Immune and hematopoietic parameters in HIV-1-infected chimpanzees during clinical progression toward AIDS

Analysis of the immune responses in chimpanzees infected with HIV type 1 isolates

The mechanisms of resistance to AIDS development in HIV-1-infected chimpanzees have remained elusive. Unique among chimpanzees naturally or experimentally infected with HIV, several animals of the Yerkes cohort have progressed to clinical AIDS with selection of isolates showing increased pathogenicity for chimpanzees. We compared progressors vs. nonprogressors among the HIV-infected chimpanzees that made up this cohort, eight of which have been infected with HIV-1 for over 14 years. The additional two progressors were infected de novo with chimpanzee-pathogenic HIV, rapidly leading to a progressor status. Nonprogressors were characterized by normal CD4(+) T cell counts and the absence of detectable viremia. In contrast, progressor chimpanzees had relatively high plasma viral loads associated with a dramatic loss of CD4(+) T cells. The analysis of immune responses showed a similar amplitude and breadth of ELISPOT T cell responses in both groups. HIV-specific proliferative responses were, however, absent in the progressor animals, which also exhibited increased levels of immune activation characterized by elevated levels of the circulating chemokines IP-10 and MCP-1. Of interest was the conservation of potent NK cell activity in all animals, potentially contributing to the extended symptom-free survival of progressor animals. Modest anti-HIV antibody titers were detectable in the nonprogressor group, but these antibodies exhibited good neutralizing activity. In progressors, however, two sets of data were noted: in animals that gradually selected for pathogenic isolates, or that were superinfected, very high neutralizing antibody titers were observed, although none to the pathogenic HIV. In contrast, two animals infected de novo with chimpanzee pathogenic HIV failed to mount an extensive humoral response and both failed to develop neutralizing antibodies to the virus. Taken together, pathogenic HIV infection in chimpanzees is associated with rapid loss of CD4(+) T cells and proliferative responses as well as higher levels of immune activation.

Effects of HIV type 1 infection on hematopoiesis in Botswana

Clinical observations suggest that HIV-1 infection causes higher anemia rates in patients in southern Africa than in those in the United States. To explore this difference we performed a cross-sectional exploratory study on the effect of HIV-1 infection on hematopoiesis in Botswana by examining hematological presentation, HIV disease state, hematopoietic progenitor cell number, and circulating viral levels in HIV-infected patients and HIV-uninfected controls. We found significant associations between CD34(+) and CD4(+) cell counts in HIV-positive patients. Significant relationships were also seen between the CD34(+) CD4(+) cell population and hemoglobin levels, as well as colony-forming ability. These associations, however, were not seen in uninfected controls. Circulating viral p24 levels were found to correlate significantly with CD34(+) cell count, CD34(+) CD4(+) cell count, and colony-forming ability. These results demonstrate a direct association between HIV-1 infection in southern Africa and hematopoietic progenitor cell health.

Human and simian immunodeficiency virus-mediated upregulation of the apoptotic factor TRAIL occurs in antigen-presenting cells from AIDS-susceptible but not from AIDS-resistant species

Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections lead to AIDS in humans and rhesus macaques (RM), while they are asymptomatic in species naturally infected with SIV, such as chimpanzees, sooty mangabeys (SM), and African green monkeys (AGM). Differential CD4(+) T-cell apoptosis may be responsible for these species-specific differences in susceptibility to disease. To identify factors that influence the different apoptotic responses of these species, we analyzed virus-infected human and nonhuman primate peripheral blood mononuclear cells (PBMC). We found that the apoptotic factor TRAIL was present at higher levels in human and RM PBMC cultures and was mediating, at least in part, CD4(+) T-cell apoptosis in these cultures. The species-specific increase in TRAIL and death receptor expression observed with cultures also occurred in vivo in SIV-infected RM but not in SIV-infected SM. In human and RM myeloid immature dendritic cells and macrophages, the virus-induced expression of TRAIL and other interferon-inducible genes, which did not occur in the same cells from chimpanzee, SM, and AGM, was Tat dependent. Our results link the differential induction of TRAIL in human and nonhuman primate cells to species-specific differences in disease susceptibility.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.

