Consistent subtype-specific anti-HIV type 1 T lymphocyte responses in Indian subjects recently infected with HIV type 1

Anti-HIV-1-specific T cell responses in early HIV-1 infection have been found to be important in deciding the course of disease progression. But there are few data concerning nonsubtype B HIV infection. HIV-1 subtype C is the most prevalent subtype in India. HIV-1 Gag-specific T cell responses in 12 Indian subjects with recent HIV-1 infection were characterized by an ELISpot assay at two consecutive visits and their correlation with plasma viral load and CD4(+) T lymphocyte counts was studied. Ten of the 12 subjects demonstrated T cell responses to either one or both Gag B and C peptides, on at least one visit. Five of 10 responders showed a consistent response (response at both visits): 4 exhibited a Gag C-specific consistent response and 1 showed a consistent response to Gag B. The remaining five patients, showing response at only one of the two visits, were considered inconsistent responders. None of the individuals showed a consistent response to both B and C Gag peptides. Marginally significant correlation was observed between consistency of the response and lower plasma viral load (p = 0.062). The subtype-specific Gag C response was also found to be correlated with lower viral load as compared with the response to Gag B (r = -0.336, p = 0.054 for subtype C and r = -0.234, p = 0.13 for subtype B). The data suggest that the patients exhibiting consistent subtype-specific responses to HIV-1 Gag might have better control of viral replication in early HIV infection.     

HIV rebound after discontinuation of antiretroviral therapy increases and expands HIV-specific CD8+ responses but has no impact on its functionality

A higher functionality of CD8(+) T cells might contribute to low-level HIV replication in long-term nonprogressors (LTNPs). However, the contrary could also be true, being the function of CD8(+) T cells modulated by HIV replication. We tested whether enhanced HIV replication following antiretroviral therapy interruption could modify the functional profile of HIV-specific CD8(+) responses. Production of MIP-1beta, IL-2, TNF-alpha, and CD107 expression by CD8(+) T cells in response to Gag and Nef optimal peptide pools was analyzed using polychromatic flow cytometry in nine HIV-infected individuals followed for 12 months after discontinuation of antiretroviral therapy. At baseline, CD8(+) T cell subsets with the greatest contribution to response were MIP-beta(+)TNF-alpha(-)IL-2(-)CD107(+) and MIP-beta(+)TNF-alpha(-)IL-2(-)CD107. Most responses were mediated by subsets expressing only one or two molecules. After 12 months of discontinuing antiretroviral therapy, no significant differences were observed in the functional profile of Gag- and Nef-specific CD8(+) responses. However, viral rebound induced a significant increase in the heterogeneity of Gag-specific CD8(+) responses. In summary, viral replication following discontinuation of antiretroviral therapy has no significant impact on qualitative aspects of HIV-specific CD8(+) responses. Thus, a higher functionality of CD8(+) responses does not seem to be the consequence of low-level virus replication.     

Inverse correlation between memory Gag-specific cytotoxic T lymphocytes and viral replication in human immunodeficiency virus-infected children

A previous study showed that, during the first year of life, the presence of cytotoxic T lymphocytes (CTLs) in human immunodeficiency virus (HIV)-infected children is associated with a lack of rapid progression to acquired immunodeficiency syndrome. The goal of the study was to address the role of CTLs in children who survived after age 5 years. Memory HIV-specific CTLs directed against Env, Gag, Nef, and Pol proteins were measured in a group of 47 highly active antiretroviral therapy-naive HIV-infected children. Both Gag- and Pol-specific CTLs were positively correlated with CD4(+) T cell counts. Gag-, Nef-, and Pol-specific CTLs were inversely correlated with virus load. The inverse correlation between virus load and Gag-specific CTLs was independent of CD4(+) T cell counts. In conclusion, this study showed the beneficial role of HIV-specific CTLs in children who survived after age 5 years.     

