Humanized mice in translational biomedical research

Intra-bone marrow transplantation of human CD34(+) cells into NOD/LtSz-scid IL-2rgamma(null) mice permits multilineage engraftment without previous irradiation

BACKGROUND AIMS

Non-irradiated immunodeficient recipients provide the best physiologic setting for revealing hematopoietic stem cell (HSC) functions after xenotransplantion. An approach that efficiently permits the detection of human hematopoietic repopulating cells in non-irradiated recipients is therefore highly desired.

METHODS

We compared side-by-side the ability to reconstitute hematopoiesis via intra-bone marrow transplantation (IBMT) in three commonly used mouse strains avoiding previous irradiation.

RESULTS

Non-irradiated NOD/SCID and NOD/SCID (beta2m-/- mouse strains prevent engraftment even after IBMT. In contrast, combining the robustness of the NOD/SCID IL-2Rgamma-/- recipient with the sensitivity of IBMT facilitates the detection, without previous host irradiation, of human SCID-repopulating cells 10 weeks after transplantation. The level of chimerism averaged 14% and multilineage engraftment (lymphoid dominant) was observed consistently in all mice. Analysis of injected and non-injected bones, spleen and peripheral blood demonstrated that engrafting cells were capable of in vivo migration and expansion.

CONCLUSIONS

Combining the robustness of the NOD/SCID IL-2Rgamma-/- mouse strain with the sensitivity of IBMT strongly facilitates long-term multilineage engraftment and migration for human CD34(+) cells without the need for previous irradiation.

Humanized mouse models to study human diseases

PURPOSE OF REVIEW

Update on humanized mouse models and their use in biomedical research.

RECENT FINDINGS

The recent description of immunodeficient mice bearing a mutated IL-2 receptor gamma chain (IL2rgamma) facilitated greatly the engraftment and function of human hematolymphoid cells and other cells and tissues. These mice permit the development of human immune systems, including functional T and B cells, following engraftment of hematopoietic stem cells (HSCs). The engrafted functional human immune systems are capable of T and B cell-dependent immune responses, antibody production, antiviral responses, and allograft rejection. Immunodeficient IL2rgamma(null) mice also support heightened engraftment of primary human cancers and malignant progenitor cells, permitting in-vivo investigation of pathogenesis and function. In addition, human-specific infectious agents for which animal models were previously unavailable can now be studied in vivo using these new-generation humanized mice.

SUMMARY

Immunodeficient mice bearing an IL2rgamma(null) mutated gene can be engrafted with functional human cells and tissues, including human immune systems, following engraftment with human hematolymphoid cells. These mice are now used as in-vivo models to study human hematopoiesis, immunity, regeneration, stem cell function, cancer, and human-specific infectious agents without putting patients at risk.

T cells and stromal fibroblasts in human tumor microenvironments represent potential therapeutic targets

The immune system of cancer patients recognizes tumor-associated antigens expressed on solid tumors and these antigens are able to induce tumor-specific humoral and cellular immune responses. Diverse immunotherapeutic strategies have been used in an attempt to enhance both antibody and T cell responses to tumors. While several tumor vaccination strategies significantly increase the number of tumor-specific lymphocytes in the blood of cancer patients, most vaccinated patients ultimately experience tumor progression. CD4+ and CD8+ T cells with an effector memory phenotype infiltrate human tumor microenvironments, but most are hyporesponsive to stimulation via the T cell receptor (TCR) and CD28 under conditions that activate memory T cells derived from the peripheral blood of the cancer patients or normal donors. Attempts to identify cells and molecules responsible for the TCR signaling arrest of tumor-infiltrating T cells have focused largely upon the immunosuppressive effects of tumor cells, tolerogenic dendritic cells and regulatory T cells. Here we review potential mechanisms by which human T cell function is arrested in the tumor microenvironment with a focus on the immunomodulatory effects of stromal fibroblasts. Determining in vivo which cells and molecules are responsible for the TCR arrest in human tumor-infiltrating T cells will be necessary to formulate and test strategies to prevent or reverse the signaling arrest of the human T cells in situ for a more effective design of tumor vaccines. These questions are now addressable using novel human xenograft models of tumor microenvironments.

Th1 and Th17 immunocompetence in humanized NOD/SCID/IL2rgammanull mice

We evaluated the immunocompetence of human T cells in humanized NOD-SCID interleukin (IL)-2r-gamma-null (hu-NSG) mice bearing a human thymic organoid, after multilineage reconstitution with isogeneic human leukocytes. Delayed type hypersensitivity (DTH) response was assessed by a direct footpad challenge of the immunized hu-NSG host, or by transfer of splenocytes from immunized hu-NSG, along with antigen, into footpads of C.B-17 scid mice (trans vivo [tv] DTH). Both methods revealed cellular immunity to tetanus toxoid (TT) or collagen type V (ColV). Immunohistochemical analysis of the swollen footpads revealed infiltration of human CD45(+) cells, including CD3(+) T cells, CD68(+) macrophages, and murine Ly6G(+) neutrophils. We observed a significant correlation between the percentage of circulating human CD4(+) cells and the direct DTH swelling response to TT. The tvDTH response to TT was inhibited by anti-interferon-gamma, whereas the tvDTH response to collagen V was inhibited by anti-IL-17 antibody, mimicking the cytokine bias of adult human T cells to these antigens. hu-NSG mice were also capable of mounting a B-cell response (primarily IgM) to TT antigen. The activation of either Th1- or Th17-dependent cellular immune response supports the utility of hu-NSG mice as a surrogate model of allograft rejection and autoimmunity.

Use of mouse models to study the mechanisms and consequences of RBC clearance

Mice provide tractable animal models for studying the pathophysiology of various human disorders. This review discusses the use of mouse models for understanding red-blood-cell (RBC) clearance. These models provide important insights into the pathophysiology of various clinically relevant entities, such as autoimmune haemolytic anaemia, haemolytic transfusion reactions, other complications of RBC transfusions and immunomodulation by Rh immune globulin therapy. Mouse models of both antibody- and non-antibody-mediated RBC clearance are reviewed. Approaches for exploring unanswered questions in transfusion medicine using these models are also discussed.

NOD-scid IL2rgamma(null) mouse model of human skin transplantation and allograft rejection

BACKGROUND

Transplantation of human skin on immunodeficient mice that support engraftment with functional human immune systems would be an invaluable tool for investigating mechanisms involved in wound healing and transplantation. Nonobese diabetic (NOD)-scid interleukin-2 gamma chain receptor (NSG) readily engraft with human immune systems, but human skin graft integrity is poor. In contrast, human skin graft integrity is excellent on CB17-scid bg (SCID.bg) mice, but they engraft poorly with human immune systems.

METHODS

Human skin grafts transplanted onto immunodeficient NSG, SCID.bg, and other immunodeficient strains were evaluated for graft integrity, preservation of graft endothelium, and their ability to be rejected after engraftment of allogeneic peripheral blood mononuclear cells.

