Higher susceptibility of NOG mice to xenotransplanted tumors

Working with Miraculous Mice: Mus musculus as a Model Organism

The laboratory mouse has been described as a "miracle" model organism, providing a window by which we may gain an understanding of ourselves. Since the first recorded mouse experiment in 1664, the mouse has become the most used animal model in biomedical research. Mice are ideally suited as a model organism because of their small size, short gestation period, large litter size, and genetic similarity to humans. This article provides a broad overview of the laboratory mouse as a model organism and is intended for undergraduates and those new to working with mice. We delve into the history of the laboratory mouse and outline important terminology to accurately describe research mice. The types of laboratory mice available to researchers are reviewed, including outbred stocks, inbred strains, immunocompromised mice, and genetically engineered mice. The critical role mice have played in advancing knowledge in the areas of oncology, immunology, and pharmacology is highlighted by examining the significant contribution of mice to Nobel Prize winning research. International mouse mutagenesis programs and accurate phenotyping of mouse models are outlined. We also explain important considerations for working with mice, including animal ethics; the welfare principles of replacement, refinement, and reduction; and the choice of mouse model in experimental design. Finally, we present practical advice for maintaining a mouse colony, which involves adequate training of staff, the logistics of mouse housing, monitoring colony health, and breeding strategies. Useful resources for working with mice are also listed. The aim of this overview is to equip the reader with a broad appreciation of the enormous potential and some of the complexities of working with the laboratory mouse in a quest to improve human health. © 2024 The Author(s). Current Protocols published by Wiley Periodicals LLC.

Characterization of novel, severely immunodeficient PrkdcΔex57/Δex57 mice

Severely immunodeficient mice are useful for understanding the pathogenesis of certain tumors and for developing therapeutic agents for such tumors. In addition, engraftment of these mice with human hematopoietic cells can yield information that helps us understand the in vivo molecular mechanisms underlying actual human viral infections. In our present research, we discovered a novel, severely immunodeficient strain of mice having a mutation in exon 57 of the Prkdc gene (PrkdcΔex57/Δex57) in an inbred colony of B10.S/SgSlc mice. Those PrkdcΔex57/Δex57 mice showed thymic hypoplasia and lack of mature T cells and B cells in peripheral lymphoid tissues, resulting in very low levels of production of serum immunoglobulins. In addition, those mice were highly susceptible to influenza viruses due to the lack of acquired immune cells. On the other hand, since they had sufficient numbers of NK cells, they rejected tumor transplants, similarly to Prkdc+/+ mice. Next, we generated Foxn1nu/nuPrkdcΔex57/Δex57Il2rg-/- (NPG) mice on the BALB/cSlc background, which lack all lymphocytes such as T cells, B cells and innate lymphoid cells, including NK cells. As expected, these mice were able to undergo engraftment of human tumor cell lines. These findings suggest that PrkdcΔex57/Δex57 mice will be useful as a novel model of immunodeficiency, while NPG mice will be useful for xenografting of various malignancies.

Animal models of bone metastatic prostate cancer

Metastatic disease is a main cause of mortality in prostate cancer and remains to be incurable despite emerging new treatment agents. Development of novel treatment agents are confined within the boundaries of our knowledge of bone metastatic prostate cancer. Exploration into the underlying mechanism of metastatic tumorigenesis and treatment resistance will further expose novel targets for novel treatment agents. Up to date, many of these researches have been conducted with animal models which have served as classical tools that play a pivotal role in understanding the fundamental nature of cancer. The ability to reproduce the natural course of prostate cancer would be of profound value. However, currently available models do not reproduce the entire process of tumorigenesis to bone metastasis and are limited to reproducing small portions of the entire process. Therefore, knowledge of available models and understanding the strengths and weaknesses for each model is key to achieve research objectives. In this article, we take an overview of cell line injection animal models and patient derived xenograft models that have been applied to the research of human prostate cancer bone metastasis.

The development and improvement of immunodeficient mice and humanized immune system mouse models

Animal models play an indispensable role in the study of human diseases. However, animal models of different diseases do not fully mimic the complex internal environment of humans. Immunodeficient mice are deficient in certain genes and do not express these or show reduced expression in some of their cells, facilitating the establishment of humanized mice and simulation of the human environment in vivo. Here, we summarize the developments in immunodeficient mice, from the initial nude mice lacking T lymphocytes to NOD/SCID rg^null mice lacking T, B, and NK cell populations. We describe existing humanized immune system mouse models based on immunodeficient mice in which human cells or tissues have been transplanted to establish a human immune system, including humanized-peripheral blood mononuclear cells (Hu-PBMCs), humanized hematopoietic stem cells (Hu-HSCs), and humanized bone marrow, liver, thymus (Hu-BLT) mouse models. The different methods for their development involve varying levels of complexity and humanization. Humanized mice are widely used in the study of various diseases to provide a transitional stage for clinical research. However, several challenges persist, including improving the efficiency of reconstructing the human B cell immune response, extending lifespan, improving the survival rate of mice to extend the observation period, and improving the development of standardized commercialized models and as well as their use. Overall, there are many opportunities and challenges in the development of humanized immune system mouse models which can provide novel strategies for understanding the mechanisms and treatments of human disease.

A novel anti-c-Kit antibody-drug conjugate to treat wild-type and activating-mutant c-Kit-positive tumors

c‐Kit overexpression and activating mutations, which are reported in various cancers, including gastrointestinal stromal tumor (GIST), small‐cell lung cancer (SCLC), acute myeloid leukemia, acral melanoma, and systemic mastocytosis (SM), confer resistance to tyrosine kinase inhibitors (TKIs). To overcome TKI resistance, an anti‐c‐Kit antibody–drug conjugate was developed in this study to treat wild‐type and mutant c‐Kit‐positive cancers. NN2101, a fully human IgG1, was conjugated to DM1, a microtubule inhibitor, through N‐succinimidyl‐4‐(N‐maleimidomethyl) cyclohexane‐1‐carboxylate (SMCC) (to give NN2101‐DM1). The antitumor activity of NN2101‐DM1 was evaluated in vitro and in vivo using various cancer cell lines. NN2101‐DM1 exhibited potent growth‐inhibitory activities against c‐Kit‐positive cancer cell lines. In a mouse xenograft model, NN2101‐DM1 exhibited potent growth‐inhibitory activities against imatinib‐resistant GIST and SM cells. In addition, NN2101‐DM1 exhibited a significantly higher anti‐cancer effect than carboplatin/etoposide against SCLC cells where c‐Kit does not mediate cancer pathogenesis. Furthermore, the combination of NN2101‐DM1 with imatinib in imatinib‐sensitive GIST cells induced complete remission compared with treatment with NN2101‐DM1 or imatinib alone in mouse xenograft models. These results suggest that NN2101‐DM1 is a potential therapeutic agent for wild‐type and mutant c‐Kit‐positive cancers.

