Scientists Transform Old Blood Cells Into Rejuvenating Brain Stem Cells

A team of researchers at the University of Bonn and University Hospital of Bonn has accomplished something that sounds like biological fiction: they took blood cells from people ranging in age from newborns to a 101-year-old, converted them into brain stem cells, and watched those new cells grow progressively younger over the course of two months.

The work hinges on a fundamental fact about how cells work. Once a stem cell becomes specialized—a fat cell, a muscle cell, a blood cell—it stays that way. The transformation is permanent. Scientists have long known they could reverse this process by pushing a cell all the way back to an embryonic blank slate, then coaxing it into a new form. But that route is circuitous and time-consuming. The Bonn team took a shortcut. They used a virus to deliver two genetic factors directly into erythroid progenitor cells, the immature precursors to red blood cells, and forced them to become induced neural stem cells—the building blocks of brain tissue. No embryonic detour required.

By day twelve, the cells had switched identities. They shed their blood-cell proteins and began expressing the proteins of neural cells. The researchers then tracked what happened next using two methods that read the epigenetic clock—the accumulated DNA changes that mark biological aging. What they found was counterintuitive: the converted cells didn't just reset to a younger state and stay there. They kept getting younger. Over fifty to one hundred days, the cells continued to de-age, eventually reaching an epigenetic age equivalent to only about five percent of the donor's actual age. A cell from a sixty-year-old donor, in other words, became biologically equivalent to a cell from a three-year-old.

But the question that matters is whether this was real rejuvenation or merely cosmetic. Oliver Brüstle, director of the Institute of Reconstructive Neurobiology at the University Hospital of Bonn, and his colleagues tested this directly. The rejuvenated cells didn't just look young on paper—they behaved like young cells. They showed less DNA damage, lower mitochondrial toxicity, and better recycling abilities than their aged counterparts. They continued to grow younger even when conditions prevented them from dividing, suggesting their rejuvenation wasn't simply a side effect of cell division. The converted cells matched the functional benefits of cells that had been reset all the way to the embryonic stage, but through a far more efficient route.

The implications reach toward treatment. Previous work by the same Bonn group showed that engineered neural cells could integrate into mouse brains and form connections with existing neural tissue. That opens a door to potential therapies for neurodegenerative diseases, where the brain's own stem cells have aged and lost function. But before that future arrives, the researchers see immediate value in the current work as a research tool. The slow, extended rejuvenation—unfolding over weeks rather than days—creates an ideal window for studying what accelerates or slows the aging process itself. Brüstle notes that this extended timeline allows investigators to test which factors and substances might speed up or inhibit cellular rejuvenation, turning the converted cells into a living laboratory for understanding aging at its most fundamental level.

The study does carry limitations. The researchers acknowledge potential mathematical biases in how they measured de-aging, the lack of naturally aged neural stem cells to use as a direct comparison, and the uncertainty about whether cells behaving one way in a dish will behave the same way inside a living brain. But the core finding stands: old blood cells can be transformed into neural stem cells that grow younger as they age, and those cells function like genuinely young tissue. The work was published in the journal Aging Cell.