CD7 expression distinguishes subsets of CD4(+) T cells with distinct functional properties and ability to support replication of HIV-1.

Enrichment of a subset of CD4(+)CD45R0(+)CD7(-) T cells has been observed in HIV-infected individuals. We have investigated the ability of CD7(+) and CD7(-) T cells to support replication of HIV and show that virus replicates preferentially in CD7(+) cells. Several possible mechanisms that may underlie such differences in susceptibility to HIV were studied. Our data demonstrate that mitogen stimulation induces poor expression of CD25 and IL-2 in CD7(-) compared with CD7(+) cells. We also show that uninfected CD7(-) cells are more resistant to mitogen-induced apoptosis than CD7(+) cells. Our data support the view that the CD7(-) subset is inherently resistant to HIV replication and that this is due in part to reduced CD25 expression and IL-2 production.

HIV infection alters the production of both type 1 and 2 cytokines but does not induce a polarized type 1 or 2 state.

OBJECTIVE: To test the T-helper (TH)1/TH2 cytokine paradigm in HIV infection. DESIGN AND METHODS: Cytokine profiles in two separate studies of HIV patients and controls are presented: (i) a longitudinal study of HIV patients with CD4 counts > 500 x 10(6)/l tested at three timepoints compared with controls; (ii) a blinded cross-sectional study of controls and patients with high (> 500 x 10(6)/l) and low (< 500 x 10(6)/l) CD4 counts. Peripheral blood mononuclear cells (PBMC) from patients and controls were tested for the production of two type 1 [interleukin (IL)-2, interferon (IFN)-gamma] and two type 2 (IL-4, IL-10) cytokines by enzyme-linked immunosorbent assay. Both spontaneous and mitogen-induced cytokine production was measured. RESULTS: HIV infection was noted to have the following effects on cytokine production: (i) it led to the in vivo activation of type 2 cytokines in a small group of individuals with high CD4 numbers characterized by the spontaneous release of IL-4 and IL-10. Longitudinal data showed high spontaneous IL-4 and IL-10 to be a consistent feature of the patient group (at each timepoint some patients were high producers) but to be variable in a given individual; (ii) HIV infection impaired the ability of PBMC to respond to stimuli (selected for their ability to optimally induce each cytokine) in terms of IL-2, IL-4 and IL-10 production in patients with both high and low CD4 cell counts; and (iii) conversely, HIV infection led to an overproduction of IFN-gamma in patients with high CD4 counts; patients with low CD4 produced normal levels of IFN-gamma. CONCLUSIONS: Our observations did not suggest polarization of the type 1/type 2 cytokine profile in HIV patients. Instead, the data suggested more complex changes to type 1/type 2 cytokine patterns in HIV infection than originally proposed by the TH1/TH2 dichotomy.

Th1 cells specific for HIV-1 gag p24 are less efficient than Th0 cells in supporting HIV replication, and inhibit virus replication in Th0 cells.

This report provides three lines of evidence to suggest that T-helper type 1 (Th1) and type 0 (Th0) cells could play an opposing role in acquired immune deficiency syndrome (AIDS). Using a panel of Th1 and Th0 clones specific for human immunodeficiency virus-1 (HIV-1) gag p24, derived from seronegative volunteers immunized with gag p24: Ty virus-like particles, a Th1 clone specific for tuberculin (PPD), and a Th0 clone derived by random activation from the same volunteer, we have demonstrated the following differences in the capacity of these clones to regulate the in vitro replication of HIV. (1) Th1 clones were less efficient than Th0 clones in supporting HIV replication, both in their resting state (by 10-1000-fold) and after antigen activation (by five to 100-fold). Furthermore, the infectious titre of HIV recovered from the Th0 population was more than 1000-fold higher than virus from the Th1 population, and the number of HIV-infected Th0 cells was five to 16 times higher than the number of infected Th1 cells. (2) Antigen- or mitogen-activated Th1, but not Th0 clones, inhibited HIV in bystander CEM-4 cells. Th1 cells also inhibited HIV in autologous and allogeneic Th0 cells. The level of inhibition in these experiments ranged from 50% to 100% and was three to 10-fold higher and more sustained in the presence of p24-specific clones compared to the PPD-specific Th1 clone. The capacity of Th1 cells to inhibit HIV in neighbouring cells was also reflected in the reduced replication of HIV in the clones immediately after antigen activation compared to unstimulated cells. Kinetic studies of virus production, cytokine release and proliferation showed that inhibition of HIV was associated with peak cytokine release and preceeded proliferation. (3) The Th1 clones had higher cytolytic potential than the Th0 clones. Therefore, the HIV inhibitory activity of Th1 cells could be partly due to cell to cell killing. These data demonstrate the opposing effects of Th1 and Th0 cells on the in vitro replication of HIV, and suggest that Th1 cells might be important in immunity whereas Th0/Th2 cells might lay a role in promoting disease.

