Induction of functional human macrophages from bone marrow promonocytes by M-CSF in humanized mice

Emerging Preclinical Applications of Humanized Mouse Models in the Discovery and Validation of Novel Immunotherapeutics and Their Mechanisms of Action for Improved Cancer Treatment

Cancer therapeutics have undergone immense research over the past decade. While chemotherapies remain the mainstay treatments for many cancers, the advent of new molecular techniques has opened doors for more targeted modalities towards cancer cells. Although immune checkpoint inhibitors (ICIs) have demonstrated therapeutic efficacy in treating cancer, adverse side effects related to excessive inflammation are often reported. There is a lack of clinically relevant animal models to probe the human immune response towards ICI-based interventions. Humanized mouse models have emerged as valuable tools for pre-clinical research to evaluate the efficacy and safety of immunotherapy. This review focuses on the establishment of humanized mouse models, highlighting the challenges and recent advances in these models for targeted drug discovery and the validation of therapeutic strategies in cancer treatment. Furthermore, the potential of these models in the process of uncovering novel disease mechanisms is discussed.

Humanized MISTRG as a preclinical in vivo model to study human neutrophil-mediated immune processes

Introduction

MISTRG mice have been genetically modified to allow development of a human myeloid compartment from engrafted human CD34+ haemopoietic stem cells, making them particularly suited to study the human innate immune system in vivo. Here, we characterized the human neutrophil population in these mice to establish a model that can be used to study the biology and contribution in immune processes of these cells in vivo.

Methods and results

We could isolate human bone marrow neutrophils from humanized MISTRG mice and confirmed that all neutrophil maturation stages from promyelocytes (CD11b–CD16–) to end-stage segmented cells (CD11b+CD16+) were present. We documented that these cells possessed normal functional properties, including degranulation, reactive oxygen species production, adhesion, and antibody-dependent cellular cytotoxicity towards antibody-opsonized tumor cells ex vivo. The acquisition of functional capacities positively correlated with the maturation state of the cell. We found that human neutrophils were retained in the bone marrow of humanized MISTRG mice during steady state. However, the mature segmented CD11b+CD16+ human neutrophils were released from the bone marrow in response to two well-established neutrophil-mobilizing agents (i.e., G-CSF and/or CXCR4 antagonist Plerixafor). Moreover, the neutrophil population in the humanized MISTRG mice actively reacted to thioglycolate-induced peritonitis and could infiltrate implanted human tumors, as shown by flow cytometry and fluorescent microscopy.

Discussion

These results show that functional human neutrophils are generated and can be studied in vivo using the humanized MISTRG mice, providing a model to study the various functions of neutrophils in inflammation and in tumors.

Modeling CSF-1 receptor deficiency diseases - how close are we?

The role of colony-stimulating factor-1 receptor (CSF-1R) in macrophage and organismal development has been extensively studied in mouse. Within the last decade, mutations in the CSF1R have been shown to cause rare diseases of both pediatric (Brain Abnormalities, Neurodegeneration, and Dysosteosclerosis, OMIM #618476) and adult (CSF1R-related leukoencephalopathy, OMIM #221820) onset. Here we review the genetics, penetrance, and histopathological features of these diseases and discuss to what extent the animal models of Csf1r deficiency currently available provide systems in which to study the underlying mechanisms involved.

Improvement of human myeloid and natural killer cell development in humanized mice via hydrodynamic injection of transposon plasmids containing multiple human cytokine genes

Humanized mice reconstituted with a functional human immune system (HIS) are instrumental in studying human immunity and immune disorders in vivo. The poor or lack of cross-reactivity between mouse cytokines and human cells limits the development and/or function of human immune cell subsets including human myeloid, natural killer and B cells. Here we explored the potential to achieve long-term production of human cytokines in immunodeficient mice using a transposon-plasmid-based hydrodynamic injection approach. We constructed a transposon-plasmid carrying five human cytokine coding sequences (named PB-5F), and observed that four of the cytokines (granulocyte-macrophage colony-stimulating factor, interleukin (IL)-15, IL-6 and IL-3) were detectable in sera and three (granulocyte-macrophage colony-stimulating factor, IL-15 and IL-6) showed long-term production in immunodeficient mice that received a single hydrodynamic injection of PB-5F plus the transposase plasmid (Super PB). Furthermore, a single injection of PB-5F/Super PB markedly enhanced the reconstitution of human myeloid cells and natural killer cells, and promoted human B-cell maturation in HIS mice. Taken together, our data revealed that hydrodynamic injection of the PB-5F/Super PB vectors may serve as a convenient and efficacious means to promote human immune function in HIS mice.