POU2F2-IL-31 Autoregulatory Circuit Converts Hepatocytes into the Origin Cells of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) originates from fully differentiated hepatocytes, but the decisive events for converting hepatocytes to the cells of origin for HCC are still unclear. Liver cancer stem cells (LCSCs) cause HCC but are not bona fide cells of origin. Here, the expressions of POU2F2 and IL-31 are identified in macroscopically normal livers of diethylnitrosamine-challenged mice. An autoregulatory circuit formed by mutual induction between POU2F2 and IL-31 drives hepatocytes to progress to LCSCs by acquiring stemness, as well as stimulates them to in vivo grow and malignantly progress. The development of the autoregulatory circuit is a decisive event for converting hepatocytes into the cells of origin, since hepatocytes expressing the circuit have acquired tumorigenic potential before progressing to LCSCs. Nonetheless, acquiring stemness is still required for the cells of origin to initiate hepatocarcinogenesis. The circuit also occurs in human cirrhotic tissues, partially elucidating how premalignant lesions progress to HCC.

Spontaneous granulocytic leukemia in a NOD/Shi-scid IL-2Rγnull mouse

Here, we report a case of spontaneous granulocytic leukemia in a 51-week-old male NOD/Shi-scid IL-2Rγ ^null (NOG) mouse. The mouse showed progressive anemia and rough respiratory movement. Macroscopically, the spleen was discolored and enlarged. Histologically, the bone marrow of the sternum and femur was highly cellular and almost exclusively filled with neoplastic cells. The nuclei of neoplastic cells were large, oval to slightly irregular in shape, and a small number of cells had kidney- or ring-shaped nuclei. Neoplastic cells extensively infiltrated the organs, and the spleen and liver were prominently involved. Immunohistochemically, a large population of neoplastic cells in the red pulp of the spleen and sinusoid of the liver was positive for myeloperoxidase. Based on the histological features, this case was diagnosed with granulocytic leukemia. This novel information on spontaneous tumors may be helpful for the appropriate use of this mouse strain in further research.

A novel model of chronic limb ischemia to therapeutically evaluate the angiogenic effects of drug candidates

Critical limb ischemia (CLI) is a severe state of peripheral artery disease with high unmet clinical needs. Further, there are no effective treatment options for patients with CLI. Based on preclinical study results, predicting the clinical efficacy of CLI treatments is typically difficult because conventional hindlimb ischemia (HLI) rodent models display spontaneous recovery from ischemia, which is not observed in patients with CLI. Therefore, we aimed to develop a novel chronic and severe HLI model to properly evaluate the therapeutic effects of drug candidates for CLI. Severe HLI mice (Type-N) were generated by increasing the excised area of blood vessels in a hindlimb of NOG mice. Immunohistochemistry and gene expression analysis at 9 wk after the Type-N operation revealed that the ischemic limb was in a steady state with impaired angiogenesis, like that observed in patients with CLI. We did selection of chronic Type-N mice based on the number of necrotic nails and blood flow rate at 2 wk after surgery because some Type-N mice showed mild symptoms. Therapeutic treatment with cilostazol, which is used for intermittent claudication, did not restore blood flow in chronic Type-N mice. In contrast, therapeutic transplantation of pericytes and vascular endothelial cells, which can form new blood vessels in vivo, significantly improved blood flow in a subset of Type-N mice. These findings suggest that this novel chronic and severe HLI model may be a valuable standard animal model for therapeutic evaluation of the angiogenic effects of CLI drug candidates.NEW & NOTEWORTHY We developed a chronic and severe hindlimb ischemia (HLI) mouse model for preclinical research on critical limb ischemia (CLI). This model partially reflects human CLI pathology in that it does not show spontaneous restoration of blood flow or expression of angiogenic genes in the ischemic limb. This novel model may be valuable for therapeutic evaluation of the angiogenic effects of CLI drug candidates.

Short-term in vitro glutamine restriction differentially impacts the chromosomal stability of transformed and non-transformed cells

Glutamine (Gln) is a non-essential amino acid central for generating building blocks and cellular energy in tumours and rapidly proliferating non-transformed cells. However, the influence of Gln on regulating chromosomal stability of transformed and non-transformed cells remain poorly understand. We hypothesised that Gln is required for maintaining a homeostatic level of chromosomal stability. To this end, transformed cells HeLa and A375 and non-transformed cells NCM460 and HUVEC cells were intervened with varying concentrations of Gln (10, 1, 0.1 and 0.01 mM), with or without cisplatin (0.1 µg/ml), for 24 h. The cytokinesis-block micronucleus (MN) assay was used to determine chromosomal instability (CIN), the extent of which is reflected by the frequency of MN, nucleoplasmic bridge (NPB) and nuclear bud (NB). We demonstrated an unexpected decrease in the spontaneous rate of MN, but not NPB and NB, after Gln restriction in HeLa and A375 cells. Gln restriction reduced cisplatin-induced MN, but not NPB and NB, in HeLa and A375 cells. We further revealed that Gln restriction suppressed the proliferation of HeLa cells with high CIN induced by nocodazole, partially explaining why Gln restriction decreased the frequency of spontaneous and cisplatin-induced MN in transformed cells. In contrast, Gln restriction increased MN and NB, but not NPB, in NCM460 cells. In HUVEC cells, Gln restriction increased MN, NPB and NB. Meanwhile, Gln restriction sensitised NCM460 cells to cisplatin-induced genotoxicity. A similar but more pronounced pattern was observed in HUVEC cells. Collectively, these results suggest that the in vitro influences of Gln metabolism on CIN depend on cellular contexts: Transformed cells require high Gln to fine tune their CIN in an optimal rate to maximise genomic heterogeneity and fitness, whereas non-transformed cells need high Gln to prevent CIN.

