Predominant development of mature and functional human NK cells in a novel human IL-2-producing transgenic NOG mouse

Technical considerations and strategies for generating and optimizing humanized mouse tumor models in immuno-oncology research

The field of cancer immunotherapy has experienced significant progress, resulting in the emergence of numerous biological drug candidates requiring in vivo efficacy testing and a better understanding of their mechanism of action (MOA). Humanized immune system (HIS) models are valuable tools in this regard. However, there is a lack of systematic guidance on HIS modeling. To address this issue, the present study aimed to establish and optimize a variety of HIS models for immune-oncology (IO) study, including genetically engineered mouse models and HIS models with human immune components reconstituted in severely immunocompromised mice. The efficacy and utility of these models were tested with several marketed or investigational IO drugs according to their MOA, followed by immunophenotypic analysis and efficacy evaluation. The results of the present study demonstrated that the HIS models responded to various IO drugs as expected and that each model had unique niches, utilities and limitations. Researchers should carefully choose the appropriate models based on the MOA and the targeted immune cell populations of the investigational drug. The present study provides valuable methodologies and actionable technical guidance on designing, generating or utilizing appropriate HIS models to address specific questions in translational IO.

Humanized Mouse Models of Bacterial Infections

Bacterial infections continue to represent a significant healthcare burden worldwide, causing considerable mortality and morbidity every year. The emergence of multidrug-resistant bacterial strains continues to rise, posing serious risks to controlling global disease outbreaks. To develop novel and more effective treatment and vaccination programs, there is a need for clinically relevant small animal models. Since multiple bacterial species have human-specific tropism for numerous virulence factors and toxins, conventional mouse models do not fully represent human disease. Several human disease characteristic phenotypes, such as lung granulomas in the case of Mycobacterium tuberculosis infections, are absent in standard mouse models. Alternatively, certain pathogens, such as Salmonella enterica serovar typhi and Staphylococcus aureus, can be well tolerated in mice and cleared quickly. To address this, multiple groups have developed humanized mouse models and observed enhanced susceptibility to infection and a more faithful recapitulation of human disease. In the last two decades, multiple humanized mouse models have been developed to attempt to recapitulate the human immune system in a small animal model. In this review, we first discuss the history of immunodeficient mice that has enabled the engraftment of human tissue and the engraftment methods currently used in the field. We then highlight how humanized mouse models successfully uncovered critical human immune responses to various bacterial infections, including Salmonella enterica serovar Typhi, Mycobacterium tuberculosis, and Staphylococcus aureus.

Human CD56+CD39+ dNK cells support fetal survival through controlling trophoblastic cell fate: immune mechanisms of recurrent early pregnancy loss

Decidual natural killer (dNK) cells are the most abundant immune cells at the maternal-fetal interface during early pregnancy in both mice and humans, and emerging single-cell transcriptomic studies have uncovered various human dNK subsets that are disrupted in patients experiencing recurrent early pregnancy loss (RPL) at early gestational stage, suggesting a connection between abnormal proportions or characteristics of dNK subsets and RPL pathogenesis. However, the functional mechanisms underlying this association remain unclear. Here, we established a mouse model by adoptively transferring human dNK cells into pregnant NOG (NOD/Shi-scid/IL-2Rγnull) mice, where human dNK cells predominantly homed into the uteri of recipients. Using this model, we observed a strong correlation between the properties of human dNK cells and pregnancy outcome. The transfer of dNK cells from RPL patients (dNK-RPL) remarkably worsened early pregnancy loss and impaired placental trophoblast cell differentiation in the recipients. These adverse effects were effectively reversed by transferring CD56+CD39+ dNK cells. Mechanistic studies revealed that CD56+CD39+ dNK subset facilitates early differentiation of mouse trophoblast stem cells (mTSCs) towards both invasive and syncytial pathways through secreting macrophage colony-stimulating factor (M-CSF). Administration of recombinant M-CSF to NOG mice transferred with dNK-RPL efficiently rescued the exacerbated pregnancy outcomes and fetal/placental development. Collectively, this study established a novel humanized mouse model featuring functional human dNK cells homing into the uteri of recipients and uncovered the pivotal role of M-CSF in fetal-supporting function of CD56+CD39+ dNK cells during early pregnancy, highlighting that M-CSF may be a previously unappreciated therapeutic target for intervening RPL.

Mouse Models for Head and Neck Squamous Cell Carcinoma

The prognosis and survival rate of head and neck squamous cell carcinoma (HNSCC) have remained unchanged for years, and the pathogenesis of HNSCC is still not fully understood, necessitating further research. An ideal animal model that accurately replicates the complex microenvironment of HNSCC is urgently needed. Among all the animal models for preclinical cancer research, tumor-bearing mouse models are the best known and widely used due to their high similarity to humans. Currently, mouse models for HNSCC can be broadly categorized into chemical-induced models, genetically engineered mouse models (GEMMs), and transplanted mouse models, each with its distinct advantages and limitations. In chemical-induced models, the carcinogen spontaneously initiates tumor formation through a multistep process. The resemblance of this model to human carcinogenesis renders it an ideal preclinical platform for studying HNSCC initiation and progression from precancerous lesions. The major drawback is that these models are time-consuming and, like human cancer, unpredictable in terms of timing, location, and number of lesions. GEMMs involve transgenic and knockout mice with gene modifications, leading to malignant transformation within a tumor microenvironment that recapitulates tumorigenesis in vivo, including their interaction with the immune system. However, most HNSCC GEMMs exhibit low tumor incidence and limited prognostic significance when translated to clinical studies. Transplanted mouse models are the most widely used in cancer research due to their consistency, availability, and efficiency. Based on the donor and recipient species matching, transplanted mouse models can be divided into xenografts and syngeneic models. In the latter, transplanted cells and host are from the same strain, making syngeneic models relevant to study functional immune system. In this review, we provide a comprehensive summary of the characteristics, establishment methods, and potential applications of these different HNSCC mouse models, aiming to assist researchers in choosing suitable animal models for their research.

Against all odds: The road to success in the development of human immune reconstitution mice

The mouse genome has a high degree of homology with the human genome, and its physiological, biochemical, and developmental regulation mechanisms are similar to those of humans; therefore, mice are widely used as experimental animals. However, it is undeniable that interspecies differences between humans and mice can lead to experimental errors. The differences in the immune system have become an important factor limiting current immunological research. The application of immunodeficient mice provides a possible solution to these problems. By transplanting human immune cells or tissues, such as peripheral blood mononuclear cells or hematopoietic stem cells, into immunodeficient mice, a human immune system can be reconstituted in the mouse body, and the engrafted immune cells can elicit human-specific immune responses. Researchers have been actively exploring the development and differentiation conditions of host recipient animals and grafts in order to achieve better immune reconstitution. Through genetic engineering methods, immunodeficient mice can be further modified to provide a favorable developmental and differentiation microenvironment for the grafts. From initially only being able to reconstruct single T lymphocyte lineages, it is now possible to reconstruct lymphoid and myeloid cells, providing important research tools for immunology-related studies. In this review, we compare the differences in immune systems of humans and mice, describe the development history of human immune reconstitution from the perspectives of immunodeficient mice and grafts, and discuss the latest advances in enhancing the efficiency of human immune cell reconstitution, aiming to provide important references for immunological related researches.