Protocol for generating human immune system mice and hydrodynamic injection to analyze human hematopoiesis in vivo

Human immune system (HIS) mice provide a valuable platform to investigate and modulate human hematopoiesis development in vivo. Here, we describe detailed protocols for the construction of HIS mice, modulation of human hematopoiesis in vivo using hydrodynamic injection of plasmids encoding cytokines of interest, and flow cytometry analysis of humanization levels and human immune subsets. This approach can be easily applied to screen or verify factors that regulate human hematopoiesis and immune system.

For complete details on the use and execution of this protocol, please refer to Cardoso et al. (2021) and Li et al. (2017).

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The protocol for construction of human immune system mice

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Detailed procedure for hydrodynamic injection

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Characterization of human immune subpopulations by flow cytometry

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In vivo modulation of human hematopoiesis

Inhibitory effects of Atlantic cod (Gadus morhua) peptides on RANKL-induced osteoclastogenesis in vitro and osteoporosis in ovariectomized mice

Atlantic cod (Gadus morhua) is one of the most important fishes in the world with high nutritional value and economic value. However, the impact and underlying mechanism of the G....

Functions of macrophage colony-stimulating factor (CSF1) in development, homeostasis, and tissue repair

Macrophage colony-stimulating factor (CSF1) is the primary growth factor required for the control of monocyte and macrophage differentiation, survival, proliferation and renewal. Although the cDNAs encoding multiple isoforms of human CSF1 were cloned in the 1980s, and recombinant proteins were available for testing in humans, CSF1 has not yet found substantial clinical application. Here we present an overview of CSF1 biology, including evolution, regulation and functions of cell surface and secreted isoforms. CSF1 is widely-expressed, primarily by cells of mesenchymal lineages, in all mouse tissues. Cell-specific deletion of a floxed Csf1 allele in mice indicates that local CSF1 production contributes to the maintenance of tissue-specific macrophage populations but is not saturating. CSF1 in the circulation is controlled primarily by receptor-mediated clearance by macrophages in liver and spleen. Administration of recombinant CSF1 to humans or animals leads to monocytosis and expansion of tissue macrophage populations and growth of the liver and spleen. In a wide variety of tissue injury models, CSF1 administration promotes monocyte infiltration, clearance of damaged cells and repair. We suggest that CSF1 has therapeutic potential in regenerative medicine.

Humanized Mice for Infectious and Neurodegenerative disorders

Humanized mice model human disease and as such are used commonly for research studies of infectious, degenerative and cancer disorders. Recent models also reflect hematopoiesis, natural immunity, neurobiology, and molecular pathways that influence disease pathobiology. A spectrum of immunodeficient mouse strains permit long-lived human progenitor cell engraftments. The presence of both innate and adaptive immunity enables high levels of human hematolymphoid reconstitution with cell susceptibility to a broad range of microbial infections. These mice also facilitate investigations of human pathobiology, natural disease processes and therapeutic efficacy in a broad spectrum of human disorders. However, a bridge between humans and mice requires a complete understanding of pathogen dose, co-morbidities, disease progression, environment, and genetics which can be mirrored in these mice. These must be considered for understanding of microbial susceptibility, prevention, and disease progression. With known common limitations for access to human tissues, evaluation of metabolic and physiological changes and limitations in large animal numbers, studies in mice prove important in planning human clinical trials. To these ends, this review serves to outline how humanized mice can be used in viral and pharmacologic research emphasizing both current and future studies of viral and neurodegenerative diseases. In all, humanized mouse provides cost-effective, high throughput studies of infection or degeneration in natural pathogen host cells, and the ability to test transmission and eradication of disease.

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.

