Experimental teratoma

Anti-Gene IGF-I Vaccines in Cancer Gene Therapy: A Review of a Case of Glioblastoma

OBJECTIVE

Vaccines for the deadliest brain tumor - glioblastoma (GBM) - are generally based on targeting growth factors or their receptors, often using antibodies. The vaccines described in the review were prepared to suppress the principal cancer growth factor - IGF-I, using anti-gene approaches either of antisense (AS) or of triple helix (TH) type. Our objective was to increase the median survival of patients treated with AS and TH cell vaccines.

METHODOLOGY

The cells were transfected in vitro by both constructed IGF-I AS and IGF-I TH expression episomal vectors; part of these cells was co-cultured with plant phytochemicals, modulating IGF-I expression. Both AS and TH approaches completely suppressed IGF-I expression and induced MHC-1 / B7 immunogenicity related to the IGF-I receptor signal.

RESULTS

This immunogenicity proved to be stronger in IGF-I TH than in IGF-I AS-prepared cell vaccines, especially in TH / phytochemical cells. The AS and TH vaccines generated an important TCD8+ and TCD8+CD11b- immune response in treated GBM patients and increased the median survival of patients up to 17-18 months, particularly using TH vaccines; in some cases, 2- and 3-year survival was reported. These clinical results were compared with those obtained in therapies targeting other growth factors.

CONCLUSION

The anti-gene IGF-I vaccines continue to be applied in current GBM personalized medicine. Technical improvements in the preparation of AS and TH vaccines to increase MHC-1 and B7 immunogenicity have, in parallel, allowed to increase in the median survival of patients.

Greener Grass: The Modern History of Epithelial Stem Cell Innovation

The field of epithelial stem cell development has been irrevocably shaped by the work of American scientist Howard Green, whose breakthroughs in stem cell culture methods translated to therapeutic practice. In this review, we chronicle the milestones that propelled the field of regenerative medicine of the skin forward over the last fifty years. We detail the early discoveries made by Green and his collaborators, highlight clinical cases that made life-saving use of his findings, and discuss the accomplishments of other scientists who later innovated upon his discoveries.

To Better Generate Organoids, What Can We Learn From Teratomas?

The genomic profile of animal models is not completely matched with the genomic profile of humans, and 2D cultures do not represent the cellular heterogeneity and tissue architecture found in tissues of their origin. Derived from 3D culture systems, organoids establish a crucial bridge between 2D cell cultures and in vivo animal models. Organoids have wide and promising applications in developmental research, disease modeling, drug screening, precision therapy, and regenerative medicine. However, current organoids represent only single or partial components of a tissue, which lack blood vessels, native microenvironment, communication with near tissues, and a continuous dorsal-ventral axis within 3D culture systems. Although efforts have been made to solve these problems, unfortunately, there is no ideal method. Teratoma, which has been frequently studied in pathological conditions, was recently discovered as a new in vivo model for developmental studies. In contrast to organoids, teratomas have vascularized 3D structures and regions of complex tissue-like organization. Studies have demonstrated that teratomas can be used to mimic multilineage human development, enrich specific somatic progenitor/stem cells, and even generate brain organoids. These results provide unique opportunities to promote our understanding of the vascularization and maturation of organoids. In this review, we first summarize the basic characteristics, applications, and limitations of both organoids and teratomas and further discuss the possibility that in vivo teratoma systems can be used to promote the vascularization and maturation of organoids within an in vitro 3D culture system.

Assessment of established techniques to determine developmental and malignant potential of human pluripotent stem cells

The International Stem Cell Initiative compared several commonly used approaches to assess human pluripotent stem cells (PSC). PluriTest predicts pluripotency through bioinformatic analysis of the transcriptomes of undifferentiated cells, whereas, embryoid body (EB) formation in vitro and teratoma formation in vivo provide direct tests of differentiation. Here we report that EB assays, analyzed after differentiation under neutral conditions and under conditions promoting differentiation to ectoderm, mesoderm, or endoderm lineages, are sufficient to assess the differentiation potential of PSCs. However, teratoma analysis by histologic examination and by TeratoScore, which estimates differential gene expression in each tumor, not only measures differentiation but also allows insight into a PSC's malignant potential. Each of the assays can be used to predict pluripotent differentiation potential but, at this stage of assay development, only the teratoma assay provides an assessment of pluripotency and malignant potential, which are both relevant to the pre-clinical safety assessment of PSCs.

The modulatory effect of cell–cell contact on the tumourigenic potential of pre-malignant epithelial cells: a computational exploration

Malignant development cannot be attributed alone to genetic changes in a single cell, but occurs as a result of the complex interplay between the failure of cellular regulation mechanisms and the presence of a permissive microenvironment. Although E-cadherin is classified as a 'metastasis suppressor' owing to its role in intercellular adhesion, the observation that it may be downregulated at a premalignant stage is indicative of additional roles in neoplastic development. We have used an agent-based computational model to explore the emergent behaviour resulting from the interaction of single and subpopulations of E-cadherin-compromised cells with unaffected normal epithelial cells within a monolayer environment. We have extended this to investigate the importance of local tissue perturbations in the form of scratch-wounding, or ablation of randomly-dispersed normal cells, on the growth of a single cell exhibiting E-cadherin loss. Our results suggest that the microenvironment with respect to localized cell density and normal/E-cadherin-compromised neighbours is crucial in determining whether an abnormal individual cell proliferates or remains dormant within the monolayer. These predictions raise important questions relating to the propensity for individual mutations to give rise to disease, and future experimental exploration of these will enhance our understanding of a complex, multifactorial pathological process.

