Host CCL3L1 gene copy number in relation to HIV-1-specific CD4+ and CD8+ T-cell responses and viral load in South African women

HIV-specific T-cell responses play an important role in control of infection. Because CCL3 has immune modulatory and antiviral activities, we hypothesized that host CCL3 genotype (CCL3L1 gene duplications) would influence the development of effective HIV-specific immune responses. Copy numbers of CCL3L1 were determined for 71 HIV-infected women, and HIV-specific CD4 and CD8 T-cell responses to overlapping peptide pools spanning the HIV-1 subtype C genome were simultaneously measured by an interferon-gamma and interleukin-2 whole-blood flow cytometric assay. Host CCL3L1 copy number correlated negatively with viral load (r=-0.239, P=0.045), as did magnitudes of Gag CD4 (r=-0.362, P=0.002) and CD8 (r=-0.261, P=0.028) T-cell responses. Patients with a Gag CD4 response (P=0.002) or dominant Gag CD8 (P=0.006) response had significantly lower viral loads than those whose dominant response targeted another region of the genome, whereas a dominant Nef-specific CD8 T-cell response was associated with higher HIV viral load. CCL3L1 copy number greater than or equal to the population median of 5 was significantly associated with increased magnitude of CD4 Gag responses (P=0.017), and women who had CD4 and CD8 Gag-specific responses had significantly lower viral loads (P=0.004) and higher CCL3L1 copy number (P=0.015) than those women with only CD8 Gag-specific responses.     

Direct measurement of CD4+ and CD8+ T-cell responses to CMV in HIV-1-infected subjects

Data from murine models of chronic viral infection suggest that CD4+ T-cell responses to viral pathogens are important in sustaining the number and/or function of CD8+ cytotoxic T-cell (CTL) effectors. In this study, we used cytokine flow cytometry (CFC), staining with HLA-A*0201-peptide tetramers, and peptide stimulation with epitopic peptides to study functional CD4+ and CD8+ T-cell responses to cytomegalovirus (CMV) in human subjects coinfected with CMV and the human immunodeficiency virus, type 1 (HIV-1). We show that strong CD4+ and CD8+ T-cell responses to CMV antigens are sustained over time in HIV-1-infected individuals. Those who maintain a strong CD4+ T-cell response to CMV are also likely to maintain higher frequencies of CD8+ T cells capable of binding to HLA-A*0201-CMV pp65 (A2-pp65) tetramers as well as responses to pp65 peptide stimulation with effector cytokine production. These data support the hypothesis that declines in frequencies of CD4+ T-cell responses to CMV are associated with an inability to sustain high levels of CMV-specific CD8+ T-cell responses in HIV-1-infected subjects. These declines may precede the onset of CMV-associated end organ disease.     

Changes in CD4+ T-cell differentiation phenotype during structured treatment interruption in patients with chronic HIV-1 infection

Markers of maturation and activation were measured on peripheral CD4+ T cells in chronically HIV-1-infected patients in a randomized, controlled pilot study of structured treatment interruption (STI). Eight subjects underwent 2 cycles of 1 month off and 1 month on highly active antiretroviral therapy (HAART), followed by a final 3-month interruption. During STI, CD4+ T-cell percentage remained relatively stable in 4 of 8 subjects. The remaining 4 STI subjects had significant rapid decline in CD4+ T-cell percentage during STI, followed by return to pre-STI baseline while on HAART. Changes in overall CD4+ T-cell percentage corresponded with fluctuations in the CD45RA+CCR7+ naive and CD45RA-CCR7+ central memory subsets. Subjects with variable CD4+ T-cell percentages tended to have higher pre-HAART plasma HIV-1 RNA set-points and experienced higher levels of plasma HIV-1 RNA rebound during STI. These results suggest that interruptions should be avoided whenever possible in patients on HAART with high plasma HIV-1 RNA set-points.     