Detection of HIV type 1 gag-specific CD4(+) T cell responses in acutely infected infants

Multiple HIV-1-specific cytokine and proliferative responses by CD4(+) T cells have not been studied in acutely infected infants. Using an intracellular cytokine staining assay, 34 untreated clade C HIV-1-infected infants (2-102 days old) were assessed for IFN-gamma, 28/34 for IL-2, and 26/34 for TNF-alpha responses to all HIV-1 proteins. Responses were detected in 29%, 36%, and 15% of infants, respectively. Twelve of the original 34 infants were then studied longitudinally for 14 months to determine the effect of viral load on IFN-gamma Gag-specific responses: seven infants were treated for 1 year, stopped treatment, and resumed when CD4% was < 20 and five infants were treated only when the CD4% was <20. Following treatment cessation, there was an immediate increase in viral load followed by an increase in the magnitude of CD4(+) Gag-specific responses. Despite this, the majority of infants (54%) had to restart treatment by 24 months of age, indicating that the immune responses were antigen driven but not associated with protection. Among untreated infants HIV-specific CD4(+) responses were detected sporadically indicating a dysfunctional immune response in the face of constant exposure to high levels of viremia.     

Higher frequency of HIV-1-specific T cell immune responses in African American children vertically infected with HIV-1

The progression of human immunodeficiency virus (HIV) disease and plasma levels of HIV may differ between racial groups. We compared HIV-specific T cell responses between vertically HIV-1-infected Hispanic and African American children. Subjects were matched for sex, age, viral load, and CD4(+) cell count in 18 pairs; T cell responses were measured by cytokine-enhanced interferon- gamma assay. Peripheral blood mononuclear cells were stimulated with HIV consensus peptides from Gag, Nef, and Tat. The influence of ethnicity, sex, age, viral load, and CD4(+) cell count on T cell responses was determined through linear regression analyses. After adjustment for CD4(+) count, age, and log(10) viral load, African American children demonstrated significantly higher Gag responses (average, 486 spot-forming cells higher; P=.01) than Hispanic children; this was significantly driven by robust responses in African American girls near the age of puberty, many of whom carried the human leukocyte antigen class I B*58 allele.     

Association of Gag-specific T lymphocyte responses during the early phase of human immunodeficiency virus type 1 infection and lower virus load set point

T lymphocyte responses to human immunodeficiency virus (HIV) type 1 Gag were measured in 9 patients by interferon-gamma enzyme-linked immunospot assay at 3 time points within 12 months of infection. Patients with early recognition of HIV-1 Gag had lower subsequent HIV-1 load set points, as measured during the first 2 years of infection, compared with those of patients with undetectable Gag-specific responses (median, 4.27 vs. 5.05 log(10) HIV-1 RNA copies/mL, respectively; P=.028). An inverse correlation existed between the magnitude of the Gag-specific responses and the HIV-1 load set point (r=-0.733; P=.025). Early sustained T lymphocyte responses to HIV-1 Gag may be important for the establishment of virus load set point.     

Characterization of HIV-specific proliferative T cell responses in HIV-infected persons

Virus-specific helper T cell responses are thought to be an important host defense in HIV infection. The proliferative responses to HIV p24, p55, and gp120 were tested in a cohort of 27 HIV-infected subjects. Vigorous proliferative responses directed at the Gag protein with stimulation indices in excess of 6 were detected in 10 of the individuals tested but an Env-specific response was present in only 1 subject. Viral load and proliferative activity to Gag were inversely correlated in untreated individuals. Proliferation was also observed in some individuals treated in the chronic phase of infection, and responses were maintained over time in the absence of detectable viremia. Positive proliferative responses could also occasionally be detected in treated persons with CD4(+) cell counts below 200/microl. Thus, vigorous Gag-specific proliferative responses are present in a minority of HIV-infected individuals and can be detected in individuals receiving highly active antiretroviral therapy at advanced disease stages. Proliferative responses are maintained for an extended time period in the presence of antiviral therapy.     

Prognostic value of HIV-1 Gag-specific CD4+ T-cell responses for progression to AIDS analyzed in a prospective cohort study

The causal relationship between HIV-specific CD4+ T-cell responses and viral control and the effect of these responses on the natural history of HIV infection is unclear. In a detailed longitudinal study, functional HIV-1 Gag-specific CD4+ T cells were analyzed in long-term asymptomatic individuals (LTA; n = 6) and progressors to AIDS (n = 7) with a median follow-up of, respectively, 118 and 57 months. Next, HIV-specific CD4+ T-helper cell responses were measured in a prospective cohort study among 96 HIV seroconverters and were related to clinical endpoints using Cox proportional hazard analyses. In the detailed study, no difference for HIV-specific helper-cell responses between LTAs and progressors was observed early in infection, but Gag-specific CD4+ T cells producing IL-2 or IFNgamma were lost in progressors late in infection. Multivariate proportional hazard analyses in the prospective cohort study showed that HIV-specific IL-2+, IFNgamma+, or IL-2+IFNgamma+ CD4+ T cells early after seroconversion had no prognostic value for the rate of progression to AIDS. Our results are compatible with viral load determining the nature and magnitude of HIV-specific CD4+ T-cell responses, rather than HIV-specific CD4+ T-cell responses controlling HIV plasma viral load.     

