The extent of early viral replication is a critical determinant of the natural history of simian immunodeficiency virus infection

Different patterns of viral replication correlate with the natural history of disease progression in humans and macaques infected with human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), respectively. However, the viral and host factors influencing these patterns of viral replication in vivo are poorly understood. We intensively studied viral replication in macaques receiving identical inocula of SIV. Marked differences in viral replication patterns were apparent within the first week following inoculation, a time prior to the development of measurable specific immune effector responses to viral antigens. Plasma viral RNA levels measured on day 7 postinoculation correlated with levels measured in the postacute phase of infection. Differences in the susceptibility of host cells from different animals to in vitro SIV infection correlated with the permissiveness of the animals for early in vivo viral replication and hence with the postacute set point level of plasma viremia. These results suggest that host factors that exert their effects prior to full development of specific immune responses are critical in establishing the in vivo viral replication pattern and associated clinical course in subjects infected with SIV and, by extension, with HIV-1.

Promonocytic U937 subclones expressing CD4 and CXCR4 are resistant to infection with and cell-to-cell fusion by T-cell-tropic human immunodeficiency virus type 1

Different strains of human immunodeficiency virus type 1 (HIV-1) vary markedly in the ability to infect cells of the monocyte/macrophage (M/M) lineage. M/M are generally resistant to infection with T-cell-tropic (T-tropic) strains of HIV-1. Recently, the chemokine receptors CCR5 and CXCR4 were identified as cofactors for fusion/entry of macrophage- and T-tropic strains of HIV-1, respectively. To investigate the mechanisms of resistance of M/M to T-tropic HIV-1 infection, we examined a number of subclones of the U937 promonocytic cell line. We found that certain subclones of U937 (plus clones) could, while others (minus clones) could not, support replication of T-tropic strains of HIV-1. We demonstrate that (i) both minus and plus clones support HIV-1 replication when transfected with an infectious molecular cDNA clone of a T-tropic HIV-1; (ii) minus clones do not, but plus clones do, efficiently support fusion with cells expressing HIV-1 IIIB Env; (iii) both plus and minus clones (with the exception of one clone) express physiologically functional CXCR4 protein as well as CD4 on the cell surface; (iv) introduction of CXCR4 into the CXCR4-negative clone does not restore fusogenicity with or susceptibility to T-tropic HIV-1; and (v) a ligand (stromal cell-derived factor 1) for or a monoclonal antibody (12G5) to CXCR4 does not effectively inhibit HIV-mediated cell-to-cell fusion of U937 cells. These data indicate that resistance to T-tropic HIV-1 infection of U937 minus clones occurs at fusion/ entry events and that expression of functional CXCR4 and CD4 is not a sole determinant for susceptibility to T-tropic HIV-1 infection; furthermore, they suggest that other factors are positively or negatively involved in HIV-mediated cell-to-cell fusion in U937 promonocytic cells.

Cloning and analysis of the promoter region of CCR5, a coreceptor for HIV-1 entry

The chemokine receptor CCR5 is a cofactor for cellular entry of macrophage-tropic strains of HIV-1. Expression of CCR5 is restricted to T cells, macrophages, and certain cell lines; however, the mechanisms controlling its expression remain largely unknown. To delineate these mechanisms, approximately 1.0 kb of DNA from the immediate 5' upstream region of CCR5 was cloned and characterized. CCR5 promoter activity was up-regulated by PMA, and a region spanning -417 to +61 relative to the transcription start site was sufficient for the basal and induced activity. DNase I footprinting assays demonstrated several protected areas within this region, and gel shift assays determined binding sites for transcriptional factors Oct-1, Oct-2, T cell factor 1alpha, and GATA1. CCR5 promoter activity was also induced by IL-2 or anti-CD3 Ab, while stimulation with anti-CD28 Ab markedly reduced CD3-mediated up-regulation of the CCR5 promoter. Flow cytometry confirmed the findings at the level of cell surface expression. Further delineation of the regulation of the CCR5 promoter will be important for a more comprehensive understanding of the pathogenesis of HIV disease.