Bispecific immune cell engager enhances the anticancer activity of CD16+ NK cells and macrophages in vitro, and eliminates cancer metastasis in NK humanized NOG mice

BACKGROUND

In a prior report, we detailed the isolation and engineering of a bispecific killer cell engager, referred to as BiKE:E5C1. The BiKE:E5C1 exhibits high affinity/specificity for the CD16a activating receptor on natural killer (NK) cells and human epidermal growth factor receptor 2 (HER2) on cancer cells. In vitro studies have demonstrated that BiKE:E5C1 can activate the NK cells and induce the killing of HER2+ ovarian and breast cancer cells, surpassing the performance of the best-in-class monoclonal antibody, Trazimera (trastuzumab). To advance this BiKE technology toward clinical application, the objective of this research was to demonstrate the ability of BiKE:E5C1 to activate CD16+ immune cells such as NK cells and macrophages to kill cancer cells, and eradicate metastatic HER2+ tumors in NK humanized NOG mice.

METHODS

We assessed BiKE:E5C1's potential to activate CD16-expressing peripheral blood (PB)-NK cells, laNK92 cells, and THP-1-CD16A monocyte-macrophages through flowcytometry and antibody-dependent cell-mediated cytotoxicity/phagocytosis (ADCC) assays. Subsequently, laNK92 cells were selected as effector cells and genetically modified to express the nanoluciferase gene, enabling the monitoring of their viability in NK humanized NOG mice using quantitative bioluminescent imaging (qBLI). To evaluate the functionality of BiKE:E5C1 in vivo, we introduced firefly luciferase-expressing ovarian cancer cells via intraperitoneal injection into hIL-15 and hIL-2 NOG mice, creating a model of ovarian cancer metastasis. Once tumor establishment was confirmed, we treated the mice with laNK92 cells plus BiKE:E5C1 and the response to therapy was assessed using qBLI.

RESULTS

Our data demonstrate that BiKE:E5C1 activates not only laNK92 cells but also PB-NK cells and macrophages, significantly enhancing their anticancer activities. ADCC assay demonstrated that IgG1 Fc region had no impact on BiKE:E5C1's anticancer activity. In vivo results reveal that both hIL-15 and hIL-2 NOG mouse models support the viability and proliferation of laNK92 cells. Furthermore, it was observed that BiKE:E5C1 activates laNK92 cells in mice, leading to eradication of cancer metastasis in both NK humanized hIL-15 and hIL-2 NOG mouse models.

CONCLUSIONS

Collectively, our in vivo findings underscore BiKE:E5C1's potential as an immune cell engager capable of activating immune cells for cancer cell elimination, thereby expanding the arsenal of available BiKEs for cancer immunotherapy.

Breast Cancer Immunity: It is TIME for the Next Chapter

Our ability to interrogate the tumor immune microenvironment (TIME) at an ever-increasing granularity has uncovered critical determinants of disease progression. Not only do we now have a better understanding of the immune response in breast cancer, but it is becoming possible to leverage key mechanisms to effectively combat this disease. Almost every component of the immune system plays a role in enabling or inhibiting breast tumor growth. Building on early seminal work showing the involvement of T cells and macrophages in controlling breast cancer progression and metastasis, single-cell genomics and spatial proteomics approaches have recently expanded our view of the TIME. In this article, we provide a detailed description of the immune response against breast cancer and examine its heterogeneity in disease subtypes. We discuss preclinical models that enable dissecting the mechanisms responsible for tumor clearance or immune evasion and draw parallels and distinctions between human disease and murine counterparts. Last, as the cancer immunology field is moving toward the analysis of the TIME at the cellular and spatial levels, we highlight key studies that revealed previously unappreciated complexity in breast cancer using these technologies. Taken together, this article summarizes what is known in breast cancer immunology through the lens of translational research and identifies future directions to improve clinical outcomes.

Progress in construction of mouse models to investigate the pathogenesis and immune therapy of human hematological malignancy

Hematological malignancy is a disease arisen by complicate reasons that seriously endangers human health. The research on its pathogenesis and therapies depends on the usage of animal models. Conventional animal model cannot faithfully mirror some characteristics of human features due to the evolutionary divergence, whereas the mouse models hosting human hematological malignancy are more and more applied in basic as well as translational investigations in recent years. According to the construction methods, they can be divided into different types (e.g. cell-derived xenograft (CDX) and patient-derived xenograft model (PDX) model) that have diverse characteristics and application values. In addition, a variety of strategies have been developed to improve human hematological malignant cell engraftment and differentiation in vivo. Moreover, the humanized mouse model with both functional human immune system and autologous human hematological malignancy provides a unique tool for the evaluation of the efficacy of novel immunotherapeutic drugs/approaches. Herein, we first review the evolution of the mouse model of human hematological malignancy; Then, we analyze the characteristics of different types of models and summarize the ways to improve the models; Finally, the way and value of humanized mouse model of human immune system in the immunotherapy of human hematological malignancy are discussed.

Humanized Mouse Models for Immuno-oncology Drug Discovery

Breakthroughs in cancer treatment with immunotherapeutics have provided long-term patient benefits for many different types of cancer. However, complete response is not achieved in many patients and tumor types, and the mechanisms underlying this lack of response are poorly understood. Despite this, numerous new targets, therapeutics, and drug combinations are being developed and tested in clinical trials. Preclinical models that recapitulate the complex human tumor microenvironment and the interplay between tumor and immune cells within the cancer-immunity cycle are needed to improve our understanding and screen new therapeutics for efficacy and safety/toxicity. Humanized mice, encompassing human tumors and human immune cells engrafted on immunodeficient mice, have been widely used for many years in immuno-oncology, with developments to improve both the humanization and the translational value central to the next generation of models. In this overview, we discuss recent advances in humanized models relevant to immuno-oncology drug discovery, the advantages and limitations of such models, the application of humanized models for efficacy and safety assessments of immunotherapeutics, and the potential opportunities. © 2023 Crown Bioscience. Current Protocols published by Wiley Periodicals LLC.

Mouse Models for HTLV-1 Infection and Adult T Cell Leukemia

Adult T cell leukemia (ATL) is an aggressive hematologic disease caused by human T cell leukemia virus type 1 (HTLV-1) infection. Various animal models of HTLV-1 infection/ATL have been established to elucidate the pathogenesis of ATL and develop appropriate treatments. For analyses employing murine models, transgenic and immunodeficient mice are used because of the low infectivity of HTLV-1 in mice. Each mouse model has different characteristics that must be considered before use for different HTLV-1 research purposes. HTLV-1 Tax and HBZ transgenic mice spontaneously develop tumors, and the roles of both Tax and HBZ in cell transformation and tumor growth have been established. Severely immunodeficient mice were able to be engrafted with ATL cell lines and have been used in preclinical studies of candidate molecules for the treatment of ATL. HTLV-1-infected humanized mice with an established human immune system are a suitable model to characterize cells in the early stages of HTLV-1 infection. This review outlines the characteristics of mouse models of HTLV-1 infection/ATL and describes progress made in elucidating the pathogenesis of ATL and developing related therapies using these mice.

