HIV/AIDS: in search of an animal model

AIDS is among the most devastating diseases of our time, claiming the lives of approximately 3 million people per year. The primary cause of AIDS, human immunodeficiency virus type 1 (HIV-1), is a pathogen that is highly specific for humans and generally does not infect or cause disease in other species. This property complicates the generation of animal models that are urgently needed to test new antiretroviral therapies and vaccines. The most practical animal models developed to date consist of infection of rhesus macaques with a simian immunodeficiency virus (SIV) or chimeric HIV/SIV viruses. Although these models are useful for particular applications, the fact that SIV is a distinct virus compared with HIV-1 represents a significant limitation to their use. Here, we discuss the uses and limitations of existing models and recent advances that might lead to better animal models for HIV/AIDS.     

Effect of electrical stimulation on HIV-1-infected HeLa cells cultured on an electrode surface

Acquired immunodeficiency syndrome (AIDS) is a disease caused by infection with the human immunodeficiency virus (HIV). Although drug therapy for AIDS is available, problems such as side effects associated with drug therapy and the appearance of resistant HIV strains have arisen. Therefore, therapies based on new principles other than drug treatment are required. In the present study, the effect of electrical stimulation on HIV-1(LAI) chronically infected HeLa (P6 HeLa/HIV-1(LAI)) cells cultured on an electrode surface was examined. The results indicated that sensitivity to electrical stimulation was much higher in P6 HeLa/HIV-1(LAI) cells than in uninfected P6 HeLa cells. When electrical stimulation was applied at 1.0 V (vs. Ag/AgCl) for 20 min, the proportion of damage to cell membrane among P6 HeLa/HIV-1(LAI) cells, as evaluated by Trypan blue staining, was approximately 4 times higher than that for uninfected P6 HeLa cells. Furthermore, in comparison with uninfected P6 HeLa cells, the proliferation of P6 HeLa/HIV-1(LAI) cells was significantly suppressed after electrical stimulation. This technique was proven to selectively kill P6 HeLa/HIV-1(LAI) cells, when compared with uninfected control cells.     

Animal models of AIDS

Animal models of AIDS are essential for understanding the pathogenesis of retrovirus-induced immune deficiency and encephalopathy and for development and testing of new therapies and vaccines. AIDS and related disorders are etiologically linked to members of the lentivirus subfamily of retroviruses; these lymphocytopathic lentiviruses are designated human immuno-deficiency virus type 1 (HIV-1) and human immuno-deficiency virus type 2 (HIV-2). The only animals susceptible to experimental HIV-1 infection are the chimpanzee, gibbon ape, and rabbit but AIDS-like disease has not yet been reported in these species. Macaques can be persistently infected with some strains of HIV-2 but no AIDS-like disease has resulted. It is not yet clear how suitable HIV-infected SCID-hu mice will be as a model for AIDS. Several subfamilies of naturally occurring cytopathic retroviruses cause immune suppression, including fatal immunodeficiency syndromes in chickens, mice, cats, and monkeys. Domestic cats suffer immunosuppression from both an onco-virus, feline leukemia virus, and a member of the lentivirus subfamily, feline immunodeficiency virus (FIV). Asian macaques are susceptible to fatal simian AIDS from a type D retrovirus, indigenous in macaques, and from a lentivirus, simian immunodeficiency virus (SIV), which is indigenous to healthy African monkeys. SIV is the animal lentivirus most closely related to HIV. Of these animal models, the lentivirus infections of cats (FIV) and macaques (SIV) appear to bear the closest similarity in their pathogenesis to HIV infection and AIDS. This review will summarize these various animal model systems for AIDS and illustrate their usefulness for antiviral therapy and vaccinology.     

