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

Mechanisms underlying HIV-associated cognitive impairment and emerging therapies for its management

People living with HIV are affected by the chronic consequences of neurocognitive impairment (NCI) despite antiretroviral therapies that suppress viral replication, improve health and extend life. Furthermore, viral suppression does not eliminate the virus, and remaining infected cells may continue to produce viral proteins that trigger neurodegeneration. Comorbidities such as diabetes mellitus are likely to contribute substantially to CNS injury in people living with HIV, and some components of antiretroviral therapy exert undesirable side effects on the nervous system. No treatment for HIV-associated NCI has been approved by the European Medicines Agency or the US Food and Drug Administration. Historically, roadblocks to developing effective treatments have included a limited understanding of the pathophysiology of HIV-associated NCI and heterogeneity in its clinical manifestations. This heterogeneity might reflect multiple underlying causes that differ among individuals, rather than a single unifying neuropathogenesis. Despite these complexities, accelerating discoveries in HIV neuropathogenesis are yielding potentially druggable targets, including excessive immune activation, metabolic alterations culminating in mitochondrial dysfunction, dysregulation of metal ion homeostasis and lysosomal function, and microbiome alterations. In addition to drug treatments, we also highlight the importance of non-pharmacological interventions. By revisiting mechanisms implicated in NCI and potential interventions addressing these mechanisms, we hope to supply reasons for optimism in people living with HIV affected by NCI and their care providers.

Use of Hu-PBL Mice to Study Pathogenesis of Human-Restricted Viruses

Different humanized mouse models have been developed to study human diseases such as autoimmune illnesses, cancer and viral infections. These models are based on the use of immunodeficient mouse strains that are transplanted with human tissues or human immune cells. Among the latter, mice transplanted with hematopoietic stem cells have been widely used to study human infectious diseases. However, mouse models built upon the transplantation of donor-specific mature immune cells are still under development, especially in the field of viral infections. These models can retain the unique immune memory of the donor, making them suitable for the study of correlates of protection upon natural infection or vaccination. Here, we will review some of these models and how they have been applied to virology research. Moreover, the future applications and the potential of these models to design therapies against human viral infections are discussed.

Methamphetamine and Cannabis: A Tale of Two Drugs and their Effects on HIV, Brain, and Behavior

HIV infection and drug use intersect epidemiologically, and their combination can result in complex effects on brain and behavior. The extent to which drugs affect the health of persons with HIV (PWH) depends on many factors including drug characteristics, use patterns, stage of HIV disease and its treatment, comorbid factors, and age. To consider the range of drug effects, we have selected two that are in common use by PWH: methamphetamine and cannabis. We compare the effects of methamphetamine with those of cannabis, to illustrate how substances may potentiate, worsen, or even buffer the effects of HIV on the CNS. Data from human, animal, and ex vivo studies provide insights into how these drugs have differing effects on the persistent inflammatory state that characterizes HIV infection, including effects on viral replication, immune activation, mitochondrial function, gut permeability, blood brain barrier integrity, glia and neuronal signaling. Moving forward, we consider how these mechanistic insights may inform interventions to improve brain outcomes in PWH. This review summarizes literature from clinical and preclinical studies demonstrating the adverse effects of METH, as well as the potentially beneficial effects of cannabis, on the interacting systemic (e.g., gut barrier leakage/microbial translocation, immune activation, inflammation) and CNS-specific (e.g., glial activation/neuroinflammation, neural injury, mitochondrial toxicity/oxidative stress) mechanisms underlying HIV-associated neurocognitive disorders.

CCR5 editing by Staphylococcus aureus Cas9 in human primary CD4+ T cells and hematopoietic stem/progenitor cells promotes HIV-1 resistance and CD4+ T cell enrichment in humanized mice

BACKGROUND

The chemokine receptor CCR5, which belongs to the superfamily of G protein-coupled receptors, is the major co-receptor for HIV-1 entry. Individuals with a homozygous CCR5Δ32 mutation have a long lasting and increased resistance to HIV-1 infection. Therefore, CCR5 represents an optimal target for HIV-1/AIDS gene therapy. The CRISPR/Cas9 system has been developed as one of the most efficacious gene editing tools in mammalian cells and the small-sized version from Staphylococcus aureus (SaCas9) has an advantage of easier delivery compared to the most commonly used version from Streptococcus pyogenes Cas9 (SpCas9).

RESULTS

Here, we demonstrated that CCR5 could be specifically and efficiently edited by CRISPR/SaCas9 together with two sgRNAs, which were identified through a screening of 13 sgRNAs. Disruption of CCR5 expression by lentiviral vector-mediated CRISPR/SaCas9 led to increased resistance against HIV-1 infection in human primary CD4+ T cells. Moreover, humanized mice engrafted with CCR5-disrupted CD4+ T cells showed selective survival and enrichment when challenged with CCR5 (R5)-tropic HIV-1 in comparison to mock-treated CD4+ T cells. We also observed CCR5 could be targeted by CRISPR/SaCas9 in human CD34+ hematopoietic stem/progenitor cells without obvious differentiation deficiencies.

CONCLUSIONS

This work provides an alternative approach to disrupt human CCR5 by CRISPR/SaCas9 for a potential gene therapy strategy against HIV-1/AIDS.

The Preconditioning of Busulfan Promotes Efficiency of Human CD133+ Cells Engraftment in NOD Shi-SCID IL2Rγcnull (NOG) Mice via Intra-Bone Marrow Injection

Human CD133⁺ stem cells were injected into the bone marrow cavity of NOG (NOD Shi-SCID IL2Rγc^null) mice with or without preconditioning of busulfan in order to assess the efficiency of human CD133⁺ cells engraftment. Peripheral blood from CD133⁺-engrafted NOG mice was analyzed by flow cytometry. The results showed that human CD19⁺ B lymphocytes could be detected at 4 weeks post-transplantation, and human CD4⁺, CD8⁺ subsets of T lymphocytes, CD19^– CD14^– HLA-DR⁺ DCs and CD19^– CD14⁺ monocytes could be detected at 16 weeks post-transplantation. The survival rate of mice in busulfan-untreated group (100%) was slightly higher than that in the busulfan-pretreated group (83%) (P > 0.05). However, the differentiation efficiency of CD133⁺ stem cells in busulfan-pretreated group was significantly higher than that in the untreated group (P < 0.05). This data imply that CD133⁺ cells could be a good resource for a humanized mouse model, and the preconditioning of busulfan could be more conducive to accelerating the differentiation of human CD133⁺ cells in NOG mice by intra-bone marrow injection.

Humanized Mouse Models of Rheumatoid Arthritis for Studies on Immunopathogenesis and Preclinical Testing of Cell-Based Therapies

Rodent models of rheumatoid arthritis (RA) have been used over decades to study the immunopathogenesis of the disease and to explore intervention strategies. Nevertheless, mouse models of RA reach their limit when it comes to testing of new therapeutic approaches such as cell-based therapies. Differences between the human and the murine immune system make it difficult to draw reliable conclusions about the success of immunotherapies. To overcome this issue, humanized mouse models have been established that mimic components of the human immune system in mice. Two main strategies have been pursued for humanization: the introduction of human transgenes such as human leukocyte antigen molecules or specific T cell receptors, and the generation of mouse/human chimera by transferring human cells or tissues into immunodeficient mice. Recently, both approaches have been combined to achieve more sophisticated humanized models of autoimmune diseases. This review discusses limitations of conventional mouse models of RA-like disease and provides a closer look into studies in humanized mice exploring their usefulness and necessity as preclinical models for testing of cell-based therapies in autoimmune diseases such as RA.