Presence of an inducible HIV-1 latent reservoir during highly active antiretroviral therapy

Although highly active antiretroviral therapy (HAART) in the form of triple combinations of drugs including protease inhibitors can reduce the plasma viral load of some HIV-1-infected individuals to undetectable levels, it is unclear what the effects of these regimens are on latently infected CD4+ T cells and what role these cells play in the persistence of HIV-1 infection in individuals receiving such treatment. The present study demonstrates that highly purified CD4+ T cells from 13 of 13 patients receiving HAART with an average treatment time of 10 months and with undetectable (<500 copies HIV RNA/ml) plasma viremia by a commonly used bDNA assay carried integrated proviral DNA and were capable of producing infectious virus upon cellular activation in vitro. Phenotypic analysis of HIV-1 produced by activation of latently infected CD4+ T cells revealed the presence in some patients of syncytium-inducing virus. In addition, the presence of unintegrated HIV-1 DNA in infected resting CD4+ T cells from patients receiving HAART, even those with undetectable plasma viremia, suggests persistent active virus replication in vivo.

Cloning and analysis of the promoter region of CXCR4, a coreceptor for HIV-1 entry

The chemokine receptor CXCR4 (also designated fusin and LESTR) is a cofactor for fusion and entry of T cell-tropic strains of HIV-1. CXCR4 is expressed in various cell types; however, the mechanisms involved in the regulation of its expression remain unknown. To delineate these mechanisms, approximately 1.2 kb of DNA from the immediate 5' upstream region of CXCR4 gene was cloned, sequenced, and characterized. Transient expression assays using CXCR4 promoter/luciferase gene reporter constructs revealed that stimulation with PMA plus ionomycin up-regulates the CXCR4 promoter activity in the A3.01 CD4+ T cell line and PBL and that a DNA fragment from -93 to +59 relative to the transcription start site contributes markedly to the basal and induced activity. This fragment contains a consensus TATA box, two potential GC boxes, and a potential nuclear respiratory factor (NRF)-1 binding site, which were confirmed by gel mobility shift assays and footprinting analysis. Mutagenesis studies revealed that a NRF-1 site is especially important for the basal and induced activity of the CXCR4 promoter. Transient expression assays further revealed that stimulation of PBL with either IL-2 or Abs to CD3 and CD28 enhances the CXCR4 promoter activity. Inducibility of the CXCR4 promoter activity by T cell stimulation suggests that overexpression of CXCR4 may be one of the mechanisms whereby immune activation and/or perturbation of the cytokine network up-regulate HIV expression and replication and thus contribute to the progression of HIV disease.

Cloning and analysis of the promoter region of CXCR4, a coreceptor for HIV-1 entry

The chemokine receptor CXCR4 (also designated fusin and LESTR) is a cofactor for fusion and entry of T cell-tropic strains of HIV-1. CXCR4 is expressed in various cell types; however, the mechanisms involved in the regulation of its expression remain unknown. To delineate these mechanisms, approximately 1.2 kb of DNA from the immediate 5' upstream region of CXCR4 gene was cloned, sequenced, and characterized. Transient expression assays using CXCR4 promoter/luciferase gene reporter constructs revealed that stimulation with PMA plus ionomycin up-regulates the CXCR4 promoter activity in the A3.01 CD4+ T cell line and PBL and that a DNA fragment from -93 to +59 relative to the transcription start site contributes markedly to the basal and induced activity. This fragment contains a consensus TATA box, two potential GC boxes, and a potential nuclear respiratory factor (NRF)-1 binding site, which were confirmed by gel mobility shift assays and footprinting analysis. Mutagenesis studies revealed that a NRF-1 site is especially important for the basal and induced activity of the CXCR4 promoter. Transient expression assays further revealed that stimulation of PBL with either IL-2 or Abs to CD3 and CD28 enhances the CXCR4 promoter activity. Inducibility of the CXCR4 promoter activity by T cell stimulation suggests that overexpression of CXCR4 may be one of the mechanisms whereby immune activation and/or perturbation of the cytokine network up-regulate HIV expression and replication and thus contribute to the progression of HIV disease.

