Human immunodeficiency virus type 1 (HIV-1)-specific CD4+ T cells that proliferate in vitro detected in samples from most viremic subjects and inversely associated with plasma HIV-1 levels

DNA prime/MVTT boost regimen with HIV-1 mosaic Gag enhances the potency of antigen-specific immune responses

HIV-1 diversity and latent reservoir are the major challenges for the development of an effective AIDS vaccine. It is well indicated that Gag-specific CD8⁺ T cells serve as the dominant host immune surveillance for HIV-1 control, but it still remains a challenge for vaccine design to induce broader and stronger cytotoxic T cell immunity against the virus. Genetic variation of the HIV-1 gag gene across different clades is one of the reasons for the reduction of antigenic epitope coverage. Here, we report an immunization strategy with heterologous vaccines expressing a mosaic Gag antigen aimed to increase antigenic breadth against a wider spectrum of HIV-1 strains. Priming using a DNA vaccine via in vivo electroporation, followed by boosting with a live replication-competent modified vaccinia TianTan (MVTT) vectored vaccine, elicited greater and broader protective Gag-specific immune responses in mice. Compared to DNA or MVTT homologous immunization, the heterologous DNA/MVTT vaccination resulted in higher frequencies of broadly reactive, Gag-specific, polyfunctional, long-lived cytotoxic CD8⁺ T cells, as well as increased anti-Gag antibody titer. Importantly, the DNA/MVTT heterologous vaccination induced protection against EcoHIV and mesothelioma AB1-Gag challenges. In summary, the stronger protective Gag-specific immunity induced by the heterologous regimen using two safe vectors shows promise for further development to enhance anti-HIV-1 immunity. Our study has important implications for immunogen design and the development of an effective HIV-1 heterologous vaccination strategy.

Antigen-specific T-cell-mediated immunity after HIV-1 infection: implications for vaccine control of HIV development

The definition of immune correlates of protection in HIV-1 infection is pivotal to the design of successful vaccine candidates and strategies. Although significant methodological and conceptual strides have been made in our understanding of HIV-specific cellular immunity, we have not yet defined those parameters that have a role in controlling the spread of HIV infection. This review discusses the basis of our understanding of HIV-specific cellular immunity and identifies its shortcomings. Furthermore, potential protective characteristics will be proposed that may ultimately be required for an effective vaccine designed to stimulate cellular immunity against HIV-1.

Characteristics and outcomes of initial virologic suppressors during analytic treatment interruption in a therapeutic HIV-1 gag vaccine trial

BACKGROUND

In the placebo-controlled trial ACTG A5197, a trend favoring viral suppression was seen in the HIV-1-infected subjects who received a recombinant Ad5 HIV-1 gag vaccine.

OBJECTIVE

To identify individuals with initial viral suppression (plasma HIV-1 RNA set point <3.0 log(10) copies/ml) during the analytic treatment interruption (ATI) and evaluate the durability and correlates of virologic control and characteristics of HIV sequence evolution.

METHODS

HIV-1 gag and pol RNA were amplified and sequenced from plasma obtained during the ATI. Immune responses were measured by flow cytometric analysis and intracellular cytokine expression assays. Characteristics of those with and without initial viral suppression were compared using the Wilcoxon rank sum and Fisher's exact tests.

RESULTS

Eleven out of 104 participants (10.6%) were classified as initial virologic suppressors, nine of whom had received the vaccine. Initial virologic suppressors had significantly less CD4+ cell decline by ATI week 16 as compared to non-suppressors (median 7 CD4+ cell gain vs. 247 CD4+ cell loss, P = 0.04). However, of the ten initial virologic suppressors with a pVL at ATI week 49, only three maintained pVL <3.0 log(10) copies/ml. HIV-1 Gag-specific CD4+ interferon-γ responses were not associated with initial virologic suppression and no evidence of vaccine-driven HIV sequence evolution was detected. Participants with initial virologic suppression were found to have a lower percentage of CD4+ CTLA-4+ cells prior to treatment interruption, but a greater proportion of HIV-1 Gag-reactive CD4+ TNF-α+ cells expressing either CTLA-4 or PD-1.