Building the Next Generation of Humanized Hemato-Lymphoid System Mice

Since the late 1980s, mice have been repopulated with human hematopoietic cells to study the fundamental biology of human hematopoiesis and immunity, as well as a broad range of human diseases in vivo. Multiple mouse recipient strains have been developed and protocols optimized to efficiently generate these “humanized” mice. Here, we review three guiding principles that have been applied to the development of the currently available models: (1) establishing tolerance of the mouse host for the human graft; (2) opening hematopoietic niches so that they can be occupied by human cells; and (3) providing necessary support for human hematopoiesis. We then discuss four remaining challenges: (1) human hematopoietic lineages that poorly develop in mice; (2) limited antigen-specific adaptive immunity; (3) absent tolerance of the human immune system for its mouse host; and (4) sub-functional interactions between human immune effectors and target mouse tissues. While major advances are still needed, the current models can already be used to answer specific, clinically-relevant questions and hopefully inform the development of new, life-saving therapies.

Advances in Human Immune System Mouse Models for Studying Human Hematopoiesis and Cancer Immunotherapy

Immunotherapy has established itself as a promising tool for cancer treatment. There are many challenges that remain including lack of targets and some patients across various cancers who have not shown robust clinical response. One of the major problems that have hindered the progress in the field is the dearth of appropriate mouse models that can reliably recapitulate the complexity of human immune-microenvironment as well as the malignancy itself. Immunodeficient mice reconstituted with human immune cells offer a unique opportunity to comprehensively evaluate immunotherapeutic strategies. These immunosuppressed and genetically modified mice, with some overexpressing human growth factors, have improved human hematopoietic engraftment as well as created more functional immune cell development in primary and secondary lymphoid tissues in these mice. In addition, several new approaches to modify or to add human niche elements to further humanize these immunodeficient mice have allowed a more precise characterization of human hematopoiesis. These important refinements have opened the possibility to evaluate not only human immune responses to different tumor cells but also to investigate how malignant cells interact with their niche and most importantly to test immunotherapies in a more preclinically relevant setting, which can ultimately lead to better success of these drugs in clinical trials.

Abeliophyllum distichum Nakai alleviates postmenopausal osteoporosis in ovariectomized rats and prevents RANKL-induced osteoclastogenesis in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Abeliophyllum distichum Nakai (AD), called Miseon, is one of Korea's monotypic endemic species. As a folk remedy, the AD has been used to treat inflammatory disease, stomachaches, diarrhea, and gynecologic disease in Korea. Some researchers have reported that the AD has anti-cancer, anti-inflammatory, and anti-oxidant effects. But the protective effect of AD leaf for osteoporosis has not been reported yet.

AIM OF THE STUDY

This study aimed to analyze the effects and mechanism of AD-ethyl acetate fraction (EA) extract on the osteoporosis, one of the gynecologic disease.

MATERIALS AND METHODS

The RAW 264.7 cells were used as a model for RANKL-induced osteoclastogenesis. We measured the TRAcP activity, expressions of NFATc1, c-fos, and MAPK to investigate the effect of AD-EA. OVX-induced osteoporosis rat model was used as menopausal osteoporosis. After both ovaries were removed through a surgical procedure, and AD-EA or 17b-estradiol was orally administered for 8 weeks. BMD of femurs was measured as well as the bone morphometric parameter, such as BV/TV, trabecular thickness, number and surface using a micro CT.

RESULTS

AD-EA significantly inhibited TRAcP activity, actin ring formation, pit formation and the expressions of osteoclast-related genes in a dose-dependent manner through the inhibition of the MAPK and c-fos/NFATc1 pathway. In addition, low dose administration of AD-EA improved the deterioration of trabecular bone microarchitecture caused by OVX through the inhibition of bone resorption by TRAcP and CTK.

CONCLUSIONS

These results suggest that AD-EA may contribute to the therapy of osteoporosis caused by menopause in women.