Macrophage-tropic HIV and SIV envelope proteins induce a signal through the CCR5 chemokine receptor

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) enter target cells by forming a complex between the viral envelope protein and two cell-surface membrane receptors: CD4 and a 7-span transmembrane chemokine receptor. Isolates of HIV that differ in cellular tropism use different subsets of chemokine receptors as entry cofactors: macrophage-tropic HIVs primarily use CCR5, whereas T-cell-tropic and dual-tropic isolates use CXCR4 receptors. HIV-mediated signal transduction through CCR5 is not required for efficient fusion and entry of HIV in vitro. Here we show that recombinant envelope proteins from macrophage-tropic HIV and SIV induce a signal through CCR5 on CD4+ T cells and that envelope-mediated signal transduction through CCR5 induces chemotaxis of T cells. This chemotactic response may contribute to the pathogenesis of HIV in vivo by chemo-attracting activated CD4+ cells to sites of viral replication. HIV-mediated signalling through CCR5 may also enhance viral replication in vivo by increasing the activation state of target cells. Alternatively, envelope-mediated CCR5 signal transduction may influence viral-associated cytopathicity or apoptosis.

Viral dynamics of primary viremia and antiretroviral therapy in simian immunodeficiency virus infection

Mathematical modeling of viral replication dynamics, based on sequential measurements of levels of virion-associated RNA in plasma during antiretroviral treatment, has led to fundamental new insights into human immunodeficiency virus type 1 pathogenesis. We took advantage of the simian immunodeficiency virus (SIV)-infected macaque model to perform detailed measurements and mathematical modeling during primary infection and during treatment of established infection with the antiretroviral drug (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA). The calculated clearance half-life for productively infected cells during resolution of the peak viremia of primary infection was on the order of 1 day, with slightly shorter clearance half-lives calculated during PMPA treatment. Viral reproduction rates upon discontinuation of PMPA treatment after 2 weeks were approximately twofold greater than those obtained just prior to initiation of treatment in the same animals, likely reflecting accumulation of susceptible target cells during treatment. The basic reproductive ratio (R0) for the spread of SIV infection in vivo, which represents the number of productively infected cells derived from each productively infected cell at the beginning of infection, was also estimated. This parameter quantifies the extent to which antiviral therapy or vaccination must limit the initial spread of virus to prevent establishment of chronic disseminated infection. The results thus provide an important guide for efforts to develop vaccines against SIV and, by extension, human immunodeficiency virus.

Neutralizing antibody responses to human immunodeficiency virus type 1 in primary infection and long-term-nonprogressive infection

The role of neutralizing antibodies in human immunodeficiency virus type 1 (HIV-1) infection is poorly understood and was assessed by evaluating responses at different stages of infection. Undiluted sera from long-term nonprogressors (LTNP) had broad neutralizing antibodies against heterologous primary isolates and were more likely to neutralize the contemporaneous autologous isolate than were sera from short-term nonprogressors and progressors. In primary infection, envelope-specific IgG was detected before the initial decline in plasma viremia, but neutralizing antibodies developed more slowly. Here, neutralizing antibodies against strains SF-2 and MN were sometimes the first to be detected, but titers were low for at least 17 weeks from onset of symptoms. Neutralizing antibodies against the early autologous isolate were detected for 4 patients by 5-40 weeks but were undetectable in 2 additional patients for 27-45 weeks. The results indicate that neutralizing antibody responses are slow to develop during primary infection and are uniquely broad in LTNP.

