METHODS: Wharton's Jelly Mesenchymal Stem Cells (WJMSCs) were isolated from four independent umbilical cord samples and were characterized following the International Society for Cellular Therapy (ISCT) guidelines. Small extracellular vesicles (sEVs) were isolated separately from these four WJMSCs samples using the Tangential Flow Filtration (TFF) method and were characterized per Minimal Information for Studies of Extracellular Vesicles (MISEV2018) guidelines. Each isolated and concentrated sEV preparation was standardized and its purity was determined by the ratio of the number of particles to protein concentration.
RESULTS: All the WJMSCs samples passed the Mesenchymal Stem Cells (MSCs) characterization QC tests. Qualitatively, EVs-positive markers (CD63 and TSG101) and intact bilipid membrane vesicles were detected in all the sEV preparations. Quantitatively, the protein and particle concentrations revealed that all the sEV preparations were "impure" with < 1.5 × 109 particles/µg protein. Albumin was co-isolated in all the sEV preparations.
CONCLUSION: In short, all characterized and standardized individual and pooled sEV preparations were deemed "impure" due to albumin co-isolation using the TFF method. For therapeutic development, it is essential to report protein and particle concentrations in EV preparations based on these QC results.