Primary human immunodeficiency virus type 1 viremia and central nervous system invasion in a novel hu-PBL-immunodeficient mouse strain

Patient-Derived-Xenografts in Mice: A Preclinical Platform for Cancer Research

The use of patient-derived xenografts (PDXs) has dramatically improved drug development programs. PDXs (1) reproduce the pathological features and the genomic profile of the parental tumors more precisely than other preclinical models, and (2) more faithfully predict therapy response. However, PDXs have limitations. These include the inability to completely capture tumor heterogeneity and the role of the immune system, the low engraftment efficiency of certain tumor types, and the consequences of the human-host interactions. Recently, the use of novel mouse strains and specialized engraftment techniques has enabled the generation of "humanized" PDXs, partially overcoming such limitations. Importantly, establishing, characterizing, and maintaining PDXs is costly and requires a significant regulatory, administrative, clinical, and laboratory infrastructure. In this review, we will retrace the historical milestones that led to the implementation of PDXs for cancer research, review the most recent innovations in the field, and discuss future avenues to tackle deficiencies that still exist.

Against all odds: The road to success in the development of human immune reconstitution mice

The mouse genome has a high degree of homology with the human genome, and its physiological, biochemical, and developmental regulation mechanisms are similar to those of humans; therefore, mice are widely used as experimental animals. However, it is undeniable that interspecies differences between humans and mice can lead to experimental errors. The differences in the immune system have become an important factor limiting current immunological research. The application of immunodeficient mice provides a possible solution to these problems. By transplanting human immune cells or tissues, such as peripheral blood mononuclear cells or hematopoietic stem cells, into immunodeficient mice, a human immune system can be reconstituted in the mouse body, and the engrafted immune cells can elicit human-specific immune responses. Researchers have been actively exploring the development and differentiation conditions of host recipient animals and grafts in order to achieve better immune reconstitution. Through genetic engineering methods, immunodeficient mice can be further modified to provide a favorable developmental and differentiation microenvironment for the grafts. From initially only being able to reconstruct single T lymphocyte lineages, it is now possible to reconstruct lymphoid and myeloid cells, providing important research tools for immunology-related studies. In this review, we compare the differences in immune systems of humans and mice, describe the development history of human immune reconstitution from the perspectives of immunodeficient mice and grafts, and discuss the latest advances in enhancing the efficiency of human immune cell reconstitution, aiming to provide important references for immunological related researches.

Biopharmaceutics 4.0, Advanced Pre-Clinical Development of mRNA-Encoded Monoclonal Antibodies to Immunosuppressed Murine Models

Administration of mRNA against SARS-CoV-2 has demonstrated sufficient efficacy, tolerability and clinical potential to disrupt the vaccination field. A multiple-arm, cohort randomized, mixed blind, placebo-controlled study was designed to investigate the in vivo expression of mRNA antibodies to immunosuppressed murine models to conduct efficacy, safety and bioavailability evaluation. Enabling 4.0 tools we reduced animal sacrifice, while interventions were designed compliant to HARRP and SPIRIT engagement: (a) Randomization, blinding; (b) pharmaceutical grade formulation, monitoring; (c) biochemical and histological analysis; and (d) theoretic, statistical analysis. Risk assessment molded the study orientations, according to the ARRIVE guidelines. The primary target of this protocol is the validation of the research hypothesis that autologous translation of Trastuzumab by in vitro transcribed mRNA-encoded antibodies to immunosuppressed animal models, is non-inferior to classical treatments. The secondary target is the comparative pharmacokinetic assessment of the novel scheme, between immunodeficient and healthy subjects. Herein, the debut clinical protocol, investigating the pharmacokinetic/pharmacodynamic impact of mRNA vaccination to immunodeficient organisms. Our design, contributes novel methodology to guide the preclinical development of RNA antibody modalities by resolving efficacy, tolerability and dose regime adjustment for special populations that are incapable of humoral defense.

Three-dimensional human placenta-like bud synthesized from induced pluripotent stem cells

Placental dysfunction is related to the pathogenesis of preeclampsia and fetal growth restriction, but there is no effective treatment for it. Recently, various functional three-dimensional organs have been generated from human induced-pluripotent cells (iPSCs), and the transplantation of these iPSCs-derived organs has alleviated liver failure or diabetes mellitus in mouse models. Here we successfully generated a three-dimensional placental organ bud from human iPSCs. The iPSCs differentiated into various lineages of trophoblasts such as cytotrophoblast-like, syncytiotrophoblast-like, and extravillous trophoblast-like cells, forming organized layers in the bud. Placental buds were transplanted to the murine uterus, where 22% of the buds were successfully engrafted. These iPSC-derived placental organ buds could serve as a new model for the study of placental function and pathology.

Humanized Mice for the Evaluation of Novel HIV-1 Therapies

With the discovery of antiretroviral therapy, HIV-1 infection has transitioned into a manageable but chronic illness, which requires lifelong treatment. Nevertheless, complete eradication of the virus has still eluded us. This is partly due to the virus’s ability to remain in a dormant state in tissue reservoirs, ‘hidden’ from the host’s immune system. Also, the high mutation rate of HIV-1 results in escape mutations in response to many therapeutics. Regardless, the development of novel cures for HIV-1 continues to move forward with a range of approaches from immunotherapy to gene editing. However, to evaluate in vivo pathogenesis and the efficacy and safety of therapeutic approaches, a suitable animal model is necessary. To this end, the humanized mouse was developed by McCune in 1988 and has continued to be improved on over the past 30 years. Here, we review the variety of humanized mouse models that have been utilized through the years and describe their specific contribution in translating HIV-1 cure strategies to the clinic.

Patient-Derived Tumor Xenograft Models: Toward the Establishment of Precision Cancer Medicine

Patient-derived xenografts (PDXs) describe models involving the implantation of patient-derived tumor tissue into immunodeficient mice. Compared with conventional preclinical models involving the implantation of cancer cell lines into mice, PDXs can be characterized by the preservation of tumor heterogeneity, and the tumor microenvironment (including stroma/vasculature) more closely resembles that in patients. Consequently, the use of PDX models has improved the predictability of clinical therapeutic responses to 80% or greater, compared with approximately 5% for existing models. In the future, molecular biological analyses, omics analyses, and other experiments will be conducted using recently prepared PDX models under the strong expectation that the analysis of cancer pathophysiology, stem cells, and novel treatment targets and biomarkers will be improved, thereby promoting drug development. This review outlines the methods for preparing PDX models, advances in cancer research using PDX mice, and perspectives for the establishment of precision cancer medicine within the framework of personalized cancer medicine.

