Cryptopatches are essential for the development of human GALT

Humanized Mouse Systems to Study Viral Infection: A New Era in Immunology Research

For decades, scientists have relied on traditional animal models to study viral infection and the immune response. However, these models have limitations, and the search for more accurate and reliable ways to study the human-pathogen interphase has led to the development of humanized mouse systems. These revolutionary models have transformed how we understand viral infection and the human immune system's interactions with viruses to control or exacerbate disease. They are also paving the way for new treatments and therapies. In this article, we explore the history and development of humanized mouse systems and their advantages, limitations, and applications in viral immunology research. We describe the different types of humanized mouse models, including their generation and utility for studying human pathogens, with an emphasis on human-specific viruses. In addition, we discuss areas for further refinement and future applications.

A germ-free humanized mouse model shows the contribution of resident microbiota to human-specific pathogen infection

Germ-free (GF) mice, which are depleted of their resident microbiota, are the gold standard for exploring the role of the microbiome in health and disease; however, they are of limited value in the study of human-specific pathogens because they do not support their replication. Here, we develop GF mice systemically reconstituted with human immune cells and use them to evaluate the role of the resident microbiome in the acquisition, replication and pathogenesis of two human-specific pathogens, Epstein-Barr virus (EBV) and human immunodeficiency virus (HIV). Comparison with conventional (CV) humanized mice showed that resident microbiota enhance the establishment of EBV infection and EBV-induced tumorigenesis and increase mucosal HIV acquisition and replication. HIV RNA levels were higher in plasma and tissues of CV humanized mice compared with GF humanized mice. The frequency of CCR5+ CD4+ T cells throughout the intestine was also higher in CV humanized mice, indicating that resident microbiota govern levels of HIV target cells. Thus, resident microbiota promote the acquisition and pathogenesis of two clinically relevant human-specific pathogens.

Transient CD4+ T cell depletion during suppressive ART reduces the HIV reservoir in humanized mice

Lifelong treatment is required for people living with HIV as current antiretroviral therapy (ART) does not eradicate HIV infection. Latently infected cells are essentially indistinguishable from uninfected cells and cannot be depleted by currently available approaches. This study evaluated antibody mediated transient CD4+ T cell depletion as a strategy to reduce the latent HIV reservoir. Anti-CD4 antibodies effectively depleted CD4+ T cells in the peripheral blood and tissues of humanized mice. We then demonstrate that antibody-mediated CD4+ T cell depletion of HIV infected ART-suppressed animals results in substantial reductions in cell-associated viral RNA and DNA levels in peripheral blood cells over the course of anti-CD4 antibody treatment. Recovery of CD4+ T cells was observed in all tissues analyzed except for the lung 26 days after cessation of antibody treatment. After CD4+ T cell recovery, significantly lower levels of cell-associated viral RNA and DNA were detected in the tissues of anti-CD4 antibody-treated animals. Further, an 8.5-fold reduction in the levels of intact HIV proviral DNA and a 3.1-fold reduction in the number of latently infected cells were observed in anti-CD4-antibody-treated animals compared with controls. However, there was no delay in viral rebound when ART was discontinued in anti-CD4 antibody-treated animals following CD4+ T cell recovery compared with controls. Our results suggest that transient CD4+ T cell depletion, a long-standing clinical intervention that might have an acceptable safety profile, during suppressive ART can reduce the size of the HIV reservoir in humanized mice.

Current Advances in Humanized Mouse Models for Studying NK Cells and HIV Infection

Human immunodeficiency virus (HIV) has infected millions of people worldwide and continues to be a major global health problem. Scientists required a small animal model to study HIV pathogenesis and immune responses. To this end, humanized mice were created by transplanting human cells and/or tissues into immunodeficient mice to reconstitute a human immune system. Thus, humanized mice have become a critical animal model for HIV researchers, but with some limitations. Current conventional humanized mice are prone to death by graft versus host disease induced by the mouse signal regulatory protein α and CD47 signaling pathway. In addition, commonly used humanized mice generate low levels of human cytokines required for robust myeloid and natural killer cell development and function. Here, we describe recent advances in humanization procedures and transgenic and knock-in immunodeficient mice to address these limitations.

In vivo development of immune tissue in human intestinal organoids transplanted into humanized mice

Human intestinal organoids (HIOs) derived from pluripotent stem cells provide a valuable model for investigating human intestinal organogenesis and physiology, but they lack the immune components required to fully recapitulate the complexity of human intestinal biology and diseases. To address this issue and to begin to decipher human intestinal-immune crosstalk during development, we generated HIOs containing immune cells by transplanting HIOs under the kidney capsule of mice with a humanized immune system. We found that human immune cells temporally migrate to the mucosa and form cellular aggregates that resemble human intestinal lymphoid follicles. Moreover, after microbial exposure, epithelial microfold cells are increased in number, leading to immune cell activation determined by the secretion of IgA antibodies in the HIO lumen. This in vivo HIO system with human immune cells provides a framework for future studies on infection- or allergen-driven intestinal diseases.

Anatomical and physiological aspects of the HIV infection pathogenesis in animal models

Understanding the entire pathogenesis of HIV infection, from penetration at the gates of infection to the induction of severe immunodeficiency, is an essential tool for the development of new treatment methods. Less than 40 years of research into the mechanisms of HIV infection that lead to the development of acquired immunodeficiency syndrome have accumulated a huge amount of information, but HIV's own unique variability identifies new whitespaces. Despite the constant improvement of the protocols of antiretroviral therapy and the success of its use, it has not yet been possible to stop the spread of HIV infection. The development of new protocols and the testing of new groups of antiretroviral drugs is possible, first of all, due to the improvement of animal models of the HIV infection pathogenesis. Their relevance, undoubtedly increases, but still depends on specific research tasks, since none of the in vivo models can comprehensively simulate the mechanism of the infection pathology in humans which leads to multi-organ damage. The aim of the review was to provide up-to-date information on known animal models of HIV infection, focusing on the method of their infection and anatomical, physiological and pathological features.