Polymorphism of human and primate RANTES, CX3CR1, CCR2 and CXCR4 genes with regard to HIV/SIV infection

Among genes that influence human susceptibility to HIV (human immunodeficiency virus) infection or AIDS (acquired immunodeficiency syndrome) progression, chemokine-receptor and chemokine genes were extensively studied because of their role as HIV co-receptors or co-receptor competitors, respectively. We have studied in non-human primates (chimpanzee, gorilla, gibbon, orang-utan, crab-eating and rhesus macaque, baboon and marmoset) the RANTES, CCR2 and CX3CR1 gene sequences in regions surrounding human mutations that were associated with susceptibility to HIV or AIDS progression: RANTES G-403A and C-28G, CCR2 V64I, CX3CR1 V249I and CX3CR1 T280M. Among these five dimorphisms, only RANTES G-403A is observed in one of the eight primate species studied here (gibbon). This suggests that these mutations appeared recently in humans and probably do not account for variable HIV/SIV disease progression in primates. It is noteworthy that chimpanzees, which are naturally resistant to HIV-1- and HIV-2-induced AIDS, do not have the human mutations associated with delayed disease progression. Inter-species and intra-species polymorphic positions are observed in primates and we discuss the potential impact of these mutations on HIV/SIV disease progression. Particularly, we identified polymorphisms in old-world monkey (OWM) genes, and it could be of great importance to analyse the possible association between these polymorphisms and disease progression in OWM species that are currently used in research for HIV vaccine and therapy.

Human and simian immunodeficiency virus-infected chimpanzees do not have increased intracellular levels of beta-chemokines in contrast to infected humans

This study was undertaken to explain why chimpanzees infected with HIV-1 (human immunodeficiency virus type 1) or SIV(cpz) (simian immunodeficiency virus of chimpanzee) are relatively resistant to AIDS (acquired immunodeficiency syndrome). The numbers of beta-chemokine-positive cells were compared between uninfected and infected humans and chimpanzees using three-color cytofluorometry. In humans, the percentage of beta-chemokine-positive cells was significantly higher in CD8(+) T and natural killer (NK) cells than in CD4(+) T cells in both uninfected and HIV-1-infected individuals. In the presence of HIV-1 infection, however, both CD8(+) and CD4(+) T cell subsets contained significantly more beta-chemokine-positive cells than in the absence of infection. Interestingly, in chimpanzees two important differences were noted. First, their percentage of beta-chemokine-positive CD8(+) T and NK cells was significantly higher than in uninfected humans. Second, in contrast to humans, infection with either HIV-1 or with SIV(cpz) was not associated with increased numbers of beta-chemokine-positive cells. These results indicate that: constitutive high levels of intracellular beta-chemokines in chimpanzees' CD8 lymphocytes and NK cells do not necessarily correspond to lower levels of virus replication during the chronic phase of infection; and increased percentages of beta-chemokine-positive cells in HIV-infection are not a correlate of disease resistance. The data suggest that neither pre-nor post-exposure levels of intracellular beta-chemokines are correlated with the subsequent control of disease progression.

In vitro replication of SIVcpz is suppressed by beta-chemokines and CD8+ T cells but not by natural killer cells of infected chimpanzees

Unlike humans, chimpanzees are relatively resistant to AIDS after infection with HIV-1 or simian immunodeficiency virus of chimpanzee (SIVcpz). We hypothesized that resistance to disease progression is associated with efficient suppression of virus replication possibly by beta-chemokines secreted by CD8+ lymphocytes and especially natural killer (NK) cells. In vitro suppression of virus replication can be easily studied in SIVcpz-infected chimpanzees because they produce high infectious virus titers in their peripheral blood. A study was undertaken to assess the sensitivity of SIVcpz to beta-chemokines in vitro and to investigate the role of endogenous beta-chemokines in relation to the in vitro capacity of CD8+ lymphocytes and NK cells of chimpanzees to suppress SIVcpz replication. Our results show that SIVcpz uses CCR5 as a coreceptor to gain cell entry and is sensitive to recombinant beta-chemokines in vitro. Here we report that despite their potent capacity to produce RANTES, NK cells of infected chimpanzees do not suppress SIVcpz replication in vitro, in contrast to CD8+ lymphocytes. We also show that endogenous beta-chemokines are not the predominant factors mediating in vitro suppression.

