Humanized mice in translational biomedical research

A murine model of falciparum-malaria by in vivo selection of competent strains in non-myelodepleted mice engrafted with human erythrocytes

To counter the global threat caused by Plasmodium falciparum malaria, new drugs and vaccines are urgently needed. However, there are no practical animal models because P. falciparum infects human erythrocytes almost exclusively. Here we describe a reliable falciparum murine model of malaria by generating strains of P. falciparum in vivo that can infect immunodeficient mice engrafted with human erythrocytes. We infected NOD(scid/beta2m-/-) mice engrafted with human erythrocytes with P. falciparum obtained from in vitro cultures. After apparent clearance, we obtained isolates of P. falciparum able to grow in peripheral blood of engrafted NOD(scid/beta2m-/-) mice. Of the isolates obtained, we expanded in vivo and established the isolate Pf3D7(0087/N9) as a reference strain for model development. Pf3D7(0087/N9) caused productive persistent infections in 100% of engrafted mice infected intravenously. The infection caused a relative anemia due to selective elimination of human erythrocytes by a mechanism dependent on parasite density in peripheral blood. Using this model, we implemented and validated a reproducible assay of antimalarial activity useful for drug discovery. Thus, our results demonstrate that P. falciparum contains clones able to grow reproducibly in mice engrafted with human erythrocytes without the use of myeloablative methods.

Creation of "humanized" mice to study human immunity

"Humanized" mice are a promising translational model for studying human hematopoiesis and immunity. Their utility has been enhanced by the development of new stocks of immunodeficient hosts, most notably mouse strains such as NOD-scid IL2rgamma(null) mice that lack the IL-2 receptor common gamma chain. These stocks of mice lack adaptive immune function, display multiple defects in innate immunity, and support heightened levels of human hematolymphoid engraftment. Humanized mice can support studies in many areas of immunology, including autoimmunity, transplantation, infectious diseases, and cancer. These models are particularly valuable in experimentation where there is no appropriate small animal model of the human disease, as in the case of certain viral infections. This unit details the creation of humanized mice by engraftment of immunodeficient mice with hematopoietic stem cells or peripheral blood mononuclear cells, provides methods for evaluating engraftment, and discusses considerations for choosing the appropriate model system to meet specific goals.

Restricted expression of Epstein-Barr virus latent genes in murine B cells derived from embryonic stem cells

Background

Several human malignancies are associated with Epstein-Barr virus (EBV) and more than 95% of the adult human population carries this virus lifelong. EBV efficiently infects human B cells and persists in this cellular compartment latently. EBV-infected B cells become activated and growth transformed, express a characteristic set of viral latent genes, and acquire the status of proliferating lymphoblastoid cell lines in vitro. Because EBV infects only primate cells, it has not been possible to establish a model of infection in immunocompetent rodents. Such a model would be most desirable in order to study EBV's pathogenesis and latency in a suitable and amenable host.

Methodology/Principal Findings

We stably introduced recombinant EBV genomes into mouse embryonic stem cells and induced their differentiation to B cells in vitro to develop the desired model. In vitro differentiated murine B cells maintained the EBV genomes but expression of viral genes was restricted to the latent membrane proteins (LMPs). In contrast to human B cells, EBV's nuclear antigens (EBNAs) were not expressed detectably and growth transformed murine B cells did not arise in vitro. Aberrant splicing and premature termination of EBNA mRNAs most likely prevented the expression of EBNA genes required for B-cell transformation.

Conclusions/Significance

Our findings indicate that fundamental differences in gene regulation between mouse and man might block the route towards a tractable murine model for EBV.

The use of rodent models to investigate host-bacteria interactions related to periodontal diseases

Even though animal models have limitations, they are often superior to in vitro or clinical studies in addressing mechanistic questions and serve as an essential link between hypotheses and human patients. Periodontal disease can be viewed as a process that involves four major stages: bacterial colonization, invasion, induction of a destructive host response in connective tissue and a repair process that reduces the extent of tissue breakdown. Animal studies should be evaluated in terms of their capacity to test specific hypotheses rather than their fidelity to all aspects of periodontal disease initiation and progression. Thus, each of the models described below can be adapted to test discrete components of these four major steps, but not all of them. This review describes five different animal models that are appropriate for examining components of host-bacteria interactions that can lead to breakdown of hard and soft connective tissue or conditions that limit its repair as follows: the mouse calvarial model, murine oral gavage models with or without adoptive transfer of human lymphocytes, rat ligature model and rat Aggregatibacter actinomycetemcomitans feeding model.