MHC II - EGFP knock-in mouse model is a suitable tool for systems and quantitative immunology

Immunology is a rapidly evolving field of research with sophisticated models and methods. However, detailed data on total immune cell counts and population distributions remain surprisingly scarce. Nevertheless, recently established quantitative approaches could help us understand the overall complexity of the immune system. Here, we studied a major histocompatibility complexclass II - enhanced green fluorescent protein knock-in mouse model to precisely identify and manipulate lymphoid structures. By combining flow cytometry with light sheet microscopy, we quantified MHC II⁺ populations of the small intestine and associated individual mesenteric lymph nodes, with 36.7 × 10⁶ cells in lamina propria, 3.0 × 10⁵ cells in scattered lymphoid tissue and 1.1 × 10⁶ cells in Peyer's patches. In addition to these whole-organ cell counts, we assessed approximately 1 × 10⁶ total villi in the small intestine and 450 scattered lymphoid tissue follicles. By direct noninvasive microscopic observation of a naturally fully translucent mouse organ, the cornea, we quantified 12 ± 4 and 35 ± 7 cells/mm² Langerhans- and macrophage-like populations, respectively. Ultimately, our findings show that flow cytometry with quantitative imaging data analysis enables us to avoid methodological discrepancies while gaining new insights into the relevance of organ-specific quantitative approaches for immunology.

Baseline and time-updated factors in preclinical development of anionic dendrimers as successful anti-HIV-1 vaginal microbicides

Although a wide variety of topical microbicides provide promising in vitro and in vivo efficacy, most of them failed to prevent sexual transmission of human immunodeficiency virus type 1 (HIV-1) in human clinical trials. In vitro, ex vivo, and in vivo models must be optimized, considering the knowledge acquired from unsuccessful and successful clinical trials to improve the current gaps and the preclinical development protocols. To date, dendrimers are the only nanotool that has advanced to human clinical trials as topical microbicides to prevent HIV-1 transmission. This fact demonstrates the importance and the potential of these molecules as microbicides. Polyanionic dendrimers are highly branched nanocompounds with potent activity against HIV-1 that disturb HIV-1 entry. Herein, the most significant advancements in topical microbicide development, trying to mimic the real-life conditions as closely as possible, are discussed. This review also provides the preclinical assays that anionic dendrimers have passed as microbicides because they can improve current antiviral treatments' efficacy. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Short histological kaleidoscope - recent findings in histology. Part II

This article focuses on the latest histological knowledge in the field regarding the peripheral lymphoid system [mucosa-associated lymphoid tissue (MALT), bronchus-associated lymphoid tissue (BALT), gut-associated lymphoid tissue (GALT)], the thymus stroma, some of the various corpuscles of the human body (Hassall's corpuscles in thymus, arenaceous corpuscles in pineal gland, corpora amylacea in prostate and other locations) and Fañanas glial cells in the cerebellum.

The Pivotal Role of Microbiota in Modulating the Neuronal-Glial-Epithelial Unit

The enteric nervous system (ENS) consists of enteric neurons and enteric glial cells (EGCs) and controls the function of the epithelial barrier. Thus, a novel concept of neuronal-glial-epithelial unit in the gut was put forward by analogy with neuronal-glial-endothelial unit in the brain. The environment in the gastrointestinal (GI) tract is complex as it harbours millions of bacteria, which extensively attach with intestinal epithelium. The cross-talk between the neuronal-glial-endothelial unit and microbiota plays a pivotal role in modulating the epithelial barrier's permeability, intestinal development and immune response. And evidence shows dysbiosis is the potent risk factor in the pathologic process of Parkinson's disease (PD) and inflammatory bowel disease (IBD). In this review, we summarize the compelling results in favor of microbiota serving as the key modulator in the neuronal-glial-epithelial unit development and function, with profound effects on intestinal homeostasis.

Antinuclear antibodies produced in HLA-DR transgenic humanized mice developed chronic graft-versus-host disease

Background

Chronic graft versus host disease (GVHD) has been reported in humanized mice after the implantation of human hematopoietic stem cells (hu-HSC). As such, humanized mice have been applied to a mouse model of chronic GVHD; however, B-cell activation and autoantibody production did not occur, and the clinical features of chronic GVHD were not sufficiently reproduced. The purpose of this study was to establish an improved humanized mouse model with chronic GVHD using HLA-DR transgenic NOD/Shi-scid, IL-2RγKO (NOG) mice.

Methods

CD34-positive cells were isolated from blood extracted from HLA-DRB1∗0405-positive umbilical cords using magnetic cell isolation. Then these were transplanted into NOG-Iab KO, HLA-DR 0405 Tg mice aged 8–16 weeks. GVHD symptoms were observed 26 weeks after transplantation. Histological findings of the skin, lung, liver, and spleen were compared with those of non-humanized mice. Antinuclear antibodies (ANA) were measured by indirect immunofluorescence using sera isolated 26 weeks after transplantation.

Results

Although GVHD symptoms were not observed in humanized (hu-HSC) NOG-Iab KO, HLA-DR 0405 Tg mice during the observation period, histological findings of human T-cell infiltration were observed in the skin, liver, and lung, suggesting that GVDH was present; human tingible body macrophages or clusters of BCL-6-positive human B-cells were observed in the spleen. Furthermore, human IgG ANA with peripheral or homogeneous staining patterns were also detected in the sera.

