Humanized mice in translational biomedical research

Synergistic effect of human CycT1 and CRM1 on HIV-1 propagation in rat T cells and macrophages

BACKGROUND

In vivo studies of HIV-1 pathogenesis and testing of antiviral strategies have been hampered by the lack of an immunocompetent small animal model that is highly susceptible to HIV-1 infection. Although transgenic rats that express the HIV-1 receptor complex hCD4 and hCCR5 are susceptible to infection, HIV-1 replicates very poorly in these animals. To demonstrate the molecular basis for developing a better rat model for HIV-1 infection, we evaluated the effect of human CyclinT1 (hCycT1) and CRM1 (hCRM1) on Gag p24 production in rat T cells and macrophages using both established cell lines and primary cells prepared from hCycT1/hCRM1 transgenic rats.

RESULTS

Expression of hCycT1 augmented Gag production 20-50 fold in rat T cells, but had little effect in macrophages. Expression of hCRM1 enhanced Gag production 10-15 fold in macrophages, but only marginally in T cells. Expression of both factors synergistically enhanced p24 production to levels approximately 10-40% of those detected in human cells. R5 viruses produced in rat T cells and macrophages were fully infectious.

CONCLUSION

The expression of both hCycT1 and hCRM1 appears to be fundamental to developing a rat model that supports robust propagation of HIV-1.

Molecular pathogenesis of Staphylococcus aureus infection

S. aureus has evolved a comprehensive strategy to address the challenges posed by the human immune system. The emergence of community-associated methicillin-resistant S. aureus (CA-MRSA) infections in individuals with no predisposing conditions suggests an increased pathogenicity of the bacterium, which may be related to acquisition of novel genetic elements. Remarkably, despite an abundance of research, the underlying cause of the epidemic is not known. Here, the various strategies used by S. aureus to evade obstacles laid out by the human host during colonization and infection were reviewed. The controversies surrounding MRSA research were described, and how acquisition of the novel genes could explain the increased incidence and severity of CA-MRSA diseases was described.

Human T regulatory cell therapy: take a billion or so and call me in the morning

Immune system regulation is of paramount importance to host survival. In settings of autoimmunity and alloimmunity, control is lost, resulting in injury to vital organs and tissues. Naturally occurring, thymic-derived T regulatory (Treg) cells that express CD4, CD25, and the forkhead box protein 3 (FoxP3) are potent suppressors of these adverse immune responses. Preclinical studies have shown that either freshly isolated or ex vivo expanded Treg cells can prevent both local and systemic organ and tissue destruction. Although promising, human Treg cell infusion therapy has heretofore been difficult to implement in the clinic, and relatively few clinical trials have been initiated. This review will focus on the preclinical models that provide the rationale for current trials and it will address both the challenges and opportunities in human Treg cell therapy.

Sepsis-induced human lymphocyte apoptosis and cytokine production in "humanized" mice

Sepsis is the leading cause of death in critically ill patients in the United States with over 210,000 deaths annually. One stumbling block to an effective therapy of sepsis has been the lack of a clinically relevant animal model. There are important distinctions in the mouse versus human immune system regarding the host response to invading pathogens. These differences may explain the disappointing results in many sepsis clinical trials despite the clear efficacy of these agents in mouse models of sepsis. The purpose of the present study was to develop a "humanized" mouse model of sepsis and to determine if the model recapitulated the major findings of lymphocyte apoptosis and cytokine response that exist in patients with sepsis. Two-day-old NOD-scid IL2rgamma(null) mice received an adoptive transfer of hCD34(+) hematopoietic cord blood stem cells. These mice acquired a functional human innate and adaptive immune system, as evidenced by the development of all lineages of human immune cells as well as by mounting a DTH response. Eight weeks post-transfer, mice were made septic using the highly clinical relevant CLP model of sepsis, and sepsis induced marked elevations in human pro- and anti-inflammatory cytokines as well as a dramatic increase in human T and B cell apoptosis. Collectively, these results show that the humanized mouse model recapitulates many of the classic findings in patients with sepsis. Therefore, it represents an advanced, clinically relevant model for mechanistic studies of sepsis and testing of novel therapies.