RESULTS

Human skin transplanted onto NSG mice develops an inflammatory infiltrate, consisting predominately of host Gr1(+) cells, that is detrimental to the survival of human endothelium in the graft. Treatment of graft recipients with anti-Gr1 antibody reduces this cellular infiltrate, preserves graft endothelium, and promotes wound healing, tissue development, and graft remodeling. Excellent graft integrity of the transplanted skin includes multilayered stratified human epidermis, well-developed human vasculature, human fibroblasts, and passenger leukocytes. Injection of unfractionated, CD4 or CD8 allogeneic human peripheral blood mononuclear cell induces a rapid destruction of the transplanted skin graft.

CONCLUSIONS

NSG mice treated with anti-Gr1 antibody provide a model optimized for both human skin graft integrity and engraftment of a functional human immune system. This model provides the opportunity to investigate mechanisms orchestrating inflammation, wound healing, revascularization, tissue remodeling, and allograft rejection and can provide guidance for improving outcomes after clinical transplantation.

Current humanized mouse models for studying human immunology and HIV-1 immuno-pathogenesis

A robust animal model for "hypothesis-testing/mechanistic" research in human immunology and immuno-pathology should meet the following criteria. First, it has well-studied hemato-lymphoid organs and target cells similar to those of humans. Second, the human pathogens establish infection and lead to relevant diseases. Third, it is genetically inbred and can be manipulated via genetic, immunological and pharmacological means. Many human-tropic pathogens such as HIV-1 fail to infect murine cells due to the blocks at multiple steps of their life cycle. The mouse with a reconstituted human immune system and other human target organs is a good candidate. A number of human-mouse chimeric models with human immune cells have been developed in the past 20 years, but most with only limited success due to the selective engraftment of xeno-reactive human T cells in hu-PBL-SCID mice or the lack of significant human immune responses in the SCID-hu Thy/Liv mouse. This review summarizes the current understanding of HIV-1 immuno-pathogenesis in human patients and in SIV-infected primate models. It also reviews the recent progress in the development of humanized mouse models with a functional human immune system, especially the recent progress in the immunodeficient mice that carry a defective gammaC gene. NOD/SCID/gammaC(-/-) (NOG or NSG) or the Rag2(-/-)gammaC(-/-) double knockout (DKO) mice, which lack NK as well as T and B cells (NTB-null mice), have been used to reconstitute a functional human immune system in central and peripheral lymphoid organs with human CD34(+) HSC. These NTB-hu HSC humanized models have been used to investigate HIV-1 infection, immuno-pathogenesis and therapeutic interventions. Such models, with further improvements, will contribute to study human immunology, human-tropic pathogens as well as human stem cell biology in the tissue development and function in vivo.

Irrespective of CD34 expression, lineage-committed cell fraction reconstitutes and re-establishes transformed Philadelphia chromosome-positive leukemia in NOD/SCID/IL-2Rgammac-/- mice

Stem cells of acute myeloid leukemia (AML) have been identified as immunodeficient mouse-repopulating cells with a Lin(-)CD34(+)38(-) phenotype similar to normal hematopoietic stem cells. To identify the leukemia-propagating stem cell fraction of Philadelphia chromosome-positive (Ph(+)) leukemia, we serially transplanted human leukemia cells from patients with chronic myeloid leukemia blast crisis (n = 3) or Ph(+) acute lymphoblastic leukemia (n = 3) into NOD/SCID/IL-2Rgammac(-/-) mice. Engrafted cells were almost identical to the original leukemia cells as to phenotypes, IGH rearrangements, and karyotypes. CD34(+)CD38(-)CD19(+), CD34(+)38(+)CD19(+), and CD34(-)CD38(+)CD19(+) fractions could self-renew and transfer the leukemia, whereas the CD34(-)CD38(+)CD19(+) fraction did not stably propagate in NOD/SCID mice. These findings suggest that leukemia-repopulating cells in transformed Ph(+) leukemia are included in a lineage-committed but multilayered fraction, and that CD34(+) leukemia cells potentially emerge from CD34(-) populations.

Human nasal polyp microenvironments maintained in a viable and functional state as xenografts in NOD-scid IL2rgamma(null) mice

OBJECTIVES

The objective was to develop a model with which to study the cellular and molecular events associated with nasal polyp progression. To accomplish this, we undertook to develop a system in which nondisrupted human nasal polyp tissue could be successfully implanted into severely immunocompromised mice, in which the histopathology of the original nasal polyp tissue, including inflammatory lymphocytes, epithelial and goblet cell hyperplasia, and subepithelial fibrosis, could be preserved for prolonged periods.

METHODS

Small, non-disrupted pieces of human nasal polyp tissues were subcutaneously implanted into NOD-scid IL2rgamma(null) mice. Xenografts at 8 to 12 weeks after implantation were examined histologically and immunohistochemically to identify human inflammatory leukocytes and to determine whether the characteristic histopathologic characteristics of the nasal polyps were maintained for a prolonged period. The xenografts, spleen, lung, liver, and kidneys were examined histologically and immunohistochemically and were evaluated for changes in volume. The sera of these mice were assayed for human cytokines and immunoglobulin.

RESULTS

Xenografts of human nasal polyp tissues were established after their subcutaneous implantation into NOD-scid IL2rgamma(null) mice. The xenografts were maintained in a viable and functional state for up to 3 months, and retained a histopathologic appearance similar to that of the original tissue, with a noticeable increase in goblet cell hyperplasia and marked mucus accumulation in the submucosal glands compared to the original nasal polyp tissue. Inflammatory lymphocytes present in the polyp microenvironment were predominantly human CD8+ T cells with an effector memory phenotype. Human CD4+ T cells, CD138+ plasma cells, and CD68+ macrophages were also observed in the xenografts. Human immunoglobulin and interferon-gamma were detected in the sera of xenograft-bearing mice. The polyp-associated lymphocytes proliferated and were found to migrate from the xenografts to the spleens of the recipient mice, resulting in a significant splenomegaly. A progressive increase in the volume of the xenografts was observed with little or no evidence of mouse cell infiltration into the human leukocyte antigen-positive human tissue. An average twofold increase in polyp volume was found at 3 months after engraftment.

CONCLUSIONS

The use of innate and adaptive immunodeficient NOD-scid mice homozygous for targeted mutations in the interleukin-2 receptor gamma-chain locus NOD-scid IL2rgamma(null) for establishing xenografts of nondisrupted pieces of human nasal polyp tissues represents a significant improvement over the previously reported xenograft model that used partially immunoincompetent CB17-scid mice as tissue recipients. The absence of the interleukin-2 receptor gamma-chain results in complete elimination of natural killer cell development, as well as severe impairments in T and B cell development. These mice, lacking both innate and adaptive immune responses, significantly improve upon the long-term engraftment of human nasal polyp tissues and provide a model with which to study how nasal polyp-associated lymphocytes and their secreted biologically active products contribute to the histopathology and progression of this chronic inflammatory disease.

New horizons for studying human hepatotropic infections

The liver serves as a target organ for several important pathogens, including hepatitis B and C viruses (HBV and HCV, respectively) and the human malaria parasites, all of which represent serious global health problems. Because these pathogens are restricted to human hepatocytes, research in small animals has been compromised by the frailty of the current mouse xenotransplantation models. In this issue of the JCI, Bissig et al. demonstrate robust HBV and HCV infection in a novel xenotransplantation model in which large numbers of immunodeficient mice with liver injury were engrafted with significant quantities of human hepatocytes. This technical advance paves the way for more widespread use of human liver chimeric mice and forms the basis for creating increasingly complex humanized mouse models that could prove useful for studying immunopathogenesis and vaccine development against hepatotropic pathogens.

