Humanized Mice for Studying Human Immune Responses and Generating Human Monoclonal Antibodies

B cell development and antibody responses in human immune system mice: current status and future perspective

Humanized immune system (HIS) mice have been developed and used as a small surrogate model to study human immune function under normal or disease conditions. Although variations are found between models, most HIS mice show robust human T cell responses. However, there has been unsuccessful in constructing HIS mice that produce high-affinity human antibodies, primarily due to defects in terminal B cell differentiation, antibody affinity maturation, and development of primary follicles and germinal centers. In this review, we elaborate on the current knowledge about and previous attempts to improve human B cell development in HIS mice, and propose a potential strategy for constructing HIS mice with improved humoral immunity by transplantation of human follicular dendritic cells (FDCs) to facilitate the development of secondary follicles.

Developing Humanized Animal Models with Transplantable Human iPSC-Derived Cells

Establishing reliable and reproducible animal models for disease modelling, drug screening and the understanding of disease susceptibility and pathogenesis is critical. However, traditional animal models differ significantly from humans in terms of physiology, immune response, and pathogenesis. As a result, it is difficult to translate laboratory findings into biomedical applications. Although several animal models with human chimeric genes, organs or systems have been developed in the past, their limited engraftment rate and physiological functions are a major obstacle to realize convincing models of humans. The lack of human transplantation resources and insufficient immune tolerance of recipient animals are the main challenges that need to be overcome to generate fully humanized animals. Recent advances in gene editing and pluripotent stem cell-based xenotransplantation technologies offer opportunities to create more accessible human-like models for biomedical research. In this article, we have combined our laboratory expertise to summarize humanized animal models, with a focus on hematopoietic/immune system and liver. We discuss their generation strategies and the potential donor cell sources, with particular attention given to human pluripotent stem cells. In particular, we discuss the advantages, limitations and emerging trends in their clinical and pharmaceutical applications. By providing insights into the current state of humanized animal models and their potential for biomedical applications, this article aims to advance the development of more accurate and reliable animal models for disease modeling and drug screening.

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

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

Advanced Immune Cell Profiling by Multiparameter Flow Cytometry in Humanized Patient-Derived Tumor Mice

"Humanized" mice have been widely used for the characterization of human cancer progression and as a powerful preclinical model. Standardization of multicolor phenotyping could help to identify immune cell patterns involved in checkpoint-related complications. Therefore, we applied established protocols for immune cell profiling to our humanized Patient-Derived Xenograft (hPDX) model. hPDX are characterized by the co-existence of a human immune system and a patient-derived tumor transplant. These mice possess a human-like immune system after CD34+ stem cell transplantation while the reconstitution level of the immune system was not related to the quantity of transplanted CD34+ cells. Contamination ≤ 1.2% by CD3+ cells in the hematopoietic stem cell (HSC) transplant did not trigger abnormal T cell maturation. Different B and T cell differentiation stages were identified, as well as regulatory T cells (Tregs) and exhausted T cells that expressed TIGIT, PD-1, or KLRG1. Overall, the application of standardized protocols for the characterization of immune cells using flow cytometry will contribute to a better understanding of immune-oncologic processes.

Murine models of dengue virus infection for novel drug discovery

INTRODUCTION

Dengue virus (DENV) is the causative agent of the most prevalent human disease transmitted by mosquitoes in tropical and subtropical regions worldwide. At present, no antiviral drug is available and the difficulties to develop highly protective vaccines against the four DENV serotypes maintain the requirement of effective options for dengue chemotherapy.

AREAS COVERED

The availability of animal models that reproduce human disease is a very valuable tool for the preclinical evaluation of potential antivirals. Here, the main murine models of dengue infection are described, including immunocompetent wild-type mice, immunocompromised mice deficient in diverse components of the interferon (IFN) pathway and humanized mice. The main findings in antiviral testing of DENV inhibitory compounds in murine models are also presented.

EXPERT OPINION

At present, there is no murine model that fully recapitulates human disease. However, immunocompromised mice deficient in IFN-α/β and -γ receptors, with their limitations, have shown to be the most suitable system for antiviral preclinical testing. In fact, the AG129 mouse model allowed the identification of celgosivir, an inhibitor of cellular glucosidases, as a promising option for DENV therapy. However, clinical trials still were not successful, emphasizing the difficulties in the transition from preclinical testing to human treatment.

Applicability and implementation of the collagen-induced arthritis mouse model, including protocols (Review)

Animal models of rheumatoid arthritis (RA) are essential for studying the pathogenesis of RA in vivo and determining the efficacy of anti-RA drugs. During the past decades, numerous rodent models of arthritis have been evaluated as potential models and the modeling methods are relatively well-developed. Among these models, the collagen-induced arthritis (CIA) mouse model is the first choice and the most widely used because it may be generated rapidly and inexpensively and is relatively similar in pathogenesis to human RA. To date, there have been numerous classic studies and reviews discussing related pathogeneses and modeling methods. Based on this knowledge, combined with the latest convenient and effective methods for CIA model construction, the present review aims to introduce the model to beginners and clarify important details regarding its use. Information on the origin and pathogenesis of the CIA model, the protocol for establishing it, the rate of successful arthritis induction and the methods used to evaluate the severity of arthritis are briefly summarized. With this information, it is expected that researchers who have recently entered the field or are not familiar with this information will be able to start quickly, avoid unnecessary errors and obtain reliable results.

