Chemokine receptor CCR5 genotype influences the kinetics of human immunodeficiency virus type 1 infection in human PBL-SCID mice.

Individuals homozygous for a 32-bp deletion (delta 32) in the CCR5 gene encoding the coreceptor for macrophage-tropic human immunodeficiency virus type 1 (HIV-1) are resistant to virus infection, and heterozygous individuals show some slowing of disease progression. The impact of the CCR5 genotype on HIV-1 infection was assessed in vitro and in the human PBL-SCID (hu-PBL-SCID) model. Cells and hu-PBL-SCID mice from CCR5 delta 32/delta 32 donors were resistant to infection with macrophage-tropic HIV-1 and showed slower replication of dual-tropic HIV-1. hu-PBL-SCID mice derived from CCR5 delta 32/+ heterozygotes showed delayed replication of macrophage-tropic HIV-1 despite a small and variable effect of heterozygosity on viral replication in vitro. The level of CCR5 expression appears to limit replication of macrophage-tropic and dual-tropic HIV-1 strains in vivo.     

Direct evidence of lower viral replication rates in vivo in human immunodeficiency virus type 2 (HIV-2) infection than in HIV-1 infection

Studies have shown that human immunodeficiency virus type 2 (HIV-2) is less pathogenic than HIV-1, with a lower rate of disease progression. Similarly, plasma viral loads are lower in HIV-2 infection, suggesting that HIV-2 replication is restricted in vivo in comparison to that of HIV-1. However, to date, in vivo studies characterizing replication intermediates in the viral life cycle of HIV-2 have been limited. In order to test the hypothesis that HIV-2 has a lower replication rate in vivo than HIV-1 does, we quantified total viral DNA, integrated proviral DNA, cell-associated viral mRNA, and plasma viral loads in peripheral blood samples from groups of therapy-na?ve HIV-1-infected (n = 21) and HIV-2-infected (n = 18) individuals from Dakar, Senegal, with CD4(+) T-cell counts of >200/microl. Consistent with our previous findings, total viral DNA loads were similar between HIV-1 and HIV-2 and plasma viral loads were higher among HIV-1-infected individuals. Proportions of DNA in the integrated form were also similar between these viruses. In contrast, levels of viral mRNA were lower in HIV-2 infection. Our study indicates that HIV-2 is able to establish a stable, integrated proviral infection in vivo, but that accumulation of viral mRNA is attenuated in HIV-2 infection relative to that in HIV-1 infection. The differences in viral mRNA are consistent with the differences in plasma viral loads between HIV-1 and HIV-2 and suggest that lower plasma viral loads, and possibly the attenuated pathogenesis of HIV-2, can be explained by lower rates of viral replication in vivo.     

Mutational analysis of human immunodeficiency virus type 1 (HIV-1) accessory genes: requirement of a site in the nef gene for HIV-1 replication in activated CD4+ T cells in vitro and in vivo.

Human immunodeficiency virus type 1 (HIV-1) accessory genes including nef, vif, and vpr are important factors that determine the replication and pathogenesis of HIV-1. The state of activation is also important for the replication of HIV-1. We evaluated the properties of nef-, vif-, and vpr-minus macrophage-tropic HIV-1(JR) CSF in primary CD4+ Th1- or Th2-like cell cultures which had been activated through CD3 molecules in the presence of interleukin-2 (IL-2) and IL-12 (Th1-like culture) or IL-4 (Th2-like culture), respectively. In activated Th1- or Th2-like cultures, replication of nef-minus HIV-1(JR-CSF) was markedly lower than that of wild-type HIV-1. Subsequent analysis by site-directed mutagenesis showed that (i) the presence of an acidic amino acid-rich domain (amino acid residues 72 to 75) in the Nef protein was critical for the enhancement of viral DNA synthesis, resulting in increased virus growth rate, and (ii) prolines that form part of Src homology 3 binding domain were not essential for viral replication. We also confirmed the importance of sites by using an HIV-1-infected animal model, the hu-PBL-SCID mouse system, representing HIV-1 replication and pathogenesis in activated CD4+ T cells in vivo. These results indicate that Nef accelerates viral replication in activated CD4+ T cells.     