Critical role of natural killer cells in the rejection of human hepatocytes after xenotransplantation into immunodeficient mice

The severe combined immunodeficiency/albumin linked-urokinase type plasminogen activator (SCID/Alb-uPA) human liver chimeric mouse model has added a new dimension to studies of liver based human diseases and has important potential for study of human hepatic drug metabolism. However, it remains unclear if natural killer (NK) cell in SCID/Alb-uPA mice has an important negative impact on engraftment and expansion of human hepatocytes after transplantation. Here, we explore the role of mouse NK cells in the rejection of transplanted human hepatocytes in SCID/Alb-uPA mice. We assessed NK cell activity in vivo, using (125)I-iodo-2'-deoxyuridine incorporation assay. Low serum human alpha-1 antitrypsin (hAAT, <10 microg/ml) recipients, representing graft failure, showed resistance to engraftment of MHC class I knockout marrow (indicating high NK cell activity), while NK cell-depleted low hAAT recipients and high hAAT (>100 microg/ml) recipients accepted MHC class I knockout marrow, indicating a correlation between low NK cell activity, in vivo, and high level human hepatocyte engraftment. We also showed that higher level engraftment of human hepatocytes was achieved in both NK cell-depleted SCID/Alb-uPA mice and Rag2(-/-)gammac(-/-)/Alb-uPA (T,B and NK cell deficient) mice compared with untreated SCID/Alb-uPA mice. These results support a critical role for mouse NK cells in the rejection of human hepatocytes xenotransplanted to immunodeficient mice.

IL-7 enhances thymic human T cell development in "human immune system" Rag2-/-IL-2Rgammac-/- mice without affecting peripheral T cell homeostasis

IL-7 is a central cytokine in the development of hematopoietic cells, although interspecies discrepancies have been reported. By coculturing human postnatal thymus hematopoietic progenitors and OP9-huDL1 stromal cells, we found that murine IL-7 is approximately 100-fold less potent than human IL-7 for supporting human T cell development in vitro. We investigated the role of human IL-7 in newborn BALB/c Rag2(-/-)gamma(c)(-/-) mice transplanted with human hematopoietic stem cells (HSC) as an in vivo model of human hematopoiesis using three approaches to improve IL-7 signaling: administration of human IL-7, ectopic expression of human IL-7 by the transplanted human HSC, or enforced expression of a murine/human chimeric IL-7 receptor binding murine IL-7. We show that premature IL-7 signaling at the HSC stage, before entrance in the thymus, impeded T cell development, whereas increased intrathymic IL-7 signaling significantly enhanced the maintenance of immature thymocytes. Increased thymopoiesis was also observed when we transplanted BCL-2- or BCL-x(L)-transduced human HSC. Homeostasis of peripheral mature T cells in this humanized mouse model was not improved by any of these strategies. Overall, our results provide evidence for an important role of IL-7 in human T cell development in vivo and highlight the notion that IL-7 availability is but one of many signals that condition peripheral T cell homeostasis.

Adult T-cell leukemia/lymphoma development in HTLV-1-infected humanized SCID mice

The molecular and genetic factors induced by human T-lymphotropic virus type-1 (HTLV-1) that initiate adult T-cell leukemia/lymphoma (ATLL) remain unclear, in part from the lack of an animal model that accurately recapitulates leukemogenesis. HTLV-1-infected humanized nonobese diabetic severe combined immunodeficiency (HU-NOD/SCID) mice were generated by inoculation of NOD/SCID mice with CD34(+) hematopoietic progenitor and stem cells (CD34(+) HP/HSCs) infected ex vivo with HTLV-1. HTLV-1-HU-NOD/SCID mice exclusively developed CD4(+) T-cell lymphomas with characteristics similar to ATLL and elevated proliferation of infected human stem cells (CD34(+)CD38(-)) in the bone marrow were observed in mice developing malignancies. Purified CD34(+) HP/HSCs from HTLV-1-infected patient peripheral blood mononuclear cells revealed proviral integrations suggesting viral infection of human bone marrow-derived stem cells. NOD/SCID mice reconstituted with CD34(+) HP/HSCs transduced with a lentivirus vector expressing the HTLV-1 oncoprotein (Tax1) also developed CD4(+) lymphomas. The recapitulation of a CD4(+) T-cell lymphoma in HU-NOD/SCID mice suggests that HSCs provide a viral reservoir in vivo and act as cellular targets for cell transformation in humans. This animal model of ATLL will provide an important tool for the identification of molecular and cellular events that control the initiation and progression of the lymphoma and potential therapeutic targets to block tumor development.

Bioluminescent imaging demonstrates that transplanted human embryonic stem cell-derived CD34(+) cells preferentially develop into endothelial cells

Human embryonic stem cells (hESCs) provide an important resource for novel regenerative medicine therapies and have been used to derive diverse cell populations, including hematopoietic and endothelial cells. However, it remains a challenge to achieve significant engraftment of hESC-derived blood cells when transplanted into animal models. To better understand mechanisms that enhance or limit the in vivo developmental potential of hESC-derived cells, we utilized hESCs that express firefly luciferase (luc) to allow noninvasive, real-time bioluminescent imaging of hESC-derived CD34(+) cells transplanted into the liver of neonatal immunodeficient mice. Serial imaging demonstrated stable engraftment and expansion of the luc(+) hESC-derived cells in vivo over several months. While we found that these hESC-derived CD34(+) cells have bipotential ability to generate both hematopoietic and endothelial lineages in vitro, these studies demonstrate preferential differentiation into endothelial cells in vivo, with only low levels of hematopoietic cell engraftment. Therefore, these studies reveal key differences in the developmental potential of hESC-derived cells using in vitro and in vivo analyses. Although transplanted hESC-derived CD34(+) cells are well-suited for revascularization therapies, additional measures are needed to provide higher levels of long-term hematopoietic engraftment.

Bone marrow-derived human hematopoietic stem cells engraft NOD/SCID mice and traffic appropriately to an inflammatory stimulus in the joint

OBJECTIVE

Studies of human inflammatory arthritis would be significantly aided by the development of better animal models. Our hypothesis is that it is possible to develop humanized arthritis models through novel techniques of hematopoietic stem and progenitor cell (HSPC) delivery.

METHODS

Bone marrow was obtained from patients with osteoarthritis who were undergoing total hip replacement. HSPC were enriched by negative selection and injected into the femur of irradiated anti-CD122 treated nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Human cell engraftment was analyzed by flow cytometry. Arthritis was induced by an intraarticular injection of Chlamydia trachomatis and injected knee joints were examined 5 days later by histology and immunohistochemistry.

RESULTS

Human bone marrow HSPC successfully engrafted NOD/SCID mice, with some mice showing up to 90% engrafted human cells. Human B lymphoid and myeloid cells were detected in the bone marrow and spleen 6 weeks following transfer of HSPC, and engrafted recipient mice remained healthy up to 12 weeks postinjection. Chlamydia-injected mice that had been repopulated with HSPC had synovial inflammation, consisting of human neutrophils and macrophages.

