Mice engrafted with human fetal thymic tissue and hematopoietic stem cells develop pathology resembling chronic graft-versus-host disease

Fetal liver CD34+ contain human immune and endothelial progenitors and mediate solid tumor rejection in NOG mice

BACKGROUND

Transplantation of CD34+ hematopoietic stem and progenitor cells (HSPC) into immunodeficient mice is an established method to generate humanized mice harbouring a human immune system. Different sources and methods for CD34+ isolation have been employed by various research groups, resulting in customized models that are difficult to compare. A more detailed characterization of CD34+ isolates is needed for a better understanding of engraftable hematopoietic and potentially non-hematopoietic cells. Here we have performed a direct comparison of CD34+ isolated from cord blood (CB-CD34+) or fetal liver (FL-CD34+ and FL-CD34+CD14-) and their engraftment into immunocompromised NOD/Shi-scid Il2rgnull (NOG) mice.

METHODS

NOG mice were transplanted with either CB-CD34+, FL-CD34+ or FL-CD34+CD14- to generate CB-NOG, FL-NOG and FL-CD14--NOG, respectively. After 15-20 weeks, the mice were sacrificed and human immune cell reconstitution was assessed in blood and several organs. Liver sections were pathologically assessed upon Haematoxylin and Eosin staining. To assess the capability of allogenic tumor rejection in CB- vs. FL-reconstituted mice, animals were subcutaneously engrafted with an HLA-mismatched melanoma cell line. Tumor growth was assessed by calliper measurements and a Luminex-based assay was used to compare the cytokine/chemokine profiles.

RESULTS

We show that CB-CD34+ are a uniform population of HSPC that reconstitute NOG mice more rapidly than FL-CD34+ due to faster B cell development. However, upon long-term engraftment, FL-NOG display increased numbers of neutrophils, dendritic cells and macrophages in multiple tissues. In addition to HSPC, FL-CD34+ isolates contain non-hematopoietic CD14+ endothelial cells that enhance the engraftment of the human immune system in FL-NOG mice. We demonstrate that these CD14+CD34+ cells are capable of reconstituting Factor VIII-producing liver sinusoidal endothelial cells (LSEC) in FL-NOG. However, CD14+CD34+ also contribute to hepatic sinusoidal dilatation and immune cell infiltration, which may culminate in a graft-versus-host disease (GVHD) pathology upon long-term engraftment. Finally, using an HLA-A mismatched CDX melanoma model, we show that FL-NOG, but not CB-NOG, can mount a graft-versus-tumor (GVT) response resulting in tumor rejection.

CONCLUSION

Our results highlight important phenotypical and functional differences between CB- and FL-NOG and reveal FL-NOG as a potential model to study hepatic sinusoidal dilatation and mechanisms of GVT.

X-ray irradiation effectively inactivated lymphocytes in transfusion in vivo monitored by the bioluminescence transfusion-associated graft-versus-host disease model

BACKGROUND AND OBJECTIVES

Transfusion of cold-stored whole blood is the preferred resuscitation method for trauma patients but may cause transfusion-associated graft-versus-host disease (TA-GVHD). Standard clinical practice to prevent this is to irradiate blood components with gamma-rays. X-ray irradiations are also a safe and effective alternative to gamma-ray irradiation. We established a visual mouse model of TA-GVHD to compare the viability and function of lymphocytes exposed to gamma- and x-ray irradiation.

MATERIALS AND METHODS

A haploidentical transplantation mouse model was established to simulate TA-GVHD with Balb/c mice as donors and hybrid F1 CB6 mice (Balb/c × C57) as recipients. Spleen cells from Tg-Fluc+ Balb/c mice were isolated and irradiated with gamma-rays and x-rays. Lymphocyte activation, apoptosis and proliferation post phorbol 1 2-myristate 1 3-acetate (PMA) stimulation were evaluated. After transfusion, we monitored Fluc+ lymphocytes daily by bioluminescence imaging. Recipients were euthanized on day 21, and tissues were examined pathologically and for inflammatory cytokines.

RESULTS

The viability of gamma- or x-ray irradiated lymphocytes decreased significantly with slight changes in proliferation in vivo after transfusion. Compared with the non-irradiated group, both the gamma- and x-ray irradiated groups showed significantly decreased clinical scoring and inflammatory cytokine levels. The fluorescence intensity of the body and target organs was reduced after irradiation.

CONCLUSION

No recipients acquired TA-GVHD after lymphocyte transfusion subjected to gamma- or x-rays, showing that x-rays inactivate as well as gamma rays and are suitable for irradiating whole blood.

Mesenchymal stromal cells ameliorate chronic GVHD by boosting thymic regeneration in a CCR9-dependent manner in mice

Chronic graft-versus-host disease (cGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Mature donor T cells within the graft contribute to severe damage of thymic epithelial cells (TECs), which are known as key mediators in the continuum of acute GVHD (aGVHD) and cGVHD pathology. Mesenchymal stromal cells (MSCs) are reportedly effective in the prevention and treatment of cGVHD. In our previous pilot clinical trial in patients with refractory aGVHD, the incidence and severity of cGVHD were decreased, along with an increase in levels of blood signal joint T-cell receptor excision DNA circles after MSCs treatment, which indicated an improvement in thymus function of patients with GVHD, but the mechanisms leading to these effects remain unknown. Here, we show in a murine GVHD model that MSCs promoted the quantity and maturity of TECs as well as elevated the proportion of Aire-positive medullary TECs, improving both CD4+CD8+ double-positive thymocytes and thymic regulatory T cells, balancing the CD4:CD8 ratio in the blood. In addition, CCL25-CCR9 signaling axis was found to play an important role in guiding MSC homing to the thymus. These studies reveal mechanisms through which MSCs ameliorate cGVHD by boosting thymic regeneration and offer innovative strategies for improving thymus function in patients with GVHD.

Generation of the NeoThy mouse model for human immune system studies

Humanized mouse models, created via transplantation of human hematopoietic tissues into immune-deficient mice, support a number of research applications, including transplantation immunology, virology and oncology studies. As an alternative to the bone marrow, liver, thymus humanized mouse, which uses fetal tissues for generating a chimeric human immune system, the NeoThy humanized mouse uses nonfetal tissue sources. Specifically, the NeoThy model incorporates hematopoietic stem and progenitor cells from umbilical cord blood (UCB) as well as thymus tissue that is typically discarded as medical waste during neonatal cardiac surgeries. Compared with fetal thymus tissue, the abundant quantity of neonatal thymus tissue offers the opportunity to prepare over 1,000 NeoThy mice from an individual thymus donor. Here we describe a protocol for processing of the neonatal tissues (thymus and UCB) and hematopoietic stem and progenitor cell separation, human leukocyte antigen typing and matching of allogenic thymus and UCB tissues, creation of NeoThy mice, assessment of human immune cell reconstitution and all experimental steps from planning and design to data analysis. This entire protocol takes a total of ~19 h to complete, with steps broken up into multiple sessions of 4 h or less that can be paused and completed over multiple days. The protocol can be completed, after practice, by individuals with intermediate laboratory and animal handling skills, enabling researchers to make effective use of this promising in vivo model of human immune function.

