Human Neonatal Thymus-Derived Mesenchymal Stromal Cells: Characterization, Differentiation, and Immunomodulatory Properties

Mesenchymal stromal cells represent an attractive cell population for cell transplantation and tissue engineering purposes. The aim of this study was to search for neonatal thymus-derived mesenchymal stromal cells (nTMSC) and further characterize the differentiation and immunomodulatory properties thereof. The thymus glands of 13 infants undergoing congenital cardiac surgery were removed. After in vitro isolation and expansion, we identified adherent stromal cells with substantial proliferation potential. As characterized by FACS, the pattern of surface antigen expression of nTMSC resembled bone marrow stromal cells. Full mesenchymal differentiation potential is maintained during proliferation as confirmed by cultures for osteogenic, chondrogenic, and adipogenic lineages. After 5-azacytidine enrichment, morphological characteristics of cardiomyocytes were achieved. For immunologic investigations, the influence of nTMSC on the proliferative behavior of peripheral blood mononuclear cells was studied as a measure of the immune response. The nTMSC did not stimulate an allogeneic reaction in this coculture. Further, the expression of immunologically relevant markers was measured. Alike MSC from other origins, nTMSC did not express MHC-II. In contrast to mature MSC, some nTMSC even lack the expression of MHC-I. Our results confirm that the neonatal thymus contains mesenchymal stromal cells (nTMSC) with full mesenchymal differentiation potential and immunomodulatory properties.