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 post-infection. 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.     

Longitudinal follow up of SIVmac pathogenesis in rhesus macaques of Chinese origin: emergence of B cell lymphoma

Two subspecies of rhesus (Rh) macaques, the Chinese (Ch) and Indian (Ind) subspecies were infected intravenously with 100TCID50 SIVmac239. CD4+, CD8+ T cells, plasma viral loads, depletion of intestinal lymphocytes with memory phenotype, humoral immune responses and clinical courses were monitored for 600 days. The pathogenesis of SIVmac was also compared with primary human immunodeficiency virus (HIV) infection of humans. Plasma viral loads in Ch Rh were lower in the acute and chronic phases compared with Ind Rh. SIVmac pathogenesis in Ch Rh was closer to virus loads in untreated HIV infected humans. Ch Rh had higher CD4/CD8 ratios, stronger antibody responses and interestingly, less depletion of intestinal memory CCR5+ CD4+ T lymphocytes compared with Ind Rh. One Ch Rh developed B cell origin lymphoma at 570 days post-infection, the first such report in this subspecies. Three of four Ind Rh developed AIDS within 6 months. The findings indicate that Ch Rh are more resistant to SIVmac pathogenesis compared with Ind Rh and that Ch Rh paralleled HIV-1 infections in untreated adult humans. The SIVmac infected Ch Rh subspecies are an acceptable model for HIV/AIDS.     

Resistance of chimpanzee T cells to human immunodeficiency virus type 1 Tat-enhanced oxidative stress and apoptosis.

CD4+ T-cell depletion in AIDS patients involves induction of apoptosis in human immunodeficiency virus (HIV)-infected and noninfected T cells. The HIV type 1 (HIV-1)-transactivating protein Tat enhances apoptosis and activation-induced cell death (AICD) of human T cells. This effect is mediated by the CD95 (APO-1/Fas) receptor-CD95 ligand (CD95L) system and may be linked to the induction of oxidative stress by Tat. Here we show that HIV-1 Tat-induced oxidative stress is necessary for sensitized AICD in T cells caused by CD95L expression. Tat-enhanced apoptosis and CD95L expression in T cells are inhibited by neutralizing anti-Tat antibodies, antioxidants, and the Tat inhibitor Ro24-7429. Chimpanzees infected with HIV-1 show viral replication resembling early infection in humans but do not show T-cell depletion or progression towards AIDS. The cause for this discrepancy is unknown. Here we show that unlike Tat-treated T cells in humans, Tat-treated chimpanzee T cells do not show downregulation of manganese superoxide dismutase or signs of oxidative stress. Chimpanzee T cells are also resistant to Tat-enhanced apoptosis, AICD, and CD95L upregulation.     

Membrane-fusing capacity of the human immunodeficiency virus envelope proteins determines the efficiency of CD+ T-cell depletion in macaques infected by a simian-human immunodeficiency virus

The mechanism of the progressive loss of CD4+ T lymphocytes, which underlies the development of AIDS in human immunodeficiency virus (HIV-1)-infected individuals, is unknown. Animal models, such as the infection of Old World monkeys by simian-human immunodeficiency virus (SHIV) chimerae, can assist studies of HIV-1 pathogenesis. Serial in vivo passage of the nonpathogenic SHIV-89.6 generated a virus, SHIV-89.6P, that causes rapid depletion of CD4+ T lymphocytes and AIDS-like illness in monkeys. SHIV-KB9, a molecularly cloned virus derived from SHIV-89.6P, also caused CD4+ T-cell decline and AIDS in inoculated monkeys. It has been demonstrated that changes in the envelope glycoproteins of SHIV-89.6 and SHIV-KB9 determine the degree of CD4+ T-cell loss that accompanies a given level of virus replication in the host animals (G. B. Karlsson et. al., J. Exp. Med. 188:1159-1171, 1998). The envelope glycoproteins of the pathogenic SHIV mediated membrane fusion more efficiently than those of the parental, nonpathogenic virus. Here we show that the minimal envelope glycoprotein region that specifies this increase in membrane-fusing capacity is sufficient to convert SHIV-89.6 into a virus that causes profound CD4+ T-lymphocyte depletion in monkeys. We also studied two single amino acid changes that decrease the membrane-fusing ability of the SHIV-KB9 envelope glycoproteins by different mechanisms. Each of these changes attenuated the CD4+ T-cell destruction that accompanied a given level of virus replication in SHIV-infected monkeys. Thus, the ability of the HIV-1 envelope glycoproteins to fuse membranes, which has been implicated in the induction of viral cytopathic effects in vitro, contributes to the capacity of the pathogenic SHIV to deplete CD4+ T lymphocytes in vivo.     

