HIV-1-specific CD4+ T cell responses in chronically HIV-1 infected blippers on antiretroviral therapy in relation to viral replication following treatment interruption

Anti-Tat immunity defines CD4+ T-cell dynamics in people living with HIV on long-term cART

BACKGROUND

Low-level HIV viremia originating from virus reactivation in HIV reservoirs is often present in cART treated individuals and represents a persisting source of immune stimulation associated with sub-optimal recovery of CD4⁺ T cells. The HIV-1 Tat protein is released in the extracellular milieu and activates immune cells and latent HIV, leading to virus production and release. However, the relation of anti-Tat immunity with residual viremia, persistent immune activation and CD4⁺ T-cell dynamics has not yet been defined.

METHODS

Volunteers enrolled in a 3-year longitudinal observational study were stratified by residual viremia, Tat serostatus and frequency of anti-Tat cellular immune responses. The impact of anti-Tat immunity on low-level viremia, persistent immune activation and CD4⁺ T-cell recovery was investigated by test for partitions, longitudinal regression analysis for repeated measures and generalized estimating equations.

FINDINGS

Anti-Tat immunity is significantly associated with higher nadir CD4⁺ T-cell numbers, control of low-level viremia and long-lasting CD4⁺ T-cell recovery, but not with decreased immune activation. In adjusted analysis, the extent of CD4⁺ T-cell restoration reflects the interplay among Tat immunity, residual viremia and immunological determinants including CD8⁺ T cells and B cells. Anti-Env immunity was not related to CD4⁺ T-cell recovery.

INTERPRETATION

Therapeutic approaches aiming at reinforcing anti-Tat immunity should be investigated to improve immune reconstitution in people living with HIV on long-term cART.

TRIAL REGISTRATION

ISS OBS T-002 ClinicalTrials.gov identifier: NCT01024556 FUNDING: Italian Ministry of Health, special project on the Development of a vaccine against HIV based on the Tat protein and Ricerca Corrente 2019/2020.

Persistent Low-level Viremia While on Antiretroviral Therapy Is an Independent Risk Factor for Virologic Failure

BACKGROUND

Whether persistent low-level viremia (pLLV) predicts virologic failure (VF) is unclear. We used data from the US Military HIV Natural History Study (NHS), to examine the association of pLLV and VF.

METHODS

NHS subjects who initiated combination antiretroviral therapy (ART) after 1996 were included if they had 2 or more VLs measured with a lower limit of detection of ≤50 copies/mL. VF was defined as a confirmed VL ≥200 copies/mL or any VL >1000 copies/mL. Participants were categorized into mutually exclusive virologic categories: intermittent LLV (iLLV) (VL of 50-199 copies/mL on <25% of measurements), pLLV (VL of 50-199 copies/mL on ≥25% of measurements), high-level viremia (hLV) (VL of 200-1000 copies/mL), and continuous suppression (all VL <50 copies/mL). Cox proportional hazards models were used to evaluate the association between VF and LLV; hazard ratios and 95% confidence interval (CI) are presented.

RESULTS

Two thousand six subjects (median age 29.2 years, 93% male, 41% black) were included; 383 subjects (19%) experienced VF. After adjusting for demographics, VL, CD4 counts, ART regimen, prior use of mono or dual antiretrovirals, and time to ART start, pLLV (3.46 [2.42-4.93]), and hLV (2.29 [1.78-2.96]) were associated with VF. Other factors associated with VF include black ethnicity (1.33 [1.06-1.68]) and antiretroviral use prior to ART (1.79 [1.34-2.38]). Older age at ART initiation (0.71 [0.61-0.82]) and non-nucleoside reverse transcriptase inhibitor (0.68 [0.51-0.90]) or integrase strand transfer inhibitor use (0.26 [0.13-0.53]) were protective.

CONCLUSION

Our data add to the body of evidence that suggests persistent LLV is associated with deleterious virologic consequences.