Genetic variability of the V1 and V2 env domains of SIVcpz-ant and neutralization pattern of plasma viruses in a chimpanzee infected naturally

Specific neutralizing epitope changes have been observed in a chimpanzee infected naturally with SIVcpz, which differ from HIV-1 infecting humans. To characterize further these changes, a longitudinal study of env genomic sequence variation of SIVcpz-ant isolates was undertaken in this animal. The V1 and V2 regions of the env were determined to arise from specific recombination events. To determine whether recombination of the V1 and V2 domains was possibly associated with the emergence of neutralization escape viruses, envelope sequences and gene length polymorphisms from PBMC and plasma viral variants were studied over a 7-year period. PBMCs and plasma-associated infectious virus titers as well as plasma RNA viral loads were monitored longitudinally. The first 5 viruses isolated from the plasma were found to be neutralization escape variants. Sequence analysis of their V1 and the V2 regions indicated that a 20 amino acid stretch of the V1 region had undergone recombination and was also associated with the emergence of isolates eliciting strong neutralization responses. These findings support the hypothesis that recombination of the V1 and V2 regions of the envelope play a role in neutralization escape of SIVcpz in chimpanzees infected naturally. Furthermore, the data confirm that the neutralizing antibody response plays an important role in the decline of plasma infectious virus titers in HIV-1 related SIVcpz nonpathogenic infection.

Inhibitory and enhancing effects of IFN-gamma and IL-4 on SHIV(KU) replication in rhesus macaque macrophages: correlation between Th2 cytokines and productive infection in tissue macrophages during late-stage infection

HIV-1 is dual-tropic for CD4+ T lymphocytes and macrophages, but virus production in the macrophages becomes manifest only during late-stage infection, after CD4+ T cell functions are lost, and when opportunistic pathogens begin to flourish. In this study, the SHIV/macaque model of HIV pathogenesis was used to assess the role of cytokines in regulating virus replication in the two cell types. We injected complete Freund's adjuvant (CFA) intradermally into SHIV(KU)-infected macaques, and infused Schistosoma mansoni eggs into the liver and lungs of others. Tissues examined from these animals demonstrated that macrophages induced by CFA did not support viral replication while those induced by S. mansoni eggs had evidence of productive infection. RT-PCR analysis showed that both Th1 (IL-2 and IFN-gamma) and Th2 cytokines (IL-4 and IL-10) were present in the CFA lesions but only the Th2 cytokines were found in the S. mansoni lesions. Follow-up studies in macaque cell cultures showed that whereas IFN-gamma caused enhancement of virus replication in CD4+ T cells, it curtailed viral replication in infected macrophages. In contrast, IL-4 enhanced viral replication in infected macrophages. These studies strongly suggest that cytokines regulate the sequential phases of HIV replication in CD4 T cells and macrophages.

HIV vaccines for prevention of infection and disease in humans

Phase I and II studies have been carried out with several candidate HIV-1 vaccines in seronegative volunteers. Vaccines consisting of rgp 120 stimulated moderate levels of neutralizing antibodies against homologous, TCLA adapted viruses, but did not induce CD8+ CTL responses. Canarypox vectors stimulate CD8+ CTL responses, but little neutralizing activity. The latter can be increased in titer by boosting recipients of canarypox vectors with rgp120 vaccines. Large-scale placebo-controlled efficacy trials are underway with two rgp120 vaccines: AIDSVAX B/B (VaxGen, Inc.) in the United States, and AIDSVAX B/E in Thailand. The canarypox-rgp120 combined regimen has been proposed for study in an intermediate-sized, "test-of-concept" efficacy trial by the NIAID-sponsored HVTN, with an experimental design intended to provide information on the potential in vitro correlates of immunity. The results from these studies, and the methodology used in their conduct, should facilitate the refinement of conventional and novel approaches to the development of safe and effective HIV vaccines.

