Human Hepatocyte-Derived Induced Pluripotent Stem Cells: MYC Expression, Similarities to Human Germ Cell Tumors, and Safety Issues

Figure 2

Human embryonic stem cells and teratoma formation. Teratomas generated were partly cystic (a) and partly solid (b) (Hematoxylin and Eosin (H&E), original magnification 20x). Tumors were composed of structures derived from all three germ layers; cystic glands were divided by paucicellular mesenchymal septa, in which a few slightly immature glandular structures were embedded (c, H&E 200x). Glands (arrows) and immature cartilage plates (stars) are shown as derivatives from the endodermal and mesodermal layers, respectively (d, H&E 200x). In one tumor, a small and solid 0.2 cm nodule (arrow) was located in an intramuscular position at a distance of 0.2 cm from the main cystic portion and close to the mouse vas deferens (arrowhead) (e, H&E 20x). The nodule was composed of immature neuroglial tissue (arrowhead), cartilage (star), and glands; a minority of the glandular structures were atypical (arrow) (f, H&E 100x). At higher magnification (g, H&E 200x), these glands were formed of cells showing nuclear atypia and increased apoptotic rate. Upon immunohistochemical evaluation, MYC reactivity was faint and focal, expressed in approximately 20% of the atypical cells (h, 200x).

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