Mesenchymal Stromal Cells Expanded in Human Allogenic Cord Blood Serum Display Higher Self-Renewal and Enhanced Osteogenic Potential

Recent clinical trials using ex vivo expanded mesenchymal stromal cells (MSCs) have raised interest in the safety and function of cultured MSCs. Here, to assess the feasibility of using allogenic human umbilical cord blood serum (CBS) for humanized clinical-grade expansion of MSCs, we characterized MSCs expanded in CBS and compared them to MSCs expanded in fetal bovine serum (FBS). MSCs in CBS exhibited a higher preservation of colony-forming cells and an accelerated expansion over serial passages with increased Oct-4 expression compared to those cultured in FBS. Notably, CBS-expanded MSCs exhibited a unique differentiation potential characterized by a shift from adipogenic to osteogenic differentiation. The differentiation shift was associated with enhanced basal and Runx2-mediated transcriptional activation of the osteocalcin promoter, as well as increased accumulation of beta-catenin and the yes-associated protein (YAP) which was independent of changes in TAZ (transcriptional co-activator with PDZ-binding motif) levels. Interestingly, the phenotypes were reversed when the FBS and CBS media were switched, suggesting the unique stimulatory effects of CBS rather than the selection of heterogeneous MSC subpopulations. The distinct regulatory effects of CBS on MSC included selective activation of platelet-derived growth factor and epidermal growth factor signals in MSCs, but not in FBS. Taken together, these results provide insight into the dynamic regulation of MSCs during ex vivo culture and show that the ex vivo culture of MSCs in allogenic human CBS provides a novel tool for the accelerated expansion of a population of MSCs that exhibit a higher self-renewal and an enhanced osteogenic potential.