Conclusion

Hu-HSC NOG-Iab KO, HLA-DR 0405 Tg mice differed from conventional models in terms of B-cell activation and ANA production. This study is the first to report on B-cell activation and autoantibody production in humanized mice with chronic GVHD, suggesting that hu-HSC NOG-Iab KO, HLA-DR 0405 Tg mice could be applied to a new humanized mouse model of chronic GVHD.

Spatial and temporal key steps in early-life intestinal immune system development and education

Education of our intestinal immune system early in life strongly influences adult health. This education strongly relies on series of events that must occur in well-defined time windows. From initial colonization by maternal-derived microbiota during delivery to dietary changes from mother's milk to solid foods at weaning, these early-life events have indeed long-standing consequences on our immunity, facilitating tolerance to environmental exposures or, on the contrary, increasing the risk of developing noncommunicable diseases such as allergies, asthma, obesity, and inflammatory bowel diseases. In this review, we provide an outline of the recent advances in our understanding of these events and how they are mechanistically related to intestinal immunity development and education. First, we review the susceptibility of neonates to infections and inflammatory diseases, related to their immune system and microbiota changes. Then, we highlight the maternal factors involved in protection and education of the mucosal immune system of the offspring, the role of the microbiota, and the nature of neonatal immune system until weaning. We also present how the development of some immune responses is intertwined in temporal and spatial windows of opportunity. Finally, we discuss pending questions regarding the neonate particular immune status and the activation of the intestinal immune system at weaning.

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.

Secretory IgA in Intestinal Mucosal Secretions as an Adaptive Barrier against Microbial Cells

Secretory IgA (SIgA) is the dominant antibody class in mucosal secretions. The majority of plasma cells producing IgA are located within mucosal membranes lining the intestines. SIgA protects against the adhesion of pathogens and their penetration into the intestinal barrier. Moreover, SIgA regulates gut microbiota composition and provides intestinal homeostasis. In this review, we present mechanisms of SIgA generation: T cell-dependent and -independent; in different non-organized and organized lymphoid structures in intestinal lamina propria (i.e., Peyer’s patches and isolated lymphoid follicles). We also summarize recent advances in understanding of SIgA functions in intestinal mucosal secretions with focus on its role in regulating gut microbiota composition and generation of tolerogenic responses toward its members.

Moving beyond the mousetrap: current and emerging humanized mouse and rat models for investigating prevention and cure strategies against HIV infection and associated pathologies

The development of safe and effective combination antiretroviral therapies for human immunodeficiency virus (HIV) infection over the past several decades has significantly reduced HIV-associated morbidity and mortality. Additionally, antiretroviral drugs have provided an effective means of protection against HIV transmission. Despite these advances, significant limitations exist; namely, the inability to eliminate HIV reservoirs, the inability to reverse lymphoid tissues damage, and the lack of an effective vaccine for preventing HIV transmission. Evaluation of the safety and efficacy of therapeutics and vaccines for eliminating HIV reservoirs and preventing HIV transmission requires robust in vivo models. Since HIV is a human-specific pathogen, that targets hematopoietic lineage cells and lymphoid tissues, in vivo animal models for HIV-host interactions require incorporation of human hematopoietic lineage cells and lymphoid tissues. In this review, we will discuss the construction of mouse models with human lymphoid tissues and/or hematopoietic lineage cells, termed, human immune system (HIS)-humanized mice. These HIS-humanized mouse models can support the development of functional human innate and adaptive immune cells, along with primary (thymus) and secondary (spleen) lymphoid tissues. We will discuss applications of HIS-humanized mouse models in evaluating the safety and efficacy of therapeutics against HIV reservoirs and associated immunopathology, and delineate the human immune response elicited by candidate HIV vaccines. In addition to focusing on how these HIS-humanized mouse models have already furthered our understanding of HIV and contributed to HIV therapeutics development, we discuss how emerging HIS-humanized rat models could address the limitations of HIS-mouse models.

Heat Stress Causes Immune Abnormalities via Massive Damage to Effect Proliferation and Differentiation of Lymphocytes in Broiler Chickens

Broiler chickens are highly sensitive to high ambient temperatures due to their feathers, lack of skin sweat glands, and high productivity. Heat stress (HS) is a major concern for the poultry industry because it negatively affects growth as well as immune functions, which increase the potential risk of infectious disease outbreaks. Therefore, it is vital to elucidate HS's effect on the avian immune system, especially considering the global rise in average surface temperature. Our study identified a series of immunological disorders in heat-stressed broiler chickens. We exposed 22-day-old broiler chickens to a continuous HS condition (34.5 ± 0.5°C) for 14 days and immunized them with a prototype bovine serum albumin (BSA) antigen. The plasma and lymphoid tissues (thymus, bursa of Fabricius, and spleen) were harvested at the end of the experiments to investigate the induction of BSA-specific immune responses. Our results revealed that plasma titers of immunoglobulin (Ig)Y, IgM, and IgA antibodies specific for BSA were lower than those of thermoneutral chickens immunized with BSA. Furthermore, the spleens of the heat-stressed broiler chickens displayed severe depression of Bu1⁺ B cells and CD3⁺ T cells, including CD4⁺ T cells and CD8⁺ T cells, and lacked a fully developed germinal center (GC), which is crucial for B cell proliferation. These immunological abnormalities might be associated with severe depression of CD4⁻CD8⁻ or CD4⁺CD8⁺ cells, which are precursors of either helper or killer T cells in the thymus and Bu1⁺ B cells in the bursa of Fabricius. Importantly, HS severely damaged the morphology of the thymic cortex and bursal follicles, where functional maturation of T and B cells occur. These results indicate that HS causes multiple immune abnormalities in broiler chickens by impairing the developmental process and functional maturation of T and B cells in both primary and secondary lymphoid tissues.

