Correlation between breadth of memory HIV-specific cytotoxic T cells, viral load and disease progression in HIV infection

Clonal succession after prolonged antiretroviral therapy rejuvenates CD8+ T cell responses against HIV-1

Human immunodeficiency virus 1 (HIV-1) infection is characterized by a dynamic and persistent state of viral replication that overwhelms the host immune system in the absence of antiretroviral therapy (ART). The impact of prolonged treatment on the antiviral efficacy of HIV-1-specific CD8+ T cells has nonetheless remained unknown. Here, we used single-cell technologies to address this issue in a cohort of aging individuals infected early during the pandemic and subsequently treated with continuous ART. Our data showed that long-term ART was associated with a process of clonal succession, which effectively rejuvenated HIV-1-specific CD8+ T cell populations in the face of immune senescence. Tracking individual transcriptomes further revealed that initially dominant CD8+ T cell clonotypes displayed signatures of exhaustion and terminal differentiation, whereas newly dominant CD8+ T cell clonotypes displayed signatures of early differentiation and stemness associated with natural control of viral replication. These findings reveal a degree of immune resilience that could inform adjunctive treatments for HIV-1.

Mosaic HIV-1 vaccination induces anti-viral CD8+ T cell functionality in the phase 1/2a clinical trial APPROACH

IMPORTANCE

The functionality of CD8+ T cells against human immunodeficiency virus-1 (HIV-1) antigens is indicative of HIV-progression in both animal models and people living with HIV. It is, therefore, of interest to assess CD8+ T cell responses in a prophylactic vaccination setting, as this may be an important component of the immune system that inhibits HIV-1 replication. T cell responses induced by the adenovirus serotype 26 (Ad26) mosaic vaccine regimen were assessed previously by IFN-γ ELISpot and flow cytometric assays, yet these assays only measure cytokine production but not the capacity of CD8+ T cells to inhibit replication of HIV-1. In this study, we demonstrate direct anti-viral function of the clinical Ad26 mosaic vaccine regimen through ex vivo inhibition of replication of diverse clades of HIV-1 isolates in the participant's own CD4+ T cells.

HIV-1 capsids from B27/B57+ elite controllers escape Mx2 but are targeted by TRIM5α, leading to the induction of an antiviral state

Elite controllers (ECs) are a rare subset of HIV-1 slow progressors characterized by prolonged viremia suppression. HLA alleles B27 and B57 promote the cytotoxic T lymphocyte (CTL)-mediated depletion of infected cells in ECs, leading to the emergence of escape mutations in the viral capsid (CA). Whether those mutations modulate CA detection by innate sensors and effectors is poorly known. Here, we investigated the targeting of CA from B27/B57⁺ individuals by cytosolic antiviral factors Mx2 and TRIM5α. Toward that aim, we constructed chimeric HIV-1 vectors using CA isolated from B27/B57⁺ or control subjects. HIV-1 vectors containing B27/B57⁺-specific CA had increased sensitivity to TRIM5α but not to Mx2. Following exposure to those vectors, cells showed increased resistance against both TRIM5α-sensitive and -insensitive HIV-1 strains. Induction of the antiviral state did not require productive infection by the TRIM5α-sensitive virus, as shown using chemically inactivated virions. Depletion experiments revealed that TAK1 and Ubc13 were essential to the TRIM5α-dependent antiviral state. Accordingly, induction of the antiviral state was accompanied by the activation of NF-κB and AP-1 in THP-1 cells. Secretion of IFN-I was involved in the antiviral state in THP-1 cells, as shown using a receptor blocking antibody. This work identifies innate activation pathways that are likely to play a role in the natural resistance to HIV-1 progression in ECs.

Some HIV-1-infected individuals show a natural capacity to control viral propagation. In individuals that have the HLA B27 or B57 allele, HIV-1 control is associated with mutations in viral proteins that arise as a result of immune pressure from cytotoxic T lymphocytes. HIV-1 capsid protein mutations found in these subjects render HIV-1 more sensitive to detection by TRIM5α, a cytoplasmic innate effector that targets retroviral capsids. We show here that HIV-1 bearing such mutations is restricted by TRIM5α but not by Mx2, another capsid-targeting innate effector. As a result, cells have decreased permissiveness to subsequent HIV-1 infections, a phenomenon that could contribute to the inefficient disease progression observed in these individuals. This knowledge might find applications in the development of immune interventions to increase human cells resistance to HIV-1.