APAF-1 is related to an undifferentiated state in the testicular germ cell tumor pathway

Apoptotic protease activating factor-1 (APAF-1) is a key regulator gene of apoptosis, located downstream from p53. Loss of APAF-1 expression is associated with chemorefractory malignant melanoma and neuronal cell differentiation. In order to make clear the function of APAF-1 in the carcinogenesis of germ cell tumors, we evaluated the expression levels of APAF-1 and several apoptosis and differentiation markers by immunohistochemistry in formalin-fixed paraffin-embedded samples from 43 cases of testicular germ cell tumor (TGCT) and six specimens of normal testis tissue. Expression of cleaved caspase-3, Oct-3/4, and Ki-67 were also examined by immunohistochemistry to evaluate apoptotic reactivity, tumor differentiation, and proliferation activity, respectively. APAF-1 was downregulated in two TGCT cell lines by siRNA transfection, and subsequent expression of the Ki-67 and Oct-3/4 genes and differentiation markers of three embryonic germ layers including keratin16 (KRT16) for ectoderm, vimentin (VIM) for mesoderm and GATA4 for endoderm were then tested. No significant relationship was found between APAF-1 expression and apoptotic activity in TGCTs. Expression of APAF-1, Oct-3/4, and Ki-67 was significantly higher in seminomas than in non-seminomas. In TGCTs, higher APAF-1 expression was correlated with higher proliferation (high Ki-67) and a lower degree of differentiation (high Oct-3/4). Interestingly, the expression of APAF-1 gradually decreased in accordance with tumor differentiation (seminoma and embryonal carcinoma > teratoma). Downregulation of APAF-1 in TGCT cell lines resulted in a decrease of Ki-67 and Oct-3/4 and an increase of VIM and KRT16 gene expression. These data show that higher expression of APAF-1 is related to an undifferentiated state in the TGCT pathway.

Caspase activity mediates the differentiation of embryonic stem cells

Embryonic stem cells (ESCs) are capable of indefinite self-renewal while retaining the ability to differentiate to any of the three germ layers that give rise to all somatic cell types. An emerging view is that a core set of transcription factors, including Oct4, Sox2, and Nanog, form a robust autoregulatory circuit that maintains ESCs in a self-renewing state. To accommodate the capacity of such cells to undergo germ layer-specific differentiation, we predicted a posttranslational mechanism that could negatively regulate these core self-renewal factors. Here we report caspase-induced cleavage of Nanog in differentiating ESCs. Stem cells lacking the Casp3 gene showed marked defects in differentiation, while forced expression of a caspase cleavage-resistant Nanog mutant in ESCs strongly promoted self-renewal. These results link a major component of the programmed cell-death pathway to the regulation of ESC development.

A plant-derived remedy for repair of infarcted heart

Background

Myocardial infarction (MI) due to coronary artery disease remains one of the leading causes of premature death. Replacement of infarcted heart tissue with regenerating myocardium from endogenous progenitor pools or exogenously introduced stem cells remains a therapeutic ideal. Their impracticality mainly lies in their low efficiency in cardiogenic differentiation (CD). Our recent studies with an acute MI animal model have already demonstrated the therapeutic effect of the MeOH extract of Geum japonicum (EGJ), providing clear evidence of myocardial regeneration.

Methods and Findings

The present study further isolated the active component contained in EGJ using bioassay-guided isolation and investigated its efficacy in the treatment of infarcted heart in animal MI models. We demonstrated that substantial repair of infarcted heart in animal MI models by EGJ can be mimicked by the isolated candidate compound (cardiogenin) in MI animal models. Clear evidence of newly regenerated endogenous mesenchymal stem cells (MSCs) derived cardiomyocytes was observed throughout the infarct zone, accompanied by significantly improved functional performance of the heart. Transplantation of MSCs pretreated with EGJ or cardiogenin into a MI animal model also resulted in substantial regeneration of functional myocardium, implying that the activated MSCs carry all the necessary blueprints for myocardial regeneration. Signaling pathways specific to cell survival, CD identified in embryonic heart induction and angiogenesis were activated in both cardiogenin-treated MSCs and cardiogenin-induced regenerating myocardium.

Conclusions

This study has demonstrated the therapeutic effects of cardiogenin in infarcted heart repair, and identified the associated signalling pathways for effective cardiogenic differentiation of MSCs, cell survival and angiogenesis. These findings should enable new treatment strategies for MI to be developed immediately.

Transplantation of undifferentiated murine embryonic stem cells in the heart: teratoma formation and immune response

Embryonic stem (ES) cells are promising for cardiac repair, but directing their differentiation toward cardiomyocytes remains challenging. We investigated whether the heart guides ES cells toward cardiomyocytes in vivo and whether allogeneic ES cells were immunologically tolerated. Undifferentiated mouse ES cells consistently formed cardiac teratomas in nude or immunocompetent syngeneic mice. Cardiac teratomas contained no more cardiomyocytes than hind-limb teratomas, suggesting lack of guided differentiation. ES cells also formed teratomas in infarcted hearts, indicating injury-related signals did not direct cardiac differentiation. Allogeneic ES cells also caused cardiac teratomas, but these were immunologically rejected after several weeks, in association with increased inflammation and up-regulation of class I and II histocompatibility antigens. Fusion between ES cells and cardiomyocytes occurred in vivo, but was rare. Infarct autofluorescence was identified as an artifact that might be mistaken for enhanced GFP expression and true regeneration. Hence, undifferentiated ES cells were not guided toward a cardiomyocyte fate in either normal or infarcted hearts, and there was no evidence for allogeneic immune tolerance of ES cell derivatives. Successful cardiac repair strategies involving ES cells will need to control cardiac differentiation, avoid introducing undifferentiated cells, and will likely require immune modulation to avoid rejection.

