Analysis of total human immunodeficiency virus (HIV)-specific CD4(+) and CD8(+) T-cell responses: relationship to viral load in untreated HIV infection

Human immunodeficiency virus (HIV)-specific T-cell responses are thought to play a key role in viral load decline during primary infection and in determining the subsequent viral load set point. The requirements for this effect are unknown, partly because comprehensive analysis of total HIV-specific CD4(+) and CD8(+) T-cell responses to all HIV-encoded epitopes has not been accomplished. To assess these responses, we used cytokine flow cytometry and overlapping peptide pools encompassing all products of the HIV-1 genome to study total HIV-specific T-cell responses in 23 highly active antiretroviral therapy na?ve HIV-infected patients. HIV-specific CD8(+) T-cell responses were detectable in all patients, ranging between 1.6 and 18.4% of total CD8(+) T cells. HIV-specific CD4(+) T-cell responses were present in 21 of 23 patients, although the responses were lower (0.2 to 2.94%). Contrary to previous reports, a positive correlation was identified between the plasma viral load and the total HIV-, Env-, and Nef-specific CD8(+) T-cell frequency. No correlation was found either between viral load and total or Gag-specific CD4(+) T-cell response or between the frequency of HIV-specific CD4(+) and CD8(+) T cells. These results suggest that overall frequencies of HIV-specific T cells are not the sole determinant of immune-mediated protection in HIV-infection.     

Transient mobilization of human immunodeficiency virus (HIV)-specific CD4 T-helper cells fails to control virus rebounds during intermittent antiretroviral therapy in chronic HIV type 1 infection

Immune control of human immunodeficiency virus (HIV) is not restored by highly active antiretroviral therapies (HAART) during chronic infection. We examined the capacity of repeated structured therapeutic interruptions (STI) to restore HIV-specific CD4 and CD8 T-cell responses that controlled virus production. Eleven STI (median duration, 7 days; ranges, 4 to 24 days) were performed in three chronically HIV-infected patients with CD4 counts above 400/mm(3) and less than 200 HIV RNA copies/ml after 18 to 21 months of HAART; treatment resumed after 1 week or when virus became detectable. HIV-specific T-cell responses were analyzed by proliferation, gamma interferon (IFN-gamma) production, and enzyme-linked immunospot assays. Seven virus rebounds were observed (median, 4,712 HIV-1 RNA copies/ml) with a median of 7 days during which CD4 and CD8 counts did not significantly change. After treatment resumed, the viral load returned below 200 copies/ml within 3 weeks. Significant CD4 T-cell proliferation and IFN-gamma production against HIV p24 appeared simultaneously with or even before the virus rebounds in all patients. These CD4 responses lasted for less than 3 weeks and disappeared before therapeutic control of the virus had occurred. Increases in the numbers of HIV-specific CD8 T cells were delayed compared to changes in HIV-specific CD4 T-cell responses. No delay or increase in virus doubling time was observed after repeated STI. Iterative reexposure to HIV during short STI in chronically infected patients only transiently mobilized HIV-specific CD4 T1-helper cells, which might be rapidly altered by virus replication. Such kinetics might explain the failure at delaying subsequent virus rebounds and raises concerns about strategies based on STI to restore durable HIV-specific T-cell responses in chronic HIV infection.     

The duration of exposure to HIV modulates the breadth and the magnitude of HIV-specific memory CD4+ T cells