Progress and challenges in therapies for AIDS in nonhuman primate models

Efforts to develop animal models for human immunodeficiency virus type-1 (HIV-1) vaccine testing have focused on lentivirus infection of nonhuman primates. A long-term goal of this primate research is to utilize the models to understand the mechanisms of pathogenesis leading to AIDS. Because the time to disease is compressed relative to HIV infection in humans, therapeutic strategies and compounds can be tested in nonhuman primate models in a shorter time frame and under more controlled conditions than are possible in many clinical studies. Recent interventive studies in primates using antiviral drugs or passive immune globulin (IgG) have demonstrated that multiple log reductions in plasma virus can be achieved and sustained, with accompanying health benefits. Information gained about timing and dosage may be of utility in designing clinical studies. The development of reliable and predictable animal models for effective therapies and vaccines against AIDS remains a critical priority for primate research.     

Human immunodeficiency virus type 1 nef quasispecies in pathological tissue.

The role of the nef gene in human immunodeficiency virus type 1 (HIV-1) infection is poorly understood. To provide a basis for studies on the role of nef in AIDS, we used targeted polymerase chain reaction amplification and DNA sequencing to determine the structure of nef genes in pathologic tissue from HIV-1-infected children and adults. We find that the nef reading frame is open in 92% of clones derived from both brain and lymphocytic tissue of children, suggesting that nef is expressed in these tissues. One HIV-1 clone, BRVA, obtained by coculture from the brain of an adult AIDS patient with progressive dementia, was previously shown to contain a duplicated region in nef. We show here that similar duplications are widespread in both adults and children with AIDS. However, coculture strongly selects against the broad spectrum of nef quasispecies found in tissue. These findings suggest functional selection for nef quasispecies in pathologic tissues during HIV-1 infection of the human host.     

Sulfotyrosine dipeptide: Synthesis and evaluation as HIV-entry inhibitor

Human immunodeficiency virus type 1 (HIV-1) is responsible for the worldwide AIDS pandemic. Due to the lack of prophylactic HIV-1 vaccine, drug treatment of the infected patients becomes essential to reduce the viral load and to slow down progression of the disease. Because of drug resistance, finding new antiviral agents is necessary for AIDS drug therapies. The interaction of gp120 and co-receptor (CCR5/CXCR4) mediates the entry of HIV-1 into host cells, which has been increasingly exploited in recent years as the target for new antiviral agents. A conserved co-receptor binding site on gp120 that recognizes sulfotyrosine (sTyr) residues represents a structural target to design novel HIV entry inhibitors. In this work, we developed an efficient synthesis of sulfotyrosine dipeptide and evaluated it as an HIV-1 entry inhibitor.     

Thermodynamic rules for the design of high affinity HIV-1 protease inhibitors with adaptability to mutations and high selectivity towards unwanted targets

Protease inhibitors are key components in the chemotherapy of HIV-1 infection. However, the long term efficacy of antiretroviral therapies is hampered by issues of patient compliance often associated with the presence of severe side effects, and above all by the appearance of drug resistance. The development of new protease inhibitors with high potency, low susceptibility to mutations and minimal affinity for unwanted targets is an urgent goal. The engineering of these adaptive inhibitors requires identification of the critical determinants of affinity, adaptability, and selectivity. Analysis of the binding database for existing clinical and experimental inhibitors has allowed us to address the following questions in a quantitative fashion: (1) Is there an optimal binding affinity? Or, are the highest affinity inhibitors necessarily the best inhibitors? (2) What is the dependence of optimal affinity on adaptability and selectivity? (3) What are the determinants of adaptability to mutations associated with drug resistance? (4) How selectivity against unwanted targets can be improved? It is shown that the optimal affinity is a function of the effective target concentration and the desired adaptability and selectivity factors. Furthermore, knowledge of the enthalpic and entropic contributions to the binding affinity to the wild type provides a way of anticipating the response of an inhibitor to mutations associated with drug resistance, and therefore, a valuable guideline for optimization.     

A chimeric simian/human immunodeficiency virus expressing a primary patient human immunodeficiency virus type 1 isolate env causes an AIDS-like disease after in vivo passage in rhesus monkeys.

