Posted on 09/22/2025 11:44:28 AM PDT by Red Badger
In A Nutshell
* Stroke-injured mice that received lab-grown brain cells regained smoother walking and better coordination compared to untreated mice.
* Most transplanted cells matured into working brain cells, and many became the very type of nerve cells that strokes usually wipe out.
* The therapy didn’t just fill gaps: it calmed brain inflammation, strengthened tiny blood vessels, helped seal the brain’s natural protective barrier, and nudged the brain’s own stem cells to grow new neurons.
* If ongoing safety tests succeed, researchers think the first human trials could begin in the next 5–7 years.
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ZURICH, Switzerland — Scientists have shown that transplanting lab-grown brain cells into stroke-damaged tissue can improve motor skills and encourage repair in brain circuits that were once thought beyond recovery. In a new study, researchers found that mice given these cellular transplants regained coordination and movement patterns that had been severely impaired by stroke.
Led by a team at the University of Zurich (UZH) Institute for Regenerative Medicine, researchers grew human stem cells into specialized brain cells called neural progenitor cells (NPCs) and transplanted them into the brains of mice after a stroke. The transplanted cells survived for more than five weeks and interacted with surrounding brain tissue in ways that promoted healing.
How Mice Recovered Movement Lost From Stroke Damage
To test whether the therapy worked, researchers tracked the animals’ movements using advanced video analysis. Mice that received the transplant walked with smoother patterns, placed their paws more accurately, and showed better coordination than mice given sham treatments.
The study followed 28 mice that experienced a stroke in the sensorimotor cortex, a brain region that controls movement. One week later, half the mice received 250,000 NPCs injected directly into the damaged tissue, while the rest received only vehicle solutions.
Five weeks later, the differences were clear. In precise ladder-walking tests, mice without treatment continued to stumble with their affected limbs, while those with transplanted cells performed much closer to healthy animals.
Human neural stem cells in culture. Cell nuclei are stained in blue, the neural stem cell-specific filament protein Nestin is shown in green, and the neural stem cell transcription factor Sox1 in red. (Credit: UZH)
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What The Transplanted Stem Cells Became
Inside the brain, the transplanted cells did not stay in their progenitor form. Instead, about 78 percent developed into mature neurons. Nearly half of those became GABAergic interneurons, the very type of neuron commonly lost during stroke and linked to lasting disability.
Genetic analysis confirmed that the new neurons carried markers typical of these interneurons and had extended connections into surrounding brain regions. This suggests they were not just surviving, but attempting to integrate into existing brain circuits.
How The Cells Supported Repair
The study, published in Nature Communications, also uncovered how the transplanted cells influenced recovery beyond simply replacing lost neurons. Analysis revealed that the grafts communicated with host tissue using several molecular signaling pathways, including neurexin, neuregulin, neural cell adhesion molecule, and SLIT.
These interactions were linked with a broad set of improvements. Mice that received the therapy had stronger blood vessel growth in damaged areas, reduced inflammatory signals, and more stable blood–brain barrier function. The treatment also appeared to stimulate the brain’s own stem cells in a region called the subventricular zone, which produced new neurons.
The research team concluded that the transplanted cells acted like coordinators, replacing missing neurons while also encouraging the brain’s natural repair mechanisms.
This image shows a coronal section through the mouse brain after stroke and neural stem cell transplantation. The dashed circle indicates the stroke area. The neurite projections of the transplanted human cells are stained in dark brown. Neurites extend locally into the cortex (CX) but also via the corpus callosum (CC) into the other brain hemisphere. (Credit: UZH)
What Still Stands In The Way
Despite these promising findings, important barriers remain before the approach can be tried in people. The study was conducted in immunodeficient mice, which means the animals could not reject the human cells. In real-world patients, immune rejection would be a serious concern.
The research also did not directly prove that the transplanted neurons formed fully functional connections with the brain’s existing circuits. While earlier work hints that such integration can occur, this remains to be confirmed in future studies.
Timing, location, and dosage are also unknown for human stroke survivors. Past clinical trials using other types of stem cells for stroke recovery failed to produce consistent benefits, highlighting the challenges in translating animal results into patient care.
Even so, this study has advantages compared with older attempts. The neural progenitor cells were generated using standardized clinical procedures without genetic modification, making them suitable for medical-grade production. Safety features have also been built into the cells, including switches that could be used to eliminate them if problems arise.
The authors believe that, if safety studies continue to succeed, first-in-human trials might be possible within the next five to seven years. “We need to minimize risks and simplify a potential application in humans,” says Christian Tackenberg, the Scientific Head of Division in the Neurodegeneration Group at the UZH Institute for Regenerative Medicine. “Stroke could be one of the next diseases for which a clinical trial becomes possible.”
Disclaimer:
This article is for general informational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for guidance on medical conditions or treatments.
Paper Summary
Methodology
The researchers used a photothrombotic stroke model in immunodeficient Rag2-/- mice to create reproducible brain damage in the sensorimotor cortex. Human induced pluripotent stem cells were differentiated into neural progenitor cells using a defined, xeno-free protocol. Seven days post-stroke, 250,000 NPCs were transplanted directly into the peri-infarct tissue adjacent to the stroke core. The study followed 28 mice (11 NPC-treated, 11 vehicle controls, 4 sham controls) for 43 days using behavioral testing, bioluminescence imaging to track cell survival, and endpoint histological analysis.
Results
Transplanted NPCs survived for over 5 weeks and differentiated primarily into neurons (78% MAP2-positive), with 44% becoming GABAergic interneurons based on single-nucleus RNA sequencing. NPC treatment led to significant improvements in motor function as measured by rotarod testing and automated gait analysis using DeepLabCut software. Treated mice showed enhanced angiogenesis, reduced microglial activation, increased neurofilament expression, and improved blood-brain barrier integrity. Single-cell analysis revealed graft-host communication through neurexin, neuregulin, NCAM, and SLIT signaling pathways.
Limitations
The study was conducted in immunodeficient mice rather than immunocompetent animals, limiting clinical translation. Functional integration of transplanted neurons was not directly demonstrated through electrophysiological recordings. The research used external reference datasets for RNA sequencing analysis which may introduce batch effects. Long-term safety beyond 43 days was not assessed, and the optimal transplantation parameters for humans remain undefined.
Funding and Disclosures
This work was supported by the Swiss 3R Competence Center, Swiss National Science Foundation, Neuroscience Center Zurich, and Mäxi Foundation. The authors declared no competing interests. One co-author (Roger M. Nitsch) is affiliated with Neurimmune, a biotechnology company, though no specific conflicts were reported.
Publication Information
Weber RZ, Achón Buil B, Rentsch NH, et al. “Neural xenografts contribute to long-term recovery in stroke via molecular graft-host crosstalk,” published in Nature Communications on September 16, 2025. DOI: 10.1038/s41467-025-63725-3.
Way cool!
I was wondering if it could work to restore missing brains in Rats? I am referring to democRATS naturally.
Try it out on a mentally slow janitor, of course!
In a related story, the stroke-damaged mice still had higher IQs that Ocrazio-Cortex and Jazzy Crockfull combined.
If I ever see a stroke damaged mouse I’ll be sure to pass this along.
Democrat John Fetterman has a stroke and upon recovery ends up smarter.
What’s going to be “fun” is when they learn to repair and/or splice spinal cords. This could potentially lead to brain transplants. See Heinlein’s “For Thou Art With Me” for possible outcomes.
But walking like a mouse doesn't cut it.
Egyption = Egyptian
Indeed!!
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