High activation and skewed T cell differentiation are associated with low IL-17A levels in a hu-PBL-NSG-SGM3 mouse model of HIV infection

The humanized NOD/SCID/IL-2 receptor γ-chain^null (NSG) mouse model has been widely used for the study of HIV pathogenesis. Here, NSG mice with transgenic expression of human stem cell factor (SCF), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-3 (NSG-SGM3) were injected with peripheral blood leukocytes (PBL mice) from two HIV-infected (HIV⁺ ) patients who were under anti-retroviral therapy (ART; referred as HIV⁺ mice) or one HIV-seronegative healthy volunteer (HIV^- ). Such mice are either hu-PBL-NSG-SGM3 HIV⁺ or HIV^- mice, depending on the source of PBL. The kinetics of HIV replication and T cell responses following engraftment were evaluated in peripheral blood and secondary lymphoid tissues. High HIV replication and low CD4 : CD8 ratios were observed in HIV⁺ mice in the absence of anti-retroviral therapy (ART). Consistent with high activation and skewed differentiation of T cells from the HIV-infected donor, HIV⁺ mice exhibited a higher T cell co-expression of human leukocyte antigen D-related (HLA-DR) and CD38 than HIV^- mice, as well as a shifted differentiation to a CCR7^- CD45RA⁺ terminal effector profile, even in the presence of ART. In addition, HIV replication and the activation/differentiation disturbances of T cells were associated with decreased plasma levels of IL-17A. Thus, this hu-PBL-NSG-SGM3 mouse model recapitulates some immune disturbances occurring in HIV-infected patients, underlying its potential use for studying pathogenic events during this infection.

Progress in HIV-1 antibody research using humanized mice

PURPOSE OF REVIEW

Recent discoveries of highly potent broadly HIV-1 neutralizing antibodies provide new opportunities to successfully prevent, treat, and potentially cure HIV-1 infection. To test their activity in vivo, humanized mice have been shown to be a powerful model and were used to investigate antibody-mediated prevention and therapy approaches. In this review, we will summarize recent findings in humanized mice that have informed on the potential use of broadly neutralizing antibodies targeting HIV-1 in humans.

RECENT FINDINGS

Humanized mouse models have been used to demonstrate the antiviral efficacy of HIV-1 neutralizing antibodies in vivo. It has been shown that a combination of antibodies can suppress viremia below the limit of detection and targets the HIV-1 reservoir. Moreover, passively administered antibodies and vector-mediated antibody production protect humanized mice from HIV-1 infection. Finally, immunization studies in knock-in/transgenic mice carrying human antibody gene segments have informed on potential vaccination strategies to induce broad and potent HIV-1 neutralizing antibodies.

SUMMARY

Humanized mouse models are of great value for HIV-1 research. They represent a highly versatile in vivo system to investigate novel approaches for HIV-1 prevention and therapy and expedite the critical translation from basic findings to clinical application.

Assessment of human platelet survival in the NOD/SCID mouse model: technical considerations

BACKGROUND

The NOD/SCID mouse model is a unique and sophisticated method to study the survival of human platelets (PLTs) in vivo. Meanwhile, several research groups adopted this model to analyze a wide range of PLT antibodies. Differences exist between the research groups regarding the method of PLT injection, the amount and route of antibody injection, and the preparation of blood samples collected from the animal, making it difficult to compare results between studies.

STUDY DESIGN AND METHODS

We compared the survival of human PLTs infused into NOD/SCID mice via the tail vein or the retro-orbital plexus. The percentage of circulating human PLTs in the mouse circulation was determined by flow cytometry. Murine blood samples were prepared using two different methods: 1) direct fixation of whole blood samples and 2) isolation of PLTs by density gradient centrifugation.

RESULTS

Recovery of human PLTs after tail vein injection was comparable to retro-orbital injection (13% vs. 11% of all circulating PLTs, p = 0.401). However, the survival rate of tail vein-infused PLTs was higher than that of retro-orbitally injected PLTs (median PLT survival after 5 hr 84% vs. 56%, p = 0.025). Moreover, we observed that determination of circulating human PLTs in directly fixed murine whole blood samples shows better reproducibility compared to the density gradient centrifugation method.

CONCLUSIONS

Tail vein injection of human PLTs into the NOD/SCID mice is superior to retro-orbital injection in terms of human PLT survival. Direct fixation of whole blood samples allows better reproducibility of results compared to the density gradient centrifugation method.

Human Cytotoxic T Lymphocyte-Mediated Acute Liver Failure and Rescue by Immunoglobulin in Human Hepatocyte Transplant TK-NOG Mice

Hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTLs) are critical in eliminating infection. We developed an animal model in which HBV-infected human hepatocytes are targeted by HBV-specific CTLs. After HBV inoculation in human hepatocyte-transplanted herpes simplex virus type-1 thymidine kinase-NOG mice, human peripheral blood mononuclear cells (PBMCs) were administered, and albumin, HBV DNA, alanine aminotransferase (ALT), and cytokine levels were analyzed. Histopathological and flow-cytometric analysis of infiltrating human immune cells were performed, and the efficacy of CTL-associated antigen-4 immunoglobulin (CTLA4Ig) against liver damage was evaluated. PBMC treatment resulted in massive hepatocyte damage with elevation of ALT, granzyme A, and gamma interferon and decrease in albumin and HBV DNA. The number of liver-infiltrating human lymphocytes and CD8-positive cells was significantly higher in HBV-infected mice. HBV-specific CTLs were detected by core and polymerase peptide-major histocompatibility complex-tetramer, and the population of regulatory T cells was significantly decreased in HBV-infected mice. Serum hepatitis B surface (HBs) antigen became negative, and HBs antibody appeared. CTLA4Ig treatment strongly inhibited infiltration of mononuclear cells. CTLA4Ig treatment will be used to treat patients who develop severe acute hepatitis B to prevent liver transplantation or lethality. This animal model is useful for virological and immunological analysis of HBV infection and to develop new therapies for severe acute hepatitis B.

IMPORTANCE

Without liver transplantation, some HBV-infected patients will die from severe liver damage due to acute overreaction of the immune system. No effective treatment exists, due in part to the lack of a suitable animal model. An animal model is necessary to investigate the mechanism of hepatitis and to develop therapeutic strategies to prevent acute liver failure in HBV infection. We developed an animal model in which HBV-infected human hepatocytes are targeted by human HBV-specific CTLs. In this model, HBV-infected human hepatocytes were transplanted into severely immunodeficient NOG mice in order to reconstruct elements of the human immune system. Using this model, we found that CTL-associated antigen-4 immunoglobulin was able to suppress damage to HBV-infected hepatocytes, suggesting an approach to treatment. This animal model is useful for virological and immunological analysis of HBV infection and to develop new therapies for severe acute hepatitis B.

Novel enhanced green fluorescent protein-expressing NOG mouse for analyzing the microenvironment of xenograft tissues

The interaction between transplanted cells and host tissues is important for the growth and maintenance of transplanted cells. To analyze the mechanisms of these interactions, a systemic fluorescent protein-expressing mouse is a useful recipient. In this study, we generated a novel NOG strain, which strongly expresses enhanced green fluorescent protein (EGFP; PgkEGFP-NOG), especially in the liver, kidney, gastrointestinal tract, and testis. Because the host tissues expressed EGFP, xenotransplanted human cancer cells were clearly identified as EGFP-negative colonies in PgkEGFP-NOG mice. Immunohistochemical analysis revealed that EGFP-expressing stromal tissues formed a complicated tumor microenvironment within xenograft tissues. Moreover, a similar microenvironment was observed in human iPS cell-derived teratomas. Collectively, these results indicated that a suitable microenvironment is essential for the growth and maintenance of xenotransplanted cells and that PgkEGFP-NOG mice represent a useful animal model for analyzing the mechanisms of microenvironment formation.

