Interleukin-15 modulates interferon-gamma and beta-chemokine production in patients with HIV infection: implications for immune-based therapy

Interleukin (IL)-15 is a cytokine that has lymphocyte stimulatory activity similar to that of IL-2, and plays important immunoregulatory functions during HIV disease. To evaluate the role of IL-15 in HIV infection the following patients were studied: 18 antiretroviral-naive patients with advanced disease; 19 patients with continuous viral suppression and immunological response after 48-120 weeks of highly active antiretroviral therapy (HAART); and 12 patients with evidence of virological and immunological HAART treatment failure. Nineteen healthy blood donors were included as controls. The production of IL-15 by human peripheral blood monocytes stimulated with lipopolysaccharide and Mycobacterium avium complex, the priming effect of IL-15 on IFN-gamma production from purified CD4(+) and CD8(+) T cells, and the ability of IL-15 to stimulate the beta-chemokine release from purified CD4(+) and CD8(+) T cells were analyzed. In the present work IL-15 production by human peripheral blood monocytes was significantly increased in HIV-infected patients with long-term virological and immunological response to HAART. IL-15 enhanced the in vitro priming of CD4(+) and CD8(+) T cells for IFN-gamma production, also in patients receiving HAART. Finally, IL-15 had positive effects on RANTES, MIP-1alpha, and MIP-1beta release by CD4(+) and CD8(+) T cells. In conclusion IL-15 could affect the immune response of HIV-infected patients by augmenting and/or modulating IFN-gamma production and beta-chemokine release. These data about functional properties of IL-15 could provide new implications for immune-based therapies in HIV infection.     

HIV-specific cytotoxic cell frequencies measured directly ex vivo by the Lysispot assay can be higher or lower than the frequencies of IFN-gamma-secreting cells: anti-HIV cytotoxicity is not generally impaired relative to other chronic virus responses

CD8(+) T cells in HIV-infected patients are believed to contribute to the containment of the virus and the delay of disease progression. However, the frequencies of HIV-specific CD8(+) T cells, as measured by IFN-gamma secretion and tetramer binding, often do not correlate with a delay in disease progression during chronic infection. Using the Lysispot and ELISPOT assays, we measured the frequencies of cytotoxic and IFN-gamma-secreting T cells responding to overlapping peptides from Gag, Nef, Env, and Pol consensus HIV-1 clade B sequences. PBMC from the majority of HIV-infected subjects have significant frequencies of HIV-specific cells that killed targets within 5 h directly ex vivo. The relative frequencies of IFN-gamma-secreting and cytotoxic cells varied markedly between different HIV peptide pools within the same patient, and some T cells lysed targets without secreting IFN-gamma. These results indicate that measurement of IFN-gamma production alone may be insufficient to evaluate the breadth of the HIV-specific T cell response. Also, neither the CTL to IFN-gamma ratios nor the ex vivo CTL frequencies specific for different HIV proteins were consistently lower than responses specific for two other chronic viral infections, human CMV and EBV, within the same subjects. Thus ex vivo cytotoxic T cell frequencies do not provide evidence for a model of "preterminal differentiation" of HIV-specific CD8(+) T cells during chronic HIV infection. Analysis of the frequency of directly cytotoxic HIV-specific T cells may be of considerable value in the assessment of disease progression and the potential efficacy of HIV vaccines.     

Peripheral blood cytotoxic gammadelta T lymphocytes from patients with human immunodeficiency virus type 1 infection and AIDS lyse uninfected CD4+ T cells,and their cytocidal potential correlates with viral load