CONCLUSION

Bone marrow-derived human HSPC engraft NOD/SCID mice and traffic appropriately to an inflammatory stimulus in the joint, thus offering the potential for direct studies on the immunopathogenesis and treatment of human arthritis.

Generation of knockout rats with X-linked severe combined immunodeficiency (X-SCID) using zinc-finger nucleases

Background

Although the rat is extensively used as a laboratory model, the inability to utilize germ line-competent rat embryonic stem (ES) cells has been a major drawback for studies that aim to elucidate gene functions. Recently, zinc-finger nucleases (ZFNs) were successfully used to create genome-specific double-stranded breaks and thereby induce targeted gene mutations in a wide variety of organisms including plants, drosophila, zebrafish, etc.

Methodology/Principal Findings

We report here on ZFN-induced gene targeting of the rat interleukin 2 receptor gamma (Il2rg) locus, where orthologous human and mouse mutations cause X-linked severe combined immune deficiency (X-SCID). Co-injection of mRNAs encoding custom-designed ZFNs into the pronucleus of fertilized oocytes yielded genetically modified offspring at rates greater than 20%, which possessed a wide variety of deletion/insertion mutations. ZFN-modified founders faithfully transmitted their genetic changes to the next generation along with the severe combined immune deficiency phenotype.

Conclusions and Significance

The efficient and rapid generation of gene knockout rats shows that using ZFN technology is a new strategy for creating gene-targeted rat models of human diseases. In addition, the X-SCID rats that were established in this study will be valuable in vivo tools for evaluating drug treatment or gene therapy as well as model systems for examining the treatment of xenotransplanted malignancies.

Parameters for establishing humanized mouse models to study human immunity: analysis of human hematopoietic stem cell engraftment in three immunodeficient strains of mice bearing the IL2rgamma(null) mutation

"Humanized" mouse models created by engraftment of immunodeficient mice with human hematolymphoid cells or tissues are an emerging technology with broad appeal across multiple biomedical disciplines. However, investigators wishing to utilize humanized mice with engrafted functional human immune systems are faced with a myriad of variables to consider. In this study, we analyze HSC engraftment methodologies using three immunodeficient mouse strains harboring the IL2rgamma(null) mutation; NOD-scid IL2rgamma(null), NOD-Rag1(null) IL2rgamma(null), and BALB/c-Rag1(null) IL2rgamma(null) mice. Strategies compared engraftment of human HSC derived from umbilical cord blood following intravenous injection into adult mice and intracardiac and intrahepatic injection into newborn mice. We observed that newborn recipients exhibited enhanced engraftment as compared to adult recipients. Irrespective of the protocol or age of recipient, both immunodeficient NOD strains support enhanced hematopoietic cell engraftment as compared to the BALB/c strain. Our data define key parameters for establishing humanized mouse models to study human immunity.

Humanized SFTPA1 and SFTPA2 transgenic mice reveal functional divergence of SP-A1 and SP-A2: formation of tubular myelin in vivo requires both gene products

Surfactant protein A (SP-A) plays a role in lung innate immunity and surfactant-related functions. Two functional genes, SP-A1 (SFTPA1) and SP-A2 (SFTPA2), are present in humans and primates (rodents have one gene). Single gene SP-A1 or SP-A2 proteins expressed in vitro are functional. To study their role in vivo, we generated humanized transgenic (hTG) C57BL/6 mice, SP-A1(6A(4)) and SP-A2(1A(3)). The SP-A cDNA in experimental constructs was driven by the 3.7-kb SP-C promoter. Positive hTG mice were bred with SP-A knock-out mice to generate F8 offspring for study. Epithelial alveolar type II cells were SP-A-positive, and Clara cells were negative by immunohistochemistry in hTG mice. The levels of SP-A in lungs of two hTG lines used were comparable with those in human lungs. Southern blot analysis indicated that two cDNA copies of either SP-A1(6A(4)) or SP-A2(1A(3)) were integrated as a concatemer into the genome of each of the two hTG lines. Electron microscopy analysis revealed that hTG mice with a single SP-A1(6A(4)) or SP-A2(1A(3)) gene product lacked tubular myelin (TM), but hTG mice carrying both had TM. Furthermore, TM was observed in human bronchoalveolar lavage fluid only if both SP-A1 and SP-A2 gene products were present and not in those containing primarily (>99.7%) either SP-A1 or SP-A2 gene products. In vivo rescue study confirmed that TM can only be restored after administering exogenous SP-A containing both SP-A1 and SP-A2 into the lungs of SP-A knock-out mice. These observations indicate that SP-A1 and SP-A2 diverged functionally at least in terms of TM formation.

Bridging mice to men: using HLA transgenic mice to enhance the future prediction and prevention of autoimmune type 1 diabetes in humans

Similar to the vast majority of cases in humans, the development of type 1 diabetes (T1D) in the NOD mouse model is due to T-cell mediated autoimmune destruction of insulin-producing pancreatic beta cells. Particular major histocompatibility complex (MHC) haplotypes (designated HLA in humans and H2 in mice) provide the primary genetic risk factor for T1D development. It has long been appreciated that within the MHC, particular unusual class II genes contribute to the development of T1D in both humans and NOD mice by allowing for the development and functional activation of beta-cell autoreactive CD4 T cells. However, studies in NOD mice have revealed that through interactions with other background susceptibility genes, the quite common class I variants (K(d), D(b)) characterizing this strain's H2 ( g7 ) MHC haplotype aberrantly acquire an ability to support the development of beta cell autoreactive CD8 T-cell responses also essential to T1D development. Similarly, recent studies indicate that in the proper genetic context some quite common HLA class I variants also aberrantly contribute to T1D development in humans. This chapter will focus on how "humanized" HLA transgenic NOD mice can be created and used to identify class I-dependent beta cell autoreactive CD8 T-cell populations of clinical relevance to T1D development. There is also discussion on how HLA transgenic NOD mice can be used to develop protocols that may ultimately be useful for the prevention of T1D in humans by attenuating autoreactive CD8 T-cell responses against pancreatic beta cells.

In vivo modulation of gene expression by lentiviral transduction in "human immune system" Rag2-/- gamma c -/- mice

Over the last two decades, several humanized mouse models have been used to experimentally analyze the function and development of the human immune system. Recent advances have lead to the establishment of new murine-human chimeric models with improved characteristics, both in terms of human engraftment efficiency and in situ multilineage human hematopoietic development. We describe here the use of newborn BALB/c Rag2(-/-)gamma(c) (-/-) mice as recipients of human hematopoietic progenitor cells to produce "human immune system" (HIS) (BALB-Rag/gamma) mice, using human fetal liver progenitors. The two major subsets of the human dendritic cell lineage, namely, BDCA2(+)CD11c(-) plasmacytoid dendritic cells and BDCA2(-)CD11c(+) conventional dendritic cells, can be found in HIS (BALB-Rag/gamma) mice. In order to manipulate the expression of genes of interest, the human hematopoietic progenitor cells can be genetically engineered ex vivo by lentiviral transduction before performing xenograft transplantation. Using this mouse model, the human immune system can be assessed for both fundamental and pre-clinical purposes.