Combinatorial assessments of brain tissue metabolomics and histopathology in rodent models of human immunodeficiency virus infection

Metabolites are biomarkers for a broad range of central nervous system disorders serving as molecular drivers and byproducts of disease pathobiology. However, despite their importance, routine measures of brain tissue metabolomics are not readily available based on the requirements of rapid tissue preservation. They require preservation by microwave irradiation, rapid freezing or other methods designed to reduce post mortem metabolism. Our research on human immunodeficiency virus type one (HIV-1) infection has highlighted immediate needs to better link histology to neural metabolites. To this end, we investigated such needs in well-studied rodent models. First, the dynamics of brain metabolism during ex vivo tissue preparation was shown by proton magnetic resonance spectroscopy in normal mice. Second, tissue preservation methodologies were assessed using liquid chromatography tandem mass spectrometry and immunohistology to measure metabolites and neural antigens. Third, these methods were applied to two animal models. In the first, immunodeficient mice reconstituted with human peripheral blood lymphocytes then acutely infected with HIV-1. In the second, NOD scid IL2 receptor gamma chain knockout mice were humanized with CD34+ human hematopoietic stem cells and chronically infected with HIV-1. Replicate infected animals were treated with nanoformulated antiretroviral therapy (nanoART). Results from chronic infection showed that microgliosis was associated with increased myoinostitol, choline, phosphocholine concentrations and with decreased creatine concentrations. These changes were partially reversed with nanoART. Metabolite responses were contingent on the animal model. Taken together, these studies integrate brain metabolomics with histopathology towards uncovering putative biomarkers for neuroAIDS.

Antimicrobial peptide LL-37 produced by HSV-2-infected keratinocytes enhances HIV infection of Langerhans cells

Herpes simplex virus (HSV)-2 shedding is associated with increased risk for sexually acquiring HIV. Because Langerhans cells (LCs), the mucosal epithelium resident dendritic cells, are suspected to be one of the initial target cell types infected by HIV following sexual exposure, we examined whether and how HSV-2 affects HIV infection of LCs. Although relatively few HSV-2/HIV-coinfected LCs were detected, HSV-2 dramatically enhanced the HIV susceptibility of LCs within skin explants. HSV-2 stimulated epithelial cell production of antimicrobial peptides (AMPs), including human β defensins and LL-37. LL-37 strongly upregulated the expression of HIV receptors in monocyte-derived LCs (mLCs), thereby enhancing their HIV susceptibility. Culture supernatants of epithelial cells infected with HSV-2 enhanced HIV susceptibility in mLCs, and this effect was abrogated by blocking LL-37 production. These data suggest that HSV-2 enhances sexual transmission of HIV by increasing HIV susceptibility of LCs via epithelial cell production of LL-37.

Pharmacokinetics and modeling of immune cell trafficking: quantifying differential influences of target tissues versus lymphocytes in SJL and lipopolysaccharide-treated mice

BACKGROUND

Immune cell trafficking into the CNS and other tissues plays important roles in health and disease. Rapid quantitative methods are not available that could be used to study many of the dynamic aspects of immune cell-tissue interactions.

METHODS

We used pharmacokinetics and modeling to quantify and characterize the trafficking of radioactively labeled lymphocytes into brain and peripheral tissues. We used variance from two-way ANOVAs with 2 × 2 experimental designs to model the relative influences of lymphocytes and target tissues in trafficking.

RESULTS

We found that in male CD-1 mice, about 1 in 5,000 intravenously injected lymphocytes entered each gram of brain. Uptake by brain was 2 to 3 times higher in naïve SJL females, but uptake by spleen and clearance from blood was lower, demonstrating a dichotomy in immune cell distribution. Treatment of CD-1 mice with lipopolysaccharide (LPS) increased immune cell uptake into brain but decreased uptake by spleen and axillary nodes.

CONCLUSIONS

Differences in brain uptake and in uptake by spleen between SJL and CD-1 mice were primarily determined by lymphocytes, whereas differences in uptake with LPS were primarily determined by lymphocytes for the brain but by the tissues for the spleen and the axillary lymph node. These results show that immune cells normally enter the CNS and that tissues and immune cells interact in ways that can be quantified by pharmacokinetic models.

The mouse is out of the bag: insights and perspectives on HIV-1-infected humanized mouse models

Human immunodeficiency virus type 1 (HIV-1), which is the causative agent of acquired immunodeficiency syndrome, is a human-specific virus. Because HIV-1 cannot infect and cause disorders in other animals, it has been an arduous struggle to study the dynamics of HIV-1 infection in vivo. To understand and elucidate HIV-1 pathogenesis in vivo, several small animal models for HIV-1 infection have been established and improved over the last 20 years. Recently, a novel murine model, 'humanized mouse', has been generated. A humanized mouse has the potential to maintain human hematopoiesis including human CD4(+) leukocytes and, therefore, is able to support persistent HIV-1 infection in vivo. We herein describe the current state-of-the-art in HIV-1-infected humanized mice and introduce insights and perspectives of their use for HIV-1 studies in vivo.

Dynamics of memory and naïve CD8+ T lymphocytes in humanized NOD/SCID/IL-2Rgammanull mice infected with CCR5-tropic HIV-1

Creating a novel small animal model of HIV-1 infection that can support long-term systemic HIV-1 infection and produce HIV-1-specific immune response has a great benefit for studying HIV-1 pathogenesis in vivo. In the present study, we have generated a humanized mouse, NOG-hCD34 mouse, by transplanting newborn NOD/SCID/IL-2Rgamma(null) mice with human hematopoietic stem cells through hepatic injection. These mice were infected with a CCR5-tropic HIV-1 and were analyzed for plasma viral load, changes in peripheral blood T lymphocytes, and HIV-1-specific antibody production. High level of viral replication, increase in effector/memory CD8(+) T lymphocytes, class-switching to IgG, and production of HIV-1-specific IgGs were observed. Our findings suggest that NOG-hCD34 mice may have a wide variety of application in HIV-1 research.

Comparison of human cord blood engraftment between immunocompromised mouse strains

The nonobese diabetic/severe combined immune deficiency (NOD-scid) xenotransplantation model is the "gold standard" for assaying human hematopoietic stem cell activity. Systematic advancements, such as depletion of natural killer cell activity with anti-CD122 antibody, direct intrafemoral injection, and deletion or truncation of IL2Rgamma, have improved human cell engraftment; however, questions remain whether these mouse models are equivalent or, if not, which model is superior for assaying hematopoietic stem cell activity. To address this, we compared overall engraftment and multilineage differentiation of near-limiting doses of lineage-depleted human umbilical cord blood cells by direct intrafemoral injection into NOD/Lt-scid, NOD/Shi-scid, NOD/Lt-scid/IL2Rgamma(null) (NSG), and NOD/Shi-scid/IL2Rgamma(null) mice. Transplantation into NSG mice generated moderately higher human engraftment levels in bone marrow compared with other strains. At limiting doses, NSG mice of both sexes were 3.6-fold more sensitive in detecting SCID-repopulating cells compared with NOD/Lt-scid mice. However, NSG females exhibited higher engraftment at limiting cell doses, resulting in an overall increase in SCID-repopulating cell detection of 9-fold. Both NSG and NOD/Shi-scid/IL2Rgamma(null) support significantly improved engraftment in peripheral tissues compared with NOD/Lt-scid and NOD/Shi-scid mice, whereas NSG mice provide greater human engraftment in bone marrow than all other strains, especially at limiting doses.