Raltegravir blocks the infectivity of red-fluorescent-protein (mCherry)-labeled HIV-1JR-FL in the setting of post-exposure prophylaxis in NOD/SCID/Jak3-/- mice transplanted with human PBMCs

Employing NOD/SCID/Jak3-/- mice transplanted with human PBMCs (hNOJ mice) and replication-competent, red-fluorescent-protein (mCherry; mC)-labeled HIV-1JR-FL (HIVmC), we examined whether early antiretroviral treatment blocked the establishment of HIV-1 infection. The use of hNOJ mice and HIVmC enabled us to visually locate infection foci and to examine the early dynamics of HIVmC infection without using a large amount of antiretroviral unlike in non-human primate models. Although when raltegravir (RAL) administration was begun 1 day after intraperitoneal (ip) inoculation of HIVmC, no plasma p24 or plasma HIV-1-RNA (pRNA) were detected in 10 of 12 hNOJ (hNOJmCRAL+) mice as assessed on the last day of the 14-day continuous twice-daily RAL administration, all 10 untreated hNOJmC (hNOJmCRAL-) mice became positive for p24 and pRNA and had significantly swollen lymph nodes in peritoneal cavity and abundant p24+/mC+/CD3+/CD4+ T cells and p24+/mC+/CD68+ monocytes/macrophages were identified in their omenta and mesenteric lymphoid tissues/lymph nodes upon necropsy of the mice on day 14. In 12 hNOJmCRAL+ mice, no significantly swollen lymph nodes were seen compared to hNOJmCRAL- mice; however, in the omentum of the 2 hNOJmCRAL+ mice that were positive for pRNA and in site RNA, mC+/p24+/CD3+/CD83+ cells were identified, suggesting that viral breakthrough occurred later in the observation period. The present data suggest that the use of hNOJ mouse model and HIVmC may shed light on the study of early-phase dynamics of HIV-1 infection and cellular events in post-exposure/pre-exposure prophylaxis.

Transgenic mice expressing HIV-1 envelope protein gp120 in the brain as an animal model in neuroAIDS research

HIV-1 infection causes injury to the central nervous system (CNS) and is often associated with neurocognitive disorders. One model for brain damage seen in AIDS patients is the transgenic (tg) mouse expressing a soluble envelope protein gp120 of HIV-1 LAV in the brain in astrocytes under the control of the promoter of glial fibrillary acidic protein. These GFAP-gp120tg mice manifest several key neuropathological features observed in AIDS brains, such as decreased synaptic and dendritic density, increased numbers of activated microglia, and pronounced astrocytosis. Several recent studies show that brains of GFAP-gp120tg mice and neurocognitively impaired HIV patients share also a significant number of differentially regulated genes, activation of innate immunity and other cellular signaling pathways, disturbed neurogenesis, and learning deficits. These findings support the continued relevance of the GFAP-gp120tg mouse as a useful model to investigate neurodegenerative mechanisms and develop therapeutic strategies to mitigate the consequences associated with HIV infection of the CNS, neuroAIDS, and HAND.

Early phase dynamics of traceable mCherry fluorescent protein-carrying HIV-1 infection in human peripheral blood mononuclear cells-transplanted NOD/SCID/Jak3-/- mice

We attempted to elucidate early-phase dynamics of HIV-1 infection using replication-competent, red-fluorescent-protein (mCherry)-labeled HIV-1JR-FL (HIVJR-FLmC) and NOD/SCID/Jak3-/- mice transplanted with Individual-A's human peripheral blood mononuclear cells (hPBMC)(hNOJ mice). On day 7 following HIVJR-FLmC inoculation, mCherry-signal-emitting infection foci were readily identified in the subserosa of 10 of 10 HIVJR-FLmC-inoculated hNOJ mice, although infection foci were not located without the mCherry signal in unlabeled HIV-1JR-FL-inoculated mice (n = 6). Even on day 14, infection foci were hardly located in the unlabeled HIV-1JR-FL-inoculated mice, while in all of 7 HIVJR-FLmC-inoculated hNOJ mice examined, mCherry-signal-emitting lymph nodes were easily identified, in which active viral replication was present. On day 14, a significantly larger number of mesenteric lymph nodes were seen in HIVJR-FLmC-exposed hNOJ mice than in HIVJR-FLmC-unexposed mice (P = 0.0025). The weights of mesenteric lymph nodes of those HIVJR-FLmC-exposed hNOJ mice were also greater than those of HIVJR-FLmC-unexposed mice (P = 0.0005). When hNOJ mice were inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, significantly greater viremia was seen than in cell-free HIVJR-FLmC-inoculated hNOJ mice as examined on day 7. In the lymph nodes of those mice inoculated with HIVJR-FLmC-exposed hPBMC from Individual-B, a substantial number of Individual-B's HIVJR-FLmC-infected cells were identified together with Individual-A's cells as examined on day 14. The present HIVJR-FLmC-infected mouse model represents the first system reported using traceable HIVJR-FLmC and human target cells, not using SIV or simian cells, which should be of utility in studies of early-phases of HIV-1 transmission and in evaluating the effects of potential agents for post-exposure and pre-exposure prophylaxis.

Creation of an immunodeficient HLA-transgenic mouse (HUMAMICE) and functional validation of human immunity after transfer of HLA-matched human cells

Research on human immunology has been hindered by the lack of optimal small animal models, given that the protective immune responses of human and non-human species show significant differences. However, due to ethical constraints[1] and the high cost of clinical trials, it is urgent to improve the current animal models that can mimic faithfully human physiology, particularly the human immune system (HIS). HIS mice had been generated recently by engrafting human hematopoietic stem cells (hHSCs) or human peripheral mononuclear cells (hPBMCs) into highly immuno-deficient mice such as NSG, NOG or NRG mice. However, a major experimental drawback for studies using these models is the rapid onset of Graft-versus-Host Disease (GvHD). In the present study, we overcome this limitation by generating new immuno-deficient mice named "HUMAMICE" (HLA-A2^+/+/DR1^+/+/H-2-β₂m^-/-/IAβ^-/-/Rag2^-/-/IL2rγ^-/-/Perf^-/- mice), which expressed human HLA molecules instead of mouse MHC molecules (H-2), and whose immuno-deficient status was reversed by transferring functional HLA-matched PBMCs thus producing mice with an immuno-competent status with a functional human immune system. We showed that in this HLA-matched context, the hPBMC-transfer led to high lymphocytes engraftment rates without GvHD over three months in this novel mouse model. Furthermore, to evaluate the utility of the hPBMC-HUMAMICE, we immunized them with commercial vaccine of Hepatitis B virus (HBsAg, Hepvac@) which resulted in robust and reproducible production of high levels of HBsAg-specific antibodies, implying that both transferred T and B lymphocytes were functional in HUMAMICE. These responses are comparable to those observed in human clinical trials with this identical vaccine. In conclusion, these findings indicated that the HLA-matched-hPBMC-HUMAMICE represents a promising model for dissecting human immune responses in various human diseases, including infectious diseases, cancers and tumors, and to facilitate the development of novel vaccines and cellular therapies.

Improvements and Limitations of Humanized Mouse Models for HIV Research: NIH/NIAID "Meet the Experts" 2015 Workshop Summary

The number of humanized mouse models for the human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) and other infectious diseases has expanded rapidly over the past 8 years. Highly immunodeficient mouse strains, such as NOD/SCID/gamma chain(null) (NSG, NOG), support better human hematopoietic cell engraftment. Another improvement is the derivation of highly immunodeficient mice, transgenic with human leukocyte antigens (HLAs) and cytokines that supported development of HLA-restricted human T cells and heightened human myeloid cell engraftment. Humanized mice are also used to study the HIV reservoir using new imaging techniques. Despite these advances, there are still limitations in HIV immune responses and deficits in lymphoid structures in these models in addition to xenogeneic graft-versus-host responses. To understand and disseminate the improvements and limitations of humanized mouse models to the scientific community, the NIH sponsored and convened a meeting on April 15, 2015 to discuss the state of knowledge concerning these questions and best practices for selecting a humanized mouse model for a particular scientific investigation. This report summarizes the findings of the NIH meeting.