CONCLUSIONS

Among individuals participating in a rAd5 therapeutic HIV-1 gag vaccine trial, initial viral suppression was found in a subset of patients, but this response was not sustained. The association between CTLA-4 and PD-1 expression on CD4+ T cells and virologic outcome warrants further study in trials of other therapeutic vaccines in development.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00080106.

Factors associated with viral rebound in HIV-1-infected individuals enrolled in a therapeutic HIV-1 gag vaccine trial

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) vaccines directed to the cell-mediated immune system could have a role in lowering the plasma HIV-1 RNA set point, which may reduce infectivity and delay disease progression.

METHODS

Randomized, placebo-controlled trial involving HIV-1-infected participants who received a recombinant adenovirus serotype 5 (rAd5) HIV-1 gag vaccine or placebo. Sequence-based HLA typing was performed for all 110 participants who initiated analytic treatment interruption (ATI) to assess the role of HLA types previously associated with HIV prognosis. Plasma HIV-1 gag and pol RNA sequences were obtained during the ATI. Virologic endpoints and HLA groups were compared between treatment arms using the 2-sample rank sum test. A linear regression model was fitted to derive independent correlates of ATI week 16 plasma viral load (w16 PVL).

RESULTS

Vaccinated participants with neutral HLA alleles had lower median w16 PVLs than did vaccinated participants with protective HLA alleles (P = .01) or placebo participants with neutral HLA alleles (P = .02). Factors independently associated with lower w16 PVL included lower pre-antiretroviral therapy PVL, greater Gag sequence divergence from the vaccine sequence, decreased proportion of HLA-associated polymorphisms in Gag, and randomization to the vaccine arm.

CONCLUSIONS

Therapeutic vaccination with a rAd5-HIV gag vaccine was associated with lower ATI week 16 PVL even after controlling for viral and host genetic factors.

CLINICAL TRIALS REGISTRATION

NCT00080106.

In vitro naïve T cell proliferation failure predicts poor post-immunization responses to neoantigen, but not recall antigens, in HIV-infection

Immune reconstitution after HAART is incomplete, but no widely accepted method to quantify subclinical immune deficiency is available. We immunized 9 HIV-negative subjects and 29 HIV-infected patients with CD4>/=450 cells/microL and undetectable HIV RNA levels with 2 doses of diphtheria/tetanus toxoid (TT) and KLH, a presumed neoantigen. We quantified the response by lymphoproliferative assay, delayed-type hypersensitivity (DTH), and antibody titers up to 59days after enrollment. We assessed T cell proliferative capacity using anti-Vbeta3 and anti-Vbeta5 antibody stimulation, which we herein show induced predominant proliferation of naïve T cells. Subjects with detectable responses to KLH tended to exhibit greater proliferative responses to anti-Vbeta3/Vbeta5 stimulation; no such pattern was seen with response to TT. Several measures of in vitro T cell proliferative capacity correlated significantly with DTH and antibody responses to KLH, but not with TT responses; this association was independent of naïve T cell numbers. Our results indicate that naïve T cell proliferation predicts response to neo-, but not recall antigens, and suggest that it may be a meaningful reflection of in vivo immune competence in HIV-infected persons.

A steady state of CD4+ T cell memory maturation and activation is established during primary subtype C HIV-1 infection

The functional integrity of CD4(+) T cells is crucial for well-orchestrated immunity and control of HIV-1 infection, but their selective depletion during infection creates a paradox for understanding a protective response. We used multiparameter flow cytometry to measure activation, memory maturation, and multiple functions of total and Ag-specific CD4(+) T cells in 14 HIV-1- and CMV- coinfected individuals at 3 and 12 mo post HIV-1 infection. Primary HIV-1 infection was characterized by elevated levels of CD38, HLA-DR, and Ki67 in total memory and Gag-specific CD4(+) and CD8(+) T cells. In both HIV-infected and 15 uninfected controls, the frequency of activated cells was uniformly distributed among early differentiated (ED; CD45RO(+)CD27(+)), late differentiated (CD45RO(+)CD27(-)), and fully differentiated effector (CD45RO(-)CD27(-)) memory CD4(+) T cells. In HIV-1-infected individuals, activated CD4(+) T cells significantly correlated with viremia at 3 mo postinfection (r = 0.79, p = 0.0007) and also harbored more gag provirus DNA copies than nonactivated cells (p = 0.04). Moreover, Gag-specific ED CD4(+) T cells inversely associated with plasma viral load (r = -0.87, p < 0.0001). Overall, we show that low copy numbers of gag provirus and plasma RNA copies associated with low CD4 activation as well as accumulation of ED HIV-specific CD4(+) memory. Significant positive correlations between 3 and 12 mo activation and memory events highlighted that a steady state of CD4(+) T cell activation and memory maturation was established during primary infection and that these cells were unlikely to be involved in influencing the course of viremia in the first 12 mo of HIV-1 infection.

