Intersubtype human immunodeficiency virus type 1 superinfection following seroconversion to primary infection in two injection drug users

In this study, we describe two cases of human immunodeficiency virus type 1 (HIV-1) intersubtype superinfection with CRF01_AE and subtype B strains, which occurred in two injection drug users participating in a prospective cohort study in Bangkok, Thailand. In both cases, the superinfecting strain was detected by molecular and serologic analyses several weeks after complete seroconversion to the primary infection with a strain belonging to a different subtype. Superinfection occurred despite specific T-cell and humoral antibody responses to the primary virus. In both cases, cross-subtype immune responses were limited or absent prior to the second infection. These data show that, in some individuals, the quality and quantity of the immune response elicited by primary HIV-1 infection may not protect against superinfection. This finding has important implications for vaccine design. HIV-1 vaccines, at a minimum, will need to include potent, broadly protective, conserved immunogens derived from several group M subtypes.     

Human immunodeficiency virus type 1 superinfection occurs despite relatively robust neutralizing antibody responses

Superinfection by a second human immunodeficiency virus type 1 (HIV-1) strain indicates that gaps in protective immunity occur during natural infection. To define the role of HIV-1-specific neutralizing antibodies (NAbs) in this setting, we examined NAb responses in 6 women who became superinfected between ~1 to 5 years following initial infection compared to 18 women with similar risk factors who did not. Although superinfected individuals had less NAb breadth than matched controls at ~1 year postinfection, no significant differences in the breadth or potency of NAb responses were observed just prior to the second infection. In fact, four of the six subjects had relatively broad and potent NAb responses prior to infection by the second strain. To more specifically examine the specificity of the NAbs against the superinfecting virus, these variants were cloned from five of the six individuals. The superinfecting variants did not appear to be inherently neutralization resistant, as measured against a pool of plasma from unrelated HIV-infected individuals. Moreover, the superinfected individuals were able to mount autologous NAb responses to these variants following reinfection. In addition, most superinfected individuals had NAbs that could neutralize their second viral strains prior to their reinfection, suggesting that the level of NAbs elicited during natural infection was not sufficient to block infection. These data indicate that preventing infection by vaccination will likely require broader and more potent NAb responses than those found in HIV-1-infected individuals.     

Human immunodeficiency virus type 1 Nef incorporation into virions does not increase infectivity

The viral protein Nef contributes to the optimal infectivity of human and simian immunodeficiency viruses. The requirement for Nef during viral biogenesis particles suggests that Nef might play a role in this process. Alternatively, because Nef is incorporated into viruses, it might play a role when progeny virions reach target cells. We challenged these hypotheses by manipulating the amounts of Nef incorporated in viruses while keeping its expression level constant in producer cells. This was achieved by forcing the incorporation of Nef into viral particles by fusing a Vpr sequence to the C-terminal end of Nef. A cleavage site for the viral protease was introduced between Nef and Vpr to allow the release of Nef fragments from the fusion protein during virus maturation. We show that the resulting Nef-CS-Vpr fusion partially retains the ability of Nef to downregulate cell surface CD4 and that high amounts of Nef-CS-Vpr are incorporated into viral particles compared with what is seen for wild-type Nef. The fusion protein is processed during virion maturation and releases Nef fragments similar to those found in viruses produced in the presence of wild-type Nef. Unlike viruses produced in the presence of wild-type Nef, viruses produced in the presence of Nef-CS-Vpr do not have an increase in infectivity and are as poorly infectious as viruses produced in the absence of Nef. These findings demonstrate that the presence of Nef in viral particles is not sufficient to increase human immunodeficiency virus type 1 infectivity and suggest that Nef plays a role during the biogenesis of viral particles.     

Human immunodeficiency virus type 1 Vpr induces apoptosis following cell cycle arrest.

The human immunodeficiency virus type 1 (HIV-1) vpr gene encodes a protein which induces arrest of cells in the G2 phase of the cell cycle. Here, we demonstrate that following the arrest of cells in G2, Vpr induces apoptosis in human fibroblasts, T cells, and primary peripheral blood lymphocytes. Analysis of various mutations in the vpr gene revealed that the extent of Vpr-induced G2 arrest correlated with the levels of apoptosis. However, the alleviation of Vpr-induced G2 arrest by treatment with the drug pentoxifylline did not abrogate apoptosis. Together these studies indicate that induction of G2 arrest, but not necessarily continued arrest in G2, was required for Vpr-induced apoptosis to occur. Finally, Vpr-induced G2 arrest has previously been correlated with inactivation of the Cdc2 kinase. Some models of apoptosis have demonstrated a requirement for active Cdc2 kinase for apoptosis to occur. Here we show that accumulation of the hypophosphorylated or active form of the Cdc2 kinase is not required for Vpr-induced apoptosis. These studies indicate that Vpr is capable of inducing apoptosis, and we propose that both the initial arrest of cells and subsequent apoptosis may contribute to CD4 cell depletion in HIV-1 disease.     