Assessing the in vitro suppressive capacity of regulatory T cells

Regulatory T cells (Treg) play a vital role in controlling peripheral immune responses in order to prevent autoimmunity and control inflammation. Altered Treg activities have been associated with the pathogenesis of multiple disorders including autoimmunity, allergy, cancer, and infection with persistent pathogens. As such, a great deal of interest has recently been directed towards developing additional tools and methods to better understand the mechanisms of suppression employed by Treg. The in vitro suppression assay has emerged as a valuable means by which to assess the functional capacity and activity of Treg. In this review, we summarize the merits and limitations of the various in vitro assays that have been utilized to assess Treg activity and present a novel two color proliferation assay that allows simultaneous monitoring of both regulatory and effector T cell activity. As further immunomodulatory therapies are explored, the need for additional methodologies to understand the cellular and molecular mechanisms of immune regulation conferred by Treg will play an increasingly important role.

Immunological barriers to embryonic stem cell-derived therapies

Replacement of diseased tissues with healthy cells derived from embryonic stem (ES) cells has a potential to become, in the future, a better alternative to current treatments of a number of conditions characterized by irreversible tissue injury, such as heart and liver failure, diabetes mellitus and neurodegeneration. However, several obstacles have to be overcome before this new therapeutic modality becomes part of a standard clinical practice. First of all, ethical and safety issues have to be resolved, the methodologies must be developed to enable obtaining sufficient amounts of differentiated cells, and the immune rejection of allogeneic cells must be prevented in order to ensure their long-term engraftment and function. Data on immunological properties of human and murine ES cells and their differentiated derivatives are controversial, ranging from those claiming unique immune-privileged properties for ES cells to those which refute these conclusions. This indicates that much more research is required to definitively understand the immunological features and engraftment capacity of ES cell derivatives. We review here the current state of the art in this new and exciting field of ES cell immunology and discuss the implications of these findings for the development of ES cell-based therapies.

The growth and potential of human antiviral monoclonal antibody therapeutics

Monoclonal antibodies (mAbs) have long provided powerful research tools for virologists to understand the mechanisms of virus entry into host cells and of antiviral immunity. Even so, commercial development of human (or humanized) mAbs for the prophylaxis, preemptive and acute treatment of viral infections has been slow. This is surprising, as new antibody discovery tools have increased the speed and precision with which potent neutralizing human antiviral mAbs can be identified. As longstanding barriers to antiviral mAb development, such as antigenic variability of circulating viral strains and the ability of viruses to undergo neutralization escape, are being overcome, deeper insight into the mechanisms of mAb action and engineering of effector functions are also improving the efficacy of antiviral mAbs. These successes, in both industrial and academic laboratories, coupled with ongoing changes in the biomedical and regulatory environments, herald an era when the commercial development of human antiviral mAb therapies will likely surge.

Genetic therapies against HIV

Highly active antiretroviral therapy prolongs the life of HIV-infected individuals, but it requires lifelong treatment and results in cumulative toxicities and viral-escape mutants. Gene therapy offers the promise of preventing progressive HIV infection by sustained interference with viral replication in the absence of chronic chemotherapy. Gene-targeting strategies are being developed with RNA-based agents, such as ribozymes, antisense, RNA aptamers and small interfering RNA, and protein-based agents, such as the mutant HIV Rev protein M10, fusion inhibitors and zinc-finger nucleases. Recent advances in T-cell-based strategies include gene-modified HIV-resistant T cells, lentiviral gene delivery, CD8(+) T cells, T bodies and engineered T-cell receptors. HIV-resistant hematopoietic stem cells have the potential to protect all cell types susceptible to HIV infection. The emergence of viral resistance can be addressed by therapies that use combinations of genetic agents and that inhibit both viral and host targets. Many of these strategies are being tested in ongoing and planned clinical trials.