Phenotype and function of protective T cell immune responses in HIV

PURPOSE OF REVIEW

Definition of T cell immune correlates in HIV infection remains a lofty goal towards our understanding of the HIV-specific immune response. This review will focus upon recent developments and controversies in our understanding of protective T cell responses against HIV.

RECENT FINDINGS

It has become clear that multiple functions and phenotypic markers of T cells must be assessed to accurately characterize the complexity of CD4 and CD8 T cell responses. While evidence indicates that a hallmark of protective immune responses in HIV infection is the presence of 'polyfunctional' T cell responses, a disconnect remains between the function and phenotype of effective HIV-specific T cells. Moreover, there may be inherent differences in the ability of specific human leukocyte antigen class I families to promote CD8 T cell effector versus polyfunctional responses. It remains to be determined how polyfunctional responses arise in HIV infection, which functions are important for control, and whether surface phenotype markers provide an indication of protective capacity.

SUMMARY

Polyfunctional and phenotypic assessment of T cell responses have clearly advanced our understanding of HIV specific immune responses. Critical questions remain, however, especially whether polyfunctional T cell responses control, or are controlled by, HIV replication.

Design and preclinical development of a recombinant protein and DNA plasmid mixed format vaccine to deliver HIV-derived T-lymphocyte epitopes

Coordinated interactions between helper and cytotoxic T-lymphocytes (HTL and CTL) are needed for optimal effector cell functions and the establishment of immunological memory. We, therefore, designed a mixed format vaccine based on the use of highly conserved HIV-derived T-lymphocyte epitopes wherein the HTL epitopes were delivered as a recombinant protein and the CTL epitopes which were encoded in a DNA vaccine plasmid. Immunogenicity testing in HLA transgenic mice and GLP preclinical safety testing in rabbits and guinea pigs were used to document the utility of this approach and to support Phase 1 trial clinical testing. Both vaccine components were immunogenic and safely co-administered.

Effect of lentivirus encoding HIV-1 Nef-U3 shRNA on the function of HIV-specific memory CD4(+) T cells in patients with chronic HIV-1 infection

OBJECTIVE

To determine whether HIV-1-specific CD4 T cells with proliferative capacity are eliminated or functionally defective because of HIV-1 reactivation.

DESIGN

The loss of proliferative capacity by HIV-1-specific CD4 T cells compromises the host's ability to maintain protective immunity against HIV-1 and is a hallmark of disease progression. We used a recombinant lentivirus encoding an HIV-specific short hairpin (sh)RNA (Lenti shNef366) with known HIV-inhibitory activity to analyze the functional state of HIV-1-specific CD4 T cells.

METHODS

T lymphocytes from untreated chronically HIV-infected patients with documented high viral loads (above 10 000 HIV-RNA) were transduced with Lenti shNef366, and the proliferation, differentiation, and cytokine production of HIV-specific CD4 T cells were analyzed.

RESULTS

Lenti shNef366 restored the proliferation of HIV p24-specific CD4 T cells in eight of 12 patients tested, affecting primarily CD27 or CD28 CD4 T cells that were at an intermediate stage of differentiation. Although cytokine production by CD4 T cells remained poor after transduction with Lenti shNef366, improved proliferative capacity was associated with significantly higher levels of expression of CD107a.

CONCLUSION

In chronic stages of HIV-1 infection with high levels of HIV replication, proliferation-competent HIV-specific CD4 T cells in an intermediate stage of differentiation are present but are exquisitely and strongly impaired. Blocking HIV reactivation may restore a key functional property of memory T cells.