Genetic Alterations and Checkpoint Expression: Mechanisms and Models for Drug Discovery

In this chapter, we will sketch a story that begins with the breakdown of chromosome homeostasis and genomic stability. Genomic alterations may render tumor cells eternal life at the expense of immunogenicity. Although antitumor immunity can be primed through neoantigens or inflammatory signals, tumor cells have evolved countermeasures to evade immune surveillance and strike back by modulating immune checkpoint related pathways. At present, monoclonal antibody drugs targeting checkpoints like PD-1 and CTLA-4 have significantly prolonged the survival of a variety of cancer patients, and thus have marked a great achievement in the history of antitumor therapy. Nevertheless, this is not the end of the story. As the relationship between genomic alteration and checkpoint expression is being delineated though the advances of preclinical animal models and emerging technologies, novel checkpoint targets are on the way to be discovered.

Humanized mouse models of genetic immune disorders and hematological malignancies

The immune system is quite remarkable having both the ability to tolerate innocuous and self-antigens while possessing a robust capacity to recognize and eradicate infectious pathogens and foreign entities. The genetics that encode this delicate balancing act include multiple genes and specialized cell types. Over the past several years, whole exome and whole genome sequencing has uncovered the genetics driving many human immune-mediated diseases including monogenic disorders and hematological malignancies. With the advent of genome editing technologies, the ability to correct genetic immune defects in autologous cells holds great promise for a number of conditions. Since assessment of novel therapeutic strategies have been difficult in mice, in recent years, immunodeficient mice capable of engrafting human cells and tissue have been developed and utilized for a variety of research applications. In this review, we discuss immune-humanized mice as a research tool to study human immunobiology and genetic immune disorders in vivo and the promise of future applications.

Macrophages reprogrammed by lung cancer microparticles promote tumor development via release of IL-1β

Despite their mutual antagonism, inflammation and immunosuppression coexist in tumor microenvironments due to tumor and immune cell interactions, but the underlying mechanism remains unclear. Previously, we showed that tumor cell-derived microparticles induce an M2 phenotype characterized by immunosuppression in tumor-infiltrating macrophages. Here, we further showed that lung cancer microparticles (L-MPs) induce macrophages to release a key proinflammatory cytokine, IL-1β, thus promoting lung cancer development. The underlying mechanism involves the activation of TLR3 and the NLRP3 inflammasome by L-MPs. More importantly, tyrosine kinase inhibitor treatment-induced L-MPs also induce human macrophages to release IL-1β, leading to a tumor-promoting effect in a humanized mouse model. These findings demonstrated that in addition to their anti-inflammatory effect, L-MPs induce a proinflammatory phenotype in tumor-infiltrating macrophages, promoting the development of inflammatory and immunosuppressive tumor microenvironments.

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.

HTLV-1 viral oncogene HBZ drives bone destruction in adult T cell leukemia

Osteolytic bone lesions and hypercalcemia are common, serious complications in adult T cell leukemia/lymphoma (ATL), an aggressive T cell malignancy associated with human T cell leukemia virus type 1 (HTLV-1) infection. The HTLV-1 viral oncogene HBZ has been implicated in ATL tumorigenesis and bone loss. In this study, we evaluated the role of HBZ on ATL-associated bone destruction using HTLV-1 infection and disease progression mouse models. Humanized mice infected with HTLV-1 developed lymphoproliferative disease and continuous, progressive osteolytic bone lesions. HTLV-1 lacking HBZ displayed only modest delays to lymphoproliferative disease but significantly decreased disease-associated bone loss compared with HTLV-1-infected mice. Gene expression array of acute ATL patient samples demonstrated increased expression of RANKL, a critical regulator of osteoclasts. We found that HBZ regulated RANKL in a c-Fos-dependent manner. Treatment of HTLV-1-infected humanized mice with denosumab, a monoclonal antibody against human RANKL, alleviated bone loss. Using patient-derived xenografts from primary human ATL cells to induce lymphoproliferative disease, we also observed profound tumor-induced bone destruction and increased c-Fos and RANKL gene expression. Together, these data show the critical role of HBZ in driving ATL-associated bone loss through RANKL and identify denosumab as a potential treatment to prevent bone complications in ATL patients.