HIV-1 infection of human CD4+ T cells in vitro. Differential induction of apoptosis in these cells.

The H9 and CEM CD4+ T cell lines were infected with HIV-1 (NY5/LAV-1 isolate) and monitored for losses in cell viability, syncytium formation, and internucleosomal DNA cleavage (a marker for apoptosis). H9 cells were found to undergo cell death via apoptosis as a result of HIVNY5 infection, but this effect was not apparent in CEM cell cultures. The differential effects of HIV-1NY5 in terms of its apoptosis-inducing properties correlated with the relative abilities of H9 and CEM cells in supporting replication of this HIV-1 isolate, since infected CEM cell cultures produced 10-fold lower levels of HIV-1 p24 protein, and very few of these cells stained positive for cell-associated p24 by comparison with H9 cell cultures infected at the same multiplicity of infection. Furthermore, a different HIV-1 isolate (RF), which replicated equally efficiently in both H9 and CEM cells, produced similar levels of apoptosis in these cultures. HIV-1NY5 was also found to be capable of inducing apoptosis in purified peripheral blood CD4+ T cells as well as inhibiting anti-CD3-driven proliferation of these cells. In contrast, incubation of purified CD8+ T cells with HIV-1NY5 under similar conditions produced no cytopathic effects. Substantial levels of apoptosis were also recorded in HIV-1NY5-infected PHA blasts cell cultures. Soluble rHIV-1IIIB type CHO-derived gp120 was found to mimic the effects of HIV in terms of inhibition of anti-CD3/TCR mAb-induced proliferation of T cells, but apoptosis was not detected in gp120-treated T cell cultures whether cross-linked or used in conjunction with anti-CD3 mAb or not. We conclude therefore that both HIV-1NY5 and HIV-1RF isolates have the capacity to directly trigger apoptotic cell death in CD4+ T cells and that this appears to be at least partly associated with the efficiency of virus replication in these cells.

T cell responses to peptides covering the gag p24 region of HIV-1 occur in HIV-1 seronegative individuals.

We demonstrate that peptides (16 amino acids long) covering the sequence of the HIV-1 core protein p24 induce significant proliferation in peripheral blood mononuclear cells (PBMC) of several (greater than 50%) healthy seronegative volunteers as well as seronegative homosexual men. The nature of this response was characterized and compared with those of HIV-infected patients. Several peptides induced responses; however, the most frequent responses in both seropositive and seronegative individuals were noted to the following peptides: 1 and 2 (aa 133-157); 6 and 7 (aa 183-207); 15 (aa 273-287); and 17 and 18 (aa 293-317). The response pattern was related to the disease stage of the patients; seronegative individuals as well as asymptomatic seropositive individuals (CDC II/III) responded to low concentrations of several peptides, but symptomatic patients (CDC IV) only responded to high concentrations of a few peptides. Cell separation studies of PBMC from healthy volunteers showed that the responding cells were CD4+ and expressed the CD45RO differentiation antigen. Furthermore, cord-blood mononuclear cells with less than 5% of CD45RO T cells did not proliferative to any of the peptides. Finally, CD4+ T cell lines specific for both peptides and p24 protein were successfully established from the PBMC of seronegative individuals confirming the data obtained with freshly isolated cells. These studies therefore suggest that the CD4+ cell response to p24 is not strictly disease related, instead, the response may be due to priming of the host with cross-reactive antigens.