Epstein-Barr virus and the pathogenesis of Burkitt's lymphoma: more questions than answers

Burkitt's lymphoma (BL) was first described as a clinical entity in children in Central Africa by Denis Burkitt in 1958. The particular epidemiological features of this tumor initiated the search for a virus as the causative agent and led to the discovery of Epstein-Barr virus (EBV) by Epstein and coworkers in 1964. It became apparent in the seventies and eighties that the tumor is not restricted to Central Africa, but occurs with lesser incidence all over the world (sporadic BL) and is also particularly frequent in HIV infected individuals, and that not all BL cases are associated with EBV: about 95% of the cases in Central Africa, 40 to 50% of the cases in HIV-infected individuals and 10 to 20% of the sporadic cases harbour the viral information and express at least one viral antigen (EBNA1) and a number of non-coding viral RNAs. In contrast, all BL cases regardless of their geographical origin exhibit one of three c-myc/Ig chromosomal translocations leading to the activation of the c-myc gene as a crucial event in the development of this disease. Although epidemiological evidence clearly points to a role of the virus in the African cases, the role of EBV in the pathogenesis of BL has remained largely elusive. This review summarizes current concepts and ideas how EBV might contribute to the development of BL in the light of the progress made in the last decade and discusses the problems of the experimental systems available to test such hypotheses.

The expanding role of mouse genetics for understanding human biology and disease

It has taken about 100 years since the mouse first captured our imagination as an intriguing animal for it to become the premier genetic model organism. An expanding repertoire of genetic technology, together with sequencing of the genome and biological conservation, place the mouse at the foremost position as a model to decipher mechanisms underlying biological and disease processes. The combined approaches of embryonic stem cell-based technologies, chemical and insertional mutagenesis have enabled the systematic interrogation of the mouse genome with the aim of creating, for the first time, a library of mutants in which every gene is disrupted. The hope is that phenotyping the mutants will reveal novel and interesting phenotypes that correlate with genes, to define the first functional map of a mammalian genome. This new milestone will have a great impact on our understanding of mammalian biology, and could significantly change the future of medical diagnosis and therapeutic development, where databases can be queried in silico for potential drug targets or underlying genetic causes of illnesses. Emerging innovative genetic strategies, such as somatic genetics, modifier screens and humanized mice, in combination with whole-genome mutagenesis will dramatically broaden the utility of the mouse. More significantly, allowing genome-wide genetic interrogations in the laboratory, will liberate the creativity of individual investigators and transform the mouse as a model for making original discoveries and establishing novel paradigms for understanding human biology and disease.

Novel humanized murine models for HIV research

There are few models in which HIV pathogenesis, particularly gut-associated lymphoid tissue CD4(+) T-cell depletion, can be studied and in which potential clinical interventions against HIV disease can be evaluated. HIV cannot be studied in normal mice due to the limited species tropism of the virus. Through the pioneering efforts of many investigators, humanized mice are now routinely used to rapidly advance HIV research. It is important to recognize that not all humanized murine models are equal, and their strengths and weaknesses must be taken into consideration to obtain information that is most relevant to the human condition. This review distinguishes the major humanization protocols and highlights each model's recent contributions to HIV research, including mucosal transmission, gut-associated lymphoid tissue pathogenesis, and the evaluation of novel therapeutic and prevention approaches to potentially treat HIV disease and prevent the further spread of AIDS.