Exosomes from HIV-1-infected Cells Stimulate Production of Pro-inflammatory Cytokines through Trans-activating Response (TAR) RNA

HIV-1 infection results in a chronic illness because long-term highly active antiretroviral therapy can lower viral titers to an undetectable level. However, discontinuation of therapy rapidly increases virus burden. Moreover, patients under highly active antiretroviral therapy frequently develop various metabolic disorders, neurocognitive abnormalities, and cardiovascular diseases. We have previously shown that exosomes containing trans-activating response (TAR) element RNA enhance susceptibility of undifferentiated naive cells to HIV-1 infection. This study indicates that exosomes from HIV-1-infected primary cells are highly abundant with TAR RNA as detected by RT-real time PCR. Interestingly, up to a million copies of TAR RNA/μl were also detected in the serum from HIV-1-infected humanized mice suggesting that TAR RNA may be stable in vivo. Incubation of exosomes from HIV-1-infected cells with primary macrophages resulted in a dramatic increase of proinflammatory cytokines, IL-6 and TNF-β, indicating that exosomes containing TAR RNA could play a direct role in control of cytokine gene expression. The intact TAR molecule was able to bind to PKR and TLR3 effectively, whereas the 5' and 3' stems (TAR microRNAs) bound best to TLR7 and -8 and none to PKR. Binding of TAR to PKR did not result in its phosphorylation, and therefore, TAR may be a dominant negative decoy molecule in cells. The TLR binding through either TAR RNA or TAR microRNA potentially can activate the NF-κB pathway and regulate cytokine expression. Collectively, these results imply that exosomes containing TAR RNA could directly affect the proinflammatory cytokine gene expression and may explain a possible mechanism of inflammation observed in HIV-1-infected patients under cART.

Therapeutic doses of irradiation activate viral transcription and induce apoptosis in HIV-1 infected cells

The highly active antiretroviral therapy reduces HIV-1 RNA in plasma to undetectable levels. However, the virus continues to persist in the long-lived resting CD4(+) T cells, macrophages and astrocytes which form a viral reservoir in infected individuals. Reactivation of viral transcription is critical since the host immune response in combination with antiretroviral therapy may eradicate the virus. Using the chronically HIV-1 infected T lymphoblastoid and monocytic cell lines, primary quiescent CD4(+) T cells and humanized mice infected with dual-tropic HIV-1 89.6, we examined the effect of various X-ray irradiation (IR) doses (used for HIV-related lymphoma treatment and lower doses) on HIV-1 transcription and viability of infected cells. Treatment of both T cells and monocytes with IR, a well-defined stress signal, led to increase of HIV-1 transcription, as evidenced by the presence of RNA polymerase II and reduction of HDAC1 and methyl transferase SUV39H1 on the HIV-1 promoter. This correlated with the increased GFP signal and elevated level of intracellular HIV-1 RNA in the IR-treated quiescent CD4(+) T cells infected with GFP-encoding HIV-1. Exposition of latently HIV-1infected monocytes treated with PKC agonist bryostatin 1 to IR enhanced transcription activation effect of this latency-reversing agent. Increased HIV-1 replication after IR correlated with higher cell death: the level of phosphorylated Ser46 in p53, responsible for apoptosis induction, was markedly higher in the HIV-1 infected cells following IR treatment. Exposure of HIV-1 infected humanized mice with undetectable viral RNA level to IR resulted in a significant increase of HIV-1 RNA in plasma, lung and brain tissues. Collectively, these data point to the use of low to moderate dose of IR alone or in combination with HIV-1 transcription activators as a potential application for the "Shock and Kill" strategy for latently HIV-1 infected cells.

Interview: Nanomedicine and the fight against HIV/AIDS

Ahead of the 4th Annual Meeting of the American Society of Nanomedicine, this collection of interviews brings together experts from the fields of nanomedicine and HIV/AIDS treatment. Professor André Nel gives us a general introduction and update on the nanomedicine field and how he hopes it will progress. Professor Susan Swindells describes the current challenges faced in the clinic for HIV/AIDS treatment. Professor Tatiana Bronich explains the research efforts being undertaken by the nanomedicine community for the treatment of microbial infections and HIV/AIDS specifically. Finally, Professor Howard Gendelman looks to the future and assesses the potential and challenges of nanomedicine approaches for HIV eradication.

Humanised models of infection in the evaluation of anti-malarial drugs

Humanised mice have a crucial role for drug discovery in malaria, which is the most important parasitic disease in the world and is caused by protozoa of the genus Plasmodium that selectively infect human hepatocytes and erythrocytes. There are currently reliable humanised murine models for hepatic and erythrocytic stages of Plasmodium falciparum, which is the most pathogenic malarial species. These models are useful in the evaluation of drugs for malaria prevention and treatment, notably in exploiting the thousands of antimalarial hits discovered. The development of a humanised model for Plasmodium vivax and the validation of the P. falciparum models to inform optimal clinical studies are the next key goals to be achieved.

Overcoming current limitations in humanized mouse research

Immunodeficient mice engrafted with human cells and tissues have provided an exciting alternative to in vitro studies with human tissues and nonhuman primates for the study of human immunobiology. A major breakthrough in the early 2000s was the introduction of a targeted mutation in the interleukin 2 (IL-2) receptor common gamma chain (IL2rg(null)) into mice that were already deficient in T and B cells. Among other immune defects, natural killer (NK) cells are disrupted in these mice, permitting efficient engraftment with human hematopoietic cells that generate a functional human immune system. These humanized mouse models are becoming increasingly important for preclinical studies of human immunity, hematopoiesis, tissue regeneration, cancer, and infectious diseases. In particular, humanized mice have enabled studies of the pathogenesis of human-specific pathogens, including human immunodeficiency virus type 1, Epstein Barr virus, and Salmonella typhi. However, there are a number of limitations in the currently available humanized mouse models. Investigators are continuing to identify molecular mechanisms underlying the remaining defects in the engrafted human immune system and are generating "next generation" models to overcome these final deficiencies. This article provides an overview of some of the emerging models of humanized mice, their use in the study of infectious diseases, and some of the remaining limitations that are currently being addressed.

Animal models for depression associated with HIV-1 infection

Antiretroviral therapy has greatly extended the lifespan of people living with human immunodeficiency virus (PLHIV). As a result, the long-term effects of HIV infection, in particular those originating in the central nervous system (CNS), such as HIV associated depression, have gained importance. Animal models for HIV infection have proved very useful for understanding the disease and developing treatment strategies. However, HIV associated depression remains poorly understood and so far there is neither a fully satisfactory animal model, nor a pathophysiologically guided treatment for this condition. Here we review the neuroimmunological, neuroendocrine, neurotoxic and neurodegenerative basis for HIV depression and discuss strategies for employing HIV animal models, in particular humanized mice which are susceptible to HIV infection, for the study of HIV depression.

Engrafted human cells generate adaptive immune responses to Mycobacterium bovis BCG infection in humanized mice

Background

Currently used mouse models fail to fully reflect human immunity to tuberculosis (TB), which hampers progress in research and vaccine development. Bone marrow-liver-thymus (BLT) mice, generated by engrafting human fetal liver, thymus, and hematopoietic stem cells in severely immunodeficient NOD/SCID/IL-2Rγ^-/- (NSG) mice, have shown potential to model human immunity to infection. We engrafted HLA-A2-positive fetal tissues into NSG mice transgenically expressing human leukocyte antigen (HLA)-A2.1 (NSG-A2) to generate NSG-A2-BLT mice and characterized their human immune response to Mycobacterium bovis bacillus Calmette-Guerin (BCG) infection to assess the utility of this model for investigating human TB.