Host factors in the pathogenesis of HIV disease

Host factors play an important role in determining rates of disease progression in human immunodeficiency virus (HIV)-infected individuals. HIV is able to subvert the host immune system by infecting CD4+ T cells that normally orchestrate immune responses and by inducing the secretion of proinflammatory cytokines that the virus can utilize to its own replicative advantage. The recognition that certain chemokine receptors serve as necessary co-factors for HIV entry into its target cells as well as the fact that ligands for these receptors can modulate the efficiency of HIV infection has expanded the number and scope of host factors that may impact the pathogenesis of HIV disease. This area of investigation will no doubt yield novel therapeutic strategies for intervention in HIV disease; however, caution is warranted in light of the enormous complexity of the pleiotropic cytokine and chemokine networks and the uncertainty inherent in manipulating these systems. HIV-infected long-term non-progressors represent an excellent model to study potential host factors involved in HIV disease pathogenesis. Genetic factors certainly have a major impact on the immune responses mounted by the host. In this regard, a polymorphism in the gene for the HIV co-receptor CC chemokine receptor 5 (CCR5), which serves as a co-receptor for macrophage (M)-tropic strains of HIV, affords a high degree of protection against HIV infection in individuals homozygous for the genetic defect and some degree of protection against disease progression in HIV-infected heterozygotes. HIV-specific immune responses, including cytotoxic T-lymphocyte (CTL) responses and neutralizing antibody responses, also appear to play salutary roles in protecting against disease progression.

Expression of HLA class I-specific inhibitory natural killer cell receptors in HIV-specific cytolytic T lymphocytes: impairment of specific cytolytic functions

Human T lymphocytes have been shown to express inhibitory natural killer cell receptors (NKR), which can down-regulate T cell antigen receptor-mediated T cell function, including cytolytic activity. In the present study, we demonstrate that CD3+NKR+ cells can be identified in HIV-infected patients. HIV-specific cytolytic activity was analyzed in five patients in whom autologous lymphoblastoid B cell lines could be derived as a source of autologous target cells. Phytohemagglutinin-activated T cell populations that had been cultured in interleukin 2 displayed HIV-specific cytotoxic T lymphocyte (CTL) activity against HIV env, gag, pol, and nef in 3 of 5 patients. Addition of anti-NKR mAb of IgM isotype could increase the specific CTL activity. Moreover, in one additional patient, HIV-specific CTL activity was undetectable; however, after addition of anti-NKR mAb such CTL activity appeared de novo. Similar results were obtained by analysis of CD3+NKR+ clones derived from two patients. These data provide direct evidence that CD3+NKR+ cells may include antigen (HIV)-specific CTLs and that mAb-mediated masking of inhibitory NKR may revert the down-regulation of CTL function.

Heterozygosity for a defective gene for CC chemokine receptor 5 is not the sole determinant for the immunologic and virologic phenotype of HIV-infected long-term nonprogressors

HIV-1-infected long-term nonprogressors are a heterogeneous group of individuals with regard to immunologic and virologic markers of HIV-1 disease. CC chemokine receptor 5 (CCR5) has recently been identified as an important coreceptor for HIV-1 entry into CD4+ T cells. A mutant allele of CCR5 confers a high degree of resistance to HIV-1 infection in homozygous individuals and partial protection against HIV disease progression in heterozygotes. The frequency of CCR5 heterozygotes is increased among HIV-1- infected long-term nonprogressors compared with progressors; however, the host defense mechanisms responsible for nonprogression in CCR5 heterozygotes are unknown. We hypothesized that nonprogressors who were heterozygous for the mutant CCR5 gene might define a subgroup of nonprogressors with higher CD4+ T cell counts and lower viral load compared with CCR5 wild-type nonprogressors. However, in a cohort of 33 HIV-1-infected long-term nonprogressors, those who were heterozygous for the mutant CCR5 gene were indistinguishable from CCR5 wild-type nonprogressors with regard to all measured immunologic and virologic parameters. Although epidemiologic data support a role for the mutant CCR5 allele in the determination of the state of long-term nonprogression in some HIV-1- infected individuals, it is not the only determinant. Furthermore, long-term nonprogressors with the wild-type CCR5 genotype are indistinguishable from heterozygotes from an immunologic and virologic standpoint.

