HIV-1 induced activation of CD4+ T cells creates new targets for HIV-1 infection in human lymphoid tissue ex vivo

We demonstrate mechanisms by which HIV-1 appears to facilitate its own infection in ex vivo-infected human lymphoid tissue. In this system, HIV-1 readily infects various CD4+ T cells, but productive viral infection was supported predominantly by activated T cells expressing either CD25 or HLA-DR or both (CD25/HLA-DR) but not other activation markers: There was a strong positive correlation (r=0.64, P=.001) between virus production and the number of CD25+/HLA-DR+ T cells. HIV-1 infection of lymphoid tissue was associated with activation of both HIV-1-infected and uninfected (bystanders) T cells. In these tissues, apoptosis was selectively increased in T cells expressing CD25/HLA-DR and p24gag but not in cells expressing either of these markers alone. In the course of HIV-1 infection, there was a significant increase in the number of activated (CD25+/HLA-DR+) T cells both infected and uninfected (bystander). By inducing T cells to express particular markers of activation that create new targets for infection, HIV-1 generates in ex vivo lymphoid tissues a vicious destructive circle of activation and infection. In vivo, such self-perpetuating cycle could contribute to HIV-1 disease.     

Segregation of R5 and X4 HIV-1 variants to memory T cell subsets differentially expressing CD62L in ex vivo infected human lymphoid tissue

OBJECTIVE: The mechanisms of HIV-triggered immunodeficiency were examined by determining the segregation of R5 and X4 HIV-1 variants into memory T cell subsets expressing differentially a homing receptor, CD62L-selectin, in human lymphoid tissue. METHODS: Subpopulations of CD3 and intracellular p24 gag-positive cells in human lymphoid tissue infected ex vivo with X4 HIV-1 variant NL4-3 and R5 HIV-1 variant AD8 were analysed for expression of the T cell memory markers CD45RO and CD45RA, the T cell homing receptor for lymphoid tissue CD62L, and the HIV-1 coreceptors CCR5 and CXCR4. RESULTS: Memory CD4 T cells were the predominant targets for productive infection of lymphoid tissue ex vivo with both R5 and X4 HIV-1. R5 HIV-1 predominantly infected CD62L-negative memory T cells, which selectively express CCR5. In contrast, X4 HIV-1 variants predominantly infected CD62L+ memory T cells, although CXCR4 coreceptor was equally expressed by memory T cells of both CD62L-positive and CD62L-negative subsets. A high proportion of X4 HIV-1, but not of R5 HIV-1, productively infected T cells, displayed a CD45RA+CD45RO+ phenotype. CONCLUSION: The selective expression of the CCR5 coreceptor by CD62L-negative terminally differentiated memory T cells correlates with the preferential productive infection of these cells with the R5 HIV-1 variant. The predominance of X4 HIV-1 variants in less-differentiated memory T cells may be related to their recent activation state, as suggested by the coexpression of both CD45RA and CD45RO molecules on their surface. Differential homing of CD62L-positive and CD62L-negative cells suggests different routes of dissemination of X4 and R5 viruses.     

CXCR4 utilization is sufficient to trigger CD4+ T cell depletion in HIV-1-infected human lymphoid tissue

The human chemokine receptors CCR5 and CXCR4 have emerged as the predominant cofactors, along with CD4, for cellular entry of HIV-1 in vivo whereas the contribution of other chemokine receptors to HIV disease has not been yet determined. CCR5-specific (R5) viruses predominate during primary HIV-1 infection whereas viruses with specificity for CXCR4 (R5/X4 or X4 viruses) often emerge in late stages of HIV disease. The evolution of X4 viruses is associated with a rapid decline in CD4+ T cells, although a causative relationship between viral tropism and CD4+ T cell depletion has not yet been proven. To rigorously test this relationship, we assessed CD4+ T cell depletion in suspensions of human peripheral blood mononuclear cells and in explants of human lymphoid tissue on exposure to paired viruses that are genetically identical (isogenic) except for select envelope determinants specifying reciprocal tropism for CXCR4 or CCR5. In both systems, X4 HIV-1 massively depleted CD4+ lymphocytes whereas matched R5 viruses depleted such cells only mildly despite comparable viral replication kinetics. These findings demonstrate that the coreceptor specificities of HIV-1 are a causal factor in CD4+ T cell depletion ex vivo and strongly support the hypothesis that the evolution of viral envelope leading to usage of CXCR4 in vivo accelerates loss of CD4+ T cells, causing immunodeficiency.     

