In vivo differentiation of hES cells

For mES cell lines, pluripotency is validated in utero, in embryo reconstitution experiments (see Chapters 2 and 3). As such manipulations are prohibited for hES cell lines, their pluripotency can only be proved legitimately using model systems; and until sufficient guided in vitro differentiation techniques have been formulated, the raising of teratomas in immunosuppressed mice will remain the method of choice for producing from hES cells a full range of differentiated cell phenotypes (Protocol 2). And so the detection of derivatives of the three primary germ layers in teratomas is prerequisite to ascribing the characteristic of plur-ipotency to any novel hES cell line. Figure 1 illustrates the range of cell types and complex structures that can be found in mature teratomas.

An added advantage of this experimental, in vivo model lies in its possible relevance to the study of human neoplasia; for monitoring tumour growth and invasion, as well as for analysing the angiogenic response developing within the teratoma (43). However, a recent study showed that during teratoma formation, spontaneous vasculogenesis from hES cells occurs but reaches an immature

Figure 1 (see Plate 10) Teratoma formation by the hEScell line, H13, In Immunocompromised mice. (A-D) Sections of a teratoma 10weeks after xenografting, stained with haematoxylin and eosin. (A) Low-magnification view of the teratoma. (B-D) Higher magnifications showing tissues derived from all three germ layers: (B) bone formation (mesodermal in origin; solid arrow) near stratified squamous epithelium (ectodermal; dashed arrows); (C) hyaline cartilage development (mesodermal; solid arrow); and (D) columnar heterogeneous epithelium (endodermal; dashed arrows). Scale bars = 100mm.

Figure 1 (see Plate 10) Teratoma formation by the hEScell line, H13, In Immunocompromised mice. (A-D) Sections of a teratoma 10weeks after xenografting, stained with haematoxylin and eosin. (A) Low-magnification view of the teratoma. (B-D) Higher magnifications showing tissues derived from all three germ layers: (B) bone formation (mesodermal in origin; solid arrow) near stratified squamous epithelium (ectodermal; dashed arrows); (C) hyaline cartilage development (mesodermal; solid arrow); and (D) columnar heterogeneous epithelium (endodermal; dashed arrows). Scale bars = 100mm.

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