RESUMEN
The early emergence of macrophages and their large pattern of tissue distribution during development suggest that they may play a critical role in the initial steps of embryogenesis. In the present study, we show that monocytic cells derived from human embryonic stem cells (hESCs) and from fetal liver follow a differentiation pathway different to that of adult cells, leading to specific functions. Embryonic and fetal monocytic cells differentiated from a CD14(low)CD16(-) precursor to form CD14(high)CD16(+) cells without producing the CD14(high)CD16(-) cell population that predominates in adult peripheral blood. Both demonstrated an enhanced expression of genes encoding tissue-degrading enzymes, chemokines, and scavenger receptors, as was previously reported for M2 macrophages. Compared with adult blood monocytes, embryonic and fetal monocytic cells secreted high amounts of proteins acting on tissue remodeling and angiogenesis, and most of them expressed the Tie2 receptor. Furthermore, they promoted vascular remodeling in xenotransplanted human tumors. These findings suggest that the regulation of human fetal and embryonic monocytic cell differentiation leads to the generation of cells endowed mainly with anti-inflammatory and remodeling functions. Trophic and immunosuppressive functions of M2-polarized macrophages link fetus and tumor development, and hESCs offer a valuable experimental model for in vitro studies of mechanisms sustaining these processes.