In vitro and in vivo responses to interleukin 12 are maintained until the late SIV infection stage but lost during AIDS

The in vitro proliferative responses of macaque peripheral blood mononuclear cells (PBMCs) to IL-12 appeared similar before and early after SIV infection, whereas macaque PBMCs sampled during symptomatic stages of SIV infection showed markedly decreased responses. IL-12 was administered to SIVmac239-infected rhesus macaques either during the asymptomatic or the AIDS stage of infection in efforts to evaluate the effect of this cytokine on immune responses, viral loads, and hematopoietic functions in vivo. IFN-gamma secretion levels induced during the asymptomatic or early symptomatic phase were similar to preinfection induced levels, whereas in later AIDS stages this response was lost. The constitutive levels of other measured cytokines were not affected by IL-12 administration in vivo. The frequency and activity of circulating NK cells were markedly enhanced at early stages but not at symptomatic stages of SIV infection. pCTL frequencies were enhanced at early symptomatic stages but not at late AIDS stages. Despite its immunomodulatory effect, IL-12 did not seem to exacerbate or inhibit the replication of SIV in vivo, or the frequency of circulating infected lymphocytes. IL-12 administration was associated with a significant yet subclinical and transient decrease in hematocrit and hemoglobin levels without evidence of hemolysis, hemodilution, or reduction in the frequency of colony-forming unit potential of bone marrow CD34+ cells. This phenomenon may be explained by a functional inhibition of differentiation rather than an altered generation of bone marrow precursors. Thus, these results suggest that IL-12 may benefit HIV-1-infected patients only as long as their immune system retains its capability to respond to cytokine stimulation.

A novel role for tumor necrosis factor-alpha in regulating susceptibility of activated CD4+ T cells from human and nonhuman primates for distinct coreceptor using lentiviruses

Although CD4+ T-cell activation has long been shown to promote infection and replication of simian immunodeficiency virus (SIV) and HIV, recent studies have documented that not all activated CD4+ T cells from human and nonhuman primates are susceptible to infection with HIV/SIV, respectively. Activation of CD4+ T cells with anti-CD3 + anti-CD28 conjugated beads led to induction of a state of anti-viral resistance to infection with strains of viruses that primarily use CCR5 as a coreceptor. The studies reported herein were designed to address the mechanism by which anti-CD3 + anti-CD28-induced stimulation in turn induced antiviral resistance. Results of these studies show that the anti-viral resistance induced by activation of CD4+ T cells with anti-CD3 + anti-CD28 is primarily conferred by the synthesis of tumor necrosis factor-alpha (TNF-alpha), and highlight a unique regulatory role for TNF-alpha in regulating synthesis of MIP-1alpha, MIP-1beta, and regulated-on-activation normal T-expressed and secreted cells, which contributes to this state of antiviral resistance to R5-tropic strains of HIV/SIV. However, while TNF-alpha has a protective role in antiviral resistance of activated CD4+ T cells to R5-tropic viruses, it enhances CXCR4 expression of CD4+ T cells and mediates increased susceptibility to infection with X4-tropic strains of HIV and recombinant SIVs. The results of the studies reported herein also suggest that it is not the Th1 v/s Th2 cytokine profile but the mode of CD4+ T-cell activation that dictates the synthesis of distinct cytokines which regulate the expression of chemokines and chemokine receptors which in turn regulate and confer susceptibility/resistance to R5 v/s X4-tropic HIV and SIV.

