Extracellular vesicles released from human amniotic fluid stem cells modulate macrophages.

BACKGROUND: Human amniotic fluid stem cells (hAFSCs) secrete extracellular vesicles (EVs) that modulate fetal immunity. Because fetal and neonatal macrophages largely rely on innate responses, development of a targeted method to switch their inflammatory phenotype would fill a critical therapeutic gap in perinatal medicine. We therefore elucidated whether the hAFSC-EV surface marker CD44 functions as a "delivery code" for preferential uptake by inflammatory macrophages. METHODS AND RESULTS: hAFSCs and hAFSC-EVs were isolated and characterized by performing flow cytometry, transmission electron microscopy, nanoparticle tracking analysis, and western blotting. The hAFSC-EVs were co-cultured with macrophages derived from the human monocytic leukemia cell line THP-1. The uptake of hAFSC-EVs was evaluated using fluorescence microscopy and flow cytometry. The effects of hAFSC-EVs on macrophages were analyzed by western blotting and real-time quantitative polymerase chain reaction. Our analyses revealed that inhibiting CD44 expression with a functional antibody blocked hAFSC-EV uptake by macrophages and led to changes in the cellular phenotype. Furthermore, inhibiting the uptake of CD44-positive hAFSC-EVs suppressed the expression of some pro-inflammatory cytokines. These findings suggest that CD44-positive hAFSC-EVs play a crucial role in the anti-inflammatory effects of hAFSCs. CONCLUSIONS: Our study provides insights into the specific delivery of hAFSC-EVs into inflammatory macrophages and sheds light on the potential therapeutic applications of these EVs for regulating inflammatory macrophage phenotypes.