The impact of exposure to Ag on the development and maintenance of human CD4(+) memory T cells in general and HIV infection in particular is partially understood. In this study, we measured HIV-specific CD4(+) T cell proliferative responses against HIV proteins and derived peptides one year after highly active antiretroviral therapy initiation in 39 HIV-infected patients who initiated therapy at different times following infection. We show that a brief exposure to HIV of <1 month does not allow the generation of significant detectable frequencies of HIV-specific CD4(+) memory T cells. Patients having prolonged cumulative exposure to high viral load due to therapy failures also demonstrated limited HIV-specific CD4(+) T cell responses. In contrast, patients exposed to significant levels of virus for periods ranging from 3 to 18 mo showed brisk and broad HIV-specific CD4(+) T cell responses 1 year following the onset of therapy intervention. We also demonstrate that the nadir CD4(+) T cell count before therapy initiation correlated positively with the breadth and magnitude of these responses. Our findings indicate that the loss of proliferative HIV-specific CD4(+) T cell responses is associated with the systemic progression of the disease and that a brief exposure to HIV does not allow the establishment of detectable frequencies of HIV-specific memory CD4(+) T cells.     

CD8+ T cells specific for EBV, cytomegalovirus, and influenza virus are activated during primary HIV infection

Primary viral infections, including primary HIV infection, trigger intense activation of the immune system, with marked expansion of CD38(+)CD8(+) T cells. Whether this expansion involves only viral-specific cells or includes a degree of bystander activation remains a matter of debate. We therefore examined the activation status of EBV-, CMV-, and influenza virus (FLU)-specific CD8(+) T cells during primary HIV infection, in comparison to HIV-specific CD8(+) T cells. The activation markers CD38 and HLA-DR were strongly expressed on HIV-specific CD8(+) T cells. Surprisingly, CD38 expression was also up-regulated on CD8(+) T cells specific for other viruses, albeit to a lesser extent. Activation marker expression returned to normal or near-normal values after 1 year of highly active antiretroviral therapy. HIV viral load correlated with CD38 expression on HIV-specific CD8(+) T cells but also on EBV-, CMV-, and FLU-specific CD8(+) T cells. In primary HIV infection, EBV-specific CD8(+) T cells also showed increased Ki67 expression and decreased Bcl-2 expression, compared with values observed in HIV-seronegative control subjects. These results show that bystander activation occurs during primary HIV infection, even though HIV-specific CD8(+) T cells express the highest level of activation. The role of this bystander activation in lymphocyte homeostasis and HIV pathogenesis remains to be determined.     

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.     

Multifunctional human immunodeficiency virus (HIV) gag-specific CD8+ T-cell responses in rectal mucosa and peripheral blood mononuclear cells during chronic HIV type 1 infection

The intestinal tract is a lymphocyte-rich site that undergoes severe depletion of memory CD4(+) T cells within days of simian immunodeficiency virus or human immunodeficiency virus type 1 (HIV-1) infection. An ensuing influx of virus-specific CD8(+) T cells, which persist throughout the chronic phase of infection, has also been documented in the gastrointestinal tract. However, little is known of the functionality of these effector cells or their relationship to the disease course. In this study, we measured CD8(+) T-cell responses to HIV-1 peptides in paired rectal and blood samples from chronically infected patients. In both blood and rectum, there was an immunodominant CD8(+) T-cell response to HIV Gag compared to Pol and Env (P < 0.01). In contrast, cytomegalovirus pp65 peptides elicited gamma interferon (IFN-gamma) secretion strongly in peripheral blood mononuclear cells (PBMC) but weakly in rectal CD8(+) T cells (P = 0.015). Upon stimulation with HIV peptides, CD8(+) T cells from both sites were capable of mounting complex responses including degranulation (CD107 expression) and IFN-gamma and tumor necrosis factor alpha (TNF-alpha) production. In rectal tissue, CD107 release was frequently coupled with production of IFN-gamma or TNF-alpha. In patients not on antiretroviral therapy, the magnitude of Gag-specific responses, as a percentage of CD8(+) T cells, was greater in the rectal mucosa than in PBMC (P = 0.054); however, the breakdown of responding cells into specific functional categories was similar in both sites. These findings demonstrate that rectal CD8(+) T cells are capable of robust and varied HIV-1-specific responses and therefore likely play an active role in eliminating infected cells during chronic infection.     