Correlation between gag-specific CD8 T-cell responses, viral load, and CD4 count in HIV-1 infection is dependent on disease status

BACKGROUND: It still remains controversial which kind of relationships exist between HIV-1-specific CD8 T-cell responses and HIV RNA load or CD4 count over the course of the infection. This study was designed to investigate the role of HIV-specific CD8 responses in patients with different disease status. METHODS: Three cohorts of patients were selected according to CD4 count levels: long-term nonprogressors (LTNPs, n = 19), asymptomatic progressors (CD4 counts between 500 and 350 cells/mm(3), n = 14), and progressors (CD4 counts <350 cells/mm(3), n = 23). Six of the LTNPs experiencing a quick loss of CD4 T-cells and another 6 LTNPs with stable CD4 counts were followed up. T-cell responses were studied using interferon (IFN) gamma-ELISpot assay against HIV p24 and 11 pools of HIV-Gag peptides. RESULTS: No significant differences were found in Gag-specific CD8 responses among the 3 cohorts. However, inverse correlations were identified between CD8 responses and CD4 counts in asymptomatic progressors and between CD4 responses and viral loads in progressors. In addition, the sequential dynamics of CD8 responses in 6 LTNPs showed that with a quick loss of CD4 T-cells around the range of 500 to 300 cells/mm(3), more vigorous CD8 responses were induced simultaneously, and plasma viremia was still kept relatively stable. CONCLUSIONS: These data suggest that the relationship between CD8 response and viral load or CD4 count is not universally consistent throughout the entire course of HIV-1 infection. Gag-specific CD8 responses may play differential roles in different stages of HIV-1 infection, and the maintenance of a threshold level of CD4 T-cells may contribute to mediate effective HIV-specific responses in natural control of HIV-1 infection.     

CD8 T-cell proliferative capacity is compromised in primary HIV-1 infection

Understanding the correlates of immunity that control HIV-1 infection is imperative to our understanding of HIV-1 disease and vaccine development. HIV-1-specific cytotoxic T lymphocytes are fundamental to the control of viremia; however, which T-cell repertoire components enact this control remains unclear. We hypothesize that polyfunctional HIV-1-specific CD8 T cells capable of viral control are present in most patients early in infection and these cells are distinguished by their ability to secrete interleukin (IL)-2 and proliferate. We examined HIV-1-specific CD8 T-cell proliferation and cytokine secretion in primary HIV-1 infection (PHI) using known HIV-1 cytotoxic T-cell epitopes to exclude CD4 bystander effect. We found that only a subset of patients with PHI demonstrated "CD4-independent" CD8 proliferation ex vivo. The remainder of the patients lacked HIV-1-specific CD8 T cells with proliferative capacity, even after the addition of exogenous IL-2. Among the proliferators, IL-2 production from the total HIV-specific CD8 T-cell population correlated with proliferation. Surprisingly, though, we did not routinely detect both IL-2 secretion and proliferative capacity from the same antigen-specific CD8 T cells. Thus, there are distinct and heterogeneous populations of CD8 T cells, phenotypically characterized by either proliferation or IL-2 secretion and few with dual capacity. Generation of these responses may be an important measure of HIV-1 control but are not universal after PHI. Furthermore, the heterogeneity of this population suggests that a simple measure of an effective vaccine response remains elusive.     

Immunodominance of HIV-1-specific CD8(+) T-cell responses in acute HIV-1 infection: at the crossroads of viral and host genetics

The development of HIV-1-specific CD8(+) T-cell responses during acute HIV-1 infection is associated with a dramatic decline in HIV-1 replication and the resolution of the acute retroviral syndrome. These HIV-1-specific CD8(+) T cells typically target a small number of viral epitopes in a distinct hierarchical order, and high-level viremia in chronic progressive infection leads to broadly diversified HIV-1-specific CD8(+) T-cell responses with a less clear immunodominance pattern. It is argued here that the specific hierarchical pattern of immune responses in acute HIV-1 infection is the result of a tightly regulated process that, among other factors, is critically impacted by the kinetics of viral protein expression, the HLA class I background of the infected individual and the autologous sequence of the infecting virus.     