Two base pair deletion in IL2 receptor γ gene in NOD/SCID mice induces a highly severe immunodeficiency

Genome editing has recently emerged as a powerful tool for generating mutant mice. Small deletions of nucleotides in the target genes are frequently found in CRISPR/Cas9 mediated mutant mice. However, there are very few reports analyzing the phenotypes in small deleted mutant mice generated by CRISPR/Cas9. In this study, we generated a mutant by microinjecting sgRNAs targeting the IL2 receptor γ gene and Cas9 protein, into the cytoplasm of IVF-derived NOD.CB17/Prkdcscid/JKrb (NOD/SCID) mice embryos, and further investigated whether a 2 bp deletion of the IL2 receptor γ gene affects severe deficiency of immune cells as seen in NOD/LtSz-scid IL2 receptor γ^−/− (NSG) mice. Our results show that the thymus weight of mutant mice is significantly less than that of NOD/SCID mice, whereas the spleen weight was marginally less. T and B cells in the mutant mice were severely deficient, and NK cells were almost absent. In addition, tumor growth was exceedingly increased in the mutant mice transplanted with HepG2, Raji and A549 cells, but not in nude and NOD/SCID mice. These results suggest that the NOD/SCID mice with deletion of 2 bp in the IL2 receptor γ gene shows same phenotype as NSG mice. Taken together, our data indicates that small deletions by genome editing is sufficient to generate null mutant mice.

Patient-Derived Orthotopic Xenograft Models of Pediatric Brain Tumors: In a Mature Phase or Still in Its Infancy?

In recent years, molecular profiling has led to the discovery of an increasing number of brain tumor subtypes, and associated therapeutic targets. These molecular features have been incorporated in the 2016 new World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS), which now distinguishes tumor subgroups not only histologically, but also based on molecular characteristics. Despite an improved diagnosis of (pediatric) tumors in the CNS however, the survival of children with malignant brain tumors still is far worse than for those suffering from other types of malignancies. Therefore, new treatments need to be developed, based on subgroup-specific genetic aberrations. Here, we provide an overview of the currently available orthotopic xenograft models for pediatric brain tumor subtypes as defined by the 2016 WHO classification, to facilitate the choice of appropriate animal models for the preclinical testing of novel treatment strategies, and to provide insight into the current gaps and challenges.

Recent Advances in Allergy Research Using Humanized Mice

The prevalence rates of allergic diseases are increasing worldwide, particularly in industrial countries. To date, many mouse models have been generated for allergy research; studies conducted using these models have suggested the importance of cross-talk between immune cells and tissue-resident non-immune cells in the onset of allergic diseases. However, there are several differences between the immune systems of rodents and humans, and human studies are limited. Thus, mice reconstituted with human immune cells are a novel tool for the preclinical evaluation of the efficacy and safety of developing drugs. Genetic technologies for generating humanized mice have improved markedly in recent years. In this review, we will discuss recent progress in allergy research using humanized mice and introduce our recent humanized mouse model of airway inflammation in human immune cells.

Comparison of biological features between severely immuno-deficient NOD/Shi-scid Il2rgnull and NOD/LtSz-scid Il2rgnull mice

Biological background data up to 11 weeks of age and tumorigenic susceptibility to xenotransplantation with HeLa cells were compared between severely immuno-deficient NOG and NSG mice. The body weight was lower in NOG mice than in NSG mice. Severe depletion of peripheral blood lymphocytes and lymphoid hypoplasia that are well-known characteristics of these mice were equally observed. No lymphoproliferative lesions developed in any mouse of either strain. The occurrence of ectopic exocrine gland and cyst was a common finding in the thymus of both strains. In addition, minimal spongiotic change was observed in the medulla oblongata and spinal cord in both strains, and its incidence in female NOG mice was a little higher than that in NSG mice. In the adrenal, subcapsular cell hyperplasia that is known as an age-related change in non-genetically modified mice developed earlier and its incidence was higher in NSG mice than in NOG mice. The development of female genital organs of NOG mice was slightly retarded in comparison with that of NSG mice. To evaluate tumorigenic susceptibility to xenotransplantation, female mice were implanted in the dorsal subcutis with 1×10³ to 1×10⁶ cells/head of HeLa cells, and were checked up to 16 weeks after implantation. As a result, there was no significant strain difference on tumor formation rate and tumor volume. In conclusion, the present study clearly demonstrated that NOG and NSG mice showed no distinct strain differences in either biological features or biological disadvantages.

[Development of the next generation humanized mouse for drug discovery]

A humanized mouse, which is efficiently engrafted human cells and tissues, is an important tool to mimic human physiology for biomedical researches. Since 2000s, severe combined immunodeficient mouse strains such as NOG, BRG, and NSG mice have been generated. They are great recipients to create humanized mouse models compared to previous other immunodeficient strains due to their multiple dysfunctions of innate and acquired immunity. Especially, the transfer of human hematopoietic stem cells into these immunodeficient mice has been enabled to reconstitute human immune systems, because the mice show high engraftment level of human leukocyte in peripheral blood (～50%), spleen and bone marrow (60～90%) and generate well-differentiated multilineage human immune cells including lymphoid and myeloid lineage cells. Using these mice, several human disease models such as cancer, allergy, graft-versus-host disease (GVHD), and etc. have been established to understand the pathogenic mechanisms of the diseases and to evaluate the efficacy and safety of novel drugs. In this review, I provide an overview of recent advances in the humanized mouse technology, including generation of novel platforms of genetically modified NOG (next generation NOG) mice and some applications of them to create human disease models for drug discovery in preclinical researches.