HIV-specific cytotoxic cell frequencies measured directly ex vivo by the Lysispot assay can be higher or lower than the frequencies of IFN-gamma-secreting cells: anti-HIV cytotoxicity is not generally impaired relative to other chronic virus responses

CD8(+) T cells in HIV-infected patients are believed to contribute to the containment of the virus and the delay of disease progression. However, the frequencies of HIV-specific CD8(+) T cells, as measured by IFN-gamma secretion and tetramer binding, often do not correlate with a delay in disease progression during chronic infection. Using the Lysispot and ELISPOT assays, we measured the frequencies of cytotoxic and IFN-gamma-secreting T cells responding to overlapping peptides from Gag, Nef, Env, and Pol consensus HIV-1 clade B sequences. PBMC from the majority of HIV-infected subjects have significant frequencies of HIV-specific cells that killed targets within 5 h directly ex vivo. The relative frequencies of IFN-gamma-secreting and cytotoxic cells varied markedly between different HIV peptide pools within the same patient, and some T cells lysed targets without secreting IFN-gamma. These results indicate that measurement of IFN-gamma production alone may be insufficient to evaluate the breadth of the HIV-specific T cell response. Also, neither the CTL to IFN-gamma ratios nor the ex vivo CTL frequencies specific for different HIV proteins were consistently lower than responses specific for two other chronic viral infections, human CMV and EBV, within the same subjects. Thus ex vivo cytotoxic T cell frequencies do not provide evidence for a model of "preterminal differentiation" of HIV-specific CD8(+) T cells during chronic HIV infection. Analysis of the frequency of directly cytotoxic HIV-specific T cells may be of considerable value in the assessment of disease progression and the potential efficacy of HIV vaccines.     

Phenotypic, functional, and kinetic parameters associated with apparent T-cell control of human immunodeficiency virus replication in individuals with and without antiretroviral treatment

The human immunodeficiency virus (HIV)-mediated immune response may be beneficial or harmful, depending on the balance between expansion of HIV-specific T cells and the level of generalized immune activation. The current study utilizes multicolor cytokine flow cytometry to study HIV-specific T cells and T-cell activation in 179 chronically infected individuals at various stages of HIV disease, including those with low-level viremia in the absence of therapy ("controllers"), low-level drug-resistant viremia in the presence of therapy (partial controllers on antiretroviral therapy [PCAT]), and high-level viremia ("noncontrollers"). Compared to noncontrollers, controllers exhibited higher frequencies of HIV-specific interleukin-2-positive gamma interferon-positive (IL-2(+) IFN-gamma(+)) CD4(+) T cells. The presence of HIV-specific CD4(+) IL-2(+) T cells was associated with low levels of proliferating T cells within the less-differentiated T-cell subpopulations (defined by CD45RA, CCR7, CD27, and CD28). Despite prior history of progressive disease, PCAT patients exhibited many immunologic characteristics seen in controllers, including high frequencies of IL-2(+) IFN-gamma(+) CD4(+) T cells. Measures of immune activation were lower in all CD8(+) T-cell subsets in controllers and PCAT compared to noncontrollers. Thus, control of HIV replication is associated with high levels of HIV-specific IL-2(+) and IFN-gamma(+) CD4(+) T cells and low levels of T-cell activation. This immunologic state is one where the host responds to HIV by expanding but not exhausting HIV-specific T cells while maintaining a relatively quiescent immune system. Despite a history of advanced HIV disease, a subset of individuals with multidrug-resistant HIV exhibit an immunologic profile comparable to that of controllers, suggesting that functional immunity can be reconstituted with partially suppressive highly active antiretroviral therapy.     

