Human and rhesus APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H demonstrate a conserved capacity to restrict Vif-deficient HIV-1

Successful intracellular pathogens must evade or neutralize the innate immune defenses of their host cells and render the cellular environment permissive for replication. For example, to replicate efficiently in CD4(+) T lymphocytes, human immunodeficiency virus type 1 (HIV-1) encodes a protein called viral infectivity factor (Vif) that promotes pathogenesis by triggering the degradation of the retrovirus restriction factor APOBEC3G. Other APOBEC3 proteins have been implicated in HIV-1 restriction, but the relevant repertoire remains ambiguous. Here we present the first comprehensive analysis of the complete, seven-member human and rhesus APOBEC3 families in HIV-1 restriction. In addition to APOBEC3G, we find that three other human APOBEC3 proteins, APOBEC3D, APOBEC3F, and APOBEC3H, are all potent HIV-1 restriction factors. These four proteins are expressed in CD4(+) T lymphocytes, are packaged into and restrict Vif-deficient HIV-1 when stably expressed in T cells, mutate proviral DNA, and are counteracted by HIV-1 Vif. Furthermore, APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H of the rhesus macaque also are packaged into and restrict Vif-deficient HIV-1 when stably expressed in T cells, and they are all neutralized by the simian immunodeficiency virus Vif protein. On the other hand, neither human nor rhesus APOBEC3A, APOBEC3B, nor APOBEC3C had a significant impact on HIV-1 replication. These data strongly implicate a combination of four APOBEC3 proteins--APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H--in HIV-1 restriction.     

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.     

Variability of HIV infections.

Genetic variation is the hallmark of infections with lentiviruses in general and the human immunodeficiency viruses (HIV-1, HIV-2) in particular. This article reviews both experimental evidence for the variability of the HIV genome during the course of an individual infection and mathematical models that outline the potential importance of antigenic variation as a major factor to drive disease progression. The essential idea is that the virus evades immune pressure by the continuous production of new mutants resistant to current immunological attack. This results in the accumulation of antigenic diversity during the asymptomatic period. The existence of an antigenic diversity threshold is derived from the asymmetric interaction between the virus quasispecies and the CD4 cell population: CD4 cells mount immune responses some of which are directed against specific HIV variants, but each virus strain can induce depletion of all CD4 cells and therefore impair immune responses regardless of their specificity. Therefore, increasing HIV diversity enables the virus population to escape from control by the immune system. In this context the observed genetic variability is responsible for the fact that the virus establishes a persistent infection without being cleared by the immune response and induces immunodeficiency disease after a long and variable incubation period. Mathematical biology has revealed a novel mechanism for viral pathogenesis.     

Modest Attenuation of HIV-1 Vpu Alleles Derived from Elite Controller Plasma

In the absence of antiretroviral therapy, infection with human immunodeficiency virus type 1 (HIV-1) can typically not be controlled by the infected host and results in the development of acquired immunodeficiency. In rare cases, however, patients spontaneously control HIV-1 replication. Mechanisms by which such elite controllers (ECs) achieve control of HIV-1 replication include particularly efficient immune responses as well as reduced fitness of the specific virus strains. To address whether polymorphisms in the accessory HIV-1 protein Vpu are associated with EC status we functionally analyzed a panel of plasma-derived vpu alleles from 15 EC and 16 chronic progressor (CP) patients. Antagonism of the HIV particle release restriction by the intrinsic immunity factor CD317/tetherin was well conserved among EC and CP Vpu alleles, underscoring the selective advantage of this Vpu function in HIV-1 infected individuals. In contrast, interference with CD317/tetherin induced NF-κB activation was little conserved in both groups. EC Vpus more frequently displayed reduced ability to downregulate cell surface levels of CD4 and MHC class I (MHC-I) molecules as well as of the NK cell ligand NTB-A. Polymorphisms potentially associated with high affinity interactions of the inhibitory killer immunoglobulin-like receptor (KIR) KIR2DL2 were significantly enriched among EC Vpus but did not account for these functional differences. Together these results suggest that in a subgroup of EC patients, some Vpu functions are modestly reduced, possibly as a result of host selection.     

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.     