Summary of presentations at the NIH/NIAID New Humanized Rodent Models 2007 Workshop

It has long been recognized that a small animal model susceptible to HIV-1 infection with a functional immune system would be extremely useful in the study of HIV/AIDS pathogenesis and for the evaluation of vaccine and therapeutic strategies to combat this disease. By early 2007, a number of reports on various rodent models capable of being infected by and responding to HIV including some with a humanized immune system were published. The New Humanized Rodent Model Workshop, organized by the Division of AIDS (DAIDS), National Institute Allergy and Infection Diseases (NIAID), NIH, was held on September 24, 2007 at Bethesda for the purpose of bringing together key model developers and potential users. This report provides a synopsis of the presentations that discusses the current status of development and use of rodent models to evaluate the pathogenesis of HIV infection and to assess the efficacy of vaccine and therapeutic strategies including microbicides to prevent and/or treat HIV infection.

Use of animal models in the development of human vaccines

Over the past 100 years, animal infectious disease research has played a crucial role in the development of human vaccines. In fact, many of today's vaccines are based on utilizing animal pathogens, either in the form of an attenuated vaccine or as a vaccine vector. Vaccine development has become increasingly complex with chronic and newly emerging diseases, a demand for therapeutic vaccines for noninfectious diseases, extended vaccine in the neonate and the elderly, and increasing concerns regarding vaccine safety. Furthermore, the evaluation of quantity and quality of immune responses and the ability to efficiently translate the results of basic research into the clinic are critical to ensure that vaccines meet their therapeutic potential. Here, we review the importance of animal models for developing and testing novel human vaccines, discuss the limitations of existing animal models in knowledge translation, and summarize the needs and criteria for future animal models. We argue that efficient translation of basic vaccine research to clinical therapies will depend upon the availability of appropriate animal models to address each of the questions which arise during vaccine development.

Immunology in natura: clinical, epidemiological and evolutionary genetics of infectious diseases

The field of human genetics of infectious diseases defines the genes and alleles rendering individuals (clinical genetics) and populations (epidemiological genetics) vulnerable to infection, and studies those selected by previous infections (evolutionary genetics). These disciplines--clinical, epidemiological and evolutionary genetics-delineate the redundant and nonredundant functions of host defense genes for past and present survival in natura--in natural ecosystems governed by natural selection. These disciplines, in other words, assess the ecologically relevant and evolutionarily selected roles of human genes and alleles in protective immunity to diverse and evolving microorganisms. The genetic dissection of human immunity to infection in natura provides unique immunological insight, making it an indispensable complement to experimental immunology in vitro and in vivo in plants and animals.

Mucosal transmission of R5 and X4 tropic HIV-1 via vaginal and rectal routes in humanized Rag2-/- gammac -/- (RAG-hu) mice

Studies on HIV-1 mucosal transmission to evaluate early events in pathogenesis and the development of effective preventive/prophylactic methods have thus far been hampered by the lack of a suitable animal model susceptible to HIV-1 infection by either vaginal and/or rectal routes. In this regard, while primate-SIV/SHIV and cat-FIV models provided useful surrogate platforms to derive comparative data, these viruses are distinct and different from that of HIV-1. Therefore an optimal model that permits direct study of HIV-1 transmission via mucosal routes is highly desirable. The new generation of humanized NOD/SCID BLT, NOD/SCIDgammac(-/-), and Rag2(-/-)gammac(-/-) mouse models show great promise to achieve this goal. Here, we show that humanized Rag2(-/-)gammac(-/-) mice (RAG-hu) engrafted with CD34 hematopoietic progenitor cells harbor HIV-1-susceptible human cells in the rectal and vaginal mucosa and are susceptible to HIV-1 infection when exposed to cell-free HIV-1 either via vagina or rectum. Infection could be established without any prior hormonal conditioning or mucosal abrasion. Both R5 and X4 tropic viruses were capable of mucosal infection resulting in viremia and associated helper T cell depletion. There was systemic spread of the virus with infected cells detected in different organs including the intestinal mucosa. R5 virus was highly efficient in mucosal transmission by both routes whereas X4 virus was relatively less efficient in causing infection. HIV-1 infection of RAG-hu mice by vaginal and rectal routes as shown here represents the first in vivo model of HIV-1 transmission across intact mucosal barriers and as such may prove very useful for studying early events in HIV-1 pathogenesis in vivo, as well as the testing of microbicides, anti-HIV vaccines/therapeutics, and other novel strategies to prevent HIV-1 transmission.

