HIV病毒潜伏库的形成机制和对策挑战

长期以来,病毒潜伏库(latent viral reservoir,LVR)的存在严重阻碍了AIDS的有效治疗,LVR无法被人体免疫系统识别,高效抗逆转录病毒疗法(highly active antiretroviral therapy, HAART)对其无效,一旦中断抗病毒治疗,患者会出现快速耐药和病毒血症反弹.截至...     

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。     

On the origin and evolution of the human immunodeficiency virus (HIV)

The human AIDS viruses--HIV-1 and HIV-2--impose major burdens on the health and economic status of many developing countries. Surveys of other animal species have revealed that related viruses--the SIVs are widespread in a large number of African simian primates where they do not appear to cause disease. Phylogenetic analyses indicate that these SIVs are the reservoirs for the human viruses, with SIVsm from the sooty mangabey monkey the most likely source of HIV-2, and SIVcpz from the common chimpanzee the progenitor population for HIV-1. Although it is clear that AIDS has a zoonotic origin, it is less certain when HIV-1 and HIV-2 first entered human populations and whether cross-species viral transmission is common among primates. Within infected individuals the process of HIV evolution takes the form of an arms race, with the virus continually fixing mutations by natural selection which allow it to escape from host immune responses. The arms race is less intense in SIV-infected monkeys, where a weaker immune response generates less selective pressure on the virus. Such a difference in virus-host interaction, along with a broadening of co-receptor usage such that HIV strains are able to infect cells with both CCR5 and CXCR4 chemokine receptors, may explain the increased virulence of HIV in humans compared to SIV in other primates.     

Monocytes/macrophages in HIV infection and tuberculosis.

Mycobacterium tuberculosis (MTB) and human immunodeficiency virus type 1 (HIV-1) are virulent intracellular pathogens that enter and replicate within macrophages, which represent their reservoire. Public health problems are greatly compounded when the two diseases co-exist, and this is the reason why Acquired Immunodeficiency Syndrome (AIDS) and tuberculosis (TB) have been termed "the cursed duet", given the synergistic effect they exert one each other. With the depression of immunity caused by HIV-1 infection, latent MTB infection is much more likely to progress to clinically significant disease. On the other hand, TB results in activation of T cells and macrophages that may harbor latent HIV. Here some data are reviewed that can contribute to clarify the mechanisms involved in the concurrent infection, given that MTB infection has been shown to be able to: a) enhance HIV-1 replication in macrophages, b) augment CC-CKR5 (CCR5) expression on macrophage membrane, and, c) induce apoptosis in a portion of infected macrophages.     

Frequent intrapatient recombination between human immunodeficiency virus type 1 R5 and X4 envelopes: implications for coreceptor switch

Emergence of human immunodeficiency virus type 1 (HIV-1) populations that switch or broaden coreceptor usage from CCR5 to CXCR4 is intimately coupled to CD4+ cell depletion and disease progression toward AIDS. To better understand the molecular mechanisms involved in the coreceptor switch, we determined the nucleotide sequences of 253 V1 to V3 env clones from 27 sequential HIV-1 subtype B isolates from four patients with virus populations that switch coreceptor usage. Coreceptor usage of clones from dualtropic R5X4 isolates was characterized experimentally. Sequence analysis revealed that 9% of the clones from CXCR4-using isolates had originated by recombination events between R5 and X4 viruses. The majority (73%) of the recombinants used CXCR4. Furthermore, coreceptor usage of the recombinants was determined by a small region of the envelope, including V3. This is the first report demonstrating that intrapatient recombination between viruses with distinct coreceptor usage occurs frequently. It has been proposed that X4 viruses are more easily suppressed by the immune system than R5 viruses. We hypothesize that recombination between circulating R5 viruses and X4 viruses can result in chimeric viruses with the potential to both evade the immune system and infect CXCR4-expressing cells. The broadening in cell tropism of the viral population to include CXCR4-expressing cells would gradually impair the immune system and eventually allow the X4 population to expand. In conclusion, intrapatient recombination between viruses with distinct coreceptor usage may contribute to the emergence of X4 viruses in later stages of infection.     

The human immunodeficiency virus type 1 vpr gene arrests infected T cells in the G2 + M phase of the cell cycle.