Why is HIV a pathogen?

The pathogenesis of HIV begins with a profound depletion of CD4+ T cells in the gut followed by a long period of clinically silent but dynamic virus replication and diversification with high host cell turnover before the onset of AIDS. The AIDS-defining opportunistic infections and tumors mark the end-point of a long balancing act between virus and host that occurs when CD4+ T cell numbers fall below a level that can sustain immunity. Comparative studies of lentivirus infections in other species show that AIDS is not an inevitable outcome of infection because simian immunodeficiency virus in natural hosts seldom causes disease. What distinguishes pathogenic from 'passenger' infection is a systemic activation of immune responses followed by destruction of the integrity of lymphoid follicles. Macrophage and dendritic cell infection also contribute to pathogenesis. Maedi-Visna virus infection in sheep, which targets these cells but not T lymphocytes, also leads to progressive disease and death that resembles the wasting and brain diseases of HIV without the T cell immunodeficiency. Thus, lessons from pathogenic and nonpathogenic lentivirus infections provide insight into the complex syndrome called AIDS.     

Enhanced replication of HIV-1 in vivo in pigtailed macaques (Macaca nemestrina)

Non-human primate models for acquired immunodeficiency syndrome (AIDS) are important for studies of prevention and intervention strategies. Ideally, such models would make use of human immunodeficiency virus type 1 (HIV-1) and animals that are readily available for research. HIV-1 was obtained from an infected macaque, and passaged sequentially in three groups of two Macaca nemestrina neonates each. Evidence for enhanced viral replication was first found in one of the group 2 animals, and in both group 3 animals. Observations that underlie this conclusion are sustained viral recovery from peripheral blood mononuclear cells (PBMCs), increased and accelerated production of antiviral antibodies, and the ability to detect plasma viral ribonucleic acid (RNA) months after infection. There was no evidence of CD4 depletion in any of the animals during the follow-up period. These data suggest that a useful non-human primate model for AIDS can be attained in pigtailed macaques (M. nemestrina).     

Enhanced replication of HIV-1 in vivo in pigtailed macaques (Macaca nemestrina)

Non-human primate models for acquired immunodeficiency syndrome (AIDS) are important for studies of prevention and intervention strategies. Ideally, such models would make use of human immunodeficiency virus type 1 (HIV-1) and animals that are readily available for research. HIV-1 was obtained from an infected macaque, and passaged sequentially in three groups of two Macaca nemestrina neonates each. Evidence for enhanced viral replication was first found in one of the group 2 animals, and in both group 3 animals. Observations that underlie this conclusion are sustained viral recovery from peripheral blood mononuclear cells (PBMCs), increased and accelerated production of antiviral antibodies, and the ability to detect plasma viral ribonucleic acid (RNA) months after infection. There was no evidence of CD4 depletion in any of the animals during the follow-up period. These data suggest that a useful non-human primate model for AIDS can be attained in pigtailed macaques ( M. nemestrina ).     

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.     

