Researchers have successfully derived pluripotent stem cells from cultured human primordial germ cells (PGCs). These cells were cultured on mouse STO fibroblast feeder layers in the presence of human recombinant leukemia inhibitory factor (hrLIF), basic fibroblast growth factor (hrbFGF), and forskolin. Over 7–21 days, PGCs formed large multicellular colonies resembling those of mouse pluripotent stem cells, termed embryonic stem (ES) and embryonic germ (EG) cells. These cells remained alkaline phosphatase-positive and tested positive against five immunological markers (SSEA-1, SSEA-3, SSEA-4, TRA-1–60, and TRA-1–81), which are routinely used to characterize ES and EG cells. The cultured cells were karyotypically normal and stable, with both XX and XY cultures obtained. Immunohistochemical analysis of embryoid bodies (EBs) derived from these cultures revealed a wide variety of differentiated cell types, including derivatives of all three embryonic germ layers. These human PGC-derived cultures meet the criteria for pluripotent stem cells and most closely resemble EG cells. Pluripotent stem cells can be derived from two embryonic sources: ES cells from the inner cell mass of preimplantation embryos and EG cells from PGCs. Both ES and EG cells are pluripotent and demonstrate germ-line transmission in experimentally produced chimeras. Mouse ES and EG cells share several morphological characteristics, including high levels of intracellular alkaline phosphatase (AP) and specific cell surface glycolipids and glycoproteins. These properties are characteristic of, but not specific for, pluripotent stem cells. Other important characteristics include growth as multicellular colonies, normal and stable karyotypes, the ability to be continuously passaged, and the capability to differentiate into cells derived from all three embryonic germ layers. The pluripotency of ES and EG cells can be demonstrated in vitro and in vivo. EBs are differentiated cell aggregates first described as arising in human and mouse teratomas and teratocarcinomas. These aggregates range from a cluster of pluripotent stem cells enclosed by a layer of endoderm to complex structures closely resembling an embryo during early development. EBs from mouse pluripotent stem cells grown on feeder layers or in suspension may contain a variety of cell types. This property has been used as evidence of cell pluripotency and as a source of differentiating cells. With the proper combinations of growth and differentiation factors, mouse ES and EG cultures can generate cells of the hematopoietic lineage and cardiomyocytes. In addition, mouse ES cells have been used to generate in vitro cultures of neurons, skeletal muscle, and vascular endothelial cells. ES and EG cells from some species can form teratocarcinomas when injectedResearchers have successfully derived pluripotent stem cells from cultured human primordial germ cells (PGCs). These cells were cultured on mouse STO fibroblast feeder layers in the presence of human recombinant leukemia inhibitory factor (hrLIF), basic fibroblast growth factor (hrbFGF), and forskolin. Over 7–21 days, PGCs formed large multicellular colonies resembling those of mouse pluripotent stem cells, termed embryonic stem (ES) and embryonic germ (EG) cells. These cells remained alkaline phosphatase-positive and tested positive against five immunological markers (SSEA-1, SSEA-3, SSEA-4, TRA-1–60, and TRA-1–81), which are routinely used to characterize ES and EG cells. The cultured cells were karyotypically normal and stable, with both XX and XY cultures obtained. Immunohistochemical analysis of embryoid bodies (EBs) derived from these cultures revealed a wide variety of differentiated cell types, including derivatives of all three embryonic germ layers. These human PGC-derived cultures meet the criteria for pluripotent stem cells and most closely resemble EG cells. Pluripotent stem cells can be derived from two embryonic sources: ES cells from the inner cell mass of preimplantation embryos and EG cells from PGCs. Both ES and EG cells are pluripotent and demonstrate germ-line transmission in experimentally produced chimeras. Mouse ES and EG cells share several morphological characteristics, including high levels of intracellular alkaline phosphatase (AP) and specific cell surface glycolipids and glycoproteins. These properties are characteristic of, but not specific for, pluripotent stem cells. Other important characteristics include growth as multicellular colonies, normal and stable karyotypes, the ability to be continuously passaged, and the capability to differentiate into cells derived from all three embryonic germ layers. The pluripotency of ES and EG cells can be demonstrated in vitro and in vivo. EBs are differentiated cell aggregates first described as arising in human and mouse teratomas and teratocarcinomas. These aggregates range from a cluster of pluripotent stem cells enclosed by a layer of endoderm to complex structures closely resembling an embryo during early development. EBs from mouse pluripotent stem cells grown on feeder layers or in suspension may contain a variety of cell types. This property has been used as evidence of cell pluripotency and as a source of differentiating cells. With the proper combinations of growth and differentiation factors, mouse ES and EG cultures can generate cells of the hematopoietic lineage and cardiomyocytes. In addition, mouse ES cells have been used to generate in vitro cultures of neurons, skeletal muscle, and vascular endothelial cells. ES and EG cells from some species can form teratocarcinomas when injected