Presence of distinct subsets of cytolytic CD8+ T cells in chronic HIV infection

Cytolytic T lymphocytes (CTL) play an important role in the control of HIV infection. The eventual failure to contain HIV-1 infection may arise because of a functional impairment of HIV-specific CTL. We evaluated Gag-specific cytotoxicity in HIV-1-positive Ugandans. Expression of CD107, a marker for cytolytic activity, was present in CD45RA(bright) and CD45RA(dim) CD8(+) T cell populations in HIV-infected individuals. The frequency of Gag-specific CD107(+)CD45RA(bright)CD28(-)CCR7(-) CD8(+) T cells decreased with CD4 cell depletion and correlated with the presence of Gag-specific T helper response. In contrast, the frequency of Gag-specific CD107(+)CD45RA(dim)CD28(-)CCR7(-) CD8(+) T cells within the same individuals has no significant association with viral load or CD4 cell count. The ratio of CD45RA(bright) to CD45RA(dim) CTL correlates significantly with CD4 cell count. This positive association decreases with antiretroviral treatment (ARV), indicating that suppression of viral replication alters the balance of circulating Gag-specific CD8(+) effector T cells. Subsets of cytolytic T cells may have distinct antiviral functions and further characterization of these effector CD8(+) T cells may yield important information on T cell regulation and dysfunction in HIV infection.     

Differential immunogenicity of HIV-1 clade C proteins in eliciting CD8+ and CD4+ cell responses

BACKGROUND: The relative immunogenicity of human immunodeficiency virus type 1 (HIV-1) proteins for CD8+ and CD4+ cell responses has not been defined. METHODS: HIV-1-specific T cell responses were evaluated in 65 chronically HIV-1-infected untreated subjects by interferon- gamma flow cytometry with peptides spanning the clade C consensus sequence. RESULTS: The magnitude of HIV-1-specific CD8+ T cell responses correlated significantly with CD4+ cell responses, but the percentage of CD8+ T cells directed against HIV-1 (median, 2.76%) was always greater than that of CD4+ cells (median, 0.24%). Although CD8+ T cell responses were equally distributed among Gag, Pol, and the regulatory and accessory proteins, Gag was the dominant target for CD4+ cell responses. There was no consistent relationship between virus-specific CD8+ or CD4+ cell response and viral load. However, the median viral load in subjects in whom Gag was the dominant CD8+ T cell target was significantly lower than that in subjects in whom non-Gag proteins were the main target (P=.007). CONCLUSIONS: Gag-specific responses dominate the CD4+ T cell response to HIV, whereas CD8+ T cell responses are broadly distributed, which indicates differential immunogenicity of these cells against HIV-1. The preferential targeting of Gag by CD8+ T cells is associated with enhanced control of viral load.     

Quantification of HIV-specific CD8 T cells by in vitro stimulation with inactivated viral particles

OBJECTIVES: HIV-specific CD8 T cells play a central role in the immune control of virus replication. To further understand the role of CD8 T cells in clinical settings, there is a need for a diagnostic assay that quantifies HIV-specific CD8 T cells in all HIV-infected individuals. DESIGN: and methods: The CD8VIR (CD8 T cell-mediated virus-specific immune response) assay was designed to mimic viral load rebound by adding replication defective HIV particles to peripheral blood mononuclear cells. Antigen presenting cells processed the virus and presented most of the viral epitopes to T cells. Activated HIV-specific CD8 T cells were quantified by flow cytometry analysis as CD3CD8 IFNgamma producing T cells. RESULTS: The CD8VIR assay reproducibly detected a large proportion of functional HIV-specific CD8 T cells responding to viral load rebound. The whole HIV particle stimulation used in the CD8VIR assay was comparable to the sum of Gag, Pol, Env and Nef stimulations. The percentage of HIV-specific CD8 T cells also significantly correlated with the percentage of Gag-specific cytotoxicity measured by the traditional Cr release assay. HIV-specific CD8 T cells correlated with immune control of HIV in chronically infected patients. CONCLUSIONS: The CD8VIR assay quantifies the majority of HIV-specific CD8 T cells capable of killing HIV-infected cells during viral load rebound. This simple, versatile and reproducible assay can be performed from the specimen submitted for CD4 analysis. Upon clinical validation, the CD8VIR assay can be a new diagnostic tool to predict the control of viral load rebound after treatment interruption.     