Modeling Infectious Diseases in Mice with a "Humanized" Immune System

Human immune system (HIS) mice are created by transplanting human immune cells or their progenitor cells into highly immunodeficient recipient mouse hosts, thereby "humanizing" their immune systems. Over past decades, the field of HIS mice has evolved rapidly, as modifications of existing immunodeficient mouse strains have been developed, resulting in increasing levels of human tissue engraftment as humanization is optimized. Current HIS mouse models not only permit elevated levels of human cell engraftment but also demonstrate graft stability. As such, HIS mice are being extensively used to study the human innate and adaptive immune response against microbial infections in vivo. Compared to nonhumanized animal models, which are frequently infected with surrogate or adapted microbes, the HIS mouse models allow the analysis of interactions between human immune cells and bona fide pathogenic microbes, making them a more clinically relevant model. This article reviews the development of HIS mice and covers the different strategies used to humanize mice, as well as discussing the use of HIS mice for studying bacterial infections that cause human disease.

Humanized Mouse Models for the Study of Infection and Pathogenesis of Human Viruses

The evolution of infectious pathogens in humans proved to be a global health problem. Technological advancements over the last 50 years have allowed better means of identifying novel therapeutics to either prevent or combat these infectious diseases. The development of humanized mouse models offers a preclinical in vivo platform for further characterization of human viral infections and human immune responses triggered by these virus particles. Multiple strains of immunocompromised mice reconstituted with a human immune system and/or human hepatocytes are susceptible to infectious pathogens as evidenced by establishment of full viral life cycles in hope of investigating viral–host interactions observed in patients and discovering potential immunotherapies. This review highlights recent progress in utilizing humanized mice to decipher human specific immune responses against viral tropism.

Potential Pitfalls of the Humanized Mice in Modeling Sepsis

Humanized mice are a state-of-the-art tool used to study several diseases, helping to close the gap between mice and human immunology. This review focuses on the potential obstacles in the analysis of immune system performance between humans and humanized mice in the context of severe acute inflammation as seen in sepsis or other critical care illnesses. The extent to which the reconstituted human immune system in mice adequately compares to the performance of the human immune system in human hosts is still an evolving question. Although certain viral and protozoan infections can be replicated in humanized mice, whether a highly complex and dynamic systemic inflammation like sepsis can be accurately represented by current humanized mouse models in a clinically translatable manner is unclear. Humanized mice are xenotransplant animals in the most general terms. Several organs (e.g., bone marrow mesenchymal cells, endothelium) cannot interact with the grafted human leukocytes effectively due to species specificity. Also the interaction between mice gut flora and the human immune system may be paradoxical. Often, grafting is performed utilizing an identical batch of stem cells in highly inbred animals which fails to account for human heterogeneity. Limiting factors include the substantial cost and restricting supply of animals. Finally, humanized mice offer an opportunity to gain knowledge of human-like conditions, requiring careful data interpretation just as in nonhumanized animals.

Regulatory T cells control toxicity in a humanized model of IL-2 therapy

While patient selection and clinical management have reduced high-dose IL-2 (HDIL2) immunotherapy toxicities, the immune mechanisms that underlie HDIL2-induced morbidity remain unclear. Here we show that dose-dependent morbidity and mortality of IL-2 immunotherapy can be modeled in human immune system (HIS) mice. Depletion of human T cell subsets during the HDIL2 treatment reduces toxicity, pointing to the central function of T cells. Preferential expansion of effector T cells secondary to defective suppressive capacity of regulatory T (Treg) cells after HDIL2 therapy further underscores the importance of Treg in the maintenance of immune tolerance. IL-2 toxicity is induced by selective depletion or inhibition of Treg after LDIL2 therapy, and is ameliorated in HDIL2-treated HIS mice receiving the PIM-1 kinase inhibitor, Kaempferol. Modeling IL-2 pathophysiology in HIS mice offers a means to understand the functions of effector and regulatory T cells in immune-mediated toxicities associated with cancer immunotherapy.