Murine models to study human NK cells in human solid tumors

Since the first studies, the mouse models have provided crucial support for the most important discoveries on NK cells, on their development, function, and circulation within normal and tumor tissues. Murine tumor models were initially set to study murine NK cells, then, ever more sophisticated human-in-mice models have been developed to investigate the behavior of human NK cells and minimize the interferences from the murine environment. This review presents an overview of the models that have been used along time to study NK cells, focusing on the most popular NOG and NSG models, which work as recipients for the preparation of human-in-mice tumor models, the study of transferred human NK cells, and the evaluation of various enhancers of human NK cell function, including cytokines and chimeric molecules. Finally, an overview of the next generation humanized mice is also provided along with a discussion on how traditional and innovative in-vivo and in-vitro approaches could be integrated to optimize effective pre-clinical studies.

Modeling the Tumor Microenvironment and Cancer Immunotherapy in Next-Generation Humanized Mice

Cancer immunotherapy has brought significant clinical benefits to numerous patients with malignant disease. However, only a fraction of patients experiences complete and durable responses to currently available immunotherapies. This highlights the need for more effective immunotherapies, combination treatments and predictive biomarkers. The molecular properties of a tumor, intratumor heterogeneity and the tumor immune microenvironment decisively shape tumor evolution, metastasis and therapy resistance and are therefore key targets for precision cancer medicine. Humanized mice that support the engraftment of patient-derived tumors and recapitulate the human tumor immune microenvironment of patients represent a promising preclinical model to address fundamental questions in precision immuno-oncology and cancer immunotherapy. In this review, we provide an overview of next-generation humanized mouse models suitable for the establishment and study of patient-derived tumors. Furthermore, we discuss the opportunities and challenges of modeling the tumor immune microenvironment and testing a variety of immunotherapeutic approaches using human immune system mouse models.

Establishment of humanized mice and its application progress in cancer immunotherapy

The current high prevalence of malignant tumors has attracted considerable attention, and treating advanced malignancies is becoming increasingly difficult. Although immunotherapy is a hopeful alternative, it is effective in only a few people. Thus, development of preclinical animal models is needed. Humanized xenotransplantation mouse models can help with selecting treatment protocols, evaluating curative effects and assessing prognosis. This review discusses the establishment of humanized mouse models and their application prospects in cancer immunotherapy to identify tailored therapies for individual patients.

Humanized mouse models with endogenously developed human natural killer cells for in vivo immunogenicity testing of HLA class I-edited iPSC-derived cells

Human induced pluripotent stem cells (hiPSCs) genetically depleted of human leucocyte antigen (HLA) class I expression can bypass T cell alloimmunity and thus serve as a one-for-all source for cell therapies. However, these same therapies may elicit rejection by natural killer (NK) cells, since HLA class I molecules serve as inhibitory ligands of NK cells. Here, we focused on testing the capacity of endogenously developed human NK cells in humanized mice (hu-mice) using MTSRG and NSG-SGM3 strains to assay the tolerance of HLA-edited iPSC-derived cells. High NK cell reconstitution was achieved with the engraftment of cord blood-derived human hematopoietic stem cells (hHSCs) followed by the administration of human interleukin-15 (hIL-15) and IL-15 receptor alpha (hIL-15Rα). Such "hu-NK mice" rejected HLA class I-null hiPSC-derived hematopoietic progenitor cells (HPCs), megakaryocytes and T cells, but not HLA-A/B-knockout, HLA-C expressing HPCs. To our knowledge, this study is the first to recapitulate the potent endogenous NK cell response to non-tumor HLA class I-downregulated cells in vivo. Our hu-NK mouse models are suitable for the non-clinical evaluation of HLA-edited cells and will contribute to the development of universal off-the-shelf regenerative medicine.

Sustaining the T-cell activity in xenografted psoriasis skin

Xenografting of psoriasis skin onto immune deficient mice has been widely used to obtain proof-of-principle of new drug candidates. However, the lack of human T-cell activity in the grafts limits the use of the model. Here, we show that xenografting of lesional skin from psoriasis patients onto human IL-2 NOG mice results in increased numbers of human CD3+ cells in the grafts, axillary lymph nodes and blood from human IL-2 NOG mice compared to C.B-17 scid and NOG mice. In addition, disease relevant human cytokine levels were higher in graft lysates and serum from human IL-2 NOG mice. However, the epidermis was lacking and no efficacy of ustekinumab, a human anti-P40 antibody targeting both IL-12 and IL-23, was shown. Thus, despite the sustained T-cell activity, the model needs further investigations and validation to capture more aspects of psoriasis.

Enhanced development of functional human NK cells in NOD-scid-IL2rgnull mice expressing human IL15

Human innate immunity plays a critical role in tumor surveillance and in immunoregulation within the tumor microenvironment. Natural killer (NK) cells are innate lymphoid cells that have opposing roles in the tumor microenvironment, including NK cell subsets that mediate tumor cell cytotoxicity and subsets with regulatory function that contribute to the tumor immune suppressive environment. The balance between effector and regulatory NK cell subsets has been studied extensively in murine models of cancer, but there is a paucity of models to study human NK cell function in tumorigenesis. Humanized mice are a powerful alternative to syngeneic mouse tumor models for the study of human immuno-oncology and have proven effective tools to test immunotherapies targeting T cells. However, human NK cell development and survival in humanized NOD-scid-IL2rg^null (NSG) mice are severely limited. To enhance NK cell development, we have developed NSG mice that constitutively expresses human Interleukin 15 (IL15), NSG-Tg(Hu-IL15). Following hematopoietic stem cell engraftment of NSG-Tg(Hu-IL15) mice, significantly higher levels of functional human CD56+ NK cells are detectable in blood and spleen, as compared to NSG mice. Hematopoietic stem cell (HSC)-engrafted NSG-Tg(Hu-IL15) mice also supported the development of human CD3+ T cells, CD20+ B cells, and CD33+ myeloid cells. Moreover, the growth kinetics of a patient-derived xenograft (PDX) melanoma were significantly delayed in HSC-engrafted NSG-Tg(Hu-IL15) mice as compared to HSC-engrafted NSG mice demonstrating that human NK cells have a key role in limiting the tumor growth. Together, these data demonstrate that HSC-engrafted NSG-Tg(Hu-IL15) mice support enhanced development of functional human NK cells, which limit the growth of PDX tumors.