Results

NSG-A2-BLT mice were infected intravenously with BCG and the immune response of engrafted human immune cells was characterized. After ex vivo antigenic stimulation of splenocytes, interferon (IFN)-γ-producing cells were detected by ELISPOT from infected, but not uninfected NSG-A2-BLT mice. However, the levels of secreted IFN-γ, determined by ELISA, were not significantly elevated by antigenic stimulation. NSG-A2-BLT mice were susceptible to BCG infection as determined by higher lung bacillary load than the non-engrafted control NSG-A2 mice. BCG-infected NSG-A2-BLT mice developed lung lesions composed mostly of human macrophages and few human CD4⁺ or CD8⁺ T cells. The lesions did not resemble granulomas typical of human TB.

Conclusions

Engrafted human immune cells in NSG-A2-BLT mice showed partial function of innate and adaptive immune systems culminating in antigen-specific T cell responses to mycobacterial infection. The lack of protection was associated with low IFN-γ levels and limited numbers of T cells recruited to the lesions. The NSG-A2-BLT mouse is capable of mounting a human immune response to M. tuberculosis in vivo but a quantitatively and possibly qualitatively enhanced effector response will be needed to improve the utility of this model for TB research.

Simultaneous zinc-finger nuclease editing of the HIV coreceptors ccr5 and cxcr4 protects CD4+ T cells from HIV-1 infection

HIV-1 entry into CD4(+) T cells requires binding of the virus to CD4 followed by engagement of either the C-C chemokine receptor 5 (CCR5) or C-X-C chemokine receptor 4 (CXCR4) coreceptor. Pharmacologic blockade or genetic inactivation of either coreceptor protects cells from infection by viruses that exclusively use the targeted coreceptor. We have used zinc-finger nucleases to drive the simultaneous genetic modification of both ccr5 and cxcr4 in primary human CD4(+) T cells. These gene-modified cells proliferated normally and were resistant to both CCR5- and CXCR4-using HIV-1 in vitro. When introduced into a humanized mouse model of HIV-1 infection, these coreceptor negative cells engraft and traffic normally, and are protected from infection with CCR5- and CXCR4-using HIV-1 strains. These data suggest that simultaneous disruption of the HIV coreceptors may provide a useful approach for the long-term, drug-free treatment of established HIV-1 infections.

HIV-1 infection, response to treatment and establishment of viral latency in a novel humanized T cell-only mouse (TOM) model

Background

The major targets of HIV infection in humans are CD4⁺ T cells. CD4⁺ T cell depletion is a hallmark of AIDS. Previously, the SCID-hu thy/liv model was used to study the effect of HIV on thymopoeisis in vivo. However, these mice did not develop high levels of peripheral T cell reconstitution and required invasive surgery for infection and analysis. Here, we describe a novel variant of this model in which thy/liv implantation results in systemic reconstitution with human T cells in the absence of any other human hematopoietic lineages.

Results

NOD/SCID-hu thy/liv and NSG-hu thy/liv mice were created by implanting human fetal thymus and liver tissues under the kidney capsule of either NOD/SCID or NSG mice. In contrast to NOD/SCID-hu thy/liv mice that show little or no human cells in peripheral blood or tissues, substantial systemic human reconstitution occurs in NSG-hu thy/liv. These mice are exclusively reconstituted with human T cells (i.e. T-cell only mice or TOM). Despite substantial levels of human T cells no signs of graft-versus-host disease (GVHD) were noted in these mice over a period of 14 months. TOM are readily infected after parenteral exposure to HIV-1. HIV replication is sustained in peripheral blood at high levels and results in modest reduction of CD4⁺ T cells. HIV-1 replication in TOM responds to daily administration of combination antiretroviral therapy (ART) resulting in strong suppression of virus replication as determined by undetectable viral load in plasma. Latently HIV infected resting CD4⁺ T cells can be isolated from suppressed mice that can be induced to express HIV ex-vivo upon activation demonstrating the establishment of latency in vivo.

Conclusions

NSG-hu thy/liv mice are systemically reconstituted with human T cells. No other human lymphoid lineages are present in these mice (i.e. monocytes/macrophages, B cells and DC are all absent). These T cell only mice do not develop GVHD, are susceptible to HIV-1 infection and can efficiently maintain virus replication. HIV infected TOM undergoing ART harbor latently infected, resting CD4⁺ T cells.

Animal models for human herpesvirus 6 infection

Human herpesvirus (HHV)-6A and HHV-6B are two enveloped DNA viruses of β-herpesvirus family, infecting over 90% of the population and associated with several diseases, including exanthema subitum (for HHV-6B), multiple sclerosis and encephalitis, particularly in immunosuppressed patients. Animal models are highly important to better understand the pathogenesis of viral infections. Naturally developed neutralizing antibodies to HHV-6 or a related virus were found in different species of monkeys, suggesting their susceptibility to HHV-6 infection. Both HHV-6 DNA and infectious virus were detected in experimentally infected Cynomolgus and African green monkeys, although most animals remained clinically asymptomatic. Furthermore, HHV-6A infection was shown to accelerate the progression of AIDS (acquired immunodeficiency syndrome) in macaques and to lead to the development of neurological symptoms in the marmoset model. Humanized SCID (severe combined immunodeficiency) mice efficiently replicated HHV-6 and were also susceptible to coinfection with HHV-6 and HIV-1 (human immunodeficiency virus 1). As CD46 was identified as a receptor for HHV-6, transgenic mice expressing human CD46 may present a potentially interesting model for study certain aspects of HHV-6 infection and neuroinflammation.

HIV-1 transcription and latency: an update

Combination antiretroviral therapy, despite being potent and life-prolonging, is not curative and does not eradicate HIV-1 infection since interruption of treatment inevitably results in a rapid rebound of viremia. Reactivation of latently infected cells harboring transcriptionally silent but replication-competent proviruses is a potential source of persistent residual viremia in cART-treated patients. Although multiple reservoirs may exist, the persistence of resting CD4+ T cells carrying a latent infection represents a major barrier to eradication. In this review, we will discuss the latest reports on the molecular mechanisms that may regulate HIV-1 latency at the transcriptional level, including transcriptional interference, the role of cellular factors, chromatin organization and epigenetic modifications, the viral Tat trans-activator and its cellular cofactors. Since latency mechanisms may also operate at the post-transcriptional level, we will consider inhibition of nuclear RNA export and inhibition of translation by microRNAs as potential barriers to HIV-1 gene expression. Finally, we will review the therapeutic approaches and clinical studies aimed at achieving either a sterilizing cure or a functional cure of HIV-1 infection, with a special emphasis on the most recent pharmacological strategies to reactivate the latent viruses and decrease the pool of viral reservoirs.

Humanized mouse models of epstein-barr virus infection and associated diseases

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus infecting more than 90% of the adult population of the world. EBV is associated with a variety of diseases including infectious mononucleosis, lymphoproliferative diseases, malignancies such as Burkitt lymphoma and nasopharyngeal carcinoma, and autoimmune diseases including rheumatoid arthritis (RA). EBV in nature infects only humans, but in an experimental setting, a limited species of new-world monkeys can be infected with the virus. Small animal models, suitable for evaluation of novel therapeutics and vaccines, have not been available. Humanized mice, defined here as mice harboring functioning human immune system components, are easily infected with EBV that targets cells of the hematoimmune system. Furthermore, humanized mice can mount both cellular and humoral immune responses to EBV. Thus, many aspects of human EBV infection, including associated diseases (e.g., lymphoproliferative disease, hemophagocytic lymphohistiocytosis and erosive arthritis resembling RA), latent infection, and T-cell-mediated and humoral immune responses have been successfully reproduced in humanized mice. Here we summarize recent achievements in the field of humanized mouse models of EBV infection and show how they have been utilized to analyze EBV pathogenesis and normal and aberrant human immune responses to the virus.