Virus and CTL dynamics in the extrafollicular and follicular tissue compartments in SIV-infected macaques

Data from SIV-infected macaques indicate that virus-specific cytotoxic T lymphocytes (CTL) are mostly present in the extrafollicular (EF) compartment of the lymphoid tissue, with reduced homing to the follicular (F) site. This contributes to the majority of the virus being present in the follicle and represents a barrier to virus control. Using mathematical models, we investigate these dynamics. Two models are analyzed. The first assumes that CTL can only become stimulated and expand in the extrafollicular compartment, with migration accounting for the presence of CTL in the follicle. In the second model, follicular CTL can also undergo antigen-induced expansion. Consistent with experimental data, both models predict increased virus compartmentalization in the presence of stronger CTL responses and lower virus loads, and a more pronounced rise of extrafollicular compared to follicular virus during CD8 cell depletion experiments. The models, however, differ in other aspects. The follicular expansion model results in dynamics that promote the clearance of productive infection in the extrafollicular site, with any productively infected cells found being the result of immigration from the follicle. This is not observed in the model without follicular CTL expansion. The models further predict different consequences of introducing engineered, follicular-homing CTL, which has been proposed as a therapeutic means to improve virus control. Without follicular CTL expansion, this is predicted to result in a reduction of virus load in both compartments. The follicular CTL expansion model, however, makes the counter-intuitive prediction that addition of F-homing CTL not only results in a reduction of follicular virus load, but also in an increase in extrafollicular virus replication. These predictions remain to be experimentally tested, which will be relevant for distinguishing between models and for understanding how therapeutic introduction of F-homing CTL might impact the overall dynamics of the infection.

A better understanding of immune response dynamics and virus control in HIV infection is an important goal of current research. While measurements are often recorded in the blood, intricate dynamics occur in the lymphoid tissue. Recent data indicate that killer T cell responses, or CTL, show reduced homing to the follicular compartment of the lymphoid tissue, while the majority of the CTL remain in the extrafollicular site, which appears to contribute to the observed unequal distribution of virus load in the two locations. Here, these dynamics are studied with 2-compartment mathematical models. They reproduce previously published as well as newly presented experimental data from CTL depletion studies. Beyond this, the models indicate that so far unknown details of the CTL dynamics, in particular the potential of CTL to undergo antigen-induced expansion in the follicular compartment, can be important determinants of outcome. We find that antigen-induced expansion of CTL in the follicular site can result in more pronounced virus compartmentalization, and essentially in clearance of virus-producing cells from the extrafollicular site. We use the models to predict how experimental addition of engineered, follicular-homing CTL to macaques, influence the overall infection dynamics and level of virus control. Understanding these dynamics is an important step in attempts to improve the level of immune-mediated virus control.

Novel Imaging Methods for Analysis of Tissue Resident Cells in HIV/SIV

The use of advanced tissue-imaging methodologies has greatly facilitated the study of molecular mechanisms and cellular interactions in humans and animal models of disease. Particularly, in HIV research, there is an ever-increasing demand for a comprehensive analysis of immune cell dynamics at tissue level stemming from the need to advance our understanding of those interactions that regulate the generation of adaptive antigen-specific immune responses. The latter is critical for the development of vaccines to elicit broadly neutralizing antibodies as well as for the discovery of novel targets for immuno-therapies to strengthen the cytolytic arm of the immune system at local level. In this review, we focus on current and emerging imaging technologies, discuss their strengths and limitations, and examine how such technologies can inform the development of new treatments and vaccination strategies. We also present some perspective on the future of the technology development.