Evidence for rapid disappearance of initially expanded HIV-specific CD8+ T cell clones during primary HIV infection

Down-regulation of the initial burst of viremia during primary HIV infection is thought to be mediated predominantly by HIV-specific cytotoxic T lymphocytes, and the appearance of this response is associated with major perturbations of the T cell receptor repertoire. Changes in the T cell receptor repertoire of virus-specific cytotoxic T lymphocytes were analyzed in patients with primary infection to understand the failure of the cellular immune response to control viral spread and replication. This analysis demonstrated that a significant number of HIV-specific T cell clones involved in the primary immune response rapidly disappeared. The disappearance was not the result of mutations in the virus epitopes recognized by these clones. Evidence is provided that phenomena such as high-dose tolerance or clonal exhaustion might be involved in the disappearance of these monoclonally expanded HIV-specific cytotoxic T cell clones. These findings should provide insights into how HIV, and possibly other viruses, elude the host immune response during primary infection.

Cyclosporin A modulation of early virologic and immunologic events during primary simian immunodeficiency virus infection in rhesus monkeys

Virologic and immunologic effects of immunomodulation during primary simian immunodeficiency virus (SIV) infection were examined in monkeys treated with cyclosporin or vehicle for 32 days beginning 5 days before SIV inoculation. Duration of antigenemia decreased in 5 of 7 treated monkeys, 2 having delayed onset and peak of antigenemia. Although proviral DNA levels in blood and lymph nodes and infected cell numbers in lymph nodes were transiently decreased, levels were similar to those in controls by day 14. The CD4:CD8 ratio and percentage of CD4+ CD29+ cells decreased in controls 14 days after inoculation, but this decrease was delayed in treated monkeys. Two treated monkeys demonstrated rapid disease, with progressive antigenemia preceding early deaths 90-96 days after inoculation. Nevertheless, immunomodulation influenced the kinetics of primary SIV infection in some monkeys, supporting the rationale of careful exploration of the strategy of interference with the heightened state of cellular activation together with direct antiretroviral therapy in human immunodeficiency virus infection.

Increased in vitro tetanus-induced production of HIV type 1 following in vivo immunization of HIV type 1-infected individuals with tetanus toxoid

We have previously demonstrated that immunization of HIV-1-infected individuals with the common recall antigen, tetanus, induced transient increases in plasma viremia as well as an increased ability to isolate virus from CD8+ T cell-depleted peripheral blood mononuclear cells (PBMCs) under minimally stimulated culture conditions (IL-2 plus IL-4) postimmunization. In this study, HIV-1-infected individuals were immunized with tetanus toxoid and PBMCs were examined at multiple time points following immunization. Tetanus-induced production of virus was defined as an increased ability to isolate HIV-1 from CD8+ T cell-depleted PBMCs in vitro in the presence of tetanus antigen as opposed to no antigen or control antigen alone. Following immunization, in vitro tetanus-induced production of HIV-1 was observed in 8 of 13 (62%) patients compared to 2 of 13 (15%) patients prior to immunization. In four of these patients, virus could also be isolated from CD8+ T cell-depleted PBMCs in the presence of tetanus without the addition of any exogenous IL-2. Furthermore, virus could be isolated from the unfractionated PBMCs of two patients when tetanus antigen alone was added to the culture in the absence of added PHA or PHA blasts. HIV-1 was isolated predominantly from CD4+ T cells with a CD45RO+, CD25+ phenotype and was associated with a trend to elevated levels in culture supernatants of IFN-gamma, IL-6, TNF-alpha, and IL-4. These findings have important implications with regard to the role of ongoing antigen-specific immune responses in the induction of HIV-1 expression in vivo.