Origin, phenotype and autoimmune potential of T cells in human immune system mice receiving neonatal human thymus tissue

Robust human immune system (HIS) mice are created using human fetal thymus tissue and hematopoietic stem cells (HSCs). A HIS mouse model using neonatal human thymus tissue and umbilical cord blood (CB) HSCs (NeoHu) was recently described. We improved the model by removing the native murine thymus, which can also generate human T cells, and demonstrated definitively the capacity of human T cells to develop in a grafted neonatal human thymus. Human T cells derived from the neonatal thymus tissue appeared in peripheral blood early post-transplantation and CB-derived T cells appeared later. Naïve T cells were demonstrated in peripheral blood but effector memory and T peripheral helper phenotypes predominated later, in association with development of autoimmunity in some animals. Treatment of thymus grafts with 2-deoxyglucose (2-DG) increased the proportion of stem cells derived from injected HSCs, delayed onset of autoimmune disease, reduced early T cell reconstitution, and reduced effector/memory T cell conversion. Younger neonatal human thymus tissue was associated with improved T cell reconstitution. While the NeoHu model bypasses the need for fetal tissue, it has yet to demonstrate equivalent reconstitution to fetal tissue, though 2-DG can improve results by removing native thymocytes prior to transplantation.

Humanized mouse models for immuno-oncology research

Immunotherapy has emerged as a promising treatment paradigm for many malignancies and is transforming the drug development landscape. Although immunotherapeutic agents have demonstrated clinical efficacy, they are associated with variable clinical responses, and substantial gaps remain in our understanding of their mechanisms of action and specific biomarkers of response. Currently, the number of preclinical models that faithfully recapitulate interactions between the human immune system and tumours and enable evaluation of human-specific immunotherapies in vivo is limited. Humanized mice, a term that refers to immunodeficient mice co-engrafted with human tumours and immune components, provide several advantages for immuno-oncology research. In this Review, we discuss the benefits and challenges of the currently available humanized mice, including specific interactions between engrafted human tumours and immune components, the development and survival of human innate immune populations in these mice, and approaches to study mice engrafted with matched patient tumours and immune cells. We highlight the latest advances in the generation of humanized mouse models, with the aim of providing a guide for their application to immuno-oncology studies with potential for clinical translation.

Characterization of a novel potency endpoint for the evaluation of immune checkpoint blockade in humanized mice

Introduction

Humanized mice are emerging as valuable models to experimentally evaluate the impact of different immunotherapeutics on the human immune system. These immunodeficient mice are engrafted with human cells or tissues, that then mimic the human immune system, offering an alternative and potentially more predictive preclinical model. Immunodeficient NSG mice engrafted with human CD34+ cord blood stem cells develop human T cells educated against murine MHC. However, autoimmune graft versus host disease (GvHD), mediated by T cells, typically develops 1 year post engraftment.

Methods

Here, we have used the development of GvHD in NSG mice, using donors with HLA alleles predisposed to autoimmunity (psoriasis) to weight in favor of GvHD, as an endpoint to evaluate the relative potency of monoclonal and BiSpecific antibodies targeting PD-1 and CTLA-4 to break immune tolerance.

Results

We found that treatment with either a combination of anti-PD-1 & anti-CTLA-4 mAbs or a quadrivalent anti-PD-1/CTLA-4 BiSpecific (MEDI8500), had enhanced potency compared to treatment with anti-PD-1 or anti-CTLA-4 monotherapies, increasing T cell activity both in vitro and in vivo. This resulted in accelerated development of GvHD and shorter survival of the humanized mice in these treatment groups commensurate with their on target activity.

Discussion

Our findings demonstrate the potential of humanized mouse models for preclinical evaluation of different immunotherapies and combinations, using acceleration of GvHD development as a surrogate of aggravated antigenic T-cell response against host.

Latest models for the discovery and development of rheumatoid arthritis drugs

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic autoimmune disease that reduces the quality of life. The current speed of development of therapeutic agents against RA is not satisfactory. Models on which initial experiments are conducted do not fully reflect human pathogenesis. Overcoming this oversimplification might be a crucial step to accelerate studies on RA treatment.

AREAS COVERED

The current approaches to produce novel models or to improve currently available models for the development of RA drugs have been discussed. Advantages and drawbacks of two- and three-dimensional cell cultures and animal models have been described based on recently published results of the studies. Moreover, approaches such as tissue engineering or organ-on-a-chip have been reviewed.

EXPERT OPINION

The cell cultures and animal models used to date appear to be of limited value due to the complexity of the processes involved in RA. Current models in RA research should take into account the heterogeneity of patients in terms of disease subtypes, course, and activity. Several advanced models and tools using human cells and tissues have been developed, including three-dimensional tissues, liquid bioreactors, and more complex joint-on-a-chip devices. This may increase knowledge of the molecular mechanisms leading to disease development, to help identify new biomarkers for early detection, and to develop preventive strategies and more effective treatments.

Mice with humanized immune system as novel models to study HIV-associated pulmonary hypertension

People living with HIV and who receive antiretroviral therapy have a significantly improved lifespan, compared to the early days without therapy. Unfortunately, persisting viral replication in the lungs sustains chronic inflammation, which may cause pulmonary vascular dysfunction and ultimate life-threatening Pulmonary Hypertension (PH). The mechanisms involved in the progression of HIV and PH remain unclear. The study of HIV-PH is limited due to the lack of tractable animal models that recapitulate infection and pathobiological aspects of PH. On one hand, mice with humanized immune systems (hu-mice) are highly relevant to HIV research but their suitability for HIV-PH research deserves investigation. On another hand, the Hypoxia-Sugen is a well-established model for experimental PH that combines hypoxia with the VEGF antagonist SU5416. To test the suitability of hu-mice, we combined HIV with either SU5416 or hypoxia. Using right heart catheterization, we found that combining HIV+SU5416 exacerbated PH. HIV infection increases human pro-inflammatory cytokines in the lungs, compared to uninfected mice. Histopathological examinations showed pulmonary vascular inflammation with arterial muscularization in HIV-PH. We also found an increase in endothelial-monocyte activating polypeptide II (EMAP II) when combining HIV+SU5416. Therefore, combinations of HIV with SU5416 or hypoxia recapitulate PH in hu-mice, creating well-suited models for infectious mechanistic pulmonary vascular research in small animals.