The utility of the simian immunodeficiency virus of macaques (SIVmac) model of AIDS has been limited by the genetic divergence of the envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) and the SIVs. To develop a better AIDS animal model, we have been exploring the infection of rhesus monkeys with chimeric simian/human immunodeficiency viruses (SHIVs) composed of SIVmac239 expressing HIV-1 env and the associated auxiliary HIV-1 genes tat, vpu, and rev. SHIV-89.6, constructed with the HIV-1 env of a cytopathic, macrophage-tropic clone of a patient isolate of HIV-1 (89.6), was previously shown to replicate to a high degree in monkeys during primary infection. However, pathogenic consequences of chronic infection were not evident. We now show that after two serial in vivo passages by intravenous blood inoculation of naive rhesus monkeys, this SHIV (SHIV-89.6P) induced CD4 lymphopenia and an AIDS-like disease with wasting and opportunistic infections. Genetic and serologic evaluation indicated that the reisolated SHIV-89.6P expressed envelope glycoproteins that resembled those of HIV-1. When inoculated into naive rhesus monkeys, SHIV-89.6P caused persistent infection and CD4 lymphopenia. This chimeric virus expressing patient isolate HIV-1 envelope glycoproteins will be valuable as a challenge virus for evaluating HIV-1 envelope-based vaccines and for exploring the genetic determinants of HIV-1 pathogenicity.     

Genetic determinants of pediatric HIV-1 infection: vertical transmission and disease progression among children.

It is very likely that perinatal human immunodeficiency virus type 1 (HIV-1) infection is influenced by a combination of virologic and host factors. A greater understanding of the role played by various risk factors for HIV-1 infection is crucial for the design of new preventive and therapeutic strategies. In recent years, a number of studies have suggested that host genetic factors are important determinants of both the susceptibility to perinatal HIV-1 infection and the subsequent pathogenesis of acquired immunodeficiency syndrome (AIDS). Control of HIV-1 infection involves the processing of specific viral peptides and their presentation to cells of the immune system by highly polymorphic human leukocyte antigen (HLA) alleles. The contribution of multiple HLA class I and II alleles in modulating pediatric HIV/AIDS outcomes has now been confirmed by several independent groups. Penetration of HIV-1 into cells is mediated by interaction between CD4 and chemokine receptors that serve as entry coreceptors. Genetic polymorphisms in chemokine ligand and chemokine receptor genes have recently been associated both with mother-to-child HIV-1 transmission and disease progression in children. These observations suggest a key role for genetic factors in pediatric HIV-1 infection. This article describes the current state of knowledge regarding host genetic influences on pediatric HIV-1 infection and discusses the role of these genes in HIV/AIDS pathogenesis.     

SHIV-1157i及衍生病毒的研究进展

C亚型是世界上流行的HIV-1主要亚型,带有HIV-1 C亚型env区的SHIV和相应的非人灵长类模型是研究人类艾滋病的有效工具。SHIV-1157i及其衍生病毒能够成功地通过黏膜途径感染恒河猴和猪尾猴,并诱发艾滋病类似症状,而且恒河猴缓慢的发病进程与人类感染HIV-1相似。因此,掌握SHIV-1157i及其衍生病毒感染恒河猴的发病规律并探索其机制,将对研究人类HIV-1感染和发病机制,以及评价HIV-1 C亚型env区为靶点的艾滋病候选疫苗具有重要意义。     

The Tat antagonist neomycin B hexa-arginine conjugate inhibits gp-120-induced death of human neuroblastoma cells

