Stem cell and cell-free extracellular vesicle (EV) therapies are entering clinical practice faster than their quality-control systems can adapt. This review argues that proteostatic fitness—the ability of donor cells to maintain protein homeostasis under stress—is an overlooked determinant of therapeutic success. Senescence during ex vivo expansion can impair protein quality control and enrich EV cargo with proteotoxic species, including oxidized superoxide dismutase 1 (SOD1). The authors propose that senescence burden and EV proteomic integrity should become critical quality attributes, with targeted clearance of misfolded SOD1 as a possible pre-transplant strategy. Such measures could better align manufacturing release tests with the oxidative and inflammatory stress that cells face after transplantation.
Current Good Manufacturing Practice (GMP) standards for cell therapies assess identity, viability, sterility, and genetic stability. For extracellular vesicle (EV) products, Minimal Information for Studies of Extracellular Vesicles (MISEV2023) guidance adds particle size, concentration, markers, morphology, contaminants, endotoxin, and assays. Yet these checks rarely evaluate protein homeostasis in donor cells. During ex vivo expansion, stem cells can accumulate senescent cells that release inflammatory factors and damaged proteins. Senescent cells show declining heat shock responses, proteasomal activity, and autophagic flux, reducing capacity to handle misfolded proteins. Because EV cargo reflects parent-cell state, these defects may be transmitted to recipient cells. Given these challenges, deeper research is needed into proteostatic quality control across mesenchymal stromal cell (MSC) and induced pluripotent stem cell (iPSC)-derived products.
Published (DOI: 10.1016/j.rerere.2026.06.004) online 9 June 2026 in Regenesis Repair Rehabilitation , a review by researchers at the University of Manitoba in Canada and Zhujiang Hospital of Southern Medical University in China examines proteotoxic stress in stem cell therapies. The authors focus on senescence, EV cargo, and superoxide dismutase 1 (SOD1), arguing that donor-cell protein quality control is not routinely assessed by current release standards. They outline practical steps for cell-source selection, senescence gating, EV proteomic profiling, and pre-transplantation cargo sanitization. The article is a review and does not report new primary data; it synthesizes existing evidence and proposes quality-control changes.
The review details how ex vivo expansion drives senescence, marked by increased p16/p21, senescence-associated β-galactosidase (SA-β-Gal) activity, persistent DNA damage, and a senescence-associated secretory phenotype (SASP). In mesenchymal stromal cells (MSCs), early-passage cells mount a heat shock response through heat shock factor 1 (HSF1) and 70-kDa heat shock protein (Hsp70); senescent cells lose this protection as HSF1 activity declines and stress-response genes are epigenetically suppressed. In neural stem cells (NSCs), wild-type human SOD1 becomes oxidatively modified with passage, alongside p53 elevation, SA-β-Gal activity, and cytoplasmic high mobility group box 1 (HMGB1) translocation. Oxidized SOD1 promotes mitochondrial-derived vesicle (MDV) formation; these EVs carry oxidized SOD1 and aging biomarkers, triggering mitochondrial dysfunction and secondary senescence in recipient cells. CRISPR-Cas9 screening in aged NSCs identified 24 gene knockouts, including B3galnt2 and CDKN1A (encoding p21), linking protein quality control and post-translational modification to aging. EV cargo reflects parent-cell state, and misfolded SOD1, trans-activation response element (TAR) DNA-binding protein 43 (TDP-43), and α-synuclein can seed aggregation in recipient cells. Proteasomal activity declines and autophagic flux becomes dysregulated in senescent stem cells. Current MISEV-based release tests still do not routinely screen for pathological proteins.
The authors said the field should treat proteostatic fitness as a release-critical attribute, not a research footnote. They said a product can pass identity, viability, and sterility tests yet still carry a protein-handling defect that only becomes obvious after transplantation. They added that senescence screening and EV cargo profiling could help manufacturers choose healthier donor cells, reduce batch-to-batch variability, and prevent the spread of proteotoxic species to patients. They cautioned that thresholds must be harmonized and that peptide-based sanitization still needs safety and scalability testing.
The framework includes cell-source selection, quantitative senescence thresholds, and proteomic profiling of EV cargo. For neurodegenerative applications, assays for misfolded or oxidized SOD1 could serve as exclusion criteria. Pre-transplantation cargo sanitization with the CT4 peptide has reduced spinal cord SOD1 burden by more than 50% within 48 hours and extended survival in SOD1 ^G93A mice, but feasibility, cost, scalability, immunogenicity, and off-target effects remain unresolved. If validated in MSC and iPSC products, these measures could improve therapies for acute graft-versus-host disease (aGVHD), cardiac repair, orthopedic injury, renal disease, and amyotrophic lateral sclerosis (ALS). They call for multi-site harmonization before universal release criteria.
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References
DOI
Original Source URL
https://doi.org/10.1016/j.rerere.2026.06.004
Funding i nformation
This work was supported by the ALS Canada/Brain Canada Foundation.
About Regenesis Repair Rehabilitatio n
Regenesis Repair Rehabilitatio n publishes rigorously peer-reviewed high-quality research articles, concise reviews, clinical studies, and short communications on topics relevant to the tissue/organ regeneration, repair and rehabilitation, particularly the skin tissue and its appendages. The journal covers the stem cell areas concerned with investigations about stemness maintenance and differentiation, organoids for grafting, and materials/biomaterials for injured tissue protection, healing promotion, and regeneration, 3D printing for tissue reconstruction, and novel techniques, methods, and progresses in the surgical and rehabilitation areas. The submission of manuscripts conveying original findings or thoughtful reviews concerning all the above fields of endeavor, which potentially contribute to Translational Medicine, are encouraged.
Regenesis Repair Rehabilitation
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Proteotoxic stress in stem cell therapies: The overlooked roles of senescence, EV cargo, and SOD1
9-Jun-2026
The authors declare that they have no competing interests.