Multiepitopic B- and T-cell responses induced in humans by a human immunodeficiency virus type 1 lipopeptide vaccine

We have attempted to develop an anti-human immunodeficiency virus (HIV) lipopeptide vaccine with several HIV-specific long peptides modified by C-terminal addition of a single palmitoyl chain. A mixture of six lipopeptides derived from regulatory or structural HIV-1 proteins (Nef, Gag, and Env) was prepared. A phase I study was conducted to evaluate immunogenicity and tolerance in lipopeptide vaccination of HIV-1-seronegative volunteers given three injections of either 100, 250, or 500 microg of each lipopeptide, with or without immunoadjuvant (QS21). This report analyzes in detail B- and T-cell responses induced by vaccination. The lipopeptide vaccine elicited strong and multiepitopic B- and T-cell responses. Vaccinated subjects produced specific immunoglobulin G antibodies that recognized the Nef and Gag proteins. After the third injection, helper CD4(+)-T-cell responses as well as specific cytotoxic CD8(+) T cells were also obtained. These CD8(+) T cells were able to recognize naturally processed viral proteins. Finally, specific gamma interferon-secreting CD8(+) T cells were also detected ex vivo.     

T-cell subsets that harbor human immunodeficiency virus (HIV) in vivo: implications for HIV pathogenesis

Identification of T-cell subsets that are infected in vivo is essential to understanding the pathogenesis of human immunodeficiency virus (HIV) disease; however, this goal has been beset with technical challenges. Here, we used polychromatic flow cytometry to sort multiple T-cell subsets to 99.8% purity, followed by quantitative PCR to quantify HIV gag DNA directly ex vivo. We show that resting memory CD4(+) T cells are the predominantly infected cells but that terminally differentiated memory CD4(+) T cells contain 10-fold fewer copies of HIV DNA. Memory CD8(+) T cells can also be infected upon upregulation of CD4; however, this is infrequent and HIV-specific CD8(+) T cells are not infected preferentially. Na?ve CD4(+) T-cell infection is rare and principally confined to those peripheral T cells that have proliferated. Furthermore, the virus is essentially absent from na?ve CD8(+) T cells, suggesting that the thymus is not a major source of HIV-infected T cells in the periphery. These data illuminate the underlying mechanisms that distort T-cell homeostasis in HIV infection.     

HIV Controllers Maintain a Population of Highly Efficient Th1 Effector Cells in Contrast to Patients Treated in the Long Term

HIV controllers are rare individuals who spontaneously control HIV replication in the absence of antiretroviral therapy. To identify parameters of the CD4 response that may contribute to viral control rather than merely reflect a persistently low viremia, we compared the T helper profiles in two groups of patients with more than 10 years of viral suppression: HIV controllers from the Agence Nationale de Recherche sur le SIDA et les Hépatites Virales (ANRS) CO18 cohort (n = 26) and efficiently treated patients (n = 16). Cells specific for immunodominant Gag and cytomegalovirus (CMV) peptides were evaluated for the production of 10 cytokines and cytotoxicity markers and were also directly quantified ex vivo by major histocompatibility complex (MHC) class II tetramer staining. HIV controller CD4(+) T cells were characterized by a higher frequency of gamma interferon (IFN-γ) production, perforin(+)/CD107a(+) expression, and polyfunctionality in response to Gag peptides. While interleukin 4 (IL-4), IL-17, and IL-21 production did not differ between groups, the cells of treated patients produced more IL-10 in response to Gag and CMV peptides, pointing to persistent negative immunoregulation after long-term antiretroviral therapy. Gag293 tetramer-positive cells were detected at a high frequency (0.12%) and correlated positively with IFN-γ-producing CD4(+) T cells in the controller group (R = 0.73; P = 0.003). Tetramer-positive cells were fewer in the highly active antiretroviral therapy (HAART) group (0.04%) and did not correlate with IFN-γ production, supporting the notion of a persistent immune dysfunction in HIV-specific CD4(+) T cells of treated patients. In conclusion, HIV controllers maintained a population of highly efficient Th1 effectors directed against Gag in spite of a persistently low antigenemia, while patients treated in the long term showed a loss of CD4 effector functions.     

