SCIENTIFIC STUDY REVIEW
Featured Article: Mesenchymal stem cells and secretome as modulators of neuroinflammation in neurological disorders
Original article: https://link.springer.com/article/10.1186/s12967-026-08052-x
Neuroinflammation is the immune response that occurs within the brain and nervous system. In the short term, inflammation can help protect injured tissue and support repair. When it becomes prolonged or poorly regulated, however, it may contribute to continued nerve damage and disease progression.
This process is involved in many neurological conditions, including multiple sclerosis, Parkinson’s disease, Alzheimer’s disease, stroke, traumatic brain injury, spinal cord injury, and amyotrophic lateral sclerosis.
A 2026 review by Yao and colleagues examined how mesenchymal stem cells, also called mesenchymal stromal cells or MSCs, may influence neuroinflammation. The authors focused particularly on the MSC secretome, the collection of biological substances released by these cells.
Purpose and Methodology
The authors reviewed laboratory research, animal studies, and clinical evidence involving MSCs and MSC-derived products across a range of neurological conditions.
The review examined how MSCs interact with immune and nervous-system cells, how they affect major inflammatory pathways, and how substances released by MSCs may contribute to their therapeutic effects.
This publication is a narrative review, not a clinical trial, systematic review, or meta-analysis. It brings together different types of evidence to explain proposed mechanisms and summarize the current state of clinical research.
How MSCs May Affect Neuroinflammation
One of the most important points in the review is that MSCs may not work primarily by replacing damaged nerve cells. Earlier stem cell research often focused on the idea that transplanted cells could develop into new neurons or other tissue. Current evidence suggests that much of the activity of MSCs may instead come from the substances they release into their surrounding environment, a process known as paracrine signaling.
MSCs release cytokines, growth factors, proteins, and extracellular vesicles that can communicate with nearby and distant cells. These signals may help reduce excessive inflammation, protect existing nerve cells, and support the body’s own repair processes.
The review describes effects on two important types of cells in the brain: microglia and astrocytes. Microglia are immune cells that normally help protect the central nervous system. When inflammation persists, some microglia can remain in a more inflammatory state and release substances that contribute to tissue damage. Experimental studies suggest MSCs may help shift these cells toward a more protective and repair-supporting state. MSCs may produce similar changes in astrocytes, which help support nerve cells and maintain the environment around them.
The authors also describe effects on immune cells outside the brain and on the blood-brain barrier, which helps control what can enter brain tissue from the bloodstream.
The Role of Extracellular Vesicles
A major focus of the review is on extracellular vesicles, or EVs. These small particles are released by cells and carry proteins, lipids, and genetic material to other cells. Exosomes are one type of small extracellular vesicle that has received particular attention in regenerative medicine.
MSC-derived EVs can carry microRNAs, anti-inflammatory proteins, and other signaling molecules that may influence pathways such as NF-κB, MAPK, TLR signaling, and the NLRP3 inflammasome. These pathways help regulate the production of inflammatory substances and shape how immune cells respond to injury. The review also discusses proteins such as TSG-6 and several microRNAs that have reduced inflammatory activity in laboratory and animal studies.
Because EVs may reproduce some of the biological effects of MSCs without requiring the administration of living cells, researchers are increasingly studying them as a possible cell-free therapeutic approach.
What the Clinical Evidence Showed
Clinical research is progressing, but results remain mixed. In Alzheimer’s disease, a randomized Phase 2a study of an allogeneic bone-marrow MSC product met its primary safety endpoint and reported possible signals of benefit, including slower decline in some measures of brain volume and improvements in composite clinical scores. In Parkinson’s disease, a Phase 1 study found intravenous allogeneic bone-marrow MSCs to be generally safe and well tolerated. The highest-dose group showed possible improvements in motor scores and inflammatory markers, but the study was small and designed primarily to evaluate safety.
Evidence in multiple sclerosis illustrates the uncertainty. In one randomized Phase 2 trial involving progressive MS, treatment did not meet the primary endpoint for the overall study population. However, a subgroup of patients with greater disability showed improvements in walking speed and bladder function.