Inhibition of HIV-1 replication in human lymphoid tissues ex vivo by measles virus

Human immunodeficiency virus (HIV) type 1 replication and disease progression are enhanced by various pathogens in coinfected individuals. However, acute infection with measles virus (MV) has been found to suppress HIV-1 replication in coinfected children. We investigated the mechanisms of this phenomenon using human lymphoid tissues coinfected ex vivo with HIV-1 and MV. MV inhibited both CXCR4-tropic (X4) and CCR5-tropic (R5) HIV-1, but the inhibitory effect was particularly profound for R5 virus, which transmits infection and dominates the early stages of HIV-1 disease. MV inhibits the replication of R5 HIV-1 in coinfected tissues by up-regulation of the CC chemokine RANTES, a well-known inhibitor of R5 HIV-1 infection, and this up-regulation is augmented in tissues coinfected with R5 HIV-1. Deciphering the molecular mechanisms by which MV and other pathogens alter local cytokine/chemokine networks and cause tissue microenvironments to become detrimental to HIV-1 may significantly contribute to the development of effective anti-HIV therapies.     

Pertussis toxin B-oligomer dissociates T cell activation and HIV replication in CD4 T cells released from infected lymphoid tissue

OBJECTIVE: To investigate, in human lymphoid tissue infected with HIV-1 ex vivo, the immunostimulatory and HIV inhibitory properties of pertussis toxin B oligomer (PTX-B) and of the genetically modified non-toxic PT-9K/129G. METHODS: Human tonsils from uninfected donors were infected ex vivo with R5 or X4 HIV-1 in the presence or absence of PTX-B. Virus replication was evaluated in culture supernatants; cells emigrated from tissue blocks were immunostained for lymphocytic and activation markers. HIV DNA and cell proliferation were evaluated with real-time PCR and [H]thymidine incorporation, respectively. RESULTS: Both PTX-B and PT-9K/129G inhibited HIV-1 replication. These compounds activated and stimulated the proliferation of emigrated cells, most of which were CD4 T lymphocytes. Cells emigrated from infected tissues did not produce detectable virus in unstimulated or in PTX-B- or PT-9K/129G-stimulated cultures whereas robust virus production was triggered by phytohemagglutinin (PHA) or interleukin-2 (IL-2). Analysis of HIV DNA content indicated that infected cells were present among emigrated cells and that their number greatly increased following IL-2 stimulation, whereas it remained constant in the presence of PTX-B or PT-9K/129G. CONCLUSIONS: PTX-B and PT-9K/129G inhibit both R5 and X4 HIV-1 replication in human lymphoid tissue ex vivo. In contrast to PHA and IL-2, they promote the proliferation of CD4 T lymphocytes emigrated from tissue, including HIV-infected cells, without triggering virus replication. Therefore, these emigrated CD4 T cells represent a novel model of a latent inducible HIV reservoir. Thus, PTX-B and the clinically approved PT-9K/129G are potential antiretroviral agents endowed with immunostimulatory capacity.     

Upregulation of human cytomegalovirus by HIV type 1 in human lymphoid tissue ex vivo

HIV-1 copathogens are believed to play a critical role in progression to AIDS. Human cytomegalovirus (HCMV) has a high prevalence in the general population and is a common copathogen in HIV-1-infected individuals. Important events in copathogen interactions with HIV-1 take place in lymphoid tissue where critical events in HIV-1 disease occur. Here, we used an experimental system of human lymphoid tissue ex vivo to investigate interactions of HCMV with HIV-1. We inoculated ex vivo blocks of human lymphoid tissue with a recombinant strain of HCMV, expressing the green fluorescent protein, and HIV-1 and monitored viral replication and the phenotype of productively infected cells. HCMV readily replicated in tissue blocks as revealed by the release of HCMV viral DNA and an increasing number of viral-positive cells. Immunophenotyping of HCMV-infected cells showed a preferential infection of activated lymphocytes. The number of these cells significantly increased in HIV-1-coinfected tissues. Accordingly, HCMV replication was enhanced 2- to-3 fold. This upregulation occurred in tissues infected with either CXCR4- or CCR5-utilizing HIV-1. Thus, HIV-1 creates new targets for HCMV, which may explain the strong association of HCMV with HIV-1 infection in vivo. Ex vivo-infected human lymphoid tissue constitutes a model to study the mechanisms of HCMV tissue pathogenesis and its interactions with HIV-1 and this model may provide new targets for anti-HIV-1 therapy.     