Antiretroviral pre-exposure prophylaxis prevents vaginal transmission of HIV-1 in humanized BLT mice

BACKGROUND

Worldwide, vaginal transmission now accounts for more than half of newly acquired HIV-1 infections. Despite the urgency to develop and implement novel approaches capable of preventing HIV transmission, this process has been hindered by the lack of adequate small animal models for preclinical efficacy and safety testing. Given the importance of this route of transmission, we investigated the susceptibility of humanized mice to intravaginal HIV-1 infection.

METHODS AND FINDINGS

We show that the female reproductive tract of humanized bone marrow-liver-thymus (BLT) mice is reconstituted with human CD4+ T and other relevant human cells, rendering these humanized mice susceptible to intravaginal infection by HIV-1. Effects of HIV-1 infection include CD4+ T cell depletion in gut-associated lymphoid tissue (GALT) that closely mimics what is observed in HIV-1-infected humans. We also show that pre-exposure prophylaxis with antiretroviral drugs is a highly effective method for preventing vaginal HIV-1 transmission. Whereas 88% (7/8) of BLT mice inoculated vaginally with HIV-1 became infected, none of the animals (0/5) given pre-exposure prophylaxis of emtricitabine (FTC)/tenofovir disoproxil fumarate (TDF) showed evidence of infection (Chi square = 7.5, df = 1, p = 0.006).

CONCLUSIONS

The fact that humanized BLT mice are susceptible to intravaginal infection makes this system an excellent candidate for preclinical evaluation of both microbicides and pre-exposure prophylactic regimens. The utility of humanized mice to study intravaginal HIV-1 transmission is particularly highlighted by the demonstration that pre-exposure prophylaxis can prevent intravaginal HIV-1 transmission in the BLT mouse model.

Can the new humanized mouse model give HIV research a boost

The "BLT mouse" holds promise for the preclinical evaluation of microbicides and antiretroviral prophylaxis regimens.

Comparative genomics for detecting human disease genes

Originally, comparative genomics was geared toward defining the synteny of genes between species. As the human genome project accelerated, there was an increase in the number of tools and means to make comparisons culminating in having the genomic sequence for a large number of organisms spanning the evolutionary tree. With this level of resolution and a long history of comparative biology and comparative genetics, it is now possible to use comparative genomics to build or select better animal models and to facilitate gene discovery. Comparative genomics takes advantage of the functional genetic information from other organisms, (vertebrates and invertebrates), to apply it to the study of human physiology and disease. It allows for the identification of genes and regulatory regions, and for acquiring knowledge about gene function. In this chapter, the current state of comparative genomics and the available tools are discussed in the context of developing animal model systems that reflect the clinical picture.

Human T cell development and HIV infection in human hemato-lymphoid system mice

Advances in generation of mice that on human hematopoietic stem and progenitor cell transplantation develop and maintain human hemato-lymphoid cells have fueled an already thriving field of research. We focus here on human T cell development and HIV infection in Rag2 -/- gamma(c) -/- mice transplanted as newborns with human CD34+ cord blood hematopoietic stem and progenitor cells.

Humanized SCID mouse models for biomedical research

There is a growing need for effective animal models to carry out experimental studies on human hematopoietic and immune systems without putting individuals at risk. Progress in development of small animal models for the in vivo investigation of human hematopoiesis and immunity has seen three major breakthroughs over the last three decades. First, CB 17-Prkdc(scid) (abbreviated CB 17-scid) mice were discovered in 1983, and engraftment of these mice with human fetal tissues (SCID-Hu model) and peripheral blood mononuclear cells (Hu-PBL-SCID model) was reported in 1988. Second, NOD-scid mice were developed and their enhanced ability to engraft with human hematolymphoid tissues as compared with CB17-scid mice was reported in 1995. NOD-scid mice have been the "gold standard" for studies of human hematolymphoid engraftment in small animal models over the last 10 years. Third, immunodeficient mice bearing a targeted mutation in the IL-2 receptor common gamma chain (IL2rgamma(null)) were developed independently by four groups between 2002 and 2005, and a major increase in the engraftment and function of human hematolymphoid cells as compared with NOD-scid mice has been reported. These new strains of immunodeficient IL2rgamma(null) mice are now being used for studies in human hematopoiesis, innate and adaptive immunity, autoimmunity, infectious diseases, cancer biology, and regenerative medicine. In this chapter, we discuss the current state of development of these strains of mice, the remaining deficiencies, and how approaches used to increase the engraftment and function of human hematolymphoid cells in CB 17-scid mice and in previous models based on NOD-scid mice may enhance human hematolymphoid engraftment and function in NOD-scid IL2rgamma(null) mice.