New generation humanized mice for virus research: comparative aspects and future prospects

Work with human specific viruses will greatly benefit from the use of an in vivo system that provides human target cells and tissues in a physiological setting. In this regard humanized mice (hu-Mice) have played an important role in our understanding of viral pathogenesis and testing of therapeutic strategies. Limitations with earlier versions of hu-Mice that lacked a functioning human immune system are currently being overcome. The new generation hu-Mouse models are capable of multilineage human hematopoiesis and generate T cells, B cells, macrophages and dendritic cells required for an adaptive human immune response. Now any human specific pathogen that can infect humanized mice can be studied in the context of ongoing infection and immune responses. Two leading humanized mouse models are currently employed: the hu-HSC model is created by transplantation of human hematopoietic stem cells (HSC), whereas the BLT mouse model is prepared by transplantation of human fetal liver, thymus and HSC. A number of human specific viruses such as HIV-1, dengue, EBV and HCV are being studied intensively in these systems. Both models permit infection by mucosal routes with viruses such as HIV-1 thus allowing transmission prevention studies. Cellular and humoral immune responses are seen in both the models. While there is efficient antigen specific IgM production, IgG responses are suboptimal due to inefficient immunoglobulin class switching. With the maturation of T cells occurring in the autologous human thymus, BLT mice permit human HLA restricted T cell responses in contrast to hu-HSC mice. However, the strength of the immune responses needs further improvement in both models to reach the levels seen in humans. The scope of hu-Mice use is further broadened by transplantation of additional tissues like human liver thus permitting immunopathogenesis studies on hepatotropic viruses such as HCV. Numerous studies that encompass antivirals, gene therapy, viral evolution, and the generation of human monoclonal antibodies have been conducted with promising results in these mice. For further improvement of the new hu-Mouse models, ongoing work is focused on generating new strains of immunodeficient mice transgenic for human HLA molecules to strengthen immune responses and human cytokines and growth factors to improve human cell reconstitution and their homeostatic maintenance.

Recent developments in human immunodeficiency virus-1 latency research

Almost 30 years after its initial discovery, infection with the human immunodeficiency virus-1 (HIV-1) remains incurable and the virus persists due to reservoirs of latently infected CD4(+) memory T-cells and sanctuary sites within the infected individual where drug penetration is poor. Reactivating latent viruses has been a key strategy to completely eliminate the virus from the host, but many difficulties and unanswered questions remain. In this review, the latest developments in HIV-persistence and latency research are presented.

Physiologic changes in a nonhuman primate model of HIV-associated pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is increased in HIV, but its pathogenesis is not fully understood. Nonhuman primates infected with simian immunodeficiency virus (SIV) or SIV-HIV chimeric virus (SHIV) exhibit histologic changes characteristic of human PAH, but whether hemodynamic changes accompany this pathology is unknown. Repeated measurements of pulmonary artery pressures would permit longitudinal assessments of disease development and provide insights into pathogenesis. We tested the hypothesis that SIV-infected and SHIV-infected macaques develop physiologic manifestations of PAH. We performed right heart catheterizations, echocardiography, and computed tomography (CT) scans in macaques infected with either SIV (ΔB670) or SHIV (89.6P), and compared right heart and pulmonary artery pressures, as well as pulmonary vascular changes on CT scans, with those in uninfected control animals. Right atrial, right ventricular systolic, and pulmonary artery pressures (PAPs) were significantly elevated in 100% of macaques infected with either SIV or SHIV compared with control animals, with no difference in pulmonary capillary wedge pressure. PAPs increased as early as 3 months after SIV infection. Radiographic evidence of pulmonary vascular pruning was also found. Both SIV-infected and SHIV-infected macaques exhibited histologic changes in pulmonary arteries, predominantly consisting of intimal and medial hyperplasia. This report is the first to demonstrate SHIV-infected and SIV-infected macaques develop pulmonary hypertension at a high frequency, with physiologic changes occurring as early as 3 months after infection. These studies establish an important nonhuman primate model of HIV-associated PAH that will be useful in studies of disease pathogenesis and the efficacy of interventions.

Functional in vivo delivery of multiplexed anti-HIV-1 siRNAs via a chemically synthesized aptamer with a sticky bridge

One of the most formidable impediments to clinical translation of RNA interference (RNAi) is safe and effective delivery of the siRNAs to the desired target tissue at therapeutic doses. We previously described in vivo cell type-specific delivery of anti-HIV small-interfering RNAs (siRNAs) through covalent conjugation to an anti-gp120 aptamer. In order to improve the utility of aptamers as siRNA delivery vehicles, we chemically synthesized the gp120 aptamer with a 3′ 7-carbon linker (7C3), which in turn is attached to a 16-nucleotide 2′ OMe/2′ Fl GC-rich bridge sequence. This bridge facilitates the noncovalent binding and interchange of various siRNAs with the same aptamer. We show here that this aptamer-bridge-construct complexed with three different Dicer substrate siRNAs (DsiRNAs) results in effective delivery of the cocktail of DsiRNAs in vivo, resulting in knockdown of target mRNAs and potent inhibition of HIV-1 replication. Following cessation of the aptamer-siRNA cocktail treatment, HIV levels rebounded facilitating a follow-up treatment with the aptamer cocktail of DsiRNAs. This follow-up injection resulted in complete suppression of HIV-1 viral loads that extended several weeks beyond the final injection. Collectively, these data demonstrate a facile, targeted approach for combinatorial delivery of antiviral and host DsiRNAs for HIV-1 therapy in vivo.

Development of a new humanized mouse model to study acute inflammatory arthritis

BACKGROUND

Substantial advances have been generated in understanding the pathogenesis of rheumatoid arthritis (RA). Current murine models of RA-like disease have provided great insights into the molecular mechanism of inflammatory arthritis due to the use of genetically deficient or transgenic mice. However, these studies are limited by differences that exist between human and murine immune systems. Thus, the development of an animal model that utilizes human immune cells, will afford the opportunity to study their function in the initiation and propagation of inflammatory arthritis.

METHODS

One to two-day old irradiated NOD-scid IL2rγ(null) (NSG) mice were reconstituted with human CD34+ cord blood stem cells. Leukocytes were analyzed by flow cytometry and circulating antibodies were determined by ELISA. Arthritis was induced by injecting complete Freund's adjuvant into knee or ankle joints. Mice were also treated with the TNF inhibitor, Etanercept, or PBS and joints were analyzed histologically.

RESULTS

Humanized mice were established with high reconstitution rates and were able to spontaneously produce human immunoglobulins as well as specific IgG in response to immunization. Intraperitoneal injection of thioglycolate or injection of complete Freund's adjuvant into joints resulted in migration of human immune cells to the injected sites. Arthritic humanized mice treated with Etanercept had markedly less inflammation, which was associated with decreased total numbers of human CD45+ cells, including human lymphocytes and neutrophils.

CONCLUSIONS

The humanized mouse model is a new model to study inflammatory arthritis disease using human leukocytes without rejection of engrafted tissue. Future studies may adapt this system to incorporate RA patient cord blood and develop a chimeric animal model of inflammatory arthritis using genetically predisposed immune cells.

Liver X receptor agonist inhibits HIV-1 replication and prevents HIV-induced reduction of plasma HDL in humanized mouse model of HIV infection

HIV-infected subjects are at high risk of developing atherosclerosis, in part due to virus-induced impairment of HDL metabolism. Here, using as a model of HIV infection the NOD.Cg-Prkdc(scid)IL2rg(tm1Wjl)/SzJ (NSG) mice humanized by human stem cell transplantation, we demonstrate that LXR agonist TO901317 potently reduces viral replication and prevents HIV-induced reduction of plasma HDL. These results establish that humanized mice can be used to investigate the mechanisms of HIV-induced impairment of HDL formation, a major feature of dyslipidemia associated with HIV-1 infection, and show potential benefits of developing LXR agonists for treatment of HIV-associated cardio-vascular disease.