Epithelial-mesenchymal transition in colonies of rhesus monkey embryonic stem cells: a model for processes involved in gastrulation

Rhesus monkey embryonic stem (rhES) cells were grown on mouse embryonic fibroblast (MEF) feeder layers for up to 10 days to form multilayered colonies. Within this period, stem cell colonies differentiated transiently into complex structures with a disc-like morphology. These complex colonies were characterized by morphology, immunohistochemistry, and marker mRNA expression to identify processes of epithelialization as well as epithelial-mesenchymal transition (EMT) and pattern formation. Typically, differentiated colonies were comprised of an upper and a lower ES cell layer, the former growing on top of the layer of MEF cells whereas the lower ES cell layer spread out underneath the MEF cells. Interestingly, in the central part of the colonies, a roundish pit developed. Here the feeder layer disappeared, and upper layer cells seemed to ingress and migrate through the pit downward to form the lower layer while undergoing a transition from the epithelial to the mesenchymal phenotype, which was indicated by the loss of the marker proteins E-cadherin and ZO-1 in the lower layer. In support of this, we found a concomitant 10-fold upregulation of the gene Snail2, which is a key regulator of the EMT process. Conversion of epiblast to mesoderm was also indicated by the regulated expression of the mesoderm marker Brachyury. An EMT is a characteristic process of vertebrate gastrulation. Thus, these rhES cell colonies may be an interesting model for studies on some basic processes involved in early primate embryogenesis and may open new ways to study the regulation of EMT in vitro.

A calcium-based theory of carcinogenesis

Most human cancers are initiated by chronic injuries that repeatedly kill cells and must, therefore, repeatedly raise cell calcium within nearby survivors. They may also raise calcium in distant cells via calcium waves. Here it is argued that these calcium increases initiate oncogenesis by breaking gap junctions and thus disorganizing tissues and by activating proto-oncogenes. It is also argued that these calcium increases become self-perpetuating in part through the development of an ability of cells to divide in reduced extracellular calcium, i.e., habituation to reduced extracellular calcium. I propose to test these calcium-based theories by using aequorinated mice.

A germ cell origin of embryonic stem cells?

Because embryonic stem (ES) cells are generally derived by the culture of inner cell mass (ICM) cells, they are often assumed to be the equivalent of ICM cells. However, various evidence indicates that ICM cells transition to a different cell type during ES-cell derivation. Historically, ES cells have been believed to most closely resemble pluripotent primitive ectoderm cells derived directly from the ICM. However, differences between ES cells and primitive ectoderm cells have caused developmental biologists to question whether ES cells really have an in vivo equivalent, or whether their properties merely reflect their tissue culture environment. Here, we review recent evidence that the closest in vivo equivalent of an ES cell is an early germ cell.

Fbx15 is a novel target of Oct3/4 but is dispensable for embryonic stem cell self-renewal and mouse development

Embryonic stem (ES) cells are immortal and pluripotent cells derived from early mammalian embryos. Transcription factor Oct3/4 is essential for self-renewal of ES cells and early mouse development. However, only a few Oct3/4 target genes have been identified. In this study, we found that F-box-containing protein Fbx15 was expressed predominantly in mouse undifferentiated ES cells. Inactivation of Oct3/4 in ES cells led to rapid extinction of Fbx15 expression. Reporter gene analyses demonstrated that this ES cell-specific expression required an 18-bp enhancer element located approximately 500 nucleotides upstream from the transcription initiation site. The enhancer contained an octamer-like motif and an adjacent Sox-binding motif. Deletion or point mutation of either motif abolished the enhancer activity. The 18-bp fragment became active in NIH 3T3 cells when Oct3/4 and Sox2 were coexpressed. A gel mobility shift assay demonstrated cooperative binding of Oct3/4 and Sox2 to the enhancer sequence. In mice having a beta-galactosidase gene knocked into the Fbx15 locus, 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining was detected in ES cells, early embryos (two-cell to blastocyst stages), and testis tissue. Despite such specific expression of Fbx15, homozygous mutant mice showed no gross developmental defects and were fertile. Fbx15-null ES cells were normal in morphology, proliferation, and differentiation. These data demonstrate that Fbx15 is a novel target of Oct3/4 but is dispensable for ES cell self-renewal, development, and fertility.

From teratocarcinomas to embryonic stem cells

The recent derivation of human embryonic stem (ES) cell lines, together with results suggesting an unexpected degree of plasticity in later, seemingly more restricted, stem cells (so-called adult stem cells), have combined to focus attention on new opportunities for regenerative medicine, as well as for understanding basic aspects of embryonic development and diseases such as cancer. Many of the ideas that are now discussed have a long history and much has been underpinned by the earlier studies of teratocarcinomas, and their embryonal carcinoma (EC) stem cells, which present a malignant surrogate for the normal stem cells of the early embryo. Nevertheless, although the potential of EC and ES cells to differentiate into a wide range of tissues is now well attested, little is understood of the key regulatory mechanisms that control their differentiation. Apart from the intrinsic biological interest in elucidating these mechanisms, a clear understanding of the molecular process involved will be essential if the clinical potential of these cells is to be realized. The recent observations of stem-cell plasticity suggest that perhaps our current concepts about the operation of cell regulatory pathways are inadequate, and that new approaches for analysing complex regulatory networks will be essential.