Rapid Perturbation in Viremia Levels Drives Increases in Functional Avidity of HIV-specific CD8 T Cells

The factors determining the functional avidity and its relationship with the broad heterogeneity of antiviral T cell responses remain partially understood. We investigated HIV-specific CD8 T cell responses in 85 patients with primary HIV infection (PHI) or chronic (progressive and non-progressive) infection. The functional avidity of HIV-specific CD8 T cells was not different between patients with progressive and non-progressive chronic infection. However, it was significantly lower in PHI patients at the time of diagnosis of acute infection and after control of virus replication following one year of successful antiretroviral therapy. High-avidity HIV-specific CD8 T cells expressed lower levels of CD27 and CD28 and were enriched in cells with an exhausted phenotype, i.e. co-expressing PD-1/2B4/CD160. Of note, a significant increase in the functional avidity of HIV-specific CD8 T cells occurred in early-treated PHI patients experiencing a virus rebound after spontaneous treatment interruption. This increase in functional avidity was associated with the accumulation of PD-1/2B4/CD160 positive cells, loss of polyfunctionality and increased TCR renewal. The increased TCR renewal may provide the mechanistic basis for the generation of high-avidity HIV-specific CD8 T cells. These results provide insights on the relationships between functional avidity, viremia, T-cell exhaustion and TCR renewal of antiviral CD8 T cell responses.     

Comparison of human immunodeficiency virus (HIV)-specific T-cell responses in HIV-1- and HIV-2-infected individuals in Senegal

Human immunodeficiency virus type 2 (HIV-2) infection is typically less virulent than HIV-1 infection, which may permit the host to mount more effective, sustained T-cell immunity. We investigated antiviral gamma interferon-secreting T-cell responses by an ex vivo Elispot assay in 68 HIV-1- and 55 HIV-2-infected Senegalese patients to determine if differences relate to more efficient HIV-2 control. Homologous HIV-specific T cells were detected in similar frequencies (79% versus 76%, P = 0.7) and magnitude (3.12 versus 3.08 log(10) spot-forming cells/10(6) peripheral blood mononuclear cells) in HIV-1 and HIV-2 infection, respectively. Gag-specific responses predominated in both groups (>/=64%), and significantly higher Nef-specific responses occurred in HIV-1-infected (54%) than HIV-2-infected patients (22%) (P < 0.001). Heterologous responses were more frequent in HIV-1 than in HIV-2 infection (46% versus 27%, P = 0.04), but the mean magnitude was similar. Total frequencies of HIV-specific responses in both groups did not correlate with plasma viral load and CD4(+) T-cell count in multivariate regression analyses. However, the magnitude of HIV-2 Gag-specific responses was significantly associated with lower plasma viremia in HIV-1-infected patients (P = 0.04). CD4(+) T-helper responses, primarily recognizing HIV-2 Gag, were detected in 48% of HIV-2-infected compared to only 8% of HIV-1-infected patients. These findings indicate that improved control of HIV-2 infection may relate to the contribution of T-helper cell responses. By contrast, the superior control of HIV-1 replication associated with HIV-2 Gag responses suggests that these may represent cross-reactive, higher-avidity T cells targeting epitopes within Gag regions of functional importance in HIV replication.     

Human immunodeficiency virus (HIV)-specific gamma interferon secretion directed against all expressed HIV genes: relationship to rate of CD4 decline

Immune responses to human immunodeficiency virus (HIV) are detected at all stages of infection and are believed to be responsible for controlling viremia. This study seeks to determine whether gamma interferon (IFN-gamma)-secreting HIV-specific T-cell responses influence disease progression as defined by the rate of CD4 decline. The study population consisted of 31 subjects naive to antiretroviral therapy. All were monitored clinically for a median of 24 months after the time they were tested for HIV-specific responses. The rate of CD4+-T-cell loss was calculated for all participants from monthly CD4 counts. Within this population, 17 subjects were classified as typical progressors, 6 subjects were classified as fast progressors, and 8 subjects were classified as slow progressors. Peripheral blood mononuclear cells were screened for HIV-specific IFN-gamma responses to all expressed HIV genes. Among the detected immune responses, 48% of the recognized peptides were encoded by Gag and 19% were encoded by Nef gene products. Neither the breadth nor the magnitude of HIV-specific responses correlated with the viral load or rate of CD4 decline. The breadth and magnitude of HIV-specific responses did not differ significantly among typical, fast, and slow progressors. These results support the conclusion that although diverse HIV-specific IFN-gamma-secreting responses are mounted during the asymptomatic phase, these responses do not seem to modulate disease progression rates.     