Testing human biologicals in animal host resistance models

The purpose of immunotoxicity testing is to obtain data that is meaningful for safety assessment. Host resistance assays are the best measure of a toxicant's effect on the overall ability to mount an effective immune response and protect the host from infectious disease. An outline is presented for immunotoxicological evaluation using host resistance assays. The influenza virus host resistance model is useful to evaluate the overall health of the immune system and is one of the most thoroughly characterized host resistance models. Viral clearance requires all aspects of the immune system to work together and is the ultimate measure of the health of the immune system in this model. Mechanistic immune functions may be included while measuring viral clearance and include: cytokines, macrophage activity, natural killer (NK) cell activity, cytotoxic T-lymphocyte (CTL) activity, and influenza-specific IgM and IgG. Measurement of these immunological functions provides an evaluation of innate immunity (macrophage or NK activity), an evaluation of cell-mediated immunity (CMI) (CTL activity), and an evaluation of humoral-mediated immunity (HMI) (influenza-specific IgM or IgG). Measurement of influenza-specific IgM or IgG also provides a measurement of T-dependent antibody response (TDAR) since influenza is a T-dependent antigen. There are several targeted host resistance models that may be used to answer specific questions. Should a defect in neutrophil and/or macrophage function be suspected, Streptococcus pneumoniae, Pseudomonas aeruginosa, or Listeria monocytogenes host resistance models are useful. Anti-inflammatory pharmaceuticals or therapeutics for rheumatoid arthritis or Crohn's disease that target TNFalpha may also be evaluated for immunotoxicity using the S. pneumoniae intranasal host resistance assay. Marginal zone B (MZB) cells are required for production of antibody to T-independent antigens such as the polysaccharide capsule of the encapsulated bacteria that are so prominent in causing blood-borne infections and pneumonia. Intravenous infection with Streptococcus pneumoniae, an encapsulated bacterium, results in a blood-borne infection that requires MZB cells for clearance. The systemic S. pneumoniae host resistance assay evaluates whether a therapeutic test article exerts immunotoxicity on MZB cells and measures the T-independent antibody response (TIAR). Suppression of CMI or in some cases HMI may result in reactivation of latent virus that may result in a fatal disease such as progressive multifocal leukoencephalopathy (PML). The murine cytomegalovirus (MCMV) reactivation model may be used to evaluate a pharmaceutical agent to determine if suppression of CMI or HMI results in reactivation of latent virus. Candida albicans is another host resistance model to test potential immunotoxicity. Host resistance assays have been the ultimate measure of immunotoxicity testing for environmental chemicals and pharmaceutical small molecules. Human biologicals are now an important component of the drug development armamentarium for biotech and pharmaceutical companies. Many human biologicals are fusions of IgG, and/or target immune mediators, immunological receptors, adhesion molecules, and/or are indicated for diseases that have immune components. It is therefore necessary to thoroughly evaluate human biological therapeutics for immunotoxicity. Numerous biologicals that are pharmacologically active in rodents can be evaluated using well-characterized rodent host resistance assays. However, biologicals not active in rodents may use surrogate biologicals for testing in rodent host resistance assays, or may use host resistance assays in genetically engineered mice that mimic the effect of the human biological pharmacological agent.

Expansion of human regulatory T-cells from patients with type 1 diabetes

OBJECTIVE

Regulatory T-cells (Tregs) have catalyzed the field of immune regulation. However, translating Treg-based therapies from animal models of autoimmunity to human clinical trials requires robust methods for the isolation and expansion of these cells-a need forming the basis for these studies.

RESEARCH DESIGN AND METHODS

Tregs from recent-onset type 1 diabetic patients and healthy control subjects were isolated by fluorescence-activated cell sorting and compared for their capacity to expand in vitro in response to anti-CD3-anti-CD28-coated microbeads and IL-2. Expanded cells were examined for suppressive function, lineage markers and FOXP3, and cytokine production.

RESULTS

Both CD4+CD127(lo/-) and CD4+CD127(lo/-)CD25+ T-cells could be expanded and used as Tregs. However, expansion of CD4+CD127(lo/-) cells required the addition of rapamycin to maintain lineage purity. In contrast, expansion of CD4+CD127(lo/-)CD25+ T-cells, especially the CD45RA+ subset, resulted in high yield, functional Tregs that maintained higher FOXP3 expression in the absence of rapamycin. Tregs from type 1 diabetic patients and control subjects expanded similarly and were equally capable of suppressing T-cell proliferation. Regulatory cytokines were produced by Tregs after culture; however, a portion of FOXP3+ cells were capable of producing interferon (IFN)-gamma after reactivation. IFN-gamma production was observed from both CD45RO+ and CD45RA+ Treg populations.

CONCLUSIONS

The results support the feasibility of isolating Tregs for in vitro expansion. Based on expansion capacity, FOXP3 stability, and functional properties, the CD4+CD127(lo/-)CD25+ T-cells represent a viable cell population for cellular therapy in this autoimmune disease.

Antibody to the dendritic cell surface activation antigen CD83 prevents acute graft-versus-host disease