A novel clinically relevant graft-versus-leukemia model in humanized mice

The prognosis for acute myeloid leukemia (AML) relapse post allogeneic hematopoietic stem cell transplantation (alloSCT) is dismal. Novel effective treatment is urgently needed. Clinical benefit of alloSCT greatly relies on the graft-versus-leukemia (GVL) effect. The mechanisms that mediate immune escape of leukemia (thus causing GVL failure) remain poorly understood. Studies of human GVL have been hindered by the lack of optimal clinically relevant models. Here, using our large, longitudinal clinical tissue bank that include AML cells and G-CSF mobilized donor hematopoietic stem cells (HSCs), we successfully established a novel GVL model in humanized mice. Donor HSCs were injected into immune-deficient NOD-Cg-Prkdcscid IL2rgtm1Wjl /SzJ (NSG) mice to build humanized mice. Immune reconstitution in these mice recapitulated some clinical scenario in the patient who received the corresponding HSCs. Allogeneic but HLA partially matched patient-derived AML cells were successfully engrafted in these humanized mice. Importantly, we observed a significantly reduced (yet incomplete elimination of) leukemia growth in humanized mice compared with that in control NSG mice, demonstrating a functional (but defective) GVL effect. Thus, for the first time, we established a novel humanized mouse model that can be used for studying human GVL responses against human AML cells in vivo. This novel clinically relevant model provides a valuable platform for investigating the mechanisms of human GVL and development of effective leukemia treatments.

The oral histopathological and immunological characteristics of a xenogeneic mouse chronic graft-versus-host disease model

BACKGROUND

Oral lesions are important clinical manifestations of chronic graft-verse-host disease (cGVHD). However, the oral characteristics of cGVHD mouse model are not yet clear. This study aims to demonstrate oral histopathological and immunological characteristics of a xenogeneic cGVHD mouse model.

MATERIALS AND METHODS

2.5 × 10⁶ , 5.0 × 10⁶ , 7.5 × 10⁶ , and 10.0 × 10⁶  human peripheral blood mononuclear cells (hPBMCs) were intravenously transplanted into NCG mice to induce cGVHD. After transplantation, clinical observations were recorded. Tissue samples from salivary glands and oral mucosa were stained with H&E, Masson Trichrome, and immunofluorescence, and the histopathology of oral tissues was scored according to our modified criteria.

RESULTS

NCG mice showed signs of cGVHD onset after transplantation. The oral histopathological lesion incidences in each group were 37.50%, 50.00%, 62.50%, and 75.00%, respectively. Oral histopathological lesion incidence and histopathological scores were positively correlated with the amount of infused hPBMCs. Epithelial atrophy, epithelial cells vacuolar degeneration, and basal cells liquefaction denaturation were observed in oral mucosa, and acinar destruction and collagen deposition were observed in the salivary glands. Human CD45⁺ , CD4⁺ , CD8⁺ , IL-17⁺ , and FoxP3⁺ cells infiltrated into oral tissues. In the 5.0 × 10⁶  hPBMCs group, oral histopathological changes mainly began between days 30 and 45 post-transplantation, and became more severe after day 45. The oral histopathological scores also gradually increased.

CONCLUSION

Inflammation in oral mucosa epithelium and salivary glands, and CD4⁺ and CD8⁺ T cells dominating infiltration are the main oral features in the xenogeneic cGVHD mouse model. The severity of oral histopathological lesions shows a dose and time correlation. These may be helpful to oral cGVHD research.

Role of the thymus in spontaneous development of a multi-organ autoimmune disease in human immune system mice

We evaluated the role of the thymus in development of multi-organ autoimmunity in human immune system (HIS) mice. T cells were essential for disease development and the same T cell clones with varying phenotypes infiltrated multiple tissues. De novo-generated hematopoietic stem cell (HSC)-derived T cells were the major disease drivers, though thymocytes pre-existing in grafted human thymi contributed if not first depleted. HIS mice with a native mouse thymus developed disease earlier than thymectomized mice with a thymocyte-depleted human thymus graft. Defective structure in the native mouse thymus was associated with impaired negative selection of thymocytes expressing a transgenic TCR recognizing a self-antigen. Disease developed without direct recognition of antigens on recipient mouse MHC. While human thymus grafts had normal structure and negative selection, failure to tolerize human T cells recognizing mouse antigens presented on HLA molecules may explain eventual disease development. These new insights have implications for human autoimmunity and suggest methods of avoiding autoimmunity in next-generation HIS mice.

Current Concepts and Advances in Graft-Versus-Host Disease Immunology

Worldwide, each year over 30,000 patients undergo an allogeneic hema-topoietic stem cell transplantation with the intent to cure high-risk hematologic malignancy, immunodeficiency, metabolic disease, or a life-threatening bone marrow failure syndrome. Despite substantial advances in donor selection and conditioning regimens and greater availability of allograft sources, transplant recipients still endure the morbidity and mortality of graft-versus-host disease (GVHD). Herein, we identify key aspects of acute and chronic GVHD pathophysiology, including host/donor cell effectors, gut dysbiosis, immune system and cytokine imbalance, and the interface between inflammation and tissue fibrosis. In particular, we also summarize the translational application of this heightened understanding of immune dysregulation in the design of novel therapies to prevent and treat GVHD.

Advances in Humanized Mouse Models to Improve Understanding of HIV-1 Pathogenesis and Immune Responses

Although antiretroviral therapy has transformed human immunodeficiency virus-type 1 (HIV-1) from a deadly infection into a chronic disease, it does not clear the viral reservoir, leaving HIV-1 as an uncurable infection. Currently, 1.2 million new HIV-1 infections occur globally each year, with little decrease over many years. Therefore, additional research is required to advance the current state of HIV management, find potential therapeutic strategies, and further understand the mechanisms of HIV pathogenesis and prevention strategies. Non-human primates (NHP) have been used extensively in HIV research and have provided critical advances within the field, but there are several issues that limit their use. Humanized mouse (Hu-mouse) models, or immunodeficient mice engrafted with human immune cells and/or tissues, provide a cost-effective and practical approach to create models for HIV research. Hu-mice closely parallel multiple aspects of human HIV infection and disease progression. Here, we highlight how innovations in Hu-mouse models have advanced HIV-1 research in the past decade. We discuss the effect of different background strains of mice, of modifications on the reconstitution of the immune cells, and the pros and cons of different human cells and/or tissue engraftment methods, on the ability to examine HIV-1 infection and immune response. Finally, we consider the newest advances in the Hu-mouse models and their potential to advance research in emerging areas of mucosal infections, understand the role of microbiota and the complex issues in HIV-TB co-infection. These innovations in Hu-mouse models hold the potential to significantly enhance mechanistic research to develop novel strategies for HIV prevention and therapeutics.

Development of Mast Cell and Eosinophil Hyperplasia and HLH/MAS-Like Disease in NSG-SGM3 Mice Receiving Human CD34+ Hematopoietic Stem Cells or Patient-Derived Leukemia Xenografts

Immunocompromised mouse strains expressing human transgenes are being increasingly used in biomedical research. The genetic modifications in these mice cause various cellular responses, resulting in histologic features unique to each strain. The NSG-SGM3 mouse strain is similar to the commonly used NSG (NOD scid gamma) strain but expresses human transgenes encoding stem cell factor (also known as KIT ligand), granulocyte-macrophage colony-stimulating factor, and interleukin 3. This report describes 3 histopathologic features seen in these mice when they are unmanipulated or after transplantation with human CD34+ hematopoietic stem cells (HSCs), virally transduced hCD34+ HSCs, or a leukemia patient-derived xenograft. The first feature is mast cell hyperplasia: unmanipulated, naïve mice develop periductular pancreatic aggregates of murine mast cells, whereas mice given the aforementioned human cells develop a proliferative infiltrative interstitial pancreatic mast cell hyperplasia but with human mast cells. The second feature is the predisposition of NSG-SGM3 mice given these human cells to develop eosinophil hyperplasia. The third feature, secondary hemophagocytic lymphohistiocytosis/macrophage activation syndrome (HLH/MAS)-like disease, is the most pronounced in both its clinical and histopathologic presentations. As part of this disease, a small number of mice also have histiocytic infiltration of the brain and spinal cord with subsequent neurologic or vestibular signs. The presence of any of these features can confound accurate histopathologic interpretation; therefore, it is important to recognize them as strain characteristics and to differentiate them from what may be experimentally induced in the model being studied.