CXCR4-tropic HIV-1 suppresses replication of CCR5-tropic HIV-1 in human lymphoid tissue by selective induction of CC-chemokines

In infected individuals, human immunodeficiency virus type 1 (HIV-1) exist as a "swarm" of quasi species compartmentalized in tissues where individual viral variants may interact locally. We have used human lymphoid tissue, where the critical events of HIV disease occur, to study local interactions in model HIV-1 binary swarms ex vivo. We infected tissue blocks with binary mixtures consisting either of CCR5-dependent and CXCR4-dependent variants or of 2 dual-tropic HIV-1 variants, of which one is skewed to utilization of CXCR4 and the other of CCR5. HIV-1 variants that use CXCR4 suppress replication of CCR5-dependent HIV-1 variants, whereas CCR5-dependent HIV-1 variants do not affect replication of CXCR4-dependent HIV-1. CC-chemokines that inhibit replication of CCR5-dependent HIV-1 variants were up-regulated by CXCR4-dependent HIV-1, thus possibly contributing to this suppression. Tissue-specific chemokine/cytokine network modulations triggered by individual HIV-1 variants may be an important mechanism of local interactions among HIV-1 quasi species in infected tissue.     

Decline in CD4+ cell numbers reflects increase in HIV-1 replication

Changes in CD4+ cell numbers were studied in relation to the presence of HIV-1 antigen (HIV-1-Ag) in serum from homosexual men followed prospectively. During 30 months of follow-up the mean CD4+ cell number (x 10(9) per liter) was stable in 134 at entry HIV-1 antibody (HIV-1-Ab) seropositives, who remained HIV-1-Ag negative (from 0.59 to 0.62) and declined in 38 at entry HIV-1-Ab seropositives who were persistently HIV-1-Ag positive (from 0.43 to 0.34). In sera of 9 of 65 HIV-1-Ab seroconverters HIV-1-Ag was detected only once, 3 months before or concomitantly with antibody seroconversion. Another 11 men became persistently HIV-1-Ag positive with antibody seroconversion or 2-6 weeks thereafter. A decline in CD4+ cell numbers was seen between 6 months before and the moment of HIV-1-Ab seroconversion, independently of duration and level of antigen expression. This indicates initial HIV-1 replication in both HIV-1-Ag negatives and positives. Following antibody seroconversion, HIV-1-Ag negatives had higher CD4+ cell numbers than HIV-1-Ag positives. Similarly to those who were HIV antigenemic from entry of the study, the HIV-1-Ab seroconverters who concomitantly with seroconversion or shortly thereafter became HIV-1 antigenemic showed a steady and significant (p = 0.01) decline in CD4+ cell numbers. In those who remained HIV-1-Ag negative after antibody seroconversion, CD4+ cell numbers were stable during follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)     

Poor CD4 T cell restoration after suppression of HIV-1 replication may reflect lower thymic function

OBJECTIVE: To characterize immune phenotype and thymic function in HIV-1-infected adults with excellent virologic and poor immunologic responses to highly active antiretroviral therapy (HAART). METHODS: Cross-sectional study of patients with CD4 T cell rises of > or = 200 x 10(6) cells/l (CD4 responders; n = 10) or < 100 x 10(6) cells/l (poor responders; n = 12) in the first year of therapy. RESULTS: Poor responders were older than CD4 responders (46 versus 38 years; P < 0.01) and, before HAART, had higher CD4 cell counts (170 versus 35 x 106 cells/l; P = 0.11) and CD8 cell counts (780 versus 536 x 10(6) cells/l; P = 0.02). After a median of 160 weeks of therapy, CD4 responders had more circulating naive phenotype (CD45+CD62L+) CD4 cells (227 versus 44 x 10(6) cells/l; P = 0.001) and naive phenotype CD8 cells (487 versus 174 x 10(6) cells/l; P = 0.004) than did poor responders (after 130 weeks). Computed tomographic scans showed minimal thymic tissue in 11/12 poor responders and abundant tissue in 7/10 responders (P = 0.006). Poor responders had fewer CD4 cells containing T cell receptor excision circles (TREC) compared with CD4 responders (2.12 versus 27.5 x 10(6) cells/l; P = 0.004) and had shorter telomeres in CD4 cells (3.8 versus 5.3 kb; P = 0.05). Metabolic labeling studies with deuterated glucose indicated that the lower frequency of TREC-containing lymphocytes in poor responders was not caused by accelerated proliferation kinetics. CONCLUSION: Poor CD4 T cell increases observed in some patients with good virologic response to HAART may be caused by failure of thymic T cell production.     