Human Immunodeficiency Virus Type 1 Strains R5 and X4 Induce Different Pathogenic Effects in hu-PBL-SCID Mice, Depending on the State of Activation/Differentiation of Human Target Cells at the Time of Primary Infection

In a previous study, we had found that the extent of T-cell dysfunctions induced by a T-tropic strain of human immunodeficiency virus type 1 (HIV-1) in SCID mice reconstituted with human peripheral blood lymphocytes (hu-PBLs) (hu-PBL-SCID mice) was related to the in vivo state of activation of the human lymphocytes. In this article, we compared the effect of infection of hu-PBL-SCID mice with either T-tropic (X4) or M-tropic (R5) strains of HIV-1 by performing virus inoculation at either 2 h or 2 weeks after the hu-PBL transfer, when the human T cells exhibited a marked activation state or a predominant memory phenotype, respectively. A comparable level of infection was found when hu-PBL-SCID mice were challenged with either the SF162 R5 or the IIIB X4 strain of HIV at 2 h postreconstitution, while at 2 weeks, the R5 virus infection resulted in a higher level of HIV replication than the X4 virus. The R5 strain induced a marked human CD4(+) T-cell depletion along with a drop in levels of human immunoglobulin M in serum and release of soluble factors at both infection times, while the X4 virus induced severe immune dysfunctions only at 2 h. Of interest, injection of hu-PBLs into SCID mice resulted in a marked up-regulation of CCR5 on human CD4(+) T cells. The percentage of CXCR4(+) cells did not change after transplantation, even though a significant decrease in antigen expression was observed. Comparative experiments with two molecular clones of HIV-1 (X4 SF2 and R5 SF162) and two envelope recombinant viruses generated from these viruses showed that R5 viruses (SF162 and the chimeric env-SF162-SF2) caused an extensive depletion of human CD4(+) T cells in SCID mice at both 2 h and 2 weeks after reconstitution, while the X4 viruses (SF2 and the chimeric env-SF2-SF162) induced CD4 T-cell depletion only when infection was performed at the 2-h reconstitution time. These results emphasize the importance of the state of activation/differentiation of human CD4(+) T cells and gp120-coreceptor interactions at the time of primary infection in determining HIV-1 pathogenicity in the hu-PBL-SCID mouse model.     

Low plasma human immunodeficiency virus type 2 viral load is independent of proviral load: low virus production in vivo

Levels of virus in the plasma are closely related to the pathogenicity of human immunodeficiency virus type 1 (HIV-1). HIV-2 is much less pathogenic than HIV-1, and infection with HIV-2 leads to significantly lower plasma viral load. To identify the source of this difference, we measured both viral RNA and proviral DNA in matched samples from 34 HIV-2-infected individuals. Nearly half had undetectable viral RNA loads (<100 copies/ml), but levels of proviral DNA were relatively high and confirmed that quantities of provirus in HIV-1 and HIV-2 infection were similar. Overall, HIV-2 proviral DNA load did not correlate with viral RNA load, and higher viral RNA load was associated with increased production of plasma virus from the proviral template. These results suggest that low viral load in HIV-2 infection is due to decreased rates of viral production, rather than differences in target cell infectivity.     

Human immunodeficiency virus type 1 T-cell tropism is determined by events prior to provirus formation.

Different strains of human immunodeficiency virus type 1 (HIV-1) vary in the ability to replicate in cells that bear the HIV-1 receptor, CD4. The mechanism responsible for these cell tropism differences is unknown. We examined different isolates of HIV-1 with regard to replication in specific tumor-derived CD4-positive T-cell lines and normal peripheral blood lymphocytes. To investigate early events in the virus life cycle at low multiplicities of infection, we used a modification of the polymerase chain reaction method. Use of a molecularly cloned primary HIV-1 isolate, HIV-1 JR-CSF, restricted for replication in T-cell lines, demonstrated that little or no viral DNA or RNA was synthesized in nonpermissive cells after infection. However, transfection of proviral DNA resulted in efficient transient virus production from these cells. Therefore, we conclude that at least one block to infection for HIV-1 strains in nonpermissive T cells occurs at a point in entry or uncoating before provirus formation.     