Transgenesis by lentiviral vectors: lack of gene silencing in mammalian embryonic stem cells and preimplantation embryos

The introduction of foreign genes into early mouse embryos and embryonic stem (ES) cells is invaluable for the analysis of gene function and regulation in the living animal. The use of vectors derived from retroviruses as gene transfer vehicles in this setting has had limited success because of silencing of transgene expression. Here, we show that vectors derived from lentiviruses, which are complex retroviruses, can efficiently deliver genes to murine ES cells and that transgene expression is stable during proliferation of undifferentiated ES cells. The transgene is expressed during differentiation of ES cells in vitro (embryoid bodies) and in vivo (teratomas). Transfer of lentivector-transduced ES cells into blastocysts resulted in chimeric animals that expressed the transgene in multiple tissues. Embryos derived from crossings of chimeric mice expressed the transgene, indicating successful germ-line transmission. Infection of murine preimplantation embryos at morula stage with lentiviral vectors resulted in stable transduction and expression of the transgene in mouse embryos and in newborn mice. Finally, human ES cells were transduced by lentiviral vectors and expressed the transgene over several passages. Thus, lentiviral vectors represent a significant improvement over oncoretroviral vectors used previously for gene transfer into murine ES cells and preimplantation embryos. Ability to transfer foreign genes into human ES cells has potential relevance for the development of gene and cell-based therapies.

Adrenal teratoma in four domestic ferrets (Mustela putorius furo)

Teratomas are histologically complex neoplasms that are composed of structures derived from multiple germ cell layers (ectoderm, mesoderm, and endoderm). These neoplasms are uncommon in domestic animals and are usually found in the gonads. This paper describes teratomas of the adrenal gland in four domestic ferrets (Mustela putorius furo). Three of four of the neoplasms contained tissues from ectodermal, mesodermal, and endodermal germ cell layers; two of four contained rudimentary teeth. In one case, malignant epithelial cells had metastasized to local lymph nodes. Teratomas, although uncommon, should be included in the differential diagnosis for adrenal neoplasms in domestic ferrets.

Hybrids of pluripotent and nullipotent human embryonal carcinoma cells: partial retention of a pluripotent phenotype

To investigate whether the failure of human EC cells that do not differentiate is due to the loss of key differentiation-permissive functions or the acquisition of specific inhibitory functions, we tested the ability to differentiate of 2 hybrids produced between a relatively nullipotent human EC cell line, 2102Ep, and a pluripotent human EC cell line NTERA2. Both hybrids, which exhibited an EC phenotype, were able to differentiate readily in response to retinoic acid. Furthermore, 1 hybrid produced a well-differentiated xenograft tumor, which contained, like the NTERA2 tumors, glandular structures, loose mesenchymal tissues and nodules of cartilage, after injection into a SCID mouse. Thus, the failure of 2102Ep EC cells to differentiate is recessive and due to the loss of a key gene function or functions. Nevertheless, the hybrids differed from the pluripotent NTERA2 line by failing to differentiate in neurons, indicating that 2102Ep cells also had acquired a specific, dominantly-acting, inhibitory mutation specific to the neural lineage. Furthermore, the expression of collagen II by one hybrid before and after induction with retinoic suggested a propensity for spontaneous differentiation not evident in the parental NTERA2 cells. Thus, the mechanisms that restrict the differentiation capacity of the nullipotent 2102Ep line are complex and include both recessive and dominant acting factors.

Development of tumors from bovine primordial germ cells transplanted to athymic mice

Intact genital ridges containing primordial germ cells (PGC) and isolated PGC from murine and bovine embryos were examined for in vivo growth and differentiation after transplantation under the kidney capsule of athymic mice. Genital ridges were collected from day 11.5 and 12.5 murine and day 34 and 37 bovine embryos. Murine genital ridges and isolated PGC collected at 11.5 days post-coitus (dpc) and isolated murine PGC collected at 12.5 dpc developed into tumors. Day 34 and 37 bovine genital ridges, but not isolated PGC developed into tumors. The bovine origin of the tumors was confirmed by an analysis of the bovine DNA sequences. Tumors from both species consisted primarily of mesoderm-derived cell types, including connective tissue, cartilage, smooth muscle, fibroblasts, osteoblasts and bone matrix. No detectable ectodermal derivatives were observed in tumors of either species. Undifferentiated stem cells were not detected in the tumors, suggesting that the tumors were benign teratomas. Results of this study demonstrate the pluripotency of bovine PGC by experimental induction of teratomas after xenotransplantation under the kidney capsule of athymic mice. Stimulation of PGC survival and proliferation in an ectopic graft could be useful toward the isolation of pluripotent embryo-derived stem cells.

Teratocarcinomas and human embryology: pluripotent human EC cell lines. Review article

The histogenesis of germ cell tumours (GCT) reflects the normal processes of gametogenesis, fertilisation and subsequent embryonic cell differentiation. Understanding the mechanisms that control the differentiation of embryonal carcinoma (EC) cells into a variety of embryonic and extraembryonic cell types is pertinent to understanding the progression of GCT. EC cells also provide a tool for analysing the mechanisms that control differentiation during embryonic development, and particularly the mechanisms that control differentiation along alternative cell line, NTERA2, into neurones and other cell types in response to agents such as retinoic acid, HMBA and the bone morphogenetic proteins. We have also compared the pluripotent NTERA2 EC cells with other human EC cell lines that exhibit a much reduced capacity for cell differentiation. A variety of genes are activated during NTERA2 differentiation. In particular we have identified a novel human member of the wnt family. This wnt gene is activated following retinoic acid induction of differentiation but is later down-regulated as the cells mature into neurones and other cell types. We have also observed expression of genes belonging to the Frizzled family, which is likely to include genes encoding receptors for the wnt gene products. Thus in the NTERA2 system, genes pertinent to regulating cell differentiation during embryonic development are activated and appear to play a role in modulating how these pluripotent human EC cells differentiate.

