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Objectives To define the features of human amniotic mesenchymal stromal cell secretome and its protective properties in experimental models of acute brain injury. Design Prospective experimental study. Setting Laboratory research. Subjects C57Bl/6 mice. Interventions Mice subjected to sham or traumatic brain injury by controlled cortical impact received human amniotic mesenchymal stromal cells or phosphate-buffered saline infused intracerebroventricularly or intravenously 24 hours after injury. Organotypic cortical brain slices exposed to ischemic injury by oxygen-glucose deprivation were treated with human amniotic mesenchymal stromal cells or with their secretome (conditioned medium) in a transwell system. Measurements and main results Traumatic brain injured mice receiving human amniotic mesenchymal stromal cells intravenously or intracerebroventricularly showed early and lasting functional and anatomical brain protection. cortical slices injured by oxigen-glucose deprivation and treated with human amniotic mesenchymal stromal cells or conditioned medium showed comparable protective effects (neuronal rescue, promotion of M2 microglia polarization, induction of trophic factors) indicating that the exposure of human amniotic mesenchymal stromal cells to the injured tissue is not necessary for the release of bioactive factors. Using sequential size-exclusion and gel-filtration chromatography, we identified a conditioned medium subfraction, which specifically displays these highly protective properties and we found that this fraction was rich in bioactive molecules with molecular weight smaller than 700 Da. Quantitative RNA analysis and mass spectrometry-based peptidomics showed that the active factors are not proteins or RNAs. The metabolomic profiling of six metabolic classes identified a list of molecules whose abundance was selectively elevated in the active conditioned medium fraction. Conclusions Human amniotic mesenchymal stromal cell-secreted factors protect the brain after acute injury. Importantly, a fraction rich in metabolites, and containing neither proteic nor ribonucleic molecules was protective. This study indicates the profiling of protective factors that could be useful in cell-free therapeutic approaches for acute brain injury.

Investigators developing cellular therapy for stroke face many challenges. Preclinical models used for cellular therapy studies should be relevant to human stroke and predictive of benefit despite differences in stroke size, cerebrovascular anatomy, immune status, and neurological responses. Translating preclinical testing to human trials is compounded by consideration of delivery method and translation of dosing with cell survival. Many issues must be approached in designing clinical trials of cellular therapy for stroke, including appropriate outcome measures, controlling for confounding factors such as rehabilitation therapy, and possible surrogate outcomes using imaging such as MRI and newer imaging techniques. It is also important to establish standardized clinical protocols and clinical database registries in advance of early proof-of-concept studies. Investigators must adopt a standardized nomenclature and characterization schema for cell products to accurately define potency and determine clinical outcome from early proof-of-concept studies. The S tem Cell T herapies as an E merging P aradigm in S troke (STEPS) meeting was organized to bring together clinical and basic researchers with industry and regulatory representatives to assess the critical issues in the field and to create a framework to guide future investigations.