A dendritic cell-based vaccine for treating HIV infection: background and preliminary results

Antibody response against human immunodeficiency virus-1 (HIV) is ineffective and cellular immune response is not strong enough to achieve the complete suppression or at least a strong control of viral replication in HIV- infected patients. In 2001, we showed in vitro that dendritic cells (DCs) of HIV-infected patients loaded with autologous HIV chemically inactivated by aldrithiol-2 were capable of raising an HIV-specific cellular immune response powerful enough to allow the destruction of autologous HIV- infected CD4 T cells. In 2003, we showed that simian immunodeficiency virus (SIV)-infected macaques vaccinated with inactivated SIV-loaded autologous DCs raised a strong SIV-specific cellular response. Ten months after vaccination, plasma viral load of 7 out of the 10 vaccinated monkeys remained 1000-fold lower than initially. In December 2004, we published results observed in 18 untreated HIV-infected patients vaccinated with autologous monocyte-derived DCs loaded with autologous inactivated HIV. A year following vaccination, 8 patients had a plasma viral load decrease >90%; among them, 4 had viral load <1000 copies mL(-1). Moreover, by one year, the viral load decline of the 18 patients was significantly correlated with their percentage of HIV-1-gag-specific CD8(+) T cells expressing perforin and that of HIV-1-specific CD4(+) T(H)1 cells. This is the first demonstration of the capacity of a therapeutic vaccine to induce an effective HIV-specific T cell response associated with sustained viral suppression in untreated viremic patients. The manipulation of antigen presenting cells to elicit virus-specific cellular responses is a promising tool to control persistant viral infections.     

Association of HIV-1 load and CD4 lymphocyte count with mortality among untreated African children over one year of age

OBJECTIVE: To examine the association of viral load and CD4 lymphocyte count with mortality among HIV-infected children over one year of age. DESIGN: A prospective study. HIV-infected children were enrolled during the first year of life and followed for more than 2 years at the Queen Elizabeth Central Hospital in Blantyre, Malawi (southeast Africa). METHODS: Morbidity and mortality information was collected every 3 months, and physical examination and blood testing (for viral level and CD4 cell percentage) were performed every 6 months. Kaplan-Meier analyses and proportional hazards models were used to estimate survival and to examine the association of primary predictors with mortality. RESULTS: Of 155 HIV-infected children originally enrolled, 115 (74%) had viral load testing and 82 (53%) had both viral load and CD4 cell percentage testing after their first year. Among children over one year of age, significant associations were found between mortality and the log10 viral load and CD4 cell percentage in both univariate and multivariate models. Independent of the CD4 cell value, a one unit log10 increase in HIV RNA level increased the hazard of child mortality by more than twofold. Children with low CD4 cell counts (< 15%) and high viral loads (> or = 250,000 copies/ml median value) had the worst survival; children with high CD4 cell counts (> or = 15%) and low viral loads (< 250,000 copies/ml) had the best survival. CONCLUSION: As in developed countries, viral load and CD4 cell count are the main predictors of mortality among African children. Making these tests available adds to the challenges to be considered if antiviral therapies were to be adopted in these countries.     

Immunization with HIV Gag targeted to dendritic cells followed by recombinant New York vaccinia virus induces robust T-cell immunity in nonhuman primates

Protein vaccines, if rendered immunogenic, would facilitate vaccine development against HIV and other pathogens. We compared in nonhuman primates (NHPs) immune responses to HIV Gag p24 within 3G9 antibody to DEC205 ("DEC-HIV Gag p24"), an uptake receptor on dendritic cells, to nontargeted protein, with or without poly ICLC, a synthetic double stranded RNA, as adjuvant. Priming s.c. with 60 μg of both HIV Gag p24 vaccines elicited potent CD4(+) T cells secreting IL-2, IFN-γ, and TNF-α, which also proliferated. The responses increased with each of three immunizations and recognized multiple Gag peptides. DEC-HIV Gag p24 showed better cross-priming for CD8(+) T cells, whereas the avidity of anti-Gag antibodies was ～10-fold higher with nontargeted Gag 24 protein. For both protein vaccines, poly ICLC was essential for T- and B-cell immunity. To determine whether adaptive responses could be further enhanced, animals were boosted with New York vaccinia virus (NYVAC)-HIV Gag/Pol/Nef. Gag-specific CD4(+) and CD8(+) T-cell responses increased markedly after priming with both protein vaccines and poly ICLC. These data reveal qualitative differences in antibody and T-cell responses to DEC-HIV Gag p24 and Gag p24 protein and show that prime boost with protein and adjuvant followed by NYVAC elicits potent cellular immunity.     