Rodent models for HIV-associated neurocognitive disorders

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) reflect the spectrum of neural impairments seen during chronic viral infection. Current research efforts focus on improving antiretroviral and adjunctive therapies, defining disease onset and progression, facilitating drug delivery, and halting neurodegeneration and viral resistance. Because HIV is species-specific, generating disease in small-animal models has proved challenging. After two decades of research, rodent HAND models now include those containing a human immune system. Antiviral responses, neuroinflammation and immunocyte blood-brain barrier (BBB) trafficking follow HIV infection in these rodent models. We review these and other rodent models of HAND and discuss their unmet potential in reflecting human pathobiology and in facilitating disease monitoring and therapeutic discoveries.

[Mice are not Men and yet… how humanized mice inform us about human infectious diseases]

The study of human pathologies is often limited by the absence of animal models which are robust, cost-effective and reproduce the hallmarks of human infections. While mice have been frequently employed to study human diseases, many of important pathogens display unique human tropism. These last two decades the graft of human progenitor cells or tissues into -immunodeficient mice has allowed the elaboration of so called humanized mice. Humanized mouse technology has made rapid progress, and it is now possible to achieve high levels of human chimerism in various organs and tissues, particularly the immune system and the liver. The review briefly summarizes the different models of humanized mice available for in vivo experiments. With a focus on lymphotropic, monocytotropic and hepatotropic viruses, we here discuss the current status and future prospects of these models for studying the pathogenesis of infectious diseases. Furthermore, they provide a powerful tool for the development of innovative therapies.

Drug discovery in the next decade: innovation needed ASAP

Pharmaceutical companies must find a better way to increase their output of truly new drugs for the benefit of patients and for their business survival. Here, I highlight a general perspective from within pharmaceutical research as it pertains to research advances in chemistry, biology, pharmacology, pharmacokinetics and toxicology that, if well integrated, stands to put the industry on a productive path. In addition, I provide a complementary perspective on the corporate culture aspect of innovation. I also introduce a new concept, termed 'innovation ASAP' (iASAP; asking powerful questions, seeking the outliers, accepting defeat and populating astutely) and provide support for it using examples of several successful drugs.

Genetic knockouts suggest a critical role for HIV co-receptors in models of HIV gp120-induced brain injury

Infection with HIV-1 frequently affects the brain and causes NeuroAIDS prior to the development of overt AIDS. The HIV-1 envelope protein gp120 interacts with host CD4 and chemokine co-receptors to initiate infection of macrophages and lymphocytes. In addition, the virus or fragments of it, such as gp120, cause macrophages to produce neurotoxins and trigger neuronal injury and apoptosis. Moreover, the two major HIV co-receptors, the chemokine receptors CCR5 and CXCR4, serve numerous physiological functions and are widely expressed beyond immune cells, including cells in the brain. Therefore, HIV co-receptors are poised to play a direct and indirect part in the development of NeuroAIDS. Although rodents are not permissive to infection with wild type HIV-1, viral co-receptors - more than CD4 - are highly conserved between species, suggesting the animals can be suitable models for mechanistic studies addressing effects of receptor-ligand interaction other than infection. Of note, transgenic mice expressing HIV gp120 in the brain share several pathological hallmarks with NeuroAIDS brains. Against this background, we will discuss recently completed or initiated, ongoing studies that utilize HIV co-receptor knockout and viral gp120-transgenic mice as models for in vitro and in vivo experimentation in order to address the potential roles of HIV gp120 and its co-receptors in the development of NeuroAIDS.

Systemic administration of combinatorial dsiRNAs via nanoparticles efficiently suppresses HIV-1 infection in humanized mice

We evaluated the in vivo efficacy of structurally flexible, cationic PAMAM dendrimers as a small interfering RNA (siRNA) delivery system in a Rag2(-)/-γc-/- (RAG-hu) humanized mouse model for HIV-1 infection. HIV-infected humanized Rag2-/-γc-/- mice (RAG-hu) were injected intravenously (i.v.) with dendrimer-siRNA nanoparticles consisting of a cocktail of dicer substrate siRNAs (dsiRNAs) targeting both viral and cellular transcripts. We report in this study that the dendrimer-dsiRNA treatment suppressed HIV-1 infection by several orders of magnitude and protected against viral induced CD4(+) T-cell depletion. We also demonstrated that follow-up injections of the dendrimer-cocktailed dsiRNAs following viral rebound resulted in complete inhibition of HIV-1 titers. Biodistribution studies demonstrate that the dendrimer-dsiRNAs preferentially accumulate in peripheral blood mononuclear cells (PBMCs) and liver and do not exhibit any discernable toxicity. These data demonstrate for the first time efficacious combinatorial delivery of anti-host and -viral siRNAs for HIV-1 treatment in vivo. The dendrimer delivery approach therefore represents a promising method for systemic delivery of combinations of siRNAs for treatment of HIV-1 infection.

The role of monocyte-lineage cells in human immunodeficiency virus persistence: mechanisms and progress

Human immunodeficiency virus type 1 (HIV-1) persistence is a major barrier to the successful treatment and eradication of acquired immunodeficiency syndrome (AIDS). In addition to resting CD4(+) T cells, a significant long-lived compartment of HIV-1 infection in vivo includes blood monocytes and tissue macrophages. Studying HIV-1 persistence in monocyte-lineage cells is critical because these cells are important HIV-1 target cells in vivo. Monocyte-lineage cells, including monocytes, dendritic cells (DCs) and macrophages, play a significant role in HIV-1 infection and transmission. These cells have been implicated as viral reservoirs that facilitate HIV-1 latency and persistence. A better understanding of HIV-1 interactions with monocyte-lineage cells can potentially aid in the development of new approaches for intervention. This minireview highlights the latest advances in understanding the role of monocyte-lineage cells in HIV-1 persistence and emphasizes new insights into the mechanisms underlying viral persistence.

HTLV-1 propels thymic human T cell development in "human immune system" Rag2⁻/⁻ gamma c⁻/⁻ mice

Alteration of early haematopoietic development is thought to be responsible for the onset of immature leukemias and lymphomas. We have previously demonstrated that Tax(HTLV-1) interferes with ß-selection, an important checkpoint of early thymopoiesis, indicating that human T-cell leukemia virus type 1 (HTLV-1) infection has the potential to perturb thymic human αβ T-cell development. To verify that inference and to clarify the impact of HTLV-1 infection on human T-cell development, we investigated the in vivo effects of HTLV-1 infection in a "Human Immune System" (HIS) Rag2⁻/⁻γ(c)⁻/⁻ mouse model. These mice were infected with HTLV-1, at a time when the three main subpopulations of human thymocytes have been detected. In all but two inoculated mice, the HTLV-1 provirus was found integrated in thymocytes; the proviral load increased with the length of the infection period. In the HTLV-1-infected mice we observed alterations in human T-cell development, the extent of which correlated with the proviral load. Thus, in the thymus of HTLV-1-infected HIS Rag2⁻/⁻γc⁻/⁻ mice, mature single-positive (SP) CD4⁺ and CD8⁺ cells were most numerous, at the expense of immature and double-positive (DP) thymocytes. These SP cells also accumulated in the spleen. Human lymphocytes from thymus and spleen were activated, as shown by the expression of CD25: this activation was correlated with the presence of tax mRNA and with increased expression of NF-kB dependent genes such as bfl-1, an anti-apoptotic gene, in thymocytes. Finally, hepato-splenomegaly, lymphadenopathy and lymphoma/thymoma, in which Tax was detected, were observed in HTLV-1-infected mice, several months after HTLV-1 infection. These results demonstrate the potential of the HIS Rag2⁻/⁻γ(c)⁻/⁻ animal model to elucidate the initial steps of the leukemogenic process induced by HTLV-1.