Analysis of nonhuman primate peripheral blood mononuclear cells for susceptibility to HIV-1 infection and HIV coreceptor expression

HIV-1 infection of nonhuman primates does not lead to the acquired immunodeficiency syndrome seen in humans. The basis for this lack of disease progression in these animals is still unknown. In this study, primary nonhuman primate peripheral blood mononuclear cells (PBMC) were tested for their susceptibility to in vitro infection by several different primary HIV-1 isolates representing distinct subtypes or clades. None of the five HIV-1 subtypes tested were able to readily establish an infection in chimpanzee or baboon PBMC, as determined by p24 antigen capture assays. To address the mechanism of in vitro resistance to HIV-1 infection, PBMC were analyzed for HIV coreceptor mRNA expression and cell surface expression. Flow cytometry analysis of the nonhuman primate PBMC demonstrated that they do express CD4, CCR3, CCR5, and CXCR4 on their cell surface. Therefore, the level of restriction in the virus replication cycle does not appear to lie at the point of entry in these cells.

Diverse host responses and outcomes following simian immunodeficiency virus SIVmac239 infection in sooty mangabeys and rhesus macaques

Sooty mangabeys naturally infected with simian immunodeficiency virus (SIV) do not develop immunodeficiency despite the presence of viral loads of 10(5) to 10(7) RNA copies/ml. To investigate the basis of apathogenic SIV infection in sooty mangabeys, three sooty mangabeys and three rhesus macaques were inoculated intravenously with SIVmac239 and evaluated longitudinally for 1 year. SIVmac239 infection of sooty mangabeys resulted in 2- to 4-log-lower viral loads than in macaques and did not reproduce the high viral loads observed in natural SIVsmm infection. During acute SIV infection, polyclonal cytotoxic T-lymphocyte (CTL) activity coincident with decline in peak plasma viremia was observed in both macaques and mangabeys; 8 to 20 weeks later, CTL activity declined in the macaques but was sustained and broadly directed in the mangabeys. Neutralizing antibodies to SIVmac239 were detected in the macaques but not the mangabeys. Differences in expression of CD38 on CD8(+) T lymphocytes or in the percentage of naive phenotype T cells expressing CD45RA and CD62L-selection did not correlate with development of AIDS in rhesus macaques. In macaques, the proportion of CD4(+) T lymphocytes expressing CD25 declined during SIV infection, while in mangabeys, CD25-expressing CD4(+) T lymphocytes increased. Longitudinal evaluation of cytokine secretion by flow cytometric analysis of unstimulated lymphocytes revealed elevation of interleukin-2 and gamma interferon in a macaque and only interleukin-10 in a concurrently infected mangabey during acute SIV infection. Differences in host responses following experimental SIVmac239 infection may be associated with the divergent outcome in sooty mangabeys and rhesus macaques.

Loss of CD4+ T cells in human immunodeficiency virus type 1-infected chimpanzees is associated with increased lymphocyte apoptosis

Supportive evidence that apoptosis contributes to loss of CD4+ lymphocytes in human immunodeficiency virus type 1 (HIV-1)-infected humans comes from an apparent lack of abnormal apoptosis in apathogenic lentivirus infections of nonhuman primates, including HIV-1 infection of chimpanzees. Two female chimpanzees were inoculated, one cervically and the other intravenously, with HIV-1 derived from the LAI/LAV-1b strain, which was isolated from a chimpanzee infected with the virus for 8 years. Within 6 weeks of infection, both recipient chimpanzees developed a progressive loss of CD4+ T cells which correlated with persistently high viral burdens and increased levels of CD4+ T-cell apoptosis both in vitro and in vivo. Lymph nodes from both animals also revealed evidence of immune hyperactivation. Intermediate levels of T-cell apoptosis in both peripheral blood and lymph nodes were seen in a third chimpanzee that had been infected with the LAI/LAV-1b strain for 9 years; this animal has maintained depressed CD4/CD8 T-cell ratios for the last 3 years. Similar analyses of cells from 4 uninfected animals and 10 other HIV-1-infected chimpanzees without loss of CD4+ cells revealed no difference in levels of apoptosis in these two control groups. These results demonstrate a correlation between immune hyperactivation, T-cell apoptosis, and chronic loss of CD4+ T cells in HIV-1-infected chimpanzees, providing additional evidence that apoptosis is an important factor in T-cell loss in AIDS. Furthermore, the results show that some HIV-1 strains are pathogenic for chimpanzees and that this species is not inherently resistant to HIV-1-induced disease.