Expansion of Simian Immunodeficiency Virus (SIV)-Specific CD8 T Cell Lines from SIV-Naive Mauritian Cynomolgus Macaques for Adoptive Transfer

CD8 T cells play a crucial role in the control of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). However, the specific qualities and characteristics of an effective CD8 T cell response remain unclear. Although targeting breadth, cross-reactivity, polyfunctionality, avidity, and specificity are correlated with HIV control, further investigation is needed to determine the precise contributions of these various attributes to CD8 T cell efficacy. We developed protocols for isolating and expanding SIV-specific CD8 T cells from SIV-naive Mauritian cynomolgus macaques (MCM). These cells exhibited an effector memory phenotype, produced cytokines in response to cognate antigen, and suppressed viral replication in vitro. We further cultured cell lines specific for four SIV-derived epitopes, Nef103-111 RM9, Gag389-394 GW9, Env338-346 RF9, and Nef254-262 LT9. These cell lines were up to 94.4% pure, as determined by major histocompatibility complex (MHC) tetramer analysis. After autologous transfer into two MCM recipients, expanded CD8 T cells persisted in peripheral blood and lung tissue for at least 24 weeks and trafficked to multiple extralymphoid tissues. However, these cells did not impact the acute-phase SIV load after challenge compared to historic controls. The expansion and autologous transfer of SIV-specific T cells into naive animals provide a unique model for exploring cellular immunity and the control of SIV infection and facilitate a systematic evaluation of therapeutic adoptive transfer strategies for eradication of the latent reservoir.

IMPORTANCE

CD8 T cells play a crucial role in the control of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). Autologous adoptive transfer studies followed by SIV challenge may help define the critical elements of an effective T cell response to HIV and SIV infection. We developed protocols for isolating and expanding SIV-specific CD8 T cells from SIV-naive Mauritian cynomolgus macaques. This is an important first step toward the development of autologous transfer strategies to explore cellular immunity and potential therapeutic applications in the SIV model.

Role of individual's T-cell immunome in controlling HIV-1 progression

Viral and host factors can influence HIV-1 progression, among them human leucocyte antigen (HLA) has shown the strongest effect. However, studies on the functional contribution of HLA in controlling HIV progression toward AIDS are limited by multiple issues, including the viral strain variability within the study subjects. In this study, in a cohort of children infected with a monophyletic strain (CRF02_AG) during an outbreak, we evaluated the HIV-1 Gag, Vif, Vpr, Tat and hepatitis C virus E1/E2 (as control) proteins circulating in a cohort for the capability to be presented by the HLA molecules in the same population. A total of 70 Non-progressors and 37 Progressors to AIDS were evaluated. In the presence of a constant capability of HIV-1 to mutate in the region containing epitopes of Gag protein, the number of epitopes recognized in silico by the combination of the HLA alleles along the Gag consensus sequence is significantly higher in the Non-progressors compared with Progressors (HLA-A: Non-progressors = 1.532 ± 1.211, Progressors = 0.7714 ± 1.031, P = 0.0016; HLA-B: Non-progressors = 1.556 ± 1.298, Progressors = 1.000 ± 0.817, P = 0.0319; HLA-DR: Non-progressors = 13.30 ± 9.488, Progressors = 7.294 ± 6.952, P = 0.0006). Similar results were obtained for the other HIV-1 proteins Vif and Vpr, whereas no differences were obtained in the number of epitopes for the hepatitis C virus E1/E2 protein sequence or for the scrambled HIV-1 sequence. Finally, the results were confirmed also in a subgroup of subjects where both HLA typing and Gag sequence were available. In conclusion, in the absence of bias due to viral strain diversity, it is the overall fitting of the HLA molecules that are capable of better binding HIV-1 proteins in determining the major role in the control of HIV-1 replication and progression to AIDS.

Accelerated crossing of fitness valleys through division of labor and cheating in asexual populations

Complex traits can require the accumulation of multiple mutations that are individually deleterious. Their evolution requires a fitness valley to be crossed, which can take relatively long time spans. A new evolutionary mechanism is described that accelerates the emergence of complex phenotypes, based on a “division of labor” game and the occurrence of cheaters. If each intermediate mutation leads to a product that can be shared with others, the complex type can arise relatively quickly as an emergent property among cooperating individuals, without any given individual having to accumulate all mutations. Moreover, the emergence of cheaters that destroy cooperative interactions can lead to the emergence of individuals that have accumulated all necessary mutations on a time scale that is significantly faster than observed in the absence of cooperation and cheating. Application of this mechanism to somatic and microbial evolution is discussed, including evolutionary processes in tumors, biofilms, and viral infections.