Phylogenetic Analyses Comparing HIV Sequences from Plasma at Virologic Failure to Cervix Versus Blood Sequences from Antecedent Antiretroviral Therapy Suppression

Identifying tissue sources of HIV that rebound following "failure" of antiretroviral therapy (ART) is critical to evaluating cure strategies. To assess the role of the uterine cervix and peripheral blood mononuclear cells (PBMC) as viral reservoirs, nearest-neighbor phylogenetic analyses compared genetic relatedness of tissue sequences during ART suppression to those detected in plasma at viral rebound. Blood and genital tract specimens from a natural history cohort of HIV-infected women were collected over 5 years. HIV DNA sequences extracted from PBMC and cervical biopsies during ART suppression and plasma RNA from rebound (defined as HIV RNA >3 log₁₀ copies/mL) were derived by single-genome amplification. Phylogenetic and nearest-neighbor analyses of HIV env sequences and drug resistance in pol sequences were compared between tissues. Nine instances of plasma viral rebound (median HIV RNA 3.6 log₁₀ c/mL; IQR: 3.1-3.8) were detected in 7 of 57 women. Nearest-neighbor analyses found rebound plasma sequences were closer to uterine cervical sequences in 4/9 (44%), closer to PBMC in 3/9 (33%), and ambiguous in 2/9 (22%) cases. Rebound plasma clades (n = 27) shared identical sequences in seven instances with the cervix versus two with PBMC. Novel drug resistance mutations were detected in 4/9 (44%) rebounds. The observed tendency for greater sharing of identical HIV variants and greater nearest-neighbor association between rebounding plasma and uterine cervical versus PBMC sequences suggests that the uterine cervix may be a relevant HIV reservoir. The cervix, a readily accessible tissue in women that can be repeatedly sampled, could help assess the HIV reservoir when evaluating cure strategies.

Analytical antiretroviral therapy interruption does not irreversibly change preinterruption levels of cellular HIV

OBJECTIVE

The impact of short-term analytical treatment interruptions (ATI) on the levels of cellular HIV and of residual activation after subsequent antiretroviral therapy (ART)-mediated plasma HIV viral load re-suppression remains under active investigation.

DESIGN

Peripheral blood mononuclear cells (PBMC) from 23 ART-suppressed, chronically HIV-1-infected patients were evaluated at the initiation of an ATI, during ATI, and following plasma re-suppression of HIV with ART.

METHODS

T-cell activation was measured by flow cytometry. Total cellular HIV DNA, and episomal 2-long terminal repeat (2-LTR) circles were measured by droplet digital PCR (ddPCR). Cellular HIV multiply spliced RNA (tat/rev), unspliced (gag), and poly(A) tailed transcripts [poly(A)] were measured by reverse transcriptase-ddPCR. Analyses were performed using R version 2.5.1 or JMP Pro 11.

RESULTS

ATI (median ATI duration, 4 weeks) resulted in a rise of plasma HIV RNA (median = 72900 copies/ml), decrease in CD4+ T cells/μl (median = 511.5 cells/μl; P = 0.0001), increase in T-cell activation, and increase in cellular HIV DNA and RNA. Mean fluorescence intensity of CD38 on CD4+HLA-DR+ T cells at baseline was positively associated with total HIV DNA levels during ATI (pol: P = 0.03, Rho = 0.44). Upon ART resumption, plasma HIV re-suppression occurred after a median of 13 weeks and resulted in restoration of pre-ATI CD4+ T cells/μl, T-cell activation, and levels of cellular HIV DNA and RNA.

CONCLUSION

Monitored viremia and immune activation during an ATI in ART-suppressed chronic HIV-infected patients does not change the amount of persistent cellular HIV RNA or total HIV DNA after ART-mediated re-suppression.

Plasmacytoid dendritic cell and functional HIV Gag p55-specific T cells before treatment interruption can inform set-point plasma HIV viral load after treatment interruption in chronically suppressed HIV-1(+) patients

The identification of immune correlates of HIV control is important for the design of immunotherapies that could support cure or antiretroviral therapy (ART) intensification-related strategies. ART interruptions may facilitate this task through exposure of an ART partially reconstituted immune system to endogenous virus. We investigated the relationship between set-point plasma HIV viral load (VL) during an ART interruption and innate/adaptive parameters before or after interruption. Dendritic cell (DC), natural killer (NK) cell and HIV Gag p55-specific T-cell functional responses were measured in paired cryopreserved peripheral blood mononuclear cells obtained at the beginning (on ART) and at set-point of an open-ended interruption from 31 ART-suppressed chronically HIV-1(+) patients. Spearman correlation and linear regression modeling were used. Frequencies of plasmacytoid DC (pDC), and HIV Gag p55-specific CD3(+)  CD4(-)  perforin(+)  IFN-γ(+) cells at the beginning of interruption associated negatively with set-point plasma VL. Inclusion of both variables with interaction into a model resulted in the best fit (adjusted R(2)  = 0·6874). Frequencies of pDC or HIV Gag p55-specific CD3(+)  CD4(-)  CSFE(lo)  CD107a(+) cells at set-point associated negatively with set-point plasma VL. The dual contribution of pDC and anti-HIV T-cell responses to viral control, supported by our models, suggests that these variables may serve as immune correlates of viral control and could be integrated in cure or ART-intensification strategies.