Selective infection of CD4+ effector memory T lymphocytes leads to preferential depletion of memory T lymphocytes in R5 HIV-1-infected humanized NOD/SCID/IL-2Rgammanull mice

To investigate the events leading to the depletion of CD4(+) T lymphocytes during long-term infection of human immunodeficiency virus type 1 (HIV-1), we infected human CD34(+) cells-transplanted NOD/SCID/IL-2Rgamma(null) mice with CXCR4-tropic and CCR5-tropic HIV-1. CXCR4-tropic HIV-1-infected mice were quickly depleted of CD4(+) thymocytes and both CD45RA(+) naïve and CD45RA(-) memory CD4(+) T lymphocytes, while CCR5-tropic HIV-1-infected mice were preferentially depleted of CD45RA(-) memory CD4(+) T lymphocytes. Staining of HIV-1 p24 antigen revealed that CCR5-tropic HIV-1 preferentially infected effector memory T lymphocytes (T(EM)) rather than central memory T lymphocytes. In addition, the majority of p24(+) cells in CCR5-tropic HIV-1-infected mice were activated and in cycling phase. Taken together, our findings indicate that productive infection mainly takes place in the activated T(EM) in cycling phase and further suggest that the predominant infection in T(EM) would lead to the depletion of memory CD4(+) T lymphocytes in CCR5-tropic HIV-1-infected mice.

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.

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.

Comparative study on the effect of human BST-2/Tetherin on HIV-1 release in cells of various species

In this study, we first demonstrate that endogenous hBST-2 is predominantly expressed on the plasma membrane of a human T cell line, MT-4 cells, and that Vpu-deficient HIV-1 was less efficiently released than wild-type HIV-1 from MT-4 cells. In addition, surface hBST-2 was rapidly down-regulated in wild-type but not Vpu-deficient HIV-1-infected cells. This is a direct insight showing that provirus-encoded Vpu has the potential to down-regulate endogenous hBST-2 from the surface of HIV-1-infected T cells. Corresponding to previous reports, the aforementioned findings suggested that hBST-2 has the potential to suppress the release of Vpu-deficient HIV-1. However, the molecular mechanism(s) for tethering HIV-1 particles by hBST-2 remains unclear, and we speculated about the requirement for cellular co-factor(s) to trigger or assist its tethering ability. To explore this possibility, we utilize several cell lines derived from various species including human, AGM, dog, cat, rabbit, pig, mink, potoroo, and quail. We found that ectopic hBST-2 was efficiently expressed on the surface of all analyzed cells, and its expression suppressed the release of viral particles in a dose-dependent manner. These findings suggest that hBST-2 can tether HIV-1 particles without the need of additional co-factor(s) that may be expressed exclusively in primates, and thus, hBST-2 can also exert its function in many cells derived from a broad range of species. Interestingly, the suppressive effect of hBST-2 on HIV-1 release in Vero cells was much less pronounced than in the other examined cells despite the augmented surface expression of ectopic hBST-2 on Vero cells. Taken together, our findings suggest the existence of certain cell types in which hBST-2 cannot efficiently exert its inhibitory effect on virus release. The cell type-specific effect of hBST-2 may be critical to elucidate the mechanism of BST-2-dependent suppression of virus release.

Higher susceptibility of NOG mice to xenotransplanted tumors

The purpose of tumorigenicity testing, as applied not only to cell substrates used for viral vaccine manufacture but also stem cells used for cell-based therapy, is to discriminate between cells that have the capacity to form tumors and cells that do not. Therefore, tumorigenicity testing is essential in assessing the safety of these biological materials. Recently developed NOD/Shi-scid IL2Rg(null) (NOG) mice have been shown to be superior to NOD/Shi-scid (SCID) mice for xenotransplantation of both normal and cancerous cells. To select a suitable mouse strain as a xenogenic host for tumorigenicity testing, we compared the susceptibility of NOG (T, B, and NK cell-defective), SCID (T and B cell-defective), and the traditionally used nude (T cell-defective) mice to tumor formation from xenotransplanted HeLa S3 cells. When 10(4) HeLa S3 cells were subcutaneously inoculated into the flanks of these mice, the tumor incidence on day 22 was 10/10 (100%) in NOG, 2/10 (20%) in SCID, and 0/10 (0%) in nude mice. The subcutaneous tumors formed reproducibly and semiquantitatively in a dose-dependent manner. Unexpectedly, half of the NOG mice (5/10) that had been inoculated with a mere 10(1) HeLa S3 cells formed progressively growing subcutaneous tumors on day 78. We confirmed that the engrafted tumors originated from inoculated HeLa S3 cells by immunohistochemical staining with anti-HLA antibodies. These data suggest that NOG mice may be the best choice as a suitable strain for testing tumorigenicity.

Establishment of a humanized model of liver using NOD/Shi-scid IL2Rgnull mice

Severely immunodeficient NOD/Shi-scid IL2Rg(null) (NOG) mice are used as recipients for human tissue transplantation, which produces chimeric mice with various types of human tissue. NOG mice expressing transgenic urokinase-type plasminogen activator in the liver (uPA-NOG) were produced. Human hepatocytes injected into uPA-NOG mice repopulated the recipient livers with human cells. The uPA-NOG model has several advantages over previously produced chimeric mouse models of human liver: (1) the severely immunodeficient NOG background enables higher xenogeneic cell engraftment; (2) the absence of neonatal lethality enables mating of homozygotes, which increased the efficacy of homozygote production; and (3) donor xenogeneic human hepatocytes could be readily transplanted into young uPA-NOG mice, which provide easier surgical manipulation and improved recipient survival.

Babesia rodhaini: the protective effect of pyruvate kinase deficiency in mice

Despite the evidence suggesting that mouse pyruvate kinase (PK) deficiency provides protection against malaria in rodents, there has been no investigation of a parallel protective effect against babesiosis caused by Babesia rodhaini. Here, we examined whether a PK-deficient co-isogenic mouse strain (CBA-Pk-1(slc)) was protected against B. rodhaini infection. We demonstrated that deficiency in pyruvate kinase correlated with a significant protective effect, with survival rates of 50%, 58% and 56% in groups inoculated with 10, 10(3) and 10(5) parasitized erythrocytes, respectively. In contrast, control CBA (CBA-Pk-1(+)) mice exhibited 100% lethality, regardless of the infectious dose. In addition, CBA-Pk-1(slc) mice showed decreased levels of parasitemia when compared to CBA-Pk-1(+) mice, in groups given 10, 10(3) or 10(5) parasitized erythrocytes. These results indicate that similar to PK deficiency in rodents, PK deficiency in mice affects the in vivo growth of B. rodhaini and protects the mice from lethal babesiosis.