Correlates of protective cellular immunity revealed by analysis of population-level immune escape pathways in HIV-1

HLA class I-associated polymorphisms identified at the population level mark viral sites under immune pressure by individual HLA alleles. As such, analysis of their distribution, frequency, location, statistical strength, sequence conservation, and other properties offers a unique perspective from which to identify correlates of protective cellular immunity. We analyzed HLA-associated HIV-1 subtype B polymorphisms in 1,888 treatment-naïve, chronically infected individuals using phylogenetically informed methods and identified characteristics of HLA-associated immune pressures that differentiate protective and nonprotective alleles. Over 2,100 HLA-associated HIV-1 polymorphisms were identified, approximately one-third of which occurred inside or within 3 residues of an optimally defined cytotoxic T-lymphocyte (CTL) epitope. Differential CTL escape patterns between closely related HLA alleles were common and increased with greater evolutionary distance between allele group members. Among 9-mer epitopes, mutations at HLA-specific anchor residues represented the most frequently detected escape type: these occurred nearly 2-fold more frequently than expected by chance and were computationally predicted to reduce peptide-HLA binding nearly 10-fold on average. Characteristics associated with protective HLA alleles (defined using hazard ratios for progression to AIDS from natural history cohorts) included the potential to mount broad immune selection pressures across all HIV-1 proteins except Nef, the tendency to drive multisite and/or anchor residue escape mutations within known CTL epitopes, and the ability to strongly select mutations in conserved regions within HIV's structural and functional proteins. Thus, the factors defining protective cellular immune responses may be more complex than simply targeting conserved viral regions. The results provide new information to guide vaccine design and immunogenicity studies.

Breast milk cellular HIV-specific interferon γ responses are associated with protection from peripartum HIV transmission

OBJECTIVE

Breast milk is a major route of infant HIV infection, yet the majority of breast-fed, HIV-exposed infants escape infection by unknown mechanisms. This study aimed to investigate the role of HIV-specific breast milk cells in preventing infant HIV infection.

DESIGN

A prospective study was designed to measure associations between maternal breast milk HIV-specific interferon-γ (IFN-γ) responses and infant HIV-1 detection at 1 month of age.

METHODS

In a Kenyan cohort of HIV-infected mothers, blood and breast milk HIV-gag IFN-γ ELISpot responses were measured. Logistic regression was used to measure associations between breast milk IFN-γ responses and infant HIV infection at 1 month of age.

RESULTS

IFN-γ responses were detected in breast milk from 117 of 170 (69%) women. IFN-γ responses were associated with breast milk viral load, levels of macrophage inflammatory protein (MIP) 1α, MIP-1β, regulated upon activation, normal T-cell expressed, and secreted and stromal-cell derived factor 1 and subclinical mastitis. Univariate factors associated with infant HIV infection at 1 month postpartum included both detection and breadth of breast milk IFN-γ response (P = 0.08, P = 0.04, respectively), breast milk MIP-1β detection (P = 0.05), and plasma (P = 0.004) and breast milk (P = 0.004) viral load. In multivariate analyses adjusting for breast milk viral load and MIP-1β, breast milk IFN-γ responses were associated with an approximately 70% reduction in infant HIV infection [adjusted odds ratio (aOR) 0.29, 95% confidence interval (CI) 0.092-0.91], and each additional peptide pool targeted was associated with an approximately 35% reduction in infant HIV (aOR 0.65, 95% CI 0.44-0.97).

CONCLUSION

These data show breast milk HIV-gag-specific IFN-γ cellular immune responses are prevalent and may contribute to protection from early HIV transmission. More broadly, these data suggest breast milk cellular responses are potentially influential in decreasing mother-to-child transmission of viruses.

Specific CD8+ T cell responses correlate with control of simian immunodeficiency virus replication in Mauritian cynomolgus macaques

Specific major histocompatibility complex (MHC) class I alleles are associated with an increased frequency of spontaneous control of human and simian immunodeficiency viruses (HIV and SIV). The mechanism of control is thought to involve MHC class I-restricted CD8(+) T cells, but it is not clear whether particular CD8(+) T cell responses or a broad repertoire of epitope-specific CD8(+) T cell populations (termed T cell breadth) are principally responsible for mediating immunologic control. To test the hypothesis that heterozygous macaques control SIV replication as a function of superior T cell breadth, we infected MHC-homozygous and MHC-heterozygous cynomolgus macaques with the pathogenic virus SIVmac239. As measured by a gamma interferon enzyme-linked immunosorbent spot assay (IFN-γ ELISPOT) using blood, T cell breadth did not differ significantly between homozygotes and heterozygotes. Surprisingly, macaques that controlled SIV replication, regardless of their MHC zygosity, shared durable T cell responses against similar regions of Nef. While the limited genetic variability in these animals prevents us from making generalizations about the importance of Nef-specific T cell responses in controlling HIV, these results suggest that the T cell-mediated control of virus replication that we observed is more likely the consequence of targeting specificity rather than T cell breadth.