Effects of different antigenic stimuli on thymic function and interleukin-7/CD127 system in patients with chronic HIV infection

BACKGROUND

We tested if an increase in immune activation and a decrease in CD4⁺ T cells induced by different antigenic stimuli could be associated with changes in the thymic function and the interleukin (IL)-7/CD127 system.

METHODS

Twenty-six HIV-infected patients under combined antiretroviral therapy (cART) were randomized to receive, during 12 months, a complete immunization schedule (7 vaccines and 15 doses) or placebo. Thereafter, cART was interrupted during 6 months. Changes in the thymic function and the IL-7/CD127 system after 3 different antigenic stimuli (vaccines, episodes of low-level intermittent viremia before cART interruption, or viral load rebound after cART interruption) were assessed.

RESULTS

During the period on cART, neither vaccines nor low-level viremia influenced thymic function or IL-7/CD127 system parameters. By analyzing the cohort as a whole while on cART, a significant improvement was observed in the thymic function as measured by an increase in the thymic volume (P = 0.024), T-cell receptor excision circle-bearing cells (P = 0.012), and naive CD4⁺ and CD8⁺ T cells (P = 0.069 both). No significant changes were observed in the IL-7/CD127 system. After cART interruption, a decrease in T-cell receptor excision circles (P < 0.001) and naive CD8⁺ T cells (P < 0.001), an increase in IL-7 and expression of CD127 on naive and memory CD4⁺ T cells (P = 0.028, P = 0.088, and P = 0.04, respectively), and a significant decrease in CD127 on naive and memory CD8⁺ T cells (P = 0.01, P = 0.006, respectively) were observed.

CONCLUSIONS

Low-level transient antigenic stimuli during cART were not associated with changes in the thymic function or the IL-7/CD127 system. Conversely, viral load rebound very early after cART interruption influenced the thymic function and the IL-7/CD127 system. Clinical Trials.gov number NCT00329251.

Residual viremia in patients on antiretroviral therapy incorporating nevirapine is not associated with the gag-specific cellular immune response

To determine whether residual plasma viremia in HIV(+) patients on nevirapine-including antiretroviral therapy (ART) is related to anti-HIV cellular immune responses, a case-control study was conducted comparing residual viremia in patients with detectable and undetectable Gag-specific T-cell responses. Gag-specific responses were measured by IFN-γ ELISpot. Residual viremia was determined at two consecutive hospital visits by an ultra-sensitive technique with a detection limit of 2 copies/ml. Median residual viremia was not different in patients with a positive Gag-specific ELISpot (n = 25) compared to those with a negative Gag-specific ELISpot (n = 30, P = 0.91). Ten of 25 (40%) patients with consistent detectable residual viremia and 4 of 12 (33%) patients with consistently undetectable residual viremia had a positive Gag-specific ELISpot. Undetectable residual viremia was associated with the duration of ART including nevirapine (P < 0.05), but not with the Gag-specific ELISpot response. Gag-specific CTL in patients on ART therefore appear to have no impact on the virus-producing cells that are responsible for residual viremia during ART.

Do HIV-specific CTL continue to have an antiviral function during antiretroviral therapy? If not, why not, and what can be done about it?

Pharmacological reactivation of human immunodeficiency virus (HIV) expression from latent proviruses coupled with fully suppressive antiretroviral therapy (ART) has been suggested as a strategy to eradicate HIV infection. In order for this strategy to be effective, latently infected cells must be killed either by the cytopathic effect of reactivated HIV gene expression, or by HIV-specific cytotoxic T lymphocyte (CTL). However, a review of current data reveals little evidence that CTL retain an antiviral effector capacity in patients on fully suppressive ART, implying that the HIV-specific CTL present in these patients will not be able to eliminate HIV-infected CD4(+) T cells effectively. If this is due to functional impairment or a quantitative deficit of HIV-specific CTL during ART, then therapeutic vaccination may improve the prospects for eradicating latent reservoirs. However, data from the macaque simian immunodeficiency virus (SIV) model indicate that in vivo, SIV-specific CTL are only effective during the early stages of the viral replication cycle, and this constitutes an alternative explanation why HIV-specific CTL do not appear to have an impact on HIV reservoirs during ART. In that case, immunotoxins that target HIV-expressing cells may be a more promising approach for HIV eradication.