Technical Improvement and Application of Hydrodynamic Gene Delivery in Study of Liver Diseases

Development of an safe and efficient in vivo gene delivery method is indispensable for molecular biology research and the progress in the following gene therapy. Over the past few years, hydrodynamic gene delivery (HGD) with naked DNA has drawn increasing interest in both research and potential clinic applications due to its high efficiency and low risk in triggering immune responses and carcinogenesis in comparison to viral vectors. This method, involving intravenous injection (i.v.) of massive DNA in a short duration, gives a transient but high in vivo gene expression especially in the liver of small animals. In addition to DNA, it has also been shown to deliver other substance such as RNA, proteins, synthetic small compounds and even viruses in vivo. Given its ability to robustly mimic in vivo hepatitis B virus (HBV) production in liver, HGD has become a fundamental and important technology on HBV studies in our group and many other groups. Recently, there have been interesting reports about the applications and further improvement of this technology in other liver research. Here, we review the principle, safety, current application and development of hydrodynamic delivery in liver disease studies, and discuss its future prospects, clinical potential and challenges.

The clinical and immunological performance of 28 days survival model of cecal ligation and puncture in humanized mice

Sepsis triggers a coordinated and thorough immune system response with long-term unfavorable sequelae after the initial insult. Long-term recovery from sepsis has garnered increasing attention recently, but a lack of suitable animal models impairs progress in this area. Our study, therefore, aimed to address the performance of the immune system in a survivable model of sepsis (cecal ligation and sepsis; CLP) for up to 28 d after the initial injury in humanized mice. Our model mimics human sepsis with weight loss and post-sepsis hypothermia. Within the first 7 d of sepsis, the M1 inflammatory cell subtype predominated, as evidenced by increased CD16 expression, but at 28 d, a mixed population of M1 and M2 inflammatory cells emerged, as evidenced by increased secretion of transforming growth factor TGFβ and CD206 expression. This change was accompanied by normalized production of interleukin (IL)-6, tumor necrosis factor TNFα and IL-10 at 28 d. Furthermore, the ability of MO to become regulatory DC or the frequency of endogenous DC were severely affected at 28 days. Thus, sepsis results in profound and persistent changes in the function of myeloid cells up to 28 days after CLP demonstrating the persistence of the new acquired immunological features long after resolution of the sepsis.

In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis

In vivo interrogation of the function of genes implicated in tumorigenesis is limited by the need to generate and cross germline mutant mice. Here we describe approaches to model colorectal cancer (CRC) and metastasis, which rely on in situ gene editing and orthotopic organoid transplantation in mice without cancer-predisposing mutations. Autochthonous tumor formation is induced by CRISPR-Cas9-based editing of the Apc and Trp53 tumor suppressor genes in colon epithelial cells and by orthotopic transplantation of Apc-edited colon organoids. ApcΔ/Δ;KrasG12D/+;Trp53Δ/Δ (AKP) mouse colon organoids and human CRC organoids engraft in the distal colon and metastasize to the liver. Finally, we apply the orthotopic transplantation model to characterize the clonal dynamics of Lgr5+ stem cells and demonstrate sequential activation of an oncogene in established colon adenomas. These experimental systems enable rapid in vivo characterization of cancer-associated genes and reproduce the entire spectrum of tumor progression and metastasis.

Long-term Monocyte Dysfunction after Sepsis in Humanized Mice Is Related to Persisted Activation of Macrophage-Colony Stimulation Factor (M-CSF) and Demethylation of PU.1, and It Can Be Reversed by Blocking M-CSF In Vitro or by Transplanting Naïve Autologous Stem Cells In Vivo

The duration of post-sepsis long-term immune suppression is poorly understood. Here, we focused on the role of monocytes (MO) as the pivotal cells for long-term regulation of post-sepsis milieu. Lost ability of MO to adapt is seen in several acute conditions, but it is unclear for how long MO aberrancy post-sepsis can persist. Interestingly, the positive feedback loop sustaining secretion of macrophage-colony stimulation factor (M-CSF) can persist even after resolution of sepsis and significantly alters performance of MO. Here, we investigated the activation of M-CSF, and it as critical regulator of PU.1 in mice surviving 28 days after sepsis. Our primary readout was the ability of MO to differentiate into dendritic cells (DCs; MO→iDC) in vitro since this is one of the critical processes regulating a successful transition from innate to acquired immunity. We utilized a survival modification of the cecal ligation and puncture (CLP) model of sepsis in humanized mice. Animals were sacrificed 28 days after CLP (t_CLP+28d). Untouched (CONTR) or sham-operated (SHAM) animals served as controls. Some animals received rescue from stem cells originally used for grafting 2 weeks after CLP. We found profound decrease of MO→iDC in the humanized mice 28 days after sepsis, demonstrated by depressed expression of CD1a, CD83, and CD209, diminished production of IL-12p70, and depressed ability to stimulate T cells in mice after CLP as compared to SHAM or CONTR. In vitro defect in MO→iDC was accompanied by in vivo decrease of BDCA-3⁺ endogenous circulating DC. Interestingly, post-CLP MO had persistent activation of M-CSF pathway, shown by exaggerated secretion of M-CSF, activation of PU.1, and demethylation of SPII. Neutralization of the M-CSF in vitro reversed the post-CLP MO→iDC aberration. Furthermore, transplantation of naïve, autologous stem cell-derived MO restored CLP-deteriorated ability of MO to become DC, measured as recovery of CD1a expression, enhanced production of IL-12p70, and ability of IL-4 and GM-CSF MO to stimulate allogeneic T cells. Our results suggest the role of epigenetic mediated M-CSF aberration in mediating post-sepsis immune system recovery.