Progression of human immunodeficiency virus type 1 (HIV-1) infection in humans is marked by declining CD4+-T-cell counts and increasing virus load (VL). Cytotoxic T lymphocytes (CTL) play an important role in the lysis of HIV-infected cells, especially during the early phase of asymptomatic infection. CTL responses in the later phase of disease progression may not be as effective since progressors with lower CD4+-T-cell counts have consistently higher VL despite having elevated CTL counts. We hypothesized that, apart from antiviral effects, some CTL might also contribute to AIDS pathogenesis by depleting CD4+ T cells and that this CTL activity may correlate with the VL in AIDS patients. Therefore, a cross-sectional study of 31 HIV-1-infected patients at various clinical stages was carried out. Purified CTL from these donors as well as HIV-seronegative controls were used as effectors against different human cell targets by using standard 51Cr release cytolytic assays. A direct correlation between VL and CTL-mediated, major histocompatibility complex (MHC)-unrestricted lysis of primary CD4+-T-cell, CEM.NKR, and K562 targets was observed. CD4+-T-cell counts and duration of infection also correlated with MHC-unrestricted cytolytic activity. Our data clearly show that gammadelta CTL are abnormally expanded in the peripheral blood of HIV-infected patients and that the Vdelta1 subset of gammadelta T cells is the main effector population responsible for this type of cytolysis. The present data suggest that gammadelta CTL can contribute to the depletion of bystander CD4+ T cells in HIV-infected patients as a parallel mechanism to HIV-associated immunopathogenesis and hence expedite AIDS progression.     

CD127 and CD25 expression defines CD4+ T cell subsets that are differentially depleted during HIV infection

Decreased CD4(+) T cell counts are the best marker of disease progression during HIV infection. However, CD4(+) T cells are heterogeneous in phenotype and function, and it is unknown how preferential depletion of specific CD4(+) T cell subsets influences disease severity. CD4(+) T cells can be classified into three subsets by the expression of receptors for two T cell-tropic cytokines, IL-2 (CD25) and IL-7 (CD127). The CD127(+)CD25(low/-) subset includes IL-2-producing naive and central memory T cells; the CD127(-)CD25(-) subset includes mainly effector T cells expressing perforin and IFN-gamma; and the CD127(low)CD25(high) subset includes FoxP3-expressing regulatory T cells. Herein we investigated how the proportions of these T cell subsets are changed during HIV infection. When compared with healthy controls, HIV-infected patients show a relative increase in CD4(+)CD127(-)CD25(-) T cells that is related to an absolute decline of CD4(+)CD127(+)CD25(low/-) T cells. Interestingly, this expansion of CD4(+)CD127(-) T cells was not observed in naturally SIV-infected sooty mangabeys. The relative expansion of CD4(+)CD127(-)CD25(-) T cells correlated directly with the levels of total CD4(+) T cell depletion and immune activation. CD4(+)CD127(-)CD25(-) T cells were not selectively resistant to HIV infection as levels of cell-associated virus were similar in all non-naive CD4(+) T cell subsets. These data indicate that, during HIV infection, specific changes in the fraction of CD4(+) T cells expressing CD25 and/or CD127 are associated with disease progression. Further studies will determine whether monitoring the three subsets of CD4(+) T cells defined based on the expression of CD25 and CD127 should be used in the clinical management of HIV-infected individuals.     

Combination of Immune and Viral Factors Distinguishes Low-Risk versus High-Risk HIV-1 Disease Progression in HLA-B*5701 Subjects

HLA-B*5701 is the host factor most strongly associated with slow HIV-1 disease progression, although rates can vary within this group. Underlying mechanisms are not fully understood but likely involve both immunological and virological dynamics. The present study investigated HIV-1 in vivo evolution and epitope-specific CD8(+) T cell responses in six HLA-B*5701 patients who had not received antiretroviral treatment, monitored from early infection for up to 7 years. The subjects were classified as high-risk progressors (HRPs) or low-risk progressors (LRPs) based on baseline CD4(+) T cell counts. Dynamics of HIV-1 Gag p24 evolution and multifunctional CD8(+) T cell responses were evaluated by high-resolution phylogenetic analysis and polychromatic flow cytometry, respectively. In all subjects, substitutions occurred more frequently in flanking regions than in HLA-B*5701-restricted epitopes. In LRPs, p24 sequence diversity was significantly lower; sequences exhibited a higher degree of homoplasy and more constrained mutational patterns than HRPs. The HIV-1 intrahost evolutionary rate was also lower in LRPs and followed a strict molecular clock, suggesting neutral genetic drift rather than positive selection. Additionally, polyfunctional CD8(+) T cell responses, particularly to TW10 and QW9 epitopes, were more robust in LRPs, who also showed significantly higher interleukin-2 (IL-2) production in early infection. Overall, the findings indicate that HLA-B*5701 patients with higher CD4 counts at baseline have a lower risk of HIV-1 disease progression because of the interplay between specific HLA-linked immune responses and the rate and mode of viral evolution. The study highlights the power of a multidisciplinary approach, integrating high-resolution evolutionary and immunological data, to understand mechanisms underlying HIV-1 pathogenesis.     