Activation of idiotype-specific CD4+ T-cell line: cellular processing of exogenous self-immunoglobulin

An idiotype (Id)-specific long-term cultured T-cell line has been generated from BALB/c mice immunized with M315 (alpha, lambda 2). The cell line comprises both CD3+ and CD4+ but CD8- cells. The T-cell line is stimulated in a class II major histocompatibility complex (MHC)-restricted manner, and is capable of producing interleukin-2 (IL-2) in response to the Id along with Iad-bearing antigen-presenting cells (APC). Fine Id specificity analysis has shown that changes in amino acid residues, Phe-94, Arg-95 and Asn-96, located on the VL-315, resulting from a somatic mutation mechanism of the mouse V lambda 2 gene, contribute to the T-cell activation. Pretreatment of APC with either glutaraldehyde or paraformaldehyde prevented both Fv-315 and VL-315 from triggering the T cells. This suggested that further processing of VL is required for T-cell activation. To clarify this point, we have generated a synthetic peptide, designated P18, which spans residues 91-108 of VL-315. In sharp contrast to VL, prefixed APC were capable of presenting P18 to stimulate the T-cell line to induce IL-2.     

Low CD4+ T-cell counts in HIV patients receiving effective antiretroviral therapy are associated with CD4+ T-cell activation and senescence but not with lower effector memory T-cell function

The adverse effects of immune activation on CD4(+) T-cell recovery and the relationship between CD4(+) T-cell counts and effector T-cell function were examined in HIV-1 patients receiving long-term effective ART. Patients with nadir CD4(+) T-cell counts <100/microl, > 12 months on ART and >6 months with <50 HIV RNA copies/ml were stratified by current CD4(+) T-cell counts and patients from the lowest (n = 15) and highest (n = 12) tertiles were studied. We assessed proliferation (Ki67), activation (HLA-DR, CD38) and replicative senescence (CD57) by flow cytometry and CD4(+) T-cell responses to CMV by IFN-gamma ELISpot. Proportions of CD4(+) T-cells expressing HLA-DR or CD57 were strong univariate predictors of total (P = 0.0002 and P = 0.002) and naive (P < 0.0001 and P < 0.0001, respectively) CD4(+) T-cell counts, suggesting that CD4(+) T-cell activation drives the depletion of naive CD4(+) T-cells. This was clearest in patients with a small/undetectable thymus. IFN-gamma responses to CMV were similar in patients with low or high CD4(+) T-cell counts.     

Systemic vaccination induces clonally diverse SIV-specific CD8+ T-cell populations in systemic and mucosal compartments

An HIV-1 vaccine must elicit a clonally diverse virus-specific CD8+ T-cell response to contain mutant virus forms, and these responses must be present in mucosal tissues, which are the site of early HIV-1 replication. We show that systemic delivery of prototype vaccine vectors in rhesus monkeys induced SIV (simian immunodeficiency virus)-specific CD8+ T-cell responses in systemic and mucosal compartments with comparable clonal compositions. Although clonal sharing was maintained between the peripheral blood and lungs, the clonal constituents of the vaccine-induced CD8+ T-cell populations in the gastrointestinal mucosal tissues evolved away from the peripheral blood population. A phenotypic characterization indicated that the divergence was a consequence of differential trafficking and retention of the vaccine-induced cells in mucosal compartments. These findings highlight the circulation of vaccine-induced CD8+ T-cell populations between systemic and mucosal compartments and the importance of the expression of specific homing molecules for localization in mucosal tissues.     

Antiretroviral therapy-induced dominant interleukin-2 HIV-1 Gag CD4+ T cell response: evidence of functional recovery of HIV-1-specific CD4+ T cells