Human immunodeficiency virus type 1 clade B superinfection: evidence for differential immune containment of distinct clade B strains

Sequential infection with different strains of human immunodeficiency virus type 1 (HIV-1) is a rarely identified phenomenon with important implications for immunopathogenesis and vaccine development. Here, we identify an individual whose good initial control of viremia was lost in association with reduced containment of a superinfecting strain. Subject 2030 presented with acute symptoms of HIV-1 infection with high viremia and an incomplete seroconversion as shown by Western blotting. A low set point of viremia (approximately 1,000 HIV-1 copies/ml) was initially established without drug therapy, but a new higher set point (approximately 40,000 HIV-1 copies/ml) manifested about 5 months after infection. Drug susceptibility testing demonstrated a multidrug-resistant virus initially but a fully sensitive virus after 5 months, and an analysis of pol genotypes showed that these were two phylogenetically distinct strains of virus (strains A and B). Replication capacity assays suggested that the outgrowth of strain B was not due to higher fitness conferred by pol, and env sequences indicated that the two strains had the same R5 coreceptor phenotype. Delineation of CD8+-T-lymphocyte responses against HIV-1 showed a striking pattern of decay of the initial cellular immune responses after superinfection, followed by some adaptation of targeting to new epitopes. An examination of targeted sequences suggested that differences in the recognized epitopes contributed to the poor immune containment of strain B. In conclusion, the rapid overgrowth of a superinfecting strain of HIV-1 of the same subtype raises major concerns for effective vaccine development.     

Reactivation of human immunodeficiency virus type 2 in macaques after simian immunodeficiency virus SIVmac superinfection.

By superinfection of human immunodeficiency virus type 2 (HIV-2) strain HIV-2ben-infected macaques with simian immunodeficiency virus (SIV) strain SIVmac, we investigated the mutual influences of an apathogenic and a pathogenic virus in vivo. Four rhesus and two cynomolgus monkeys were infected with HIV-2ben in 1988 and 1989, respectively. Virus could be reisolated from five of six animals 6 weeks after infection. The monkeys remained healthy over the next 2 to 3 years. PCR for viral RNA became negative, and virus could no longer be reisolated by coculture. All six macaques were superinfected with the pathogenic SIVmac251/32H. Subsequently, five monkeys became persistently viremic, while one animal was protected against the SIVmac infection. In the peripheral blood mononuclear cells and cocultures of the five viremic animals, DNA from both HIV-2 and SIVmac was present. The plasma contained RNA from both viruses. Thus, superinfection with SIVmac activated HIV-2. A proliferative T-cell response against both HIV-2 and SIVmac was measured in all animals after superinfection. Such a response was regularly seen after infection with the apathogenic HIV-2 but never when the pathogenic SIVmac alone was administered. While naive control monkeys inoculated with SIVmac251/32H regularly develop AIDS-like symptoms soon after infection and have to be killed, none of the preinfected animals has developed AIDS-like symptoms, but two of six animals developed tumors. After the SIVmac challenge, however, apoptotic lymphocytes were detected in the peripheral blood mononuclear cells of all animals. Thus, the presence of an apathogenic viral variant seems to retard the disease occurring after infection with a pathogenic virus rather than to confirm total protection. This partial protection appears to depend on a specific proliferative T-cell response early after infection.     

Human immunodeficiency virus type 1 virion density is not determined by nucleocapsid basic residues

The human immunodeficiency virus type 1 (HIV-1) Gag polyprotein is sufficient for assembly and release of virion-like particles from the plasma membrane. To promote assembly, the Gag polyprotein must polymerize to form a shell that lines the inner membrane of nascent virions. Several techniques have been used to functionally map the domain required for Gag polymerization (the I domain). Among these methods, isopycnic centrifugation has been used under the assumption that changes in virion density reflect impairment in Gag-Gag interaction. If virion density is determined by efficient Gag-Gag interaction, then mutation of basic residues in the nucleocapsid (NC) domain should disrupt virion density, since these residues constitute the I domain. However, we have previously shown that simultaneous disruption of up to 10 HIV-1 NC basic residues has no obvious effect on virion density. To rule out the possibility that HIV-1 NC basic residues other than those previously mutated might be important for virion density, mutations were introduced at the remaining sites and the ability of these mutations to affect Gag-Gag interaction and virion density was analyzed. Included in our analysis is a mutant in which all NC basic residues are replaced with alanine. Our results show that disruption of HIV-1 NC basic residues has an enormous effect on Gag-Gag interaction but only a minimal effect on the density of those virions that are still produced. Therefore, the determinants of the I domain and of virion density are genetically distinguishable.     