Allogeneic (allo) hematopoietic stem cell transplantation is an effective therapy for hematological malignancies but it is limited by acute graft-versus-host disease (GVHD). Dendritic cells (DC) play a major role in the allo T cell stimulation causing GVHD. Current immunosuppressive measures to control GVHD target T cells but compromise posttransplant immunity in the patient, particularly to cytomegalovirus (CMV) and residual malignant cells. We showed that treatment of allo mixed lymphocyte cultures with activated human DC-depleting CD83 antibody suppressed alloproliferation but preserved T cell numbers, including those specific for CMV. We also tested CD83 antibody in the human T cell-dependent peripheral blood mononuclear cell transplanted SCID (hu-SCID) mouse model of GVHD. We showed that this model requires human DC and that CD83 antibody treatment prevented GVHD but, unlike conventional immunosuppressants, did not prevent engraftment of human T cells, including cytotoxic T lymphocytes (CTL) responsive to viruses and malignant cells. Immunization of CD83 antibody-treated hu-SCID mice with irradiated human leukemic cell lines induced allo antileukemic CTL effectors in vivo that lysed (51)Cr-labeled leukemic target cells in vitro without further stimulation. Antibodies that target activated DC are a promising new therapeutic approach to the control of GVHD.

Development of a humanized mouse model to study the role of macrophages in allograft injury

BACKGROUND

Nearly half of all infiltrating leukocytes in rejecting human allografts are macrophages, yet, in comparison with T cells, much less is known about the contribution of this cell type to rejection. Our laboratory has previously described models of rejection of human skin or artery grafts in immunodeficient mouse hosts mediated by adoptively transferred allogeneic T cells. However, mature human monocyte/macrophages have consistently failed to engraft in these animals. Here, we describe the introduction of human CD68+ macrophages into irradiated immunodeficient mice by transplantation of enriched CD34+ hematopoietic stem-cells isolated from peripheral blood of G-colony-stimulating factor pretreated adults.

METHODS

We investigated strains of immunodeficient mice bearing human tissue grafts (skin and artery) inoculated with 1 x 10(6) human CD34+ adult hematopoietic stem cells, peripheral blood monuclear cells autologous to the CD34 donor, or both for human cell engraftment.

RESULTS

In the absence of T cells, CD68+ CD14+ macrophages infiltrate allogeneic human skin but produce little injury or thrombosis. Both responses are enhanced when combined with adoptive transfer of T cells autologous to the hematopoietic stem cells as exemplified by the induction of the macrophage activation marker CD163. CD68+ macrophages also infiltrate allogeneic arterial interposition grafts, producing intimal expansion and calcification in the absence of T cells.

CONCLUSIONS

These new models may be used to study the role of human macrophages in transplant rejection and other pathologies in vivo.

Humanized mice for the study of type 1 diabetes and beta cell function

Our understanding of the basic biology of diabetes has been guided by observations made using animal models, particularly rodents. However, humans are not mice, and outcomes predicted by murine studies are not always representative of actual outcomes in the clinic. In particular, investigators studying diabetes have relied heavily on mouse and rat models of autoimmune type 1-like diabetes, and experimental results using these models have not been representative of many of the clinical trials in type 1 diabetes. In this article, we describe the availability of new models of humanized mice for the study of three areas of diabetes. These include the use of humanized mice for the study of (1) human islet stem and progenitor cells, (2) human islet allograft rejection, and (3) human immunity and autoimmunity. These humanized mouse models provide an important preclinical bridge between in vitro studies and rodent models and the translation of discoveries in these model systems to the clinic.

Use of humanized severe combined immunodeficient mice for human vaccine development

The severe combined immunodeficient (SCID) mouse has no adaptive immunity, lacking mature T and B cells in the peripheral blood or the lymphoid organs. It has been used extensively in biomedical research as a valuable translational model for xeno-engraftment of human tissues and cells. This review focuses on the engraftment of human peripheral blood cells and tissues in SCID mice, as well as in the newly established and more permissive SCID mice deficient in the IL-2 receptor gamma-chain. Human immune responses could be elicited and assessed in these humanized SCID mice upon vaccination or sensitization with allogeneic tissues. A translational model is proposed to attain preclinical data for testing human vaccines.

Hepatocyte transplantation in animal models

More than 30 years after the first hepatocyte transplant to treat the Gunn rat, the animal model for Crigler-Najjar syndrome, there are still a number of impediments to hepatocyte transplantation. Numerous animal models are still used in work aimed at improving hepatocyte engraftment and/or long-term function. Although other cell sources, particularly hepatic and extrahepatic stem cells, are being explored, adult hepatocytes remain the cells of choice for the treatment of liver diseases by cell therapy. In recent years, diverse approaches have been developed in various animal models to enhance hepatocyte transduction and amplification in vitro and cell engraftment and functionality in vivo. They have led to significant progress in hepatocyte transplantation for the treatment of patients with metabolic diseases and for bridging patients with acute injury until their own livers regenerate. This review presents and considers the results of this work with a special emphasis on procedures that might be clinically applicable.