Genetically engineered mouse models in drug discovery research

Genetically modified mouse models have been proven to be a powerful tool in drug discovery. The ability to genetically modify the mouse genome by removing or replacing a specific gene has enhanced our ability to identify and validate target genes of interest. In addition, many human diseases can be mimicked in the mouse and signaling pathways have been shown to be conserved. In spite of these advantages the technology has limitations. In transgenic animals there may be significant heterogeneity among different founders. In knock-out animals the predicted phenotypes are not always readily observed and occasionally a completely novel and unexpected phenotype emerges. To address the latter and ensure that a deep knowledge of the target of interest is obtained, we have developed a comprehensive phenotyping program which has identified novel phenotypes as well as any potential safety concerns which may be associated with a particular target. Finally we continue to explore innovative technologies as they become available such as RNAi for temporal and spatial gene knock-down and humanized models that may better simulate human disease states.

Development of novel major histocompatibility complex class I and class II-deficient NOD-SCID IL2R gamma chain knockout mice for modeling human xenogeneic graft-versus-host disease

Immunodeficient mice have been used as recipients of human peripheral blood mononuclear cells (PBMC) for in vivo analyses of human xeno-graft-versus-host disease (GVHD). This xeno-GVHD model system in many ways mimics the human disease. The model system is established by intravenous or intraperitoneal injection of human PBMC or spleen cells into unconditioned or irradiated immunodeficient recipient mice. Recently, the development of several stocks of immunodeficient Prkdc ( scid ) (scid) and recombination activating 1 or 2 gene (Rag1 or Rag2) knockout mice bearing a targeted mutation in the gene encoding the IL2 receptor gamma chain (IL2rgamma) have been reported. The addition of the mutated IL2rgamma gene onto an immunodeficient mouse stock facilitates heightened engraftment with human PBMC. Stocks of mice with mutations in the IL2rgamma gene have been studied in several laboratories on NOD-scid, NOD-Rag1 ( null ), BALB/c-Rag1 ( null ), BALB/c-Rag2 ( null ), and Stock-H2(d)-Rag2 ( null ) strain backgrounds. Parameters to induce human xeno-GVHD in H2(d)-Rag2 ( null ) IL2rgamma ( null ) mice have been published, but variability in the frequency of disease and kinetics of GVHD were observed. The availability of the NOD-scid IL2rgamma ( null ) stock that engrafts more readily with human PBMC than does the Stock-H2(d)-Rag2 ( null ) IL2rgamma ( null ) stock should lead to a more reproducible humanized mouse model of GVHD and for the use in drug evaluation and validation. Furthermore, GVHD in human PBMC-engrafted scid mice has been postulated to result predominately from a human anti-mouse major histocompatibility complex (MHC) class II reactivity. Our recent development of NOD-scid IL2rgamma ( null ) beta2m ( null ) and NOD-scid IL2rgamma ( null ) Ab ( null ) stocks of mice now make it possible to investigate directly the role of host MHC class I and class II in the pathogenesis of GVHD in humanized mice using NOD-scid IL2rgamma ( null ) stocks that engraft at high levels with human PBMC and are deficient in murine MHC class I, class II, or both classes of MHC molecules.

Therapeutic effects of γ-irradiation in a primary effusion lymphoma mouse model

Primary effusion lymphoma (PEL) is a unique and recently identified non-Hodgkin's lymphoma in immunocompromised individuals. PEL is caused by the Kaposi sarcoma-associated herpes virus/human herpes virus 8 (KSHV/HHV-8) and has a peculiar presentation involving liquid growth in the serous body cavity, chemotherapy resistance and poor prognosis. In search of a new therapeutic modality for PEL, we examined the effect of γ-irradiation on PEL-derived cell lines (BCBL-1, BC-1, and BC-3) in vitro and in vivo. An MTT assay and trypan blue exclusion assay revealed that irradiation significantly suppressed cell proliferation in the PEL cell lines in a dose-dependent manner, and induced apoptosis. The PEL cell lines were relatively radiosensitive compared with other hematological tumor cell lines (Raji, Jurkat, and K562 cells). Inoculation of the BC-3 cell line into the peritoneal cavity of Rag2/Jak3 double-deficient mice led to massive ascites formation, and subcutaneous injection of BCBL-1 led to solid lymphoma formation. Total body irradiation (4 Gy × 2) with bone marrow transplantation resulted in the complete recovery of both types of PEL-inoculated mice. These results suggest that total body irradiation with bone marrow transplantation can be successfully applied for the treatment of chemotherapy-resistant PEL.

Expression of human cytokines dramatically improves reconstitution of specific human-blood lineage cells in humanized mice

Adoptive transfer of human hematopoietic stem cells (HSCs) into mice lacking T, B and natural killer (NK) cells leads to development of human-blood lineage cells in the recipient mice (humanized mice). Although human B cell reconstitution is robust and T cell reconstitution is reasonable in the recipient mice, reconstitution of NK cells and myeloid cells is generally poor or undetectable. Here, we show that the poor reconstitution is mainly the result of a deficiency of appropriate human cytokines that are necessary for the development and maintenance of these cell lineages. When plasmid DNA encoding human IL-15 and Flt-3/Flk-2 ligand were delivered into humanized mice by hydrodynamic tail-vein injection, the expression of the human cytokine lasted for 2 to 3 weeks and elevated levels of NK cells were induced for more than a month. The cytokine-induced NK cells expressed both activation and inhibitory receptors, killed target cells in vitro, and responded robustly to a virus infection in vivo. Similarly, expression of human GM-CSF and IL-4, macrophage colony stimulating factor, or erythropoietin and IL-3 resulted in significantly enhanced reconstitution of dendritic cells, monocytes/macrophages, or erythrocytes, respectively. Thus, human cytokine gene expression by hydrodynamic delivery is a simple and efficient method to improve reconstitution of specific human-blood cell lineages in humanized mice, providing an important tool for studying human immune responses and disease progression in a small animal model.

Pathogenic mechanisms of allergic inflammation: atopic asthma as a paradigm

Prospective studies tracking birth cohorts over periods of years indicate that the seeds for atopic asthma in adulthood are sewn during early life. The key events involve programming of functional phenotypes within the immune and respiratory systems which determine long-term responsiveness to ubiquitous environmental stimuli, particularly respiratory viruses and aeroallergens. A crucial component of asthma pathogenesis is early sensitization to aeroallergens stemming from a failure of mucosal tolerance mechanisms during the preschool years, which is associated with delayed postnatal maturation of a range of adaptive and innate immune functions. These maturational defects also increase risk for severe respiratory infections, and the combination of sensitization and infections maximizes risk for early development of the persistent asthma phenotype. Interactions between immunoinflammatory pathways stimulated by these agents also sustain the disease in later life as major triggers of asthma exacerbations. Recent studies on the nature of these interactions suggest the operation of an infection-associated lung:bone marrow axis involving upregulation of FcERlalpha on myeloid precursor populations prior to their migration to the airways, thus amplifying local inflammation via IgE-mediated recruitment of bystander atopic effector mechanisms. The key participants in the disease process are airway mucosal dendritic cells and adjacent epithelial cells, and transiting CD4(+) effector and regulatory T-cell populations, and increasingly detailed characterization of their roles at different stages of pathogenesis is opening up novel possibilities for therapeutic control of asthma. Of particular interest is the application of genomics-based approaches to drug target identification in cell populations of interest, exemplified by recent findings discussed below relating to the gene network(s) triggered by activation of Th2-memory cells from atopics.

