In the early 2000s, a handful of young scientists at Stanford turned the university’s Palo Alto campus into the mouse-stitching-together capital of the world. Reviving a centuries-old procedure known as parabiosis, they connected the circulatory systems of dozens of pairs of rodents, young sutured to old, so that they’d pump one another’s blood back and forth. The grisly experiments rejuvenated the aging mice, making them stronger and healthier, and introducing the 21st century’s longevity enthusiasts to the therapeutic potential of young blood.

While much work remains to be done on how this regenerative process actually works, Stanford’s parabiosis studies have since inspired the creation of a handful of ambitious startups aimed at producing similarly dramatic effects in humans. Today, the latest young-blood medicine-maker, Elevian, emerged from stealth with $5.5 million from investors including Peter Diamandis, one of the more prominent faces in the Silicon Valley “death disruption” scene.

Beneath all the hype is some striking science. Blood, particularly the yellow liquid part of it known as plasma, is chock full of proteins and other compounds that act like a readout of how all the cells in the body are functioning. Research has shown that the ratios of those components change as animals, including humans, age. Older blood carries more signs of tissue damage than young blood, which often contains compounds that can stimulate cell growth and repair. Elevian has singled out one of these proteins, a growth differentiation factor known as GDF11, as the chief source of young blood’s rejuvenating effects.

At the outset, the company is developing drugs based on GDF11 to treat Alzheimer’s, coronary heart disease, and age-related muscle dysfunction. But its founders say any disease of the elderly is on the table. “What’s really unique here is that you can improve the function of tissue that’s already been damaged, regardless of what caused the damage,” says Lee Rubin, a neuroscientist at Harvard and one of Elevian’s five scientific cofounders. “That suggests a way forward for treating many different disorders.”

Rubin began studying longevity in 2006, when he left a career in biotech to join the Harvard faculty. He soon found himself teaching a course on aging with a young stem cell biologist named Amy Wagers, a pioneer of Stanford’s parabiosis studies. She was looking for collaborators to continue her work on the East Coast, to tease out the impact of young blood on different kinds of tissues. Together they discovered that young blood sparks the formation of new neurons in the brain. Working with other Harvard researchers, Wagers found that it could also reverse age-related thickening of the walls of the heart.

Bolstered by these results, Wagers and her collaborators went looking for the ingredients in young blood responsible for the rejuvenating effects. One molecule, a growth protein known as GDF11, jumped out. In two eye-popping papers in Science in 2014, Wagers’ group reported that GDF11, injected on its own, made old mice stronger, increased blood flow to their brains, and even improved their memories. Those results have since become a subject of sore scientific debate—researchers at pharmaceutical firm Novartis published a subsequent report suggesting that high doses of GDF11 actually cause muscle wasting in mice.

Despite the controversy, Elevian has licensed the Harvard team’s portfolio of patents around GDF11, which includes the protein as it’s found naturally in the body, according to cofounder and CEO Mark Allen. One challenge is that GDF11 degrades quickly, so he says Elevian is also investigating drug formulations that don’t require daily injections. “We’re working with biology, so we have to respect its complexity,” Allen says.