Molecular biology of vestibular schwannomas

Recent advances in molecular biology have led to a better understanding of the etiology of vestibular schwannomas. The underlying purpose of vestibular schwannoma research is the development of new treatment options; however, such options have not yet been established. A fundamental understanding of the underlying molecular events leading to tumor formation began when mutations in the neurofibromatosis type 2 (NF2) tumor suppressor gene were identified in vestibular schwannomas. The clinical characteristics of vestibular schwannomas and neurofibromatosis type 2 (NF2) syndromes have both been related to alterations in the NF2 gene. Genetic screening for NF2 is now available. When utilized with clinical screening, such as magnetic resonance imaging (MRI), conventional audiometry, and auditory brainstem response (ABR), the early detection of NF2 can be made, which consequently makes a significant difference in the ability to successfully treat vestibular schwannomas. Additionally, the signaling pathways affected by merlin, the product of the NF2 gene, are becoming better understood. Nf2-transgenic and knockout mice as well as vestibular schwannoma xenograft models are now ready for novel therapeutic testing. Hopefully, better treatment options will be forthcoming soon.

Humanized mouse models to study the human haematopoietic stem cell compartment

The ideal way to assess hematopoietic stem cells is to observe their growth in the endogenous microenvironment where they would receive the appropriate signals. With colonies of inbred mice, it is possible to myeloablate recipients and transplant hematopoietic cells from genetically similar mice and observe the growth of primitive hematopoietic cells in their endogenous environment for a significant proportion (10 months) of an organisms lifespan (29 months average). It is not possible to perform these experiments in humans, but xenotransplantation mouse models provide the closest paradigm for the human hematopoietic environment at the present time.

Genetically modified mouse models in cancer studies

Genetically modified animals represent a resource of immense potential for cancer research. Classically, genetic modifications in mice were obtained through selected breeding experiments or treatments with powerful carcinogens capable of inducing random mutagenesis. A new era began in the early 1980s when genetic modifications by inserting foreign DNA genes into the cells of an animal allowed for the development of transgenic mice. Since that moment, genetic modifications have been able to be made in a predetermined way. Gene targeting emerged later as a method of in vivo mutagenesis whereby the sequence of a predetermined gene is selectively modified within an intact cell. In this review we focus on how genetically modified mice can be created to study tumour development, and how these models have contributed to an understanding of the genetic alterations involved in human cancer. We also discuss the strengths and weaknesses of the different mouse models for identifying cancer genes, and understanding the consequences of their alterations in order to obtain the maximum benefit for cancer patients.

Early development of human hematopoietic and acquired immune systems in new born NOD/Scid/Jak3null mice intrahepatic engrafted with cord blood-derived CD34 + cells

An animal model in which the human immune system can be reconstituted is necessary to study acquired immunity in vivo. We report here a novel model, the NOD/SCID/JAK3(null) mouse, for the human immune system's development. Newborn mice transplanted with human cord blood CD34(+) cells intrahepatically, developed human T and B cells, and myeloid and plasmacytoid dendritic cells. The T and B cells had a naïve to memory phenotype, and included plasma cells. The human acquired immune system can be reconstituted from CD34(+) cells in NOD/SCID/JAK3(null) mice. This model is a powerful tool for the study of human immunity.

Building networks for immunodeficiency diseases and immunology training

The RIKEN Research Center for Allergy and Immunology in Japan is reaching out regionally to the primary immunodeficiency disease community and internationally to graduate students and postdoctoral fellows.

Human BLyS facilitates engraftment of human PBL derived B cells in immunodeficient mice

The production of fully immunologically competent humanized mice engrafted with peripheral lymphocyte populations provides a model for in vivo testing of new vaccines, the durability of immunological memory and cancer therapies. This approach is limited, however, by the failure to efficiently engraft human B lymphocytes in immunodeficient mice. We hypothesized that this deficiency was due to the failure of the murine microenvironment to support human B cell survival. We report that while the human B lymphocyte survival factor, B lymphocyte stimulator (BLyS/BAFF) enhances the survival of human B cells ex vivo, murine BLyS has no such protective effect. Although human B cells bound both human and murine BLyS, nuclear accumulation of NF-κB p52, an indication of the induction of a protective anti-apoptotic response, following stimulation with human BLyS was more robust than that induced with murine BLyS suggesting a fundamental disparity in BLyS receptor signaling. Efficient engraftment of both human B and T lymphocytes in NOD rag1^−/− Prf1^−/− immunodeficient mice treated with recombinant human BLyS is observed after adoptive transfer of human PBL relative to PBS treated controls. Human BLyS treated recipients had on average 40-fold higher levels of serum Ig than controls and mounted a de novo antibody response to the thymus-independent antigens in pneumovax vaccine. The data indicate that production of fully immunologically competent humanized mice from PBL can be markedly facilitated by providing human BLyS.