The Development of Next-generation PBMC Humanized Mice for Preclinical Investigation of Cancer Immunotherapeutic Agents

Investigation of the efficacy and mechanisms of human immuno-oncology agents has been hampered due to species-specific differences when utilizing preclinical mouse models. Peripheral blood mononuclear cell (PBMC) humanized mice provide a platform for investigating the modulation of the human immune-mediated antitumor response while circumventing the limitations of syngeneic model systems. Use of humanized mice has been stymied by model-specific limitations, some of which include the development of graft versus host disease, technical difficulty and cost associated with each humanized animal, and insufficient engraftment of some human immune subsets. Recent advances have addressed many of these limitations from which have emerged humanized models that are more clinically relevant. This review characterizes the expanded usage, advantages and limitations of humanized mice and provides insights into the development of the next generation of murine humanized models to further inform clinical applications of cancer immunotherapeutic agents.

Human CD34+ Hematopoietic Stem Cell-Engrafted NSG Mice: Morphological and Immunophenotypic Features

Immunodeficient mice engrafted with human immune cells represent an innovative tool to improve translatability of animal models for the study of human diseases. Immunophenotyping in these mice focuses on engraftment rates and cellular differentiation in blood and secondary lymphoid organs, and is predominantly carried out by FACS (fluorescent activated cell sorting) analysis; information on the morphological aspects of engraftment and the prevalence of histologic lesions is limited. We histologically examined 3- to 6-month-old NSG mice, naïve or engrafted with CD34⁺ human hemopoietic stem cells (HSC), and employed a quantitative immunohistochemical approach to identify human and murine cell compartments, comparing the results with the FACS data. NSG mice mainly exhibited incidental findings in lungs, kidneys, testes, and adrenal glands. A 6-month-old NSG mouse had a mediastinal lymphoblastic lymphoma. The lymphoid organs of NSG mice lacked typical lymphoid tissue architecture but frequently exhibited small periarteriolar leukocyte clusters in the spleen. Mice engrafted with human HSC frequently showed nephropathy, ovarian atrophy, cataract, and abnormal retinal development, lesions considered secondary to irradiation. In addition, 20% exhibited multisystemic granulomatous inflammatory infiltrates, dominated by human macrophages and T cells, leading to the observed 7% mortality and morbidity. Immunophenotypic data revealed variable repopulation of lymphoid organs with hCD45⁺ human cells, which did not always parallel the engraftment levels measured via FACS. The study describes the most common pathological features in young NSG mice after human HSC engraftment. As some of these lesions contribute to morbidity, morphological assessment of the engraftment at tissue level might help improve immunophenotypic evaluations of this animal model.

The humanized mouse: Emerging translational potential

The humanized mouse (HM) has emerged as a valuable animal model in cancer research. Engrafted with components of a human immune system and subsequently implanted with tumor tissue from cell lines or in the form of patient-derived xenografts, the HM provides a unique platform in which the tumor microenvironment (TME) can be evaluated in vivo. This model may also be beneficial in the assessment of potential cancer treatments including immune checkpoint inhibitors. However, to maximize its utility, researchers need to understand the critical factors necessary to ensure that the tumor immune interactions in the HM are representative of those within cancer patients. In most current HM models, the human T cells residing in the HM are educated in a murine thymus, allogeneic to implanted tumor tissue, and/or alloreactive to mouse tissues, making their interaction and reactivity with tumor cells suspect. There are several strategies underway to harmonize the immune-tumor environment in the HM. Once the essential components of the HM-tumor TME interface have been identified and understood, the HM model will permit not only the discovery of effective immunotherapy treatments, but it can be used to predict patient responses to great clinical benefit.

Double-filtered leukoreduction as a method for risk reduction of transfusion-associated graft-versus-host disease

Background

Transfusion-associated graft-versus-host disease (TA-GvHD) is caused by leukocytes, specifically T cells within a transfused blood product. Currently, the prevention of transfusion-associated graft-versus-host disease is performed by irradiation of blood products. With a sufficient reduction of leukocytes, the risk for TA-GvHD can be decreased. With consistent advances in current state-of-the-art blood filters, we herein propose that double filtration can sufficiently reduce leukocytes to reduce the risk for TA-GvHD.

Materials

Thirty RBC concentrates were filtered with leukocyte filters, followed by storage at 1–6 ^oC for 72 hours, and then a second filtration was performed. Residual leukocytes in the double-filtered RBC units (n = 30) were assessed with flow cytometric methods, and an additional assay with isolated peripheral blood mononuclear cells (PBMCs) (n = 6) was done by both flow cytometric methods and an automated hematology analyzer. Quality of the RBCs after filtration was evaluated by hematological and biochemical tests. In vitro T cell expansion was performed using anti-CD3/CD28-coated Dynabeads or anti-CD3 (OKT3). In vivo experiment for GvHD was performed by using NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ (NSG) mice.

Results

Double-filtered blood products showed residual leukocyte levels below detection limits, which calculated to be below 1200–2500 cells per blood unit. In vitro expansion rate of T cells showed that 6x10³ and 1x10³ cell-seeded specimens showed 60.8±10.6 fold and 10.2±9.7-fold expansion, respectively. Cell expansion was not sufficiently observed in wells planted with 1x10² or 10 cells. In vivo experiments showed that mice injected with 1x10⁵ or more cells cause fatal GvHD. GvHD induced inflammation was observed in mice injected with 1x10⁴ or more cells. No evidence of GvHD was found in mice injected with 10³ cells.

Conclusions

Our study suggests that additional removal of contaminating lymphocytes by a second leukodepletion step may further reduce the risk for TA-GvHD.

Recent Advancements and Applications of Human Immune System Mice in Preclinical Immuno-Oncology

Significant advances in immunotherapies have resulted in the increasing need of predictive preclinical models to improve immunotherapeutic drug development, treatment combination, and to prevent or minimize toxicity in clinical trials. Immunodeficient mice reconstituted with human immune system (HIS), termed humanized mice or HIS mice, permit detailed analysis of human immune biology, development, and function. Although this model constitutes a great translational model, some aspects need to be improved as the incomplete engraftment of immune cells, graft versus host disease and the lack of human cytokines and growth factors. In this review, we discuss current HIS platforms, their pathology, and recent advances in their development to improve the quality of human immune cell reconstitution. We also highlight new technologies that can be used to better understand these models and how improved characterization is needed for their application in immuno-oncology safety, efficacy, and new modalities therapy development.