Infection of HIV-specific CD4 T helper cells and the clonal composition of the response

A hallmark of human immunodeficiency virus is its ability to infect CD4+ T helper cells, thus impairing helper cell responses and consequently effector responses whose maintenance depends on help (such as killer T cells and B cells). In particular, the virus has been shown to infect HIV-specific helper cells preferentially. Using mathematical models, we investigate the consequence of this assumption for the basic dynamics between HIV and its target cells, assuming the existence of two independently regulated helper cell clones, directed against different epitopes of the virus. In contrast to previous studies, we examine a relatively simple scenario, only concentrating on the interactions between the virus and its target cells, not taking into account any helper-dependent effector responses. Further, there is no direct competition for space or antigenic stimulation in the model. Yet, a set of interesting outcomes is observed that provide further insights into factors that shape helper cell responses. Despite the absence of competition, a stronger helper cell clone can still exclude a weaker one because the two clones are infected by the same pathogen, an ecological concept called "apparent competition". Moreover, we also observe "facilitation": if one of the helper cell clones is too weak to become established in isolation, the presence of a stronger clone can provide enhanced antigenic stimulation, thus allowing the weaker clone to persist. The dependencies of these outcomes on parameters is explored. Factors that reduce viral infectivity and increase the death rate of infected cells promote coexistence, which is in agreement with the observation that stronger immunity correlates with broader helper cell responses. The basic model is extended to explicitly take into account helper-dependent CTL responses and direct competition. This study sheds further light onto the factors that can influence the clonal composition of HIV-specific helper cell responses, which has implications for the overall pattern of disease progression.

Polyfunctional analysis of Gag and Nef specific CD8+ T-cell responses in HIV-1 infected Indian individuals

Polyfunctional CD8+ T-cells have been described as most competent in controlling viral replication. We studied the impact of antigen persistence on the polyfunctional immune responses of CD8+ T-lymphocytes to HIV Gag and Nef peptides and polyclonal stimuli in 40 ART naïve HIV infected individuals and analyzed the alterations in T-cell functionality in early and late stages of infection. Significantly elevated level of global response and polyfunctional profile of CD8+ T-cells were observed to polyclonal stimulation, than HIV specific antigens in chronically infected individuals. However no key differences were observed in CD8+ T-cell functional profile in any of the 15 unique subsets for Gag and Nef specific antigens. The subjects in early stage of infection (defined as a gap of 6 months or less between seroconversion and enrolment and with no apparent clinical symptoms) had a higher degree of response functionality (4+ or 3+ different functions simultaneously) than in the late stage infection (defined as time duration since seroconversion greater than 6 months). The data suggest that persistence of antigen during chronic infection leads to functional impairment of HIV specific responses.

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.

Elicitation of broad CTL response against HIV-1 by the DNA vaccine encoding artificial multi-component fusion protein MultiHIV--study in domestic pigs

Broad CTL response against HIV-1 is one factor that helps to control the viral replication. We have constructed a DNA vaccine that encodes a large artificial fusion protein (MultiHIV) and shown it to be immunogenic in mice, swine and macaques. Inbred mice revealed CTL response only against two epitopes due to limited MHC class I variability. To assess the quality of the CTL response we addressed this question in domestic swine. Number of presented epitopes varied between 7 and 14 among the five selected animals. Epitopes detected in swine are localised in the same antigenic regions recognised in humans. This can be explained by the fact that swine MHC-I (SLA-I) complex is remarkably similar to human HLA-I. These results also indicate that immunogenicity profile of vaccines in domestic swine may predict the outcome of human immunisation.

