Abstract
The rapid clinical expansion of therapies based on stem cells and cell-free extracellular vesicles (EVs) has outpaced the development of rigorous quality control standards. Current Good Manufacturing Practice (GMP) standards evaluate identity, viability, sterility, and genetic stability, but do not routinely assess protein homeostasis in donor cells. Cellular senescence, which frequently emerges during ex vivo expansion, impairs protein quality control and yields an EV secretome enriched with proteotoxic cargo. In neural stem cells (NSCs), oxidized superoxide dismutase 1 (SOD1) accumulates during senescence and is packaged into EVs that propagate neuronal toxicity and secondary senescence in recipient cells. While established primarily in NSCs, analogous proteostatic decline across other stem cell types warrants targeted validation in mesenchymal stromal cell (MSC) and induced pluripotent stem cell (iPSC)-derived products. Donor cell proteostatic fitness is a plausible determinant of therapeutic outcome. Evaluating senescence burden and EV proteomic integrity should therefore become a standard critical quality attribute within cell and EV manufacturing pipelines. Practical steps toward this goal include the careful selection of cell sources, the establishment of quantitative senescence thresholds, and proteomic profiling of EV cargo. Targeted cargo sanitization strategies, such as selective clearance of misfolded SOD1, shows promise for pre-transplant conditioning, although clinical feasibility, scalability, and off-target effects require further study.