The mouse resource at National Resource Center for Mutant Mice

Mouse models are essential for dissecting disease mechanisms and defining potential drug targets. There are more than 18,500 mouse strains available for research communities in National Resource Center for Mutant Mice (NRCMM) of China, affiliated with Model Animal Research Center of Nanjing University and Gempharmatech Company. In 2019, Gempharmatech launched the Knockout All Project (KOAP) aiming to generate null mutants and gene floxed strains for all protein-coding genes in mouse genome within 5 years. So far, KOAP has generated 8,004 floxed strains and 9,769 KO (knockout) strains (updated to Oct, 2021). NRCMM also created hundreds of Cre transgenic lines, mutant knock-in models, immuno-deficient models, and humanized mouse models. As a member of the international mouse phenotyping consortium (IMPC), NRCMM provides comprehensive phenotyping services for mouse models. In summary, NRCMM will continue to support biomedical community with new mouse models as well as related services.

Autologous humanized mouse models of iPSC-derived tumors enable characterization and modulation of cancer-immune cell interactions

Modeling the tumor-immune cell interactions in humanized mice is complex and limits drug development. Here, we generated easily accessible tumor models by transforming either primary skin fibroblasts or induced pluripotent stem cell-derived cell lines injected in immune-deficient mice reconstituted with human autologous immune cells. Our results showed that fibroblastic, hepatic, or neural tumors were all efficiently infiltrated and partially or totally rejected by autologous immune cells in humanized mice. Characterization of tumor-immune infiltrates revealed high expression levels of the dysfunction markers Tim3 and PD-1 in T cells and an enrichment in regulatory T cells, suggesting rapid establishment of immunomodulatory phenotypes. Inhibition of PD-1 by Nivolumab in humanized mice resulted in increased immune cell infiltration and a slight decrease in tumor growth. We expect that these versatile and accessible cancer models will facilitate preclinical studies and the evaluation of autologous cancer immunotherapies across a range of different tumor cell types.

Development of Humanized Mouse Models for Studying Human NK Cells in Health and Disease

Humanized mice, which we define as immunodeficient mice that have been reconstituted with a human immune system, represent promising preclinical models for translational research and precision medicine as they allow modeling and therapy of human diseases in vivo. The first generation of humanized mice showed insufficient development, diversity and function of human immune cells, in particular human natural killer (NK) cells and type 1 innate lymphoid cells (ILC1). This limited the applicability of humanized mice for studying ILC1 and NK cells in the context of human cancers and immunotherapeutic manipulation. However, since 2014, several next-generation humanized mouse models have been developed that express human IL-15 either as a transgene or knock-in (NOG-IL15, NSG-IL15, NSG-IL7-IL15, SRG-15) or show improved development of human myeloid cells, which express human IL-15 and thereby promote human NK cell development (NSG-SGM3, MISTRG, BRGSF). Here we compare the various next-generation humanized mouse models and describe the methodological procedures for creating mice with a functioning human immune system and how they can be used to study and manipulate human NK cells in health and disease.

Humanized Mice as a Valuable Pre-Clinical Model for Cancer Immunotherapy Research

Immunotherapy with checkpoint inhibitors opened new horizons in cancer treatment. Clinical trials for novel immunotherapies or unexplored combination regimens either need years of development or are simply impossible to perform like is the case in cancer patients with limited life expectancy. Thus, the need for preclinical models that rapidly and safely allow for a better understanding of underlying mechanisms, drug kinetics and toxicity leading to the selection of the best regimen to be translated into the clinic, is of high importance. Humanized mice that can bear both human immune system and human tumors, are increasingly used in recent preclinical immunotherapy studies and represent a remarkably unprecedented tool in this field. In this review, we describe, summarize, and discuss the recent advances of humanized mouse models used for cancer immunotherapy research and the challenges faced during their establishment. We also highlight the lack of preclinical studies using this model for radiotherapy-based research and argue that it can be a great asset to understand and answer many open questions around radiation therapy such as its presumed associated "abscopal effect".

Generation of Novel Human Red Blood Cell-Bearing Humanized Mouse Models Based on C3-Deficient NOG Mice

Despite recent advances in immunodeficient mouse models bearing human red blood cells (hRBCs), the elimination of circulating hRBCs by residual innate immune systems remains a significant challenge. In this study, we evaluated the role of mouse complement C3 in the elimination of circulating hRBCs by developing a novel NOG substrain harboring a truncated version of the murine C3 gene (NOG-C3^ΔMG2-3). Genetic C3 deletion prolonged the survival of transfused hRBCs in the circulation. Chemical depletion and functional impairment of mouse macrophages, using clodronate liposomes (Clo-lip) or gadolinium chloride (GdCl₃), respectively, further extended the survival of hRBCs in NOG-C3^ΔMG2-3 mice. Low GdCl₃ toxicity allowed the establishment of hRBC-bearing mice, in which hRBCs survived for more than 4 weeks with transfusion once a week. In addition, erythropoiesis of human hematopoietic stem cells (hHSCs) was possible in NOG-C3^ΔMG2-3/human GM-CSF-IL-3 transgenic mice with Clo-lip treatment. These findings indicate that mouse models harboring hRBCs can be achieved using NOG-C3^ΔMG2-3 mice, which could facilitate studies of human diseases associated with RBCs.

Development of humanized mouse with patient-derived xenografts for cancer immunotherapy studies: A comprehensive review

Immunotherapy has revolutionized cancer treatment, however, not all tumor types and patients are completely responsive to this approach. Establishing predictive pre-clinical models would allow for more accurate and practical immunotherapeutic drug development. Mouse models are extensively used as in vivo system for biomedical research. However, due to the significant differences between rodents and human, it is impossible to translate most of the findings from mouse models to human. Pharmacological development and advancing personalized medicine using patient-derived xenografts relies on producing mouse models in which murine cells and genes are substituted with their human equivalent. Humanized mice (HM) provide a suitable platform to evaluate xenograft growth in the context of a human immune system. In this review, we discussed recent advances in the generation and application of HM models. We also reviewed new insights into the basic mechanisms, pre-clinical evaluation of onco-immunotherapies, current limitations in the application of these models as well as available improvement strategies. Finally, we pointed out some issues for future studies.

Fit-For-All iPSC-Derived Cell Therapies and Their Evaluation in Humanized Mice With NK Cell Immunity

Human induced pluripotent stem cells (iPSCs) can be limitlessly expanded and differentiated into almost all cell types. Moreover, they are amenable to gene manipulation and, because they are established from somatic cells, can be established from essentially any person. Based on these characteristics, iPSCs have been extensively studied as cell sources for tissue grafts, blood transfusions and cancer immunotherapies, and related clinical trials have started. From an immune-matching perspective, autologous iPSCs are perfectly compatible in principle, but also require a prolonged time for reaching the final products, have high cost, and person-to-person variation hindering their common use. Therefore, certified iPSCs with reduced immunogenicity are expected to become off-the-shelf sources, such as those made from human leukocyte antigen (HLA)-homozygous individuals or genetically modified for HLA depletion. Preclinical tests using immunodeficient mice reconstituted with a human immune system (HIS) serve as an important tool to assess the human alloresponse against iPSC-derived cells. Especially, HIS mice reconstituted with not only human T cells but also human natural killer (NK) cells are considered crucial. NK cells attack so-called “missing self” cells that do not express self HLA class I, which include HLA-homozygous cells that express only one allele type and HLA-depleted cells. However, conventional HIS mice lack enough reconstituted human NK cells for these tests. Several measures have been developed to overcome this issue including the administration of cytokines that enhance NK cell expansion, such as IL-2 and IL-15, the administration of vectors that express those cytokines, and genetic manipulation to express the cytokines or to enhance the reconstitution of human myeloid cells that express IL15R-alpha. Using such HIS mice with enhanced human NK cell reconstitution, alloresponses against HLA-homozygous and HLA-depleted cells have been studied. However, most studies used HLA-downregulated tumor cells as the target cells and tested in vitro after purifying human cells from HIS mice. In this review, we give an overview of the current state of iPSCs in cell therapies, strategies to lessen their immunogenic potential, and then expound on the development of HIS mice with reconstituted NK cells, followed by their utilization in evaluating future universal HLA-engineered iPSC-derived cells.