Acute Plasma Biomarkers of T Cell Activation Set-Point Levels and of Disease Progression in HIV-1 Infection

T cell activation levels, viral load and CD4⁺ T cell counts at early stages of HIV-1 infection are predictive of the rate of progression towards AIDS. We evaluated whether the inflammatory profile during primary HIV-1 infection is predictive of the virological and immunological set-points and of disease progression. We quantified 28 plasma proteins during acute and post-acute HIV-1 infection in individuals with known disease progression profiles. Forty-six untreated patients, enrolled during primary HIV-1 infection, were categorized into rapid progressors, progressors and slow progressors according to their spontaneous progression profile over 42 months of follow-up. Already during primary infection, rapid progressors showed a higher number of increased plasma proteins than progressors or slow progressors. The plasma levels of TGF-β1 and IL-18 in primary HIV-1 infection were both positively associated with T cell activation level at set-point (6 months after acute infection) and together able to predict 74% of the T cell activation variation at set-point. Plasma IP-10 was positively and negatively associated with, respectively, T cell activation and CD4⁺ T cell counts at set-point and capable to predict 30% of the CD4⁺ T cell count variation at set-point. Moreover, plasma IP-10 levels during primary infection were predictive of rapid progression. In primary infection, IP-10 was an even better predictor of rapid disease progression than viremia or CD4⁺ T cell levels at this time point. The superior predictive capacity of IP-10 was confirmed in an independent group of 88 HIV-1 infected individuals. Altogether, this study shows that the inflammatory profile in primary HIV-1 infection is associated with T cell activation levels and CD4⁺ T cell counts at set-point. Plasma IP-10 levels were of strong predictive value for rapid disease progression. The data suggest IP-10 being an earlier marker of disease progression than CD4⁺ T cell counts or viremia levels.     

Natural killer cell function is well preserved in asymptomatic human immunodeficiency virus type 2 (HIV-2) infection but similar to that of HIV-1 infection when CD4 T-cell counts fall

Natural killer (NK) cells are potent effectors of natural immunity and their activity prevents human immunodeficiency virus type 1 (HIV-1) viral entry and viral replication. We sought to determine whether NK immune responses are associated with different clinical course of HIV-1 and HIV-2 infections. A cross-sectional analysis of NK cell responses was undertaken in 30 HIV-1 and 30 HIV-2 subjects in each of three categories of CD4(+)-T-cell counts (>500, 200 to 500, and <200 cells/microl) and in 50 HIV-uninfected control subjects. Lytic activity and gamma interferon (IFN-gamma) secretion were measured by chromium release and enzyme-linked immunospot assays, respectively. Flow cytometry was used to assess intracellular cytokines and chemokines. Levels of NK cytotoxicity were significantly higher in HIV-2 than in HIV-1 infections in subjects with high CD4(+)-T-cell counts and were similar to that of the healthy controls. In these HIV-2 subjects, cytolytic activity was positively correlated to NK cell count and inversely related to plasma viremia. Levels of intracellular MIP-1beta, RANTES, tumor necrosis factor alpha, and IFN-gamma produced by NK CD56(bright) cells were significantly higher in HIV-2- than HIV-1-infected subjects with high CD4(+)-T-cell counts but fell to similar levels as CD4 counts dropped. The data suggest efficient cytolytic and chemokine-suppressive activity of NK cells early in HIV-2 infection, which is associated with high CD4(+) T-cell counts. Enhancement of these functions may be important in immune-based therapy to control HIV disease.     