Development of human Graafian follicles following transplantation of human ovarian tissue into NOD/SCID/gammac null mice

PROBLEM

Transplantation of human ovarian cortex into host mice may permit various kinds of challenges in reproductive medicine. A novel immunodeficient mouse strain (NOD/SCID/gammacnull: NOG) has been developed as a host of transplantation of human tissue.

METHOD OF STUDY

Human ovarian cortex was transplanted into various sites of NOG mice and human follicular development was examined by immunohistochemistry.

RESULTS

Transplantation of human ovarian tissue into NOG mice resulted in approximately similar tissue survival and follicle growth as did transplantation into non-obese diabetic-severe combined immunodeficient mice. The human Graafian follicle from NOG mouse expressed the same steroidogenic enzymes as observed in human Graafian follicles, which developed in the human body. The NOG mice's ovarian bursa was better placed for transplantation than the back skin or kidney capsule.

CONCLUSION

These results represent the successful generation and biological confirmation of the human Graafian follicles from the human ovarian cortex in the NOG mice.

Humanized Rag2(-/-)gammac(-/-) (RAG-hu) mice can sustain long-term chronic HIV-1 infection lasting more than a year

HIV-1 infection is characterized by life-long viral persistence and continued decline of helper CD4 T cells. The new generation of humanized mouse models that encompass RAG-hu, hNOG and BLT mice have been shown to be susceptible to HIV-1 infection and display CD4 T cell loss. Productive infection has been demonstrated with both R5 and X4 tropic strains of HIV-1 via direct injection as well as mucosal exposure. However the duration of infection in these mice was evaluated for a limited time lasting only weeks post infection, and it is not established how long the viremia can be sustained, and if the CD4 T cell loss persists throughout the life of the infected humanized mice. In the present study we followed the HIV-1 infected RAG-hu mice to determine the long-term viral persistence and CD4 T cell levels. Our results showed that viremia persists life-long lasting for more than a year, and that CD4 T cell levels display a continuous declining trend as seen in the human. These studies provide a chronic HIV-1 infection humanized mouse model that can be used to dissect viral latency, long-term drug evaluation and immune-based therapies.

From genes to function: the next challenge to understanding multiple sclerosis

Susceptibility to multiple sclerosis is jointly determined by genetic and environmental factors, and progress has been made in defining some of these genetic associations, as well as their possible interactions with the environment. However, definitive proof for the involvement of specific genetic determinants in the disease will only come from studies that examine their functional roles in disease pathogenesis. New and combined approaches are needed to analyse the complexity of gene regulation and the functional contribution of each genetic determinant to disease susceptibility or pathophysiology. These studies should proceed in parallel with the use of genetically defined human populations to explore how both genetic and environmental factors affect the function of the pathways in individuals with and without disease, and how these determine the inherited risk of multiple sclerosis.

Dengue virus markers of virulence and pathogenicity

The increased spread of dengue fever and its more severe form, dengue hemorrhagic fever, have made the study of the mosquito-borne dengue viruses that cause these diseases a public health priority. Little is known about how or why the four different (serotypes 1-4) dengue viruses cause pathology in humans only, and there have been no animal models of disease to date. Therefore, there are no vaccines or antivirals to prevent or treat infection and mortality rates of dengue hemorrhagic fever patients can reach up to 20%. Cases occur mainly in tropical zones within developing countries worldwide, and control measures have been limited to the elimination of the mosquito vectors. Thus, it is imperative that we develop new methods of studying dengue virus pathogenicity. This article presents new approaches that may help us to understand dengue virus virulence and the specific mechanisms that lead to dengue fever and severe disease.

Humanized mice for modeling human infectious disease: challenges, progress, and outlook

Over 800 million people worldwide are infected with hepatitis viruses, human immunodeficiency virus (HIV), and malaria, resulting in more than 5 million deaths annually. Here we discuss the potential and challenges of humanized mouse models for developing effective and affordable therapies and vaccines, which are desperately needed to combat these diseases.

The state of the art: immune-mediated mechanisms of monoclonal antibodies in cancer therapy

A number of antibody products have now become accepted as effective anti-cancer therapies. Despite being mainly designed to act by inhibiting functional tumour antigens, there is increasing evidence that Fc-mediated engagement of the immune system is an important contributor to the efficacy of several of these therapies. The optimisation of this engagement offers the potential not only to augment efficacy against existing targets, but also to exploit non-functional tumour antigens. Antibodies that achieve efficacy wholly or predominantly through Fc-mediated mechanisms, represent rich opportunities for future therapeutics in oncology. This mini review summarises some of the key challenges, which need to be addressed to select the most effective molecules. These include the identification of optimal antibody characteristics and improvement of the drug discovery process, in particular, the relevance and predictive power of existing in vitro and in vivo screening methods. Advances in our understanding of tumour immunobiology and successful application of technologies designed to enhance immune system engagement will further aid this process.

Dengue virus infection and virus-specific HLA-A2 restricted immune responses in humanized NOD-scid IL2rgammanull mice

Background

The lack of a suitable animal model to study viral and immunological mechanisms of human dengue disease has been a deterrent to dengue research.

Methodology/Principal Findings

We sought to establish an animal model for dengue virus (DENV) infection and immunity using non-obese diabetic/severe combined immunodeficiency interleukin-2 receptor γ-chain knockout (NOD-scid IL2rγ^null) mice engrafted with human hematopoietic stem cells. Human CD45⁺ cells in the bone marrow of engrafted mice were susceptible to in vitro infection using low passage clinical and established strains of DENV. Engrafted mice were infected with DENV type 2 by different routes and at multiple time points post infection, we detected DENV antigen and RNA in the sera, bone marrow, spleen and liver of infected engrafted mice. Anti-dengue IgM antibodies directed against the envelope protein of DENV peaked in the sera of mice at 1 week post infection. Human T cells that developed following engraftment of HLA-A2 transgenic NOD-scid IL2rγ^null mice with HLA-A2⁺ human cord blood hematopoietic stem cells, were able to secrete IFN-γ, IL-2 and TNF-α in response to stimulation with three previously identified A2 restricted dengue peptides NS4b 2353_(111–119), NS4b 2423_(181–189), and NS4a 2148_(56–64).

Conclusions/Significance

This is the first study to demonstrate infection of human cells and functional DENV-specific T cell responses in DENV-infected humanized mice. Overall, these mice should be a valuable tool to study the role of prior immunity on subsequent DENV infections.

Improved murine model of malaria using Plasmodium falciparum competent strains and non-myelodepleted NOD-scid IL2Rgammanull mice engrafted with human erythrocytes

Murine models of Plasmodium falciparum malaria may become crucial tools in drug discovery. Here we show that non-myelodepleted NOD-scid IL2Rgamma(null) mice engrafted with human erythrocytes support an infectious burden up to tenfold higher than that supported by engrafted NOD-scid beta2microglobulin(null) mice. The new model was validated for drug discovery and was used to assess the therapeutic efficacy of 4-pyridones, selective inhibitors of P. falciparum cytochrome bc1.