Establishment of Immunodeficient Retinal Degeneration Model Mice and Functional Maturation of Human ESC-Derived Retinal Sheets after Transplantation

Increasing demand for clinical retinal degeneration therapies featuring human ESC/iPSC-derived retinal tissue and cells warrants proof-of-concept studies. Here, we established two mouse models of end-stage retinal degeneration with immunodeficiency, NOG-rd1-2J and NOG-rd10, and characterized disease progress and immunodeficient status. We also transplanted human ESC-derived retinal sheets into NOG-rd1-2J and confirmed their long-term survival and maturation of the structured graft photoreceptor layer, without rejection or tumorigenesis. We recorded light responses from the host ganglion cells using a multi-electrode array system; this result was consistent with whole-mount immunostaining suggestive of host-graft synapse formation at the responding sites. This study demonstrates an application of our mouse models and provides a proof of concept for the clinical use of human ESC-derived retinal sheets.

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Two mouse models of immunodeficient end-stage retinal degeneration were established

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Immunodeficient host permitted transplantation of human ESC-derived retinal sheets

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Transplanted human ESC-derived retinal sheets survived long term and maturated

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After transplantation, light responses were recorded from the degenerated host retina

CRISPR/Cas9-Mediated Deletion of Foxn1 in NOD/SCID/IL2rg-/- Mice Results in Severe Immunodeficiency

Immunodeficient mice engrafted with either normal or cancerous human cells are widely used in basic and translational research. In particular, NOD/SCID/IL2rg^−/− mice can support the growth of various types of human cancer cells. However, the hairs of these mice interfere with the observation and imaging of engrafted tissues. Therefore, novel hairless strains exhibiting comparable immunodeficiency would be beneficial. Recently, the CRISPR/Cas9 system has been used for efficient multiplexed genome editing. In the present study, we generated a novel strain of nude NOD/SCID/IL2rg^−/− (NSIN) mice by knocking out Foxn1 from NOD/SCID/IL2rg^−/− (NSI) mice using the CRISPR/Cas9 system. The NSIN mice were deficient in B, T, and NK cells and not only showed impaired T cell reconstitution and thymus regeneration after allogeneic bone marrow nucleated cell transplantation but also exhibited improved capacity to graft both leukemic and solid tumor cells compared with NSI, NOG, and NDG mice. Moreover, the NSIN mice facilitated the monitoring and in vivo imaging of both leukemia and solid tumors. Therefore, our NSIN mice provide a new platform for xenograft mouse models in basic and translational research.

Humanized mouse models: Application to human diseases

Humanized mice are superior to rodents for preclinical evaluation of the efficacy and safety of drug candidates using human cells or tissues. During the past decade, humanized mouse technology has been greatly advanced by the establishment of novel platforms of genetically modified immunodeficient mice. Several human diseases can be recapitulated using humanized mice due to the improved engraftment and differentiation capacity of human cells or tissues. In this review, we discuss current advanced humanized mouse models that recapitulate human diseases including cancer, allergy, and graft-versus-host disease.

Hepatocyte growth factor produced in lung fibroblasts enhances non-small cell lung cancer cell survival and tumor progression

Background

The influence of lung fibroblasts on lung cancer progression is not fully understood.

Methods

Lung fibroblasts (HFL1, MRC5, and IMR90 cells) and non-small cell lung cancer (NSCLC)-derived cell lines (A549, EBC1, and HI1017) were cultured under serum-free conditions, and the resulting culture media were designated “cell-conditioned media”. Cell survival (viability) was assessed by WST-1 assay. Concentrations of hepatocyte growth factor (HGF) were measured by ELISA. The BALB/c-nu mouse strain was used for the xenograft model.

Results

Lung fibroblast-conditioned media enhanced the survival of the three NSCLC cell lines tested. HGF was produced to a greater extent by lung fibroblasts than NSCLC cells. Exogenous HGF enhanced the survival of NSCLC cells. Either an anti-HGF neutralizing antibody or the Met inhibitor PHA-665752 inhibited the fibroblast-conditioned media-enhanced survival of NSCLC cells. The co-inoculation of mice with NSCLC cells and fibroblasts enhanced tumorigenicity and tumor progression in a mouse xenograft model. PHA-665752 significantly inhibited tumor progression that occurred after the co-inoculation of NSCLC cells and fibroblasts. In addition, HGF production by fibroblasts was stimulated by NSCLC cells.

Conclusions

The current study provides evidence for an interaction between fibroblasts and NSCLC cells via the HGF/Met signaling pathway, which affects NSCLC cell survival and tumor progression. These findings may contribute to the development of anti-cancer-associated fibroblast therapeutic strategies.

Trial registration

No trial registration is required because this study is not a clinical trial. This study does not include any participants or patients.

Characterization of in vivo tumorigenicity tests using severe immunodeficient NOD/Shi-scid IL2Rγnull mice for detection of tumorigenic cellular impurities in human cell-processed therapeutic products

The contamination of human cell-processed therapeutic products (hCTPs) with tumorigenic cells is one of the major concerns in the manufacturing and quality control of hCTPs. However, no quantitative method for detecting the tumorigenic cellular impurities is currently standardized. NOD/Shi-scid IL2Rγnull (NOG) mice have shown high xeno-engraftment potential compared with other well-known immunodeficient strains, e.g. nude mice. Hypothesizing that tumorigenicity test using NOG mice could be a sensitive and quantitative method to detect a small amount of tumorigenic cells in hCTPs, we examined tumor formation after subcutaneous transplantation of HeLa cells, as a model of tumorigenic cells, in NOG mice and nude mice. Sixteen weeks after inoculation, the 50% tumor-producing dose (TPD50) values of HeLa cells were stable at 1.3 × 104 and 4.0 × 105 cells in NOG and nude mice, respectively, indicating a 30-fold higher sensitivity of NOG mice compared to that of nude mice. Transplanting HeLa cells embedded with Matrigel in NOG mice further decreased the TPD50 value to 7.9 × 10 cells, leading to a 5000-fold higher sensitivity, compared with that of nude mice. Additionally, when HeLa cells were mixed with 106 or 107 human mesenchymal stem cells as well as Matrigel, the TPD50 values in NOG mice were comparable to those of HeLa cells alone with Matrigel. These results suggest that the in vivo tumorigenicity test using NOG mice with Matrigel is a highly sensitive and quantitative method to detect a trace amount of tumorigenic cellular impurities in human somatic cells, which can be useful in the quality assessment of hCTPs.