CCR5 density levels on primary CD4 T cells impact the replication and Enfuvirtide susceptibility of R5 HIV-1

OBJECTIVE AND DESIGN: Studies in cell lines have demonstrated that CCR5 coreceptor levels influence the replication efficiency and Enfuvirtide (T-20) susceptibility of R5 HIV-1 strains. At present, however, the role that CCR5 levels on primary CD4 T cells--which are markedly lower than in cell lines and vary only approximately fivefold among most donors--may play in virus replication levels or susceptibility to T-20 is not known. In the present study we evaluated the impact of differences in CCR5 levels among donor CD4 T cells on the infection efficiency and T-20 susceptibility of R5 HIV-1. METHODS: CD4 and CCR5 density levels were determined by Quantitative FACS analysis. Virus infectivity assays were conducted in cell lines and primary cells. Associations between coreceptor density, virus replication and T-20 sensitivity were tested using the Spearman's correlation test. RESULTS: We found a positive correlation (r, 0.55; P = 0.011) between CCR5 density levels on primary CD4 T cells and replication of R5 HIV-1. In cell lines expressing physiologically relevant levels of CD4 and CCR5, T-20 was significantly more potent in cells with low CCR5 levels. In addition, T20 50% inhibitory concentrations for R5 HIV-1 replication varied approximately 100-fold among primary cells from different donors and they were positively correlated with CCR5 density values (r, 0.84; P = 0.00004). CONCLUSIONS: These results suggest that CCR5 density levels in HIV-1 patients may impact the activity of T-20 against R5 strains and that therapeutic approaches to alter CCR5 density may potentiate T-20.     

Antigen-driven CD4+ T cell and HIV-1 dynamics: residual viral replication under highly active antiretroviral therapy

Antigen-induced stimulation of the immune system can generate heterogeneity in CD4+ T cell division rates capable of explaining the temporal patterns seen in the decay of HIV-1 plasma RNA levels during highly active antiretroviral therapy. Posttreatment increases in peripheral CD4+ T cell counts are consistent with a mathematical model in which host cell redistribution between lymph nodes and peripheral blood is a function of viral burden. Model fits to patient data suggest that, although therapy reduces HIV replication below replacement levels, substantial residual replication continues. This residual replication has important consequences for long-term therapy and the evolution of drug resistance and represents a challenge for future treatment strategies.     

Productive infection of both CD4+ and CD4- human cell lines with HIV-1, HIV-2 and SIVagm

Human monolayer cells of various origins were shown to be susceptible to infection by HIV-1, HIV-2 and simian immunodeficiency virus obtained from African green monkeys (SIVagm). Immunoperoxidase staining revealed infection of 2-7% of the monolayer cells, although in order to achieve infection approximately 50-fold more virus was necessary than with CD4(+)-permissive lymphoma cells. No CD4-receptor antigen expression by fibroblastoid cells was detectable by immunofluorescence using several monoclonal antibodies (MAbs), although a low level of CD4-specific messenger RNA expression was revealed by Northern analysis (with the exception of Tera-1 and RD cells). Attempts to block viral infection by anti-CD4 MAbs indicated a CD4 receptor-mediated mechanism for all lines tested except RD cells. We conclude that a low level of CD4-receptor expression is sufficient to allow infection of fibroblastoid cells. The infectability of a CD4-negative cell line indicates a second pathway of cellular infection, possibly mediated by a cellular receptor distinct from the CD4 molecule.     