Virological outcome after structured interruption of antiretroviral therapy for human immunodeficiency virus infection is associated with the functional profile of virus-specific CD8+ T cells

A clear understanding of the antiviral effects of CD8(+) T cells in the context of chronic human immunodeficiency virus (HIV) infection is critical for the development of prophylactic vaccines and therapeutics designed to support T-cell-mediated immunity. However, defining the potential correlates of effective CD8(+) T-cell immunity has proven difficult; notably, comprehensive analyses have demonstrated that the size and shape of the CD8(+) T-cell response are not necessarily indicative of efficacy determined by measures of plasma viral load. Here, we conducted a detailed quantitative and qualitative analysis of CD8(+) T-cell responses to autologous virus in a cohort of six HIV-infected individuals with a history of structured interruption of antiretroviral therapy (ART) (SIT). The magnitude and breadth of the HIV-specific response did not, by themselves, explain the changes observed in plasma virus levels after the cessation of ART. Furthermore, mutational escape from targeted epitopes could not account for the differential virological outcomes in this cohort. However, the functionality of HIV-specific CD8(+) T-cell populations upon antigen encounter, determined by the simultaneous and independent measurement of five CD8(+) T-cell functions (degranulation and gamma interferon, macrophage inflammatory protein 1beta, tumor necrosis factor alpha, and interleukin-2 levels) reflected the emergent level of plasma virus, with multiple functions being elicited in those individuals with lower levels of viremia after SIT. These data show that the quality of the HIV-specific CD8(+) T-cell response, rather than the quantity, is associated with the dynamics of viral replication in the absence of ART and suggest that the effects of SIT can be assessed by measuring the functional profile of HIV-specific CD8(+) T cells.     

Putative immunodominant human immunodeficiency virus-specific CD8(+) T-cell responses cannot be predicted by major histocompatibility complex class I haplotype

Recent studies of human immunodeficiency virus (HIV)-specific CD8(+) T cells have focused on responses to single, usually HLA-A2-restricted epitopes as surrogate measures of the overall response to HIV. However, the assumption that a response to one epitope is representative of the total response is unconfirmed. Here we assess epitope immunodominance and HIV-specific CD8(+) T-cell response complexity using cytokine flow cytometry to examine CD8(+) T-cell responses in 11 HLA-A2(+) HIV(+) individuals. Initial studies demonstrated that only 4 of 11 patients recognized the putative immunodominant HLA-A2-restricted p17 epitope SLYNTVATL, suggesting that the remaining subjects might lack significant HIV-specific CD8(+) T-cell responses. However, five of six SLYNTVATL nonresponders recognized other HIV epitopes, and two of four SLYNTVATL responders had greater responses to HIV peptides restricted by other class I alleles. In several individuals, no HLA-A2-restricted epitopes were recognized, but CD8(+) T-cell responses were detected to epitopes restricted by other HLA class I alleles. These data indicate that an individual's overall CD8(+) T-cell response to HIV is not adequately represented by the response to a single epitope and that individual major histocompatibility complex class I alleles do not predict an immunodominant response restricted by that allele. Accurate quantification of total HIV-specific CD8(+) T-cell responses will require assessment of the response to all possible epitopes.     