Role of dendritic cells in immunopathogenesis of human immunodeficiency virus infection

The role of dendritic cells (DC) in the pathogenesis of human immunodeficiency virus (HIV) disease has been a subject of considerable interest for several years. Initial studies focused on the infection, dysfunction, and depletion of DC in HIV-infected individuals. More recent studies have begun to identify the functional role of DC in the initiation and propagation of viral replication in T cells in HIV-infected individuals. This review discusses recent data regarding the role of DC in HIV disease with the aim of delineating basic immunopathogenic principles of infection and the development of therapeutic strategies.

Nuclear factor-kappa B potently up-regulates the promoter activity of RANTES, a chemokine that blocks HIV infection

The complex network of cytokines that are involved in inflammatory and immunoregulatory responses plays a critical role in the pathogenesis of HIV infection. RANTES (regulated upon activation, normal T cell expressed and secreted) is a cytokine that belongs to the beta-chemokine family; it is chemoattractant for CD4+/CD45RO T cells, it is produced by various cell types including CD8+ and CD4+ T cells as well as monocytes/macrophages, and has recently been shown to suppress replication of macrophage-tropic strains of HIV in CD4+ T cells. To investigate the molecular mechanisms of RANTES expression, the RANTES promoter region was analyzed by transient expression and gel-mobility shift assays. We demonstrate that: 1) RANTES promoter activity is up-regulated by PMA plus ionomycin, coexpression of the p65 subunit of nuclear factor (NF)-kappa B, the proinflammatory cytokines TNF-alpha and IL-1 beta, and the CD28 costimulatory pathway; 2) the RANTES promoter region contains four NF-kappa B binding sites at positions -30, -44, -213, and -579 relative to the transcription start site; 3) one site (-213) is an NF-AT (nuclear factor of activated T cells) binding site that also has weak affinity to NF-kappa B, and the most distal site (-579) also serves as a CD28-responsive element; and 4) mutation on any of those NF-kappa B sites or coexpression of I kappa B alpha (cytoplasmic inhibitor of NF-kappa B) markedly reduced the promoter activity. Thus, NF-kappa B, a potent transcriptional activator of HIV expression, is also involved in the expression of RANTES, a chemokine that blocks infection by macrophage-tropic strains of HIV.

Nuclear factor-kappa B potently up-regulates the promoter activity of RANTES, a chemokine that blocks HIV infection

The complex network of cytokines that are involved in inflammatory and immunoregulatory responses plays a critical role in the pathogenesis of HIV infection. RANTES (regulated upon activation, normal T cell expressed and secreted) is a cytokine that belongs to the beta-chemokine family; it is chemoattractant for CD4+/CD45RO T cells, it is produced by various cell types including CD8+ and CD4+ T cells as well as monocytes/macrophages, and has recently been shown to suppress replication of macrophage-tropic strains of HIV in CD4+ T cells. To investigate the molecular mechanisms of RANTES expression, the RANTES promoter region was analyzed by transient expression and gel-mobility shift assays. We demonstrate that: 1) RANTES promoter activity is up-regulated by PMA plus ionomycin, coexpression of the p65 subunit of nuclear factor (NF)-kappa B, the proinflammatory cytokines TNF-alpha and IL-1 beta, and the CD28 costimulatory pathway; 2) the RANTES promoter region contains four NF-kappa B binding sites at positions -30, -44, -213, and -579 relative to the transcription start site; 3) one site (-213) is an NF-AT (nuclear factor of activated T cells) binding site that also has weak affinity to NF-kappa B, and the most distal site (-579) also serves as a CD28-responsive element; and 4) mutation on any of those NF-kappa B sites or coexpression of I kappa B alpha (cytoplasmic inhibitor of NF-kappa B) markedly reduced the promoter activity. Thus, NF-kappa B, a potent transcriptional activator of HIV expression, is also involved in the expression of RANTES, a chemokine that blocks infection by macrophage-tropic strains of HIV.