Limited CD4+ T cell proliferation leads to preservation of CD4+ T cell counts in SIV-infected sooty mangabeys

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections result in chronic virus replication and progressive depletion of CD4+ T cells, leading to immunodeficiency and death. In contrast, ‘natural hosts’ of SIV experience persistent infection with high virus replication but no severe CD4+ T cell depletion, and remain AIDS-free. One important difference between pathogenic and non-pathogenic infections is the level of activation and proliferation of CD4+ T cells. We analysed the relationship between CD4+ T cell number and proliferation in HIV, pathogenic SIV in macaques, and non-pathogenic SIV in sooty mangabeys (SMs) and mandrills. We found that CD4+ T cell proliferation was negatively correlated with CD4+ T cell number, suggesting that animals respond to the loss of CD4+ T cells by increasing the proliferation of remaining cells. However, the level of proliferation seen in pathogenic infections (SIV in rhesus macaques and HIV) was much greater than in non-pathogenic infections (SMs and mandrills). We then used a modelling approach to understand how the host proliferative response to CD4+ T cell depletion may impact the outcome of infection. This modelling demonstrates that the rapid proliferation of CD4+ T cells in humans and macaques associated with low CD4+ T cell levels can act to ‘fuel the fire’ of infection by providing more proliferating cells for infection. Natural host species, on the other hand, have limited proliferation of CD4+ T cells at low CD4+ T cell levels, which allows them to restrict the number of proliferating cells susceptible to infection.     

Suppression of simian immunodeficiency virus replication in vitro by CD8+ lymphocytes

The AIDS-like disease in rhesus monkeys induced by the simian immunodeficiency virus (SIV) has been used as a model to explore the nature of the T lymphocyte response after infection with viruses of the human immunodeficiency virus family. Activated CD8+ lymphocytes are present in increased numbers in the paracortex of lymph nodes of SIV-infected rhesus monkeys with a lymphadenopathy syndrome. We demonstrate that SIV is more readily isolated from CD8+ lymphocyte-depleted PBL of SIV-infected animals than from their unfractionated PBL. Rather than reflecting the fact that the CD8+ lymphocyte-depleted cell populations are simply enriched for CD4+ lymphocytes, this indicates that CD8+ cells themselves are critical in this regulatory interaction. In fact, CD8+ lymphocytes from SIV-infected but not uninfected rhesus monkeys can block SIV replication in vitro in PBL populations. A T lymphocyte population that blocks replication of viruses of the HIV family may contribute to containing the progression of AIDS.     

CD4+ T cells from CD4C/HIVNef transgenic mice show enhanced activation in vivo with impaired proliferation in vitro but are dispensable for the development of a severe AIDS-like organ disease

The cellular and molecular mechanisms of dysfunction and depletion of CD4+ T lymphocytes over the course of human immunodeficiency virus type 1 (HIV-1) infection are still incompletely understood, but chronic immune activation is thought to play an important role in disease progression. We studied CD4+ T-cell biology in CD4C/HIV transgenic (Tg) mice, in which Nef expression is sufficient to induce a severe AIDS-like disease including a preferential decrease of CD4+ T cells. We show here that Nef-expressing Tg CD4+ T cells exhibit an activated/memory-like phenotype which appears to be independent of antigenic stimulation, as documented in experiments involving breeding with AD10 TcR Tg mice. In addition, in vivo bromodeoxyuridine incorporation showed that a larger proportion of Tg than non-Tg CD4+ T cells entered the S phase. However, in vitro, Tg CD4+ T cells were found to have a very limited capacity to divide in response to stimulation with anti-CD3 and anti-CD28 or in allogeneic mixed leukocyte reactions. Interestingly, despite these observations, the deletion of Tg CD4+ T cells had little impact on the development of other AIDS-like organ phenotypes. Thus, the Nef-induced chronic activation of CD4+ T cells may exhaust the T-cell pool and may contribute to the thymic atrophy and the low number of CD4+ T cells observed in these Tg mice.     

RANTES and MCP-3 inhibit the replication of T-cell-tropic human immunodeficiency virus type 1 strains (SF-2, MN, and HE).