Diminished proliferation of human immunodeficiency virus-specific CD4+ T cells is associated with diminished interleukin-2 (IL-2) production and is recovered by exogenous IL-2

Virus-specific CD4(+) T-cell function is thought to play a central role in induction and maintenance of effective CD8(+) T-cell responses in experimental animals or humans. However, the reasons that diminished proliferation of human immunodeficiency virus (HIV)-specific CD4(+) T cells is observed in the majority of infected patients and the role of these diminished responses in the loss of control of replication during the chronic phase of HIV infection remain incompletely understood. In a cohort of 15 patients that were selected for particularly strong HIV-specific CD4(+) T-cell responses, the effects of viremia on these responses were explored. Restriction of HIV replication was not observed during one to eight interruptions of antiretroviral therapy in the majority of patients (12 of 15). In each case, proliferative responses to HIV antigens were rapidly inhibited during viremia. The frequencies of cells that produce IFN-gamma in response to Gag, Pol, and Nef peptide pools were maintained during an interruption of therapy. In a subset of patients with elevated frequencies of interleukin-2 (IL-2)-producing cells, IL-2 production in response to HIV antigens was diminished during viremia. Addition of exogenous IL-2 was sufficient to rescue in vitro proliferation of DR0101 class II Gag or Pol tetramer(+) or total-Gag-specific CD4(+) T cells. These observations suggest that, during viremia, diminished in vitro proliferation of HIV-specific CD4(+) T cells is likely related to diminished IL-2 production. These results also suggest that relatively high frequencies of HIV-specific CD4(+) T cells persist in the peripheral blood during viremia, are not replicatively senescent, and proliferate when IL-2 is provided exogenously.     

Increased sequence diversity coverage improves detection of HIV-specific T cell responses

The accurate identification of HIV-specific T cell responses is important for determining the relationship between immune response, viral control, and disease progression. HIV-specific immune responses are usually measured using peptide sets based on consensus sequences, which frequently miss responses to regions where test set and infecting virus differ. In this study, we report the design of a peptide test set with significantly increased coverage of HIV sequence diversity by including alternative amino acids at variable positions during the peptide synthesis step. In an IFN-gamma ELISpot assay, these "toggled" peptides detected HIV-specific CD4(+) and CD8(+) T cell responses of significantly higher breadth and magnitude than matched consensus peptides. The observed increases were explained by a closer match of the toggled peptides to the autologous viral sequence. Toggled peptides therefore afford a cost-effective and significantly more complete view of the host immune response to HIV and are directly applicable to other variable pathogens.     

Mature dendritic cells infected with canarypox virus elicit strong anti-human immunodeficiency virus CD8+ and CD4+ T-cell responses from chronically infected individuals

Recombinant canarypox virus vectors containing human immunodeficiency virus type 1 (HIV-1) sequences are promising vaccine candidates, as they replicate poorly in human cells. However, when delivered intramuscularly the vaccines have induced inconsistent and in some cases transient antigen-specific cytotoxic T-cell (CTL) responses in seronegative volunteers. An attractive way to enhance these responses would be to target canarypox virus to professional antigen-presenting cells such as dendritic cells (DCs). We studied (i) the interaction between canarypox virus and DCs and (ii) the T-cell responses induced by DCs infected with canarypox virus vectors containing HIV-1 genes. Mature and not immature DCs resisted the cytopathic effects of canarypox virus and elicited strong effector CD8+ T-cell responses from chronically infected HIV+ individuals, e.g., cytolysis, and secretion of gamma interferon (IFN-gamma) and beta-chemokines. Furthermore, canarypox virus-infected DCs were >30-fold more efficient than monocytes and induced responses that were comparable to those induced by vaccinia virus vectors or peptides. Addition of exogenous cytokines was not necessary to elicit CD8+ effector cells, although the presence of CD4+ T cells was required for their expansion and maintenance. Most strikingly, canarypox virus-infected DCs were directly able to stimulate HIV-specific, IFN-gamma-secreting CD4 helper responses from bulk as well as purified CD4+ T cells. Therefore, these results suggest that targeting canarypox virus vectors to mature DCs could potentially elicit both anti-HIV CD8+ and CD4+ helper responses in vivo.