Quantitative evaluation of the immunodeficiency of a mouse strain by tumor engraftments

Background

The mouse is an organism that is widely used as a mammalian model for studying human physiology or disease, and the development of immunodeficient mice has provided a valuable tool for basic and applied human disease research. Following the development of large-scale mouse knockout programs and genome-editing tools, it has become increasingly efficient to generate genetically modified mouse strains with immunodeficiency. However, due to the lack of a standardized system for evaluating the immuno-capacity that prevents tumor progression in mice, an objective choice of the appropriate immunodeficient mouse strains to be used for tumor engrafting experiments is difficult.

Methods

In this study, we developed a tumor engraftment index (TEI) to quantify the immunodeficiency response to hematologic malignant cells and solid tumor cells of six immunodeficient mouse strains and C57BL/6 wild-type mouse (WT).

Results

Mice with a more severely impaired immune system attained a higher TEI score. We then validated that the NOD-scid-IL2Rg−/− (NSI) mice, which had the highest TEI score, were more suitable for xenograft and allograft experiments using multiple functional assays.

Conclusions

The TEI score was effectively able to reflect the immunodeficiency of a mouse strain.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-015-0156-y) contains supplementary material, which is available to authorized users.

Design of a Tumorigenicity Test for Induced Pluripotent Stem Cell (iPSC)-Derived Cell Products

Human Pluripotent Stem Cell (PSC)-derived cell therapy holds enormous promise because of the cells' "unlimited" proliferative capacity and the potential to differentiate into any type of cell. However, these features of PSC-derived cell products are associated with concerns regarding the generation of iatrogenic teratomas or tumors from residual immature or non-terminally differentiated cells in the final cell product. This concern has become a major hurdle to the introduction of this therapy into the clinic. Tumorigenicity testing is therefore a key preclinical safety test in PSC-derived cell therapy. Tumorigenicity testing becomes particularly important when autologous human induced Pluripotent Stem Cell (iPSC)-derived cell products with no immuno-barrier are considered for transplantation. There has been, however, no internationally recognized guideline for tumorigenicity testing of PSC-derived cell products for cell therapy. In this review, we outline the points to be considered in the design and execution of tumorigenicity tests, referring to the tests and laboratory work that we have conducted for an iPSC-derived retinal pigment epithelium (RPE) cell product prior to its clinical use.

Higher susceptibility of NOD/LtSz-scid Il2rg (-/-) NSG mice to xenotransplanted lung cancer cell lines

Purpose

No lung cancer xenograft model using non-obese diabetic (NOD)-scid Il2rg^−/− mice has been reported. The purpose of this study is to select a suitable mouse strain as a xenogenic host for testing tumorigenicity of lung cancer.

Materials and methods

We directly compared the susceptibility of four immunodeficient mouse strains, c-nu, C.B-17 scid, NOD-scid, and NOD/LtSz-scid Il2rg^−/− (NSG) mice, for tumor formation from xenotransplanted lung cancer cell lines. Various numbers (10¹–10⁵ cells/head) of two lung cancer cell lines, A549 and EBC1, were subcutaneously inoculated and tumor sizes were measured every week up to 12 weeks.

Results

When 10⁴ EBC1 cells were inoculated, no tumor formation was observed in BALB/c-nu or C.B-17 scid mice. Tumors developed in two of the five NOD-scid mice (40%) and in all the five NSG mice (100%). When 10³ EBC1 cells were injected, no tumors developed in any strain other than NSG mice, while tumorigenesis was achieved in all the five NSG mice (100%, P=0.0079) within 9 weeks. NSG mice similarly showed higher susceptibility to xenotransplantation of A549 cells. Tumor formation was observed only in NSG mice after inoculation of 10³ or fewer A549 cells (40% vs 0% in 15 NSG mice compared with others, respectively, P=0.0169). We confirmed that the engrafted tumors originated from inoculated human lung cancer cells by immunohistochemical staining with human cytokeratin and vimentin.

Conclusion

NSG mice may be the most suitable strain for testing tumorigenicity of lung cancer, especially if only a few cells are available.

Pigment epithelium-derived factor secreted from retinal pigment epithelium facilitates apoptotic cell death of iPSC

We show that pigment epithelium-derived factor (PEDF), which is secreted from primary or iPSC-derived retinal pigment epithelium (RPE), dramatically inhibits the growth of iPSCs. PEDF is detected abundantly in culture supernatants of primary or iPSC-derived RPE. Apoptotic cell death is induced in iPSC when co-cultured with RPE, a process that is significantly blocked by addition of antibody against PEDF. Indeed, addition of recombinant PEDF to the iPSC cell culture induces apoptotic cell death in iPSCs, but the expression of pluripotency related-genes is maintained, suggesting that PEDF causes cell death, not differentiation, of iPSCs. To recapitulate this event in vivo, we examined tumor formation in NOG mice after subcutaneous injection of iPSCs with or without an iPSC-derived RPE sheet (2.5 × 10⁵ RPE cells). We observed that the tumor forming potential of iPSCs was significantly suppressed by simultaneous transplantation with an iPSC-derived RPE sheet.

Novel enhanced green fluorescent protein-expressing NOG mouse for analyzing the microenvironment of xenograft tissues

The interaction between transplanted cells and host tissues is important for the growth and maintenance of transplanted cells. To analyze the mechanisms of these interactions, a systemic fluorescent protein-expressing mouse is a useful recipient. In this study, we generated a novel NOG strain, which strongly expresses enhanced green fluorescent protein (EGFP; PgkEGFP-NOG), especially in the liver, kidney, gastrointestinal tract, and testis. Because the host tissues expressed EGFP, xenotransplanted human cancer cells were clearly identified as EGFP-negative colonies in PgkEGFP-NOG mice. Immunohistochemical analysis revealed that EGFP-expressing stromal tissues formed a complicated tumor microenvironment within xenograft tissues. Moreover, a similar microenvironment was observed in human iPS cell-derived teratomas. Collectively, these results indicated that a suitable microenvironment is essential for the growth and maintenance of xenotransplanted cells and that PgkEGFP-NOG mice represent a useful animal model for analyzing the mechanisms of microenvironment formation.