NOD/Shi-scid IL2rgamma(null) (NOG) mice more appropriate for humanized mouse models

"Humanized mice," in which various kinds of human cells and tissues can be engrafted and retain the same functions as in humans, are extremely useful because human diseases can be studied directly. Using the newly combined immunodeficient NOD-scid IL2rgamma(null) mice and Rag2(null) IL2rgamma(null) humanized mice, it has became possible to expand applications because various hematopoietic cells can be differentiated by human hematopoietic stem cell transplantation, and the human immune system can be reconstituted to some degree. This work has attracted attention worldwide, but the development and use of immunodeficient mice in Japan are not very well known or understood. This review describes the history and characteristics of the NOD/Shi-scid IL2rgamma(null) (NOG) and BALB/cA-Rag2(null) IL2rgamma(null) mice that were established in Japan, including our unpublished data from researchers who are currently using these mice. In addition, we also describe the potential development of new immunodeficient mice that can be used as humanized mice in the future.

Animal models of human pneumonia

Pneumonia is a medical and public health priority, and advances against this disease will require improved knowledge of biological mechanisms. Human pneumonia is modeled with experimental infections of animals, most frequently mice. Mouse models are leading to important discoveries relevant to pneumonia, but their limitations must be carefully considered. Several approaches to establishing pneumonia in mice have been developed, and each has specific strengths and weaknesses. Similarly, procedures for characterizing microbial and host responses to infection have unique advantages and disadvantages. Mice are not small humans, and the applicability of results from murine models to human disease depends on understanding the similarities and differences between species. Additional considerations such as mouse strain, microbe strain, and prior mouse-microbe interactions also influence the design and interpretation of experiments. Results from studies of pneumonia in animals, combined with complementary basic and translational studies, are elucidating mechanisms responsible for susceptibility to and pathophysiology of lung infection.

Small-diameter biodegradable scaffolds for functional vascular tissue engineering in the mouse model

The development of neotissue in tissue engineered vascular grafts remains poorly understood. Advances in mouse genetic models have been highly informative in the study of vascular biology, but have been inaccessible to vascular tissue engineers due to technical limitations on the use of mouse recipients. To this end, we have developed a method for constructing sub-1mm internal diameter (ID) biodegradable scaffolds utilizing a dual cylinder chamber molding system and a hybrid polyester sealant scaled for use in a mouse model. Scaffolds constructed from either polyglycolic acid or poly-l-lactic acid nonwoven felts demonstrated sufficient porosity, biomechanical profile, and biocompatibility to function as vascular grafts. The scaffolds implanted as either inferior vena cava or aortic interposition grafts in SCID/bg mice demonstrated excellent patency without evidence of thromboembolic complications or aneurysm formation. A foreign body immune response was observed with marked macrophage infiltration and giant cell formation by post-operative week 3. Organized vascular neotissue, consisting of endothelialization, medial generation, and collagen deposition, was evident within the internal lumen of the scaffolds by post-operative week 6. These results present the ability to create sub-1mm ID biodegradable tubular scaffolds that are functional as vascular grafts, and provide an experimental approach for the study of vascular tissue engineering using mouse models.