Humanized Mouse Models to Evaluate Cancer Immunotherapeutics

Immunotherapy is at the forefront of cancer treatment. The advent of numerous novel approaches to cancer immunotherapy, including immune checkpoint antibodies, adoptive transfer of CAR (chimeric antigen receptor) T cells and TCR (T cell receptor) T cells, NK (natural killer) cells, T cell engagers, oncolytic viruses, and vaccines, is revolutionizing the treatment for different tumor types. Some are already in the clinic, and many others are underway. However, not all patients respond, resistance develops, and as available therapies multiply there is a need to further understand how they work, how to prioritize their clinical evaluation, and how to combine them. For this, animal models have been highly instrumental, and humanized mice models (i.e., immunodeficient mice engrafted with human immune and cancer cells) represent a step forward, although they have several limitations. Here, we review the different humanized models available today, the approaches to overcome their flaws, their use for the evaluation of cancer immunotherapies, and their anticipated evolution as tools to help personalized clinical decision-making.

Targeting a membrane-proximal epitope on mesothelin increases the tumoricidal activity of a bispecific antibody blocking CD47 on mesothelin-positive tumors

Mesothelin (MSLN) is a cell surface glycoprotein overexpressed in several solid malignancies, including gastric, lung, mesothelioma, pancreatic and ovarian cancers. While several MSLN-targeting therapeutic approaches are in development, only limited efficacy has been achieved in patients. A potential shortcoming of several described antibody-based approaches is that they target the membrane distal region of MSLN and, additionally, are known to be handicapped by the high levels of circulating soluble MSLN in patients. We show here, using monoclonal antibodies (mAbs) targeting different MSLN-spanning epitopes, that the membrane-proximal region resulted in more efficient killing of MSLN-positive tumor cells in antibody-dependent cell-mediated cytotoxicity (ADCC) assays. Surprisingly, no augmented killing was observed in antibody-dependent cellular phagocytosis (ADCP) by mAbs targeting this membrane-proximal region. To further increase the ADCP potential, we, therefore, generated bispecific antibodies (bsAbs) coupling a high-affinity MSLN binding arm to a blocking CD47 arm. Here, targeting the membrane-proximal domain of MSLN demonstrated enhanced ADCP activity compared to membrane-distal domains when the bsAbs were used in in vitro phagocytosis killing assays. Importantly, the superior anti-tumor activity was also translated in xenograft tumor models. Furthermore, we show that the bsAb approach targeting the membrane-proximal epitope of MSLN optimized ADCC activity by augmenting FcγR-IIIA activation and enhanced ADCP via a more efficient blockade of the CD47/SIRPα axis.

Humanization of Immunodeficient Animals for the Modeling of Transplantation, Graft Versus Host Disease, and Regenerative Medicine

The humanization of animals is a powerful tool for the exploration of human disease pathogenesis in biomedical research, as well as for the development of therapeutic interventions with enhanced translational potential. Humanized models enable us to overcome biologic differences that exist between humans and other species, while giving us a platform to study human processes in vivo. To become humanized, an immune-deficient recipient is engrafted with cells, tissues, or organoids. The mouse is the most well studied of these hosts, with a variety of immunodeficient strains available for various specific uses. More recently, efforts have turned to the humanization of other animal species such as the rat, which offers some technical and immunologic advantages over mice. These advances, together with ongoing developments in the incorporation of human transgenes and additional mutations in humanized mouse models, have expanded our opportunities to replicate aspects of human allotransplantation and to assist in the development of immunotherapies. In this review, the immune and tissue humanization of various species is presented with an emphasis on their potential for use as models for allotransplantation, graft versus host disease, and regenerative medicine.

Leveraging Patient-Derived Models for Immunotherapy Research

As cancer immunotherapies become mainstream for the treatment of many different cancer types and the numbers of new agents continue to increase, the need for experimental models is also rising. An approach to develop and study models for immune-oncology that has garnered intense interest in recent years is that of using patient-derived models. Patient-derived models can recapitulate many of the features and heterogeneity of the corresponding human tumors. Historically these models have been used to study cancer cell-intrinsic properties of tumors and drugs that target tumor cells directly. In recent years, increasing recognition of the role immune cells play in cancer and how these represent good therapeutic targets has led to efforts to optimize and use patient-derived models for cancer immunotherapy studies. Patient-derived models are now being used to study the properties of cancer cells that modulate their ability to respond to immune stimulation. Further efforts are underway to use and develop patient-derived models that incorporate human immune cells in vitro and in vivo (humanized mice) so that cancer cell-immune cell interactions can be studied in the context of cancer immunotherapies. As these models are further refined, leveraging patient-derived models for cancer immunotherapy research can provide insight into mechanisms of sensitivity and resistance to cancer immunotherapies, uncover new targets, reveal how specific agents work, and be used to evaluate the antitumor efficacy of therapeutic regimens.

Humanized Mouse as a Tool to Predict Immunotoxicity of Human Biologics

Advancements in science enable researchers to constantly innovate and create novel biologics. However, the use of non-human animal models during the development of biologics impedes identification of precise in vivo interactions between the human immune system and treatments. Due to lack of this understanding, adverse effects are frequently observed in healthy volunteers and patients exposed to potential biologics during clinical trials. In this study, we evaluated and compared the effects of known immunotoxic biologics, Proleukin^®/IL-2 and OKT3 in humanized mice (reconstituted with human fetal cells) to published clinical outcomes. We demonstrated that humanized mice were able to recapitulate in vivo pathological changes and human-specific immune responses, such as elevated cytokine levels and modulated lymphocytes and myeloid subsets. Given the high similarities of immunological side effects observed between humanized mice and clinical studies, this model could be used to assess immunotoxicity of biologics at a pre-clinical stage, without placing research participants and/or patients at risk.

