CD25(+)CD4(+) regulatory T cells from the peripheral blood of asymptomatic HIV-infected individuals regulate CD4(+) and CD8(+) HIV-specific T cell immune responses in vitro and are associated with favorable clinical markers of disease status.

Human immunodeficiency virus (HIV) disease is associated with loss of CD4(+) T cells, chronic immune activation, and progressive immune dysfunction. HIV-specific responses, particularly those of CD4(+) T cells, become impaired early after infection, before the loss of responses directed against other antigens; the basis for this diminution has not been elucidated fully. The potential role of CD25(+)CD4(+) regulatory T cells (T reg cells), previously shown to inhibit immune responses directed against numerous pathogens, as suppressors of HIV-specific T cell responses was investigated. In the majority of healthy HIV-infected individuals, CD25(+)CD4(+) T cells significantly suppressed cellular proliferation and cytokine production by CD4(+) and CD8(+) T cells in response to HIV antigens/peptides in vitro; these effects were cell contact dependent and IL-10 and TGF-beta independent. Individuals with strong HIV-specific CD25(+) T reg cell function in vitro had significantly lower levels of plasma viremia and higher CD4(+): CD8(+) T cell ratios than did those individuals in whom this activity could not be detected. These in vitro data suggest that CD25(+)CD4(+) T reg cells may contribute to the diminution of HIV-specific T cell immune responses in vivo in the early stages of HIV disease.

The common gamma-chain cytokines IL-2, IL-7, IL-15, and IL-21 induce the expression of programmed death-1 and its ligands.

The programmed death (PD)-1 molecule and its ligands (PD-L1 and PD-L2), negative regulatory members of the B7 family, play an important role in peripheral tolerance. Previous studies have demonstrated that PD-1 is up-regulated on T cells following TCR-mediated activation; however, little is known regarding PD-1 and Ag-independent, cytokine-induced T cell activation. The common gamma-chain (gamma c) cytokines IL-2, IL-7, IL-15, and IL-21, which play an important role in peripheral T cell expansion and survival, were found to up-regulate PD-1 and, with the exception of IL-21, PD-L1 on purified T cells in vitro. This effect was most prominent on memory T cells. Furthermore, these cytokines induced, indirectly, the expression of PD-L1 and PD-L2 on monocytes/macrophages in PBMC. The in vivo correlate of these observations was confirmed on PBMC isolated from HIV-infected individuals receiving IL-2 immunotherapy. Exposure of gamma c cytokine pretreated T cells to PD-1 ligand-IgG had no effect on STAT5 activation, T cell proliferation, or survival driven by gamma c cytokines. However, PD-1 ligand-IgG dramatically inhibited anti-CD3/CD28-driven proliferation and Lck activation. Furthermore, following restimulation with anti-CD3/CD28, cytokine secretion by both gamma c cytokine and anti-CD3/CD28 pretreated T cells was suppressed. These data suggest that gamma c cytokine-induced PD-1 does not interfere with cytokine-driven peripheral T cell expansion/survival, but may act to suppress certain effector functions of cytokine-stimulated cells upon TCR engagement, thereby minimizing immune-mediated damage to the host.

CD25+ regulatory T cells isolated from HIV-infected individuals suppress the cytolytic and nonlytic antiviral activity of HIV-specific CD8+ T cells in vitro.

HIV infection is characterized by CD4(+) T cell depletion and progressive immune dysfunction; particularly impacted are HIV-specific T cell responses. An important component of immune-mediated control of HIV replication, killing of infected cells, appears to be impaired, in part due to poor cytolytic activity of HIV-specific cytotoxic T cells (CTL). In vitro, several functions of HIV-specific T cells, such as cytokine production, can be enhanced by the depletion of the immunosuppressive CD25(+) FoxP3(+) CD4(+) regulatory (Treg) cell subset. However, the effect of CD25(+) Treg cells on virus-specific cytolytic activity in the context of HIV or any human viral infection has not been investigated. The present study demonstrates that CD25(+) Treg cells isolated from the peripheral blood of HIV-infected subjects significantly suppress HIV Gag-specific cytolytic activity in vitro. In addition, CD25(+) Treg cells suppress effector function (coexpression of TNF-alpha and IFN-gamma) of HIV-specific CD8(+) T cells that proliferate in response to HIV antigen. Finally, the secretion of HIV-inhibitory CC-chemokines by HIV-specific and nonspecific CD8(+) T cells is significantly reduced in the presence of CD25(+) Treg cells. These data suggest that CD25(+) Treg-mediated suppression of the antiviral activity of HIV-specific CD8(+) T cells could impact the ability of HIV-infected individuals to control HIV replication in vivo.

Neonatal natural killer cells produce chemokines and suppress HIV replication in vitro.

The innate immune system may be critical in the prevention of perinatal HIV infection. Since neonates have limited immunological experience, they may rely more on the ability of the innate immune system to defend against infection than their adult counterparts. To assess the potential of human neonatal natural killer (nNK) cells to suppress HIV infection in a noncytolytic manner, we evaluated their ability to secrete chemokines and inhibit HIV replication in vitro. nNK cells were cocultured with autologous, HIV-infected CD4(+) T cells and their suppressive activity against HIV was compared to nCD8(+) T cells and adult NK cells. We found that nNK cells could suppress HIV replication in autologous CD4(+) T cells infected with a CCR5-utilizing virus, but were unable to suppress replication by a CXCR4-utilizing virus. nNK cell-mediated suppression of HIV replication was comparable to that of nCD8(+) T cells and greater than that of NK cells from adults. Suppression was mediated by soluble factors, and was abrogated by the addition of an excess of anti-CC-chemokine Ab directed at CCR5 ligand chemokines. In contrast, inhibition of HIV replication by autologous nCD8(+) T cells was not fully abrogated with anti-CC-chemokine Abs indicating, as previously reported in HIV-infected adults, that other factors in addition to chemokines play a role in CD8(+) T cell-mediated suppression of HIV replication. Our results show that nNK cells can inhibit HIV replication via a chemokine-mediated mechanism, and support a potential role for the innate immune system in preventing perinatal transmission of HIV in a noncytolytic manner.