A new Hu-PBL model for the study of human islet alloreactivity based on NOD-scid mice bearing a targeted mutation in the IL-2 receptor gamma chain gene

Immunodeficient NOD-scid mice bearing a targeted mutation in the IL2 receptor common gamma chain (Il2rgamma(null)) readily engraft with human stem cells. Here we analyzed human peripheral blood mononuclear cells (PBMC) for their ability to engraft NOD-scid Il2rgamma(null) mice and established engraftment kinetics, optimal cell dose, and the influence of injection route. Even at low PBMC input, NOD-scid Il2rgamma(null) mice reproducibly support high human PBMC engraftment that plateaus within 3-4 weeks. In contrast to previous stocks of immunodeficient mice, we observed low intra- and inter-donor variability of engraftment. NOD-scid Il2rgamma(null) mice rendered hyperglycemic by streptozotocin treatment return to normoglycemia following transplantation with human islets. Interestingly, these human islet grafts are rejected following injection of HLA-mismatched human PBMC as evidenced by return to hyperglycemia and loss of human C-peptide. These data suggest that humanized NOD-scid Il2rgamma(null) mice may represent an important surrogate for investigating in vivo mechanisms of human islet allograft rejection.

The mouse ascending: perspectives for human-disease models

The laboratory mouse is widely considered the model organism of choice for studying the diseases of humans, with whom they share 99% of their genes. A distinguished history of mouse genetic experimentation has been further advanced by the development of powerful new tools to manipulate the mouse genome. The recent launch of several international initiatives to analyse the function of all mouse genes through mutagenesis, molecular analysis and phenotyping underscores the utility of the mouse for translating the information stored in the human genome into increasingly accurate models of human disease.

Repopulation of adult and neonatal mice with human hepatocytes: a chimeric animal model

We report the successful transplantation of human hepatocytes in immunodeficient, fumarylacetoacetate hydrolase-deficient (fah(-/-)) mice. Engraftment occurs over the entire liver acinus upon transplantation. A few weeks after transplantation, increasing concentrations of human proteins (e.g., human albumin and human C3a) can be measured in the blood of the recipient mouse. No fusion between mouse and human hepatocytes can be detected. Three months after transplantation, up to 20% of the mouse liver is repopulated by human hepatocytes, and sustained expression of lentiviral vector transduced gene can be observed. We further report the development of a hepatocyte transplantation method involving a transcutaneous, intrahepatic injection in neonatal mice. Human hepatocytes engraft over the entire injected lobe with an expansion pattern similar to those observed with intrasplenic transplantation.

Developmental pathways that generate natural-killer-cell diversity in mice and humans

Natural killer (NK) cells are large granular lymphocytes capable of producing inflammatory cytokines and spontaneously killing malignant, infected or 'stressed' cells. These NK-cell functions are controlled by cell-surface receptors that titrate stimulatory and inhibitory signals. However, we remain puzzled about where and when NK cells develop and differentiate, and this has fuelled the debate over the diversification of the peripheral NK-cell pool: are NK cells functionally homogeneous or are there subsets with specialized effector functions? In this Review, we consider the developmental relationships and biological significance of the diverse NK-cell subsets in mice and humans, and discuss how new humanized mouse models may help to characterize them further.

Generation of pro-T cells in vitro: potential for immune reconstitution

Immunodeficient individuals are susceptible to opportunistic infection. While stem cell transplantation can restore a functional immune system, T cells are slow to recover and limited in eliciting adaptive immune responses. Approaches to selectively enhance T cell function have focused on boosting thymopoiesis to generate new T cells or expanding existing T cells. By taking advantage of the role of Notch signaling in T cell development, we have developed an in vitro system able to generate large numbers of progenitor T cells from human hematopoietic stem cells. Here, we discuss this in vitro system and its implications for the potential treatment of T cell immunodeficiency.

Characterization of the NOD/scid-[Tg]DR1 mouse expressing HLA-DRB1*01 transgene: a model of SCID-hu mouse for vaccine development

OBJECTIVE

We previously showed enhanced engraftment of human T cells in the transgenic NonObese Diabetic/severe combined immunodeficient (NOD/scid)-DR1 mice, compared to NOD/scid mice. We now characterize their immunobiology, innate immunity, and intrahepatic neonatal engraftment of cord blood mononuclear cells (CBMNC), and test immune responses of these chimeric mice to an experimental cancer vaccine.