Beta 1 integrin is essential for teratoma growth and angiogenesis

Teratomas are benign tumors that form after ectopic injection of embryonic stem (ES) cells into mice and contain derivatives of all primitive germ layers. To study the role of beta 1 integrin during teratoma formation, we compared teratomas induced by normal and beta1-null ES cells. Injection of normal ES cells gave rise to large teratomas. In contrast, beta 1-null ES cells either did not grow or formed small teratomas with an average weight of <5% of that of normal teratomas. Histological analysis of beta 1-null teratomas revealed the presence of various differentiated cells, however, a much lower number of host-derived stromal cells than in normal teratomas. Fibronectin, collagen I, and nidogen were expressed but, in contrast to normal teratomas, diffusely deposited in beta1-null teratomas. Basement membranes were present but with irregular shape and detached from the cell surface. Normal teratomas had large blood vessels with a smooth inner surface, containing both host- and ES cell-derived endothelial cells. In contrast, beta 1-null teratomas had small vessels that were loosely embedded into the connective tissue. Furthermore, endothelial cells were always of host-derived origin and formed blood vessels with an irregular inner surface. Although beta 1- deficient endothelial cells were absent in teratomas, beta 1-null ES cells could differentiate in vitro into endothelial cells. The formation of a complex vasculature, however, was significantly delayed and of poor quality in beta1-null embryoid bodies. Moreover, while vascular endothelial growth factor induced proliferation of endothelial cells as well as an extensive branching of blood vessels in normal embryoid bodies, it had no effect in beta 1-null embryoid bodies.

Development of bovine and porcine embryonic teratomas in athymic mice

Inner cell masses (ICM) and embryonic discs from bovine and porcine blastocysts of various ages were transplanted under the kidney capsule of athymic (nude) mice to evaluate growth of teratocarcinomas containing both differentiated tissues and undifferentiated stem cells. Inner cell masses were isolated immunosurgically from Day 8, Day 9 and Day 10 porcine blastocysts and from Day 8, Day 10 and Day 12 bovine blastocysts. Embryonic discs were mechanically dissected from Day 11 and Day 12 porcine embryos and from Day 14 bovine embryos. Day 6 egg cylinders were dissected from BALB/C embryos and from hybrid embryos of a cross between BALB/C and an outbred strain of mouse. Two to four ICM, embryonic discs or egg cylinders were transplanted under the kidney capsule of each athymic host. After 8 weeks, graft hosts were killed and their tumors removed, fixed and prepared for histological and immunohistochemical examination. Embryonic teratomas developed at high frequency from murine egg cylinders and from Day 11 and Day 12 porcine and Day 14 bovine embryos. Tumors were observed only infrequently from younger bovine and porcine blastocysts. Murine embryonic tumors were composed of numerous differentiated cell types of ectodermal, mesodermal and endodermal origins, but representation of the three embryonic germ layers was somewhat more restricted in bovine and porcine embryonic tumors. No undifferentiated stem cells were detected in tumors of any of the three species. These results demonstrate that teratomas will develop from bovine and porcine embryos when grafted to an immunocompromised host, but the presence of undifferentiated teratocarcinoma stem cells from these species has yet to be achieved.

Expression of serum albumin and of alphafetoprotein in murine normal and neoplastic primitive embryonic structures

Alphafetoprotein (AFP), a major serum protein synthesized during the embryo-fetal and postnatal period (in the yolk sac, then in the liver), is also an oncoprotein. The intracellular presence of AFP and of serum albumin (SA) in normal and neoplastic neural crest and neural tube derivatives was previously demonstrated. In this work we have studied the comparative expression of AFP and SA in primitive neuroectoblastic structures of mouse embryos (6 and 7 days "post coitum") and mouse teratocarcinomas (derived from the PCC4 cell line). Using immunofluorescence technique, antibodies to SA gave a positive reaction in embryos of 7 days, while AFP was not detected during this period. By mRNA in situ hybridization, SA mRNA gave a strong signal in both 6 and 7 day embryos, whereas AFP mRNA gave a weak signal only in 7-day embryos. The distribution of SA and AFP and their mRNAs was investigated in primitive neuroectoblastic structures of the teratocarcinomas by in situ hybridization and immunostaining. Only SA protein was detectable by immunostaining. SA mRNA gave a strong signal in differentiating structures as well as in undifferentiated cell clusters. AFP mRNA was observed only in differentiating structure. Dot-blot hybridization indicated that the level of SA transcripts was at least 6-fold higher than that of AFP transcripts in the teratocarcinomas investigated. In teratocarcinoma-bearing mice injected intraperitoneally with 125I-radiolabeled SA and AFP, significant accumulations of both SA and AFP were demonstrated in the tumors, SA being about 3-fold higher than that of AFP after normalization to quantity of uptake in liver. External in vivo photoscanning confirmed this relationship of accumulated radiolabeled proteins. The last observation could be useful in vivo for diagnosis of teratocarcinoma. We conclude that the expression of SA relative to AFP and the external cellular uptake of SA relative to AFP are similar in normal embryonic developing tissues and in the corresponding morphologically neoplastic tissues of the teratocarcinomas. The same SA:AFP relationship constitutes an oncofetal marker of primitive neuroectoblastic structures.