Several patients with acquired immunodeficiency syndrome (AIDS) develop neurological complications, which are referred to as human immunodeficiency virus (HIV)-associated dementia (HAD). The HIV-1 coat glycoprotein gp-120 has been proposed as the major etiologic agent for neuronal loss reported postmortem in the brain of AIDS patients. Chemokine receptors may play a role in gp-120-triggered neurotoxicity, both in vitro and in vivo, thus being an intriguing target for developing therapeutic strategies aimed to prevent or reduce neuronal damage occurring during HIV infection. We have previously shown that human CHP100 neuroblastoma cells express CXCR4 and CCR5 chemokine receptors and that interaction between gp-120 and these receptors contributes to cytotoxicity elicited by the protein. Here, we examined the neuroprotective potential of neomycin B hexa-arginine conjugate (NeoR), a recently synthesized compound with anti-HIV activity. We found that gp-120-triggered death is significantly reduced by NeoR, and this protective effect seems related to the ability of NeoR to interact with CXCR4 receptors. The ability of NeoR to cross the blood-brain barrier, as demonstrated in mice by systemic administration of the fluorescein conjugate drug, makes this compound a powerful and attractive therapeutic agent.     

AIDS dementia and HIV-1-induced neurotoxicity: Possible pathogenic associations and mechanisms

AIDS Dementia Complex (ADC) is a syndrome of cognitive, behavioral, and motor deficits resulting from HIV-1 infection within the brain. ADC is characterized by variable degrees of neuronal cell death and gliosis that likely result, at least, in part from release of metabolic products, cytokines, and viral proteins from infected macrophages, although a unifying explanation for the neurological dysfunction has yet to be established. Major unanswered questions include: (i) do neurologic symptoms result from neuronal cell death and/or dysfunction in surviving neurons?; (ii) are viral genomic sequences determinants of neurotoxicity?; (iii) is HIV infection of neurons and astrocytes relevant to pathogenesis?, and (iv) what circulating factors within the brain affect neuronal cell survival and function? This review addresses the association between HIV-1 replication within the brain, production of potential neurotoxins and possible mechanisms of induction of neurotoxicity and neuronal dysfunction contributing to the pathogenesis of ADC.     

Derivation and characterization of a highly pathogenic isolate of human immunodeficiency virus type 2 that causes rapid CD4+ cell depletion in Macaca nemestrina

With few exceptions, humans are the only species known to develop acquired immunodeficiency syndrome (AIDS) after human immunodeficiency virus (HIV) infection. We report here that an isolate of HIV type 2, EHO, readily established persistent infection in 100% of Macaca nemestrina in three consecutive transmission studies. Of the eight infected animals, five showed persistently high virus load and six developed AIDS-like diseases or CD4+ cell depletion within 4 years of infection. The pathology and clinical signs closely parallel those of HIV-1 infection of humans, including lymphadenopathy, anemia, CD4+ cell depletion, and opportunistic infections. A cell-free virus stock was established from the lymph nodes of an animal that developed AIDS-like diseases. This virus, HIV-2/287, was highly pathogenic in M. nemestrina, causing CD4+ cell depletion within 2-8 weeks postinfection. While both HIV-2 EHO and HIV-2/287 use predominantly CXCR4, the latter shows greatly enhanced replicative capacity in macaque peripheral blood mononuclear cells (PBMCs). The establishment of a human immunodeficiency virus that causes rapid and reproducible CD4 cell depletion in macaques could facilitate the study of HIV pathogenesis and the development of effective vaccines and therapy against AIDS.     

The role of monocyte-lineage cells in human immuno-deficiency 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.     

AIDS and HIV-1 Infection: Clinical Entities in Geriatric Dentistry1

The number of AIDS cases in individuals 50 years of age or older in the United States is reported to exceed 9000. Contaminated blood and blood transfusions are major contributors to HIV-1 infection in this age group. Sexual transmission and infection through intravenous drug abuse are also potential avenues of HIV-1 transmission in the older population. AIDS presents with a variety of clinical manifestations, including dementia, frequently seen in non-HIV-1-infected older people. Neurological deficiencies associated with AIDS are very common and may lead to misdiagnosis in the elderly. The observed incubation period of HIV-1 infection is longer than previously estimated, increasing the risk of older individuals exposed to HIV-1 in the past to develop AIDS. Oral manifestations may present as one of the early clinical signs of AIDS. Little is known concerning AIDS in the geriatric population. It demands consideration by dental professionals treating older individuals belonging to one of the exposure categories of the disease.     