Donor reactive regulatory T cells

PURPOSE OF REVIEW

Donor reactive regulatory T cells (Treg) play an important role in tolerance induction and maintenance in experimental transplant models. In this review we focus on the formation of the donor reactive Treg pool and explore the potential of these cells for therapeutic application in clinical transplantation.

RECENT FINDINGS

Donor reactive Treg can arise by both conversion of alloreactive nonregulatory cells and expansion of naturally occurring Treg (nTreg) cross-reactive with donor alloantigen but the quantitative contribution of each of these pathways is at present unclear. However, the fact that donor reactive Treg can be driven both in vivo and ex vivo by alloantigen challenge of nonregulatory precursors is encouraging as it demonstrates that the functional potential of these cells for use in clinical transplantation will not be limited by fortuitous cross-reactivity between nTreg and donor alloantigens. Treg can be generated in vivo by transplantation or alloantigen challenge in combination with Treg-permissive immunosuppression, or ex vivo by phenotypic selection or by polyclonal or antigen-specific stimulation. A number of ex-vivo protocols exist for the enrichment of Treg in the laboratory and in many cases these cells have demonstrable function both in vitro and in relevant graft-versus-host disease (GVHD) or organ transplant models. The challenge now is to understand the clinical opportunities and limitations that these populations present.

SUMMARY

Combined with appropriate immunosuppression, Treg generated/expanded in vivo or ex vivo may hold the final key to operational tolerance in clinical setting.

High diversity of the immune repertoire in humanized NOD.SCID.gamma c-/- mice

The diversity of the human immune repertoire and how it relates to a functional immune response has not yet been studied in detail in humanized NOD.SCID.gammac(-/-) immunodeficient mice. Here, we used a multiplex PCR on genomic DNA to quantify the combinatorial diversity of all possible V-J rearrangements at the TCR-beta chain and heavy chain Ig locus. We first show that the combinatorial diversity of the TCR-beta chain generated in the thymus was well preserved in the periphery, suggesting that human T cells were not vastly activated in mice, in agreement with phenotypic studies. We then show that the combinatorial diversity in NOD.SCID.gammac(-/-) mice reached 100% of human reference samples for both the TCR and the heavy chain of Ig. To document the functionality of this repertoire, we show that a detectable but weak HLA-restricted cellular immune response could be elicited in reconstituted mice after immunization with an adenoviral vector expressing HCV envelope glycoproteins. Altogether, our results suggest that humanized mice express a diversified repertoire and are able to mount antigen-specific immune responses.

Human peripheral blood leucocyte non-obese diabetic-severe combined immunodeficiency interleukin-2 receptor gamma chain gene mouse model of xenogeneic graft-versus-host-like disease and the role of host major histocompatibility complex

Immunodeficient non-obese diabetic (NOD)-severe combined immune-deficient (scid) mice bearing a targeted mutation in the gene encoding the interleukin (IL)-2 receptor gamma chain gene (IL2rgamma(null)) engraft readily with human peripheral blood mononuclear cells (PBMC). Here, we report a robust model of xenogeneic graft-versus-host-like disease (GVHD) based on intravenous injection of human PBMC into 2 Gy conditioned NOD-scid IL2rgamma(null) mice. These mice develop xenogeneic GVHD consistently (100%) following injection of as few as 5 x 10(6) PBMC, regardless of the PBMC donor used. As in human disease, the development of xenogeneic GVHD is highly dependent on expression of host major histocompatibility complex class I and class II molecules and is associated with severely depressed haematopoiesis. Interrupting the tumour necrosis factor-alpha signalling cascade with etanercept, a therapeutic drug in clinical trials for the treatment of human GVHD, delays the onset and progression of disease. This model now provides the opportunity to investigate in vivo mechanisms of xenogeneic GVHD as well as to assess the efficacy of therapeutic agents rapidly.

Autoregulatory lentiviral vectors allow multiple cycles of doxycycline-inducible gene expression in human hematopoietic cells in vivo

The efficient control of gene expression in vivo from lentiviral vectors remains technically challenging. To analyze inducible gene expression in a human setting, we generated 'human immune system' (HIS) mice by transplanting newborn BALB/c Rag2(-/-)IL-2Rgamma(c)(-/-) immunodeficient mice with human hematopoietic stem cells transduced with a doxycycline-inducible lentiviral vector. We compared several methods of doxycycline delivery to mice, and could accurately measure doxycycline in vivo using a new sensitive detection assay. Two different lentiviral vector designs with constitutive (TRECMV-V14) or autoregulatory (TREAuto-V14) expression of an optimized reverse tetracycline transactivator were used to transduce human hematopoietic stem cells. After transplantation into immunodeficient mice, we analyzed the expression of the green fluorescent protein (GFP) reporter gene in the human hematopoiesis-derived cells that develop and accumulate in the generated HIS mice. We show efficient inducible GFP expression in adult HIS mice containing TREAuto-V14-transduced human cells, whereas GFP expression is poor with the TRECMV-V14 vector. Multiple cycles of doxycycline exposure in the TREAuto-V14 group result in repeated cycles of GFP expression with no loss of intensity. These findings are of major interest for gene therapy and basic research settings that require inducible gene expression.

Male germline and embryonic stem cell lines from NOD mice: efficient derivation of GS cells from a nonpermissive strain for ES cell derivation

The nonobese diabetic (NOD) mouse is a valuable model for human type 1 diabetes and the development of humanized mice. Although the importance of this mouse strain is widely recognized, its usefulness is constrained by the absence of NOD embryonic stem (ES) lines with adequate germline transmission competence. In the present study, we established two germline transmission-competent types of cell lines from NOD mice; these cell lines, male germline stem (GS) cells and ES cells, were derived from NOD spermatogonia and blastocysts, respectively. NOD-GS cells proliferated in vitro and differentiated into mature sperm after transplantation into testis. NOD-ES cell lines were effectively established from NOD blastocysts using culture medium containing inhibitors for fibroblast growth receptor, MEK, and GSK3. Both the NOD-GS and NOD-ES cell lines transmitted their haplotypes to progeny, revealing a novel strategy for gene modification in a pure NOD genetic background. Our results also suggest that the establishment of GS cells is an effective procedure in nonpermissive mouse strains or other species for ES cell derivation.

Potent activity of a nucleoside reverse transcriptase inhibitor, 4'-ethynyl-2-fluoro-2'-deoxyadenosine, against human immunodeficiency virus type 1 infection in a model using human peripheral blood mononuclear cell-transplanted NOD/SCID Janus kinase 3 knockout mice

4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), a recently discovered nucleoside reverse transcriptase inhibitor, exhibits activity against a wide spectrum of wild-type and multidrug-resistant clinical human immunodeficiency virus type 1 (HIV-1) isolates (50% effective concentration, 0.0001 to 0.001 microM). In the present study, we used human peripheral blood mononuclear cell-transplanted, HIV-1-infected NOD/SCID/Janus kinase 3 knockout mice for in vivo evaluation of the anti-HIV activity of EFdA. Administration of EFdA decreased the replication and cytopathic effects of HIV-1 without identifiable adverse effects. In phosphate-buffered saline (PBS)-treated mice, the CD4+/CD8+ cell ratio in the spleen was low (median, 0.04; range, 0.02 to 0.49), while that in mice receiving EFdA was increased (median, 0.65; range, 0.57 to 1.43). EFdA treatment significantly suppressed the amount of HIV-1 RNA (median of 9.0 x 10(2) copies/ml [range, 8.1 x 10(2) to 1.1 x 10(3) copies/ml] versus median of 9.9 x 10(4) copies/ml [range, 8.1 x 10(2) to 1.1 x 10(3) copies/ml]; P < 0.001), the p24 level in plasma (2.5 x 10(3) pg/ml [range, 8.2 x 10(2) to 5.6 x 10(3) pg/ml] versus 2.8 x 10(2) pg/ml [range, 8.2 x 10(1) to 6.3 x 10(2) pg/ml]; P < 0.001), and the percentage of p24-expressing cells in the spleen (median of 1.90% [range, 0.33% to 3.68%] versus median of 0.11% [range, 0.00% to 1.00%]; P = 0.003) in comparison with PBS-treated mice. These data suggest that EFdA is a promising candidate for a new age of HIV-1 chemotherapy and should be developed further as a potential therapy for individuals with multidrug-resistant HIV-1 variants.