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.

Humanized mouse models of immunological diseases and precision medicine

With the increase in knowledge resulting from the sequencing of the human genome, the genetic basis for the underlying differences in individuals, their diseases, and how they respond to therapies is starting to be understood. This has formed the foundation for the era of precision medicine in many human diseases that is beginning to be implemented in the clinic, particularly in cancer. However, preclinical testing of therapeutic approaches based on individual biology will need to be validated in animal models prior to translation into patients. Although animal models, particularly murine models, have provided significant information on the basic biology underlying immune responses in various diseases and the response to therapy, murine and human immune systems differ markedly. These fundamental differences may be the underlying reason why many of the positive therapeutic responses observed in mice have not translated directly into the clinic. There is a critical need for preclinical animal models in which human immune responses can be investigated. For this, many investigators are using humanized mice, i.e., immunodeficient mice engrafted with functional human cells, tissues, and immune systems. We will briefly review the history of humanized mice, the remaining limitations, approaches to overcome them and how humanized mouse models are being used as a preclinical bridge in precision medicine for evaluation of human therapies prior to their implementation in the clinic.

Ex Vivo Gene Therapy: Graft-versus-host Disease (GVHD) in NSG™ (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ) Mice Transplanted with CD34+ Human Hematopoietic Stem Cells

A therapeutic option for monogenic disorders is gene therapy with ex vivo-transduced autologous hematopoietic stem cells (HSCs). Safety or efficacy studies of ex vivo-modified HSCs are conducted in humanized mouse models after ablation of the murine bone marrow and transfer of human CD34⁺ HSCs. Engrafted human CD34⁺ cells migrate to bone marrow and differentiate into various human hematopoietic lineages. A 12-week study was conducted in NSG™ mice to evaluate engraftment, differentiation, and safety of human CD34⁺ cells that were transduced (ex vivo) with a proprietary lentiviral vector encoding a human gene (BMRN-1) or a mock (green fluorescent protein) vector. Several mice intravenously injected with naive CD34⁺ cells or transduced CD34⁺ cells had variable lymphohistiocytic inflammatory cell infiltrates and microgranulomas in the liver and lungs consistent with graft-versus-host disease (GVHD). Spleen, bone marrow, stomach, reproductive tract, but not the skin had similar inflammatory changes. Ex vivo viral transduction of CD34⁺ cells did not impact engraftment or predispose to xenogeneic GVHD.

BLT-Immune Humanized Mice as a Model for Nivolumab-Induced Immune-Mediated Adverse Events: Comparison of the NOG and NOG-EXL Strains

Checkpoint inhibitors represent a new class of therapeutics in the treatment of cancer that has demonstrated remarkable clinical effectiveness. However, some patients have experienced serious immune-mediated adverse effects including pneumonitis, hepatitis, colitis, nephritis, dermatitis, encephalitis, and adrenal or pituitary insufficiency. These adverse events were not predicted by nonclinical studies. To determine if bone marrow-liver-thymus (BLT) immune humanized mice could demonstrate these adverse effects, we studied the effect of nivolumab on 2 strains of BLT-humanized mice, NOD.Cg-Prkdcscid Il2rgtm1Sug/JicTac (NOG) and NOD.Cg-Prkdcscid Il2rgtm1Sug Tg(SV40/HTLV-IL3, CSF2)10-7Jic/JicTac (NOG-EXL). Mice were treated with 2.5, 5.0, or 10.0 mg/kg nivolumab or saline twice weekly for 28 days. BLT-NOG mice had significantly reduced survival compared with BLT-NOG-EXL mice. In spite of the difference in survival, both BLT-humanized strains showed adverse reactions similar to those reported in humans, including pneumonitis and hepatitis, with nephritis, dermatitis and adrenalitis also noted in some individuals. Additional histopathologic findings included pancreatic atrophy, myositis, and osteomyelitis in some animals. T-cell activation increased with concomitant loss of PD-1 detection. These findings show that BLT immune humanized mice can demonstrate immune-mediated adverse effects of antiPD1 therapy, and may represent a model that can be used to better understand toxicity of this class of drugs.

Humanized Mouse Models of Rheumatoid Arthritis for Studies on Immunopathogenesis and Preclinical Testing of Cell-Based Therapies

Rodent models of rheumatoid arthritis (RA) have been used over decades to study the immunopathogenesis of the disease and to explore intervention strategies. Nevertheless, mouse models of RA reach their limit when it comes to testing of new therapeutic approaches such as cell-based therapies. Differences between the human and the murine immune system make it difficult to draw reliable conclusions about the success of immunotherapies. To overcome this issue, humanized mouse models have been established that mimic components of the human immune system in mice. Two main strategies have been pursued for humanization: the introduction of human transgenes such as human leukocyte antigen molecules or specific T cell receptors, and the generation of mouse/human chimera by transferring human cells or tissues into immunodeficient mice. Recently, both approaches have been combined to achieve more sophisticated humanized models of autoimmune diseases. This review discusses limitations of conventional mouse models of RA-like disease and provides a closer look into studies in humanized mice exploring their usefulness and necessity as preclinical models for testing of cell-based therapies in autoimmune diseases such as RA.

Co-activation of macrophages and T cells contribute to chronic GVHD in human IL-6 transgenic humanised mouse model

Background

Graft-versus host disease (GVHD) is a complication of stem cell transplantation associated with significant morbidity and mortality. Non-specific immune-suppression, the mainstay of treatment, may result in immune-surveillance dysfunction and disease recurrence.

Methods

We created humanised mice model for chronic GVHD (cGVHD) by injecting cord blood (CB)-derived human CD34⁺CD38⁻CD45RA⁻ haematopoietic stem/progenitor cells (HSPCs) into hIL-6 transgenic NOD/SCID/Il2rgKO (NSG) newborns, and compared GVHD progression with NSG newborns receiving CB CD34⁻ cells mimicking acute GVHD. We characterised human immune cell subsets, target organ infiltration, T-cell repertoire (TCR) and transcriptome in the humanised mice.

Findings

In cGVHD humanised mice, we found activation of T cells in the spleen, lung, liver, and skin, activation of macrophages in lung and liver, and loss of appendages in skin, obstruction of bronchioles in lung and portal fibrosis in liver recapitulating cGVHD. Acute GVHD humanised mice showed activation of T cells with skewed TCR repertoire without significant macrophage activation.

Interpretation

Using humanised mouse models, we demonstrated distinct immune mechanisms contributing acute and chronic GVHD. In cGVHD model, co-activation of human HSPC-derived macrophages and T cells educated in the recipient thymus contributed to delayed onset, multi-organ disease. In acute GVHD model, mature human T cells contained in the graft resulted in rapid disease progression. These humanised mouse models may facilitate future development of new molecular medicine targeting GVHD.