Accumulation of DC-SIGN+CD40+ dendritic cells with reduced CD80 and CD86 expression in lymphoid tissue during acute HIV-1 infection

BACKGROUND: Dendritic cells (DC) are target cells for HIV-1 and play a key role in antigen presentation and activation of T cells. OBJECTIVE: To characterize interdigitating DC in lymphoid tissue (LT) with regard to maturation, expression of cytokines and co-stimulatory molecules in HIV-1-positive patients. METHODS: DC were characterized by immunohistochemistry and in situ imaging in LT from patients with acute HIV-1 infection (aHI), antiretroviral treated patients, long-term non-progressors/slow progressors with HIV-1 infection (LTNP/SLP), patients with AIDS, HIV-1-negative controls and patients with acute Epstein-Barr virus (EBV) infection. RESULTS: A significant increase of interdigitating DC expressing CD1a, S-100b, CD83 and DC-SIGN was found in LT from patients with aHI (P < 0.02). The co-stimulatory molecules CD80 and CD86 were, however, only partially upregulated and the complete parafollicular network found in acute EBV infection was not generated, despite increased expression of interleukins 1alpha, 1beta, 12; interleukin 1alpha receptor antagonist; interferon alpha; and CD40 expression. LTNP/SLP and treated aviremic subjects had increased frequency of interdigitating DC, albeit lower than in aHI, and low expression of CD80 and CD86. In contrast, patients with AIDS had fewer DC and reduced cytokine expression in LT. CONCLUSIONS: In the early phase of HIV-1 infection, there was a migration of DC to LT comparable to that found in acute EBV infection. The infiltration of DC in LT in acute EBV infection was accompanied by upregulation of CD80 and CD86 expression, which did not occur in aHI. This co-stimulatory defect in aHI may have an impact on the development of HIV-1-specific T cell immunity.     

Stable changes in CD4+ T lymphocyte miRNA expression after exposure to HIV-1

MicroRNAs (miRNAs) inhibit HIV-1 expression by either modulating host innate immunity or by directly interfering with viral mRNAs. We evaluated the expression of 377 miRNAs in CD4(+) T cells from HIV-1 élite long-term nonprogressors (éLTNPs), naive patients, and multiply exposed uninfected (MEU) patients, and we observed that the éLTNP patients clustered with naive patients, whereas all MEU subjects grouped together. The discriminatory power of miRNAs showed that 21 miRNAs significantly differentiated éLTNP from MEU patients and 23 miRNAs distinguished naive from MEU patients, whereas only 1 miRNA (miR-155) discriminated éLTNP from naive patients. We proposed that miRNA expression may discriminate between HIV-1-infected and -exposed but negative patients. Analysis of miRNAs expression after exposure of healthy CD4(+) T cells to gp120 in vitro confirmed our hypothesis that a miRNA profile could be the result not only of a productive infection but also of the exposure to HIV-1 products that leave a signature in immune cells. The comparison of normalized Dicer and Drosha expression in ex vivo and in vitro condition revealed that these enzymes did not affect the change of miRNA profiles, supporting the existence of a Dicer-independent biogenesis pathway.     

Critical role of CD4 T cells in maintaining lymphoid tissue structure for immune cell homeostasis and reconstitution

Loss of the fibroblastic reticular cell (FRC) network in lymphoid tissues during HIV-1 infection has been shown to impair the survival of naive T cells and limit immune reconstitution after antiretroviral therapy. What causes this FRC loss is unknown. Because FRC loss correlates with loss of both naive CD4 and CD8 T-cell subsets and decreased lymphotoxin-β, a key factor for maintenance of FRC network, we hypothesized that loss of naive T cells is responsible for loss of the FRC network. To test this hypothesis, we assessed the consequences of antibody-mediated depletion of CD4 and CD8 T cells in rhesus macaques and sooty mangabeys. We found that only CD4 T-cell depletion resulted in FRC loss in both species and that this loss was caused by decreased lymphotoxin-β mainly produced by the CD4 T cells. We further found the same dependence of the FRC network on CD4 T cells in HIV-1-infected patients before and after antiretroviral therapy and in other immunodeficiency conditions, such as CD4 depletion in cancer patients induced by chemotherapy and irradiation. CD4 T cells thus play a central role in the maintenance of lymphoid tissue structure necessary for their own homeostasis and reconstitution.