Impact of select immunologic and virologic biomarkers on CD4 cell count decrease in patients with chronic HIV-1 subtype C infection: results from Sinikithemba Cohort, Durban, South Africa

BACKGROUND

The extent to which immunologic and clinical biomarkers influence human immunodeficiency virus type 1 (HIV-1) infection outcomes remains incompletely characterized, particularly for non-B subtypes. On the basis of data supporting in vitro HIV-1 protein-specific CD8 T lymphocyte responses as correlates of immune control in cross-sectional studies, we assessed the relationship of these responses, along with established HIV-1 biomarkers, with rates of CD4 cell count decrease in individuals infected with HIV-1 subtype C.

METHODS

Bivariate and multivariate mixed-effects models were used to assess the relationship of baseline CD4 cell count, plasma viral load, human leukocyte antigen (HLA) class I alleles, and HIV-1 protein-specific CD8 T cell responses with the rate of CD4 cell count decrease in a longitudinal population-based cohort of 300 therapy-naive, chronically infected adults with baseline CD4 cell counts >200 cells/mm(3) and plasma viral loads >500 copies/mL over a median of 25 months of follow-up.

RESULTS

In bivariate analyses, baseline CD4 cell count, plasma viral load, and possession of a protective HLA allele correlated significantly with the rate of CD4 cell count decrease. No relationship was observed between HIV-1 protein-specific CD8 T cell responses and CD4 cell count decrease. Results from multivariate models incorporating baseline CD4 cell counts (201-350 vs >350 cells/mm(3)), plasma viral load (< or =100,000 vs >100,000 copies/mL), and HLA (protective vs not protective) yielded the ability to discriminate CD4 cell count decreases over a 10-fold range. The fastest decrease was observed among individuals with CD4 cell counts >350 cells/mm(3) and plasma viral loads >100,000 copies/mL with no protective HLA alleles (-59 cells/mm(3) per year), whereas the slowest decrease was observed among individuals with CD4 cell counts 201-350 cells/mm(3), plasma viral loads < or =100,000 copies/mL, and a protective HLA allele (-6 cells/mm(3) per year).

CONCLUSIONS

The combination of plasma viral load and HLA class I type, but not in vitro HIV-1 protein-specific CD8 T cell responses, differentiates rates of CD4 cell count decrease in patients with chronic subtype-C infection better than either marker alone.

Induction of novel CD8+ T-cell responses during chronic untreated HIV-1 infection by immunization with subdominant cytotoxic T-lymphocyte epitopes

OBJECTIVE

To investigate the potential to induce additional cytotoxic T-lymphocyte (CTL) immunity during chronic HIV-1 infection.

DESIGN

We selected infrequently targeted or subdominant but conserved HLA-A*0201-binding epitopes in Gag, Pol, Env, Vpu and Vif. These relatively immune silent epitopes were modified as anchor-optimized peptides to improve immunogenicity and delivered on autologous monocyte-derived dendritic cells (MDDCs).

METHODS

Twelve treatment-naïve HLA-A*0201 HIV-1-infected Danish individuals received 1 x 10 MDDCs subcutaneously (s.c.) (weeks 0, 2, 4 and 8), pulsed with seven CD8 T-cell epitopes and three CD4 T-cell epitopes. Epitope-specific responses were evaluated by intracellular cytokine staining for interferon-gamma, tumor necrosis factor alpha and interleukin-2 and/or pentamer labeling 3 weeks prior to, 10 weeks after and 32 weeks after the first immunization.

RESULTS

Previously undetected T-cell responses specific for one or more epitopes were induced in all 12 individuals. Half of the participants had sustained CD4 T-cell responses 32 weeks after immunization. No severe adverse effects were observed. No overall or sustained change in viral load or CD4 T-cell counts was observed.

CONCLUSION

These data show that it is possible to generate new T-cell responses in treatment-naive HIV-1-infected individuals despite high viral loads, and thereby redirect immunity to target new multiple and rationally selected subdominant CTL epitopes. Further optimization could lead to stronger and more durable cellular responses to selected epitopes with the potential to control viral replication and prevent disease in HIV-1-infected individuals.