Human immunodeficiency virus type 1 escape from RNA interference

Sequence-specific degradation of mRNA by short interfering RNA (siRNA) allows the selective inhibition of viral proteins that are critical for human immunodeficiency virus type 1 (HIV-1) replication. The aim of this study was to characterize the potency and durability of virus-specific RNA interference (RNAi) in cell lines that stably express short hairpin RNA (shRNA) targeting the HIV-1 transactivator protein gene tat. We found that the antiviral activity of tat shRNA was abolished due to the emergence of viral quasispecies harboring a point mutation in the shRNA target region. Our results suggest that, in order for RNAi to durably suppress HIV-1 replication, it may be necessary to target highly conserved regions of the viral genome. Alternatively, similar to present antiviral drug therapy paradigms, DNA constructs expressing multiple siRNAs need to be developed that target different regions of the viral genome, thereby reducing the probability of generating escape mutants.     

Human immunodeficiency virus type 1 Nef does not alter T-cell sensitivity to antigen-specific stimulation.

We have developed an in vitro model to study the influence that human immunodeficiency virus type 1 (HIV-1) may have on the ability of T cells to respond to antigenic challenge. We have examined consequences of HIV-1 gene expression on T-cell activation in antigen-dependent T cells that have stably integrated copies of replication-defective proviral HIV-1. Virus production by HIV-infected, antigen-dependent T cells was induced in response to antigenic stimulation and then decreased as infected cells returned to a state of quiescence. Contrary to the predictions of models proposing that Nef alters signal transduction pathways in T lymphocytes and thereby alters cellular activation, Nef expression in antigen-dependent T-cell clones did not influence their proliferative responses to low or intermediate concentrations of antigen and did not affect other measures of T-cell activation, such as induction of interleukin 2 receptor alpha-chain expression and cytokine production. In addition, we found no evidence for alteration of T-cell responsiveness to antigen by the gag, pol, vif, tat, or rev gene of HIV-1.     

Human immunodeficiency virus type 1 variability and long-term non-progression.

A high heterogeneity is found in the HIV-1 genome in vivo, not only between individuals, but also within a single individual. Different types of genetic heterogeneity of HIV-1 can be analyzed: the extension and the evolution of the viral quasispecies in blood, the variation between the virus obtained from different body compartment, the differences between isolates from diverse individuals and between HIV-1 subtypes. The virus population during primary HIV-1 infection is generally homogeneous and the intrahost viral evolution is thought to be forced (in absence of antiviral therapy) by the immune system pressure and is generally related to the length of the immunocompetent period. A group of 12 Italian and Swedish well characterized HIV-1 infected long-term nonprogressors (LNTP) have been analyzed for the viral heterogeneity, calculated in the nef gene and in the long terminal repeat (LTR). The intra-sample variations in LTNP were found comparable with those from 8 progressor patients, while a lower inter-individual diversity was observed in the former. In one LTNP the viral evolution during a four-years period was extremely low suggesting that other factors than the host immune pressure may be involved in modulating the intra- and inter-sample HIV-1 diversity.     

Human immunodeficiency virus type 1 Gag assembly through assembly intermediates

Human immunodeficiency virus Gag protein self-assembles into spherical particles, and recent reports suggest the formation of assembly intermediates during the process. To understand the nature of such assembly intermediates along with the mechanism of Gag assembly, we employed expression in Escherichia coli and an in vitro assembly reaction. When E. coli expression was performed at 37 degrees C, Gag predominantly assembled to a high order of multimer, apparently equivalent to the virus-like particles obtained following Gag expression in eukaryotic cells, through the formation of low orders of multimer characterized with a discreet sedimentation value of 60 S. Electron microscopy confirmed the presence of spherical particles in the E. coli cells. In contrast, expression at 30 degrees C resulted in the production of only the 60 S form of Gag multimer, and crescent-shaped structures or small patches with double electron-dense layers were accumulated, but no complete particles. In vitro assembly reactions using purified Gag protein, when performed at 37 degrees C, also produced the high order of Gag multimers with some 60 S multimers, whereas the 30 degrees C reaction produced only the 60 S multimers. However, when the 60 S multimers were cross-linked so as not to allow conformational changes, in vitro assembly reactions at 37 degrees C did not produce any higher order of multimers. ATP depletion did not halt Gag assembly in the E. coli cells, and the addition of GroEL-GroES to in vitro reactions did not facilitate Gag assembly, indicating that conformational changes rather than protein refolding by chaperonins, induced at 37 degrees C, were solely responsible for the Gag assembly observed here. We suggest that Gag assembles to a capsid through the formation of the 60 S multimer, possibly a key intermediate of the assembly process, accompanied with conformational changes in Gag.     

