A comparison of clinically relevant sources of mesenchymal stem cell-derived exosomes: Bone marrow and amniotic fluid.

BACKGROUND/PURPOSE: Exosomes may constitute a more practical alternative to live cells in select stem cell-based therapies. We sought to compare exosomes from two mesenchymal stem cell (MSC) sources relevant to perinatal and pediatric diseases.

METHODS: Exosomes were isolated by reagent-enhanced centrifugation from cell culture media of banked human bone marrow (bm) and amniotic fluid (af) MSCs after serum starvation. Characterization was by flow exometry for tetraspanin markers CD9, CD63, and CD81, transmission electron microscopy for size and morphology, and tunable resistive pulse sensing for size distribution and concentration. Statistical comparisons of count data were made by Poisson regression modeling and Student's T-test.

RESULTS: Exosomes of appropriate size and morphology were isolated with comparable expressions of CD9 (96% vs. 94%), CD63 (88% vs. 66%), and CD81 (71% vs. 63%) for bmMSC and afMSC, respectively. Total exosome yield (particles/mL) adjusted for number of cells was higher from afMSCs than bmMSCs by an estimated 25% (P<0.001).

CONCLUSIONS: While bone marrow and amniotic fluid mesenchymal stem cells are comparable sources of exosomes in size distribution, morphology, and expression of typical surface markers, yield may be higher from amniotic fluid cells. The amniotic fluid appears to be a preferable source of exosomes for clinical applications.

LEVEL OF EVIDENCE: N/A (bench laboratory study).