Characterization and angiogenic potential of human neonatal and infant thymus mesenchymal stromal cells.

Resident mesenchymal stromal cells (MSCs) are involved in angiogenesis during thymus regeneration. We have previously shown that MSCs can be isolated from enzymatically digested human neonatal and infant thymus tissue that is normally discarded during pediatric cardiac surgical procedures. In this paper, we demonstrate that thymus MSCs can also be isolated by explant culture of discarded thymus tissue and that these cells share many of the characteristics of bone marrow MSCs. Human neonatal thymus MSCs are clonogenic, demonstrate exponential growth in nearly 30 population doublings, have a characteristic surface marker profile, and express pluripotency genes. Furthermore, thymus MSCs have potent proangiogenic behavior in vitro with sprout formation and angiogenic growth factor production. Thymus MSCs promote neoangiogenesis and cooperate with endothelial cells to form functional human blood vessels in vivo. These characteristics make thymus MSCs a potential candidate for use as an angiogenic cell therapeutic agent and for vascularizing engineered tissues in vitro.