Human immunodeficiency virus type 1 (HIV-1) infection causes profound immunological defects in afflicted patients. Various mechanisms have been proposed to account for the immune dysfunction in AIDS ultimately leading to loss of CD4+ T cells, including HIV-1 envelope-mediated syncytium formation, apoptosis, and cytokine modulation. Here we present results which suggest a novel hypothesis for T-cell dysfunction. We show, using HIV-1 bearing a novel cell surface reporter gene, that infected cells are unable to progress normally through the cell cycle and became arrested in the G2 + M phase. Furthermore, we identify the HIV-1 vpr gene product as being both necessary and sufficient for eliciting this cell cycle arrest. Cell cycle arrest induced by Vpr correlates with an increase in the hyperphosphorylated (inactive) form of the cyclin-dependent serine/threonine kinase CDC2, consistent with an arrest of cells at the boundary of G2 and M.     

抗人类免疫缺陷病毒1型广谱中和抗体的研究进展

现行抗反转录病毒治疗药物的联合应用可有效抑制艾滋病进程并显著延长患者寿命,但由于人类免疫缺陷病毒1型(human immunodeficiency virus type 1,HIV-1)潜伏库的存在,艾滋病迄今尚无法治愈。近年发现抗HIV广谱中和抗体能有效降低患者体内病毒载量并延缓疾病进程,为研发艾滋病疫苗和治愈策略带来了曙光,尤其是序贯免疫策略的使用极大推进了广谱中和抗体的开发和应用进程。2018年,美国食品药品管理局(Food and Drug Administration,FDA)批准了第1个临床应用的广谱中性单克隆和抗体,无疑为抗HIV单克隆抗体药物的研发注入了一支强心剂。本文围绕近年来抗HIV广谱中和抗体的研究进展进行综述,探讨未来广谱中和抗体研发面临的挑战。     

A hard way to the nucleus

As a member of the Retrovirus family, human immunodeficiency virus (HIV), a causative agent of AIDS, replicates by integrating its genome into the host cell's nuclear DNA. However, in contrast to most retroviruses that depend on mitotic dissolution of the nuclear envelope to gain access to the host cell's genome, the HIV pre-integration complex can enter the nucleus of the target cell during the interphase. Such capacity greatly enhances HIV replication and allows the virus to productively infect terminally differentiated nonproliferating cells, such as macrophages. Infection of macrophages is a critical factor in the pathogenesis of diseases caused by HIV-1 and other lentiviruses. The mechanisms responsible for this unusual feature of HIV have enticed researchers since the early 90s, when the first characterization of the HIV-1 pre-integration complex was reported. Several viral factors, including matrix protein, integrase, viral protein R, and central DNA flap, have been proposed as regulators of HIV-1 nuclear import, only to be later shown as nonessential for this process. As a result, after more than a decade of intense research, there is still no consensus on which HIV-1 and cellular proteins control this critical step in HIV-1 replication. In this review, we will discuss recent advances and suggest possible solutions to the controversial issue of HIV-1 nuclear import.     

Human immunodeficiency virus-1 uses the mannose-6-phosphate receptor to cross the blood-brain barrier

HIV-1 circulates both as free virus and within immune cells, with the level of free virus being predictive of clinical course. Both forms of HIV-1 cross the blood-brain barrier (BBB) and much progress has been made in understanding the mechanisms by which infected immune cells cross the blood-brain barrier BBB. How HIV-1 as free virus crosses the BBB is less clear as brain endothelial cells are CD4 and galactosylceramide negative. Here, we found that HIV-1 can use the mannose-6 phosphate receptor (M6PR) to cross the BBB. Brain perfusion studies showed that HIV-1 crossed the BBB of all brain regions consistent with the uniform distribution of M6PR. Ultrastructural studies showed HIV-1 crossed by a transcytotic pathway consistent with transport by M6PR. An in vitro model of the BBB was used to show that transport of HIV-1 was inhibited by mannose, mannan, and mannose-6 phosphate and that enzymatic removal of high mannose oligosaccharide residues from HIV-1 reduced transport. Wheatgerm agglutinin and protamine sulfate, substances known to greatly increase transcytosis of HIV-1 across the BBB in vivo, were shown to be active in the in vitro model and to act through a mannose-dependent mechanism. Transport was also cAMP and calcium-dependent, the latter suggesting that the cation-dependent member of the M6PR family mediates HIV-1 transport across the BBB. We conclude that M6PR is an important receptor used by HIV-1 to cross the BBB.     

