Can blood from young people slow aging? Silicon Valley bets yes

To test out his hypothesis, Rando conjoined elderly mice with younger rodents so that they shared the same circulatory system, then tested their ability to heal small wounds. The results were dramatic. Elderly mice were able to repair small tears in their muscles far faster than their peers not conjoined to younger mice. The younger mice, on the other hand, healed far slower than they normally would. The results were exhilarating. They suggested that stem cells could be revitalized simply by reintroducing back into the blood stream the molecules, present in young blood, that could turn them on. The next step was finding the specific youth-promoting factors in the blood responsible for the change. But that would not be easy. "It's as big a fishing expedition as you can possibly imagine," Rando warned at the time, noting the thousands of proteins, lipids, sugars and other small molecules in the blood serum.