Basic concept of development and practical application of animal models for human diseases

The "humanized mouse" is a mouse harboring functioning human tissues used as in vivo human models for both physiological and pathological conditions. The NOD/Shi-scid IL2rgamma(null) (NOG) mouse, an excellent immunodeficient mouse used as the basis for the humanized mouse, requires strict genetic and environmental control for production and use in experiments. Genetic control using marker-assisted selection is described. In addition, NOG mice are easily affected by microbiological and proximate environmental factors, which can cause severe damage to the mice in some cases. Therefore, rigorous microbiological and environmental controls are necessary to ensure reproducibility of experimental results. At the end of this chapter, future aspects of the application of "humanized mice" based on novel super-immunodeficient mice such as NOG mice and Rag2(null) IL2rgamma(null) mice in biomedical research and testing are briefly reviewed.

Humanized mice for human retrovirus infection

Inbred mice with specific genetic defects have greatly facilitated the analysis of complex biological events. Several humanized mouse models using the C.B.-17 scid/scid mouse (referred to as the SCID mouse) have been created from two transplantation protocols, and these mice have been utilized for the investigation of human immunodeficiency virus type 1 (HIV-1) and human T-lymphotropic virus type I (HTLV-I) pathogenesis and the evaluation of antiviral compounds. To generate a more prominent small animal model for human retrovirus infection, especially for examination of the pathological process and the immune reaction, a novel immunodeficient mouse strain derived from the NOD SCID mouse was created by backcrossing with a common gamma chain (gamma(c))-knockout mouse. The NOD-SCID gamma(c)null (NOG) mouse has neither functional T and B cells nor NK cells and has been used as a recipient in humanized mouse models for transplantation of human immune cells particularly including hematopoietic stem cells (HSC). From recent advances in development of humanized mice, we are now able to provide a new version of the animal model for human retrovirus infection and human immunity.

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

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

Modulation of human immunodeficiency virus type 1 infectivity through incorporation of tetraspanin proteins

Accumulating evidence indicates that human immunodeficiency virus type 1 (HIV-1) acquires various cellular membrane proteins in the lipid bilayer of the viral envelope membrane. Although some virion-incorporated cellular membrane proteins are known to potently affect HIV-1 infectivity, the virological functions of most virion-incorporated membrane proteins remain unclear. Among these host proteins, we found that CD63 was eliminated from the plasma membranes of HIV-1-producing T cells after activation, followed by a decrease in the amount of virion-incorporated CD63, and in contrast, an increase in the infectivity of the released virions. On the other hand, we found that CD63 at the cell surface was preferentially embedded on the membrane of released virions in an HIV-1 envelope protein (Env)-independent manner and that virion-incorporated CD63 had the potential to inhibit HIV-1 Env-mediated infection in a strain-specific manner at the postattachment entry step(s). In addition, these behaviors were commonly observed in other tetraspanin proteins, such as CD9, CD81, CD82, and CD231. However, L6 protein, whose topology is similar to that of tetraspanins but which does not belong to the tetraspanin superfamily, did not have the potential to prevent HIV-1 infection, despite its successful incorporation into the released particles. Taken together, these results suggest that tetraspanin proteins have the unique potential to modulate HIV-1 infectivity through incorporation into released HIV-1 particles, and our findings may provide a clue to undiscovered aspects of HIV-1 entry.

Humanized NOD/SCID/IL2Rgamma(null) mice transplanted with hematopoietic stem cells under nonmyeloablative conditions show prolonged life spans and allow detailed analysis of human immunodeficiency virus type 1 pathogenesis

In a previous study, we demonstrated that humanized NOD/SCID/IL2Rgamma(null) (hNOG) mice constructed with human hematopoietic stem cells (HSCs) allow efficient human immunodeficiency virus type 1 (HIV-1) infection. However, HIV-1 infection could be monitored for only 43 days in the animals due to their short life spans. By transplanting HSCs without any myeloablation methods, the mice successfully survived longer than 300 days with stable engraftment of human cells. The mice showed high viremia state for more than the 3 months examined, with systemic HIV-1 infection and gradual decrease of CD4+ T cells analogous to that in humans. These capacities of the hNOG mice are very attractive for modeling mechanisms of AIDS progression and therapeutic strategy.

Human platelets circulating in mice: applications for interrogating platelet function and survival, the efficacy of antiplatelet therapeutics, and the molecular basis of platelet immunological disorders

Herein we describe a novel animal model for examining the survival and function of human platelets following their circulation in non-obese diabetic/severe combined immunodeficient mice. Resting human platelets in platelet-rich plasma are introduced into the retro-orbital plexus, where they are absorbed with high efficiency and circulate for up to 2 days, comprising 10-20% of total circulating platelets. During this period of time, the human platelets can be exposed to a number of biochemical and immunochemical reagents, including novel antithrombotic compounds, or human antiplatelet antibodies that have been implicated in platelet destruction, activation or clearance. Platelets can also be subjected to a variety of storage conditions before infusion, and their relative survival and function following storage and circulation compared. The ability to evaluate in living mice the in vivo function and survival of circulating human platelets may prove valuable for determining mechanisms of antibody-mediated platelet passivation, and aid in the development of novel antiplatelet therapeutics.

Hematopoietic stem cell–engrafted NOD/SCID/IL2Rγnull mice develop human lymphoid systems and induce long-lasting HIV-1 infection with specific humoral immune responses

Critical to the development of an effective HIV/AIDS model is the production of an animal model that reproduces long-lasting active replication of HIV-1 followed by elicitation of virus-specific immune responses. In this study, we constructed humanized nonobese diabetic/severe combined immunodeficiency (NOD/SCID)/interleukin-2 receptor γ-chain knockout (IL2Rγnull) (hNOG) mice by transplanting human cord blood–derived hematopoietic stem cells that eventually developed into human B cells, T cells, and other monocytes/macrophages and 4 dendritic cells associated with the generation of lymphoid follicle–like structures in lymphoid tissues. Expressions of CXCR4 and CCR5 antigens were recognized on CD4+ cells in peripheral blood, the spleen, and bone marrow, while CCR5 was not detected on thymic CD4+ T cells. The hNOG mice showed marked, long-lasting viremia after infection with both CCR5- and CXCR4-tropic HIV-1 isolates for more than the 40 days examined, with R5 virus–infected animals showing high levels of HIV-DNA copies in the spleen and bone marrow, and X4 virus–infected animals showing high levels of HIV-DNA copies in the thymus and spleen. Furthermore, we detected both anti–HIV-1 Env gp120– and Gag p24–specific antibodies in animals showing a high rate of viral infection. Thus, the hNOG mice mirror human systemic HIV infection by developing specific antibodies, suggesting that they may have potential as an HIV/AIDS animal model for the study of HIV pathogenesis and immune responses.

