Aging Stem Cells Lose Their Healing Power, Landmark Review Finds

Mesenchymal stem/stromal cells, or MSCs, have long been celebrated as the workhorses of regenerative medicine. Harvested from bone marrow, fat, dental pulp, periodontal ligament, and umbilical cord tissue, these cells can self-renew, morph into bone, cartilage, and fat lineages, and calm overactive immune responses. Hundreds of clinical trials have tested them for everything from broken bones to autoimmune disease. But a new systematic review published in the journal Biogerontology delivers a sobering message: when MSCs become senescent, they lose many of the very properties that make them therapeutically valuable, and transplanting them may even backfire.

The review, led by Letícia Odaguiri Watanabe and colleagues at the University of Brasília in Brazil, followed PRISMA 2020 guidelines with a protocol registered in PROSPERO. The team searched MEDLINE/PubMed, EMBASE, Web of Science, and the Cochrane Library, supplemented by grey literature searches in Google Scholar and ProQuest and manual screening of reference lists. From 4,857 initial records, the researchers ultimately included 45 studies published between 2006 and 2025, of which 35 were purely in vitro and 10 combined laboratory and animal work. Every included study had to examine human, primary, non-genetically modified MSCs, confirm senescence with at least one established marker, and compare senescent cells against non-senescent counterparts.

A central strength of the review is its explicit framing of three distinct senescence contexts. Chronological aging reflects donor-related variability, the reality that cells from an elderly patient behave differently from those of a young one. Serial passaging captures the wear and tear inflicted during laboratory expansion, a critical manufacturing step for any cell therapy product. Inflammatory stimulation, the least studied of the three, mimics the hostile, cytokine-rich environment of chronic wounds where transplanted MSCs are expected to work. The authors argue that these contexts are biologically distinct, yet the field has rarely compared them head to head, leaving clinicians unsure which form of senescence matters most for a given therapy.

The most consistent finding across all 45 studies is a dramatic decline in proliferative capacity. Whether senescence was triggered by donor age, repeated passaging, or inflammatory stress, and regardless of whether the cells came from fat, marrow, or dental tissue, senescent MSCs divided far less readily than their youthful counterparts. The authors attribute this universal loss to the core senescence machinery, chiefly the activation of the p16 and p21 cell cycle checkpoints, which appears robustly conserved across MSC populations. In practical terms, this means aged or over-expanded cell products may simply not contain enough viable, dividing cells to mount an effective regenerative response.

Differentiation, by contrast, proved far more resilient and far more confusing. Osteogenic differentiation was variably affected: under chronological aging, roughly half of the relevant studies reported reduced bone-forming potential in adipose-derived, bone marrow-derived, and dental pulp-derived cells, but occasional studies described preserved or even enhanced osteogenesis depending on donor characteristics. Serial passaging produced similarly mixed results, with some studies reporting impaired osteogenesis and others finding no significant difference or even increased bone differentiation in late-passage cells. Adipogenic and chondrogenic outcomes ranged from functional impairment to unexpected gain-of-function, with no consistent pattern across senescence models or cell sources. The authors suggest that the multilineage differentiation program may simply be less sensitive to senescence-associated changes than the cell cycle machinery itself.

Two clinically important functions emerge as clearly senescence-sensitive. The first is migration, the ability of MSCs to home to sites of injury. Although only a handful of studies assessed it, every one that did reported impaired migratory capacity in senescent cells derived from dental pulp, bone marrow, and periodontal ligament, under both aging and passaging models. Since homing is essential for transplanted cells to reach damaged tissue, this convergence has direct implications for therapeutic efficacy. The second is immunomodulation. Senescent MSCs shift their secretory profile toward the senescence-associated secretory phenotype, or SASP, releasing pro-inflammatory cytokines such as TNF-α, IL-6, IL-1β, and IL-8, alongside variable changes in anti-inflammatory mediators like IL-10 and TGF-β1. Rather than uniformly losing their immunosuppressive function, senescent MSCs appear to rewire it, sometimes in ways that fuel chronic inflammation instead of resolving it.

The in vivo evidence, though sparse, points in the same troubling direction. In animal models, senescent MSCs from bone marrow, dental pulp, and periodontal ligament showed impaired mineralization, reduced bone formation, and compromised new blood vessel formation. Aged dental pulp stem cells, for example, generated significantly less pulp regeneration and vascularized tissue than young cells. The authors highlight a particularly insidious mechanism: the bystander effect, in which senescent cells secrete pro-inflammatory cytokines and reactive oxygen species that propagate senescence to neighboring healthy cells and suppress the body’s own regenerative response. In other words, a bad batch of cells may not merely fail to heal; it may actively poison the healing environment.

Why, then, has the literature been so inconsistent? The review identifies a thicket of methodological culprits. Donor age definitions vary widely, and studies that label mature adults as aged may mask the full extent of functional decline. Senescence confirmation methods differ, with SA-β-gal staining used in over 91 percent of studies, p16 expression in about half, and p21 and p53 in fewer. There are no unified thresholds for how much senescence must be present before a cell counts as senescent, and culture conditions and analysis timing vary from lab to lab. Small sample sizes and frequent reliance on qualitative or non-comparative analyses compound the problem. The authors also acknowledge a potential selection bias in their own search strategy, which relied on the historically dominant term mesenchymal stem cell rather than the currently recommended mesenchymal stromal cell, potentially missing studies that used only the latter terminology.

Risk of bias assessments add further caution. Most in vitro studies scored low overall risk using a PETRICCS-based appraisal tool, though reporting of blinding, randomization, and replicate numbers was often incomplete. The in vivo studies, evaluated with SYRCLE’s tool, showed low to moderate methodological quality, with frequent deficiencies in blinding, random housing, and selective outcome reporting. With no clinical trials included and most evidence coming from laboratory dishes, the authors stress that translational interpretation remains limited. The heterogeneity was so substantial that a quantitative meta-analysis was impossible; all results were synthesized narratively.

Nevertheless, the review’s conclusions carry real weight for the future of cell therapy. Donor age, culture expansion, and inflammatory exposure emerge as critical determinants of MSC product quality, and the authors call for standardized senescence screening, inflammatory profiling, functional quality control criteria, and defined upper passage limits for clinical-grade cells. They also urge future studies to adopt standardized senescence models, make direct comparisons across tissue sources, and prioritize in vivo models with clinically relevant endpoints, alongside strategies to prevent or reverse senescence-related decline. As the population ages and demand for regenerative therapies grows, the message is clear: the age of the cells may matter as much as the age of the patient, and ensuring that only young, vigorous MSCs reach the clinic could mean the difference between a therapy that heals and one that quietly makes things worse.

Subject of Research: Cellular senescence in mesenchymal stem/stromal cells and its impact on regenerative medicine

Article Title: Mesenchymal stem/stromal cell senescence in aging and regenerative medicine: a systematic review

Article References: Watanabe, L. O., Cardoso, L. R., Silva, J. C. D., Di Carvalho, L., Castro, V., Carvalho, J. L., Guerra, E., & Rezende, T. M. B. (2026). Mesenchymal stem/stromal cell senescence in aging and regenerative medicine: a systematic review. Biogerontology, 27(5), Article 167. https://doi.org/10.1007/s10522-026-10501-5

Image Credits: AI Generated

DOI: 10.1007/s10522-026-10501-5

Keywords: mesenchymal stem cells, cellular senescence, SASP, aging, regenerative medicine, tissue engineering, systematic review, p16, p21, proliferation, immunomodulation, cell therapy