Definition of a new entity of malignant extragonadal germ cell tumors

Two malignant extragonadal germ cell tumors are reported, histologically classified as immature teratomas, having pseudodiploid karyotypes with complex structural rearrangements but lacking isochromosome 12p or other rearrangements involving 12p. The absence of 12p material in structural rearrangements was confirmed by chromosome painting. In the two tumors the following common chromosomal breakpoints were found: 6p21, 6p22, 6q23, and 11q13. Exactly the same chromosomal regions, 6p22::6q23 and 6p21::11q13, were involved in fusions. The two tumors belong to a new entity of extragonadal immature teratomas of adults which may be located in the retroperitoneum and posterior mediastinum and are prone to blood borne metastasis.

Gene therapy of murine teratocarcinoma: separate functions for insulin-like growth factors I and II in immunogenicity and differentiation

Teratocarcinoma is a germ-line carcinoma giving rise to an embryoid tumor with structures derived from the three embryonic layers: mesoderm, endoderm, and ectoderm. Teratocarcinoma is widely used as an in vitro model system to study regulation of cell determination and differentiation during mammalian embryogenesis. Murine embryonic carcinoma (EC) PCC3 cells express insulin-like growth factor I(IGF-I) and its receptor, while all derivative tumor structures express IGF-I and IGF-II and their receptors. Therefore the system lends itself to dissect the role of these two growth factors during EC differentiation. With an episomal antisense strategy, we define a role for IGF-I in tumorigenicity and evasion of immune surveillance. Antisense IGF-I EC transfectants are shown to elicit a curative anti-tumor immune response with tumor regression at distal sites. In contrast, IGF-II is shown to drive determination and differentiation in EC cells. Since IGF-I and IGF-II bind to type I receptor and antisense sequence used for IGF-II cannot form duplex with endogenous IGF-I transcripts, it follows that this receptor is not involved in determination and differentiation.

Differentiation of mouse embryonic stem cells in vitro: III. Morphological evaluation of tissues developed after implantation of differentiated mouse embryoid bodies

Mouse embryonic stem cells (ES) were allowed to differentiate in a liquid culture system. After 2-3 weeks, complex cystic embryoid bodies developed. These bodies were composed of several structures identified as cardiac muscle and yolk sac blood islands as well as cup-shape compartments containing a mixed population of hematopoietic stem cells. When these cystic embryoid bodies were implanted into adult mice, either subcutaneously or under the kidney capsule, they developed into various tissues. These included bone, blood vessels, cardiac muscle, nerves, and skin with hair follicles. In addition, highly differentiated, complicated tissues resembling intestinal epithelium with mucus glands or salivary glandular tissue were derived. The ES tissues from these in vitro developed embryoid bodies developed quickly within 2 to 3 weeks of implantation. This is in contrast to a minimal of 6 weeks for teratocarcinomas derived from embryonic carcinoma cells and/or the direct implantation of undifferentiated embryonic stem cells. Moreover, we found that there are different types of tissue developed upon different sites of implantation. The data suggest a local environment and/or growth factors are influential for ES tissue development. This system provides a possible means to purify and identify stem cells that give rise to specific tissues, and to study the factors regulating the commitment of these stem cells.

The stem cells of a primordial germ cell-derived teratocarcinoma have the ability to form viable mouse chimeras

A euploid testicular teratocarcinoma line, STT-3, has been established from a tumor spontaneously occurring in the testis of a 129/Sv-ter male. Developmental ability of the STT-3 stem cells was tested by injecting these cells into mouse blastocysts. The frequency and the extent of chimerism were examined in mid-gestational fetuses and in live-born mice. STT-3 stem cells form viable chimeras at a high rate and differentiate into normal tissues. This is the first reported testicular teratocarcinoma-derived stem line with a proven capacity to form viable chimeric mice upon injection into the blastocysts.

Differentiation of human embryonal carcinoma cells induces human immunodeficiency virus permissiveness which is stimulated by human cytomegalovirus coinfection

Human immunodeficiency virus (HIV) replicates in differentiated but not undifferentiated NTERA-2 human embryonal carcinoma cells; neither cell type expresses CD4. Susceptibility of the differentiated cells is enhanced by coinfection with cytomegalovirus. HIV infection induces lactoseries glycolipids, suggesting a mechanism whereby HIV might interfere with normal embryogenesis.

Differentiation-promoting effects of mammary-derived growth inhibitor (MDGI) on pluripotent mouse embryonic stem cells

Pluripotent embryonic stem cells (line BLC6), when cultivated in vitro as embryoid bodies and injected subcutaneously into syngeneic mice, form teratocarcinomas consisting of embryonal carcinoma cells and differentiated tissues of all three primary germ layers. In order to study the possible effects of the mammary-derived growth inhibitor (MDGI) on the differentiation pattern of the tumors developing in the mice, BLC6 cell-derived embryoid bodies were treated in vitro for 4 days with either MDGI or a synthetic peptide composed of the C-terminal 11 amino acids of MDGI. In those tumors, significantly more differentiated neural tissue and lesser proportions of undifferentiated embryonic carcinoma cells (ECC) were found in the MDGI- and peptide-treated groups, compared with controls. The results are discussed with respect to a possible differentiation-promoting capacity of MDGI.

