Scientists Shave 60 Years Off Human Cells by Turning Blood Into Brain Stem Cells

A Remarkable Biological Clock Reset

Imagine taking a blood sample from an 80-year-old and watching it transform — at the cellular level — into something that looks and acts like tissue from a teenager. That's exactly what scientists in Germany have achieved. Researchers from the University Hospital of Bonn and the University of Bonn have succeeded in dramatically rejuvenating human cells in a test tube by directly reprogramming red blood cell precursors into stem cells from which neurons can be derived — and during this process, the molecular clocks that indicate a cell's age were reset. The findings, published in the journal *Aging Cell*, offer scientists an unusually slow and therefore unusually observable version of a process that has long fascinated biologists: the reversal of cellular aging.

The cells' epigenetic clocks were significantly reset by the reprogramming. As a result, cells from an 80-year-old subsequently exhibited a molecular age of less than 20 years. That's not a modest improvement — it's a rollback of more than six decades of biological aging, achieved in a laboratory dish.

How the Science Actually Works

To achieve this reprogramming, researchers use a cocktail of various transcription factors. These factors cause the cell to read different genetic instructions and thus embark on a different developmental path. More specifically, the research team used a Sendai virus system to deliver just two transcription factors, SOX2 and cMYC, into erythroid progenitor cells derived from easily accessible blood samples. The simplicity of the starting material — ordinary blood — is part of what makes this approach so compelling.

What sets this method apart from previous reprogramming techniques is the route taken. It had previously only been observed when reprogramming took place in two steps: a blood cell is taken and converted into a pluripotent stem cell, which has virtually all "career paths" in the body open to it, and this stem cell is then induced to develop into a neural stem cell. Rejuvenation occurs very rapidly with this two-step method. In contrast, the Bonn research team bypassed the pluripotent stage entirely. The result was a slower, more gradual transformation — and that turns out to be a scientific gift. In their approach, rejuvenation occurred gradually and could be tracked for over 100 days.

More Than Skin Deep — These Cells Actually Behave Young

The research team tracked aging by measuring molecular clocks that record DNA modifications driven by epigenetics — modifications that alter how frequently genetic information is read without changing the underlying DNA sequence. Using the epigenetic clock algorithm developed by Steve Horvath and colleagues, the researchers measured DNA methylation age across the conversion time course. While the starting blood cells correlated precisely with the chronological age of their donors, the converted neural stem cells at low passage carried a DNA methylation age averaging only about thirteen percent of the donor's chronological age.

Crucially, this isn't just a cosmetic change on paper. As Brüstle stated, "We also know that this epigenetic rejuvenation ensures that the cells actually behave like young cells." And the team's earlier work already showed real-world function: in previous studies, the Bonn researchers had already shown that nerve cells produced in this way form connections with existing neurons after transplantation into the brains of mice.

Why This Could Matter for Brain Disease

The lead researcher noted that "rejuvenation that extends over such a long period of time is ideal as an experimental model: since the epigenetic clocks are slowly reset over several weeks, we can use this model to investigate which factors and active substances accelerate or slow down the rejuvenation process." That slow-burn timeline gives scientists an unprecedented window to study the mechanics of cellular aging in real time.

Prof. Brüstle emphasized that this is particularly relevant for the field of neuroscience: "After all, age is the most important risk factor for neurodegenerative diseases such as Alzheimer's!" The authors note that understanding and controlling cellular rejuvenation may be highly relevant to neuroscience, and the ability to derive young-appearing neural stem cells from aged blood cells could help researchers study how aging contributes to neurodegeneration and screen treatments that modify cellular aging processes. The study was a collaboration between research groups from the University Hospital of Bonn, the University of Bonn, and RWTH Aachen University, and was funded by the EU's Horizon 2020 program, the German Research Foundation, and the Federal Ministry of Research, Technology, and Space. As the science matures, the possibility of one day treating aging brains with a patient's own rejuvenated cells moves from science fiction closer to the realm of the possible.