Human immunodeficiency virus type 1 escapes from RNA interference-mediated inhibition

Short-term assays have suggested that RNA interference (RNAi) may be a powerful new method for intracellular immunization against human immunodeficiency virus type 1 (HIV-1) infection. However, RNAi has not yet been shown to protect cells against HIV-1 in long-term virus replication assays. We stably introduced vectors expressing small interfering RNAs (siRNAs) directed against the HIV-1 genome into human T cells by retroviral transduction. We report here that an siRNA directed against the viral Nef gene (siRNA-Nef) confers resistance to HIV-1 replication. This block in replication is not absolute, and HIV-1 escape variants that were no longer inhibited by siRNA-Nef appeared after several weeks of culture. These RNAi-resistant viruses contained nucleotide substitutions or deletions in the Nef gene that modified or deleted the siRNA-Nef target sequence. These results demonstrate that efficient inhibition of HIV-1 replication through RNAi is possible in stably transduced cells. Therefore, RNAi could become a realistic gene therapy approach with which to overcome the devastating effect of HIV-1 on the immune system. However, as is known for antiviral drug therapy against HIV-1, antiviral approaches involving RNAi should be used in a combined fashion to prevent the emergence of resistant viruses.     

Human immunodeficiency virus type 1 infection of human brain-derived progenitor cells

Although cells of monocytic lineage are the primary source of human immunodeficiency virus type 1 (HIV-1) in the brain, other cell types in the central nervous system, including astrocytes, can harbor a latent or persistent HIV-1 infection. In the present study, we examined whether immature, multipotential human brain-derived progenitor cells (nestin positive) are also permissive for infection. When exposed to IIIB and NL4-3 strains of HIV-1, progenitor cells and progenitor-derived astrocytes became infected, with peak p24 levels of 100 to 500 pg/ml at 3 to 6 days postinfection. After 10 days, virus production was undetectable but could be stimulated by the addition of tumor necrosis factor alpha (TNF-alpha). To bypass limitations to receptor entry, we compared the fate of infection in these cell populations by transfection with the infectious HIV-1 clone, pNL4-3. Again, transfected progenitors and astrocytes produced virus for 7 days but diminished to low levels beyond 8 days posttransfection. During the nonproductive phase, TNF-alpha stimulated virus production from progenitors as late as 5 weeks posttransfection. Astrocytes produced 5- to 20-fold more infectious virus (27 ng of p24/10(6) cells) than progenitors at the peak of 3 days posttransfection. Differentiation of infected progenitors toward an astrocyte phenotype increased virus production to levels consistent with infected astrocytes, suggesting a phenotypic difference in viral replication. Using this cell culture system of multipotential human brain-derived progenitor cells, we provide evidence that progenitor cells may be a reservoir for HIV-1 in the brains of AIDS patients.     

Human immunodeficiency virus type 1 Vpr protein does not modulate surface expression of the CD4 receptor

The CD4 receptor is required for the entry of human immunodeficiency virus (HIV) into target cells. It has long been known that Nef, Env, and Vpu participate in the removal of the viral receptor from the cell surface. Recently, it has been proposed that the HIV type 1 (HIV-1) Vpr protein may also play a role in the downmodulation of CD4 from the surfaces of infected cells (L. Conti, B. Varano, M. C. Gauzzi, P. Matarrese, M. Federico, W. Malorani, F. Belardelli, and S. Gessani, J. Virol. 74:10207-10211, 2000). To investigate the possible role of Vpr in the downregulation of the viral receptor Vpr alleles from HIV-1 and simian immunodeficiency virus were transiently expressed in transformed T cells and in 293T fibroblasts, and their ability to modulate surface CD4 was evaluated. All Vpr alleles efficiently arrested cells in the G(2) stage of the cell cycle. However, none of the tested Vpr proteins altered the expression of CD4 on the cell surface. In comparison, HIV-1 Nef efficiently downmodulated surface CD4 in all the experimental settings. Transformed T cells and primary lymphocytes were challenged with wild-type, Nef-defective, and Vpr-defective viruses. A significant reduction in the HIV-induced downmodulation of surface CD4 was observed in viruses lacking Nef. However, Vpr-deletion-containing viruses showed no defect in their ability to remove CD4 from the surfaces of infected cells. Our results indicate that Vpr does not play a role in the HIV-induced downmodulation of the CD4 receptor.     