Influence of episodes of intermittent viremia ("blips") on immune responses and viral load rebound in successfully treated HIV-infected patients

Presenting episodes of intermittent viremia (EIV) under combination antiretroviral therapy (cART) is frequent, but there exists some controversy about their consequences. They have been described as inducing changes in immune responses potentially associated with a better control of HIV infection. Conversely, it has been suggested that EIV increases the risk of virological failure. A retrospective analysis of a prospective, randomized double-blinded placebo-controlled study was performed. Twenty-six successfully treated HIV-infected adults were randomized to receive an immunization schedule or placebo, and after 1 year of follow-up cART was discontinued. The influence of EIV on T cell subsets, HIV-1-specific T cell immune responses, and viral load rebound, and the risk of developing genotypic mutations were evaluated, taking into account the immunization received. Patients with EIV above 200 copies/ml under cART had a lower proportion of CD4(+) and CD4(+)CD45RA(+)RO(-) T cells, a higher proportion of CD8(+) and CD4(+)CD38(+)HLADR(+) T cells, and higher HIV-specific CD8(+) T cell responses compared to persistently undetectable patients. After cART interruption, patients with EIV presented a significantly higher viral rebound (p=0.007), associated with greater increases in HIV-specific lymphoproliferative responses and T cell populations with activation markers. When patients with EIV between 20 and 200 copies/ml were included, most of the differences disappeared. Patients who present EIV above 200 copies/ml showed a lower CD4(+) T cell count and higher activation markers under cART. After treatment interruption, they showed greater specific immune responses against HIV, which did not prevent a higher virological rebound. EIV between 20 and 200 copies/ml did not have this deleterious effect.

Increased microbial translocation in ≤ 180 days old perinatally human immunodeficiency virus-positive infants as compared with human immunodeficiency virus-exposed uninfected infants of similar age

BACKGROUND

The effect of early versus deferred antiretroviral treatment (ART) on plasma concentration of lipopolysaccharide (LPS) and host LPS-binding molecules in human immunodeficiency virus (HIV)-infected infants up to 1 year of age was investigated.

METHODS

We evaluated 54 perinatally HIV-infected and 22 HIV-exposed uninfected infants (controls) at the first and second semester of life. All HIV-infected infants had a baseline CD4 of ≥ 25%, participated in the Comprehensive International Program of Research on AIDS Children with HIV Early Antiretroviral Therapy trial in South Africa, and were randomized in the following groups: group 1 (n = 20), ART deferred until CD4 < 25% or severe HIV disease; and group 2 (n = 34), ART initiation within 6 to 12 weeks of age. LPS, endotoxin-core antibodies, soluble CD14 (sCD14), and LPS-binding protein (LBP) were measured in cryopreserved plasma. T-cell activation was measured in fresh whole blood.

RESULTS

At the first semester, LPS concentration was higher in HIV-infected infants than in controls; sCD14, LBP, and T-cell activation were higher in group 1 than in group 2 and controls. Although LPS was not correlated with study variables, viral load was positively associated with sCD14, LBP, or endotoxin-core antibodies. At the second semester, LPS was not detectable and elevated host LPS-control molecules values were sustained in all groups and in conjunction with ART in all HIV-infected infants.

CONCLUSIONS

Although plasma concentration of LPS was higher in perinatally HIV-infected infants 0 to 6 months of age than in controls independent of ART initiation strategy, concentration of LPS-control molecules was higher in infants with deferred ART, suggesting the presence of increased microbial translocation in HIV-infected infants with sustained early viral replication.