Expansion and Adoptive Transfer of Human Vδ2+ T Cells to Assess Antitumor Effects In Vivo

Recent clinical trials have yielded promising results suggesting that γδ T cell62-based immunotherapies can be effective against hematological malignancies. Human T cells expressing Vγ9Vδ2⁺ receptors are particularly attractive candidates for this application, since they can be readily expanded in vitro in large quantities for adoptive transfer and do not require HLA-matching of donors and recipients. While it is well established that Vγ9Vδ2⁺ T cells are potently cytolytic against many human cancers and it has been shown that they can control transplanted human tumors in xenogeneic model systems, little is known about the parameters that determine the antitumor efficacy of adoptively transferred Vγ9Vδ2⁺ T cells in physiologically relevant scenarios. In particular, it may be important to separate their immunosurveillance functions from those employed in the context of an established tumor. Moreover, it is critical to understand how the presence of an immunosuppressive environment, such as one where tumor-infiltrating T cells are held in check by inhibitory ligands, affects the functions of Vγ9Vδ2⁺ T cells. This chapter describes how to establish Epstein-Barr virus (EBV) infection of human umbilical cord blood mononuclear cells (CBMCs) within immunodeficient mice, so as to drive the in vivo formation of human B cell lymphomas that contain an immunosuppressive environment. Details are provided on how to expand human Vγ9Vδ2⁺ T cells from peripheral blood mononuclear cells (PBMCs), administer them to the mice, and evaluate tumors and other tissues.

Alloimmune Responses of Humanized Mice to Human Pluripotent Stem Cell Therapeutics

There is growing interest in using embryonic stem cell (ESC) and induced pluripotent stem cell (iPSC) derivatives for tissue regeneration. However, an increased understanding of human immune responses to stem cell-derived allografts is necessary for maintaining long-term graft persistence. To model this alloimmunity, humanized mice engrafted with human hematopoietic and immune cells could prove to be useful. In this study, an in-depth analysis of graft-infiltrating human lymphocytes and splenocytes revealed that humanized mice incompletely model human immune responses toward allogeneic stem cells and their derivatives. Furthermore, using an “allogenized” mouse model, we show the feasibility of reconstituting immunodeficient mice with a functional mouse immune system and describe a key role of innate immune cells in the rejection of mouse stem cell allografts.

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Innate immunity is crucial in rejection of minor HA mismatched grafts

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Stem cell alloimmune responses modeled with an “allogenized mouse”

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Humanized mice are unable to fully model immune responses to stem cell allografts

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Splenocytes and graft-infiltrating lymphocytes display an exhausted phenotype

Humanizing the mouse immune system to study splanchnic organ inflammation

It is well known that alterations in splanchnic organ perfusion and/or immune regulation may produce inflammatory tissue injury similar to that observed in several human disorders such as ischaemia and reperfusion injury, food allergies, diabetes, inflammatory bowel disease and graft-versus-host disease. Mouse models have been tremendously important in defining the roles of the circulation, leukocyte trafficking, inflammatory mediator generation, immune regulation and the intestinal microbiota in the pathogenesis of acute and chronic inflammation. However, few of the promising interventions or therapeutics reported in mouse models of inflammatory diseases have been translated to clinically effective treatments in patients. There is growing concern that because of the significant differences that exist between the murine and human immune systems, mouse models may not adequately recapitulate the immuno-pathogenesis of inflammatory diseases. This inconvenient reality has prompted a number of investigators to undertake a series of studies to humanize the murine immune system via adoptive transfer of human lymphoid or progenitor cells into a new generation of immuno-deficient recipients. In this review, we summarize the recent advances that have been made in the development of humanized mice and describe how these mouse models are being used to study the pathophysiology of splanchnic organ inflammation. In addition, we discuss the limitations of the different approaches and present potential solutions for the continued improvement of these important animal models.

A Humanized Mouse Model Generated Using Surplus Neonatal Tissue

Here, we describe the NeoThy humanized mouse model created using non-fetal human tissue sources, cryopreserved neonatal thymus and umbilical cord blood hematopoietic stem cells (HSCs). Conventional humanized mouse models are made by engrafting human fetal thymus and HSCs into immunocompromised mice. These mice harbor functional human T cells that have matured in the presence of human self-peptides and human leukocyte antigen molecules. Neonatal thymus tissue is more abundant and developmentally mature and allows for creation of up to ∼50-fold more mice per donor compared with fetal tissue models. The NeoThy has equivalent frequencies of engrafted human immune cells compared with fetal tissue humanized mice and exhibits T cell function in assays of ex vivo cell proliferation, interferon γ secretion, and in vivo graft infiltration. The NeoThy model may provide significant advantages for induced pluripotent stem cell immunogenicity studies, while bypassing the requirement for fetal tissue.

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Neonatal tissue is a viable alternative to fetal for mouse humanization

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Over 1,000 NeoThy mice can be made from one neonatal thymus donor

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The NeoThy enables robust pre-clinical immunogenicity studies of iPSC therapies

Role of Wild-type and Recombinant Human T-cell Leukemia Viruses in Lymphoproliferative Disease in Humanized NSG Mice

Chronic infection with human T-cell leukemia virus type 1 (HTLV1) can lead to adult T-cell leukemia (ATL). In contrast, infection with HTLV2 does not lead to leukemia, potentially because of distinct virus-host interactions and an active immune response that controls virus replication and, therefore, leukemia development. We created a humanized mouse model by injecting human umbilical-cord stem cells into the livers of immunodeficient neonatal NSG mice, resulting in the development of human lymphocytes that cannot mount an adaptive immune response. We used these mice to compare the ability of molecular clones of HTLV1, HTLV2, and select recombinant viruses to induce leukemia-lymphoma in vivo. Infection with HTLV1 strongly stimulated the proliferation of CD4+ T cells, whereas HTLV2 preferentially stimulated the proliferation of CD8+ T cells; both HTLV1 and HTLV2 induced lymphoproliferative disease. Uninfected and HTLV-infected humanized mice both showed granulomatous inflammation as a background lesion. Similarly, recombinant viruses that expressed the HTLV1 envelope protein (Env) on an HTLV2 background (HTLV2-Env1) or Env2 on an HTLV1 background (HTLV1-Env2) induced lymphoproliferative disease. HTLV2-Env1 stimulated the proliferation of CD4+ T cells, whereas HTLV1-Env2 stimulated both CD4+ and CD8+ T-cell subsets. Our results show that T-cell transformation in vivo is guided by the Env protein of the virus. Furthermore, our humanized mouse model is useful for exploring the preferred T-cell tropisms of HTLV1 and HTLV2.

Modeling Human Antitumor Responses In Vivo Using Umbilical Cord Blood-Engrafted Mice

Mice engrafted with human immune cells offer powerful in vivo model systems to investigate molecular and cellular processes of tumorigenesis, as well as to test therapeutic approaches to treat the resulting cancer. The use of umbilical cord blood mononuclear cells as a source of human immune cells for engraftment is technically straightforward, and provides T lymphocytes and autologous antigen-presenting cells (including B cells, monocytes, and DCs) that bear cognate antigen presenting molecules. By using a human-specific oncogenic virus, such as Epstein-Barr virus, de novo neoplastic transformation of the human B cells can be induced in vivo in a manner that models progressive stages of tumorigenesis from nascent neoplasia to the establishment of vascularized tumor masses with an immunosuppressive environment. Moreover, since tumorigenesis occurs in the presence of autologous T cells, this type of system can be used to investigate how T cells become suppressed during tumorigenesis, and how immunotherapies counteract immunosuppression. This minireview will provide a brief overview of the use of human umbilical cord blood transplanted into immunodeficient murine hosts to model antitumor responses.