Plasma concentrations of transforming growth factor beta 1 in non-progressive HIV-1 infection correlates with markers of disease progression

The human immunodeficiency virus (HIV) infection shows variable rate of disease progression. The underlying biological and molecular mechanisms involved in determining progression of HIV infection are not fully understood. The aims of this study were to determine plasma concentrations of active TGF β 1, Th1 and Th2 cytokines in patients with non-progressive and those with progressive HIV-1 infection, as well as to determine if there is an association of these cytokines to disease progression. In a cross-sectional study of 61 HIV-1 infected individuals categorized according to disease progression as having non-progressive HIV-1 infection (n = 14) and progressive infection (n = 47), plasma levels of active TGF β 1, INF-γ, TNF-α, IL-10, IL-1β, IL-12p70 and IL-13 were compared with HIV uninfected healthy controls (n = 12). Plasma concentration of these cytokines was measured using a highly sensitive luminex200 XMAP assay. Pearson correlation test was used to assess the correlation of cytokines with CD4+ and CD8+ T cells, CD4:CD8 ratio and plasma HIV-1 RNA in the different study groups. Plasma concentrations of TGF β 1 and IL-10 were significantly decreased while IL-1β, IL-12p70 and TNF-α were increased in patients with non-progressive HIV-1 infection compared to patients with progressive infection. Plasma levels of TGF β 1 and IL-10 showed an inverse correlation with CD8+ T cell counts and CD4:CD8 ratios in patients with non-progressive HIV-1 infection, while plasma HIV-1 RNA positively correlated with CD4+ T cell counts. Plasma levels of TNF-α, IL-1β, IL-12p70 and IL-13 positively correlated with CD4+ T cell counts and inversely correlated with plasma HIV-1 RNA, CD8+ T cell count and CD4:CD8 ratio in patients with non-progressive infection. The correlation of cytokines to the state of T-lymphocyte and plasma HIV-1 RNA found in this study may provide insight into the role of cytokines in both progressive and non-progressive HIV-1 infection. Additionally, these findings may have implications for systemic cytokine-based therapies in HIV-1 infection.     

Loss of CD127 expression defines an expansion of effector CD8+ T cells in HIV-infected individuals

The immunodeficiency that follows HIV infection is related to the virus-mediated killing of infected CD4(+) T cells, the chronic activation of the immune system, and the impairment of T cell production. In this study we show that in HIV-infected individuals the loss of IL-7R (CD127) expression defines the expansion of a subset of CD8(+) T cells, specific for HIV as well as other Ags, that show phenotypic (i.e., loss of CCR7 and CD62 ligand expression with enrichment in activated and/or proliferating cells) as well as functional (i.e., production of IFN-gamma, but not IL-2, decreased ex vivo proliferative potential and increased susceptibility to apoptosis) features of effector T cells. Importantly, in HIV-infected individuals the levels of CD8(+)CD127(-) T cells are directly correlated with the main markers of disease progression (i.e., plasma viremia and CD4(+) T cell depletion) as well as with the indices of overall T cell activation. In all, these results identify the expansion of CD8(+)CD127(-) effector-like T cells as a novel feature of the HIV-associated immune perturbation. Further studies are thus warranted to determine whether measurements of CD127 expression on CD8(+) T cells may be useful in the clinical management of HIV-infected individuals.     

Increased B7-H1 expression on dendritic cells correlates with programmed death 1 expression on T cells in simian immunodeficiency virus-infected macaques and may contribute to T cell dysfunction and disease progression

Suppression of dendritic cell (DC) function in HIV-1 infection is thought to contribute to inhibition of immune responses and disease progression, but the mechanism of this suppression remains undetermined. Using the rhesus macaque model, we show B7-H1 (programmed death [PD]-L1) is expressed on lymphoid and mucosal DCs (both myeloid DCs and plasmacytoid DCs), and its expression significantly increases after SIV infection. Meanwhile, its receptor, PD-1, is upregulated on T cells in both peripheral and mucosal tissues and maintained at high levels on SIV-specific CD8(+) T cell clones in chronic infection. However, both B7-H1 and PD-1 expression in SIV controllers was similar to that of controls. Expression of B7-H1 on both peripheral myeloid DCs and plasmacytoid DCs positively correlated with levels of PD-1 on circulating CD4(+) and CD8(+) T cells, viremia, and declining peripheral CD4(+) T cell levels in SIV-infected macaques. Importantly, blocking DC B7-H1 interaction with PD-1(+) T cells could restore SIV-specific CD4(+) and CD8(+) T cell function as evidenced by increased cytokine secretion and proliferative capacity. Combined, the results indicate that interaction of B7-H1-PD-1 between APCs and T cells correlates with impairment of CD4(+) Th cells and CTL responses in vivo, and all are associated with disease progression in SIV infection. Blockade of this pathway may have therapeutic implications for HIV-infected patients.     