Chimeric plant virus particles as immunogens for inducing murine and human immune responses against human immunodeficiency virus type 1

The high-yield expression of a neutralizing epitope from human immunodeficiency virus type 1 (HIV-1) on the surface of a plant virus and its immunogenicity are presented. The highly conserved ELDKWA epitope from glycoprotein (gp) 41 was expressed as an N-terminal translational fusion with the potato virus X (PVX) coat protein. The resulting chimeric virus particles (CVPs), purified and used to immunize mice intraperitoneally or intranasally, were able to elicit high levels of HIV-1-specific immunoglobulin G (IgG) and IgA antibodies. Furthermore, the human immune response to CVPs was studied with severe combined immunodeficient mice reconstituted with human peripheral blood lymphocytes (hu-PBL-SCID). hu-PBL-SCID mice immunized with CVP-pulsed autologous dendritic cells were able to mount a specific human primary antibody response against the gp41-derived epitope. Notably, sera from both normal and hu-PBL-SCID mice showed an anti-HIV-1-neutralizing activity. Thus, PVX-based CVPs carrying neutralizing epitopes can offer novel perspectives for the development of effective vaccines against HIV and, more generally, for the design of new vaccination strategies in humans.     

R5 human immunodeficiency virus type 1 (HIV-1) replicates more efficiently in primary CD4+ T-cell cultures than X4 HIV-1

In this report, we present evidence that R5 human immunodeficiency virus type 1 (HIV-1) replicates more efficiently in primary CD4+ T cells than X4 HIV-1. By comparing CD3/CD28-costimulated CD4+ T-cell cultures infected by several X4 and R5 HIV-1 strains, we determined that R5-infected CD4+ T cells produce more virus over time than X4-infected CD4+ T cells. In the first comparison, we found that more cells were infected by the X4-tropic strain LAI than by the R5-tropic strain JR-CSF and yet that higher levels of viral production were detected in the R5-infected cultures. The differential viral production was partially due to the severe cytopathic effects of the X4 virus. We also compared cultures infected with the isogenic HIV-1 strains NL4-3 (X4) and 49.5 (R5). We found that fewer cells were infected by the R5 strain, and yet similar levels of viral production were detected in both infected cultures. Cell death played less of a role in the differential viral production of these strains, as the cell viability remained comparable in both X4- and R5-infected cultures over time. The final comparison involved the primary R5-tropic isolate KP1 and the primary dual-tropic isolate KP2. Although both strains infected similar numbers of cells and induced comparable levels of cytopathicity, viral production was considerably higher in the R5-infected culture. In summary, these data demonstrate that R5 HIV-1 has an increased capacity to replicate in costimulated CD4+ T cells compared to X4 HIV-1.     

Opposite effects of SDF-1 on human immunodeficiency virus type 1 replication

The alpha-chemokine SDF-1 binds CXCR4, a coreceptor for human immunodeficiency virus type 1 (HIV-1), and inhibits viral entry mediated by this receptor. Since chemokines are potent chemoattractants and activators of leukocytes, we examined whether the stimulation of HIV target cells by SDF-1 affects the replication of virus with different tropisms. We observed that SDF-1 inhibited the entry of X4 strains and increased the infectivity of particles bearing either a CCR5-tropic HIV-1 envelope or a vesicular stomatitis virus G envelope. In contrast to the inhibitory effect of SDF-1 on X4 strains, which is at the level of entry, the stimulatory effect does not involve envelope-receptor interactions or proviral DNA synthesis. Rather, we observed an increased ability of Tat to transactivate the HIV-1 long terminal repeat in the presence of the chemokine. Therefore, the effects of SDF-1 on the HIV-1 life cycle can be multiple and opposite, including both an inhibition of viral entry and a stimulation of proviral gene expression.     