Biscoclaurine alkaloid cepharanthine inhibits the growth of primary effusion lymphoma in vitro and in vivo and induces apoptosis via suppression of the NF-kappaB pathway

Primary effusion lymphoma (PEL) is a unique and recently identified non-Hodgkin's lymphoma that was originally identified in patients with AIDS. PEL is caused by the Kaposi sarcoma-associated herpes virus (KSHV/HHV-8) and shows a peculiar presentation involving liquid growth in the serous body cavity and a poor prognosis. As the nuclear factor (NF)-kappaB pathway is activated in PEL and plays a central role in oncogenesis, we examined the effect of a biscoclaurine alkaloid, cepharanthine (CEP) on PEL derived cell lines (BCBL-1, TY-1 and RM-P1), in vitro and in vivo. An methylthiotetrazole assay revealed that the cell proliferation of PEL cell lines was significantly suppressed by the addition of CEP (1-10 microg/ml). CEP also inhibited NF-kappaB activation and induced apoptotic cell death in PEL cell lines. We established a PEL animal model by intraperitoneal injection of BCBL-1, which led to the development of ascites and diffuse infiltration of organs, without obvious solid lymphoma formation, which resembles the diffuse nature of human PEL. Intraperitoneal administration of CEP inhibited ascites formation and diffuse infiltration of BCBL-1 without significant systemic toxicity in this model. These results indicate that NF-kappaB could be an ideal molecular target for treating PEL and that CEP is quite useful as a unique therapeutic agent for PEL.

Restoration of skeletal muscle ischemia-reperfusion injury in humanized immunodeficient mice

BACKGROUND

Ischemia and reperfusion (I/R) of tissue provokes an inflammatory process that is highly dependent on circulating natural immunoglobulin M (IgM) and the complement cascade. In mice, a single IgM specificity produced by peritoneal B cells can initiate reperfusion injury. It is unknown whether humans express natural IgM with a similar specificity. It is also unknown whether pathogenic IgM is produced solely from peritoneal B cells or can also be made by circulating B cells.

METHODS

Immunodeficient mice lacking endogenous immunoglobulin were used. Mice were reconstituted with 0.9% normal saline, human serum, or xenografted human peripheral blood lymphocytes (PBLs) and then subjected to tourniquet-induced hindlimb I/R. Serum human IgM and immunoglobulin G (IgG) were measured by enzyme-linked immunosorbent (ELISA) assay. Skeletal muscle was harvested for injury assessment by histology and for immunohistochemistry.

RESULTS

Immunodeficient mice were protected from skeletal muscle injury after hindlimb I/R. Transfer of human serum restored skeletal muscle damage. Rag2/gammaR-/- mice that were engrafted with human PBL (huPBL-SCID) had high levels of human IgM. huPBL-SCID mice developed significantly more skeletal muscle injury than control saline-treated mice (P < or = .01) and human serum-reconstituted Rag2/gammaR-/- mice (P < or = 0.01). Sham-treated huPBL-SCID mice had no muscle injury, demonstrating that human lymphocyte engraftment did not cause injury in the absence of ischemia. Deposition of human IgM was observed on injured but not sham-injured muscle.

CONCLUSION

Human serum can initiate murine skeletal muscle I/R injury. Circulating human PBL may be a source of pathogenic IgM. The huPBL-SCID mouse may be a useful model to define the specificity of pathogenic human IgM and to test therapeutics for I/R injury.

The utilization of humanized mouse models for the study of human retroviral infections

The development of novel techniques and systems to study human infectious diseases in both an in vitro and in vivo settings is always in high demand. Ideally, small animal models are the most efficient method of studying human afflictions. This is especially evident in the study of the human retroviruses, HIV-1 and HTLV-1, in that current simian animal models, though robust, are often expensive and difficult to maintain. Over the past two decades, the construction of humanized animal models through the transplantation and engraftment of human tissues or progenitor cells into immunocompromised mouse strains has allowed for the development of a reconstituted human tissue scaffold in a small animal system. The utilization of small animal models for retroviral studies required expansion of the early CB-17 scid/scid mouse resulting in animals demonstrating improved engraftment efficiency and infectivity. The implantation of uneducated human immune cells and associated tissue provided the basis for the SCID-hu Thy/Liv and hu-PBL-SCID models. Engraftment efficiency of these tissues was further improved through the integration of the non-obese diabetic (NOD) mutation leading to the creation of NODSCID, NOD/Shi-scid IL2rγ^-/-, and NOD/SCID β2-microglobulin^null animals. Further efforts at minimizing the response of the innate murine immune system produced the Rag2^-/-γ_c^-/- model which marked an important advancement in the use of human CD34+ hematopoietic stem cells. Together, these animal models have revolutionized the investigation of retroviral infections in vivo.

Phenotypic changes of human cells in human-rat liver during partial hepatectomy-induced regeneration

AIM: To examine the human hepatic parenchymal and stromal components in rat liver and the phenotypic changes of human cells in liver of human-rat chimera (HRC) generated by in utero transplantation of human cells during partial hepatectomy (PHx)-induced liver regeneration.

METHODS: Human hepatic parenchymal and stromal components and phenotypic changes of human cells during liver regeneration were examined by flow cytometry, in situ hybridization and immunohistochemistry.

RESULTS: ISH analysis demonstrated human Alu-positive cells in hepatic parenchyma and stroma of recipient liver. Functional human hepatocytes generated in this model potentially constituted human hepatic functional units with the presence of donor-derived human endothelial and biliary duct cells in host liver. Alpha fetoprotein (AFP)⁺, CD34⁺ and CD45⁺ cells were observed in the chimeric liver on day 10 after PHx-induced liver regeneration and then disappeared in PHx group, but not in non-PHx group, suggesting that dynamic phenotypic changes of human cells expressing AFP, CD34 and CD45 cells may occur during the chimeric liver regeneration. Additionally, immunostaining for human proliferating cell nuclear antigen (PCNA) showed that the number of PCNA-positive cells in the chimeric liver of PHx group was markedly increased, as compared to that of control group, indicating that donor-derived human cells are actively proliferated during PHx-induced regeneration of HRC liver.

CONCLUSION: HRC liver provides a tool for investigating human liver regeneration in a humanized animal model.