Vpr is preferentially targeted by CTL during HIV-1 infection

The HIV-1 accessory proteins Vpr, Vpu, and Vif are essential for viral replication, and their cytoplasmic production suggests that they should be processed for recognition by CTLs. However, the extent to which these proteins are targeted in natural infection, as well as precise CTL epitopes within them, remains to be defined. In this study, CTL responses against HIV-1 Vpr, Vpu, and Vif were analyzed in 60 HIV-1-infected individuals and 10 HIV-1-negative controls using overlapping peptides spanning the entire proteins. Peptide-specific IFN-gamma production was measured by ELISPOT assay and flow-based intracellular cytokine quantification. HLA class I restriction and cytotoxic activity were confirmed after isolation of peptide-specific CD8(+) T cell lines. CD8(+) T cell responses against Vpr, Vpu, and Vif were found in 45%, 2%, and 33% of HIV-1-infected individuals, respectively. Multiple CTL epitopes were identified in functionally important regions of HIV-1 Vpr and Vif. Moreover, in infected individuals in whom the breadth of HIV-1-specific responses was assessed comprehensively, Vpr and p17 were the most preferentially targeted proteins per unit length by CD8(+) T cells. These data indicate that despite the small size of these proteins Vif and Vpr are frequently targeted by CTL in natural HIV-1 infection and contribute importantly to the total HIV-1-specific CD8(+) T cell responses. These findings will be important in evaluating the specificity and breadth of immune responses during acute and chronic infection, and in the design and testing of candidate HIV vaccines.     

CD4+ T cells, including Th17 and cycling subsets, are intact in the gut mucosa of HIV-1-infected long-term nonprogressors

During acute human immunodeficiency virus (HIV) infection, there is a massive depletion of CD4(+) T cells in the gut mucosa that can be reversed to various degrees with antiretroviral therapy. Th17 cells have been implicated in mucosal immunity to extracellular bacteria, and preservation of this subset may support gut mucosal immune recovery. However, this possibility has not yet been evaluated in HIV-1-infected long-term nonprogressors (LTNPs), who maintain high CD4(+) T cell counts and suppress viral replication in the absence of antiretroviral therapy. In this study, we evaluated the immunophenotype and function of CD4(+) T cells in peripheral blood and gut mucosa of HIV-uninfected controls, LTNPs, and HIV-1-infected individuals treated with prolonged antiretroviral therapy (ART) (VL [viral load]<50). We found that LTNPs have intact CD4(+) T cell populations, including Th17 and cycling subsets, in the gut mucosa and a preserved T cell population expressing gut homing molecules in the peripheral blood. In addition, we observed no evidence of higher monocyte activation in LTNPs than in HIV-infected (HIV(-)) controls. These data suggest that, similar to nonpathogenic simian immunodeficiency virus (SIV) infection, LTNPs preserve the balance of CD4(+) T cell populations in blood and gut mucosa, which may contribute to the lack of disease progression observed in these patients.     

The anti-idiotypic antibody 1F7 selectively inhibits cytotoxic T cells activated in HIV-1 infection

Circulating CD8+ T lymphocyte numbers rise substantially following infection with HIV-1. This expanded CD8+ T cell population includes HIV-specific CTL and CTL that kill activated uninfected CD4+ lymphocytes. Experimental, epidemiological and clinical evidence supports the possibility that expansion of CD8+ CTL contributes to CD4+ T cell depletion and disease progression in human HIV infection. Therefore, modulation of CD8+ T cell numbers or of certain CD8+ CTL activated in HIV-infected individuals may be beneficial. It was found that 1F7, a mAb against an idiotype common to anti-HIV and anti-simian immunodeficiency virus (SIV) antibodies, selectively inhibited both anti-HIV CTL and CTL against uninfected CD4+ T cells. Alloantigen-specific CTL and NK cells from either HIV-infected individuals or controls were unaffected by 1F7. Prolonged incubation of CD8+ T cells from HIV-infected individuals with 1F7 induces apoptosis, which was shown to be reflected functionally in reduced total CTL activity and in especially reduced CTL activity against uninfected CD4+ lymphocytes. The selective reactivity of 1F7 with certain CD8+ CTL could be applied towards the modulation of CD8+ T cell responses involved in AIDS pathogenesis.     