Relationships between the presence of anti-Tat antibody, DNA and RNA viral load

The possible relationships between the intensity of humoral response to full length Tat protein, the amount of proviral DNA reservoir in peripheral blood mononuclear cells and RNA viral load were analyzed in plasma samples obtained from a group of HIV-1 seropositive subjects, who never received any antiretroviral therapy. All HIV-1 patients showed detectable levels of serum IgG to full-length Tat by immunoenzymatic assay. We found a higher percentage of HIV-1 seropositive subjects with low levels of antibody in the presence of barely detectable proviral DNA copies (< or =10 copies/1.5x10(5) PBMCs) and a high anti-Tat antibody response accompanied by variable (from >10(1) to > or =10(3) copies/1.5x10(5) PBMCs) levels of DNA load (p=0.011). Moreover, an inverse relationship between anti-Tat antibody titers and HIV-1 RNA viral load was demonstrated HIV-1 seropositive patients. In HIV-1-infected patients, a strong humoral immune response against HIV-1 transactivating Tat protein, able to down-modulate viral replication in peripheral blood, does not seem to inhibit the number of proviral DNA molecules in peripheral blood mononuclear cells. Even though our data strongly confirm the "positive" role of anti-Tat antibody on viral replication, the persistence of significant amount of DNA viral load in peripheral blood mononuclear cells, despite high level of anti Tat antibody, suggests a more cautious approach to HIV-1 Tat-containing vaccines, able to stimulate an immune specific response to transactivating Tat protein sufficient in inhibiting circulating virus, but not completely efficient in decreasing proviral DNA integration.     

Alpha interferon inhibits early stages of the human immunodeficiency virus type 1 replication cycle.

In this study, we have analyzed the effect of human alpha interferon (IFN-alpha) on a single replication cycle of human immunodeficiency virus type 1 (HIV-1) infection in the lymphocytic cell line CEM-174, which is highly sensitive to the antiviral effects of IFN. Pretreatment of cells with 50 to 500 U of recombinant human IFN-alpha per ml resulted in a marked reduction in viral RNA and protein synthesis. The effect of IFN-alpha was dose dependent and was amplified in multiple infection cycles. IFN-induced inhibition of viral protein synthesis could be detected only when cells were treated with IFN-alpha prior to infection or when IFN-alpha was added up to 10 h postinfection, but not if IFN-alpha was added at the later stages of HIV-1 replication cycle or after the HIV-1 infection was already established. Analysis of the integrated HIV-1 provirus showed a marked decrease in the levels of proviral DNA in IFN-treated cells. Thus, in contrast to the previous studies on established HIV-1 infection in T cells, in which the IFN block appeared to be at the posttranslational level, during de novo infection, IFN-alpha interferes with an early step of HIV-1 replication cycle that occurs prior to the integration of the proviral DNA. These results indicate that the early IFN block of HIV-1 replication, which has been previously observed only in primary marcophages, can also be detected in the IFN-sensitive T cells, indicating that the early IFN block is not limited to macrophages.     

Human immunodeficiency virus type 1 infection and replication in normal human oral keratinocytes

Recent epidemiologic studies show increasing human immunodeficiency virus type 1 (HIV-1) transmission through oral-genital contact. This paper examines the possibility that normal human oral keratinocytes (NHOKs) might be directly infected by HIV or might convey infectious HIV virions to adjacent leukocytes. PCR analysis of proviral DNA constructs showed that NHOKs can be infected by CXCR4-tropic (NL4-3 and ELI) and dualtropic (89.6) strains of HIV-1 to generate a weak but productive infection. CCR5-tropic strain Ba-L sustained minimal viral replication. Antibody inhibition studies showed that infection by CXCR4-tropic viral strains is mediated by the galactosylceramide receptor and the CXCR4 chemokine coreceptor. Coculture studies showed that infectious HIV-1 virions can also be conveyed from NHOKs to activated peripheral blood lymphocytes, suggesting a potential role of oral epithelial cells in the transmission of HIV infection.