant patients who take it for years, clinical trials in adults that combine short-term, low-dose rapamycin treatment with a vaccine make sense. Indeed, he says the U.S. National Institutes of Health seriously considered sponsoring such a trial after his Nature study was published 4 years ago, but the idea stalled. “If you use rapamycin for a couple of weeks, it’s very unlikely something would happen,” he says. “It’s certainly tempting to think about it. And with this study coming out, there’ll be more of an impetus.”
In The Scientist, Ed Yong has some more explanation of rapamycinâ€™s effects. Ironically, memory CD8+ T cells, the focus of Ahmedâ€™s previous study, were not required for rapamycin-mediated protection in the flu experiments.