Precision mouse models with expanded tropism for human pathogens

A major limitation of current humanized mouse models is that they primarily enable the analysis of human-specific pathogens that infect hematopoietic cells. However, most human pathogens target other cell types, including epithelial, endothelial and mesenchymal cells. Here, we show that implantation of human lung tissue, which contains up to 40 cell types, including nonhematopoietic cells, into immunodeficient mice (lung-only mice) resulted in the development of a highly vascularized lung implant. We demonstrate that emerging and clinically relevant human pathogens such as Middle East respiratory syndrome coronavirus, Zika virus, respiratory syncytial virus and cytomegalovirus replicate in vivo in these lung implants. When incorporated into bone marrow/liver/thymus humanized mice, lung implants are repopulated with autologous human hematopoietic cells. We show robust antigen-specific humoral and T-cell responses following cytomegalovirus infection that control virus replication. Lung-only mice and bone marrow/liver/thymus-lung humanized mice substantially increase the number of human pathogens that can be studied in vivo, facilitating the in vivo testing of therapeutics.

Implantation of lung tissue into humanized mice enables in vivo study of the human immune response to pathogens.

Oxysterols in intestinal immunity and inflammation

Cholesterol is an essential molecule for life. It is a component of the cell membrane, and it is a precursor molecule for bile acids, vitamin D and steroid hormones. Cholesterol is actively metabolized, but the impact of endogenous cholesterol metabolites on immune function, especially in the intestine, is poorly understood. In this review, I focus on oxysterols, hydroxylated forms of cholesterol, and their specialized functions in intestinal immunity. Oxysterols act through various intracellular and extracellular receptors and serve as key metabolic signals, coordinating immune activity and inflammation. Our recent work has identified an unexpected link between cholesterol metabolism, innate lymphoid cell function and intestinal homeostasis. We discovered that oxysterol sensing through the G protein-coupled receptor 183 (GPR183) directs the migration of innate lymphoid cells, which is essential for the formation of lymphoid tissue in the colon. Moreover, we found that the interaction of GPR183 with oxysterols regulates intestinal inflammation. I will discuss the therapeutic potential of oxysterols and future possibilities of treating inflammatory bowel disease through the modulation of cholesterol metabolism.

Vedolizumab-mediated integrin α4β7 blockade does not control HIV-1SF162 rebound after combination antiretroviral therapy interruption in humanized mice

OBJECTIVE

The combined combination antiretroviral therapy (cART) and anti-α4β7 RM-Act-1 antibody therapy allows macaques to durably control simian immunodeficiency virus (SIV) rebound after withdrawal of the interventions. Here, we aimed to investigate whether vedolizumab (VDZ), a clinical-grade humanized anti-α4β7 antibody, would have similar effects in controlling live HIV-1 infection in humanized mice.

DESIGN AND METHODS

The integrin α4β7 blockade by VDZ was evaluated on human primary memory CD4+ T (MEMT) cells and retinoic acid-induced gut-homing α4β7+MEMT cells (α4β7+MEMT) in vitro. The antiretroviral activity of VDZ was determined using pseudotyped R5-tropic HIV-1SF162, which displays binding activity to α4β7. The preventive and immunotherapeutic efficacies of VDZ were further investigated in humanized mice using the live HIV-1SF162 strain compared with RM-Act-1.

RESULTS

VDZ effectively and dose-dependently blocked the binding of mucosal vascular addressin cell adhesion molecule-1 (MAdCAM-1), the native ligand of α4β7, to α4β7+MEMT cells. HIV-1SF162 not only displayed binding capacity to α4β7-expressing cells, but also showed an increased infectivity in retinoic acid-induced α4β7+MEMT cells pretreated with VDZ. Moreover, VDZ failed to prevent live HIV-1SF162 infection and did not reduce the peak viral load when administrated prior to viral challenge in humanized mice. Lastly, in immunotherapeutic settings, the withdrawal of combined cART with either VDZ or RM-Act-1 resulted in an uncontrolled HIV-1SF162 rebound in humanized mice, whereas the α4β7 molecules remained significantly blocked on circulating CD4+ T cells.

CONCLUSION

VDZ neither prevents nor controls HIV-1SF162 infection both in vitro and in humanized mice. Our findings have significant implications to the clinical application of VDZ in HIV-1 preventive and immunotherapeutic interventions.

Humanized Mice Engrafted With Human HSC Only or HSC and Thymus Support Comparable HIV-1 Replication, Immunopathology, and Responses to ART and Immune Therapy

Immunodeficient mice reconstituted with human immune tissues and cells (humanized mice) are relevant and robust models for the study of HIV-1 infection, immunopathogenesis, and therapy. In this study, we performed a comprehensive comparison of human immune reconstitution and HIV-1 infection, immunopathogenesis and therapy between immunodeficient NOD/Rag2-/-/γc-/- (NRG) mice transplanted with human HSCs (NRG-hu HSC) and mice transplanted with HSCs and thymus fragments (NRG-hu Thy/HSC) from the same donors. We found that similar human lymphoid and myeloid lineages were reconstituted in NRG-hu HSC and NRG-hu Thy/HSC mice, with human T cells more predominantly reconstituted in NRG-hu Thy/HSC mice, while NRG-hu HSC mice supported more human B cells and myeloid cells reconstitution. HIV-1 replicated similarly and induced similar T cell depletion, immune activation, and dysfunction in NRG-hu HSC and NRG-hu Thy/HSC mice. Moreover, combined antiretroviral therapy (cART) inhibited HIV-1 replication efficiently with similar persistent HIV-1 reservoirs in both models. Finally, we found that blocking type-I interferon signaling under cART treatment transiently activated HIV-1 reservoirs, enhanced T cell recovery and reduced HIV-1 reservoirs in both HIV-1 infected NRG-hu HSC and NRG-hu Thy/HSC mice. In summary, we report that NRG-hu Thy/HSC and NRG-hu HSC mice support similar HIV-1 infection and similar HIV-1 immunopathology; and HIV-1 replication responds similarly to cART and IFNAR blockade therapies. The NRG-hu HSC mouse model reconstituted with human HSC only is sufficient for the study of HIV-1 infection, pathogenesis, and therapy.