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.

Human Mesenchymal Stem Cell-Educated Macrophages Are a Distinct High IL-6-Producing Subset that Confer Protection in Graft-versus-Host-Disease and Radiation Injury Models

Mesenchymal stem cells (MSCs) have immunosuppressive and tissue repair properties, but clinical trials using MSCs to prevent or treat graft-versus-host disease (GVHD) have shown mixed results. Macrophages (MØs) are important regulators of immunity and can promote tissue regeneration and remodeling. We have previously shown that MSCs can educate MØs toward a unique anti-inflammatory immunophenotype (MSC-educated MØs [MEMs]); however, their implications for in vivo models of inflammation have not been studied yet. We now show that in comparison with MØs, MEMs have increased expression of the inhibitory molecules PD-L1, PD-L2, in addition to markers of alternatively activated MØs: CD206 and CD163. RNA-Seq analysis of MEMs, as compared with MØs, show a distinct gene expression profile that positively correlates with multiple pathways important in tissue repair. MEMs also show increased expression of IL-6, transforming growth factor-β, arginase-1, CD73, and decreased expression of IL-12 and tumor necrosis factor-α. We show that IL-6 secretion is controlled in part by the cyclo-oxygenase-2, arginase, and JAK1/STAT1 pathway. When tested in vivo, we show that human MEMs significantly enhance survival from lethal GVHD and improve survival of mice from radiation injury. We show these effects could be mediated in part through suppression of human T cell proliferation and may have attenuated host tissue injury in part by enhancing murine fibroblast proliferation. MEMs are a unique MØ subset with therapeutic potential for the management of GVHD and/or protection from radiation-induced injury.

Full Length Single Chain Fc Protein (FLSC IgG1) as a Potent Antiviral Therapy Candidate: Implications for In Vivo Studies

We have previously shown that FLSC, a chimeric protein containing HIV-1BAL gp120 and the D1 and D2 domains of human CD4, blocks the binding and entry of HIV-1 into target cells by occluding CCR5, the major HIV-1 coreceptor. In an effort to improve the antiviral potential of FLSC, we fused it with the hinge-CH2-CH3 region of human IgG1. The IgG moiety should increase both the affinity and stability in vivo of FLSC, due to the resultant bivalency and an extended serum half-life, thereby increasing its antiviral potency. We previously showed that (FLSC) IgG1 indeed had greater antiviral activity against T cell infections. Here we extend these results to macrophages, for which (FLSC) IgG1 has a more potent antiviral activity than FLSC alone, due in part to its higher binding affinity for CCR5. We also test both compounds in a relevant humanized mouse model and show that, as anticipated, the IgG1 moiety confers a greatly extended half-life. These data, taken together with previous results, suggest potential clinical utility for (FLSC) IgG1 and support further developmental work toward eventual clinical trials.

Translating Treg Therapy in Humanized Mice

Regulatory T cells (Treg) control immune cell function as well as non-immunological processes. Their far-reaching regulatory activities suggest their functional manipulation as a means to sustainably and causally intervene with the course of diseases. Preclinical tools and strategies are however needed to further test and develop interventional strategies outside the human body. “Humanized” mouse models consisting of mice engrafted with human immune cells and tissues provide new tools to analyze human Treg ontogeny, immunobiology, and therapy. Here, we summarize the current state of humanized mouse models as a means to study human Treg function at the molecular level and to design strategies to harness these cells for therapeutic purposes.

Humanized Chronic Graft-versus-Host Disease in NOD-SCID il2rγ-/- (NSG) Mice with G-CSF-Mobilized Peripheral Blood Mononuclear Cells following Cyclophosphamide and Total Body Irradiation

Chronic graft-versus-host disease (cGvHD) is the major source of late phase morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Humanized acute GvHD (aGvHD) in vivo models using NOD-SCID il2rγ-/- (NSG) mice are well described and are important tools for investigating pathogenicity of human cells in vivo. However, there have been only few reported humanized cGvHD mouse models. We evaluated if prolonged inflammation driven by low dose G-CSF-mobilized human PBMCs (G-hPBMCs) would lead to cGvHD following cyclophosphamide (CTX) administration and total body irradiation (TBI) in NSG mice. Engraftment was assessed in peripheral blood (PB) and in specific target organs by either flow cytometry or immunohistochemistry (IHC). Tissue samples were harvested 56 days post transplantation and were evaluated by a pathologist. Some mice were kept for up to 84 days to evaluate the degree of fibrosis. Mice that received CTX at 20mg/kg did not show aGvHD with stable expansion of human CD45+ CD3+ T-cells in PB (mean; 5.8 to 23.2%). The pathology and fibrosis scores in the lung and the liver were significantly increased with aggregation of T-cells and hCD68+ macrophages. There was a correlation between liver pathology score and the percentage of hCD68+ cells, suggesting the role of macrophage in fibrogenesis in NSG mice. In order to study long-term survival, 6/9 mice who survived more than 56 days showed increased fibrosis in the lung and liver at the endpoint, which suggests the infiltrating hCD68+ macrophages may be pathogenic. It was shown that the combination of CTX and TBI with a low number of G-hPBMCs (1x106) leads to chronic lung and liver inflammation driven by a high infiltration of human macrophage and mature human T cells from the graft, resulting in fibrosis of lung and liver in NSG mice. In conclusion this model may serve as an important pre-clinical model to further current understanding of the roles of human macrophages in cGvHD.

Chronic graft-versus-host-disease in CD34(+)-humanized NSG mice is associated with human susceptibility HLA haplotypes for autoimmune disease

Chronic graft-versus-host disease (cGVHD) is a significant hurdle to long-term hematopoietic stem-cell transplantation success. Insights into the pathogenesis and mechanistical investigations of novel therapeutic strategies are limited as appropriate animal models are missing. The immunodeficient NSG mouse - when humanized with human bone marrow, fetal liver and thymus (BLT NSG) - is prone for cGVHD, yet mainly affects the skin. In contrast, the NSG mouse humanized exclusively with CD34(+)-selected, CD3(+)-depleted stem cells (CD34(+)NSG) has neither been described for acute nor chronic GVHD so far. This is the first report about the development of systemic autoimmune cGVHD ≥24 weeks post stem cell receipt involving lung, liver, skin, gingiva and intestine in two NSG cohorts humanized with CD34(+) grafts from different donors. Affected mice presented with sclerodermatous skin, fibrotic lung, severe hepatitis, and massive dental malformation/loss. CD4(+)-dominated, TH2-biased, bulky T-cell infiltrates featured highly skewed T cell receptor (TCR) repertoires, clonal expansions, and autoreactive TCRs. In affected tissues profibrotic IL-13 and -4 dominated over TH1 cytokines IFN-γ and TNF-α. Thus, the time point of manifestation and the phenotype match human systemic pleiotropic sclerodermatous GVHD. The CD34(+)NSG-model's intrinsic deficiency of thymus, thymus-derived regulatory T cells (nTreg) and B cells emphasizes the role of the genetic polymorphism and the cytokines in the pathogenesis of cGVHD. Importantly, the only factor discriminating diseased versus non-diseased CD34(+)NSG cohorts were two risk HLA haplotypes that in human mediate susceptibility for autoimmune disease (psoriasis). Thus, the CD34(+)NSG model may serve as a platform for addressing issues related to the pathophysiology and treatment of human autoimmunity and chronic GVHD.