Antigen sensitivity is a major determinant of CD8+ T-cell polyfunctionality and HIV-suppressive activity

CD8(+) T cells are major players in the immune response against HIV. However, recent failures in the development of T cell-based vaccines against HIV-1 have emphasized the need to reassess our basic knowledge of T cell-mediated efficacy. CD8(+) T cells from HIV-1-infected patients with slow disease progression exhibit potent polyfunctionality and HIV-suppressive activity, yet the factors that unify these properties are incompletely understood. We performed a detailed study of the interplay between T-cell functional attributes using a bank of HIV-specific CD8(+) T-cell clones isolated in vitro; this approach enabled us to overcome inherent difficulties related to the in vivo heterogeneity of T-cell populations and address the underlying determinants that synthesize the qualities required for antiviral efficacy. Conclusions were supported by ex vivo analysis of HIV-specific CD8(+) T cells from infected donors. We report that attributes of CD8(+) T-cell efficacy against HIV are linked at the level of antigen sensitivity. Highly sensitive CD8(+) T cells display polyfunctional profiles and potent HIV-suppressive activity. These data provide new insights into the mechanisms underlying CD8(+) T-cell efficacy against HIV, and indicate that vaccine strategies should focus on the induction of HIV-specific T cells with high levels of antigen sensitivity to elicit potent antiviral efficacy.

A prime-boost immunisation regimen using recombinant BCG and Pr55(gag) virus-like particle vaccines based on HIV type 1 subtype C successfully elicits Gag-specific responses in baboons

Mycobacterium bovis BCG is considered an attractive live bacterial vaccine vector. In this study, we investigated the immune response of baboons to a primary vaccination with recombinant BCG (rBCG) constructs expressing the gag gene from a South African HIV-1 subtype C isolate, and a boost with HIV-1 subtype C Pr55(gag) virus-like particles (Gag VLPs). Using an interferon enzyme-linked immunospot assay, we show that although these rBCG induced only a weak or an undetectable HIV-1 Gag-specific response on their own, they efficiently primed for a Gag VLP boost, which strengthened and broadened the immune responses. These responses were predominantly CD8+ T cell-mediated and recognised similar epitopes as those targeted by humans with early HIV-1 subtype C infection. In addition, a Gag-specific humoral response was elicited. These data support the development of HIV-1 vaccines based on rBCG and Pr55(gag) VLPs.

Differential patterns of immune escape at Tat-specific cytotoxic T cell epitopes in pigtail macaques

Cytotoxic T lymphocyte responses to conserved proteins such as Gag within HIV- or SIV-infected hosts can facilitate partial control of viremia. However, the utility of targeting variable viral proteins by CTL responses is unclear. We studied CTL responses to regulatory and accessory proteins of SIV in pigtail macaques. The regulatory and accessory proteins were the most commonly targeted proteins by CTL responses from pigtail macaques. We identified 2 novel Tat-specific CTL responses that were both restricted by the Mane-A10 allele. Viral escape at one of the Tat epitopes, KSA10, was slower in comparison to another Tat epitope KVA10. The kinetics of escape of the KSA10 Tat epitope were more similar to an immunodominant KP9 Gag epitope also restricted by Mane-A10. Our results suggest that some regulatory or accessory CTL epitopes may be useful targets for vaccination against HIV.

Continuous improvement in the immune system of HIV-infected children on prolonged antiretroviral therapy

BACKGROUND

The goal of HAART is to promote reconstitution of CD4+ T cells and other immune responses. We evaluated the extent and the kinetics of immune reconstitution in HIV-infected children over 144 weeks of successful HAART.

METHODS

Thirty-seven children receiving their first HAART regimen had plasma HIV RNA; T cells and subpopulations; T-cell rearrangement excision circles (TREC) DNA; candida, HIVCD4 and HIVCD8 enzyme-linked immunospot measured at regular intervals.

RESULTS

Plasma HIV RNA became undetectable in 81% of patients at 24 weeks and remained undetectable in 77% at 144 weeks. In contrast, CD4+% continuously increased. Distribution of T-cell subpopulations changed rapidly during the first 48 weeks of HAART and more slowly thereafter. At 144 weeks, total, naive and activated CD4+% and naive CD8+% of HIV-infected children were not significantly different from those of healthy age-matched controls, whereas total and activated CD8+% remained elevated. CD4 and CD8 TREC content increased only during the first 48 weeks of HAART. They positively correlated with each other and with total CD4+%, naive CD4+% and naive CD8+%. Candida and HIVCD4 enzyme-linked immunospot increased over time reaching peak values at 48 weeks and 144 weeks, respectively. HIVCD8 enzyme-linked immunospot decreased in magnitude over 144 weeks of HAART but retained its breadth. Baseline CD4+% positively correlated with CD4+% and with functional immune reconstitution at week 144, whereas baseline TREC correlated with TREC at week 144.