Differential HIV-1 Endocytosis and Susceptibility to Virus Infection in Human Macrophages Correlate with Cell Activation Status

HIV-1 is an enveloped virus that enters target cells by fusion either directly at the plasma membrane or at the endosomal membrane. The latter mechanism follows a rapid engulfment of HIV-1 after its receptor engagement at the cell surface, and its scale depends on cellular endocytosis/degradation rates and virus fusion kinetics. HIV-1 has recently been shown to exploit a novel Pak1-dependent macropinocytosis mechanism as a way to productively infect macrophages. However, macrophages are highly heterogeneous cells that can adapt functionally to their changing environment, and their endosomal/lysosomal pathway is highly regulated upon cell activation. These changes might impact the ability of HIV-1 to exploit endocytosis as a way to productively infect macrophages. In this study, we compared HIV-1 endocytosis/degradation rates in nonactivated, M1-activated, and M2a-activated monocyte-derived macrophages (MDMs). We found that the rate of HIV-1 endocytosis was increased in M1-activated but decreased in M2a-activated MDMs. However, both M1 and M2a activations of MDMs led specifically to a greater clathrin-mediated endocytosis of HIV-1, which was independent of CD4 and CCR5 binding. Furthermore, clathrin-mediated endocytosis is unlikely to result in productive HIV-1 infection, given that it leads to increased viral degradation. Therefore, we suggest that viral fusion following endocytosis is restricted in activated macrophages.     

Role of low CD4 levels in the influence of human immunodeficiency virus type 1 envelope V1 and V2 regions on entry and spread in macrophages

Human immunodeficiency virus type 1 (HIV-1) isolates vary in their ability to infect macrophages. Previous experiments have mapped viral determinants of macrophage infectivity to the V3 hypervariable region of the HIV-1 envelope glycoprotein. In our earlier studies, V1 and V2 sequences of HIV-1 were also shown to alter the ability of virus to spread in macrophage cultures, whereas no effect was seen in lymphocyte cultures. In the present study, determinants that allowed certain HIV-1 clones to infect and spread in macrophages were primarily mapped to the V2 region and were found to act by influencing early events of viral infection. By an assay of viral entry into macrophages, it was shown that viruses with the V2 region from the Ba-L strain of HIV-1 had >10-fold-higher entry efficiency than viruses with the V2 region derived from the NL4-3 strain. V1 region differences between these groups caused a twofold difference in entry. The known low expression of CD4 on macrophages appeared to be important in this process. In entry assays conducted with HeLa cell lines expressing various levels of CD4 and CCR5, low levels of CD4 influenced the efficiency of entry and fusion which were dependent on viral V1 and V2 envelope sequences. In contrast, no effect of V1 or V2 was seen in HeLa cells expressing high levels of CD4. Thus, the limited expression of CD4 on macrophages or other cell types could serve as a selective factor for V1 and V2 envelope sequences, and this selection could in turn influence many aspects of AIDS pathogenesis in vivo.     

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 evolution of HIV-1 and the origin of AIDS

The major cause of acquired immune deficiency syndrome (AIDS) is human immunodeficiency virus type 1 (HIV-1). We have been using evolutionary comparisons to trace (i) the origin(s) of HIV-1 and (ii) the origin(s) of AIDS. The closest relatives of HIV-1 are simian immunodeficiency viruses (SIVs) infecting wild-living chimpanzees (Pan troglodytes troglodytes) and gorillas (Gorilla gorilla gorilla) in west central Africa. Phylogenetic analyses have revealed the origins of HIV-1: chimpanzees were the original hosts of this clade of viruses; four lineages of HIV-1 have arisen by independent cross-species transmissions to humans and one or two of those transmissions may have been via gorillas. However, SIVs are primarily monkey viruses: more than 40 species of African monkeys are infected with their own, species-specific, SIV and in at least some host species, the infection seems non-pathogenic. Chimpanzees acquired from monkeys two distinct forms of SIVs that recombined to produce a virus with a unique genome structure. We have found that SIV infection causes CD4⁺ T-cell depletion and increases mortality in wild chimpanzees, and so the origin of AIDS is more ancient than the origin of HIV-1. Tracing the genetic changes that occurred as monkey viruses adapted to infect first chimpanzees and then humans may provide insights into the causes of the pathogenicity of these viruses.     

Evolving paradigms in the pathogenesis of HIV-1-associated dementia

HIV-1-associated dementia (HIV-D) remains a significant consequence of HIV-1 infection and AIDS. Since the clinical introduction of highly active antiretroviral therapy (HAART), the incidence of HIV-D has decreased, yet the prevalence has increased as patients are living longer under treatment. Additionally, a less severe form of HIV-D, minor cognitive motor disorder, has become an increasing issue. Two different models have been proposed for virus entry in the central nervous system (CNS) in HIV-D. In the 'Trojan horse' model, the virus enters the CNS early carried by macrophages and infects resident glia; later in the course of infection, virus replication is activated and additional monocyte/macrophages are recruited into the CNS via cytokine/chemokine networks and endothelial-cell-leukocyte interactions at the blood-brain barrier. In the 'late invasion' model, an inherently invasive activated monocyte subset is expanded from bone marrow as a result of immune dysregulation in the periphery in the setting of AIDS. In this review we discuss these two separate, although not mutually exclusive, means for virus entry and persistence in the CNS. Additionally, we explore mechanisms for neuronal injury and apoptosis, including the role of virus, viral and host proteins, oxidative stress and products of infected or uninfected activated microglia and astrocytes. Potential therapeutic strategies are also briefly discussed.     