IL-10 is up-regulated in multiple cell types during viremic HIV infection and reversibly inhibits virus-specific T cells

Murine models indicate that interleukin-10 (IL-10) can suppress viral clearance, and interventional blockade of IL-10 activity has been proposed to enhance immunity in chronic viral infections. Increased IL-10 levels have been observed during HIV infection and IL-10 blockade has been shown to enhance T-cell function in some HIV-infected subjects. However, the categories of individuals in whom the IL-10 pathway is up-regulated are poorly defined, and the cellular sources of IL-10 in these subjects remain to be determined. Here we report that blockade of the IL-10 pathway augmented in vitro proliferative capacity of HIV-specific CD4 and CD8 T cells in individuals with ongoing viral replication. IL-10 blockade also increased cytokine secretion by HIV-specific CD4 T cells. Spontaneous IL-10 expression, measured as either plasma IL-10 protein or IL-10 mRNA in peripheral blood mononuclear cells (PBMCs), correlated positively with viral load and diminished after successful antiretroviral therapy. IL-10 mRNA levels were up-regulated in multiple PBMC subsets in HIV-infected subjects compared with HIV-negative controls, particularly in T, B, and natural killer (NK) cells, whereas monocytes were a major source of IL-10 mRNA in HIV-infected and -uninfected individuals. These data indicate that multiple cell types contribute to IL-10-mediated immune suppression in the presence of uncontrolled HIV viremia.

Relevance of studying T cell responses in SIV-infected rhesus macaques

HIV infection, once established, is never cleared. Rare individuals do, however, control viral replication to low levels. These successful immune responses are primarily linked to certain class I MHC alleles (MHC-I). Because of this association, many AIDS vaccines in development are designed to generate virus-specific CD8+ T cells. The Merck STEP phase 2b efficacy trial of one such vaccine was recently halted, and declared a failure. Thus, basic questions regarding what constitutes an effective T cell response and how such responses could be elicited by vaccination remain open. The best animal model available to explore such issues is simian immunodeficiency virus infection of rhesus macaques, which serves as the primary proving ground for AIDS vaccines.

Dynamics of T-cell responses and memory T cells during primary simian immunodeficiency virus infection in cynomolgus macaques

Cellular immune responses make an important contribution to both the control of human immunodeficiency virus (HIV) replication and disease progression. We used a pathogenic model of SIVmac251 infection of cynomolgus macaques to longitudinally evaluate cellular immune responses in association with various rates of disease progression. We found an inverse relationship between plasma viral load and the simian immunodeficiency virus (SIV)-specific T cells responses in peripheral blood and lymph nodes. SIV-specific T-cell responses in peripheral blood were transient during primary infection, with the highest responses detected around 3 months after infection. There was also a transient increase of central memory CD8(+) T cells in peripheral blood during primary infection, and effector memory T-cell counts in peripheral lymph nodes were increased. This study emphasizes the importance of the early virus-specific immune responses in the outcome of HIV/SIV disease and provides details about the changes of virus-specific immune responses over time.

Upregulation of CTLA-4 by HIV-specific CD4+ T cells correlates with disease progression and defines a reversible immune dysfunction

In progressive viral infection, antiviral T cell function is impaired by poorly understood mechanisms. Here we report that the inhibitory immunoregulatory receptor CTLA-4 was selectively upregulated in human immunodeficiency virus (HIV)-specific CD4(+) T cells but not CD8(+) T cells in all categories of HIV-infected subjects evaluated, with the exception of rare people able to control viremia in the absence of antiretroviral therapy. CTLA-4 expression correlated positively with disease progression and negatively with the capacity of CD4(+) T cells to produce interleukin 2 in response to viral antigen. Most HIV-specific CD4(+) T cells coexpressed CTLA-4 and another inhibitory immunoregulatory receptor, PD-1. In vitro blockade of CTLA-4 augmented HIV-specific CD4(+) T cell function. These data, indicating a reversible immunoregulatory pathway selectively associated with CD4(+) T cell dysfunction, provide a potential target for immunotherapy in HIV-infected patients.