Prolonged antiretroviral treatment (ART) significantly changes the cytokine secretion capacities of HIV-1-specific T cells. However, it is unclear whether these changes result from decreased viremia or they correspond to true functional recovery of viral-specific immune response. To study this issue, we analysed the quantitative and qualitative differences of HIV-1-specific and polyclonal CD4+ and CD8+ T cells between 26 naive and 52 treated individuals. HIV-1 Gag and staphylococcal enterotoxin B (SEB)-reactive T cells were determined by flowcytometric intracellular secretion of IFN-γ or/and ΙL-2. ART resulted in increase of single IL-2 and decrease of single IFN-γ-secreting HIV-1 CD4+ T cells, while both cytokines secreting HIV-1 CD4+ T cells were presented in comparable frequencies in both groups. Viral loads correlated negatively with single IL-2 and positively with single IFN-γ-secreting HIV-1 CD4+ cells. Single IL-2 HIV-1 CD4+ T cells correlated positively with both cytokines secreting polyclonal CD8+ T cells. By qualitative analysis, a dominant IL-2 HIV-1 CD4+ T cell response (> 70% single IL-2) was identified only in ART suppressed patients, who also generated increased dual specific polyclonal CD8+ T cells. Polyfunctional HIV-1 CD4+ T cell responses were detected even in naive individuals with high viremia. In conclusion, the presence of dominant IL-2 HIV-1 CD4+ T cell response, associated with increased CD8+ T cells capable to produce IL-2, indicates that the recovery of HIV-1-specific CD4+ T cell functionality under ART is a feasible goal. Furthermore, polyfunctional HIV-1 CD4+ T cell responses seem not to be directly involved in viral replication control.     

Evaluation of HIV-1 p24 antigenemia and level of CD8+CD38+ T cells as surrogate markers of HIV-1 RNA viral load in HIV-1-infected patients in Dakar, Senegal

Alternative, affordable, and simple assays to monitor antiretroviral therapy (ART) in resource-poor settings are needed. We have evaluated and compared a heat-denatured (HD) HIV p24 amplified enzyme-linked immunosorbent assay from Perkin-Elmer and CD38CD8 T-cell levels, determined by flow cytometry, for their capacity to predict viral load (VL) in HIV-1-infected patients from Senegal. Median fluorescence intensity (MFI) of CD38 expression on memory (CD45RO) CD8 T cells correlated better with RNA VL than HD p24 antigenemia (R = 0.576, P < 0.0001 vs R = 0.548, P < 0.0001). MFI of CD38 expression on memory CD8 T cells could predict detectable RNA VL (VL = 2.6 log10) with a sensitivity of 87% and a specificity of 74%. A comparable sensitivity (89%) could be reached for HD p24 assay, but only to predict RNA VL of more than 5 logs, which might lead to unacceptable delays in clinical decision making. The clinical use of the HD p24 assay to monitor ART in Senegal would require more comparative data about the kinetics of p24 antigen and HIV RNA in peripheral blood as well as further evaluation regarding its sensitivity toward subtype A and CRF02. MFI of CD38 expression on memory CD8 T cells appeared to be a better alternative to monitor ART in HIV-infected patients from Senegal.     

CTL escape and increased viremia irrespective of HIV-specific CD4+ T-helper responses in two HIV-infected individuals

We investigated whether development of mutations leads to loss of CD8 T-cell recognition in HIV-1 infection and is possibly linked to alterations in HIV-1-specific CD4(+) T-cell responses in 2 HIV-infected individuals. In patient, H434 full genome sequencing of HIV-1 biological clones at early and late time points during disease progression showed development of fixed mutations in 16 predicted HIV-specific CTL epitopes. Loss of T-cell recognition and reactivity against wild-type and mutant epitopes was observed primarily for the HLA-B27-restricted KK10 epitope and HLA-A2-restricted SL9 epitope. Similarly, in patient H671, decreasing numbers of HLA-A3-restricted CD8(+) T cells specific for the wild-type RK9 epitope was observed after CTL escape. Only in patient H434 loss of CTL responses was paralleled by a decrease in HIV-specific IL-2(+) CD4(+) T-helper responses. This suggests that loss of T-cell reactivity may not be directly linked to HIV-specific CD4(+) T-cell responses but that increased viremia after CTL escape may influence CD4(+) T-helper responses.     

HIV-1-specific cytolytic T-lymphocyte activity correlates with lower viral load, higher CD4 count, and CD8+CD38-DR- phenotype: comparison of statistical methods for measurement.