Silencing HIV-1 In Vivo

RNA interference holds great promise for antiviral therapy, but delivering effective quantities of small interfering RNAs (siRNAs) into the right target cells in vivo represents a major challenge. Kumar et al. (2008) now report a technique to target siRNAs specifically to T cells to suppress viral infection in a humanized mouse model of HIV/AIDS.

The promise of human induced pluripotent stem cells for research and therapy

Induced pluripotent stem (iPS) cells are human somatic cells that have been reprogrammed to a pluripotent state. There are several hurdles to be overcome before iPS cells can be considered as a potential patient-specific cell therapy, and it will be crucial to characterize the developmental potential of human iPS cell lines. As a research tool, iPS-cell technology provides opportunities to study normal development and to understand reprogramming. iPS cells can have an immediate impact as models for human diseases, including cancer

Non-obese diabetic-recombination activating gene-1 (NOD-Rag1 null) interleukin (IL)-2 receptor common gamma chain (IL2r gamma null) null mice: a radioresistant model for human lymphohaematopoietic engraftment

Immunodeficient hosts engrafted with human lymphohaematopoietic cells hold great promise as a preclinical bridge for understanding human haematopoiesis and immunity. We now describe a new immunodeficient radioresistant non-obese diabetic mice (NOD) stock based on targeted mutations in the recombination activating gene-1 (Rag1(null)) and interleukin (IL)-2 receptor common gamma chain (IL2rgamma(null)), and compare its ability to support lymphohaematopoietic cell engraftment with that achieved in radiosensitive NOD.CB17-Prkdc(scid) (NOD-Prkdc(scid)) IL2rgamma(null) mice. We observed that immunodeficient NOD-Rag1(null) IL2rgamma(null) mice tolerated much higher levels of irradiation conditioning than did NOD-Prkdc(scid) IL2rgamma(null) mice. High levels of human cord blood stem cell engraftment were observed in both stocks of irradiation-conditioned adult mice, leading to multi-lineage haematopoietic cell populations and a complete repertoire of human immune cells, including human T cells. Human peripheral blood mononuclear cells also engrafted at high levels in unconditioned adult mice of each stock. These data document that Rag1(null) and scid stocks of immunodeficient NOD mice harbouring the IL2rgamma(null) mutation support similar levels of human lymphohaematopoietic cell engraftment. NOD-Rag1(null) IL2rgamma(null) mice will be an important new model for human lymphohaematopoietic cell engraftment studies that require radioresistant hosts.

Targeting the nuclear antigen 1 of Epstein-Barr virus to the human endocytic receptor DEC-205 stimulates protective T-cell responses

Dendritic cells (DCs) express many endocytic receptors that deliver antigens for major histocompatibility class (MHC) I and II presentation to CD8(+) and CD4(+) T cells, respectively. Here, we show that targeting Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) to one of them, the human multilectin DEC-205 receptor, in the presence of the DC maturation stimulus poly(I:C), expanded EBNA1-specific CD4(+) and CD8(+) memory T cells, and these lymphocytes could control the outgrowth of autologous EBV-infected B cells in vitro. In addition, using a novel mouse model with reconstituted human immune system components, we demonstrated that vaccination with alphaDEC-205-EBNA1 antibodies primed EBNA1-specific IFN-gamma-secreting T cells and also induced anti-EBNA1 antibodies in a subset of immunized mice. Because EBNA1 is the one EBV antigen that is expressed in all proliferating cells infected with this virus, our data suggest that DEC-205 targeting should be explored as a vaccination approach against symptomatic primary EBV infection and against EBV-associated malignancies.