A Hitchhiker's guide to humanized mice: new pathways to studying viral infections

Humanized mice are increasingly appreciated as an incredibly powerful platform for infectious disease research. The often very narrow species tropism of many viral infections, coupled with the sometimes misleading results from preclinical studies in animal models further emphasize the need for more predictive model systems based on human cells rather than surrogates. Humanized mice represent such a model and have been greatly enhanced with regards to their immune system reconstitution as well as immune functionality in the past years, resulting in their recommendation as a preclinical model by the US Food and Drug Administration. This review aims to give a detailed summary of the generation of human peripheral blood lymphocyte-, CD34⁺ haematopoietic stem cell- and bone marrow/liver/thymus-reconstituted mice and available improved models (e.g. myeloid- or T-cell-only mice, MISTRG, NSG-SGM3). Additionally, we summarize human-tropic viral infections, for which humanized mice offer a novel approach for the study of disease pathogenesis as well as future perspectives for their use in biomedical, drug and vaccine research.

Biological characteristics of intestinal IgE and gut diseases

Immunoglobulin E (IgE), a crucial protective substance for the intestinal tract, plays an important role in gut immunity. IgE is secreted by plasma cells in the submucosal lamina propria upon antigenic invasion and, together with certain cytokines and immune cells, is involved in the regulation of gastrointestinal immunity in normal or abnormal conditions via the high affinity IgE receptor (FcεR I) and low affinity IgE receptor (CD23⁺). In this paper, we review the structure, synthetic transport, secretory regulation, receptor classification, and function of intestinal IgE as well as the related gut diseases.

The Development of Steady-State Activation Hubs between Adult LTi ILC3s and Primed Macrophages in Small Intestine

Group 3 innate lymphoid cells (ILC3s) are important for intestinal health, particularly in controlling inflammation in response to epithelial dysregulation, but their role during homeostasis remains less well understood. We generated IL-22 reporter mice to assess production of this key cytokine by ILC3s in the small intestine during development and under basal conditions. Although IL-22 is produced by a variety of lymphocyte populations, constitutively high IL-22 expression was limited to lymphoid-tissue inducer (LTi) cells residing in lymph node-like structures in the gut called solitary intestinal lymphoid tissues (SILT). Constitutive IL-22 expression was dependent on the microbiota and MyD88 signaling, appeared upon weaning, and was present across the spectrum of SILT, including in cryptopatches. Activated SILT LTi cells colocalized with a rare subpopulation of activated macrophages constitutively positive for IL-12/23 p40 and capable of activating neonatal LTi cells in response to TLR stimulus. Thus, weaning leads to the organization of innate immune activation hubs at SILT that mature and are continuously sustained by signals from the microbiota. This functional and anatomic organization constitutes a significant portion of the steady-state IL-23/IL-22 axis.

Humanized mouse models for Epstein Barr virus infection

It is essential for the human immune system to control Epstein Barr virus (EBV), because this common human γ-herpesvirus efficiently spreads through the human population with more than 90% being persistently infected after 20 years of age even in developed countries. Moreover, it threatens each host with its potent growth transforming properties, readily immortalizing human B cells into persistently growing lymphoma cell lines. Since this virus only infects humans, mice with reconstituted human immune system components provide an informative in vivo model to study EBV infection, the associated tumor formation and immune control thereof. They recapitulate the different infection programs in human B cells, allow modeling EBV driven lymphoma formation and interrogation of the key cytotoxic lymphocyte responses that are also required to control this pathogen in humans. The respective lessons that were taught by these investigations will be discussed in this review as well as the challenges in the future to address the whole portfolio of EBV associated diseases and how they could be prevented by EBV specific immunotherapies.

Gut microbiota, metabolites and host immunity

The microbiota - the collection of microorganisms that live within and on all mammals - provides crucial signals for the development and function of the immune system. Increased availability of technologies that profile microbial communities is facilitating the entry of many immunologists into the evolving field of host-microbiota studies. The microbial communities, their metabolites and components are not only necessary for immune homeostasis, they also influence the susceptibility of the host to many immune-mediated diseases and disorders. In this Review, we discuss technological and computational approaches for investigating the microbiome, as well as recent advances in our understanding of host immunity and microbial mutualism with a focus on specific microbial metabolites, bacterial components and the immune system.

Intestinal dysbiosis and innate immune responses in axial spondyloarthritis

PURPOSE OF REVIEW

Inflammatory innate and adaptive immune cell responses to commensal bacteria underlie the pathogenesis of human chronic inflammatory diseases. Intestinal dysbiosis has been described in patients with spondyloarthritis (SpA) and seems to be correlated with histologic and immunologic alterations. Purpose of this review is to discuss the relationship occurring between intestinal dysbiosis and innate immune responses in patients with axial SpA.

RECENT FINDINGS

Intestinal dysbiosis and differential activation of intestinal immune responses in patients with SpA have been demonstrated. Furthermore, innate cells that appear to be involved in the pathogenesis of SpA may control intestinal homeostasis through induction of apoptotic cell death and deletion of activated commensal bacteria-specific T cells.

SUMMARY

Although the evidence shows that dysbiosis occurs in SpA, it is not clear the role of dysbiosis in regulating innate immune responses in SpA. Relationships between cause and effect remain to be answered.