The effect of elective cesarean delivery and intrapartum infection on fetal lymphocyte activation and susceptibility to HIV infection.

OBJECTIVE: Mother-to-child transmission of the human immunodeficiency virus may be reduced with elective cesarean delivery before labor. Because immune activation enhances the human immunodeficiency virus infection, we hypothesized that fetal lymphocytes that are obtained at elective cesarean delivery may be less activated, therefore less susceptible to human immunodeficiency virus infection than cells that are obtained after normal spontaneous vaginal delivery at term. A second hypothesis was that intrapartum infection correlates with increased lymphocyte activation and susceptibility to human immunodeficiency virus infection. STUDY DESIGN: Samples were obtained after normal spontaneous vaginal delivery (n = 13), elective cesarean delivery (n = 12), chorioamnionitis (n = 5), and preterm labor (n = 6). Activation markers were measured by flow cytometry, and cord blood mononuclear cells were infected with the human immunodeficiency virus. RESULTS: Cell activation was comparable within the normal spontaneous vaginal delivery and elective cesarean delivery groups; there was no difference in susceptibility to in vitro human immunodeficiency virus infection. Intrapartum infection (chorioamnionitis, preterm labor) was associated with increased cell activation. Chorioamnionitis/preterm labor also tended to increase cord blood mononuclear cell susceptibility to human immunodeficiency virus infection. CONCLUSION: Labor did not activate fetal lymphocytes or alter susceptibility to human immunodeficiency virus infection compared with elective cesarean delivery. Intrapartum infection was associated with cell activation, and there was a trend toward increased susceptibility to human immunodeficiency virus infection. These data suggest that fetal lymphocyte activation correlates with susceptibility to human immunodeficiency virus infection and may account for the increased mother-to-child transmission of the human immunodeficiency virus that has been seen in association with chorioamnionitis and preterm labor.

Interleukin (IL)-4 inhibits phorbol-ester induced HIV-1 expression in chronically infected U1 cells independently from the autocrine effect of endogenous tumour necrosis factor-alpha, IL-1beta, and IL-1 receptor antagonist.

The anti-inflammatory cytokine interleukin 4 (IL-4) has shown both inductive and inhibitory effects on the replication of the human immunodeficiency virus type 1 (HIV-1) in primary CD4+ T cells and mononuclear phagocytes. In this study, IL-4 did not induce virus production, but inhibited phorbol esters (PMA)-stimulated HIV expression in chronically infected promonocytic U1 cells. This effect, however, was not accounted for by a decreased secretion of endogenous TNF-alpha induced by phorbol myristate acetate (PMA). We also observed that PMA upregulated the production of both IL-1beta and of IL-1 receptor antagonist (IL-1ra). IL-4 inhibited the secretion of IL-1beta and strongly increased that of IL-1ra; however, these effects were not responsible of IL-4-mediated inhibition of PMA-induced HIV expression since anti-IL-1ra antibodies did not revert IL-4 mediated suppression. U1 cells were transiently transfected with both wild-type (WT) long terminal repeat (LTR) constructs, or with LTR plasmids containing deletions of either the NF-kappaB or the Sp-1 binding sites. IL-4 inhibited LTR-driven transcription triggered by PMA stimulation of U1 cells, and this effect was dependent upon intact NF-kappaB but not Sp-1 binding sites. Thus, IL-4 may favour a state of microbiological quiescence in infected monocytic cells bypassing the induction of HIV expression mediated by pro-inflammatory cytokines.

HIV envelope induces virus expression from resting CD4+ T cells isolated from HIV-infected individuals in the absence of markers of cellular activation or apoptosis.

Resting CD4(+) T cells containing integrated HIV provirus constitute one of the long-lived cellular reservoirs of HIV in vivo. This cellular reservoir of HIV had been thought to be quiescent with regard to virus replication based on the premise that HIV production in T cells is inexorably linked to cellular activation as determined by classical activation markers. The transition of T cells within this HIV reservoir from a resting state to an activated HIV-producing state is believed to be associated with a shorten life span due to susceptibility to activation-associated apoptosis. Evidence is mounting, however, that HIV production may occur in T cells that have not undergone classic T cell activation. HIV encodes several proteins, including envelope and Nef, which trigger a variety of signaling pathways associated with cellular activation, thereby facilitating HIV replication in nondividing cells. The present study demonstrates that production of infectious virus from resting CD4(+) T cells isolated from HIV-infected individuals can be induced following exposure of these cells to HIV-1 recombinant (oligomeric gp140) envelope protein. Envelope-mediated induction of HIV expression occurs in the presence of reverse transcriptase inhibitors and is not associated with markers of classic T cell activation, proliferation, or apoptosis. The ability of HIV envelope to induce virus replication in HIV-infected resting CD4(+) T cells without triggering apoptosis provides a mechanism for the virus itself to directly participate in the maintenance of HIV production from this cellular reservoir.