Improved Detection of in vivo Human NK Cell-Mediated Antibody-Dependent Cellular Cytotoxicity Using a Novel NOG-FcγR-Deficient Human IL-15 Transgenic Mouse

We generated an NOD/Shi-scid-IL2Rγ^null (NOG) mouse deficient for the Fcer1g and Fcgr2b genes (NOG-FcγR^−/− mice), in which monocytes/macrophages do not express activating (FcγRI, III, and IV) or inhibitory (FcγRIIB) Fcγ receptors. Antibody-dependent cellular cytotoxicity (ADCC) by innate immune cells was strongly reduced in this strain. Thus, while the growth of xenogeneic human tumors engrafted in conventional NOG mice was suppressed by innate cells upon specific antibody treatment, such growth inhibition was abrogated in NOG-FcγR^−/− mice. Using this novel strain, we further produced NOG-FcγR^−/−-mice expressing human IL-15 (NOG-FcγR^−/−-hIL-15 Tg). The mice inherited unique features from each strain, i.e., the long-term sustenance of human natural killer (NK) cells, and the elimination of mouse innate cell-mediated ADCC. As a result, segregation of human NK cell-mediated ADCC from mouse cell-mediated ADCC was possible in the NOG-FcγR^−/−-hIL-15 Tg mice. Our results suggest that NOG-FcγR^−/−-hIL-15 Tg mice are useful for validating the in vivo function of antibody drug candidates.

Patient-Derived Tumor Xenograft Models: Toward the Establishment of Precision Cancer Medicine

Patient-derived xenografts (PDXs) describe models involving the implantation of patient-derived tumor tissue into immunodeficient mice. Compared with conventional preclinical models involving the implantation of cancer cell lines into mice, PDXs can be characterized by the preservation of tumor heterogeneity, and the tumor microenvironment (including stroma/vasculature) more closely resembles that in patients. Consequently, the use of PDX models has improved the predictability of clinical therapeutic responses to 80% or greater, compared with approximately 5% for existing models. In the future, molecular biological analyses, omics analyses, and other experiments will be conducted using recently prepared PDX models under the strong expectation that the analysis of cancer pathophysiology, stem cells, and novel treatment targets and biomarkers will be improved, thereby promoting drug development. This review outlines the methods for preparing PDX models, advances in cancer research using PDX mice, and perspectives for the establishment of precision cancer medicine within the framework of personalized cancer medicine.

The Utility of Human Immune System Mice for High-Containment Viral Hemorrhagic Fever Research

Human immune system (HIS) mice are a subset of humanized mice that are generated by xenoengraftment of human immune cells or tissues and/or their progenitors into immunodeficient mice. Viral hemorrhagic fevers (VHFs) cause severe disease in humans, typically with high case fatality rates. HIS mouse studies have been performed to investigate the pathogenesis and immune responses to VHFs that must be handled in high-containment laboratory facilities. Here, we summarize studies on filoviruses, nairoviruses, phenuiviruses, and hantaviruses, and discuss the knowledge gained from using various HIS mouse models. Furthermore, we discuss the complexities of designing and interpreting studies utilizing HIS mice while highlighting additional questions about VHFs that can still be addressed using HIS mouse models.

iPSC-Derived Platelets Depleted of HLA Class I Are Inert to Anti-HLA Class I and Natural Killer Cell Immunity

The ex vivo production of platelets depleted of human leukocyte antigen class I (HLA-I) could serve as a universal measure to overcome platelet transfusion refractoriness caused by HLA-I incompatibility. Here, we developed human induced pluripotent cell-derived HLA-I-deficient platelets (HLA-KO iPLATs) in a clinically applicable imMKCL system by genetic manipulation and assessed their immunogenic properties including natural killer (NK) cells, which reject HLA-I downregulated cells. HLA-KO iPLATs were deficient for all HLA-I but did not elicit a cytotoxic response by NK cells in vitro and showed circulation equal to wild-type iPLATs upon transfusion in our newly established Hu-NK-MSTRG mice reconstituted with human NK cells. Additionally, HLA-KO iPLATs successfully circulated in an alloimmune platelet transfusion refractoriness model of Hu-NK-MISTRG mice. Mechanistically, the lack of NK cell-activating ligands on platelets may be responsible for evading the NK cell response. This study revealed the unique non-immunogenic property of platelets and provides a proof of concept for the clinical application of HLA-KO iPLATs.

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Clinically applicable iPSC-derived HLA class I knockout platelets (HLA-KO iPLATs)

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HLA-KO iPLATs do not elicit NK cell activation in vitro

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HLA-KO iPLATs circulate comparably with wild type in human NK cell-reconstituted mice

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HLA-KO iPLATs circulate competently in alloimmune PTR model mice

Generation and evaluation of a chimeric antibody against coxsackievirus and adenovirus receptor for cancer therapy

Coxsackievirus and adenovirus receptor (CAR) is a single-pass transmembrane protein that is associated with adenoviral infection. CAR is involved in the formation of epithelial tight junctions and promotes tumor growth in some cancers. Previously, we developed mouse monoclonal antibodies against human CAR and found that one, mu6G10A, significantly inhibited tumor growth in xenografts of human cancer cells. Herein, we generated and characterized a mouse-human chimeric anti-CAR antibody (ch6G10A) from mu6G10A. ch6G10A had binding activity, inducing antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity, and in vivo anti-tumor activity against CAR-expressing prostate cancer DU-145 cells. In addition, cancer tissue array analysis confirmed that CAR is highly expressed in neuroendocrine lung cancers including small cell lung cancer, and treatment with ch6G10A effectively inhibited in vivo subcutaneous tumor growth of NCI-H69 small cell lung cancer cells in nude mice. Moreover, treatment with mu6G10A effectively inhibited both in vivo orthotopic tumor growth and distant metastatic formation in mouse xenograft models of a highly metastatic subline of human small cell lung cancer DMS273 cells. These results suggest that targeting therapy to CAR with a therapeutic antibody might be effective against several cancer types including small cell lung cancer.

Human macrophages and innate lymphoid cells: Tissue-resident innate immunity in humanized mice

Macrophages and innate lymphoid cells (ILCs) are tissue-resident cells that play important roles in organ homeostasis and tissue immunity. Their intricate relationship with the organs they reside in allows them to quickly respond to perturbations of organ homeostasis and environmental challenges, such as infection and tissue injury. Macrophages and ILCs have been extensively studied in mice, yet important species-specific differences exist regarding innate immunity between humans and mice. Complementary to ex-vivo studies with human cells, humanized mice (i.e. mice with a human immune system) offer the opportunity to study human macrophages and ILCs in vivo within their surrounding tissue microenvironments. In this review, we will discuss how humanized mice have helped gain new knowledge about the basic biology of these cells, as well as their function in infectious and malignant conditions. Furthermore, we will highlight active areas of investigation related to human macrophages and ILCs, such as their cellular heterogeneity, ontogeny, tissue residency, and plasticity. In the near future, we expect more fundamental discoveries in these areas through the combined use of improved humanized mouse models together with state-of-the-art technologies, such as single-cell RNA-sequencing and CRISPR/Cas9 genome editing.

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.

[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.