CD4+ T cell targeting of human immunodeficiency virus type 1 (HIV-1) peptide sequences present in vivo during chronic, progressive HIV-1 disease

We previously detected HIV-1 Gag-specific CD4+ T cells recognizing reference strain viral epitopes in subjects with progressive, chronic infection. To test whether these CD4+ T cells persist in vivo by failing to recognize autologous HIV-1 epitopes, we compared autologous plasma HIV-1 p24 nucleotide sequences with targeted HXB.2 strain Gag p24 CD4+ T cell epitopes in nine chronically infected, untreated subjects. In five responding subjects, 10 of 26 HXB.2 strain p24 peptides targeted by CD4+ T cells exactly matched autologous plasma viral sequences. Four subjects with plasma viral loads >100,000 copies/mL had no measurable p24-specific CD4+ T cell responses despite carrying HIV-1 strains that matched HXB.2 sequences at predicted epitopes. These results show that HIV-1-specific CD4+ T cells can persist in chronic HIV-1 infection despite recognition of epitopes present in vivo. However, with high-level in vivo HIV-1 replication, CD4+ T cells targeting autologous HIV-1 may be non-responsive or absent.

Acutely dysregulated, chronically disabled by the enemy within: T-cell responses to HIV-1 infection

Human immunodeficiency virus (HIV) infection causes chronic progressive immunodeficiency and immune dysregulaton. Although simple depletion of the major target of HIV infection, the CD4+ T cell, can explain much of the immunosuppression seen, there are multiple other factors contributing to the immune dysregulation. CD4+ T-cell depletion induces a range of homeostatic mechanisms that contribute to immune activation and cell turnover, providing a milieu conducive to further viral replication and cell destruction, resulting in functional defects in various lymphoid organs. These changes are progressive and in turn compromise the homeostatic processes. Further, the infection, like any other viral infection, provokes an active immune response consisting of both CD4+ and CD8+ T-cell responses. Both appear compromised, displaying aberrant memory cell production. While some of these defects result from viral variation and the chronicity of antigen presentation, other defects of memory cell production appear very early during the primary immune response limiting the viral specific T-cell responses from the outset. This, combined with the ability of the virus to escape any successful immune responses, results in an attenuated immune response that eventually becomes exhausted, characterized by progressive deficits in T-cell repertoire. Furthermore, negative regulatory mechanisms that normally control the immune response may be aberrantly invoked, perhaps directly by the virus, further compromising the efficacy of the immune response. Rational design of effective immunotherapies depends on a clear understanding of the processes compromising the immune response to HIV.

Induction of a virus-specific effector-memory CD4+ T cell response by attenuated SIV infection

We investigated simian immunodeficiency virus (SIV)-specific CD4⁺ T cell responses in rhesus macaques chronically infected with attenuated or pathogenic SIV strains. Analysis of SIVΔnef-infected animals revealed a relatively high frequency of SIV-specific CD4⁺ T cells representing 4–10% of all CD4⁺ T lymphocytes directed against multiple SIV proteins. Gag-specific CD4⁺ T cells in wild-type SIV-infected animals were 5–10-fold lower in frequency and inversely correlated with the level of plasma viremia. SIV-specific CD4⁺ cells from SIVΔnef animals were predominantly CD27⁻CD28⁻CD45RA^lowCCR7⁻CCR5⁻, consistent with an effector–memory subset, and included a fully differentiated CD45RA⁺CCR7⁻ subpopulation. In contrast, SIV-specific CD4⁺ T cells from SIV-infected animals were mostly CD27⁺CD28⁺CD45RA⁻CCR7⁺CCR5⁺, consistent with an early central memory phenotype. The CD45RA⁺CCR7⁻CD4⁺ subset from SIVΔnef animals was highly enriched for effector CD4⁺ T cells, as indicated by the perforin expression and up-regulation of the lysosomal membrane protein CD107a after SIV Gag stimulation. SIV-specific CD4⁺ T cells in attenuated SIV-infected animals were increased in frequency in bronchioalveolar lavage and decreased in lymph nodes, consistent with an effector–memory T cell population. The ability of SIVΔnef to induce a high frequency virus-specific CD4⁺ T cell response with direct effector function may play a key role in protective immunity produced by vaccination with attenuated SIV strains.

