Dr. David Fajgenbaum was a third-year medical student when he “got critically ill out of nowhere.” After taking an important exam, he walked down the hall to the hospital's emergency room and underwent blood tests. “The doctor looked at me and said, ‘David, your liver, your kidneys, your bone marrow, your heart, and your lungs are all shutting down. We have to hospitalize you right away.’”
Eleven weeks later, following a rapid decline, Fajgenbaum’s doctors told his family he wasn't going to make it. A priest hovered over him, reading him his last rites. He was 25 years old and dying from an inflammatory condition called Castleman disease, which is so rare it wasn’t even taught in medical school. “I turned to my dad, my sisters, and my girlfriend, and I told them I was going to dedicate the rest of my life—however long that might be—to trying to find a drug that could save my life,” he says.
Fajgenbaum started asking his doctors to save blood samples and lymph node tissues for him to run experiments on—and found that he had a defect called mTOR hyperactivation, which his doctors had missed. His research led him to an mTOR inhibitor called sirolimus that’s been used to prevent organ transplant rejection for years. Because of the pathway it targeted, he suspected it might improve his disease. He told his doctors about it, one of whom prescribed it, and Fajgenbaum started taking it. It ended up saving his life—and now, more than a decade later, he continues to take three pills a day. Sirolimus has changed the treatment protocol for Castleman disease.
The experience inspired Fajgenbaum to figure out which other drugs already approved by the U.S. Food and Drug Administration could be repurposed to treat the many diseases that have no recourse. “Doctors are allowed to prescribe any drug for any disease where they think the benefit outweighs the risk,” he says. “This drug [sirolimus] was out there—how many more are out there that could save other lives, if only people were looking for them?”
In 2022, Fajgenbaum founded Every Cure, a nonprofit that uses AI to identify potential new uses for already-approved drugs. It works by comparing 4,000 drugs against 18,500 diseases, scoring each one on its likely efficacy. Once the team pinpoints promising uses, they either start testing them in the lab or connect with doctors eager to prescribe them. “People were literally dying of these diseases before, and now they can live with these solutions that were already there,” he says. In 2024, the Advanced Research Projects Agency for Health (ARPA-H) awarded the group $48 million to further develop its AI platform.
In total, Fajgenbaum’s team has identified or advanced 14 repurposed treatments for five rare diseases. Fajgenbaum recalls talking to one man who benefited from a newly discovered treatment option and was able to walk his daughter down the aisle on her wedding day. A young woman was so grateful for her life-saving treatment that she decided to become a nurse. “I get chills when I think about what these people are able to do, and it's not like we even had to create a new drug,” he says. “All I can think about is the impact and how many lives we can touch. It's just a matter of how fast we can do it, because we’re in a race against time.”