Virus population homogenization following acute human immunodeficiency virus type 1 infection

Understanding the properties of human immunodeficiency virus type 1 (HIV-1) variants capable of establishing infection is critical to the development of a vaccine against AIDS. Previous studies of men have shown that the HIV-1 env gene is homogeneous early in infection, leading to the suggestion that infection is established by a single transmitted variant. However, we report here that all of eight homosexual men evaluated beginning 3.7 to 9 weeks following onset of symptoms of acute infection harbored diverse virus populations in their blood, with median genetic distances averaging 1.08% in the env C2V5 region and 0.81% in the gag p17 gene. Within another 4.7 to 11 weeks, the variant lineage in env became more homogeneous, while gag sequences continued to diversify. Thus, the homogenization that has been reported to characterize acute infection is actually preceded by the replication of multiple virus variants. This early selective process focuses on viral properties within Env but not Gag p17. Hence, the viral homogeneity observed early in HIV-1 infection results from a selective process that occurs during the establishment of infection.     

Human immunodeficiency virus type 1 and influenza virus exit via different membrane microdomains

Directed release of human immunodeficiency virus type 1 (HIV-1) into the cleft of the virological synapse that can form between infected and uninfected T cells, for example, in lymph nodes, is thought to contribute to the systemic spread of this virus. In contrast, influenza virus, which causes local infections, is shed into the airways of the respiratory tract from free surfaces of epithelial cells. We now demonstrate that such differential release of HIV-1 and influenza virus is paralleled, at the subcellular level, by viral assembly at different microsegments of the plasma membrane of HeLa cells. HIV-1, but not influenza virus, buds through microdomains containing the tetraspanins CD9 and CD63. Consequently, the anti-CD9 antibody K41, which redistributes its antigen and also other tetraspanins to cell-cell adhesion sites, interferes with HIV-1 but not with influenza virus release. Altogether, these data strongly suggest that the bimodal egress of these two pathogenic viruses, like their entry into target cells, is guided by specific sets of host cell proteins.     

Human immunodeficiency virus type 1 controllers but not noncontrollers maintain CD4 T cells coexpressing three cytokines

Here, we evaluate the cytokine coexpression profiles of human immunodeficiency virus (HIV)-specific CD4 T cells for the expression of the cytokines gamma interferon (IFN-gamma), interleukin-2, and tumor necrosis factor alpha. In controllers, CD4 T cells producing three or two cytokines (triple producers and double producers, respectively) represented >50% of the total response. In contrast, in noncontrollers approximately 75% of responding cells produced only one cytokine (single producers), mostly IFN-gamma. Cells producing three cytokines were functionally superior to those producing single cytokines and showed an inverse correlation (P < 0.001) with viral load. These results demonstrate a strong association between the maintenance of highly functional CD4 T cells producing three cytokines and control of HIV-1.     

Human immunodeficiency virus type 1 Vif is efficiently packaged into virions during productive but not chronic infection

Packaging of the human immunodeficiency virus type 1 Vif protein into virus particles is mediated through an interaction with viral genomic RNA and results in the association of Vif with the nucleoprotein complex. Despite the specificity of this process, calculations of the amount of Vif packaged have produced vastly different results. Here, we compared the efficiency of packaging of Vif into virions derived from acutely and chronically infected H9 cells. We found that Vif was efficiently packaged into virions from acutely infected cells (60 to 100 copies per virion), while packaging into virions from chronically infected H9 cells was near the limit of detection (four to six copies of Vif per virion). Superinfection by an exogenous Vif-defective virus did not rescue packaging of endogenous Vif expressed in the chronically infected culture. In contrast, exogenous Vif expressed by superinfection of wild-type virus was readily packaged (30 to 40 copies per virion). Biochemical analyses suggest that the differences in the relative packaging efficiencies were not due to gross differences in the steady-state distribution of Vif in chronically or acutely infected cells but are likely due to differences in the relative rates of de novo synthesis of Vif. Despite its low packaging efficiency, endogenously expressed Vif was sufficient to direct the production of viruses with almost wild-type infectivity. The results from our study provide novel insights into the biochemical properties of Vif and offer an explanation for the reported differences regarding Vif packaging.