Immunogenicity testing of a novel engineered HIV-1 envelope gp140 DNA vaccine construct

DNA vaccines expressing the envelope (env) of the human immunodeficiency virus type 1 (HIV-1) have been relatively ineffective at generating strong immune responses. In this study, we described the development of a recombinant plasmid DNA (pEK2P-B) expressing an engineered codon-optimized envelope gp140 gene of primary (nonrecombinant) HIV-1 subtype B isolate 6101. Codon usage and RNA optimization of HIV-1 structural genes has been shown to increase protein expression in vitro as well as in the context of DNA vaccines in vivo. To further increase the expression, a synthetic IgE leader with kozak sequences were fused into the env gene. The cytoplasmic tail of the gene was also truncated to prevent recycling. The expression of env by the recombinant pEK2P-B was evaluated using T7 coupled transcription/translation. The construct demonstrated high expression of the HIV-1 env gene in eukaryotic cells as demonstrated in transfected 293-T and RD cells. Immunogenicity of pEK2P-B was evaluated in mice using IFN-gamma ELISpot assay, and the construct was found to be highly immunogenic and crossreactive with HIV-1 clade C env peptides. Three immunodominant peptides were also mapped out. Furthermore, by performing a CFSE flow cytometry-based proliferation assay, 2.4 and 1.5% proliferation was observed in CD4+, CD8+, and CCR+ memory T cells, respectively. Therefore, this engineered synthetic optimized env DNA vaccine may be useful in DNA vaccine and other studies of HIV-1 immunogenicity.

Initiation of antiretroviral therapy during chronic SIV infection leads to rapid reduction in viral loads and the level of T-cell immune response

In the present era of increasing resistance of human immunodeficiency virus (HIV) to antiviral drugs, exploration of adjunct therapies directed at immune responses in combination with antiretroviral drugs may be of value for the treatment of acquired immunodeficiency syndrome. In this study, we designed a model for immune therapy using SIVmac251 infection in rhesus macaques. We explored the outcomes of primary infection on viral loads and the resulting T-cell immune responses in primates. The SIV-infected rhesus macaque model exhibited features similar to those observed in HIV-1 infection of humans. Major histocompatibility complex (MHC) segregation with viral loads were found to associate with viral containment and hence the duration of the disease-free latency period. Thus a better understanding of the relative roles of MHC class I allele in control of viral replication may provide important information for prophylactic or therapeutic vaccine designs. Mamu-A01 is significantly associated with higher immune response and control of viral replication. This allele is frequent in rhesus macaques of Indian origin (22%). Interestingly, Mamu-B01 (26% animals) was associated with lower immune responses and higher viral loads. Another allele, A08 was also predominantly present in 37% of the animals in this study. We observed higher viral replication in individual SIV-infected rhesus monkeys that did not demonstrate strong cellular immune responses. The results are important for understanding SIV disease progression in different MHC Mamu alleles and also for improving the interpretation and quality of pre-clinical studies in rhesus monkeys.

Scanning the HIV genome for CD4+ T cell epitopes restricted to HLA-DP4, the most prevalent HLA class II molecule

HLA-DP4 alleles are carried by 75% of individuals and are the most frequent HLA II alleles worldwide. Because we have recently characterized the peptide-binding specificity of HLA-DP4 molecules, we developed a peptide-binding prediction method to identify HLA-DP4-restricted peptides in multiple Ags. CD4(+) T cell response plays a key role in the immune control of HIV infection, but few HIV-specific T cell epitopes with multi-individual specificity have been identified. They are mostly restricted to HLA-DR molecules, which are very polymorphic molecules. We therefore looked for HLA-DP4-restricted CD4(+) T cell epitopes in the whole genome of HIV. Twenty-one peptides were selected from the HXB2 HIV genome based on the prediction of binding to HLA-DP4 molecules. They were submitted to HLA-DP4-binding assays. Seventeen peptides bound to the HLA-DP401 molecule, whereas 15 peptides bound to HLA-DP402. Six peptides bound very tightly to HLA-DP401 and were investigated for their capacity to induce specific CD4(+) T cell lines in vitro using dendritic cells and CD4(+) T cells collected from eight seronegative HLA-DP4(+) donors. Four peptides from env and reverse transcriptase proteins induced in vitro-specific T cell lines restricted to HLA-DP4 molecules. Peptide-induced T cells recognized variants other than the HXB2 sequence and were stimulated by native Ags processed by immature dendritic cells. The reverse transcriptase peptide is present in 65% of the isolated HIV variants. To our knowledge, we describe the first HIV epitopes restricted to HLA-DP4 molecules.