Tumorigenicity studies of induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) for the treatment of age-related macular degeneration

Basic studies of human pluripotential stem cells have advanced rapidly and stem cell products are now seeing therapeutic applications. However, questions remain regarding the tumorigenic potential of such cells. Here, we report the tumorigenic potential of induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) for the treatment of wet-type, age-related macular degeneration (AMD). First, immunodeficient mouse strains (nude, SCID, NOD-SCID and NOG) were tested for HeLa cells' tumor-forming capacity by transplanting various cell doses subcutaneously with or without Matrigel. The 50% Tumor Producing Dose (TPD50 value) is the minimal dose of transplanted cells that generated tumors in 50% of animals. For HeLa cells, the TPD50 was the lowest when cells were embedded in Matrigel and transplanted into NOG mice (TPD50 = 10(1.1), n = 75). The TPD50 for undifferentiated iPSCs transplanted subcutaneously to NOG mice in Matrigel was 10(2.12); (n = 30). Based on these experiments, 1×10(6) iPSC-derived RPE were transplanted subcutaneously with Matrigel, and no tumor was found during 15 months of monitoring (n = 65). Next, to model clinical application, we assessed the tumor-forming potential of HeLa cells and iPSC 201B7 cells following subretinal transplantation of nude rats. The TPD50 for iPSCs was 10(4.73) (n = 20) and for HeLa cells 10(1.32) (n = 37) respectively. Next, the tumorigenicity of iPSC-derived RPE was tested in the subretinal space of nude rats by transplanting 0.8-1.5×10(4) iPSC-derived RPE in a collagen-lined (1 mm×1 mm) sheet. No tumor was found with iPSC-derived RPE sheets during 6-12 months of monitoring (n = 26). Considering the number of rodents used, the monitoring period, the sensitivity of detecting tumors via subcutaneous and subretinal administration routes and the incidence of tumor formation from the iPSC-derived RPE, we conclude that the tumorigenic potential of the iPSC-derived RPE was negligible.

A versatile technique for the in vivo imaging of human tumor xenografts using near-infrared fluorochrome-conjugated macromolecule probes

Here, we present a versatile method for detecting human tumor xenografts in vivo, based on the enhanced permeability and retention (EPR) effect, using near-infrared (NIR) fluorochrome-conjugated macromolecule probes. Bovine serum albumin (BSA) and two immunoglobulins—an anti-human leukocyte antigen (HLA) monoclonal antibody and isotype control IgG_2a—were labeled with XenoLight CF770 fluorochrome and used as NIR-conjugated macromolecule probes to study whole-body imaging in a variety of xenotransplantation mouse models. NIR fluorescent signals were observed in subcutaneously transplanted BxPC-3 (human pancreatic cancer) cells and HCT 116 (colorectal cancer) cells within 24 h of NIR-macromolecule probe injection, but the signal from the fluorochrome itself or from the NIR-conjugated small molecule (glycine) injection was not observed. The accuracy of tumor targeting was confirmed by the localization of the NIR-conjugated immunoglobulin within the T-HCT 116 xenograft (in which the orange-red fluorescent protein tdTomato was stably expressed by HCT 116 cells) in the subcutaneous transplantation model. However, there was no significant difference in the NIR signal intensity of the region of interest between the anti-HLA antibody group and the isotype control group in the subcutaneous transplantation model. Therefore, the antibody accumulation within the tumor in vivo is based on the EPR effect. The liver metastasis generated by an intrasplenic injection of T-HCT 116 cells was clearly visualized by the NIR-conjugated anti-HLA probe but not by the orange-red fluorescent signal derived from the tdTomato reporter. This result demonstrated the superiority of the NIR probes over the tdTomato reporter protein at enhancing tissue penetration. In another xenograft model, patient-derived xenografts (PDX) of LC11-JCK (human non-small cell lung cancer) were successfully visualized using the NIR-conjugated macromolecule probe without any genetic modification. These results suggested that NIR-conjugated macromolecule, preferably, anti-HLA antibody probe is a valuable tool for the detection of human tumors in experimental metastasis models using whole-body imaging.

[In vitro tumorigenicity tests for process control of health care products derived from human induced pluripotent stem cells]

  The goal of pharmaceutical sciences is to deliver effective and safe medicinal products to patients. To achieve this goal, we need to ensure the efficacy, safety and quality of the products. Currently, many attempts are made to utilize human induced pluripotent stem cells (hiPSCs) in regenerative medicine/cell therapy. There are significant obstacles, however, preventing the clinical use of hiPSC-derived products. One of the most obvious safety issues is the presence of residual undifferentiated cells that have tumorigenic potential. Therefore, the assessment and control of the tumorigenicity of hiPSC-derived products is essential in order to prevent tumor development by residual pluripotent stem cells after implantation. We recently examined three in vitro assay methods to detect undifferentiated cells: soft agar colony formation assay, flow cytometry assay and quantitative real-time polymerase chain reaction assay (qRT-PCR). Although the soft agar colony formation assay was unable to detect hiPSCs, the flow cytometry assay using anti-TRA-1-60 antibody detected 0.1% undifferentiated hiPSCs that were spiked in primary retinal pigment epithelial (RPE) cells. Moreover, qRT-PCR with a specific probe and primers was found to detect a trace amount of LIN28 mRNA, which is equivalent to that present in a mixture of a single hiPSC and 5.0×10(4) RPE cells. Our findings provide highly sensitive and quantitative in vitro assays essential for facilitating safety profiling of hiPSC-derived RPE cells for their clinical use.

The human hepatic cell line HepaRG as a possible cell source for the generation of humanized liver TK-NOG mice

Humanized-liver mice, in which the liver has been repopulated with human hepatocytes, have been used to study aspects of human liver physiology such as drug metabolism, toxicology and hepatitis infection. However, the procurement of human hepatocytes is a major problem in producing humanized-liver mice because of the finite nature of the patient-derived resource.

In order to overcome this limitation, the human hepatic cell line HepaRG® were evaluated as promising donor cells for liver reconstitution in the TK-NOG mouse model.