HIV subtypes induce distinct profiles of HIV-specific CD8(+) T cell responses

CD8(+) T cells play an important role in controlling HIV infection and qualitative differences in HIV-specific CD8(+) responses may determine the degree of immune control. We studied 56 HIV-infected, ARV-naive Ugandans and examined the role of subtypes in modulating their HIV-specific T cell responses. Gag-specific responses were readily detectable in our study population. Interestingly, we found significantly decreased Gag-specific cytolysis (as measured by CD107 expression) in subtype D (n = 21) compared to subtype A (n = 35) HIV infection. Sequence analyses within identified epitopes suggest patterns of conservation that are subtype specific. We conclude that HIV subtypes may promote distinct profiles of T cells responses and immune control.     

Effect of prolonged discontinuation of successful antiretroviral therapy on CD4+ T cell decline in human immunodeficiency virus-infected patients: implications for intermittent therapeutic strategies

This study evaluates the change in CD4(+) T cell counts among patients who achieved complete viral suppression and subsequently discontinued highly active antiretroviral therapy (HAART). We included 72 human immunodeficiency virus (HIV)-1-infected patients with plasma HIV RNA loads of <500 copies/mL for at least 3 months who then discontinued therapy for at least 12 weeks. The median CD4(+) T decay while off HAART was 16 cells/mm(3)/month (interquartile range, -6 to -34 cells/month). The mean follow-up after therapy ended was 45 weeks. The slope of the CD4(+) T cell decay was inversely correlated with the increase of CD4(+) T cells while receiving HAART, baseline virus load, CD4(+) T cell count at the time therapy was discontinued, age, and duration HIV RNA levels were undetectable. In a multiple regression analysis model, the increase of CD4(+) T cells while receiving therapy and age were independently associated with the rate of CD4(+) T cell loss.     

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.     

Interruption of antiretroviral treatment in HIV-infected patients with preserved immune function is associated with a low rate of clinical progression: a prospective study by AIDS Clinical Trials Group 5170

BACKGROUND: We sought to determine the safety of treatment interruption (TI) and to identify parameters that would define patients with human immunodeficiency virus (HIV) for whom TI is safer. METHODS: AIDS Clinical Trials Group 5170 was a multicenter, 96-week-long, prospective study of HIV-infected patients receiving antiretroviral therapy (ART) who had CD4(+) cell counts >350 cells/mm(3) and who underwent TI. RESULTS: A total of 167 patients were enrolled. The median nadir in CD4(+) cell count was 436 cells/mm(3). The initial decrease (i.e., during the first 8 weeks) in CD4(+) cell count after ART interruption was 20 cells/mm(3)/week; the subsequent decrease was 2.0 cells/mm(3)/week until week 96. Both the CD4(+) cell count before enrollment and the increase in CD4(+) cell count during ART predicted early decrease; later decrease was predicted by the level of interleukin-7 at enrollment. A Centers for Disease Control and Prevention (CDC) diagnosis of a category B or C event was made for 2 and 2 patients, respectively (all had CD4(+) cell counts >350 cells/mm(3)). At week 96, 17 patients had CD4(+) cell counts < or =250 cells/mm(3), and 46 patients had resumed ART; 5 patients died (unrelated to HIV or acquired immunodeficiency syndrome). In a multivariate analysis, a higher nadir in CD4(+) cell count (>400 cells/mm(3)), a lower HIV load (<50 copies/mL) at the time of TI, and an HIV load < or =22,000 copies/mL before ART predicted a longer time to the primary end point (CDC category B or C event, death, CD4(+) cell count < or =250 cells/mm(3), or resumption of ART). CONCLUSION: Disease progression after TI was low in this cohort. A higher nadir in CD4(+) cell count, a lower HIV load before ART, and an HIV load < or =50 copies/mL at the time of TI predicted a longer time to the primary end point.