Interactive association of proviral load and IFN-gamma-secreting T cell responses in HIV-1C infection

We investigated the interactive relationship between proviral DNA load and virus-specific IFN-gamma-secreting T cell responses in HIV-1C infection. The presence or absence of correlation, and inverse or direct type of correlation, if any, were dependent on targeted viral gene product. Responses to Gag p24 or to Pol were associated with lower proviral DNA load. Associations between proviral DNA load and T cell responses did not necessarily mirror relationships between plasma RNA load and T cell responses. An interaction analysis showed a synergy in that lower proviral DNA and lower plasma RNA load were associated with high Gag p24-specific IFN-gamma-secreting T cell response (interaction test P = 0.0003). Our findings support the idea that HIV proteins have differential value for vaccine design, and suggest that, for HIV-1C, Gag p24 may be one of the most attractive regions to include in vaccine designs to control both plasma RNA load and cell-associated proviral DNA load.

HIV-1-Specific CD4+ T-Cell Responses Are Not Associated With Significant Viral Epitope Variation in Persons With Persistent Plasma Viremia

OBJECTIVES

To determine whether increased sequence variation occurs in regions of endogenous HIV-1 targeted by HIV-1-specific CD4 T cells. The presence of increased variation would be suggestive of immune evasion by HIV-1.

DESIGN

We performed a cross-sectional study of untreated HIV-1-infected subjects measuring HIV-1-specific interferon (IFN)-gamma-secreting CD4 T-cell responses against epitopes in Gag p17 and p24 and concurrent endogenous plasma HIV-1 RNA epitope sequence variation.

METHODS

CD8- depleted IFNgamma enzyme-linked immunospot assays were used to identify regions of HIV-1 Gag recognized by CD4 T cells. Reverse transcriptase polymerase chain reaction and TA cloning were used to sequence endogenous plasma HIV-1 virus and identify variants.

RESULTS

CD4 T-cell epitopes in Gag p17 and p24 were identified in 5 individuals, and concurrent sequence information on endogenous HIV-1 was obtained in 4 of these individuals. Endogenous plasma HIV-1 RNA sequencing revealed no intrapatient amino acid sequence variation through identified epitopes.

CONCLUSIONS

In these chronically infected viremic subjects, circulating IFNgamma-secreting CD4 T-cell responses were directed against epitope sequences found in the predominant strain of endogenous circulating plasma HIV-1, suggesting that escape from CD4 T-cell responses is not a common process in vivo.

Characterization of HIV-1 Gag-specific T cell responses in chronically infected Indian population

India is at the epicentre of the global HIV/AIDS epidemic in South-east Asia, predominated by subtype C infections. It is important to characterize HIV-1-specific T cell responses in this particular population with the aim of identifying protective correlates of immunity to control HIV-1 infection. In this study, we performed a comprehensive analysis of the breadth and magnitude of T cell responses directed at HIV-1 subtype C Gag, one of the most conserved HIV-1 proteins. The study population consisted of antiretroviral naive, chronic HIV-1 subtype C-infected individuals at various stages of infection. We used recent advanced techniques such as enzyme-linked immunospot (ELISPOT) assay and intracellular cytokine staining to quantify the total CD4(+) and CD8(+) T cell response to HIV-1 gag at single peptide level, regardless of HLA haplotype of the infected individual. The p24-Gag was identified as the most frequently recognized subunit protein with the greatest magnitude of CD4(+) and CD8(+) T cell responses. Stronger and broader CD8 T cell responses were recognized, contrasting with the weaker and narrower CD4 T cell responses with regard to Gag protein subunits. The magnitude of the HIV-specific interferon (IFN)-gamma responses was observed to be higher than the corresponding interleukin (IL)-2 response, indicating the persistence of antigenic load in chronically infected Indian population due to the probable dysfunction of HIV-specific, IFN-gamma-secreting CD8 T cells in absence of IL-2 help.