Optimization and functional effects of stable short hairpin RNA expression in primary human lymphocytes via lentiviral vectors

Specific, potent, and sustained short hairpin RNA (shRNA)-mediated gene silencing is crucial for the successful application of RNA interference technology to therapeutic interventions. We examined the effects of shRNA expression in primary human lymphocytes (PBLs) using lentiviral vectors bearing different RNA polymerase III promoters. We found that the U6 promoter is more efficient than the H1 promoter for shRNA expression and for reducing expression of CCR5 in PBLs. However, shRNA expression from the U6 promoter resulted in a gradual decline of the transduced cell populations. With one CCR5 shRNA this decline could be attributed to elevated apoptosis but another CCR5 shRNA that caused cytotoxicity did not show evidence of apoptosis, suggesting sequence-specific mechanisms for cytotoxicity. In contrast to the U6 promoter, PBLs transduced by vectors expressing shRNAs from the H1 promoter could be maintained without major cytotoxic effects. Since a lower level of shRNA expression appears to be advantageous to maintaining the shRNA-transduced population, lentiviral vectors bearing the H1 promoter are more suitable for stable transduction and expression of shRNA in primary human T lymphocytes. Our results suggest that functional shRNA screens should include tests for both potency and adverse metabolic effects upon primary cells.

Isolation of a human erythrocyte-adapted substrain of Babesia rodhaini and analysis of the merozoite surface protein gene sequences

Babesia rodhaini is a rodent hemoparasite closely related to B. microti, the major causative agent of human babesiosis. We tested the infectivity of B. rodhaini for human erythrocytes by using the SCID mouse model in which the circulating erythrocytes were replaced with those of humans. Initially, parasites grew very poorly in the mouse model, but a variant capable of propagating in human erythrocytes emerged after an adaptation period of three weeks. In an attempt to identify parasite proteins involved in the alteration of host cell preference, an expression cDNA library of B. rodhaini was constructed and screened with immune mouse sera. Although we were able to obtain three merozoite surface protein (MSP) genes, sequences of these genes from both the parental strain and human erythrocyte-adapted substrain were identical. Our results suggest that B. rodhaini has potential ability to infect human erythrocytes, but development of this ability may not be brought about by an amino acid change in MSPs.

Mouse models for HIV-1 infection

The generation of small animal models, which preserve the ability for the generation of primary and memory immune responses of the engrafted human immune cells and in which a robust HIV-1 infection may occur, may enable the rapid screening, development and evaluation of HIV-1 protective vaccines and adjuvants. This manuscript reviews the existing mouse HIV-1 models used to study virologic, immunologic and pathogenic aspects of HIV-1 infection and disease and discusses their limitations and advantages, especially in the context of vaccine development, with special focus on the recently developed Trimera-HIV-1 animal model.

Evidence that the species barrier of human immunodeficiency virus-1 does not extend to uptake by the blood--brain barrier: comparison of mouse and human brain microvessels

HIV-1 within the CNS produces a neuroAIDS syndrome and may act as a reservoir for reinfection of the peripheral tissues. Study of how HIV-1 crosses the blood-brain barrier (BBB) has been hampered by the lack of nonprimate animal models. However, BBB transport of HIV-1 does not involve any of the known steps conferring species specificity, including binding to CD4 receptors. In vivo and in vitro studies show that HIV-1 and its glycoprotein coat, gp120, are taken up and transported across the BBB of the mouse. Here, we compared the ability of gp120 and HIV-1 to be taken up by isolated brain microvessels (IBM) freshly isolated from mice, from post-mortem human brain, and from mice that had been treated in a manner analogous to the human material (mouse post-mortem). Freshly isolated mouse IBM took up more gp120 and HIV-1 than the human or mouse post-mortem cells. We found no difference between the ability of mouse post-mortem and human IBM to take up either gp120 or HIV-1. Wheatgerm agglutinin has been previously shown to stimulate gp120 and HIV-1 uptake by the BBB; here, it stimulated the uptake of gp120 and of HIV-1 by both mouse post-mortem and human IBM, although stimulated uptake was greatest for fresh mouse IBM. These results show that the mouse can be used to study the initial phases of HIV-1 uptake by the BBB.

Human dendritic cells transduced with herpes simplex virus amplicons encoding human immunodeficiency virus type 1 (HIV-1) gp120 elicit adaptive immune responses from human cells engrafted into NOD/SCID mice and confer partial protection against HIV-1 challenge

Small-animal models are needed to test human immunodeficiency virus (HIV) vaccine efficacy following viral challenge. To this end, we examined HIV-1-specific immune responses following immunization of nonobese diabetic-severe combined immunodeficient mice that were repopulated with human peripheral blood lymphocytes (hu-PBL-NOD/SCID mice). Autologous dendritic cells (DC) were transduced ex vivo with replication-defective, helper virus-free, herpes simplex virus type 1 (HSV-1) amplicons that expressed HIV-1 gp120 and were then injected into the hu-PBL-NOD/SCID mice. This resulted in primary HIV-1-specific humoral and cellular immune responses. Serum samples from vaccinated animals contained human immunoglobulin G that reacted with HIV-1 Env proteins by enzyme-linked immunosorbent assay and neutralized the infectivity of HIV-1 LAI and ADA strains. T cells isolated from the mice responded to viral antigens by producing gamma interferon when analyzed by enzyme-linked immunospot assay. Importantly, exposure of the vaccinated animals to infectious HIV-1 demonstrated partial protection against infectious HIV-1 challenge. This was reflected by a reduction in HIV-1(ADA) and by protection of the engrafted human CD4(+) T lymphocytes against HIV-1(LAI)-induced cytotoxicity. These data demonstrate that transduction of DC by HSV amplicon vectors expressing HIV-1 gp120 induce virus-specific immune responses in hu-PBL-NOD/SCID mice. This mouse model may be a useful tool to evaluate human immune responses and protection against viral infection following vaccination.

Potent anti-R5 human immunodeficiency virus type 1 effects of a CCR5 antagonist, AK602/ONO4128/GW873140, in a novel human peripheral blood mononuclear cell nonobese diabetic-SCID, interleukin-2 receptor gamma-chain-knocked-out AIDS mouse model

We established human peripheral blood mononuclear cell (PBMC)-transplanted R5 human immunodeficiency virus type 1 isolate JR-FL (HIV-1(JR-FL))-infected, nonobese diabetic-SCID, interleukin 2 receptor gamma-chain-knocked-out (NOG) mice, in which massive and systemic HIV-1 infection occurred. The susceptibility of the implanted PBMC to the infectivity and cytopathic effect of R5 HIV-1 appeared to stem from hyperactivation of the PBMC, which rapidly proliferated and expressed high levels of CCR5. When a novel spirodiketopiperazine-containing CCR5 inhibitor, AK602/ONO4128/GW873140 (molecular weight, 614), was administered to the NOG mice 1 day after R5 HIV-1 inoculation, the replication and cytopathic effects of R5 HIV-1 were significantly suppressed. In saline-treated mice (n = 7), the mean human CD4(+)/CD8(+) cell ratio was 0.1 on day 16 after inoculation, while levels in mice (n = 8) administered AK602 had a mean value of 0.92, comparable to levels in uninfected mice (n = 7). The mean number of HIV-RNA copies in plasma in saline-treated mice were approximately 10(6)/ml on day 16, while levels in AK602-treated mice were 1.27 x 10(3)/ml (P = 0.001). AK602 also significantly suppressed the number of proviral DNA copies and serum p24 levels (P = 0.001). These data suggest that the present NOG mouse system should serve as a small-animal AIDS model and warrant that AK602 be further developed as a potential therapeutic for HIV-1 infection.