HIV-specific CD8+ lymphocytes in semen are not associated with reduced HIV shedding

Sexual contact with HIV-infected semen is a major driving force behind the global HIV pandemic. Little is known regarding the immune correlates of virus shedding in this compartment, although HIV-1-specific CD8+ T cells are present in semen. We collected blood and semen from 27 chronically HIV-infected, therapy-naive men without common sexually transmitted infections or urethral inflammation and measured HIV-1 RNA viral load and cytokine/chemokine levels in both compartments. HIV-1 RNA levels were 10-fold higher in blood than semen, but discordantly high semen shedding was associated with higher semen levels of the proinflammatory cytokines IL-6, IL-8, IL-12, and IFN-gamma. Virus-specific CD8+ T cell epitopes were mapped in blood by IFN-gamma ELISPOT, using an overlapping HIV-1 clade B peptide matrix, and blood and semen CD8+ T cell responses were then assayed ex vivo using intracellular IFN-gamma staining. HIV-specific CD8+ responses were detected in 70% of semen samples, and their frequency was similar to or higher than blood. There was no correlation between the presence of virus-specific CD8+ T cells in semen and levels of HIV-1 RNA shedding. Among participants with detectable CD8+ IFN-gamma semen responses, their relative frequency was not associated with reduced HIV-1 RNA shedding, and their absolute number was correlated with higher levels of HIV-1 RNA semen shedding (r = 0.6; p = 0.03) and of several proinflammatory cytokines. Neither the presence nor the frequency of semen HIV-specific CD8+ T cell IFN-gamma responses in semen correlated with reduced levels of HIV RNA in semen.     

Frequency and Absolute Number of FoxP3^＋ Regulatory T Cells Correlate with Disease Progression of Chronic HIV-1 Infection

CD4 CD25 Regulatory T cells (Treg) have been found to down-regulate immune activation in HIV-1 infection. However,whether the depletion of Treg benefits to the disease status of HIV infection remains undefined. To address this issue,we enumerated the Treg absolute counts and frequency in 75 antiviral-nave HIV-1-infected individuals in this study. It was found that HIV-infected patients displayed a significant decline in Treg absolute counts but a significant increase in Treg frequency. In addition,with disease progression indicated by CD4 T-cell absolute counts,circulating Treg frequency gradually increased; while Treg absolute counts were gradually decreased,suggesting that the alteration of Treg number closely correlated with disease progression in HIV infection. Functional analysis further showed that Treg efficiently inhibit both CD4 and CD8 T cell proliferation in vitro. Thus,our findings indicates that Treg actively participate in pathogenesis of chronic HIV infection,influencing the disease progression.     

Frequency and Absolute Number of FoxP3+ Regulatory T Cells Correlate with Disease Progression of Chronic HIV-1 Infection

CD4+CD25+ Regulatory T cells (Treg) have been found to down-regulate immune activation in HIV-1 infection. However, whether the depletion of Treg benefits to the disease status of HIV infection remains undefined. To address this issue, we enumerated the Treg absolute counts and frequency in 75 antiviral-na(i)ve HIV-1-infected individuals in this study. It was found that HIV-infected patients displayed a significant decline in Treg absolute counts but a significant increase in Treg frequency. In addition, with disease progression indicated by CD4 T-cell absolute counts, circulating Treg frequency gradually increased; while Treg absolute counts were gradually decreased, suggesting that the alteration of Treg number closely correlated with disease progression in HIV infection.Functional analysis further showed that Treg efficiently inhibit both CD4 and CD8 T cell proliferation in vitro. Thus, our findings indicates that Treg actively participate in pathogenesis of chronic HIV infection,influencing the disease progression.     