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 Models of Clinical Disease

Immunodeficient mice engrafted with functional human cells and tissues, that is, humanized mice, have become increasingly important as small, preclinical animal models for the study of human diseases. Since the description of immunodeficient mice bearing mutations in the IL2 receptor common gamma chain (IL2rg^null) in the early 2000s, investigators have been able to engraft murine recipients with human hematopoietic stem cells that develop into functional human immune systems. These mice can also be engrafted with human tissues such as islets, liver, skin, and most solid and hematologic cancers. Humanized mice are permitting significant progress in studies of human infectious disease, cancer, regenerative medicine, graft-versus-host disease, allergies, and immunity. Ultimately, use of humanized mice may lead to the implementation of truly personalized medicine in the clinic. This review discusses recent progress in the development and use of humanized mice and highlights their utility for the study of human diseases.

Humanizing NOD/SCID/IL-2Rγnull (NSG) mice using busulfan and retro-orbital injection of umbilical cord blood-derived CD34(+) cells

Background

Humanized mouse models are still under development, and various protocols exist to improve human cell engraftment and function.

Methods

Fourteen NOD/SCID/IL-2Rγnull (NSG) mice (4‒5 wk old) were conditioned with busulfan and injected with human umbilical cord blood (hUCB)-derived CD34⁺ hematopoietic stem cells (HSC) via retro-orbital sinuses. The bone marrow (BM), spleen, and peripheral blood (PB) were analyzed 8 and 12 weeks after HSC transplantation.

Results

Most of the NSG mice tolerated the regimen well. The percentage of hCD45⁺ and CD19⁺ cells rose significantly in a time-dependent manner. The median percentage of hCD45⁺cells in the BM was 55.5% at week 8, and 67.2% at week 12. The median percentage of hCD45⁺ cells in the spleen at weeks 8 and 12 was 42% and 51%, respectively. The median percentage of hCD19⁺ cells in BM at weeks 8 and 12 was 21.5% and 39%, respectively (P=0.04). Similarly, the median percentage of hCD19⁺ cells in the spleen at weeks 8 and 12 was 10% and 24%, respectively (P=0.04). The percentage of hCD19⁺ B cells in PB was 23% at week 12. At week 8, hCD3⁺ T cells were barely detectable, while hCD7⁺ was detected in the BM and spleen. The percentage of hCD3⁺ T cells was 2‒3% at week 12 in the BM, spleen, and PB of humanized NSG mice.

Conclusion

We adopted a simplified protocol for establishing humanized NSG mice. We observed a higher engraftment rate of human CD45⁺ cells than earlier studies without any significant toxicity. And human CD45⁺ cell engraftment at week 8 was comparable to that of week 12.