Imaging effector functions of human cytotoxic CD4+ T cells specific for Plasmodium falciparum circumsporozoite protein

Malaria vaccines, comprised of irradiated Plasmodium falciparum sporozoites or a synthetic peptide containing T and B cell epitopes of the circumsporozoite protein (CSP), elicit multifunctional cytotoxic and non-cytotoxic CD4(+) T cells in immunised volunteers. Both lytic and non-lytic CD4(+)T cell clones recognised a series of overlapping epitopes within a 'universal' T cell epitope EYLNKIQNSLSTEWSPCSVT of CSP (NF54 isolate) that was presented in the context of multiple DR molecules. Lytic activity directly correlated with T cell receptor (TCR) functional avidity as measured by stimulation indices and recognition of naturally occurring variant peptides. CD4(+) T cell-mediated cytotoxicity was contact-dependent and did not require de novo synthesis of cytotoxic mediators, suggesting a granule-mediated mechanism. Live cell imaging of the interaction of effector and target cells demonstrated that CD4(+) cytotoxic T cells recognise target cells with their leading edge, reorient their cytotoxic granules towards the zone of contact, and form a stable immunological synapse. CTL attacks induced chromatin condensation, nuclear fragmentation and formation of apoptotic bodies in target cells. Together, these findings suggest that CD4(+) CTLs trigger target cell apoptosis via classical perforin/granzyme-mediated cytotoxicity, similar to CD8(+) CTLs, and these multifunctional sporozoite- and peptide-induced CD4(+) T cells have the potential to play a direct role as effector cells in targeting the exoerythrocytic forms within the liver.

A new immunodeficient hyperglycaemic mouse model based on the Ins2Akita mutation for analyses of human islet and beta stem and progenitor cell function

AIMS/HYPOTHESIS

To develop and validate a new immunodeficient mouse strain that spontaneously develops a non-autoimmune hyperglycaemia to serve as a diabetic host for human islets and human beta stem and progenitor cells without the need for induction of hyperglycaemia by toxic chemicals with their associated side effects.

METHODS

We generated and characterised a new strain of immunodeficient spontaneously hyperglycaemic mice, the NOD-Rag1null Prf1null Ins2Akita strain and compared this strain with the NOD-scid Il2rgammanull (also known as Il2rg) immunodeficient strain rendered hyperglycaemic by administration of a single dose of streptozotocin. Hyperglycaemic mice were transplanted with human islets ranging from 1,000 to 4,000 islet equivalents (IEQ) and were monitored for normalisation of blood glucose levels.

RESULTS

NOD-Rag1null Prf1null Ins2Akita mice developed spontaneous hyperglycaemia, similar to Ins2Akita-harbouring strains of immunocompetent mice. Histological examination of islets in the host pancreas validated the spontaneous loss of beta cell mass in the absence of mononuclear cell infiltration. Human islets transplanted into spontaneously diabetic NOD-Rag1null Prf1null Ins2Akita and chemically diabetic NOD-scid Il2rgammanull mice resulted in a return to euglycaemia that occurred with transplantation of similar beta cell masses.

CONCLUSIONS/INTERPRETATION

The NOD-Rag1null Prf1null Ins2Akita mouse is the first immunodeficient, spontaneously hyperglycaemic mouse strain described that is based on the Ins2Akita mutation. This strain is suitable as hosts for human islet and human beta stem and progenitor cell transplantation in the absence of the need for pharmacological induction of diabetes. This strain of mice also has low levels of innate immunity and can be engrafted with a human immune system for the study of human islet allograft rejection.

Expanded CD34+ human umbilical cord blood cells generate multiple lymphohematopoietic lineages in NOD-scid IL2rgamma(null) mice

Umbilical cord blood (UCB) is increasingly being used for human hematopoietic stem cell (HSC) transplantation in children but often requires pooling multiple cords to obtain sufficient numbers for transplantation in adults. To overcome this limitation, we have used an ex vivo two-week culture system to expand the number of hematopoietic CD34(+) cells in cord blood. To assess the in vivo function of these expanded CD34(+) cells, cultured human UCB containing 1 x 10(6) CD34(+) cells were transplanted into conditioned NOD-scid IL2rgamma(null) mice. The expanded CD34(+) cells displayed short- and long-term repopulating cell activity. The cultured human cells differentiated into myeloid, B-lymphoid, and erythroid lineages, but not T lymphocytes. Administration of human recombinant TNFalpha to recipient mice immediately prior to transplantation promoted human thymocyte and T-cell development. These T cells proliferated vigorously in response to TCR cross-linking by anti-CD3 antibody. Engrafted TNFalpha-treated mice generated antibodies in response to T-dependent and T-independent immunization, which was enhanced when mice were co-treated with the B cell cytokine BLyS. Ex vivo expanded CD34(+) human UCB cells have the capacity to generate multiple hematopoietic lineages and a functional human immune system upon transplantation into TNFalpha-treated NOD-scid IL2rgamma(null) mice.