OBJECTIVES: The objective of this study was to use novel statistical methods to determine the correlation between HIV-1-specific cytolytic T-lymphocyte (CTL) activity and HIV-1 plasma viral load, in a blinded study of HIV-infected patients at various stages of clinical disease. METHODS: Peripheral blood mononuclear cells (PBMC) were collected and stored at enrollment and 2 weeks later, from 15 HIV-infected individuals who were receiving stable antiretroviral therapy for the previous 6 weeks and during the study period. HIV-1-specific CTL activity was measured using an antigen-specific PBMC in vitro stimulation method. Measurements of plasma viral load, as well as CD4+ and CD8+ T lymphocytes expressing T-cell activation markers (DR and CD38) were also performed at each time point. CTL activity was quantified using three separate statistical methods: area under the net HIV-specific lysis curve (AUC), lytic units (LU20), and linear regression (LR) of net HIV-specific lysis. RESULTS: HIV-1 nef-, pol- and gag-specific CTL activity (AUC method) was significantly higher in subjects with a plasma viral load < or = 30,000 RNA copies/ml, than in those with viral load >30,000 RNA copies/ml. When plasma viral load was analyzed as a continuous variable, there was a strong correlation between higher CTL activity and lower viral load for nef (r2 = .77; p < .001), pol (r2 = .63; p < .001) and gag (r2 = 0.75; p < .001) targets by the AUC, but not for the LU20 analysis. Using the LR analysis, which is less dependent on in vitro PBMC growth than the AUC analysis, an independent association was demonstrated between nef- and gag-specific CTL activity and lower viral load. Measurement of CTL activity was also significantly correlated with a higher percentage of circulating CD8+DR-CD38- T lymphocytes. CONCLUSIONS: In this blinded study using an in vitro stimulation of frozen PBMC, higher HIV-1 nef-, pol-, and gag-specific CTL activity correlated with lower plasma viral load, particularly in patients with a CD4 count <500 cells/mm3. Two new statistical methods for estimating CTL activity, AUC and LR analyses, were superior to the standard lytic unit (LU20) method for demonstrating this correlation. These data also demonstrated that higher circulating CD8+ T lymphocytes with a DR-CD38-phenotype, correlate with a lower plasma viral and load and higher HIV-specific CTL activity. This suggests that lymphocytes with this double-negative phenotype may include circulating HIV-specific CD8+ CTL.     

Limited role for CD4+ T-cell help in the initial priming of Trypanosoma cruzi-specific CD8+ T cells

Immune control of the protozoan parasite Trypanosoma cruzi requires the activation of both CD4+ and CD8+ T cells. We recently identified two T. cruzi trans-sialidase peptides that are targets of approximately 30% of all CD8+ T cells during acute T. cruzi infection in mice. To determine whether CD4+ T cells are required for generation of these dominant CD8+ T-cell responses, major histocompatibility complex class II (MHC II)-deficient mice were infected with the Brazil strain of T. cruzi and examined for the generation of antigen-specific CD8+ T cells. Strong trans-sialidase TSKB18- and TSKB20-specific CD8+ T-cell responses were generated in both the presence and the absence of CD4+ help. However, the magnitudes of the immunodominant TSKB20-specific CD8+ T-cell responses detectable using class I MHC-peptide tetramers were consistently lower in the blood and spleens of MHC II-deficient mice. Spleen cells from infected MHC II-deficient mice produced gamma interferon after in vitro stimulation with T. cruzi peptides at levels similar to those in wild-type mice, and MHC II-deficient mice displayed strong T. cruzi peptide-specific cytotoxic T-lymphocyte activity in vivo. Thus, primary CD8+ T-cell responses in experimental T. cruzi infection are generated in the absence of CD4+ T cells, providing further evidence that T. cruzi directly activates and licenses antigen-presenting cells. Nevertheless, unhelped CD8+ T cells in T. cruzi-infected mice fail to reach the frequencies achieved in the presence of CD4 T-cell help and are unable to prevent acute-phase death of these mice.     