Basement membrane components secreted by mouse yolk sac carcinoma cell lines

Three new cell lines (NE, ME, LRD) were cloned from mouse-embryo-derived teratocarcinomas and characterized on the basis of developmental, ultrastructural, and cytochemical criteria as nullipotent embryonal carcinoma (EC), pure parietal yolk sac (PYS) carcinoma and mixed parieto-visceral yolk sac carcinoma respectively. Cell lines NE and ME were composed of a monomorphous cell population; however, the morphology of ME was growth-medium-dependent. LRD was composed of a heterogeneous cell population and formed embryoid bodies. NE secreted soluble laminin, osteonectin, entactin and fibronectin but did not form visible pericellular matrix. ME formed pericellular matrix which was composed of laminin and entactin, but did not contain fibronectin. The LRD cells formed pericellular matrix which was composed of laminin, entactin and fibronectin. Whereas laminin from ME and LRD reacted with polyclonal antibodies and a monoclonal antibody to parietal yolk sac laminin, the laminin from NE cells was unreactive with the monoclonal antibody. Osteonectin was found in the supernatant of LRD and ME, but could not be demonstrated immunohistochemically in the extracellular matrix. We conclude that some extracellular matrix components, such as laminin and fibronectin, are produced not only by yolk sac carcinoma cells but by nullipotent EC as well, although the latter do not assemble them into extracellular matrix. Laminin produced by EC is immunochemically different from laminin secreted by yolk sac carcinoma. The extracellular matrix produced by mixed parieto-visceral yolk sac carcinoma is different from the matrix laid down by the pure PYS in that the latter does not contain fibronectin. The lack of osteonectin in the extracellular matrix of yolk sac carcinoma cells indicates that not all polypeptides secreted by these cell lines are incorporated into the extracellular matrix. The new cell lines described in this paper differ with regard to their capacity to form extracellular matrix and secrete its various components. Hence they could be used for further studies of basement membrane assembly in vitro.

How fixed is the differentiated state? Lessons from heterokaryons

The differentiated state is highly stable in vivo. Yet, in response to nuclear transplantation, tissue regeneration or cell fusion, the nuclei of differentiated cells exhibit a remarkable capacity to change. I review here the utility of heterokaryons, multinucleated cell hybrids, in elucidating the mechanisms that establish and maintain the differentiated state and yet allow such plasticity.

Human teratocarcinomas

Teratocarcinomas are one of the commonest forms of cancer in young adult men. Cell lines derived from these tumors, and particularly the cell lines composed of their embryonal carcinoma (EC) stem cells, may provide useful information concerning the development and subsequent pathology of teratocarcinomas in humans. In addition, it is likely that human EC cells resemble early embryonic cells and can be used as an in vitro counterpart of such cells from the human embryo. Several common properties of human EC cells have been identified, and a human EC cell line, TERA-2, that is capable of extensive somatic differentiation has been cloned. In nude mice, TERA-2 EC cells form tumors containing neural elements and glandular structures that resemble primitive gut. In culture, these EC cells can be induced to differentiate by exposure to retinoic acid and hexamethylenebisacetamide (HMBA). Differentiation is marked by the disappearance of several cell surface antigens characteristic of human EC cells, and the appearance of other antigens on the various subsets of differentiated derivatives. In retinoic acid-induced cultures, these differentiated derivatives include neurons and cells permissive for the replication of cytomegalovirus, a virus that can cause birth defects in humans. On the other hand, HMBA appears to activate an alternative pathway of differentiation for TERA-2 EC cells, although the identity of the resulting cells remains to be elucidated. In addition to providing a tool for analyzing the evolution of teratocarcinomas in human patients, the TERA-2 EC cells may provide us with insights into the mechanisms of cellular differentiation in the human embryo and a model in which to investigate how teratogenic agents such as HCMV can disrupt these processes.

An adhesion-defective variant of F9 embryonal carcinoma cells fails to differentiate into visceral endoderm

Adhesion-defective EC cells were isolated from a population of mutagenized F9 cells by serial transfer of cells that did not adhere to gelatin-coated dishes. The variant cells grew in suspension as multicellular clusters of loosely aggregated cells. The cells adhered to, but did not flatten on, fibroblast monolayers and extracellular matrix produced by parietal-like endoderm. Two different mutant cell lines exhibited increased sensitivity to the lectin abrin and decreased sensitivity to wheat germ agglutinin, suggesting that changes in cell surface glycosylation are associated with the mutant phenotype. These adhesion-defective mutants were used to study the relationship between cell-cell adhesion and endodermal differentiation. Unlike wild-type cells, when cultured with low concentrations of retinoic acid (RA) in suspension culture, the mutant cells did not form embryoid bodies but remained as loosely adhering strings of cells. Electron microscopic examination revealed that most of the differentiated variant cells resembled parietal endoderm, and this was confirmed by immunofluorescent staining for TROMA-3 marker. The levels of some of the markers that characterize the differentiative pathways were examined by immunoprecipitation and by enzyme-linked immunosorbent assay (ELISA). The variant line produced higher levels of laminin and type IV collagen compared to the wild-type cells. alpha-Fetoprotein (AFP) was produced at a significantly lower level by the variant compared to wild-type F9 cells during the differentiative process. The results show that variant cells differentiated toward parietal endoderm but have a very much restricted ability to differentiate to visceral endoderm. We conclude that aggregation and/or compaction provide some essential signals during the differentiation of F9 cells into epithelial layers of visceral endoderm.