In Vitro Methods in the Study of Viral and Prion Permeability Across the Blood–Brain Barrier

(1) Infectious agents capable of entering the central nervous system (CNS) produce some of the most dreaded diseases known to man. The infectious agent within the CNS is often protected by the blood-brain barrier (BBB), shielded from endogenous and exogenous anti-infectious agents. (2) The use of in vitro methods offers many advantages to the study of how infectious agents interact with the BBB. Two such agents which negotiate the BBB early in the course of disease before damage to the BBB are the autoimmune deficiency syndrome virus, or human immunodeficiency virus 1, and scrapie prion. Our laboratories have used in vitro methods to study these agents. (3) Here, we review some of the results form our laboratories and those of others.

Mouse serum factor(s) down-modulate the CD4 and CXCR4 molecules on human T cells conferring resistance to HIV infection in NOG mice

Human cells have developed innate immunity, exploiting several means to block virus infection, and viruses have evolved diverse strategies to resist these. We show here that the human immunodeficiency virus 1 (HIV-1) could neither progressively infect engrafted human leukemic T cells nor repress their growth in NOG mice. However, ED-40515(-) cells infected with HIV-1 before inoculation were found to significantly delay the onset of tumor growth and increased the survival period of NOG mice. ED-40515(-) tumor cells showed resistance to HIV-1 which was apparently correlated with the down-regulation of CD4 and CXCR4 molecules in NOG mice. Serum from three different mouse strains, including NOG, retained a suppressive effect on the CD4 molecule of ED-40515(-) cells in vitro. ED-40515(-) cells obtained from mice re-expressed CD4 and CXCR4 molecules upon in vitro culture and were again successfully infected with HIV-1. These findings indicate that HIV-1 may initially successfully delay or regress tumor growth in NOG mice, but eventually fails to do so because of the evolution of HIV-resistant cells due to a rapid down-modulation of CD4 and CXCR4. Our data also demonstrated that some unknown soluble factor(s) present in mouse serum was responsible for conferring resistance to HIV infection to human T cells.

Binding, internalization, and membrane incorporation of human immunodeficiency virus-1 at the blood-brain barrier is differentially regulated

Human immunodeficiency virus (HIV)-1 within the CNS induces neuro-acquired immunodeficiency syndrome and acts as a reservoir for reinfection of peripheral tissues. HIV-1 crosses the blood-brain barrier (BBB) within infected immune cells and as cell-free virus by a CD4-independent mechanism. Which proteins control free virus transport across the BBB are unknown, but work with wheatgerm agglutinin (WGA) and heparin suggests that heparan sulfate proteoglycans, sialic acid, and N-acetyl-beta-D-glucosaminyl acid bind HIV-1. Here, we found that an HIV-1 T-tropic virus was taken up by mouse brain endothelial cells in vitro and crossed the BBB in vivo and could be effluxed as intact virus. Uptake was stimulated by WGA and protamine sulfate (PS) and inhibited by heparin. BBB uptake of virus involved four distinguishable binding sites: i) reversible cell surface binding involving gp120 and sensitive to PS/heparin but insensitive to WGA; internalization with a ii) WGA-sensitive site binding gp120 and iii) a PS/heparin-sensitive site not involving gp120; iv) membrane incorporation not affected by WGA, heparin, or PS. In conclusion, binding, internalization, and membrane incorporation are separately regulated steps likely determining whether HIV-1 is incorporated into brain endothelial cells, transported across them, or returned to the circulation.

U.S.-Type Babesia microti Isolated from Small Wild Mammals in Eastern Hokkaido, Japan

Our previous report demonstrated that small wild rodents in Japan harbored two types of novel Babesia microti-like parasites (Kobe and Hobetsu types), but not the type widely distributed throughout the temperate zones of North American and Eurasian Continents (U.S. type). In this study, we surveyed small wild mammals collected at various places in the northern part of Japan, seeking for U.S.-type B. microti. A total of 197 small mammals comprising 10 species, Apodemus speciosus, A. argenteus, Clethrionomys rufocanus, C. rutilus, Eothenomys andersoni, Microtus montebelli, Tamias sibiricus, Sorex unguiculatus, S. caecutiens, and Urotrichus talpoides, were examined. Babesia parasites were detected in A. speciosus, C. rufocanus, C. rutilus, M. montebelli, S. unguiculatus, and S. caecutiens by microscopy of blood smears and by PCR targeting babesial nuclear small-subunit rRNA (rDNA) and beta-tubulin genes. Inoculation of their bloods into experimental animals gave rise to 23 parasite isolates, which included 16 from A. speciosus, 4 from C. rufocanus, and 1 each from C. rutilus, M. montebelli and S. unguiculatus. Sequencing analyses of their rDNA and beta-tubulin genes revealed that, of the 23 isolates, 20 and 3 were of Hobetsu and U.S. types, respectively. The U.S.-type B. microti strains isolated in Japan, however, were distinguishable from the isolates in the United States when their beta-tubulin gene sequences and antigen profiles in Western blots were compared. We conclude that U.S.-type B. microti exists in Japan although it has been genetically and antigenically diversified from that distributed in the United States. The results also suggest that not only rodents, but also some insectivores may serve as reservoirs for the agent of human babesiosis.

Induction of protective immune responses against R5 human immunodeficiency virus type 1 (HIV-1) infection in hu-PBL-SCID mice by intrasplenic immunization with HIV-1-pulsed dendritic cells: possible involvement of a novel factor of human CD4(+) T-cell origin

The potential of a dendritic cell (DC)-based vaccine against human immunodeficiency virus type 1 (HIV-1) infection in humans was explored with SCID mice reconstituted with human peripheral blood mononuclear cells (PBMC). HIV-1-negative normal human PBMC were transplanted directly into the spleens of SCID mice (hu-PBL-SCID-spl mice) together with autologous mature DCs pulsed with either inactivated HIV-1 (strain R5 or X4) or ovalbumin (OVA), followed by a booster injection 5 days later with autologous DCs pulsed with the same respective antigens. Five days later, these mice were challenged intraperitoneally with R5 HIV-1(JR-CSF). Analysis of infection at 7 days postinfection showed that the DC-HIV-1-immunized hu-PBL-SCID-spl mice, irrespective of the HIV-1 isolate used for immunization, were protected against HIV-1 infection. In contrast, none of the DC-OVA-immunized mice were protected. Sera from the DC-HIV-1- but not the DC-OVA-immunized mice inhibited the in vitro infection of activated PBMC and macrophages with R5, but not X4, HIV-1. Upon restimulation with HIV-1 in vitro, the human CD4(+) T cells derived from the DC-HIV-1-immunized mice produced a similar R5 HIV-1 suppressor factor. Neutralizing antibodies against human RANTES, MIP-1alpha, MIP-1beta, alpha interferon (IFN-alpha), IFN-beta, IFN-gamma, interleukin-4 (IL-4), IL-10, IL-13, IL-16, MCP-1, MCP-3, tumor necrosis factor alpha (TNF-alpha), or TNF-beta failed to reverse the HIV-1-suppressive activity. These results show that inactivated HIV-1-pulsed autologous DCs can stimulate splenic resident human CD4(+) T cells in hu-PBL-SCID-spl mice to produce a yet-to-be-defined, novel soluble factor(s) with protective properties against R5 HIV-1 infection.