Long-term CD4+ T-cell response to highly active antiretroviral therapy according to baseline CD4+ T-cell count

Current treatment guidelines for HIV infection recommend a relatively late initiation of highly active antiretroviral therapy (HAART). Nevertheless, there is still a concern that immune recovery may not be as complete once CD4+ T cells have decreased below a certain threshold. This study addressed the long-term response of CD4+ T-cell counts in patients on HAART and analyzed the influence of baseline CD4+ T-cell counts, baseline viral load, and age. An observational analysis of evolution of CD4+ T cells in 861 antiretroviral therapy-naive chronic HIV-1-infected patients who started treatment consisting of at least 3 drugs in or after 1996 was performed. Patients were classified in 4 groups according to baseline CD4+ T cells: <200 cells/mm3, 200-349 cells/mm3, 350-499 cells/mm3, and >or=500 cells/mm3. The main outcome measures were proportion of patients with CD4+ T cells <200/mm3 and >500/mm3 at last determination and rate of CD4+ T-cell recovery. Patients were followed-up for a median of 173 weeks (interquartile range [IQR], 100-234). There were no differences in follow-up between the 4 groups. CD4+ T cells increased in the whole cohort from a median of 214 cells/mm3 (IQR, 90-355) to 499 cells/mm3 (IQR, 312-733) (P<0.001). Compared with the group with a baseline CD4+ T-cell count of >or=500/mm3, the relative risk of having a last determination of CD4+ T-cell counts >200 cells/mm3 was 0.79 (95% CI, 0.75-0.83), 0.92 (95% CI, 0.89-0.96) and 1 for baseline CD4+ T cells <200 cells/mm3, 200-349 cells/mm3, and 350-499 cells/mm3, respectively. The relative risk of having a last determination of CD4+ T-cell counts >500 cells/mm3 was 0.32 (95% CI, 0.27-0.39, P<0.001), 0.69 (95% CI, 0.60-0.79, P<0.001), and 0.94 (95% CI, 0.83-1.06, P=0.38) for baseline CD4+ T-cell counts <200 cells/mm3, 200-349 cells/mm3, and 350-0499 cells/mm3, respectively, compared with a baseline CD4+ T-cell count of >or=500 cells/mm3. The increase in CD4+ T cells from baseline was statistically significant and was maintained for up to 4 years of follow-up. This increase seemed to slow down after approximately 3 years and reached a plateau after 4-5 years of follow-up even in patients who achieved and maintained viral suppression in plasma. Long-term immune recovery is possible regardless of baseline CD4+ T-cell count. However, patients who start therapy with a CD4+ T-cell count <200 cells/mm3 have poorer immunologic outcome as measured by the proportion of patients with CD4+ T cells <200/mm3 or >500/mm3 at last determination. It seems that the immune recovery slows down after approximately 3 years of HAART and reaches a plateau after 4-5 years of HAART.     

Multiple HLA-class I-specific inhibitory NK receptor expression and IL-4/IL-5 production by CD8+ T-cell clones in HIV-1 infection

Several mechanisms may contribute to the decline in HIV-1 specific CD8+ cytotoxic T-lymphocyte (CTL) activity that is observed in infected patients, including loss of CD4+ cell help, antigenic shift, impaired clonogenicity and functional impairment due to expression of inhibitory NK receptors (iNKRs). In addition to a decrease in HIV-1-specific cytolytic activity, an increased proportion of CD8+ T-cells producing IL-4 and IL-5 has been recently observed in advanced HIV-1 infection. Remarkably, an impaired HIV-1-specific CTL activity was primarily detected among the TC0/Tc2 CD8+ CTLs. A series of CD3+CD8+ T-cell clones expressing inhibitory NK receptors (iNKRs) isolated from HIV-1 infected patients was analyzed in order to determine their cytokine production pattern and to assess the extent of iNKR expression at the single cell level. Our data indicate that iNKR+CD3+CD8+ clones isolated from infected patients frequently express multiple iNKR and may produce IL-4 and IL-5 to a relevant extent.     