Immunoglobulin-like transcript 3-Fc suppresses T-cell responses to allogeneic human islet transplants in hu-NOD/SCID mice

OBJECTIVE

The aim of our study was to explore the immunomodulatory activity of soluble immunoglobulin (Ig)-like transcript (ILT) 3-Fc in pancreatic islet transplantation and to determine its mechanism of action.

RESEARCH DESIGN AND METHODS

NOD/SCID mice in which diabetes was induced by streptozotocin injection were transplanted with human pancreatic islet cells. Mice in which the transplant restored euglycemia were humanized with allogeneic peripheral blood mononuclear cells and treated with ILT3-Fc or control human IgG or left untreated. The blood glucose level was monitored twice a week, and rejection was diagnosed after two consecutive readings >350 mg/dl. Tolerated and rejected grafts were studied histologically and by immunostaining for human T-cells and insulin production. CD4 and CD8 T-cells from the spleen were studied for suppressor activity, expression of cytokines, and CD40L.

RESULTS

Although human T-cell engraftment was similar in all groups, ILT3-Fc-treated mice tolerated the islets for the entire period of observation (91 days), whereas control mice rejected the graft within 7 weeks (P < 0.0001). ILT3-Fc treatment suppressed the expression of cytokines and CD40L and induced the differentiation of human CD8(+) T suppressor cells that inhibited Th alloreactivity against graft HLA antigens. T-cells allostimulated in vitro in the presence of ILT3-Fc inhibited CD40L-induced upregulation of CD40 in human pancreatic islet cells. Histochemical studies showed dramatic differences between human pancreatic islets from tolerant, ILT3-Fc-treated mice and control recipients rejecting the grafts.

CONCLUSIONS

The data indicated that ILT3-Fc is a potent immunoregulatory agent that suppressed islet allograft rejection in humanized NOD/SCID mice.

Long-term engraftment and expansion of tumor-derived memory T cells following the implantation of non-disrupted pieces of human lung tumor into NOD-scid IL2Rgamma(null) mice

Non-disrupted pieces of primary human lung tumor implanted into NOD-scid IL2Rgamma(null) mice consistently result in successful xenografts in which tissue architecture, including tumor-associated leukocytes, stromal fibroblasts, and tumor cells are preserved for prolonged periods with limited host-vs-graft interference. Human CD45(+) tumor-associated leukocytes within the xenograft are predominantly CD3(+) T cells with fewer CD138(+) plasma cells. The effector memory T cells that had been shown to be quiescent in human lung tumor microenvironments can be activated in situ as determined by the production of human IFN-gamma in response to exogenous IL-12. Plasma cells remain functional as evidenced by production of human Ig. Significant levels of human IFN-gamma and Ig were detected in sera from xenograft-bearing mice for up to 9 wk postengraftment. Tumor-associated T cells were found to migrate from the microenvironment of the xenograft to the lung, liver, and primarily the spleen. At 8 wk postengraftment, a significant portion of cells isolated from the mouse spleens were found to be human CD45(+) cells. The majority of CD45(+) cells were CD3(+) and expressed a phenotype consistent with an effector memory T cell, consisting of CD4(+) or CD8(+) T cells that were CD45RO(+), CD44(+), CD62L(-), and CD25(-). Following adoptive transfer into non-tumor bearing NOD-scid IL2Rgamma(null) mice, these human T cells were found to expand in the spleen, produce IFN-gamma, and maintain an effector memory phenotype. We conclude that the NOD-scid IL2Rgamma(null) tumor xenograft model provides an opportunity to study tumor and tumor-stromal cell interactions in situ for prolonged periods.

Clinical application of regulatory T cells for treatment of type 1 diabetes and transplantation

Immune regulation is a complex process that depends on the maintenance of self tolerance while retaining robust immune responses against microbes. The emergence of Treg as a central mechanism for immune regulation has generated a new paradigm where Treg-resistant memory T cells and/or "defective" Treg lead to a breakdown in tolerance resulting in immune pathology. In this perspective, we highlight the opportunities and challenges in the field of Treg therapy.

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.