SIV antigen immunization induces transient antigen-specific T cell responses and selectively activates viral replication in draining lymph nodes in retroviral suppressed rhesus macaques

Background

HIV infection causes a qualitative and quantitative loss of CD4⁺ T cell immunity. The institution of anti-retroviral therapy (ART) restores CD4⁺ T cell responses to many pathogens, but HIV-specific responses remain deficient. Similarly, therapeutic immunization with HIV antigens of chronically infected, ART treated subjects results in poor induction of HIV-specific CD4 responses. In this study, we used a macaque model of ART treatment during chronic infection to study the virologic consequences of SIV antigen stimulation in lymph nodes early after immunization. Rhesus CMV (RhCMV) seropositive, Mamu A*01 positive rhesus macaques were chronically infected with SIVmac251 and treated with ART. The immune and viral responses to SIV gag and RhCMV pp65 antigen immunization in draining lymph nodes and peripheral blood were analyzed. Animals were immunized on contralateral sides with SIV gag and RhCMV pp65 encoding plasmids, which allowed lymph nodes draining each antigen to be obtained at the same time from the same animal for direct comparison.

Results

We observed that both SIV and RhCMV immunizations stimulated transient antigen-specific T cell responses in draining lymph nodes. The RhCMV-specific responses were potent and sustained (50 days post-immunization) in the periphery, while the SIV-specific responses were transient and extinguished quickly. The SIV antigen stimulation selectively induced transient SIV replication in draining lymph nodes.

Conclusions

The data are consistent with a model whereby viral replication in response to SIV antigen stimulation limits the generation of SIV antigen-specific responses and suggests a potential mechanism for the early loss and poor HIV-specific CD4⁺ T cell response observed in HIV-infected individuals.

Treatment interruption in chronic HIV-1 infection: does it deliver?

PURPOSE OF REVIEW

This review sets out to overview treatment interruption in chronic HIV-1 infection: what treatment interruption promised, results from recent trials, and what the future holds.

RECENT FINDINGS

Recent studies have produced mixed results; several trials have been prematurely halted, whereas others have reported more positive outcomes. One consistent finding has been the identification of the CD4 T-cell count nadir as a critical parameter in determining the outcome of treatment interruption.

SUMMARY

The use of treatment interruption is still controversial, but it is becoming clear that certain individuals could benefit, and partial treatment interruption strategies warrant further investigation.

Influence of a vaccination schedule on viral load rebound and immune responses in successfully treated HIV-infected patients

Vaccination is recommended for HIV-infected patients. Transient increases of viral load (VL) and risk of developing resistance to HAART have been described. In addition, VL rebounds could increase HIV-specific immune responses. Twenty-six successfully treated HIV-infected adults were randomized to receive a vaccination schedule or placebo during 12 months. Afterward, HAART was discontinued. Influences of vaccination over VL, genotypic mutations, different T cell subsets, and HIV-1-specific immune responses were evaluated. Patients did not present any secondary effect. No differences in incidence of detectable VL determinations were detected between groups [relative risk 0.54 (95% CI 0.23-1.26)]. No relevant resistance mutations were detected. The vaccinated group showed a significant drop in CD4(+) T cells (p = 0.046) associated with increases in activated T cells. HIV-1-specific lymphoproliferative responses increased more in the vaccinated group during the vaccination period. Viral rebound dynamics after interrupting HAART were similar in both groups. A vaccination schedule in successfully treated HIV patients was safe, was not associated with an increase in detectable VL, and did not increase the risk of developing resistance mutations. However, it induced an increase in T cell activation and a drop in CD4(+) T cells, although these changes did not influence the VL rebound dynamics after HAART interruption.

Delayed loss of control of plasma lipopolysaccharide levels after therapy interruption in chronically HIV-1-infected patients

OBJECTIVE

Increased circulating levels of lipopolysaccharide (LPS) have been demonstrated in HIV-1-infected progressors. We investigated the effect of antiretroviral therapy (ART) interruptions on plasma LPS levels.

DESIGN AND METHODS

Overall, 77 individuals participated in this study (51 HIV-positive and 26 healthy). Ten out of 51 HIV-positive participants were viremic ART-naive patients and 41 out of 51 were chronically suppressed patients on ART (three or more drugs, CD4 cell count more than 400 cells/microl, HIV-1 RNA less than 500 copies/ml for more than 8 months, less than 50 copies/ml at recruitment) undergoing therapy interruption. The limulus amebocyte assay was used to measure plasma LPS levels; enzyme-linked immunosorbent assay to measure plasma levels of endotoxin-core antibodies (EndoCAb), soluble (s)CD14, LPS-binding protein and IFN-alpha; immunoblotting to measure plasma gelsolin levels; and same day whole blood flow cytometry to measure levels of T-cell-activation markers (CD8/CD38, CD8/HLA-DR and CD3/CD95).