The utility of the new generation of humanized mice to study HIV-1 infection: transmission, prevention, pathogenesis, and treatment

Substantial improvements have been made in recent years in the ability to engraft human cells and tissues into immunodeficient mice. The use of human hematopoietic stem cells (HSCs) leads to multi-lineage human hematopoiesis accompanied by production of a variety of human immune cell types. Population of murine primary and secondary lymphoid organs with human cells occurs, and long-term engraftment has been achieved. Engrafted cells are capable of producing human innate and adaptive immune responses, making these models the most physiologically relevant humanized animal models to date. New models have been successfully infected by a variety of strains of Human Immunodeficiency Virus Type 1 (HIV-1), accompanied by virus replication in lymphoid and non-lymphoid organs, including the gut-associated lymphoid tissue, the male and female reproductive tracts, and the brain. Multiple forms of virus-induced pathogenesis are present, and human T cell and antibody responses to HIV-1 are detected. These humanized mice are susceptible to a high rate of rectal and vaginal transmission of HIV-1 across an intact epithelium, indicating the potential to study vaccines and microbicides. Antiviral drugs, siRNAs, and hematopoietic stem cell gene therapy strategies have all been shown to be effective at reducing viral load and preventing or reversing helper T cell loss in humanized mice, indicating that they will serve as an important preclinical model to study new therapeutic modalities. HIV-1 has also been shown to evolve in response to selective pressures in humanized mice, thus showing that the model will be useful to study and/or predict viral evolution in response to drug or immune pressures. The purpose of this review is to summarize the findings reported to date on all new humanized mouse models (those transplanted with human HSCs) in regards to HIV-1 sexual transmission, pathogenesis, anti-HIV-1 immune responses, viral evolution, pre- and post-exposure prophylaxis, and gene therapeutic strategies.

Coming of age: reconstruction of heterosexual HIV-1 transmission in human ex vivo organ culture systems

Heterosexual transmission of human immunodeficiency virus-1 (HIV-1), from men to women, involves exposure to infectious HIV-1 in semen. Therefore, the cellular and molecular processes that underlie HIV-1 transmission are closely interconnected with fundamental principles of human reproductive biology. Human ex vivo organ culture systems allow experimental reconstruction of HIV-1 transmission, using human semen and premenopausal cervicovaginal mucosal tissue, with specific emphasis on the progression from exposure to development of primary HIV-1 infection. Clearly, an isolated piece of human tissue cannot duplicate the full complexity of events in natural infections, but with correct observation of conventional medical and ethical standards, there is no opportunity to study HIV-1 exposure and primary infection in young women. Human mucosal organ cultures allow direct study of HIV-1 infection in a reproducible format while retaining major elements of complexity and variability that typify community-based HIV-1 transmission. Experimental manipulation of human mucosal tissue both allows and requires acquisition of new insights into basic processes of human mucosal immunology. Expanding from the current foundations, we believe that human organ cultures will become increasingly prominent in experimental studies of HIV-1 transmission and continuing efforts to prevent HIV-1 infection at human mucosal surfaces.

Humanized mouse models of HIV infection

Because of the limited tropism of HIV, in vivo modeling of this virus has been almost exclusively limited to other lentiviruses, such as simian immunodeficiency virus, that reproduce many important characteristics of HIV infection. However, there are significant genetic and biological differences among lentiviruses and some HIV-specific interventions are not effective against other lentiviruses in nonhuman hosts. For these reasons, much emphasis has recently been placed on developing alternative animal models that support HIV replication and recapitulate key aspects of HIV infection and pathogenesis in humans. Humanized mice, CD34+ hematopoietic progenitor cell transplanted immunodeficient mice, and in particular mice also implanted with human thymus/liver tissue (bone marrow liver thymus mice) that develop a functional human immune system, have been the focus of a great deal of attention as possible models to study virtually all aspects of HIV biology and pathogenesis. Humanized mice are systemically reconstituted with human lymphoid cells, offering rapid, reliable, and reproducible experimental systems for HIV research. Peripheral blood of humanized mice can be readily sampled longitudinally to assess reconstitution with human cells and to monitor HIV replication, permitting the evaluation of multiple parameters of HIV infection such as viral load levels, CD4+ T-cell depletion, immune activation, as well as the effects of therapeutic interventions. Of high relevance to HIV transmission is the extensive characterization and validation of the reconstitution with human lymphoid cells of the female reproductive tract and of the gastrointestinal tract of humanized bone marrow liver thymus mice that renders them susceptible to both vaginal and rectal HIV infection. Other important attributes of all types of humanized mice include: (i) their small size and cost that make them widely accessible; (ii) multiple cohorts of humanized mice can be made from multiple human donors and each cohort has identical human cells, permitting control of intragenetic variables; (iii) continuous de novo production of human immune cells from the transplanted CD34+ cells within each humanized mouse facilitates long-term experiments; (iv) both primary and laboratory HIV isolates can be used for experiments; and (v) in addition to therapeutic interventions, rectal and vaginal HIV prevention approaches can be studied. In summary, humanized mice can have an important role in virtually all aspects of HIV research, including the analysis of HIV replication, the evaluation of HIV restriction factors, the characterization of successful biomedical HIV prevention strategies, the evaluation of new treatment regimens, and the evaluation of novel HIV eradication strategies.

Drug discovery in the next decade: innovation needed ASAP

Pharmaceutical companies must find a better way to increase their output of truly new drugs for the benefit of patients and for their business survival. Here, I highlight a general perspective from within pharmaceutical research as it pertains to research advances in chemistry, biology, pharmacology, pharmacokinetics and toxicology that, if well integrated, stands to put the industry on a productive path. In addition, I provide a complementary perspective on the corporate culture aspect of innovation. I also introduce a new concept, termed 'innovation ASAP' (iASAP; asking powerful questions, seeking the outliers, accepting defeat and populating astutely) and provide support for it using examples of several successful drugs.

Humanized Rag1-/- γc-/- mice support multilineage hematopoiesis and are susceptible to HIV-1 infection via systemic and vaginal routes

Several new immunodeficient mouse models for human cell engraftment have recently been introduced that include the Rag2^−/−γc^−/−, NOD/SCID, NOD/SCIDγc^−/− and NOD/SCIDβ2m^−/− strains. Transplantation of these mice with CD34⁺ human hematopoietic stem cells leads to prolonged engraftment, multilineage hematopoiesis and the capacity to generate human immune responses against a variety of antigens. However, the various mouse strains used and different methods of engrafting human cells are beginning to illustrate strain specific variations in engraftment levels, duration and longevity of mouse life span. In these proof-of-concept studies we evaluated the Balb/c-Rag1^−/−γ^−/− strain for engraftment by human fetal liver derived CD34⁺ hematopoietic cells using the same protocol found to be effective for Balb/c-Rag2^−/−γc^−/− mice. We demonstrate that these mice can be efficiently engrafted and show multilineage human hematopoiesis with human cells populating different lymphoid organs. Generation of human cells continues beyond a year and production of human immunoglobulins is noted. Infection with HIV-1 leads to chronic viremia with a resultant CD4 T cell loss. To mimic the predominant sexual viral transmission, we challenged humanized Rag1^−/−γc^−/− mice with HIV-1 via vaginal route which also resulted in chronic viremia and helper T cell loss. Thus these mice can be further exploited for studying human pathogens that infect the human hematopoietic system in an in vivo setting.

