Tropism of the in situ growth from biopsies of childhood neuroectodermal tumors following transplantation into experimental teratoma.

Experimental teratoma induced from human pluripotent stem cells with normal karyotype can be described as a failed embryonic process and includes besides advanced organoid development also large elements of tissue with a prolonged occurrence of immature neural components. Such immature components, although benign, exhibit strong morphological resemblance with tumors of embryonic neuroectodermal origin. Here, we demonstrate that biopsy material from childhood tumors of neural embryonic origin transplanted to mature experimental teratoma can show an exclusive preference for matching tissue. Tumor specimens from five children with; Supratentorial primitive neuroectodermal tumor (sPNET); Pilocytic astrocytoma of the brainstem; Classic medulloblastoma; peripheral primitive neuroectodermal tumor (pPNET) or neuroblastoma (NB), respectively, were transplanted. Analysis of up to 120 sections of each tumor revealed an engraftment for three of the transplanted tumors: pPNET, sPNET, and NB, with a protruding growth from the latter two that were selected for detailed examination. The histology revealed a strict tropism with a non-random integration into what morphologically appeared as matched embryonic microenvironment recuperating the patient tumor histology. The findings suggest specific advantages over xenotransplantation and lead us to propose that transplantation to the human embryonic microenvironment in experimental teratoma can be a well-needed complement for preclinical in vivo studies of childhood neuroectodermal tumors.

Early events in xenograft development from the human embryonic stem cell line HS181--resemblance with an initial multiple epiblast formation.

Xenografting is widely used for assessing in vivo pluripotency of human stem cell populations. Here, we report on early to late events in the development of mature experimental teratoma from a well-characterized human embryonic stem cell (HESC) line, HS181. The results show an embryonic process, increasingly chaotic. Active proliferation of the stem cell derived cellular progeny was detected already at day 5, and characterized by the appearance of multiple sites of engraftment, with structures of single or pseudostratified columnar epithelium surrounding small cavities. The striking histological resemblance to developing embryonic ectoderm, and the formation of epiblast-like structures was supported by the expression of the markers OCT4, NANOG, SSEA-4 and KLF4, but a lack of REX1. The early neural marker NESTIN was uniformly expressed, while markers linked to gastrulation, such as BMP-4, NODAL or BRACHYURY were not detected. Thus, observations on day 5 indicated differentiation comparable to the most early transient cell populations in human post implantation development. Confirming and expanding on previous findings from HS181 xenografts, these early events were followed by an increasingly chaotic development, incorporated in the formation of a benign teratoma with complex embryonic components. In the mature HS181 teratomas not all types of organs/tissues were detected, indicating a restricted differentiation, and a lack of adequate spatial developmental cues during the further teratoma formation. Uniquely, a kinetic alignment of rare complex structures was made to human embryos at diagnosed gestation stages, showing minor kinetic deviations between HS181 teratoma and the human counterpart.

Species-specific in vivo engraftment of the human BL melanoma cell line results in an invasive dedifferentiated phenotype not present in xenografts.

For clinically relevant studies on melanoma progression and invasiveness, in vivo experimental systems with a human cellular microenvironment would be advantageous. We have compared tumor formation from a human cutaneous malignant melanoma cell line (BL), after injection as conventional xenografts in the mouse, or when injected into a predominantly species-specific environment of human embryonic stem cell-derived teratoma induced in the mouse (the hEST model). The resulting melanoma histology was generally analogous, both systems showing delimited densely packed areas with pleomorphic cells of malignant appearance. A specificity of the integration process into the human embryonic teratoma tissues was indicated by the melanoma exclusively being found in areas compatible with condensed mesenchyme, similar to neural crest development. Here, also enhanced neovascularization was seen within the human mesenchymal tissues facing the BL melanoma growth. Furthermore, in the hEST model an additional melanoma cell phenotype occurred, located at the border of, or infiltrating into, the surrounding human loose mesenchymal fibrous stroma. This BL population had a desmoplastic spindle-like appearance, with markers indicative of dedifferentiation and migration. The appearance of this apparently more aggressive phenotype, as well as the induction of human angiogenesis, shows specific interactions with the human embryonic microenvironment in the hEST model. In conclusion, these data provide exciting options for using the hEST model in molecular in vivo studies on differentiation, invasiveness, and malignancy of human melanoma, while analyzing species-specific reactions in vivo.