The role of CD4+ T cell help and CD40 ligand in the in vitro expansion of HIV-1-specific memory cytotoxic CD8+ T cell responses

CD4(+) T cells have been shown to play a critical role in the maintenance of an effective anti-viral CD8(+) CTL response in murine models. Recent studies have demonstrated that CD4(+) T cells provide help to CTLs through ligation of the CD40 receptor on dendritic cells. The role of CD4(+) T cell help in the expansion of virus-specific CD8(+) memory T cell responses was examined in normal volunteers recently vaccinated to influenza and in HIV-1 infected individuals. In recently vaccinated normal volunteers, CD4(+) T cell help was required for optimal in vitro expansion of influenza-specific CTL responses. Also, CD40 ligand trimer (CD40LT) enhanced CTL responses and was able to completely substitute for CD4(+) T cell help in PBMCs from normal volunteers. In HIV-1 infection, CD4(+) T cell help was required for optimal expansion of HIV-1-specific memory CTL in vitro in 9 of 10 patients. CD40LT could enhance CTL in the absence of CD4(+) T cell help in the majority of patients; however, the degree of enhancement of CTL responses was variable such that, in some patients, CD40LT could not completely substitute for CD4(+) T cell help. In those HIV-1-infected patients who demonstrated poor responses to CD40LT, a dysfunction in circulating CD8(+) memory T cells was demonstrated, which was reversed by the addition of cytokines including IL-2. Finally, it was demonstrated that IL-15 produced by CD40LT-stimulated dendritic cells may be an additional mechanism by which CD40LT induces the expansion of memory CTL in CD4(+) T cell-depleted conditions, where IL-2 is lacking.     

Sustained impairment of IFN-gamma secretion in suppressed HIV-infected patients despite mature NK cell recovery: evidence for a defective reconstitution of innate immunity

The impairment of NK cell functions in the course of HIV infection contributes to a decreased resistance against HIV and other pathogens. We analyzed the proportion of mature and immature NK cell subsets, and measured subsets of IFN-gamma and TNF-alpha-producing NK and T cells in viremic or therapy-suppressed HIV-infected subjects, and noninfected control donors. Viremic HIV(+) individuals had significantly lower proportions of mature CD3(-)/CD161(+)/CD56(+) NK cells and of IFN-gamma-producing NK cells compared with noninfected donors, independent of CD4(+) T cell counts. HIV-infected subjects with undetectable viral load recovered mature CD3(-)/CD161(+)/CD56(+) NK cells and cytotoxicity against tumor (K562) and HSV-infected target cells to percentages comparable with those of uninfected individuals, but their NK cells remained impaired in their ability to produce IFN-gamma. In parallel to these ex vivo findings, in vitro NK cell differentiation of CD34-positive cord blood precursors in the presence of R5 or X4 HIV-1 resulted in the production of NK cells with a normal mature phenotype, but lacking the ability to produce IFN-gamma, whereas coculture of uninfected PBMC with HIV failed to affect mature NK cell properties or IFN-gamma secretion. Altogether, our findings support the hypothesis that mature NK cell phenotype may be uncoupled from some mature functions following highly active antiretroviral therapy-mediated suppression of HIV-1, and indicate that relevant innate immune functions of NK cell subsets may remain altered despite effective viral suppression following antiretroviral treatment.     

Frequency and absolute number of FoxP3<Superscript>+</Superscript> regulatory T cells correlate with disease progression of chronic HIV-1 infection

CD4⁺CD25⁺ Regulatory T cells (Treg) have been found to down-regulate immune activation in HIV-1 infection. However, whether the depletion of Treg benefits to the disease status of HIV infection remains undefined. To address this issue, we enumerated the Treg absolute counts and frequency in 75 antiviral-naïve HIV-1-infected individuals in this study. It was found that HIV-infected patients displayed a significant decline in Treg absolute counts but a significant increase in Treg frequency. In addition, with disease progression indicated by CD4 T-cell absolute counts, circulating Treg frequency gradually increased; while Treg absolute counts were gradually decreased, suggesting that the alteration of Treg number closely correlated with disease progression in HIV infection. Functional analysis further showed that Treg efficiently inhibit both CD4 and CD8 T cell proliferation in vitro. Thus, our findings indicates that Treg actively participate in pathogenesis of chronic HIV infection, influencing the disease progression.