Anele Waters

Memory CD8+ T cells vary in differentiation phenotype in different persistent virus infections

The viruses HIV-1, Epstein–Barr virus (EBV), cytomegalovirus (CMV) and hepatitis C virus (HCV) are characterized by the establishment of lifelong infection in the human host, where their replication is thought to be tightly controlled by virus-specific CD8+ T cells. Here we present detailed studies of the differentiation phenotype of these cells, which can be separated into three distinct subsets based on expression of the costimulatory receptors CD28 and CD27. Whereas CD8+ T cells specific for HIV, EBV and HCV exhibit similar characteristics during primary infection, there are significant enrichments at different stages of cellular differentiation in the chronic phase of persistent infection according to the viral specificity, which suggests that distinct memory T-cell populations are established in different virus infections. These findings challenge the current definitions of memory and effector subsets in humans, and suggest that ascribing effector and memory functions to subsets with different differentiation phenotypes is no longer appropriate.

Characterization of CD4+ CTLs Ex Vivo

The cytotoxic potential of CD8+ T cells and NK cells plays a crucial role in the immune response to pathogens. Although in vitro studies have reported that CD4+ T cells are also able to mediate perforin-mediated killing, the in vivo existence and relevance of cytotoxic CD4+ T cells have been the subject of debate. Here we show that a population of CD4+ perforin+ T cells is present in the circulation at low numbers in healthy donors and is markedly expanded in donors with chronic viral infections, in particular HIV infection, at all stages of the disease, including early primary infection. Ex vivo analysis shows that these cells have cytotoxic potential mediated through the release of perforin. In comparison with more classical CD4+ T cells, this subset displays a distinct surface phenotype and functional profile most consistent with end-stage differentiated T cells and include Ag experienced CD4+ T cells. The existence of CD4+ cytotoxic T cells in vivo at relatively high levels in chronic viral infection suggests a role in the immune response.

Immune Activation and CD8+ T-Cell Differentiation towards Senescence in HIV-1 Infection

Progress in the fight against the HIV/AIDS epidemic is hindered by our failure to elucidate the precise reasons for the onset of immunodeficiency in HIV-1 infection. Increasing evidence suggests that elevated immune activation is associated with poor outcome in HIV-1 pathogenesis. However, the basis of this association remains unclear. Through ex vivo analysis of virus-specific CD8+ T-cells and the use of an in vitro model of naïve CD8+ T-cell priming, we show that the activation level and the differentiation state of T-cells are closely related. Acute HIV-1 infection induces massive activation of CD8+ T-cells, affecting many cell populations, not only those specific for HIV-1, which results in further differentiation of these cells. HIV disease progression correlates with increased proportions of highly differentiated CD8+ T-cells, which exhibit characteristics of replicative senescence and probably indicate a decline in T-cell competence of the infected person. The differentiation of CD8+ and CD4+ T-cells towards a state of replicative senescence is a natural process. It can be driven by excessive levels of immune stimulation. This may be part of the mechanism through which HIV-1-mediated immune activation exhausts the capacity of the immune system.

Presence of HIV-1 Gag-Specific IFN-γ+IL-2+ and CD28+IL-2+ CD4 T Cell Responses Is Associated with Nonprogression in HIV-1 Infection

HIV immunity is likely CD4 T cell dependent. HIV-specific CD4 T cell proliferative responses are reported to correlate inversely with virus load and directly with specific CD8 responses. However, the phenotype and cytokine profile of specific CD4 T cells that correlate with disease is unknown. We compared the number/function of Gag p24-specific CD4 T cells in 17 HIV-infected long-term nonprogressors (LTNPs) infected for a median of 14.6 years with those of 16 slow progressors (SPs), also HIV infected for a median of 14 years but whose CD4 count had declined to <500 cells/μl. Compared with SPs, LTNPs had higher numbers of specific CD4s that were double positive for IFN-γ and IL-2 as well as CD28 and IL-2. However, CD4 T cells that produced IL-2 alone (IL-2+IFN-γ−) or IFN-γ alone (IFN-γ+IL-2−) did not differ between LTNPs and SPs. The decrease in p24-specific CD28+IL-2+ cells with a concomitant increase of p24-specific CD28−IL-2+ cells occurred before those specific for a non-HIV Ag, CMV. p24-specific CD28−IL-2+ cells were evident in LTNPs and SPs, whereas the CMV-specific CD28−IL-2+ response was confined to SPs. The difference between LTNPs and SPs in the Gag p24 IFN-γ+IL-2+ response was maintained when responses to total Gag (p17 plus p24) were measured. The percentage and absolute number of Gag-specific IFN-γ+IL-2+ but not of IFN-γ+IL-2− CD4s correlated inversely with virus load. The Gag-specific IFN-γ+IL-2+ CD4 response also correlated positively with the percentage of Gag-specific IFN-γ+ CD8 T cells in these subjects. Accumulation of specific CD28−IL-2+ helpers and loss of IFN-γ+IL-2+ CD4 T cells may compromise specific CD8 responses and, in turn, immunity to HIV.