A topical microbicide gel formulation of CCR5 antagonist maraviroc prevents HIV-1 vaginal transmission in humanized RAG-hu mice

For prevention of HIV infection many currently licensed anti-HIV drugs and new ones in the pipeline show potential as topically applied microbicides. While macaque models have been the gold standard for in vivo microbicide testing, they are expensive and sufficient numbers are not available. Therefore, a small animal model that facilitates rapid evaluation of potential candidates for their preliminary efficacy is urgently needed in the microbicide field. We previously demonstrated that RAG-hu humanized mouse model permits HIV-1 mucosal transmission via both vaginal and rectal routes and that oral pre-exposure chemo-prophylactic strategies could be tested in this system. Here in these proof-of-concept studies, we extended this system for topical microbicide testing using HIV-1 as the challenge virus. Maraviroc, a clinically approved CCR5 inhibitor drug for HIV treatment, was formulated as a microbicide gel at 5 mM concentration in 2.2% hydroxyl ethyl cellulose. Female RAG-hu mice were challenged vaginally with HIV-1 an hour after intravaginal application of the maraviroc gel. Our results showed that maraviroc gel treated mice were fully protected against vaginal HIV-1 challenge in contrast to placebo gel treated mice which all became infected. These findings highlight the utility of the humanized mouse models for microbicide testing and, together with the recent data from macaque studies, suggest that maraviroc is a promising candidate for future microbicide clinical trials in the field.

Loss of neuronal integrity during progressive HIV-1 infection of humanized mice

Neuronal damage induced by ongoing human immunodeficiency virus type 1 (HIV-1) infection was investigated in humanized NOD/scid-IL-2Rγ(c)(null) mice transplanted at birth with human CD34-positive hematopoietic stem cells. Mice infected at 5 months of age and followed for up to 15 weeks maintained significant plasma viral loads and showed reduced numbers of CD4(+) T-cells. Prospective serial proton magnetic resonance spectroscopy tests showed selective reductions in cortical N-acetyl aspartate in infected animals. Diffusion tensor imaging revealed structural changes in cortical gray matter. Postmortem immunofluorescence brain tissue examinations for neuronal and glial markers, captured by multispectral imaging microscopy and quantified by morphometric and fluorescence emission, showed regional reduction of neuronal soma and synaptic architectures. This was evidenced by loss of microtubule-associated protein 2, synaptophysin, and neurofilament antigens. This study is the first, to our knowledge, demonstrating lost neuronal integrity after HIV-1 infection in humanized mice. As such, the model permits studies of the relationships between ongoing viral replication and virus-associated neurodegeneration.

An aptamer-siRNA chimera suppresses HIV-1 viral loads and protects from helper CD4(+) T cell decline in humanized mice

Therapeutic strategies designed to treat HIV infection with combinations of antiviral drugs have proven to be the best approach for slowing the progression to AIDS. Despite this progress, there are problems with viral drug resistance and toxicity, necessitating new approaches to combating HIV-1 infection. We have therefore developed a different combination approach for the treatment of HIV infection in which an RNA aptamer, with high binding affinity to the HIV-1 envelope (gp120) protein and virus neutralization properties, is attached to and delivers a small interfering RNA (siRNA) that triggers sequence-specific degradation of HIV RNAs. We have tested the antiviral activities of these chimeric RNAs in a humanized Rag2(-/-)γc(-/-) (RAG-hu) mouse model with multilineage human hematopoiesis. In this animal model, HIV-1 replication and CD4(+) T cell depletion mimic the situation seen in human HIV-infected patients. Our results show that treatment with either the anti-gp120 aptamer or the aptamer-siRNA chimera suppressed HIV-1 replication by several orders of magnitude and prevented the viral-induced helper CD4(+) T cell decline. In comparison to the aptamer alone, the aptamer-siRNA combination provided more extensive inhibition, resulting in a significantly longer antiviral effect that extended several weeks beyond the last injected dose. The aptamer thus acts as a broad-spectrum HIV-neutralizing agent and an siRNA delivery vehicle. The combined aptamer-siRNA agent provides an attractive, nontoxic therapeutic approach for treatment of HIV infection.

HIV reservoirs and latency models

The main impediment to a cure for HIV is the existence of long-lasting treatment resistant viral reservoirs. In this review, we discuss what is currently known about reservoirs, including their formation and maintenance, while focusing on latently infected CD4+ T cells. In addition, we compare several different in vivo and in vitro models of latency. We comment on how each model may reflect the properties of reservoirs in vivo, especially with regard to cell phenotype, since recent studies demonstrate that multiple CD4+ T cell subsets contribute to HIV reservoirs and that with HAART and disease progression the relative contribution of different subsets may change. Finally, we focus on the direct infection of resting CD4+ T cells as a source of reservoir formation and as a model of latency, since recent results help explain the misconception that resting CD4+ T cells appeared to be resistant to HIV in vitro.

Mice with human immune system components as in vivo models for infections with human pathogens

Many pathogens relevant to human disease do not infect other animal species. Therefore, animal models that reconstitute or harbor human tissues are explored as hosts for these. In this review, we will summarize recent advances to utilize mice with human immune system components, reconstituted from hematopoietic progenitor cells in vivo. Such mice can be used to study human pathogens that replicate in leukocytes. In addition to studying the replication of these pathogens, the reconstituted human immune system components can also be analyzed for initiating immune responses and control against these infections. Moreover, these new animal models of human infectious disease should replicate the reactivity of the human immune system to vaccine candidates and, especially, the adjuvants contained in them, more faithfully.

Pulmonary vascular lesions are common in SIV- and SHIV-env-infected macaques

The lack of animal models of HIV-related pulmonary arterial hypertension (HIV-PAH) severely limits investigation of this serious disease. While histological evidence of HIV-PAH has been demonstrated in macaques infected with simian immunodeficiency virus (SIV) as well as with chimeric simian/human immunodeficiency virus (SHIV) containing HIV-1-derived Nef protein, other primate models have not been studied. The objective was to document and describe the development of pulmonary vascular changes in macaques infected with SIV or with SIV containing HIV-1-derived envelope protein (SHIV-env). Lung tissue was obtained at necropsy from 13 SHIV (89.6P)-env-infected macaques and 10 SIV (ΔB670)-infected macaques. Pulmonary arterial pathology, including arterial hyperplasia and the presence of plexiform lesions, was compared to normal monkey lung. Pulmonary artery hyperplasia was present in 8 of 13 (62%) SHIV-env-infected macaques and 4/10 (36%) SIV-infected macaques. The most common histopathological lesions were intimal and medial hyperplasia of medium and large pulmonary arteries. Hyperplastic lesions were predominantly due to smooth muscle cell hyperplasia. This is the first report of pulmonary vascular lesions in SHIV-env-infected macaques and confirms prior reports of pulmonary vasculopathy in SIV-infected macaques. The finding of pulmonary arteriopathy in monkeys infected with SHIV not containing HIV-nef suggests that other factors might also be important in the development of HIV-PAH. This SHIV-env model provides a new means to investigate HIV-PAH.

Oral pre-exposure prophylaxis by anti-retrovirals raltegravir and maraviroc protects against HIV-1 vaginal transmission in a humanized mouse model

Sexual HIV-1 transmission by vaginal route is the most predominant mode of viral transmission, resulting in millions of new infections every year. In the absence of an effective vaccine, there is an urgent need to develop other alternative methods of pre-exposure prophylaxis (PrEP). Many novel drugs that are currently approved for clinical use also show great potential to prevent viral sexual transmission when administered systemically. A small animal model that permits rapid preclinical evaluation of potential candidates for their systemic PrEP efficacy will greatly enhance progress in this area of investigation. We have previously shown that RAG-hu humanized mouse model permits HIV-1 mucosal transmission via both vaginal and rectal routes and displays CD4 T cell loss typical to that seen in the human. Thus far systemic PrEP studies have been primarily limited to RT inhibitors exemplified by tenofovir and emtricitabine. In these proof-of-concept studies we evaluated two new classes of clinically approved drugs with different modes of action namely, an integrase inhibitor raltegravir and a CCR5 inhibitor maraviroc as potential systemically administered chemo-prophylactics. Our results showed that oral administration of either of these drugs fully protects against vaginal HIV-1 challenge in the RAG-hu mouse model. Based on these results both these drugs show great promise for further development as orally administered PrEPs.