A Phase 3 study in amyotrophic lateral sclerosis also did not meet its primary efficacy endpoint in the overall population. A prespecified subgroup with less severe disease showed a possible benefit, and researchers observed changes in biomarkers related to inflammation and neurodegeneration. The review also describes clinical studies in stroke, traumatic brain injury, spinal cord injury, and Huntington’s disease that reported encouraging safety findings and, in some cases, improvements in motor or functional outcomes.
Overall, the authors conclude that safety findings have generally been favorable, but clinical effectiveness remains variable across conditions and products. The most encouraging findings often come from small studies, secondary outcomes, or subgroup analyses, which reinforces the need for larger controlled trials before broad conclusions can be drawn.
Safety and Product Quality
The MSC therapies described in the review were generally well tolerated in clinical studies, but long-term safety remains important. Potential concerns with live-cell treatments include blood clotting or embolic events, unwanted tissue formation, abnormal immune responses, and malignant transformation, although some of these risks remain theoretical.
Cell-free products such as extracellular vesicles may avoid some risks associated with administering living cells, but their long-term effects are also not yet fully understood. Researchers still need to determine how EVs behave in the body, which tissues they reach, and whether higher doses could affect unintended cells.
Product consistency is another major challenge. MSCs can come from bone marrow, fat, umbilical cord, and other tissues, and their properties may vary with donor characteristics, culture conditions, storage, manufacturing techniques, dose, and route of administration. EV-based products introduce additional variability because laboratories use different methods to isolate, measure, and characterize the vesicles. These differences make it difficult to compare results across studies and remain an important barrier to standardizing MSC- and EV-based therapies.
Key Limitations of the Evidence
One of the biggest limitations is the gap between laboratory research and human outcomes.Many of the strongest findings described in the review come from animal models. These studies are useful for understanding biological mechanisms, but they do not guarantee the same results in people.
The authors note that laboratory animals are often young, genetically similar, and otherwise healthy. Patients with neurological disease may be older and have different genetics, medications, disease severity, and other health conditions. These differences may help explain why clinical trial results have been less consistent than preclinical findings.
There is also no established MSC product, dose, delivery route, or treatment schedule that can be applied across neurological diseases.
What the Review Means for Patients
The review provides a strong scientific rationale for continued research into MSCs and their secretome. It also shows why a promising biological mechanism is not the same as proven clinical benefit.
Researchers have identified several ways MSCs may influence inflammation, protect nerve cells, and support repair. Early human studies also suggest that some MSC-based products can be administered safely under controlled research conditions.
However, evidence of effectiveness remains inconsistent, and results from one neurological condition or MSC product cannot automatically be applied to another.
Clinical Takeaway
Yao and colleagues describe an important shift in how MSC therapy is understood. Rather than acting mainly as replacement cells, MSCs may exert much of their effect through the signals they release.
The MSC secretome, including extracellular vesicles, proteins, and microRNAs, may help regulate microglia, astrocytes, immune cells, and major inflammatory pathways involved in neurological disease.
The clinical evidence is still limited and mixed. Some trials have reported encouraging results, while others have not shown clear overall benefits or have found possible benefits only in certain groups of patients.
These findings support continued research rather than broad claims of effectiveness. Larger placebo-controlled trials, standardized manufacturing, reliable potency testing, consistent dosing, and longer follow-up are still needed.
Patients should not discontinue prescribed neurological treatments or replace care from a qualified physician based on these findings.
Reference
Yao D, Nie L, Liu X, et al. Mesenchymal stem cells and secretome as modulators of neuroinflammation in neurological disorders. J Transl Med. 2026;24:621. doi:10.1186/s12967-026-08052-x. View Article
Regulatory Disclaimer
Stemedix provides this review for educational and informational purposes only and represents an academic commentary on published literature. The findings do not establish a treatment as safe or effective for any individual and should not be interpreted as medical advice. Patients should consult a qualified physician before changing prescribed care.
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