The natural history and clinical significance of intermittent viraemia in patients with initial viral suppression to < 400 copies/ml.

ObjectivesTo determine the prevalence and prognostic significance of intermittent viraemia (IV) in patients who attained an undetectable viral load (VL) < 400 copies/ml within 6 months on highly active antiretroviral therapy (HAART). MethodsRetrospective analysis of viral load rebound ⩾ 400 copies/ml and CD4 cell counts rise for 765 patients followed for ⩾ 12 months following initial VL undetectability, comparing the 226 (29.5%) who maintained an undetectable VL for > 1 year from initiation of HAART and 122 (15.9%) who had one or more episodes of IV. Genotypic resistance was evaluated at the time of the first episode of IV ⩾ 2000 copies/ml. ResultsPatients with IV had a threefold higher rate of sustained virological rebound [hazards ratio (HR), 3.15; 95% confidence interval (CI), 1.72–5.77;P < 0.001). For patients with and without IV, the Kaplan–Meier estimates at 24 and 36 months after initiation of HAART were 19.3% (95% CI, 8.9–21.5) versus 7.7% (95% CI, 4.5–13.0) and 31.6% (95% CI, 21.8–44.2) versus 12.9% (95% CI, 7.5–21.5), respectively (P < 0.001). The median CD4 cell count rise at 18 and 24 months was significantly lower in those with IV than in those without: 138 [interquartile range (IQR), 58–221] versus 224 × 106 cells/l (IQR, 119–357) (P = 0.0001) and 200 (IQR, 89–294) versus 260 × 106 cells/l (IQR, 125–384) (P = 0.003), respectively. In a subgroup of 16 patients, genotypic resistance mutations were found in the reverse transcriptase gene for five (31%) and in the protease gene in one. A probable contributing factor/event was identified for most patients with IV, such as poor adherence (42.6%), intercurrent infection (26.2%) or drug interaction (6.8%). ConclusionsPatients with IV > 400 copies/ml are three times more likely to experience sustained viral rebound and to have an impaired CD4 cell rise relative to those who maintain undetectable VL. This supports the adoption of a more pro-active approach to treatment intensification and the need for caution with structured treatment interruptions.

CD4 responses to conserved HIV-1 T helper epitopes show both negative and positive associations with virus load in chronically infected subjects

Characterization of immune responses to immunodominant CD4 epitopes in HIV‐1 that are associated with control of HIV infection could be used to strengthen the efficacy of polyepitope HIV vaccines. We measured both the proliferative and the CD4 interferon (IFN)‐γ and interleukin (IL)‐2 cytokine responses specific for 11 previously identified HIV‐1 T helper epitopes in 10 HIV‐infected non‐progressors (LTNPs) (infected for a median of 15 years with a stable CD4 count of >500 cells × 106/l), and seven slow progressors (SPs) (infected for a median of 15 years with a CD4 count that had declined to <500 cells × 106/l). Both groups were antiretroviral treatment‐naive at the time of evaluation. The median virus load of SP group was higher than that of the LTNP group (P = 0·0002). The CD4 response to a peptide pool representing all potential CD4 Gag epitopes and to Gag p24 protein was also studied. Compared to SPs, LTNPs had higher numbers of Gag‐specific IFN‐γ+IL‐2+ CD4s (P = 0·0059). The Gag‐specific cytokine and proliferative responses correlated inversely with virus load (P = 0·03 and 0·0002, respectively), highlighting the potential importance of this response in immunity to HIV. A direct correlation was noted between proliferation and the Gag‐specific IL‐2 (P = 0·0053) rather than IFN‐γ response (P = 0·1336), demonstrating that the proliferation assay reflected the IL‐2 rather than the IFN‐γ secreting capacity of CD4 cells. Several subjects with diverse class II DRB1 alleles responded, confirming the 11 selected peptides to be both antigenic and conserved. CD4 cytokine responses to one Gag and two conserved Pol peptides correlated negatively with virus load. The cytokine response to two additional Pol peptides correlated positively with virus load. The data indicate that there is not an absolute correlation between the CD4 immune response to conserved and broadly antigenic helper T cell epitopes in HIV non‐progression.

Evidence for Gag p24-specific CD4 T cells with reduced susceptibility to R5 HIV-1 infection in a UK cohort of HIV-exposed-seronegative subjects.

