Mesenchymal stromal cells isolated from human fetal liver release soluble factors with a potential role in liver tissue repair

We isolated a population of proliferating cells from cultured human fetal hepatocytes of 16-22 weeks gestational age. The cells shared a similar phenotype to that of mesenchymal stromal cells (MSCs) according to the International Society for Cellular Therapy (ISCT), including plastic adherence, antigen expression profile, and in vitro multilineage differentiation potential. Fetal liver (FL)-MSCs expressed the albumin gene, and harbored a subpopulation of CK18⁺ cells (20-40%), which defined their hepatic origin. However, when subjected to in vitro hepatic differentiation, FL-MSCs did not acquire significant liver functions. Quantitative analysis of conditioned medium (CM) collected from cultured cells revealed the presence of growth factors and chemokines with potential liver regenerative properties, the most relevant of which (concentration ≥3000 pg/ml) were SDF-1 alpha, IL-6, MCP-1, IL-8, MIP-1 beta, VEGF-A, Gro-alpha, and HGF. Culturing of FL-MSCs as spheroids significantly enhanced the secretion of HGF and bFGF (approximately 5-fold) compared with culture monolayers. Moreover, CM assessed in vitro induced capillary-like organization and migration of human umbilical vein endothelial cells (HUVECs) and fibroblasts as target cells. Interestingly, exosomes isolated from CM induced similar cellular responses in vitro with high efficiency and in a dose-dependent manner. FL-MSCs underwent several in vitro subcultivations, and did not stimulate allogenic T-cell proliferation thus suggesting a low immunogenicity. Furthermore, 5-year cryopreservation did not affect cell viability (approximately 90% of viable post-thawed FL-MSCs). These observations support the feasibility of a cell bank establishment for allogenic transplantation. We concluded that FL-MSCs or they secreted factors may be a valid alternative to hepatocyte transplantation in liver cell-based therapies.