F.or years now, biologists have practiced a kind of time travel. You can take a piece of human skin and, with the right genetic modifications, turn back the inner clock until it becomes its embryonic self, stripped of its identity, and ready to become just about any human body part. Since the method’s publication in 2006, transforming adult cells into stem cells has enabled all kinds of advances. Researchers can grow organs in dishes. They can replicate what’s happening in the womb without the regulatory headaches of getting fetal tissue. It became an everyday tool on laboratory benches around the world and won a Nobel Prize.
But for David Sinclair’s purposes that was not good enough. His interest was in reversing the slings and arrows of old age, using that genetic time machine to create something that would be truly therapeutic. When cells were backwashed to an embryo-like state, they did what embryonic cells do: divide like crazy. Beyond the complicated control of the prenatal environment, that led to cancer. The mice used in such experiments died within days. “We wanted to take back the age of a tissue, but find a way to keep it from going back too far,” said Sinclair, a professor of genetics at Harvard Medical School.