Aim: To characterize HIV-1 Gag p24-specific CD4 cell responses in HIV-exposed-seronegative (ES) individuals. Methodology: Twelve ES individuals, of diverse ethnicity and wild type for the CCR5 Δ-32 mutation, were identified. Controls were HIV-negative blood donors. Gag p24-specific and total Vβ+ CD4 cells that expressed MIP-1β, IFN-γ and IL-2 were enumerated by intracytoplasmic cytokine staining. β-Chemokine expression was correlated with susceptibility to R5 HIV-1 infection, as measured by polymerase chain reaction for integrated HIV-1 and by p24 enzyme-linked immunosorbent assay. Results: Similar numbers of mitogen-stimulated and Vβ+ MIP-1β+, IFN-γ+ and IL-2+ T cells were found in ES and HIV-negative control subjects. However, all ES subjects tested had an HIV Gag p24-specific MIP-1β+, IFN-γ+ and IL-2+ CD4 T-cell response that was rare in controls. p24-Specific cells of all ES but no control subjects could be expanded by in-vitro Ag/IL-2 stimulation, and when re-stimulated with an overlapping peptide series showed evidence of a broad CD4 cell memory response directed against multiple regions of Gag p24. Mitogen-stimulated ES CD4 cells were as susceptible to HIV infection as those from control subjects, but p24-specific IFN-γ+ CD4 cells of six out of seven ES subjects tested were less susceptible to R5 HIV-1 infection than the counterpart fraction depleted of p24-specific IFN-γ+ cells. The addition of blocking anti-β-chemokine antibodies did not promote R5 HIV-1 infection of p24-specific IFN-γ+ cells. Conclusion: Specific CD4 cell immunity, characterized by a broadly directed memory Gag-p24 CD4 cell response and reduced susceptibility of specific CD4 cells to R5 HIV-1 infection, is a likely correlate of non-transmission.

During Stably Suppressive Antiretroviral Therapy Integrated HIV-1 DNA Load in Peripheral Blood is Associated with the Frequency of CD8 Cells Expressing HLA-DR/DP/DQ

Background Characterising the correlates of HIV persistence improves understanding of disease pathogenesis and guides the design of curative strategies. This study investigated factors associated with integrated HIV-1 DNA load during consistently suppressive first-line antiretroviral therapy (ART). Method Total, integrated, and 2-long terminal repeats (LTR) circular HIV-1 DNA, residual plasma HIV-1 RNA, T-cell activation markers, and soluble CD14 (sCD14) were measured in peripheral blood of 50 patients that had received 1–14 years of efavirenz-based or nevirapine-based therapy. Results Integrated HIV-1 DNA load (per 106 peripheral blood mononuclear cells) was median 1.9 log10 copies (interquartile range 1.7–2.2) and showed a mean difference of 0.2 log10 copies per 10 years of suppressive ART (95% confidence interval − 0.2, 0.6; p = 0.28). It was positively correlated with total HIV-1 DNA load and frequency of CD8+HLA-DR/DP/DQ+ cells, and was also higher in subjects with higher sCD14 levels, but showed no correlation with levels of 2-LTR circular HIV-1 DNA and residual plasma HIV-1 RNA, or the frequency of CD4+CD38+ and CD8+CD38+ cells. Adjusting for pre-ART viral load, duration of suppressive ART, CD4 cell counts, residual plasma HIV-1 RNA levels, and sCD14 levels, integrated HIV-1 DNA load was mean 0.5 log10 copies higher for each 50% higher frequency of CD8+HLA-DR/DP/DQ+ cells (95% confidence interval 0.2, 0.9; p = 0.01). Conclusions The observed positive association between integrated HIV-1 DNA load and frequency of CD8+DR/DP/DQ+ cells indicates that a close correlation between HIV persistence and immune activation continues during consistently suppressive therapy. The inducers of the distinct activation profile warrant further investigation.

Novel Drug Resistance Pattern Associated with the Mutations K70G and M184V in Human Immunodeficiency Virus Type 1 Reverse Transcriptase

ABSTRACT We describe an unusual pathway of human immunodeficiency virus type 1 reverse transcriptase resistance during therapy with tenofovir-emtricitabine, characterized initially by the mutations K70E and M184V and later by K70G and M184V, with the two mutations coexisting on the same viral genome. Phenotypic resistance to lamivudine, emtricitabine, abacavir, didanosine, and tenofovir was observed, whereas susceptibility to zidovudine and stavudine was preserved.

Reconstitution of Herpes Simplex Virus-Specific T Cell Immunity in HIV-Infected Patients Receiving Highly Active Antiretroviral Therapy

Production of herpes simplex virus (HSV)-specific interferon- gamma by peripheral-blood mononuclear cells (PBMCs) of HSV-seropositive healthy donors and human immunodeficiency virus-infected persons was determined by use of ELISPOT. The mean +/- SD number of spot-forming cells/10(6) PBMCs was 314 +/- 74 in 11 healthy donors, 360 +/- 69 in 3 long-term nonprogressors (LTNPs), 186 +/- 52 in 9 newly diagnosed patients, and 181 +/- 59 in 33 patients who were receiving highly active antiretroviral therapy (HAART) for a median period of 30 months (range, 1-109 months). In 9 patients monitored prospectively while receiving virologically and immunologically successful first-line HAART, the number of spot-forming cells increased by 5.6/month (95% confidence interval, 1.2-9.9 [P=.01]) and 21.3/100 CD4 cells/mm(3) gained (95% confidence interval, 13.8-28.7 [P<.0001]). Responses were correlated with LTNP status and CD4 cell count.