Other tissues

Among the other ectodermal derivatives the most common are cysts lined by squamous epithelium, and focally one may see structures resembling skin.

Endodermal structures include various glands and tubules lined by specialized epithelial cells. In some instances these cells resemble fetal or adult intestine (Figures 13.10 and 13.11). In other instances the glands cannot be positively identified (Figure 13.12).

Figure 13.10 Teratoma containing clear cells resembling fetal intestine.

The glandular structures can be surrounded by smooth muscle cells, suggesting intestinal development (Figure 13.13). Sometimes the glands are surrounded by nondescript mesenchymal cells and the juxtaposition of different cell types suggests complex organogenetic interaction of cells, similar to events that occur during fetal development (Figure 13.14).

Figure 13.12 Teratoma-containing glands that cannot be further characterized.

Figure 13.13 Teratomas containing an area of intestinal differentiation. The slide was immunohistochemically stained with antibodies to smooth mucle actin. With this approach one may see the layering of smooth muscle cells (brown) around the tubular intestinal epithelium, in a manner reminiscent of intestinal morphogenesis in the fetus.

Figure 13.13 Teratomas containing an area of intestinal differentiation. The slide was immunohistochemically stained with antibodies to smooth mucle actin. With this approach one may see the layering of smooth muscle cells (brown) around the tubular intestinal epithelium, in a manner reminiscent of intestinal morphogenesis in the fetus.

Figure 13.14 Teratoma composed of irregularly arranged nondescript glands and stromal tissue that cannot be further characterized on the basis of microscopy alone.
Figure 13.15 Immature teratoma containing undifferentiated hESCs. The cells are arranged into inter-anastomosing strands surrounding empty spaces. (Slide courtesy of Dr PW Andrews.)

Complex organogenesis may arise in some xenografts. Some tumors contain intestinal-like structures, juxtaposed neural tissue and choroid plexus, and some also contain signs of thyroid or early kidney formation. Bone or cartilage may be associated with skeletal muscles.

Figure 13.16 Immature teratoma containing undifferentiated hESCs. The hESCs are arranged into structures reminiscent of the early embryo and resemble embryoid bodies formed by hESCs in vitro. (Slide courtesy of Dr PW Andrews.)
Figure 13.17 Immature teratoma containing undifferentiated hESCs. The hESC are loosely arranged and many of them have undergone apoptosis. (Slide courtesy of Dr PW Andrews.)

In a minority of xenografts one may occasionally see foci of undifferentiated hESCs (Figures 13.15-13.17). These cells have a high nucleus-to-cytoplasm ratio and their nuclei are slightly irregular, containing finely dispersed chromatin and prominent nucleoli. The cells are arranged into small groups, or in interconnected strands. Typically these foci contain numerous apoptotic bodies and also scattered mitoses.

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