The effects of the C-C chemokines RANTES (regulation upon activation normal T-cell expressed and secreted) and MCP-3 (monocyte chemotactic protein 3) on human immunodeficiency virus (HIV) replication in normal human peripheral blood mononuclear cells (PBMC) activated in vitro with phytohemagglutinin (PHA) were investigated. The following T-cell line-tropic (T-tropic) HIV strains were tested: HIV type 1 (HIV-1) SF-2, HIV-1 IIIB, HIV-1 MN, HIV-1 NDK, HIV-1 HE, HIV-1 NL4-3, HIV-2 ROD, and HIV-2 EHO. The strain most sensitive to the antiviral effects of RANTES and MCP-3 appeared to be HIV-1 SF-2. A 50% inhibitory concentration for HIV-1 SF-2 of 4 ng of RANTES per ml was obtained, and that of MCP-3 was about 1 ng/ml. However, MCP-3 was inactive at 100 ng/ml. Other HIV-1 strains, such as MN and HE, were less sensitive to the antiviral effects of RANTES and MCP-3, whereas all the other HIV strains tested were insensitive. Although the ratio of CD3+ CD4+ to CD3+ CD8+ T cells was the same in HIV-infected PBMC cultures treated or untreated with the chemokines, RANTES and MCP-3 interfered with the binding of monoclonal antibody (MAb) OKT4 to the CD4 receptor on T cells but not with the binding of MAb OKT4A. Therefore, RANTES and MCP-3 not only interfere with the HIV-induced fusion process but also have some modulating effect on the CD4 cell receptor. The chemokines did not affect HIV-1 binding to PHA-stimulated PBMC. Taken together, our observations point to the important role that both RANTES and MCP-3 may play in inhibiting HIV-1 replication of certain T-tropic strains in primary PBMC cultures. This may have important implications for immunotherapeutic strategies designed to slow down disease progression in AIDS.     

Lack of gp120-induced anergy and apoptosis in chimpanzees is correlated with resistance to AIDS

Human immunodeficiency virus-1 (HIV-1) infects both humans and chimpanzees, but in the chimpanzee, HIV-1 infection leads only very rarely to loss of CD4 T cells or to AIDS-like disease. The pathogenetic basis for this difference in host range is not understood. In previous studies, using CD4 T cells from HIV-1 seronegative human donors, we demonstrated that crosslinking of CD4-bound gp120, followed by signaling through the T cell receptor for antigen (TCR), resulted in cell death by apoptosis. To determine whether activation-induced apoptosis correlates with progression to AIDS, we studied the chimpanzee. Our data suggest that, although human CD4 T cells respond to CD4 ligation with anergy and apoptosis upon activation, chimpanzee CD4 T cells do not undergo apoptosis after cross-linking of CD4-bound gp120, followed by signaling through the TCR. In addition, proliferation assays show that chimpanzee CD4 T cells do not become anergic after CD4 ligation. Thus, it is possible that, in the chimpanzee, the absence of cellular anergy and apoptotic cell death after CD4 ligation by HIV-1 gp120 protect this primate species from progression to AIDS-like disease.This investigation was supported by National Institute of Health grants AI-30575, AI-29903, AI-35513, and RR00015 (TH Finkel), AI-05060 (WC Satterfield), American Foundation for AIDS Research grants 02270-16-RG (TH Finkel) and 770188-11-PF (NK Banda), the Concerned Parents for AIDS Research, the UCHSC Cancer Center, the Eleanore and Michael Stobin Trust, and the Bender Foundation.     

An initial in vitro investigation into the potential therapeutic use of SupT1 cells to prevent AIDS in HIV-seropositive individuals