METHODS

Fluorescence in situ hybridization analysis, blood biochemistry, hematology, and fluorescein-activated cell sorting analyses of cellular subsets were performed on NOD/scid-DR1 mice, in comparison to parental NOD/scid mice. Innate immunity and lifespan were examined. Histology of engrafted tissues and short-term intrahepatic engraftment of CBMNC were performed. Intracellular interferon-gamma (IFN-gamma) production was assessed in mice immunized with cancer vaccine.

RESULTS

The DR1 transgene was located on chromosome 5 and no significant changes were observed in blood chemistry, peripheral blood counts, lymphoid subsets, natural killer cell and lipopolysaccharide response, and antigen presentation in the NOD/scid-DR1 mice, compared to NOD/scid mice. Interestingly, NOD/scid-DR1 mice had a significantly longer lifespan (approximately 14 months) than NOD/scid mice (approximately 8.5 months). Engraftment with human cord blood cells resulted in slight changes in the architecture/structure of spleens. No correlation was found between DR1 genotype of the donor CBMNC and extent of engraftment of human T cells. Enhanced engraftment of human cells was observed with intrahepatic injections of CBMNC in neonatal NOD/scid DR1 mice. Intracellular IFN-gamma was detected in human cells, when chimeric mice were immunized with a cancer vaccine.

CONCLUSION

NOD/scid-DR1 mice were similar in most of the physiological parameters as the NOD/scid mice, with the exception of longer lifespan. Intrahepatic engraftment of neonatal mice is the preferred protocol of xenotransplantation in this model and the engrafted human cells can respond to a cancer vaccine.

Maximizing mouse cancer models

Animal models of cancer provide an alternative means to determine the causes of and treatments for malignancy, thus representing a resource of immense potential for cancer medicine. The sophistication of modelling cancer in mice has increased to the extent that investigators can both observe and manipulate a complex disease process in a manner impossible to perform in patients. However, owing to limitations in model design and technology development, and the surprising underuse of existing models, only now are we realising the full potential of mouse models of cancer and what new approaches are needed to derive the maximum value for cancer patients from this investment.

Human-animal chimeras in biomedical research

Chimeras are individuals with tissues derived from more than one zygote. Interspecific chimeras have tissues derived from different species. The biological consequences of human-animal chimeras have become an issue of ethical debate. Ironically, human-animal chimeras with human blood, neurons, germ cells, and other tissues have been generated for decades. This has facilitated human biological studies and therapeutic strategies for disease.

Human-hemato-lymphoid-system mice: opportunities and challenges

With the recent advances in human-hemato-lymphoid-system mice, this commentary discusses the utility of these mice and further improvements required to generate an accessible system that allows predictive in vivo human hematology and immunology research.

Generation of human/rat xenograft animal model for the study of human donor stem cell behaviors in vivo

AIM: To accurately and realistically elucidate human stem cell behaviors in vivo and the fundamental mechanisms controlling human stem cell fates in vivo, which is urgently required in regenerative medicine and treatments for some human diseases, a surrogate human-rat chimera model was developed.

METHODS: Human-rat chimeras were achieved by in utero transplanting low-density mononuclear cells from human umbilical cord blood into the fetal rats at 9-11 d of gestation, and subsequently, a variety of methods, including flow cytometry, PCR as well as immunohistochemical assay, were used to test the human donor contribution in the recipients.

RESULTS: Of 29 live-born recipients, 19 had the presence of human CD45⁺ cells in peripheral blood (PB) detected by flow cytometry, while PCR analysis on genomic DNA from 11 different adult tissues showed that 14 selected from flow cytometry-positive 19 animals possessed of donor-derived human cell engraftment in multiple tissues (i.e. liver, spleen, thymus, heart, kidney, blood, lung, muscle, gut and skin) examined at the time of tissue collection, as confirmed by detecting human β2-microglobulin expression using immunohistochemistry. In this xenogeneic system, the engrafted donor-derived human cells persisted in multiple tissues for at least 6 mo after birth. Moreover, transplanted human donor cells underwent site-specific differentiation into CK18-positive human cells in chimeric liver and CD45-positive human cells in chimeric spleen and thymus of recipients.

CONCLUSION: Taken together, these findings suggest that we successfully developed human-rat chimeras, in which xenogeneic human cells exist up to 6 mo later. This humanized small animal model, which offers an in vivo environment more closely resembling to the situations in human, provides an invaluable and effective approach for in vivo investigating human stem cell behaviors, and further in vivo examining fundamental mechanisms controlling human stem cell fates in the future. The potential for new advances in our better understanding the living biological systems in human provided by investigators in humanized animals will remain promising.