Generation of Human Immunosuppressive Myeloid Cell Populations in Human Interleukin-6 Transgenic NOG Mice

The tumor microenvironment contains unique immune cells, termed myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) that suppress host anti-tumor immunity and promote tumor angiogenesis and metastasis. Although these cells are considered a key target of cancer immune therapy, in vivo animal models allowing differentiation of human immunosuppressive myeloid cells have yet to be established, hampering the development of novel cancer therapies. In this study, we established a novel humanized transgenic (Tg) mouse strain, human interleukin (hIL)-6-expressing NOG mice (NOG-hIL-6 transgenic mice). After transplantation of human hematopoietic stem cells (HSCs), the HSC-transplanted NOG-hIL-6 Tg mice (HSC-NOG-hIL-6 Tg mice) showed enhanced human monocyte/macrophage differentiation. A significant number of human monocytes were negative for HLA-DR expression and resembled immature myeloid cells in the spleen and peripheral blood from HSC-NOG-hIL-6 Tg mice, but not from HSC-NOG non-Tg mice. Engraftment of HSC4 cells, a human head and neck squamous cell carcinoma-derived cell line producing various factors including IL-6, IL-1β, macrophage colony-stimulating factor (M-CSF), and vascular endothelial growth factor (VEGF), into HSC-NOG-hIL-6 Tg mice induced a significant number of TAM-like cells, but few were induced in HSC-NOG non-Tg mice. The tumor-infiltrating macrophages in HSC-NOG-hIL-6 Tg mice expressed a high level of CD163, a marker of immunoregulatory myeloid cells, and produced immunosuppressive molecules such as arginase-1 (Arg-1), IL-10, and VEGF. Such cells from HSC-NOG-hIL-6 Tg mice, but not HSC-NOG non-Tg mice, suppressed human T cell proliferation in response to antigen stimulation in in vitro cultures. These results suggest that functional human TAMs can be developed in NOG-hIL-6 Tg mice. This mouse model will contribute to the development of novel cancer immune therapies targeting immunoregulatory/immunosuppressive myeloid cells.

Long-term maintenance of peripheral blood derived human NK cells in a novel human IL-15- transgenic NOG mouse

We generated a novel mouse strain expressing transgenic human interleukin-15 (IL-15) using the severe immunodeficient NOD/Shi-scid-IL-2Rγ^null (NOG) mouse genetic background (NOG-IL-15 Tg). Human natural killer (NK) cells, purified from the peripheral blood (hu-PB-NK) of normal healthy donors, proliferated when transferred into NOG-IL-15 Tg mice. In addition, the cell number increased, and the hu-PB-NK cells persisted for 3 months without signs of xenogeneic graft versus host diseases (xGVHD). These in vivo-expanded hu-PB-NK cells maintained the original expression patterns of various surface antigens, including NK receptors and killer cell immunoglobulin-like receptor (KIR) molecules. They also contained significant amounts of granzyme A and perforin. Inoculation of K562 leukemia cells into hu-PB-NK-transplanted NOG-IL-15 Tg mice resulted in significant suppression of tumor growth compared with non-transplanted mice. Furthermore, NOG-IL-15 Tg mice allowed for engraftment of in vitro-expanded NK cells prepared for clinical cell therapy. These cells exerted antibody-dependent cell-mediated cytotoxicity (ADCC) on Her2-positive gastric cancer cells in the presence of therapeutic anti-Her2 antibody, and subsequently suppressed tumor growth. Our results collectively suggest that the NOG-IL-15 Tg mice are a useful model for studying human NK biology and evaluating human NK cell-mediated in vivo cytotoxicity.

Human PBMC-transferred murine MHC class I/II-deficient NOG mice enable long-term evaluation of human immune responses

Immunodeficient mice engrafted with human peripheral blood cells are promising tools for in vivo analysis of human patient individual immune responses. However, when human peripheral blood mononuclear cells (PBMCs) are transferred into NOG (NOD/Shi-scid, IL-2rg^null) mice, severe graft versus host disease (GVHD) hinders long term detailed analysis. Administration of human PBMCs into newly developed murine MHC class I- and class II-deficient NOG (NOG-dKO; NOG- Iab, B2m-double-knockout) mice showed sufficient engraftment of human immune cells with little sign of GVHD. Immunization with influenza vaccine resulted in an increase in influenza-specific human IgG Ab, indicating induction of antigen-specific B cells in the NOG-dKO mice. Immunization with human dendritic cells pulsed with HLA-A2 restricted cytomegalovirus peptide induced specific cytotoxic T cells, indicating the induction of antigen-specific T cells in the NOG-dKO mice. Adoptive cell therapies (ACTs) using melanoma antigen recognized by T cells (MART-1)-specific TCR-transduced activated T cells showed strong tumor growth inhibition in NOG-dKO mice without any sign of GVHD accompanied by preferential expansion of the transferred MART-1-specific T cells. ACTs using cultured human melanoma infiltrating T cells also showed anti-tumor effects against autologous melanoma cells in NOG-dKO mice, in which changes in human cancer phenotypes by immune intervention, such as increased CD271 expression, could be evaluated. Therefore, NOG-dKO mice are useful tools for more detailed analysis of both the induction and effector phases of T-cell and B-cell responses for a longer period than regular NOG mice.

Humanized mouse model supports development, function, and tissue residency of human natural killer cells

Immunodeficient mice reconstituted with a human immune system represent a promising tool for translational research as they may allow modeling and therapy of human diseases in vivo. However, insufficient development and function of human natural killer (NK) cells and T cell subsets limit the applicability of humanized mice for studying cancer biology and therapy. Here, we describe a human interleukin 15 (IL15) and human signal regulatory protein alpha (SIRPA) knock-in mouse on a Rag2^-/- Il2rg^-/- background (SRG-15). Transplantation of human hematopoietic stem and progenitor cells into SRG-15 mice dramatically improved the development and functional maturation of circulating and tissue-resident human NK and CD8⁺ T cells and promoted the development of tissue-resident innate lymphoid cell (ILC) subsets. Profiling of human NK cell subsets by mass cytometry revealed a highly similar expression pattern of killer inhibitory receptors and other candidate molecules in NK cell subpopulations between SRG-15 mice and humans. In contrast to nonobese diabetic severe combined immunodeficient Il2rg^-/- (NSG) mice, human NK cells in SRG-15 mice did not require preactivation but infiltrated a Burkitt's lymphoma xenograft and efficiently inhibited tumor growth following treatment with the therapeutic antibody rituximab. Our humanized mouse model may thus be useful for preclinical testing of novel human NK cell-targeted and combinatory cancer immunotherapies and for studying how they elicit human antitumor immune responses in vivo.

Clinical responses to adoptive T-cell transfer can be modeled in an autologous immune-humanized mouse model

Immune checkpoint inhibitors and adoptive cell transfer (ACT) of autologous tumor-infiltrating T cells have shown durable responses in patients with melanoma. To study ACT and immunotherapies in a humanized model, we have developed PDXv2.0 — a melanoma PDX model where tumor cells and tumor-infiltrating T cells from the same patient are transplanted sequentially in non-obese diabetic/severe combined immune-deficient/common gamma chain (NOG/NSG) knockout mouse. Key to T-cell survival/effect in this model is the continuous presence of interleukin-2 (IL-2). Tumors that grow in PDXv2.0 are eradicated if the autologous tumor cells and T cells come from a patient that exhibited an objective response to ACT in the clinic. However, T cells from patients that are non-responders to ACT cannot kill tumor cells in PDXv2.0. Taken together, PDXv2.0 provides the potential framework to further model genetically diverse human cancers for assessing the efficacy of immunotherapies as well as combination therapies.

