Umbilical cord mesenchymal stem cell‐derived exosomes alleviate collagen‐induced arthritis by balancing the population of Th17 and regulatory T cells

Exosomes released by mesenchymal stem cells (MSCs) are thought to function as extensions of the MSCs. However, it remains unclear whether exosomes derived from human umbilical cord MSCs (HUMSCs) possess immunoregulatory functions in rheumatoid arthritis. We report that when mice with collagen‐induced arthritis were injected with exosomes derived from HUMSC (HUMSC‐Exo), their paws became less swollen, and they had lower serum pro‐inflammatory cytokine and anti‐collagen IgG levels, and decreased synovial hyperplasia. The HUMSC‐Exo appeared to restore the balance between Th17 and Treg cells, and this effect was accompanied by reduced IL‐17 and enhanced TGF‐β and IL‐10 levels. These findings suggest that HUMSC‐Exo function as important regulator of the balance between Th1/Th17 and Treg cells during immune and inflammatory responses.