A novel Flt3-deficient HIS mouse model with selective enhancement of human DC development

Humanized mice harboring human immune systems (HIS) represent a platform to study immune responses against pathogens and to screen vaccine candidates and novel immunotherapeutics. Innate and adaptive immune responses are suboptimal in HIS mice, possibly due to poor reconstitution of human antigen-presenting cells, including dendritic cells (DCs). DC homeostasis is regulated by cytokine availability, and Flt3-ligand (Flt3L) is one factor that conditions this process. Mouse myelopoiesis is essentially normal in most current HIS models. As such, developing mouse myeloid cells may limit human DC reconstitution by reducing available Flt3L and by cellular competition for specific "niches." To address these issues, we created a novel HIS model that compromises host myeloid cell development via deficiency in the receptor tyrosine kinase Flk2/Flt3. In Balb/c Rag2(-/-) Il2rg(-/-) Flt3(-/-) (BRGF) recipients, human conventional DCs and plasmacytoid DCs develop from hCD34(+) precursors and can be specifically boosted with exogenous Flt3L. Human DCs that develop in this context normally respond to TLR stimulation, and improved human DC homeostasis is associated with increased numbers of human NK and T cells. This new HIS-DC model should provide a means to dissect human DC differentiation and represents a novel platform to screen immune adjuvants and DC targeting therapies.

Diverging biological roles among human monocyte subsets in the context of tuberculosis infection

Circulating monocytes (Mo) play an essential role in the host immune response to chronic infections. We previously demonstrated that CD16(pos) Mo were expanded in TB (tuberculosis) patients, correlated with disease severity and were refractory to dendritic cell differentiation. In the present study, we investigated whether human Mo subsets (CD16(neg) and CD16(pos)) differed in their ability to influence the early inflammatory response against Mycobacterium tuberculosis. We first evaluated the capacity of the Mo subsets to migrate and engage a microbicidal response in vitro. Accordingly, CD16(neg) Mo were more prone to migrate in response to different mycobacteria-derived gradients, were more resistant to M. tuberculosis intracellular growth and produced higher reactive oxygen species than their CD16(pos) counterpart. To assess further the functional dichotomy among the human Mo subsets, we carried out an in vivo analysis by adapting a hybrid mouse model (SCID/Beige, where SCID is severe combined immunodeficient) to transfer each Mo subset, track their migratory fate during M. tuberculosis infection, and determine their impact on the host immune response. In M. tuberculosis-infected mice, the adoptively transferred CD16(neg) Mo displayed a higher lung migration index, induced a stronger pulmonary infiltration of murine leucocytes expressing pro- and anti-inflammatory cytokines, and significantly decreased the bacterial burden, in comparison with CD16(pos) Mo. Collectively, our results indicate that human Mo subsets display divergent biological roles in the context of M. tuberculosis infection, a scenario in which CD16(neg) Mo may contribute to the anti-mycobacterial immune response, whereas CD16(pos) Mo might promote microbial resilience, shedding light on a key aspect of the physiopathology of TB disease.

Application of Humanized Mice in Immunological Research

During the past decade, the development of humanized mouse models and their general applications in biomedical research greatly accelerated the translation of outcomes obtained from basic research into potential diagnostic and therapeutic strategies in clinic. In this chapter, we firstly present an overview on the history and current progress of diverse humanized mouse models and then focus on those equipped with reconstituted human immune system. The update advancement in the establishment of humanized immune system mice and their applications in the studies of the development of human immune system and the pathogenesis of multiple human immune-related diseases are intensively reviewed here, while the shortcoming and perspective of these potent tools are discussed as well. As a valuable bridge across the gap between bench work and clinical trial, progressive humanized mouse models will undoubtedly continue to play an indispensable role in the wide area of biomedical research.

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.

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.

Development and function of human innate immune cells in a humanized mouse model

Mice repopulated with human hematopoietic cells are a powerful tool for the study of human hematopoiesis and immune function in vivo. However, existing humanized mouse models are unable to support development of human innate immune cells, including myeloid cells and NK cells. Here we describe a mouse strain, called MI(S)TRG, in which human versions of four genes encoding cytokines important for innate immune cell development are knocked in to their respective mouse loci. The human cytokines support the development and function of monocytes/macrophages and natural killer cells derived from human fetal liver or adult CD34⁺ progenitor cells injected into the mice. Human macrophages infiltrated a human tumor xenograft in MI(S)TRG mice in a manner resembling that observed in tumors obtained from human patients. This humanized mouse model may be used to model the human immune system in scenarios of health and pathology, and may enable evaluation of therapeutic candidates in an in vivo setting relevant to human physiology.