The qualitative nature of the primary immune response to HIV infection is a prognosticator of disease progression independent of the initial level of plasma viremia

Following infection of the host with a virus, the delicate balance between virus replication/spread and the immune response to the virus determines the outcome of infection, i.e., persistence versus elimination of the virus. It is unclear, however, what relative roles immunologic and virologic factors play during primary viral infection in determining the subsequent clinical outcome. By studying a cohort of subjects with primary HIV infection, it has been demonstrated that qualitative differences in the primary immune response to HIV, but not quantitative differences in the initial levels of viremia are associated with different clinical outcomes.

Activated cytotoxic lymphocytes in lymph nodes from human immunodeficiency virus (HIV) 1-infected patients: a light and electronmicroscopic study

Persistent generalized lymphadenopathy often develops during HIV-infection. It is characterized by follicular hyperplasia which progresses over time to follicular involution and finally lymphocyte depletion. To determine whether activated cytotoxic T cells (CD8+) are present in the hyperplastic germinal centres, light and electronmicroscopic immunogold labelling with monoclonal antibodies were used to localize two cytotoxic molecules, perforin and TIA-1. Perforin and TIA-1-positive cells were detected in the follicles and paracortex of lymph nodes from HIV-infected patients, whereas labelling was seen only in cells of the paracortex in the hyperplastic lymph nodes from HIV-negative patients. Cytotoxic granules, staining positive for perforin and TIA-1, were identified by transmission electronmicroscopy, often in proximity to follicular dendritic cells within the hyperplastic germinal centres of only HIV-positive patients. These cytotoxic cells may play a role in the follicular dendritic cell loss and concomitant follicular involution that occur during the evolution of HIV disease.

Studies on lymphoid tissue from HIV-infected individuals: implications for the design of therapeutic strategies

Lymphoid tissue is a major reservoir of human immunodeficiency virus (HIV) infection in vivo. In addition, the lymphoid microenvironment provides a replicative advantage to the virus in that it provides a milieu of activated target cells that allows for efficient virus spread. The process of mobilization and activation of immune competent cells directed against the virus paradoxically contributes to the propagation of virus replication. Disruption of the lymphoid microenvironment during the progression of HIV disease is a poorly understood process, which may be of considerable importance pathogenically. Studies of lymph node biopsy samples taken 8 weeks apart from individuals who did not undergo any change in their therapeutic regimen (i.e., patients who either remained untreated or remained on their ongoing nucleoside analogue reverse transcriptase inhibitor monotherapy regimen) revealed little change in histopathology or viral load over the 8-week period. These results with successive lymph node biopsy samples taken from different sites indicate that an isolated lymph node biopsy accurately reflects the pathologic process associated with HIV infection and that this process diffusely involves the lymphoid system. Treatment with reverse transcriptase inhibitor monotherapy of patients in relatively early stage HIV disease had no detectable impact on the viral load in lymphoid tissue, suggesting the need to investigate more potent antiretroviral regimens during this stage of disease. Among patients with moderately advanced HIV disease, switching to combination therapy from a monotherapy regimen resulted in decreased viral replication in lymph nodes; this effect was associated with decreases in plasma viremia. Despite the fact that measures of viral replication decreased significantly, the net frequency of HIV-infected cells in peripheral blood and lymph nodes remained unchanged. Potent antiretroviral drug combinations may be capable of profound and long-term downregulation of plasma viremia. It will be essential to monitor the status of viral trapping, viral burden, and viral replication within lymphoid tissue during treatment with such drugs to determine accurately their true potential for impact on these key features of HIV pathogenesis.

gp120 is present on the plasma membrane of apoptotic CD4 cells prepared from lymph nodes of HIV-1-infected individuals: an immunoelectron microscopic study

OBJECTIVE

To study whether free gp120 can be detected on the plasma membranes of apoptotic CD4+ T lymphocytes in lymph nodes from HIV-positive patients.