We demonstrate that, in vivo, transplanted confluent culture or differentiated HepaRG® cells proliferated and differentiated toward both hepatocyte-like and biliary-like cells within the recipient liver. In contrast, proliferative HepaRG® cells could engraft TK-NOG mouse liver but could differentiate only toward biliary-like cells. The differentiation to hepatocyte-like cells was characterized by the detection of human albumin in the recipient mouse serum and was confirmed by immunohistochemical staining for human leukocyte antigen, human albumin, cytochrome P450 3A4, and multidrug resistance-associated protein 2. Biliary-like cells were characterized by positive staining for cytokeratin-19.

These results indicated that the differentiated HepaRG® cells are a possible cell source for generating humanized-liver mice, which are a useful model for in vivo studies of liver physiology.

Establishment of a human allergy model using human IL-3/GM-CSF-transgenic NOG mice

The development of animal models that mimic human allergic responses is crucial to study the pathophysiology of disease and to generate new therapeutic methodologies. Humanized mice reconstituted with human immune systems are essential to study human immune reactions in vivo and are expected to be useful for studying human allergies. However, application of this technology to the study of human allergies has been limited, largely because of the poor development of human myeloid cells, especially granulocytes and mast cells, which are responsible for mediating allergic diseases, in conventional humanized mice. In this study, we developed a novel transgenic (Tg) strain, NOD/Shi-scid-IL2rγ(null) (NOG), bearing human IL-3 and GM-CSF genes (NOG IL-3/GM-Tg). In this strain, a large number of human myeloid cells of various lineages developed after transplantation of human CD34⁺ hematopoietic stem cells. Notably, mature basophils and mast cells expressing FcεRI were markedly increased. These humanized NOG IL-3/GM-Tg mice developed passive cutaneous anaphylaxis reactions when administered anti-4-hydroxy-3-nitrophenylacetyl IgE Abs and 4-hydroxy-3-nitrophenylacetyl. More importantly, a combination of serum from Japanese cedar pollinosis patients and cedar pollen extract also elicited strong passive cutaneous anaphylaxis responses in mice. Thus, to our knowledge, our NOG IL-3/GM-Tg mice are the first humanized mouse model to enable the study of human allergic responses in vivo and are excellent tools for preclinical studies of allergic diseases.

Differential post-surgical metastasis and survival in SCID, NOD-SCID and NOD-SCID-IL-2Rγ(null) mice with parental and subline variants of human breast cancer: implications for host defense mechanisms regulating metastasis

We compare for the first time, the metastatic aggressiveness of the parental MDA-MB-231 breast cancer cell line and two luciferase-tagged in vivo-derived and selected pro-metastatic variants (LM2-4/luc⁺ and 164/8-1B/luc⁺) in SCID, NOD-SCID and NOD-SCID-IL-2Rγ^null (NSG) mice following orthotopic implantation and primary tumour resection. The variants are known to be more aggressively metastatic in SCID mice, compared to the parental line which has limited spontaneous metastatic competence in these mice. When 2×10⁶ cells were injected into the mammary fat pad, the growth of the resultant primary tumours was identical for the various cell lines in the three strains of mice. However, metastatic spread of all three cell lines, including the MDA-MB-231 parental cell line, was strikingly more aggressive in the highly immunocompromised NSG mice compared to both NOD-SCID and SCID mice, resulting in extensive multi-organ metastases and a significant reduction in overall survival. While these studies were facilitated by monitoring post-surgical spontaneous metastases using whole body bioluminescence imaging, we observed that the luciferase-tagged parental line showed altered growth and diminished metastatic properties compared to its untagged counterpart. Our results are the first to show that host immunity can have a profound impact on the spread of spontaneous visceral metastases and survival following resection of a primary tumour in circumstances where the growth of primary tumours is not similarly affected; as such they highlight the importance of immunity in the metastatic process, and by extension, suggest certain therapeutic strategies that may have a significant impact on reducing metastasis.

A novel combinatorial therapy with pulp stem cells and granulocyte colony-stimulating factor for total pulp regeneration

Treatment of deep caries with pulpitis is a major challenge in dentistry. Stem cell therapy represents a potential strategy to regenerate the dentin-pulp complex, enabling conservation and restoration of teeth. The objective of this study was to assess the efficacy and safety of pulp stem cell transplantation as a prelude for the impending clinical trials. Clinical-grade pulp stem cells were isolated and expanded according to good manufacturing practice conditions. The absence of contamination, abnormalities/aberrations in karyotype, and tumor formation after transplantation in an immunodeficient mouse ensured excellent quality control. After autologous transplantation of pulp stem cells with granulocyte-colony stimulating factor (G-CSF) in a dog pulpectomized tooth, regenerated pulp tissue including vasculature and innervation completely filled in the root canal, and regenerated dentin was formed in the coronal part and prevented microleakage up to day 180. Transplantation of pulp stem cells with G-CSF yielded a significantly larger amount of regenerated dentin-pulp complex compared with transplantation of G-CSF or stem cells alone. Also noteworthy was the reduction in the number of inflammatory cells and apoptotic cells and the significant increase in neurite outgrowth compared with results without G-CSF. The transplanted stem cells expressed angiogenic/neurotrophic factors. It is significant that G-CSF together with conditioned medium of pulp stem cells stimulated cell migration and neurite outgrowth, prevented cell death, and promoted immunosuppression in vitro. Furthermore, there was no evidence of toxicity or adverse events. In conclusion, the combinatorial trophic effects of pulp stem cells and G-CSF are of immediate utility for pulp/dentin regeneration, demonstrating the prerequisites of safety and efficacy critical for clinical applications.

Potential utility of eGFP-expressing NOG mice (NOG-EGFP) as a high purity cancer sampling system

PURPOSE

It is still technically difficult to collect high purity cancer cells from tumor tissues, which contain noncancerous cells. We hypothesized that xenograft models of NOG mice expressing enhanced green fluorescent protein (eGFP), referred to as NOG-EGFP mice, may be useful for obtaining such high purity cancer cells for detailed molecular and cellular analyses.