Computational analysis of HIV-1 resistance based on gene expression profiles and the virus-host interaction network

A very small proportion of people remain negative for HIV infection after repeated HIV-1 viral exposure, which is called HIV-1 resistance. Understanding the mechanism of HIV-1 resistance is important for the development of HIV-1 vaccines and Acquired Immune Deficiency Syndrome (AIDS) therapies. In this study, we analyzed the gene expression profiles of CD4+ T cells from HIV-1-resistant individuals and HIV-susceptible individuals. One hundred eighty-five discriminative HIV-1 resistance genes were identified using the Minimum Redundancy-Maximum Relevance (mRMR) and Incremental Feature Selection (IFS) methods. The virus protein target enrichment analysis of the 185 HIV-1 resistance genes suggested that the HIV-1 protein nef might play an important role in HIV-1 infection. Moreover, we identified 29 infection information exchanger genes from the 185 HIV-1 resistance genes based on a virus-host interaction network analysis. The infection information exchanger genes are located on the shortest paths between virus-targeted proteins and are important for the coordination of virus infection. These proteins may be useful targets for AIDS prevention or therapy, as intervention in these pathways could disrupt communication with virus-targeted proteins and HIV-1 infection.     

Cell-to-cell transmission of human immunodeficiency virus type 1 in the presence of azidothymidine and neutralizing antibody.

Very few peripheral blood lymphocytes of seropositive individuals are presumably actively infected with human immunodeficiency virus type 1 (HIV-1). During coculture of lymphocytes of a seropositive individual with mitogen-stimulated normal peripheral blood lymphocytes, the number of infected cells becomes amplified such that detectable HIV-1 is produced. We report here that in addition to transmission by extracellular virus, cell-to-cell transmission is responsible for spreading HIV-1 infection from infected to uninfected cells. Azidothymidine and virus-neutralizing antibody had no effect on cell-to-cell transmission of HIV-1. Monoclonal antibodies to the CD4 receptor, but not to the CD3 receptor, prevented cell-to-cell transmission, which suggests that CD4 receptor-mediated cell fusion is involved in cell-to-cell transmission. Spread of infection in a cell-to-cell manner may be important in development of drug therapies for HIV-1 infection.     

Targeted therapy of human immunodeficiency virus-related disease.

Since the discovery of human immunodeficiency virus (HIV) as a pathogenic retrovirus linked to acquired immunodeficiency syndrome (AIDS), a number of potentially useful strategies for antiretroviral therapy of AIDS and its related diseases have emerged. One such strategy involves use of the broad family of 2',3'-dideoxynucleosides, to which 3'-azido-2',3'-dideoxythymidine (AZT) belongs. AZT has been shown to reduce the replication of HIV in vivo and to confer significant clinical benefits in patients in both early and advanced stages of infection. Other members of the family, 2',3'-dideoxycytidine (ddC), 2',3'-dideoxyinosine (ddI), and 2',3'-didehydro-2',3'-dideoxythymidine (d4T), have also been reported to be active against HIV in short-term clinical trials. The armamentarium of antiretroviral agents is rapidly growing. Various nonnucleoside agents have recently been identified to be active against HIV in vitro. HIV-1 protease inhibitors are notable as possible new therapies for HIV-1-related diseases. However, we have faced several new challenges in the antiretroviral therapy in AIDS. These include long-term drug-related toxicities; emergence of drug-resistant HIV variants; and development of various cancers, particularly as effective therapies prolong survival. Progress in understanding structure-activity relations and clinical effectiveness will continue with dideoxynucleoside analogs. However, it seems certain that a variety of nonnucleoside analogs affecting multiple steps in viral replication will become available before long, and combination therapies using multiple antiretroviral drugs will be available. Such therapies will exert major effects against the moribidity and mortality caused by HIV.