Isolation of CD4-independent primary human immunodeficiency virus type 1 isolates that are syncytium inducing and acutely cytopathic for CD8+ lymphocytes

Previous studies have established the existence of CD4-independent simian immunodeficiency virus, human immunodeficiency virus type 2 (HIV-2), and laboratory strains of HIV-1. However, whether CD4-independent viruses may also exist in HIV-1-infected patients has remained unclear. We have recently reported the isolation of viruses from an AIDS patient that were able to infect CD8(+) cells independent of CD4, using CD8 as a receptor. Using a similar approach, here we examined viruses from 12 randomly selected patients (obtained from the AIDS Research and Reference Program, National Institutes of Health) for the presence of CD4-independent HIV-1. CD4-independent variants were isolated from infected CD8(+) cells from the viral quasispecies of 7 of 12 patients. The CD4-independent isolates were able to infect primary CD8(+) cells as well as a CD4(-) CD8(+) T-cell line. Soluble CD4 and blocking anti-CD4 or -CD8 antibody had no effect on infection of CD8(+) cells. Remarkably, two of the seven CD4-independent isolates, but not their parental bulk viruses, induced syncytia and caused acute death of infected CD8(+) cells. Some of the CD4-independent variants were also able to infect U87 cells that were negative for CD4, CD8, and common HIV coreceptors, suggesting a novel entry mechanism for these isolates. The CD4-independent isolates were derived from adults and children infected with subtypes A, B, and D. Although no common motif for CD4 independence was found, novel sequence changes were observed in critical areas of the envelopes of the CD4-independent viruses. These results demonstrate that HIV-1-infected patients can frequently harbor viruses that are able to mediate CD4-independent infection of CD8(+) cells. In addition, this study also provides evidence of primary HIV-1 variants that are syncytium inducing and acutely cytopathic for CD8(+) lymphocytes.     

Fighting a virus with a virus: a dynamic model for HIV-1 therapy

A mathematical model examined a potential therapy for controlling viral infections using genetically modified viruses. The control of the infection is an indirect effect of the selective elimination by an engineered virus of infected cells that are the source of the pathogens. Therefore, this engineered virus could greatly compensate for a dysfunctional immune system compromised by AIDS. In vitro studies using engineered viruses have been shown to decrease the HIV-1 load about 1000-fold. However, the efficacy of this potential treatment for reducing the viral load in AIDS patients is unknown. The present model studied the interactions among the HIV-1 virus, its main host cell (activated CD4+ T cells), and a therapeutic engineered virus in an in vivo context; and it examined the conditions for controlling the pathogen. This model predicted a significant drop in the HIV-1 load, but the treatment does not eradicate HIV. A basic estimation using a currently engineered virus indicated an HIV-1 load reduction of 92% and a recovery of host cells to 17% of their normal level. Greater success (98% HIV reduction, 44% host cells recovery) is expected as more competent engineered viruses are designed. These results suggest that therapy using viruses could be an alternative to extend the survival of AIDS patients.     

Endogenous inhibitors of HIV: potent anti-HIV activity of leukemia inhibitory factor

The correlates of protective immunity in HIV-1 infection include the endogenous production of compounds with anti-HIV-1 activity. These compounds can be produced independently of specific humoral or cellular immune responses. A model of compartmental inhibition of HIV-1 infection is the placenta, an organ that prevents transmission of HIV-1 to the fetus in the majority of HIV-1 pregnancies. Studies of this organ elucidated new compounds and mechanisms for prevention and treatment of HIV including the potent inhibitor of HIV-1, leukemia inhibitory factor (LIF). Besides coordinating the humoral and cellular immune responses, cytokines such as IFN-gamma exhibit intrinsic antiviral activity that represents the first line of defense against pathogens prior to the development of a specific immune response. The study of antiviral factors is particularly important in HIV/AIDS because of the direct destruction of the immune system by HIV-1. In this report, we focus on the identification and mechanism of endogenously produced anti-HIV factors and the overall function of these factors in the prevention and treatment of HIV/AIDS.