The quality of chimpanzee T-cell activation and simian immunodeficiency virus/human immunodeficiency virus susceptibility achieved via antibody-mediated T-cell receptor/CD3 stimulation is a function of the anti-CD3 antibody isotype

While human immunodeficiency virus type 1 (HIV-1) infection is associated with hyperimmune activation and systemic depletion of CD4⁺ T cells, simian immunodeficiency virus (SIV) infection in sooty mangabeys or chimpanzees does not exhibit these hallmarks. Control of immune activation is thought to be one of the major components that govern species-dependent differences in the disease pathogenesis. A previous study introduced the idea that the resistance of chimpanzees to SIVcpz infection-induced hyperimmune activation could be the result of the expression of select sialic acid-recognizing immunoglobulin (Ig)-like lectin (Siglec) superfamily members by chimpanzee T cells. Siglecs, which are absent on human T cells, were thought to control levels of T-cell activation in chimpanzees and were thus suggested as a cause for the pathogenic differences in the course of SIVcpz or HIV-1 infection. As in human models of T-cell activation, stimulation had been attempted using an anti-CD3 monoclonal antibody (MAb) (UCHT1; isotype IgG1), but despite efficient binding, UCHT1 failed to activate chimpanzee T cells, an activation block that could be partially overcome by MAb-induced Siglec-5 internalization. We herein demonstrate that anti-CD3 MAb-mediated chimpanzee T-cell activation is a function of the anti-CD3 MAb isotype and is not governed by Siglec expression. While IgG1 anti-CD3 MAbs fail to stimulate chimpanzee T cells, IgG2a anti-CD3 MAbs activate chimpanzee T cells in the absence of Siglec manipulations. Our results thus imply that prior to studying possible differences between human and chimpanzee T-cell activation, a relevant model of chimpanzee T cell activation needs to be established.     

Distinct Evolutionary Pressures Underlie Diversity in Simian Immunodeficiency Virus and Human Immunodeficiency Virus Lineages

Simian immunodeficiency virus (SIV) infection of rhesus macaques causes immune depletion and disease closely resembling human AIDS and is well recognized as the most relevant animal model for the human disease. Experimental investigations of viral pathogenesis and vaccine protection primarily involve a limited set of related viruses originating in sooty mangabeys (SIVsmm). The diversity of human immunodeficiency virus type 1 (HIV-1) has evolved in humans in about a century; in contrast, SIV isolates used in the macaque model evolved in sooty mangabeys over millennia. To investigate the possible consequences of such different evolutionary histories for selection pressures and observed diversity in SIVsmm and HIV-1, we isolated, sequenced, and analyzed 20 independent isolates of SIVsmm, including representatives of 7 distinct clades of viruses isolated from natural infection. We found SIVsmm diversity to be lower overall than HIV-1 M group diversity. Reduced positive selection (i.e., less diversifying evolution) was evident in extended regions of SIVsmm proteins, most notably in Gag p27 and Env gp120. In addition, the relative diversities of proteins in the two lineages were distinct: SIVsmm Env and Gag were much less diverse than their HIV-1 counterparts. This may be explained by lower SIV-directed immune activity in mangabeys relative to HIV-1-directed immunity in humans. These findings add an additional layer of complexity to the interpretation and, potentially, to the predictive utility of the SIV/macaque model, and they highlight the unique features of human and simian lentiviral evolution that inform studies of pathogenesis and strategies for AIDS vaccine design.     

Novel adeno-associated virus vector vaccine restricts replication of simian immunodeficiency virus in macaques

Gene transfer vectors based on recombinant adeno-associated virus (rAAV) are simple, versatile, and safe. While the conventional applications for rAAV vectors have focused on delivery of therapeutic genes, we have developed the system for delivery of vaccine antigens. In particular, we are interested in generating rAAV vectors for use as a prophylactic human immunodeficiency virus type 1 (HIV-1) vaccine. To that end, we constructed vaccine vectors that expressed genes from the simian immunodeficiency virus (SIV) for evaluation in the monkey SIV model. After a single intramuscular dose, rAAV/SIV vaccines elicited SIV-specific T cells and antibodies in macaques. Furthermore, immunized animals were able to significantly restrict replication of a live, virulent SIV challenge. These data suggest that rAAV vaccine vectors induced biologically relevant immune responses, and thus, warrant continued development as a viable HIV-1 vaccine candidate.     

Autophagy: An overlooked mechanism of HIV-1 pathogenesis and NeuroAIDS?

Human immunodeficiency virus type 1 (HIV-1) establishes a persistent infection characterized by progressive depletion of CD4⁺ lymphocytes and immunosuppression. Although extensive research has examined the importance of apoptosis as a cause of cell death associated with HIV-1 infection, the role of autophagy has been largely ignored. Our laboratory has examined the autophagic process in HIV-1-infected cells. Following infection of human peripheral blood CD4+ T-cells or U937 cells with HIV-1 for 48 hours, the autophagy proteins Beclin 1 and LC3-II were found to be markedly decreased. Beclin 1 mRNA expression and autophagosomes were also reduced in HIV-1 infected cells. Thus, our data indicate that HIV-1 infection inhibits autophagy in infected cells in contrast to the previously described induction of autophagy by gp120 in uninfected bystander cells. It is likely that HIV-1 has evolved this mechanism as part of an elaborate attempt to evade the immune system while promoting its own replication. We believe that autophagy is an overlooked mechanism in HIV-1 pathogenesis and plays a particularly important role in the early cognitive impairment and dementia often associated with advanced AIDS. A model is presented that describes the potential role of autophagy in NeuroAIDS.