VIDEO ABSTRACT

http://links.lww.com/COR/A34.

In Vivo Models of Human Immunodeficiency Virus Persistence and Cure Strategies

Current HIV therapy is not curative regardless of how soon after infection it is initiated or how long it is administered, and therapy interruption almost invariably results in robust viral rebound. Human immunodeficiency virus persistence is therefore the major obstacle to a cure for AIDS. The testing and implementation of novel yet unproven approaches to HIV eradication that could compromise the health status of HIV-infected individuals might not be ethically warranted. Therefore, adequate in vitro and in vivo evidence of efficacy is needed to facilitate the clinical implementation of promising strategies for an HIV cure. Animal models of HIV infection have a strong and well-documented history of bridging the gap between laboratory discoveries and eventual clinical implementation. More recently, animal models have been developed and implemented for the in vivo evaluation of novel HIV cure strategies. In this article, we review the recent progress in this rapidly moving area of research, focusing on the two most promising model systems: humanized mice and nonhuman primates.

Predicting HIV Pre-exposure Prophylaxis Efficacy for Women using a Preclinical Pharmacokinetic-Pharmacodynamic In Vivo Model

The efficacy of HIV pre-exposure prophylaxis (PrEP) relies on adherence and may also depend on the route of HIV acquisition. Clinical studies of systemic tenofovir disoproxil fumarate (TDF) PrEP revealed reduced efficacy in women compared to men with similar degrees of adherence. To select the most effective PrEP strategies, preclinical studies are critically needed to establish correlations between drug concentrations (pharmacokinetics [PK]) and protective efficacy (pharmacodynamics [PD]). We utilized an in vivo preclinical model to perform a PK-PD analysis of systemic TDF PrEP for vaginal HIV acquisition. TDF PrEP prevented vaginal HIV acquisition in a dose-dependent manner. PK-PD modeling of tenofovir (TFV) in plasma, female reproductive tract tissue, cervicovaginal lavage fluid and its intracellular metabolite (TFV diphosphate) revealed that TDF PrEP efficacy was best described by plasma TFV levels. When administered at 50 mg/kg, TDF achieved plasma TFV concentrations (370 ng/ml) that closely mimicked those observed in humans and demonstrated the same risk reduction (70%) previously attained in women with high adherence. This PK-PD model mimics the human condition and can be applied to other PrEP approaches and routes of HIV acquisition, accelerating clinical implementation of the most efficacious PrEP strategies.

Humanized hemato-lymphoid system mice

Over the last decades, incrementally improved xenograft mouse models, supporting the engraftment and development of a human hemato-lymphoid system, have been developed and now represent an important research tool in the field. The most significant contributions made by means of humanized mice are the identification of normal and leukemic hematopoietic stem cells, the characterization of the human hematopoietic hierarchy, and their use as preclinical therapy models for malignant hematopoietic disorders. Successful xenotransplantation depends on three major factors: tolerance by the mouse host, correct spatial location, and appropriately cross-reactive support and interaction factors such as cytokines and major histocompatibility complex molecules. Each of these can be modified. Experimental approaches include the genetic modification of mice to faithfully express human support factors as non-cross-reactive cytokines, to create free niche space, the co-transplantation of human mesenchymal stem cells, the implantation of humanized ossicles or other stroma, and the implantation of human thymic tissue. Besides the source of hematopoietic cells, the conditioning regimen and the route of transplantation also significantly affect human hematopoietic development in vivo. We review here the achievements, most recent developments, and the remaining challenges in the generation of pre-clinically-predictive systems for human hematology and immunology, closely resembling the human situation in a xenogeneic mouse environment.

Humanized mice for HIV and AIDS research

HIV has a very limited species tropism that prevents the use of most conventional small animal models for AIDS research. The in vivo analysis of HIV/AIDS has benefited extensively from novel chimeric animal models that accurately recapitulate key aspects of the human condition. Specifically, immunodeficient mice that are systemically repopulated with human hematolymphoid cells offer a viable alternative for the study of a multitude of highly relevant aspects of HIV replication, pathogenesis, therapy, transmission, prevention, and eradication. This article summarizes some of the multiple contributions that humanized mouse models of HIV infection have made to the field of AIDS research. These models have proven to be highly informative and hold great potential for accelerating multiple aspects of HIV research in the future.

CD19xCD3 DART protein mediates human B-cell depletion in vivo in humanized BLT mice

Novel therapeutic strategies are needed for the treatment of hematologic malignancies; and bispecific antibody-derived molecules, such as dual-affinity re-targeting (DART) proteins, are being developed to redirect T cells to kill target cells expressing tumor or viral antigens. Here we present our findings of specific and systemic human B-cell depletion by a CD19xCD3 DART protein in humanized BLT mice. Administration of the CD19xCD3 DART protein resulted in a dramatic sustained depletion of human CD19⁺ B cells from the peripheral blood, as well as a dramatic systemic reduction of human CD19⁺ B-cell levels in all tissues (bone marrow, spleen, liver, lung) analyzed. When human CD8⁺ T cells were depleted from the mice, no significant B-cell depletion was observed in response to CD19xCD3 DART protein treatment, confirming that human CD8⁺ T cells are the primary effector cells in this in vivo model. These studies validate the use of BLT humanized mice for the in vivo evaluation and preclinical development of bispecific molecules that redirect human T cells to selectively deplete target cells.