METHODS

Pancreato-biliary cancer cell lines were implanted subcutaneously to compare the tumorigenicity between NOG-EGFP mice and nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. To obtain high purity cancer cells, the subcutaneous tumors were harvested from the mice and enzymatically dissociated into single-cell suspensions. Then, the cells were sorted by fluorescence-activated cell sorting (FACS) for separation of the host cells and the cancer cells. Thereafter, the contamination rate of host cells in collected cancer cells was quantified by using FACS analysis. The viability of cancer cells after FACS sorting was evaluated by cell culture and subsequent subcutaneous reimplantation in NOG-EGFP mice.

RESULTS

The tumorigenicity of NOG-EGFP mice was significantly better than that of NOD/SCID mice in all of the analyzed cell lines (p < 0.01). Sorting procedures enabled an almost pure collection of cancer cells with only slight contamination by host cells. Reimplantation of the sorted cancer cells formed tumors again, which demonstrated that cell viability after sorting was well maintained.

CONCLUSIONS

This method provides a novel cancer sampling system for molecular and cellular analysis with high accuracy and should contribute to the development of personalized medicine.

Development of pluripotent stem cells for vascular therapy

Peripheral arterial disease (PAD) is characterized by reduced limb blood flow due to arterial obstruction. Current treatment includes surgical or endovascular procedures, the failure of which may result in amputation of the affected limb. An emerging therapeutic approach is cell therapy to enhance angiogenesis and tissue survival. Small clinical trials of adult progenitor cell therapies have generated promising results, although large randomized clinical trials using well-defined cells have not been performed. Intriguing pre-clinical studies have been performed using vascular cells derived from human embryonic stem cells (hESC) or human induced pluripotent stem cells (hiPSCs). In particular, hiPSC-derived vascular cells may be a superior approach for vascular regeneration. The regulatory roadmap to the clinic will be arduous, but achievable with further understanding of the reprogramming and differentiation processes; with meticulous attention to quality control; and perseverance.

Current advances in humanized mouse models

Humanized mouse models that have received human cells or tissue transplants are extremely useful in basic and applied human disease research. Highly immunodeficient mice, which do not reject xenografts and support cell and tissue differentiation and growth, are indispensable for generating additional appropriate models. Since the early 2000s, a series of immunodeficient mice appropriate for generating humanized mice has been successively developed by introducing the IL-2Rγ(null) gene (e.g., NOD/SCID/γc(null) and Rag2(null)γc(null) mice). These strains show not only a high rate of human cell engraftment, but also generate well-differentiated multilineage human hematopoietic cells after human hematopoietic stem cell (HSC) transplantation. These humanized mice facilitate the analysis of human hematology and immunology in vivo. However, human hematopoietic cells developed from HSCs are not always phenotypically and functionally identical to those in humans. More recently, a new series of immunodeficient mice compensates for these disadvantages. These mice were generated by genetically introducing human cytokine genes into NOD/SCID/γc(null) and Rag2(null)γc(null) mice. In this review, we describe the current knowledge of human hematopoietic cells developed in these mice. Various human disease mouse models using these humanized mice are summarized.

Characterization of the epithelial cell adhesion molecule (EpCAM)+ cell population in hepatocellular carcinoma cell lines

Accumulating evidence suggests that cancer stem cells (CSC) play an important role in tumorigenicity. Epithelial cell adhesion molecule (EpCAM) is one of the markers that identifies tumor cells with high tumorigenicity. The expression of EpCAM in liver progenitor cells prompted us to investigate whether CSC could be identified in hepatocellular carcinoma (HCC) cell lines. The sorted EpCAM(+) subpopulation from HCC cell lines showed a greater colony formation rate than the sorted EpCAM(-) subpopulation from the same cell lines, although cell proliferation was comparable between the two subpopulations. The in vivo evaluation of tumorigenicity, using supra-immunodeficient NOD/scid/γc(null) (NOG) mice, revealed that a smaller number of EpCAM(+) cells (minimum 100) than EpCAM(-) cells was necessary for tumor formation. The bifurcated differentiation of EpCAM(+) cell clones into both EpCAM(+) and EpCAM(-) cells was obvious both in vitro and in vivo, but EpCAM(-) clones sustained their phenotype. These clonal analyses suggested that EpCAM(+) cells may contain a multipotent cell population. Interestingly, the introduction of exogenous EpCAM into EpCAM(+) clones, but not into EpCAM(-) clones, markedly enhanced their tumor-forming ability, even though both transfectants expressed a similar level of EpCAM. Therefore, the difference in the tumor-forming ability between EpCAM(+) and EpCAM(-) cells is probably due to the intrinsic biological differences between them. Collectively, our results suggest that the EpCAM(+) population is biologically quite different from the EpCAM(-) population in HCC cell lines, and preferentially contains a highly tumorigenic cell population with the characteristics of CSC.

Generation of knockout rats with X-linked severe combined immunodeficiency (X-SCID) using zinc-finger nucleases

Background

Although the rat is extensively used as a laboratory model, the inability to utilize germ line-competent rat embryonic stem (ES) cells has been a major drawback for studies that aim to elucidate gene functions. Recently, zinc-finger nucleases (ZFNs) were successfully used to create genome-specific double-stranded breaks and thereby induce targeted gene mutations in a wide variety of organisms including plants, drosophila, zebrafish, etc.

Methodology/Principal Findings

We report here on ZFN-induced gene targeting of the rat interleukin 2 receptor gamma (Il2rg) locus, where orthologous human and mouse mutations cause X-linked severe combined immune deficiency (X-SCID). Co-injection of mRNAs encoding custom-designed ZFNs into the pronucleus of fertilized oocytes yielded genetically modified offspring at rates greater than 20%, which possessed a wide variety of deletion/insertion mutations. ZFN-modified founders faithfully transmitted their genetic changes to the next generation along with the severe combined immune deficiency phenotype.

Conclusions and Significance

The efficient and rapid generation of gene knockout rats shows that using ZFN technology is a new strategy for creating gene-targeted rat models of human diseases. In addition, the X-SCID rats that were established in this study will be valuable in vivo tools for evaluating drug treatment or gene therapy as well as model systems for examining the treatment of xenotransplanted malignancies.