Combining different types of immune therapies might benefit certain patients. Here, the authors develop an autologous immune-humanized melanoma mouse model that allows the preclinical assessment of cancer cell–T cell interactions from each individual patient and the benefits of immunotherapies combinations.

Incidence of spontaneous lymphomas in non-experimental NOD/Shi-scid, IL-2Rγnull (NOG) mice

Severely immunodeficient NOD/Shi-scid, IL-2Rγ^null (NOG) mice provide an in vivo model for human cell/tissue transplantation studies. NOG mice were established by combining interleukin-2 receptor-γ chain knockout mice and NOD/Shi-scid mice. They exhibit a high incidence of thymic lymphomas and immunoglobulin (Ig) leakiness. In this study, we assessed the incidence of malignant lymphomas and the occurrence of leakiness in 2,184 non-experimental NOG retired breeder mice aged 16-40 weeks. We established that the total incidence of lymphomas was only 0.60% (13/2,184). Most lymphomas (10/13) occurred in female mice by the age of around 25 weeks. No mice developed Ig leakiness. All lymphomas were derived from the thymus, and consisted mainly of CD3-positive and CD45R-negative lymphoblastic-like cells. Therefore, based on the absence of Ig leakiness and a very low incidence of lymphomas, including thymic lymphomas, NOG mice may be useful in regeneration medicine for xenotransplantation of human embryonic stem (ES) cells or induced pluripotent stem (iPS) cells, and in transplantation experiments involving tumor cells.

A Novel Xenogeneic Graft-Versus-Host Disease Model for Investigating the Pathological Role of Human CD4+ or CD8+ T Cells Using Immunodeficient NOG Mice

Graft-versus-host disease (GVHD) is a major complication of allogenic bone marrow transplantation and involves the infiltration of donor CD4⁺ and/or CD8⁺ T cells into various organs of the recipient. The pathological role of human CD4⁺ and CD8⁺ T cells in GVHD remains controversial. In this study, we established two novel xenogeneic (xeno)-GVHD models. Human CD4⁺ or CD8⁺ T cells were purified from peripheral blood and were transplanted into immunodeficient NOD/Shi-scid IL2rg^null (NOG) mice. Human CD8⁺ T cells did not induce major GVHD symptoms in conventional NOG mice. However, CD8⁺ T cells immediately proliferated and induced severe GVHD when transferred into NOG mice together with at least 0.5 × 10⁶ CD4⁺ T cells or into NOG human interleukin (IL)-2 transgenic mice. Human CD4⁺ T cell-transplanted NOG mice developed skin inflammations including alopecia, epidermal hyperplasia, and neutrophilia. Pathogenic T helper (Th)17 cells accumulated in the skin of CD4⁺ T cell-transplanted NOG mice. Further, an anti-human IL-17 antibody (secukinumab) significantly suppressed these skin pathologies. These results indicate that pathogenic human Th17 cells induce cutaneous GVHD via IL-17-dependent pathways. This study provides fundamental insights into the pathogenesis of xeno-GVHD, and these humanized mouse models may be useful as preclinical tools for the prevention of GVHD.

Modeling Natural Killer Cell Targeted Immunotherapies

Animal models have extensively contributed to our understanding of human immunobiology and to uncover the underlying pathological mechanisms occurring in the development of diseases. However, mouse models do not reproduce the genetic and molecular complexity inherent in human disease conditions. Human immune system (HIS) mouse models that are susceptible to human pathogens and can recapitulate human hematopoiesis and tumor immunobiology provide one means to bridge the interspecies gap. Natural killer cells are the founding member of the innate lymphoid cell family. They exert a rapid and strong immune response against tumor and pathogen-infected cells. Their antitumor features have long been exploited for therapeutic purposes in the context of cancer. In this review, we detail the development of highly immunodeficient mouse strains and the models currently used in cancer research. We summarize the latest improvements in adoptive natural killer (NK) cell therapies and the development of novel NK cell sources. Finally, we discuss the advantages of HIS mice to study the interactions between human NK cells and human cancers and to develop new therapeutic strategies.

Humanized Mouse Xenograft Models: Narrowing the Tumor-Microenvironment Gap

Cancer research has long been hampered by the limitations of the current model systems. Both cultured cells and mouse xenografts grow in an environment highly dissimilar to that of their originating tumor, frequently resulting in promising treatments that are ultimately clinically ineffective. The development of highly immunodeficient mouse strains into which human immune systems can be engrafted can help bridge this gap. Humanized mice (HM) allow researchers to examine xenograft growth in the context of a human immune system and resultant tumor microenvironment, and recent studies have highlighted the increased similarities in attendant tumor structure, metastasis, and signaling to those features in cancer patients. This setting also facilitates the examination of investigational cancer therapies, including new immunotherapies. This review discusses recent advancements in the generation and application of HM models, their promise in cancer research, and their potential in generating clinically relevant treatments. This review also focuses on current efforts to improve HM models by engineering mouse strains expressing human cytokines or HLA proteins and implanting human bone, liver, and thymus tissue to facilitate immune cell maturation and trafficking. Finally, we discuss how these improvements may help direct future HM model cancer studies. Cancer Res; 76(21); 6153-8. ©2016 AACR.

Humanized Mouse Models for Transplant Immunology

Our understanding of the molecular pathways that control immune responses, particularly immunomodulatory molecules that control the extent and duration of an immune response, have led to new approaches in the field of transplantation immunology to induce allograft survival. These molecular pathways are being defined precisely in murine models and translated into clinical practice; however, many of the newly available drugs are human-specific reagents. Furthermore, many species-specific differences exist between mouse and human immune systems. Recent advances in the development of humanized mice, namely, immunodeficient mice engrafted with functional human immune systems, have led to the availability of a small animal model for the study of human immune responses. Humanized mice represent an important preclinical model system for evaluation of new drugs and identification of the mechanisms underlying human allograft rejection without putting patients at risk. This review highlights recent advances in the development of humanized mice and their use as preclinical models for the study of human allograft responses.

Probing Human NK Cell Biology Using Human Immune System (HIS) Mice

Our incomplete understanding of the mechanisms that orchestrate human lymphocyte differentiation and condition human immune responses is in part due to the limited access to normal human tissue samples that can inform on these complex processes. In addition, in vitro culture conditions fail to recapitulate the three-dimensional microenvironments that influence cell-cell interactions and impact on immune outcomes. Small animals provide a preclinical model to dissect and probe immunity and over the past decades, development of immunodeficient hosts that can be engrafted with human hematopoietic precursors and mature cells have led to the development of new in vivo models to study human lymphocyte development and function. Natural killer (NK) cells are implicated in the recognition and elimination of pathogen-infected and transformed cells and belong to a family of diverse innate lymphoid cells (ILCs) that provide early immune defense against disease. Here, we summarize the use of humanized mouse models for the study of NK cell and group 1 ILCs and their respective roles in immunity and tissue homeostasis.