Using animal models to overcome temporal, spatial and combinatorial challenges in HIV persistence research

Research challenges associated with understanding HIV persistence during antiretroviral therapy can be categorized as temporal, spatial and combinatorial. Temporal research challenges relate to the timing of events during establishment and maintenance of HIV persistence. Spatial research challenges regard the anatomical locations and cell subsets that harbor persistent HIV. Combinatorial research challenges pertain to the order of administration, timing of administration and specific combinations of compounds to be administered during HIV eradication therapy. Overcoming these challenges will improve our understanding of HIV persistence and move the field closer to achieving eradication of persistent HIV. Given that humanized mice and non-human primate HIV models permit rigorous control of experimental conditions, these models have been used extensively as in vivo research platforms for directly addressing these research challenges. The aim of this manuscript is to provide a comprehensive review of these recent translational advances made in animal models of HIV persistence.

In vivo platforms for analysis of HIV persistence and eradication

HIV persistence in patients undergoing antiretroviral therapy is a major impediment to the cure of HIV/AIDS. The molecular and cellular mechanisms underlying HIV persistence in vivo have not been fully elucidated. This lack of basic knowledge has hindered progress in this area. The in vivo analysis of HIV persistence and the implementation of curative strategies would benefit from animal models that accurately recapitulate key aspects of the human condition. This Review summarizes the contribution that humanized mouse models of HIV infection have made to the field of HIV cure research. Even though these models have been shown to be highly informative in many specific areas, their great potential to serve as excellent platforms for discovery in HIV pathogenesis and treatment has yet to be fully developed.

Humanized Mice as Preclinical Models in Transplantation

Animal models have been instrumental in our understanding of the mechanisms of rejection and the testing of novel treatment options in the context of transplantation. We have now entered an exciting era with research on humanized mice driving advances in translational studies and in our understanding of the function of human cells in response to pathogens and cancer as well as the recognition of human allogeneic tissues in vivo. In this chapter we provide a historical overview of humanized mouse models of transplantation to date, outlining the distinct strains and share our experiences in the study of human transplantation immunology.

Role of Semen on Vaginal HIV-1 Transmission and Maraviroc Protection

We used bone marrow/liver/thymus (BLT) humanized mice to establish the effect of semen on vaginal HIV infection and on the efficacy of topically applied maraviroc. Our results demonstrate that vaginal transmission of cell-free HIV occurs efficiently in the presence of semen and that topically applied maraviroc efficiently prevents HIV transmission in the presence of semen. We also show that semen has no significant effect on the transmission of transmitted/founder viruses or cell-associated viruses.

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.

BLT humanized mice as a small animal model of HIV infection

Humanized mice are valuable models for the research and development of vaccine strategies and therapeutic interventions to control or eradicate HIV. The BLT humanized mouse model is particularly promising because the combination of transplantation of human fetal pluripotent hematopoietic stem cells with surgical engraftment of human fetal thymic tissue results in improved T cell reconstitution, maturation, and selection. To date, the BLT humanized mouse model has been used to study many aspects of HIV infection including prevention, mucosal transmission, HIV-specific innate and adaptive immunity, viral latency, and novel antiretroviral and immune-based therapies for suppression and reservoir eradication. Here we describe recent advances and applications of the BLT humanized mouse model of HIV infection and discuss opportunities to further improve this valuable small animal model.

Regulation of intestinal IgA responses

The intestine harbors enormous numbers of commensal bacteria and is under frequent attack from food-borne pathogens and toxins. A properly regulated immune response is critical for homeostatic maintenance of commensals and for protection against infection and toxins in the intestine. Immunoglobulin A (IgA) isotype antibodies function specifically in mucosal sites such as the intestines to help maintain intestinal health by binding to and regulating commensal microbiota, pathogens and toxins. IgA antibodies are produced by intestinal IgA antibody-secreting plasma cells generated in gut-associated lymphoid tissues from naïve B cells in response to stimulations of the intestinal bacteria and components. Research on generation, migration, and maintenance of IgA-secreting cells is important in our effort to understand the biology of IgA responses and to help better design vaccines against intestinal infections.

Animal models of Epstein Barr virus infection

Epstein Barr virus (EBV) was the first human tumor virus to be described. Despite its discovery now more than fifty years ago, immune control of this virus is still not very well understood and no vaccine is available. This knowledge gap is due in part to the lack of a preclinical small animal model which can faithfully recapitulate EBV infection and immune control, and would allow testing of EBV specific vaccine candidates. With the advent of mice with reconstituted human immune system compartments (HIS mice) during the past decade this is changing. We will discuss which aspects of EBV infection and its immune control can already be modeled in HIS mice, and which shortcomings still need to be overcome in order to recapitulate the immunobiology of oncogenic EBV infection.

HIV enteropathy and aging: gastrointestinal immunity, mucosal epithelial barrier, and microbial translocation

PURPOSE OF REVIEW

Despite decreases in morbidity and mortality as a result of antiretroviral therapy, gastrointestinal dysfunction remains common in HIV infection. Treated patients are at risk for complications of 'premature' aging, such as cardiovascular disease, osteopenia, neurocognitive decline, malignancies, and frailty. This review summarizes recent observations in this field.

RECENT FINDINGS

Mucosal CD4 lymphocytes, especially Th17 cells, are depleted in acute HIV and simian immune deficiency virus (SIV) infections, although other cell types also are affected. Reconstitution during therapy often is incomplete, especially in mucosa. Mucosal barrier function is affected by both HIV infection and aging and includes paracellular transport via tight junctions and uptake through areas of apoptosis; other factors may affect systemic antigen exposure. The resultant microbial translocation is associated with systemic immune activation in HIV and SIV infections. There is evidence of immune activation and microbial translocation in the elderly. The immune phenotypes of immunosenescence in HIV infection and aging appear similar. There are several targets for intervention; blockage of residual mucosal virus replication, preventing antigen uptake, modulating the microbiome, improving T cell recovery, combining therapies aimed at mucosal integrity, augmenting mucosal immunity, and managing traditional risk factors for premature aging in the general population.