HIV infection usually leads to a progressive decline in number and functionality of CD4+ T lymphocytes, resulting in AIDS development. In this study, I investigated the strategy of using inoculated SupT1 cells to move infection from HIV-1 X4 strains toward the inoculated cells, which should theoretically prevent infection and depletion of normal CD4+ T cells, preventing the development of AIDS-related pathologies. Interestingly, the persistent in vitro replication in SupT1 cells renders the virus less cytopathic and more sensitive to antibody-mediated neutralization, suggesting that replication of the virus in the inoculated SupT1 cells may have a vaccination effect in the long run. In order to mimic the scenario of a therapy in which SupT1 cells are inoculated in an HIV-seropositive patient, I used infected SupT1/PBMC cocultures and a series of control experiments. Infections were done with equal amounts of the wild type HIV-1 LAI virus. The SupT1 CD4+CD8+ T cell population was distinguished from the PBMC CD4+CD8- T cell population by FACS analysis. The results of this study show that the virus-mediated killing of primary CD4+ T cells in the SupT1/PBMC cocultures was significantly delayed, suggesting that the preferential infection of SupT1 cells can induce the virus to spare primary CD4+ T cells from infection and depletion. The preferential infection of SupT1 cells can be explained by the higher viral tropism for the SupT1 cell line. In conclusion, this study demonstrates that it's possible in an in vitro system to use SupT1 cells to prevent HIV infection of primary CD4+ T cells, suggesting that further exploration of the SupT1 cell line as a cell-based therapy against HIV-1 may prove worthwhile.     

GBV-C/HIV共感染对AIDS疾病进程和HIV病毒复制的影响

近年来,一些研究发现,GBV-C/HIV共感染可延缓HIV感染疾病的进程,然而也有一些研究得出不同的结论.本研究收集我国安徽省阜阳市HIV血清学阳性的既往献血员血浆标本,对其进行GBV-C感染的检测,研究GBV-C/HIV共感染与HIV病毒载量和CD4 T淋巴细胞绝对计数的关系.用RT-PCR和酶联免疫法检测,在203人中检出GBV-C感染52例,显示该人群GBV-C的感染率为25.6%,男性感染者(35例,67.3%)高于女性感染者(17例,32.7%).分析发现,GBV-C感染与未感染两组患者的CD4 T淋巴细胞绝对计数和HIV病毒载量数据均无统计学差异.本研究中的HIV-1感染者均未接受ART治疗,因而排除了治疗对疾病进展的影响.研究结果显示,在HIV-1感染晚期的献血人群,GBV-C/HIV共感染对CD4细胞和病毒复制水平无显著影响.由于本研究对象中无HIV-1早期感染者,因而不能判断GBV-C在HIV-1感染的早期对疾病进展有无影响.     

Gastrointestinal Viral Load and Enteroendocrine Cell Number Are Associated with Altered Survival in HIV-1 Infected Individuals

Human immunodeficiency virus type 1 (HIV-1) infects and destroys cells of the immune system leading to an overt immune deficiency known as HIV acquired immunodeficiency syndrome (HIV/AIDS). The gut associated lymphoid tissue is one of the major lymphoid tissues targeted by HIV-1, and is considered a reservoir for HIV-1 replication and of major importance in CD4+ T-cell depletion. In addition to immunodeficiency, HIV-1 infection also directly causes gastrointestinal (GI) dysfunction, also known as HIV enteropathy. This enteropathy can manifest itself as many pathological changes in the GI tract. The objective of this study was to determine the association of gut HIV-1 infection markers with long-term survival in a cohort of men who have sex with men (MSM) enrolled pre-HAART (Highly Active Antiretroviral Therapy). We examined survival over 15-years in a cohort of 42 HIV-infected cases: In addition to CD4+ T cell counts and HIV-1 plasma viral load, multiple gut compartment (duodenum and colon) biopsies were taken by endoscopy every 6 months during the initial 3-year period. HIV-1 was cultured from tissues and phenotyped and viral loads in the gut tissues were determined. Moreover, the tissues were subjected to an extensive assessment of enteroendocrine cell distribution and pathology. The collected data was used for survival analyses, which showed that patients with higher gut tissue viral load levels had a significantly worse survival prognosis. Moreover, lower numbers of serotonin (duodenum) and somatostatin (duodenum and colon) immunoreactive cell counts in the gut tissues of patients was associated with significant lower survival prognosis. Our study, suggested that HIV-1 pathogenesis and survival prognosis is associated with altered enteroendocrine cell numbers, which could point to a potential role for enteroendocrine function in HIV infection and pathogenesis.     

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.