Addendum to: Zhou D, Spector SA. Human immunodeficiency virus type-1 infection inhibits autophagy. Aids 2008;22:695-9.     

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。     

Envelope glycoproteins of human immunodeficiency virus type 1: profound influences on immune functions.

Infection by human immunodeficiency virus type 1 (HIV-1) leads to progressive destruction of the CD4+ T-cell subset, resulting in immune deficiency and AIDS. The specific binding of the viral external envelope glycoprotein of HIV-1, gp120, to the CD4 molecules initiates viral entry. In the past few years, several studies have indicated that the interaction of HIV-1 envelope glycoprotein with cells and molecules of the immune system leads to pleiotropic biological effects on immune functions, which include effects on differentiation of CD34+ lymphoid progenitor cells and thymocytes, aberrant activation and cytokine secretion patterns of mature T cells, induction of apoptosis, B-cell hyperactivity, inhibition of T-cell dependent B-cell differentiation, modulation of macrophage functions, interactions with components of complement, and effects on neuronal cells. The amino acid sequence homologies of the envelope glycoproteins with several cellular proteins have suggested that molecular mimicry may play a role in the pathogenesis of the disease. This review summarizes work done by several investigators demonstrating the profound biological effects of envelope glycoproteins of HIV-1 on immune system cells. Extensive studies have also been done on interactions of the viral envelope proteins with components of the immune system which may be important for eliciting a "protective immune response." Understanding the influences of HIV-1 envelope glycoproteins on the immune system may provide valuable insights into HIV-1 disease pathogenesis and carries implications for the trials of HIV-1 envelope protein vaccines and immunotherapeutics.     

The Establishment of an In Vivo HIV-1 Infection Model in Humanized B-NSG Mice

Suitable animal models for human immunodeficiency virus type 1(HIV-1) infection are important for elucidating viral pathogenesis and evaluating antiviral strategies in vivo. The B-NSG(NOD-PrkdcscidIl2rgtm1/Bcge) mice that have severe immune defect phenotype are examined for the suitability of such a model in this study. Human peripheral blood mononuclear cells(PBMCs) were engrafted into B-NSG mice via mouse tail vein injection, and the repopulated human T-lymphocytes were observed at as early as 3-weeks post-transplantation in mouse peripheral blood and several tissues.The humanized mice could be infected by HIV-1, and the infection recapitulated features of T-lymphocyte dynamic observed in HIV-1 infected humans, meanwhile the administration of combination antiretroviral therapy(cART) suppressed viral replication and restored T lymphocyte abnormalities. The establishment of HIV-1 infected humanized B-NSG mice not only provides a model to study virus and T cell interplays, but also can be a useful tool to evaluate antiviral strategies.     

MyD88-dependent immune activation mediated by human immunodeficiency virus type 1-encoded Toll-like receptor ligands

Immune activation is a major characteristic of human immunodeficiency virus type 1 (HIV-1) infection and a strong prognostic factor for HIV-1 disease progression. The underlying mechanisms leading to immune activation in viremic HIV-1 infection, however, are not fully understood. Here we show that, following the initiation of highly active antiretroviral therapy, the immediate decline of immune activation is closely associated with the reduction of HIV-1 viremia, which suggests a direct contribution of HIV-1 itself to immune activation. To propose a mechanism, we demonstrate that the single-stranded RNA of HIV-1 encodes multiple uridine-rich Toll-like receptor 7/8 (TLR7/8) ligands that induce strong MyD88-dependent plasmacytoid dendritic cell and monocyte activation, as well as accessory cell-dependent T-cell activation. HIV-1-encoded TLR ligands may, therefore, directly contribute to the immune activation observed during viremic HIV-1 infection. These data provide an initial rationale for inhibiting the TLR pathway to directly reduce the chronic immune activation induced by HIV-1 and the associated immune pathogenesis.     

Evasion from NK cell-mediated immune responses by HIV-1

Human immunodeficiency virus type 1 (HIV-1) mostly owes its success to its ability to evade host immune responses. Understanding viral immune escape mechanisms is a prerequisite to improve future HIV-1 vaccine design. This review focuses on the strategies that HIV-1 has evolved to evade recognition by natural killer (NK) cells.     

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.     