METHODS

Lymph-node cell suspensions prepared from three HIV-positive patients were studied by pre-embedding, double-immunogold-labeling to identify cell type, determine cell morphology, and detect the presence of bound gp120 molecules. Cells were classified by their surface antigens as helper/inducer T lymphocytes (CD4+), cytotoxic/suppressor T lymphocytes (CD8+), B cells (CD20+), and total lymphocytes [CD45+, leukocyte common antigen (LCA)+].

RESULTS

gp120 colabelled with both apoptotic and normal CD4+ T lymphocytes and LCA+ cells, but not with either apoptotic or normal CD8+ T lymphocytes or B cells. gp120 was more often identified on apoptotic than on normal CD4+ T lymphocytes. The gp120 and CD45 label were often colocalized. HIV particles were not identified to be associated with or budding from either normal or apoptotic lymphocytes.

CONCLUSIONS

Free gp120 is found bound to CD4+ T cells in lymph nodes of HIV-infected individuals and potentially mark them for premature death by apoptosis.

Inherited resistance to HIV-1 conferred by an inactivating mutation in CC chemokine receptor 5: studies in populations with contrasting clinical phenotypes, defined racial background, and quantified risk

BACKGROUND

CC chemokine receptor 5 (CCR5) is a cell entry cofactor for macrophage-tropic isolates of human immunodeficiency virus-1 (HIV-1). Recently, an inactive CCR5 allele (designated here as CCR5-2) was identified that confers resistance to HIV-1 infection in homozygotes and slows the rate of progression to AIDS in heterozygotes. The reports conflict on the effect of heterozygous CCR5-2 on HIV-1 susceptibility, and race and risk levels have not yet been fully analyzed. Here we report our independent identification of CCR5-2 and test its effects on HIV-1 pathogenesis in individuals with contrasting clinical outcomes, defined race, and quantified risk.

MATERIALS AND METHODS

Mutant CCR5 alleles were sought by directed heteroduplex analysis of genomic DNA from random blood donors. Genotypic frequencies were then determined in (1) random blood donors from North America, Asia, and Africa; (2) HIV-1+ individuals; and (3) highly exposed-seronegative homosexuals with quantified risk.

RESULTS

CCR5-2 was the only mutant allele found. It was common in Caucasians, less common in other North American racial groups, and not detected in West Africans or Tamil Indians. Homozygous CCR5-2 frequencies differed reciprocally in highly exposed-seronegative (4.5%, n = 111) and HIV-1-seropositive (0%, n = 614) Caucasians relative to Caucasian random blood donors (0.8%, n = 387). This difference was highly significant (p < 0.0001). By contrast, heterozygous CCR5-2 frequencies did not differ significantly in the same three groups (21.6, 22.6, and 21.7%, respectively). A 55% increase in the frequency of heterozygous CCR5-2 was observed in both of two cohorts of Caucasian homosexual male, long-term nonprogressors compared with other HIV-1+ Caucasian homosexuals (p = 0.006) and compared with Caucasian random blood donors. Moreover, Kaplan-Meier estimates indicated that CCR5-2 heterozygous seroconvertors had a 52.6% lower risk of developing AIDS than homozygous wild-type seroconvertors.

CONCLUSIONS

The data suggest that homozygous CCR5-2 is an HIV-1 resistance factor in Caucasians with complete penetrance, and that heterozygous CCR5-2 slows the rate of disease progression in infected Caucasian homosexuals. Since the majority (approximately 96%) of highly exposed-seronegative individuals tested are not homozygous for CCR5-2, other resistance factors must exist. Since CCR5-2 homozygotes have no obvious clinical problems, CCR5 may be a good target for the development of novel antiretroviral therapy.