Complete reconstitution of human lymphocytes from cord blood CD34+ cells using the NOD/SCID/gammacnull mice model

Establishment of an assay capable of generating all classes of human lymphocytes from hematopoietic stem cells (HSCs) will provide new insight into the mechanism of human lymphopoiesis. We report ontogenic, functional, and histologic examination results of reconstituted human lymphocytes in NOD/SCID/ gammacnull mice after the transplantation of human cord blood (CB) CD34+ cells. After transplantation, human B, natural killer (NK), and T cells were invariably identified in these mice, even though no human tissues were cotransplanted. Immature B cells resided mainly in bone marrow (BM), whereas mature B cells with surface immunoglobulins were preferentially found in spleen. NK cells were identified in BM and spleen. T cells were observed in various lymphoid organs, but serial examinations after transplantation confirmed human T lymphopoiesis occurring in the thymus. These human lymphocytes were also functionally competent. Human immunoglobulin M (IgM), IgA, and IgG were detected in the sera of these mice. T cells showed a diverse repertoire of T-cell-receptor Vbeta (TCR Vbeta) chains, proliferated in response to phytohemagglutinin, and were cytotoxic against cell lines. NK activity was demonstrated using the K562 cell line. Immunohistochemical analysis revealed that human lymphocytes formed organized structures in spleen and thymus that were analogous to those seen in humans. In the thymus, CD4 and CD8 double-positive T cells were predominant and coexpressed CD1a and Ki-67, thereby supporting the notion that T lymphopoiesis was taking place. NOD/SCID/ gammacnull mice provide a unique model to investigate human lymphopoiesis without the cotransplantation of human tissues.

Spontaneous and rapid reexpression of functional CXCR4 by human steady-state peripheral blood CD34+ cells

Although only 5% of steady-state peripheral blood (PB) CD34+ cells were found to express chemokine receptor CXCR4, 45% of the cells became CXCR4+ after incubation at 37 degrees C for 4 hours. In contrast, there were no remarkable differences between PB CD34+ cells before and after the 37 degrees C incubation in their expression of selectin ligand, VLA-4, and VLA-5 or in their affinity for VCAM-1 or fibronectin. This increase in CXCR4 expression level was inhibited by the addition of brefeldin A, actinomycin D, or cycloheximide. When PB CD34+ cells with CXCR4 expression levels enhanced by a 4-hour preincubation at 37 degrees C or bone marrow (BM) CD34+ cells were exposed overnight to stromal cell-derived factor 1 (SDF-1), the expression levels of CXCR4 were greatly reduced, and when SDF-1 was removed, CXCR4 levels were thereafter up-regulated. The reexpressed CXCR4 was able to elicit integrin-dependent migration of hematopoietic progenitor cells. There was no difference in the severe combined immunodeficient mouse repopulating cell activity between PB CD34+ cells with and cells without a 37 degrees C preincubation.

Immunohistochemical localization of steroidogenic enzymes in human follicle following xenotransplantation of the human ovarian cortex into NOD-SCID mice

There have been reports of successful follicular growth following xenogenic transplantation of the human ovarian cortex into immunodeficient mice. In this study, we examined the immunohistochemical expression and localization of steroidogenic enzymes in the graft of nonpathological human ovary following xenogenic transplantation into nonobese diabetic severe combined immune deficient (NOD-SCID) mice. We studied human follicles following xenotransplantation into NOD-SCID mice using immunohistochemistry antibodies against the cell proliferation marker (Ki 67), steroidogenic enzymes P450 cholesterol side chain cleavage (P450 scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), cytochrome P450 17alpha hydroxylase (P450 c17), cytochrome P450 aromatase (P450 arom), androgen receptor (AR), estrogen receptor (ER), and Ad4-binding protein (Ad4BP), a transcription factor for all steroidogenic P450 genes. In the pre-antral follicles of these grafts, Ki 67 and Ad4BP were detected in both the theca and granulosa cell layer. P450 scc, P450 c17, 3beta-HSD, and AR were present in only the theca cell layer, observations of which were consistent with the findings of nonpathological human ovarian cortex. P450 arom and ER were not detected in these grafts, however, and these follicles did not possess any specific feature of a dominant follicle. These findings suggest that the expression of steroidogenic enzymes in human follicles following xenogenic transplantation into NOD-SCID mice is similar to that of nonpathological human ovaries. However, these follicles do not possess any features of dominant follicles, which are known to develop into the corpus luteum.

Tunica interna endothelial cell kinase expression and hematopoietic and angiogenic potentials in cord blood CD34+ cells

Tunica interna endothelial cell kinase (TEK) is expressed in both hematopoietic and endothelial cells and plays a crucial role in hematopoiesis and angiogenesis in mouse development. In humans, however, little is known about the hematopoietic and angiogenic potentials of TEK-expressing cells in umbilical cord blood (CB) cells, which originate during the human fetal period. We therefore compared the hematopoietic and angiogenic abilities of CB CD34+TEK+ and CD34+TEK- cells by using a clonogenic assay and xenotransplantation into immunodeficient NOD/SCID mice. The results showed that colony-forming cells and cells capable of repopulating in NOD/SCID mice were present in both CD34+TEK+ and CD34+TEK- cells and that the hematopoietic activities of the cell types were similar. In contrast, the potential to differentiate into endothelial cells in vivo was greater in the CD34+TEK+ cells. All NOD/SCID mice engrafted with CD34+TEK+ cells had human CD31-expressing and VE-cadherin-expressing endothelial cells in the vessels of the ischemic muscles and/ or human endothelial cells expressing CD31, kinase-insert domain-containing receptor, and endothelial nitric oxide synthase in liver sinusoidal cells, whereas such endothelial cells were detected in only 3 of the 7 recipients engrafted with CD34+TEK- cells. This result has important implications in cell therapy using CB cells for treating hematopoietic disorders and vascular diseases.

Tumor necrosis factor-related apoptosis-inducing ligand induces neuronal death in a murine model of HIV central nervous system infection

HIV-1 infection in the brain induces neuronal apoptosis leading to HIV-associated dementia. To explore the underlying mechanism, we developed a murine model by using human peripheral blood mononuclear cell (PBMC)-transplanted nonobese diabetic (NOD)-severe combined immunodeficiency (SCID) (hu-PBMC-NOD-SCID) mice. Administration of lipopolysaccharide (LPS) to HIV-1-infected hu-PBMC-NOD-SCID mice induced infiltration of HIV-1-infected human cells into the perivascular region of the brain and neuronal apoptosis was found in macrophage (M)-tropic but not T cell (T)-tropic HIV-1-infected brains. The apoptotic neurons were frequently colocalized with the HIV-1-infected macrophages that expressed tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL). Administration of a neutralizing antibody against human TRAIL but not human TNF-alpha or Fas ligand (FasL) blocked the neuronal apoptosis in the HIV-1-infected brain. These results strongly suggest a critical contribution of TRAIL expressed on HIV-1-infected macrophages to neuronal apoptosis.