Concomitant augmentation of type 1 CD4+ and CD8+ T-cell responses during successful interferon-alpha and ribavirin treatment for chronic hepatitis C virus infection

The combined interferon-alpha (IFN-alpha) and ribavirin (IFN-alpha/ribavirin) therapy for chronic hepatitis C virus (HCV) infection results in sustained viral eradication in 31%-64% of the patients. Previous studies have strongly suggested that HCV-specific T-cell responses maybe modulated during this therapy. The objective of this study was to further define the effect of IFN-alpha/ribavirin therapy on type 1 and type 2 HCV-specific CD4(+) and CD8(+) T-cell responses during IFN-alpha/ribavirin therapy. Toward this, serial CD8(+) T-cell responses to HCV-derived epitopes and CD4(+) T-cell responses to the HCV core antigen were analyzed in four patients before (baseline), during (at 24 weeks), and at the end (at 48 weeks) of IFN-alpha/ribavirin therapy. Therapy-induced viral clearance in three patients was associated with a significant augmentation of HCV-specific type 1 CD4(+) and CD8(+) T-cell responses. In contrast, in a patient who did not respond to therapy, a significant HCV-specific CD4(+) Th2 cell reactivity was observed accompanied by a lack of augmentation of the HCV-specific CD8(+) T-cell reactivity. These results indicate that enhancement of HCV-specific CD4(+) and CD8(+) T-cell responses is an important factor in determining the response to the IFN-alpha/ribavirin therapy and the outcome of the HCV infection.     

CD27 and CD57 expression reveals atypical differentiation of human immunodeficiency virus type 1-specific memory CD8+ T cells

The failure of human immunodeficiency virus type 1 (HIV-1)-specific CD8+ T cells to control chronic HIV-1 infection could be due to the progressive loss of their capacities to undergo normal memory effector differentiation. We characterized and compared the expressions of CD27, CD28, CD57, and CD62L by Epstein-Barr virus (EBV)-, cytomegalovirus (CMV)-, and HIV-1-specific CD8+ T cells by six-color, eight-parameter flow cytometry. In contrast to the maturation of EBV- and CMV-specific memory CD8+ T cells, we found that HIV-1-specific CD8+ T cells did not display coordinated down-regulation of CD27 and up-regulation of CD57 and accumulated in an atypical CD27(high) CD57(low) subset. Moreover, the accumulation of CD27(high) CD57(low) HIV-1-specific CD8+ T cells was positively correlated with HIV-1 plasma viremia. The differentiation of HIV-1-specific CD8+ T cells to an effector subset is therefore impaired during chronic HIV-1 infection. This lack of normal CD8+ T-cell differentiation could contribute to the failure of cellular immune control of HIV-1 infection.     

Type I interferon supports primary CD8+ T-cell responses to peptide-pulsed dendritic cells in the absence of CD4+ T-cell help

CD8(+) T-cell responses to non-pathogen, cell-associated antigens such as minor alloantigens or peptide-pulsed dendritic cells (DC) are usually strongly dependent on help from CD4(+) T cells. However, some studies have described help-independent primary CD8(+) T-cell responses to cell-associated antigens, using immunization strategies likely to trigger natural killer (NK) cell activation and inflammatory cytokine production. We asked whether NK cell activation by MHC I-deficient cells, or administration of inflammatory cytokines, could support CD4(+) T-cell help-independent primary responses to peptide-pulsed DC. Injection of MHC I-deficient cells cross-primed CD8(+) T-cell responses to the protein antigen ovalbumin (OVA) and the male antigen HY, but did not stimulate CD8(+) T-cell responses in CD4-depleted mice; hence NK cell stimulation by MHC I-deficient cells did not replace CD4(+) T-cell help in our experiments. Dendritic cells cultured with tumour necrosis factor-α (TNF-α) or type I interferon-α (IFN-α) also failed to prime CD8(+) T-cell responses in the absence of help. Injection of TNF-α increased lymph node cellularity, but did not generate help-independent CD8(+) T-cell responses. In contrast, CD4-depleted mice injected with IFN-α made substantial primary CD8(+) T-cell responses to peptide-pulsed DC. Mice deficient for the type I IFN receptor (IFNR1) made CD8(+) T-cell responses to IFNR1-deficient, peptide-pulsed DC; hence IFN-α does not appear to be a downstream mediator of CD4(+) T-cell help. We suggest that primary CD8(+) T-cell responses will become help-independent whenever endogenous IFN-α secretion is stimulated by tissue damage, infection, or autoimmune disease.