Repertoire characterization and validation of gB-specific human IgGs directly cloned from humanized mice vaccinated with dendritic cells and protected against HCMV

Human cytomegalovirus (HCMV) causes serious complications to immune compromised hosts. Dendritic cells (iDCgB) expressing granulocyte-macrophage colony-stimulating factor, interferon-alpha and HCMV-gB were developed to promote de novo antiviral adaptive responses. Mice reconstituted with a human immune system (HIS) were immunized with iDCgB and challenged with HCMV, resulting into 93% protection. Immunization stimulated the expansion of functional effector memory CD8⁺ and CD4⁺ T cells recognizing gB. Machine learning analyses confirmed bone marrow T/CD4⁺, liver B/IgA⁺ and spleen B/IgG⁺ cells as predictive biomarkers of immunization (≈87% accuracy). CD8⁺ and CD4⁺ T cell responses against gB were validated. Splenic gB-binding IgM^-/IgG⁺ B cells were sorted and analyzed at a single cell level. iDCgB immunizations elicited human-like IgG responses with a broad usage of various IgG heavy chain V gene segments harboring variable levels of somatic hypermutation. From this search, two gB-binding human monoclonal IgGs were generated that neutralized HCMV infection in vitro. Passive immunization with these antibodies provided proof-of-concept evidence of protection against HCMV infection. This HIS/HCMV in vivo model system supported the validation of novel active and passive immune therapies for future clinical translation.

Human cytomegalovirus (HCMV) is a ubiquitous pathogen. As long as the immune system is functional, T and B cells can control HCMV. Yet, for patients who have debilitated immune functions, HCMV infections and reactivations cause major complications. Vaccines or antibodies to prevent or treat HCMV are not yet approved. Novel animal models for testing new immunization approaches are emerging and are important tools to identify biomedical products with a reasonable chance to work in patients. Here, we used a model based on mice transplanted with human immune cells and infected with a traceable HCMV. We tested a cell vaccine (iDCgB) carrying gB, a potent HCMV antigen. The model showed that iDCgB halted the HCMV infection in more than 90% of the mice. We found that antibodies were key players mediating protection. Using state-of-the-art methods, we were able to use the sequences of the human antibodies generated in the mice to construct and produce monoclonal antibodies in the laboratory. Proof-of-concept experiments indicated that administration of these monoclonal antibodies into mice protected them against HCMV infection. In summary, this humanized mouse model was useful to test a vaccine and to generate and test novel antibodies that can be further developed for human use.

Recent Updates on Mouse Models for Human Immunodeficiency, Influenza, and Dengue Viral Infections

Well-developed mouse models are important for understanding the pathogenesis and progression of immunological response to viral infections in humans. Moreover, to test vaccines, anti-viral drugs and therapeutic agents, mouse models are fundamental for preclinical investigations. Human viruses, however, seldom infect mice due to differences in the cellular receptors used by the viruses for entry, as well as in the innate immune responses in mice and humans. In other words, a species barrier exists when using mouse models for investigating human viral infections. Developing transgenic (Tg) mice models expressing the human genes coding for viral entry receptors and knock-out (KO) mice models devoid of components involved in the innate immune response have, to some extent, overcome this barrier. Humanized mouse models are a third approach, developed by engrafting functional human cells and tissues into immunodeficient mice. They are becoming indispensable for analyzing human viral diseases since they nearly recapitulate the human disease. These mouse models also serve to test the efficacy of vaccines and antiviral agents. This review provides an update on the Tg, KO, and humanized mouse models that are used in studies investigating the pathogenesis of three important human-specific viruses, namely human immunodeficiency (HIV) virus 1, influenza, and dengue.

Zika viral infection and neutralizing human antibody response in a BLT humanized mouse model

Many murine and non-human primate animal models have been recently developed to understand Zika viral pathogenesis. However, a major limitation with these models is the inability to directly examine the human-specific immune response. Here, we utilized a BLT humanized mouse model endowed with a transplanted human immune system. Plasma viremia could be detected within 48h after viral challenge and viremia persisted for as long as 220 days in some mice. Neutralizing human antibody was detected in infected mice and mouse sera showed reactivity with the viral envelope and capsid proteins in a radio-immunoprecipitation assay. Human monocytes/macrophages, B cells and hematopoietic stem cells in the bone marrow were found to be virus infected. These data establish that BLT mice are permissive for Zika viral infection and are capable of generating viral-specific human immune responses thus providing a human surrogate model for future testing of vaccine and antiviral therapeutic candidates.

Exploring the Immunopathogenesis of Viral Hemorrhagic Fever in Mice with a Humanized Immune System

Viral hemorrhagic fever (VHF) as a disease entity was first codified in the 1930s by soviet scientists investigating patients suffering from hantavirus infection. The group of hemorrhagic fever viruses (HFVs) has since expanded to include members from at least four different virus families: Arenaviridae, Bunyaviridae, Filoviridae, and Flaviviridae, all enveloped single-stranded RNA viruses. After infection, the natural hosts of HFVs do not develop symptoms, whereas humans can be severely affected. This observation and other evidence from experimental data suggest that the human immune system plays a crucial role in VHF pathogenesis. For this reason mice with a human immune system, referred to here as humanized mice (humice), are valuable tools that provide insight into disease mechanisms and allow for preclinical testing of novel vaccinations approaches as well as antiviral agents. In this article, we review the impact of humice in VHF research.

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.