Abstract
Umbilical cord mesenchymal stem cells (UC-MSCs) have certain advantages over other MSCs and about 300 clinical trials have been registered using UC-MSCs to treat diseases such as osteoarthritis, autoimmune diseases, and degenerative disorders, yet, only limited success has been achieved. One reason is that in vitro expanded UC-MSCs show tremendous heterogeneity and their relationship to in vivo UC-MSCs remains unknown. Here, we investigated freshly isolated, uncultured UC-MSCs by single-cell RNA sequencing (scRNA-seq) and found two populations of UC-MSCs. Although UC-MSCs share many expressed genes and may have the same origin, they can be clearly separated based on differentially expressed genes including CD73 and other markers. Moreover, group 1 MSCs are enriched in expression of genes in immune response/regulatory activities, muscle cell proliferation and differentiation, stemness, and oxidative stress while group 2 MSCs are enriched with gene expression in extracellular matrix production, osteoblast and chondrocytes differentiation, and bone and cartilage growth. These findings suggest that UC-MSCs should be separated right after isolation and individually expanded in vitro to treat different diseases.