RESULTS

Increases in viremia and T-cell-activation markers were observed during therapy interruptions. During short-term therapy interruptions of less than 12 weeks, no change in LPS levels was found, whereas negative associations between viral load and LPS levels (Spearman's Rho = -0.612, P = 0.0152), viral load and EndoCAb change (DeltaEndoCAb, correlation = -0.502, P = 0.0204), and between DeltaLPS and DeltaEndoCAb (correlation = -0.851, P = 0.0073) were observed. In contrast, increased LPS (P = 0.0171) and sCD14 (P < 0.0001) levels were observed during long-term therapy interruption of more than 12 weeks compared with levels during ART, together with no association between LPS and viral load or EndoCAb. No association between immune activation and LPS was evident at any time point.

CONCLUSION

Increased plasma LPS levels were observed only after more than 12 weeks of ART interruption, despite presence of LPS-controlling host mechanisms.

Determinants of Virological Failure after Successful Viral Load Suppression in First-Line Highly Active Antiretroviral Therapy

Background

We aimed to investigate the long-term virological outcomes of a cohort initially showing good responses to first-line highly active antiretroviral therapy (HAART) with no evidence of virological failure during the first year after achieving viral load (VL) undetectability (<50 copies/ml).

Methods

Virological failure was defined as a confirmed VL>400 copies/ml or a single VL>400 copies/ml followed by a treatment change or end of follow-up. Risk factors for low-level VL rebound (50–400 copies/ml) in the first year after achieving undetectability and for virological failure during subsequent follow-up were investigated by logistic and Poisson regression.

Results

In the first year after achieving VL undetectability, 354/1,386 (25.5%) patients experienced low-level VL rebound, the remaining patients maintained consistent undetectability. Low-level rebound occurred less commonly with non-nucleoside reverse transcriptase inhibitor (NNRTI)-based HAART than with other regimens ( P=0.01). Over median 2.2 (range 0.0–7.4) years of subsequent follow-up, 86 (6.2%) patients experienced virological failure, corresponding to 2.30 failures per 100 person-years (95% confidence interval [CI] 1.82–2.79). Independent predictors of virological failure included low-level rebound during the first year after achieving undetectability relative to consistent undetectability (rate ratio [RR] 2.18, 95% CI 1.15–4.10), female gender (RR 1.79, 95% CI 1.12–2.85) and receiving a ritonavir-boosted protease inhibitor (PI/r) relative to NNRTI-based HAART (RR 1.88, 95% CI 1.02–3.46).

Conclusions

Patients on first-line HAART who maintain consistent VL undetectability for 1 year have a low risk of subsequent virological failure. A subset might benefit from targeted interventions, including women and patients on PI/r-based HAART.

HLA class I-restricted T-cell responses may contribute to the control of human immunodeficiency virus infection, but such responses are not always necessary for long-term virus control

A rare subset of human immunodeficiency virus (HIV)-infected individuals maintains undetectable HIV RNA levels without therapy ("elite controllers"). To clarify the role of T-cell responses in mediating virus control, we compared HLA class I polymorphisms and HIV-specific T-cell responses among a large cohort of elite controllers (HIV-RNA < 75 copies/ml), "viremic" controllers (low-level viremia without therapy), "noncontrollers" (high-level viremia), and "antiretroviral therapy suppressed" individuals (undetectable HIV-RNA levels on antiretroviral therapy). The proportion of CD4(+) and CD8(+) T cells that produce gamma interferon (IFN-gamma) and interleukin-2 (IL-2) in response to Gag and Pol peptides was highest in the elite and viremic controllers (P < 0.0001). Forty percent of the elite controllers were HLA-B*57 compared to twenty-three percent of viremic controllers and nine percent of noncontrollers (P < 0.001). Other HLA class I alleles more common in elite controllers included HLA-B*13, HLA-B*58, and HLA-B*81 (P < 0.05 for each). Within elite and viremic controller groups, those with protective class I alleles had higher frequencies of Gag-specific CD8(+) T cells than those without these alleles (P = 0.01). Noncontrollers, with or without protective alleles, had low-level CD8(+) responses. Thus, certain HLA class I alleles are enriched in HIV controllers and are associated with strong Gag-specific CD8(+)IFN-gamma(+)IL-2(+) T cells. However, the absence of evidence of T cell-mediated control in many controllers suggests the presence of alternative mechanisms for viral control in these individuals. Defining mechanisms for virus control in "non-T-cell controllers" might lead to insights into preventing HIV transmission or preventing virus replication.