Distinct mechanisms of CD4+ and CD8+ T-cell activation and bystander apoptosis induced by human immunodeficiency virus type 1 virions

Apoptosis of uninfected bystander T cells contributes to T-cell depletion during human immunodeficiency virus type 1 (HIV-1) infection. HIV-1 envelope/receptor interactions and immune activation have been implicated as contributors to bystander apoptosis. To better understand the relationship between T-cell activation and bystander apoptosis during HIV-1 pathogenesis, we investigated the effects of the highly cytopathic CXCR4-tropic HIV-1 variant ELI6 on primary CD4(+) and CD8(+) T cells. Infection of primary T-cell cultures with ELI6 induced CD4(+) T-cell depletion by direct cell lysis and bystander apoptosis. Exposure of primary CD4(+) and CD8(+) T cells to nonreplicating ELI6 virions induced bystander apoptosis through a Fas-independent mechanism. Bystander apoptosis of CD4(+) T cells required direct contact with virions and Env/CXCR4 binding. In contrast, the apoptosis of CD8(+) T cells was triggered by a soluble factor(s) secreted by CD4(+) T cells. HIV-1 virions activated CD4(+) and CD8(+) T cells to express CD25 and HLA-DR and preferentially induced apoptosis in CD25(+)HLA-DR(+) T cells in a CXCR4-dependent manner. Maximal levels of binding, activation, and apoptosis were induced by virions that incorporated MHC class II and B7-2 into the viral membrane. These results suggest that nonreplicating HIV-1 virions contribute to chronic immune activation and T-cell depletion during HIV-1 pathogenesis by activating CD4(+) and CD8(+) T cells, which then proceed to die via apoptosis. This mechanism may represent a viral immune evasion strategy to increase viral replication by activating target cells while killing immune effector cells that are not productively infected.     

Use of inhibitors to evaluate coreceptor usage by simian and simian/human immunodeficiency viruses and human immunodeficiency virus type 2 in primary cells

We have used coreceptor-targeted inhibitors to investigate which coreceptors are used by human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency viruses (SIV), and human immunodeficiency virus type 2 (HIV-2) to enter peripheral blood mononuclear cells (PBMC). The inhibitors are TAK-779, which is specific for CCR5 and CCR2, aminooxypentane-RANTES, which blocks entry via CCR5 and CCR3, and AMD3100, which targets CXCR4. We found that for all the HIV-1 isolates and all but one of the HIV-2 isolates tested, the only relevant coreceptors were CCR5 and CXCR4. However, one HIV-2 isolate replicated in human PBMC even in the presence of TAK-779 and AMD3100, suggesting that it might use an undefined, alternative coreceptor that is expressed in the cells of some individuals. SIV(mac)239 and SIV(mac)251 (from macaques) were also able to use an alternative coreceptor to enter PBMC from some, but not all, human and macaque donors. The replication in human PBMC of SIV(rcm) (from a red-capped mangabey), a virus which uses CCR2 but not CCR5 for entry, was blocked by TAK-779, suggesting that CCR2 is indeed the paramount coreceptor for this virus in primary cells.     

The human immunodeficiency virus type 1 Nef and Vpu proteins downregulate the natural killer cell-activating ligand PVR

The human immunodeficiency virus type 1 (HIV-1) evades the immune responses of natural killer (NK) cells through mechanisms that have been partially deciphered. Here we show that in HIV-1-infected T lymphocytes, the early viral Nef protein downmodulates PVR (CD155, Necl-5), a ligand for the activating receptor DNAM-1 (CD226) expressed by all NK cells, CD8(+) T cells, and other cell types. This novel Nef activity is conserved by Nef proteins of laboratory HIV-1 strains (NL4-3, SF2) and of a patient-derived virus, but it is not maintained by HIV-2. Nef uses the same motifs to downregulate PVR and HLA-I molecules, likely by the same mechanisms. Indeed, as previously demonstrated for HLA-I, Nef reduces the total amounts of cell-associated PVR. Optimal downregulation of cell surface PVR by Nef also requires the presence of the late viral factor Vpu. In line with PVR reduction, the NK cell-mediated lysis of T cells infected by a wild-type but not Nef-deficient virus is virtually abrogated upon blocking of both DNAM-1 and another activating receptor, NKG2D, previously shown to mediate killing of HIV-infected cells. Together, these data demonstrate that the PVR downmodulation by Nef and Vpu is a strategy evolved by HIV-1 to prevent NK cell-mediated lysis of infected cells. The PVR downregulation reported here has the potential to affect the immune responses of other DNAM-1-positive cells besides NK cells and to alter multiple PVR-mediated cellular processes, such as adhesion and migration, and may thus greatly influence HIV-1 pathogenesis.