The fate of embryonal-carcinoma cells in mouse blastocysts

Double-labeled embryonal-carcinoma (ECa) cells were injected into blastocysts or incorporated into blastocysts by aggregation, and their fate after various periods of time in culture was investigated. ECa-247 cells labeled with fluorescent microscopheres were easily identified in whole blastocysts. These blastocysts were embedded in plastic, serially sectioned, and prepared for autoradiography. The 3H-thymidine label on the embryonal-carcinoma cells allowed precise localization of the cancer-derived cells. ECa-247 cells preferentially localized in the mural trophectoderm, with a few being seen in primitive endoderm and, even more rarely, in the inner cell mass. Selected autoradiograms were re-embedded and thin sectioned for transmission electron microscopy. The cancer-derived cells were found to have differentiated in accordance with their localization.

Differentiation potential of human embryonal carcinoma cell lines

We have established 17 embryonal carcinoma (EC) cell lines from human testicular germ cell tumors by using three different methods of in vitro cultivation. Cultures of only three of these cell lines, and of clones derived from two of them, differentiate extensively when the cells are seeded at low density. A comparison is presented of the results obtained with the three methods used to establish and maintain these cell lines, and some properties of the three pluripotential EC lines are summarized.

The relationship between embryonic, embryonal carcinoma and embryo-derived stem cells

Two types of pluripotent stem cell lines of embryonic origin are available as tools for the study of molecular and cellular differentiation in vitro. Tumor-derived embryonal carcinoma (EC) cell lines and the more recently developed embryo-derived stem (ES) cell lines have many characteristics similar to those of pluripotent cells within the embryo itself, the major difference being the cell lines' capacity for continued proliferation as undifferentiated cells. It is not known whether all EC/ES cell lines are derived from the same or different embryonic stem cells. Some differences between cell lines would be compatible with the latter. The advent of ES cells, which appear to be closer to embryonic cells, may allow the resolution of this question.

Induction of rat yolk sac carcinomas with consistent pattern of laminin, entactin, and type IV collagen biosynthesis

Twenty-four yolk sac carcinomas in Lewis rats were experimentally induced by puncturing the pregnant uterine wall with a hypodermic needle at day 9-13 of gestation. Morphologically, the tumours were composed of parietal- and visceral yolk sac carcinoma and to a less degree of trophoblastic giant cells. The tumours were adapted to ascitic growth and tissue culture, but eventually became committed to express only parietal endoderm phenotype. Immunohistochemical and metabolic labelling studies on the established lines in vivo and in vitro revealed a consistent pattern with respect to their biosynthesis of the basement membrane components laminin, entactin, and type IV collagen. This model system offers a simple approach to inducing rat yolk sac carcinomas for further morphological and biochemical characterization of the basement membrane.

Fibroblast feeder layers inhibit differentiation of retinoic acid-treated embryonal carcinoma cells by increasing the probability of stem cell renewal

The appearance of differentiated cells in embryonal carcinoma (EC) cultures can be inhibited by culturing the cells on fibroblast feeder layers. To determine whether or not feeder layers act by increasing the probability of stem cell renewal, growth and differentiation were monitored in cultures of F9 (subclone OTF9 -63) EC cells exposed to retinoic acid (RA) in either the presence or absence of feeder layers. By measuring the fraction of laminin-positive TROMA 1-positive or alkaline phosphatase-negative cells, it was determined that the frequency of differentiated cells in RA-treated F9 cultures was reduced by 70-80% when cells were cultured on fibroblast feeder layers instead of gelatin-coated dishes. Experiments in which EC cells were cultured in close proximity to a feeder layer demonstrated that cell-cell contact was required for maximal inhibition of differentiation. The probability of stem cell renewal was determined by measuring the number of colony-forming cells in RA-treated cultures as a function of time. Analysis of the data demonstrated that the probabilities of stem cell renewal were 0.5 and 0.25 during the first and second 48 h periods, respectively, following addition of RA for cells cultured without feeder layers. Cultures maintained on feeder layers exhibited a stem cell renewal probability of 0.72. Thus, feeder layers reduce the frequency of differentiated cells in RA-treated cultures by increasing the probability of stem cell renewal. Determining the mechanism by which feeder layers counteract the effect of a chemically defined differentiation inducer should help to uncover the processes that regulate the probability of stem cell renewal.

Male murine embryonal carcinoma cell line selectively metastatic to the ovaries and adrenals

Developmentally pluripotent embryonal carcinoma cells were isolated from chromosomally male embryo-derived teratocarcinoma and adapted to in vitro growth without a feeder layer. The uncloned original cell line as well as clones derived from it have a tendency to selectively localize to the ovaries and adrenals upon intravenous injection into adult female mice, but only to the adrenals when injected into male mice. The overall take of injected tumor cells was lower in males and the tumors formed slower in males than in females. These findings suggest that the growth of this karyotypically male embryonal carcinoma could be under hormonal regulation.

Yolk-sac carcinoma of extra-embryonic origin in the 129 Sv/Sl mouse

Displacement of the visceral yolk-sac in fetectomized rats and hamsters does not only induce benign teratomas but may also lead to the development of malignant yolk-sac carcinoma. In the mouse, displacement of this extraembryonic membrane readily induces teratoma but until now yolk-sac carcinoma has never been observed in this species. In the present study we report the development of yolk-sac carcinoma in 129 Sv/Sl mice after a long latent period (8 months). The tumor is composed of visceral and parietal patterns in the primary neoplasm and in its metastases. It develops from the extra-embryonal part belonging to normal (+/+), heterozygous (Sl/+) or sterile (Sl/Sl) embryos, which proves that these yolk-sac carcinomas are not of germ-cell origin.