Formation of human hepatocyte-like cells with different cellular phenotypes by human umbilical cord blood-derived cells in the human-rat chimeras

We took advantage of the proliferative and permissive environment of the developing pre-immune fetus to develop a noninjury human-rat xenograft small animal model, in which the in utero transplantation of low-density mononuclear cells (MNCs) from human umbilical cord blood (hUCB) into fetal rats at 9-11 days of gestation led to the formation of human hepatocyte-like cells (hHLCs) with different cellular phenotypes, as revealed by positive immunostaining for human-specific alpha-fetoprotein (AFP), cytokeratin 19 (CK19), cytokeratin 8 (CK8), cytokeratin 18 (CK18), and albumin (Alb), and with some animals exhibiting levels as high as 10.7% of donor-derived human cells in the recipient liver. More interestingly, donor-derived human cells stained positively for CD34 and CD45 in the liver of 2-month-old rat. Human hepatic differentiation appeared to partially follow the process of hepatic ontogeny, as evidenced by the expression of AFP gene at an early stage and albumin gene at a later stage. Human hepatocytes generated in this model retained functional properties of normal hepatocytes. In this xenogeneic system, the engrafted donor-derived human cells persisted in the recipient liver for at least 6 months after birth. Taken together, these findings suggest that the donor-derived human cells with different cellular phenotypes are found in the recipient liver and hHLCs hold biological activity. This humanized small animal model, which offers an in vivo environment more closely resembling the situations in human, provides an invaluable approach for in vivo investigating human stem cell behaviors, and further in vivo examining fundamental mechanisms controlling human stem cell fates in the future.

Are insights gained from NOD mice sufficient to guide clinical translation? Another inconvenient truth

Despite decades of research using various animal models for type 1 diabetes, we are still struggling to define the initiating autoantigens, the precise mechanisms of beta cell destruction, and suitable immune-based interventions to prevent or treat human diabetes. Animal models, such as the non-obese diabetic (NOD) mouse and the biobreeding (BB) rat, develop immune-mediated diseases with features resembling type 1 diabetes in humans. Although these animal models of autoimmune diabetes have proved to be valuable tools to study certain aspects of the disease process, they have also led to misconceptions and erroneous extrapolations, as well as false expectations with regard to the efficacy of immunotherapy. It is therefore time to ask ourselves whether we are making major strategic mistakes when employing rodent models for the study of type 1 diabetes. This review will describe where rodent models have provided us with proper guidance and where they have misled us, concluding that each model only offers partial information with undefined clinical value. Therefore, a more critical attitude and repetition of crucial observations in different model settings will be necessary in the future. I will argue that animal models have limited but evident value when it comes to teaching us about type 1 diabetes in humans, and we can take advantage of this value more efficiently.

Advances in swine biomedical model genomics

This review is a short update on the diversity of swine biomedical models and the importance of genomics in their continued development. The swine has been used as a major mammalian model for human studies because of the similarity in size and physiology, and in organ development and disease progression. The pig model allows for deliberately timed studies, imaging of internal vessels and organs using standard human technologies, and collection of repeated peripheral samples and, at kill, detailed mucosal tissues. The ability to use pigs from the same litter, or cloned or transgenic pigs, facilitates comparative analyses and genetic mapping. The availability of numerous well defined cell lines, representing a broad range of tissues, further facilitates testing of gene expression, drug susceptibility, etc. Thus the pig is an excellent biomedical model for humans. For genomic applications it is an asset that the pig genome has high sequence and chromosome structure homology with humans. With the swine genome sequence now well advanced there are improving genetic and proteomic tools for these comparative analyses. The review will discuss some of the genomic approaches used to probe these models. The review will highlight genomic studies of melanoma and of infectious disease resistance, discussing issues to consider in designing such studies. It will end with a short discussion of the potential for genomic approaches to develop new alternatives for control of the most economically important disease of pigs, porcine reproductive and respiratory syndrome (PRRS), and the potential for applying knowledge gained with this virus for human viral infectious disease studies.