SUMMARY

Aging may interact with HIV enteropathy to enhance microbial translocation and immune activation.

EBV Infection of Mice with Reconstituted Human Immune System Components

Epstein-Barr virus (EBV) was discovered 50 years ago as the first candidate human tumor virus. Since then, we have realized that this human γ-herpesvirus establishes persistent infection in the majority of adult humans, but fortunately causes EBV-associated diseases only in few individuals. This is an incredible success story of the human immune system, which controls EBV infection and its transforming capacity for decades. A better understanding of this immune control would not only benefit patients with EBV-associated malignancies, but could also provide clues how to establish such a potent, mostly cell-mediated immune control against other pathogens and tumors. However, the functional relevance of EBV-specific immune responses can only be addressed in vivo, and mice with reconstituted human immune system components (huMice) constitute a small animal model to interrogate the protective value of immune compartments during EBV infection, but also might provide a platform to test EBV-specific vaccines. This chapter will summarize the insights into EBV immunobiology that have already been gained in these models and provide an outlook into promising future avenues to develop this in vivo model of EBV infection and human immune responses further.

Hypogammaglobulinemia in BLT humanized mice--an animal model of primary antibody deficiency

Primary antibody deficiencies present clinically as reduced or absent plasma antibodies without another identified disorder that could explain the low immunoglobulin levels. Bone marrow-liver-thymus (BLT) humanized mice also exhibit primary antibody deficiency or hypogammaglobulinemia. Comprehensive characterization of B cell development and differentiation in BLT mice revealed other key parallels with primary immunodeficiency patients. We found that B cell ontogeny was normal in the bone marrow of BLT mice but observed an absence of switched memory B cells in the periphery. PC-KLH immunizations led to the presence of switched memory B cells in immunized BLT mice although plasma cells producing PC- or KLH- specific IgG were not detected in tissues. Overall, we have identified the following parallels between the humoral immune systems of primary antibody deficiency patients and those in BLT mice that make this in vivo model a robust and translational experimental platform for gaining a greater understanding of this heterogeneous array of humoral immunodeficiency disorders in humans: (i) hypogammaglobulinemia; (ii) normal B cell ontogeny in bone marrow; and (iii) poor antigen-specific IgG response to immunization. Furthermore, the development of strategies to overcome these humoral immune aberrations in BLT mice may in turn provide insights into the pathogenesis of some primary antibody deficiency patients which could lead to novel clinical interventions for improved humoral immune function.

Viral infections in mice with reconstituted human immune system components

Pathogenic viruses are often difficult to study due to their exclusive tropism for humans. The development of mice with human immune system components opens the possibility to study those human pathogens with a tropism for the human hematopoietic lineage in vivo. These include HCMV, EBV, KSHV, HIV, HTLV-1, dengue virus and JC virus. Furthermore, some human pathogens, like HSV-2, adenovirus, HCV, HBV and influenza A virus, with an additional tropism for somatic mouse tissues or for additional transplanted human tissues, mainly liver, have been explored in these models. The cellular tropism of these viruses, their associated diseases and primarily cell-mediated immune responses to these viral infections will be discussed in this review. Already some exciting information has been gained from these novel chimeric in vivo models and future avenues to gain more insights into the pathology, but also potential therapies, will be outlined. Although the respective in vivo models of human immune responses can still be significantly improved, they already provide preclinical systems for in vivo studies of important viral pathogens of humans.

Animal models of Epstein Barr virus infection

Epstein Barr virus (EBV) was the first human tumor virus to be identified. Despite 50years of research on this oncogenic virus, no therapeutic or prophylactic vaccine is available against this pathogen. In part, the development of such a vaccine is hampered by the lack of in vivo models for EBV infection and immune control. However, with the advent of mice with reconstituted human immune system components (HIS mice), certain aspects of EBV associated diseases and immune responses can be modeled in vivo. In this review, we will discuss the insights that can be gained from these experiments, and how immune system components can be manipulated to interrogate their function during EBV infection. Finally, we will compare EBV immunobiology in HIS mice to infection by EBV-related viruses in monkeys, and we will outline the strengths and weaknesses of these two in vivo models of EBV infection. Both of these models show great promise as a platform for preclinical EBV vaccine testing.

The use of BLT humanized mice to investigate the immune reconstitution of the gastrointestinal tract

The gastrointestinal (GI) track represents an important battlefield where pathogens first try to gain entry into a host. It is also a universe where highly diverse and ever changing inhabitants co-exist in an exceptional equilibrium without parallel in any other organ system of the body. The gut as an organ has its own well-developed and fully functional immune organization that is similar and yet different in many important ways to the rest of the immune system. Both a compromised and an overactive immune system in the gut can have dire and severe consequences to human health. It has therefore been of great interest to develop animal models that recapitulate key aspects of the human condition to better understand the interplay of the host immune system with its friends and its foes. However, reconstitution of the GI tract in humanized mice has been difficult and highly variable in different systems. A better molecular understanding of the development of the gut immune system in mice has provided critical cues that have been recently used to develop novel humanized mouse models that fully recapitulate the genesis and key functions of the gut immune system of humans. Of particular interest is the presence of human gut-associated lymphoid tissue (GALT) aggregates in the gut of NOD/SCID BLT humanized mice that demonstrate the faithful development of bona fide human plasma cells capable of migrating to the lamina propria and producing human IgA1 and IgA2.

E. E. Just Award lecture

What started as a game of discovery for a child with a chemistry set has resulted in a lifetime of fulfillment and dedication to science. It is deeply rewarding to continuously let my curiosity ask questions for which there are no known answers. Equally rewarding has been the opportunity to mentor young students and postdoctorate graduates through their formative years in science.