Use of Humanized Mice to Study the Pathogenesis of Autoimmune and Inflammatory Diseases

Animal models of disease have been used extensively by the research community for the past several decades to better understand the pathogenesis of different diseases and assess the efficacy and toxicity of different therapeutic agents. Retrospective analyses of numerous preclinical intervention studies using mouse models of acute and chronic inflammatory diseases reveal a generalized failure to translate promising interventions or therapeutics into clinically effective treatments in patients. Although several possible reasons have been suggested to account for this generalized failure to translate therapeutic efficacy from the laboratory bench to the patient's bedside, it is becoming increasingly apparent that the mouse immune system is substantially different from the human. Indeed, it is well known that >80 major differences exist between mouse and human immunology; all of which contribute to significant differences in immune system development, activation, and responses to challenges in innate and adaptive immunity. This inconvenient reality has prompted investigators to attempt to humanize the mouse immune system to address important human-specific questions that are impossible to study in patients. The successful long-term engraftment of human hematolymphoid cells in mice would provide investigators with a relatively inexpensive small animal model to study clinically relevant mechanisms and facilitate the evaluation of human-specific therapies in vivo. The discovery that targeted mutation of the IL-2 receptor common gamma chain in lymphopenic mice allows for the long-term engraftment of functional human immune cells has advanced greatly our ability to humanize the mouse immune system. The objective of this review is to present a brief overview of the recent advances that have been made in the development and use of humanized mice with special emphasis on autoimmune and chronic inflammatory diseases. In addition, we discuss the use of these unique mouse models to define the human-specific immunopathological mechanisms responsible for the induction and perpetuation of chronic gut inflammation.

Generation of improved mouse models for the study of hepatitis C virus

Approximately 3% of the world׳s population suffers from chronic infections with hepatitis C virus (HCV). Although current treatment regimes are capable of effectively eradicating HCV infection from these patients, the cost of these combinations of direct-acting antivirals are prohibitive. Approximately 80% of untreated chronic HCV carriers will be at high risk for developing severe liver disease, including fibrosis, cirrhosis, and hepatocellular carcinoma. A vaccine is urgently needed to lessen this global burden. Besides humans, HCV infection can be experimentally transmitted to chimpanzees, and this is the best model for studies of HCV infection and related innate and adaptive immune responses. Although the chimpanzee model yielded valuable insight, limited availability, high cost and ethical considerations limit their utility. The only small animal models of robust HCV infection are highly immunodeficient mice with human chimeric livers. However, these mice cannot be used to study adaptive immune responses and therefore a more relevant animal model is needed to assist in vaccine development. Novel strains of immunodeficient mice have been developed that allow for the engraftment of human hepatopoietic stem cells, as well as functional human lymphoid cells and tissues, effectively creating human immune systems in otherwise immunodeficient mice. These humanized mice are rapidly emerging as pre-clinical bridges for numerous pathogens that, like HCV, only cause infectious disease in humans. This review highlights the potential these new models have for changing the current landscape for HCV research and vaccine development.

CD8-positive lymphocytes in graft-versus-host disease of humanized NOD.Cg-Prkdc(scid)Il2rg(tm1Wjl)/SzJ mice

Immunocompromised mice that can support a human immune system are an increasingly important model for the investigation of haemopoietic stem/progenitor cell (HSPC) development and human infectious disease. NOD-SCID IL-2Rγ(-/-) (NSG) mice engrafted with human fetal liver and thymus prior to HSPC engraftment, commonly known as NSG-bone marrow-liver-thymus (NSG-hu-BLT) mice, are one such model and have robust reconstitution of human leucocytes within the peripheral blood and tissues. Four NSG-hu-BLT mice were submitted for diagnostic necropsy examination following the development of alopecia, pruritus and lethargy after HSPC engraftment. Histopathology revealed multifocal to coalescing single keratinocyte cell death in the epidermis and follicles with dermatitis and mild dermal fibrosis. Single-cell hepatocyte cell death was present in three cases, with various degrees of portal fibrosis. In the skin and liver, cell death was associated with lymphocytes that reacted with anti-human CD45, CD3 and CD8 antibodies, consistent with a diagnosis of graft-versus-host disease (GvHD). This study expands on recently reported microscopical features of GvHD in NSG-hu-BLT mice and suggests a role for CD8(+) T lymphocytes in the progression of the disease. NSG-hu-BLT mice represent an excellent model of GvHD, but its prevalence may compromise their use in other fields of biomedical research.

Antibody- and aptamer-strategies for GvHD prevention

Prevention of Graft-versus-Host-Disease (GvHD) by preserved Graft-versus-Leukaemia (GvL) effect is one of the major obstacles following allogeneic haematopoietic stem cell transplantation. Currently used drugs are associated with side effects and were not able to separate GvHD from the GvL-effect because of general T-cell suppression. This review focuses on murine models for GvHD and currently available treatment options involving antibodies and applications for the therapeutic use of aptamers as well as strategies for targeting immune responses by allogenic antigens.

Generation of improved humanized mouse models for human infectious diseases

The study of human-specific infectious agents has been hindered by the lack of optimal small animal models. More recently development of novel strains of immunodeficient mice has begun to provide the opportunity to utilize small animal models for the study of many human-specific infectious agents. The introduction of a targeted mutation in the IL2 receptor common gamma chain gene (IL2rg(null)) in mice already deficient in T and B cells led to a breakthrough in the ability to engraft hematopoietic stem cells, as well as functional human lymphoid cells and tissues, effectively creating human immune systems in immunodeficient mice. These humanized mice are becoming increasingly important as pre-clinical models for the study of human immunodeficiency virus-1 (HIV-1) and other human-specific infectious agents. However, there remain a number of opportunities to further improve humanized mouse models for the study of human-specific infectious agents. This is being done by the implementation of innovative technologies, which collectively will accelerate the development of new models of genetically modified mice, including; i) modifications of the host to reduce innate immunity, which impedes human cell engraftment; ii) genetic modification to provide human-specific growth factors and cytokines required for optimal human cell growth and function; iii) and new cell and tissue engraftment protocols. The development of "next generation" humanized mouse models continues to provide exciting opportunities for the establishment of robust small animal models to study the pathogenesis of human-specific infectious agents, as well as for testing the efficacy of therapeutic agents and experimental vaccines.