CONCLUSION

HIV-infected children acquired normal distribution of CD4 T cells and other subpopulations and recovered CD4-mediated HIV immunity after 144 weeks of HAART.

Effects of recombinant human growth hormone on HIV-1-specific T-cell responses, thymic output and proviral DNA in patients on HAART: 48-week follow-up

BACKGROUND

Efficacious immune-based therapy in treated chronic HIV-1 infection requires the induction of virus-specific CD4+ T cells and subsequent maturation and maintenance of specific memory CD8+ T cells. Concomitant daily administration of recombinant human growth hormone (rhGH) with highly active antiretroviral therapy (HAART) was used in chronically infected patients with lipodystrophy in an attempt to reconstitute these virus-specific T-cell responses.

METHODS

Individuals with chronic HIV-1 infection on HAART were enrolled on a randomized, double-blinded, placebo-controlled study to receive rhGH therapy. We assessed HIV-1-specific proliferative CD4+ and interferon-gamma (IFN-gamma)-producing CD8+ T-cell responses, quantified thymic output and proviral HIV-1 DNA at the following time points: baseline; after 12 weeks of rhGH therapy; at 24 weeks, after randomization into three groups [placebo weeks 12-24 (Group A), alternate-day dosing weeks 12-24 (Group B), and twice-per-week dosing weeks 12-24 (Group C)]; and at 48 weeks after all patients had received HAART alone for the final 24 weeks.

RESULTS

We found significant increases in both proliferative CD4+ and IFN-gamma-producing CD8+ HIV-1-specific T-cell responses after daily administration of rhGH. This increase was focused on HIV-1 Gag-specific T-cell responses. Following subsequent randomisation into different dosing regimens, HIV-1-specific proliferative CD4+ T-cell responses declined in patients receiving less frequent dosing of rhGH, while virus-specific IFN-gamma-producing CD8+ T-cell responses were maintained for longer periods of time. There was no significant change in thymic output and the cell-associated HIV-1 DNA remained stable in most patients. An increased anti-HIV-1 Nef-specific CD4+ T-cell proliferative response was correlated to a decrease in proviral load, and an increased HIV-1 Gag-specific IFN-gamma-producing CD8+ T-cell response correlated with an increase in proviral load.

CONCLUSION

The implication of these data is that daily dosing of rhGH with HAART, in addition to improving HIV-1-associated lipodystrophy, may reverse some of the T-lymphocyte dysfunction seen in most treated HIV-1-positive patients, in a dose-dependent manner. Such immune-based therapeutic strategies used in treated, chronic HIV-1 infection may enable the induction of virus-specific CD4+ T cells essential for the subsequent 'kick-start' and expansion of virus-specific CD8+ T cells.

TRIAL REGISTRATION

GH in Lipoatrophy IMP22350.

Full-length characterization of A1/D intersubtype recombinant genomes from a therapy-induced HIV type 1 controller during acute infection and his noncontrolling partner

To increase the understanding of mechanisms of HIV control we have genetically and immunologically characterized a full-length HIV-1 isolated from an acute infection in a rare case of undetectable viremia. The subject, a 43-year-old Danish white male (DK1), was diagnosed with acute HIV-1 infection after 1 year in Uganda. Following transient antiretroviral therapy DK1 maintained undetectable viral load for more than 10 years. His Ugandan wife (UG1) developed high viral load. HIV-1 sequences from both individuals were compared by bootscanning for recombination break points. Diversity plots and phylogenic trees were constructed and diversity and evolutionary distances were calculated. Intracellular IFN-gamma in CD8(+)CD3(+) T-lymphocyte reactions was investigated by intracellular flow cytometry (IC-FACS). Virus isolates from both patients were A1D intersubtype recombinants showing 98% sequence homology in shared regions. Four of seven crossover points were identical; however, the env gene from UG1 was subtype D, but A1 in DK1. Both viruses encoded proteins of the expected length and replicated equally well in vitro. DK1 and UG1 shared the HLA-A02 tissue type. HLA-A02-restricted CD8(+) T cell IFN-gamma IC-FACS response in DK1 was detected against only one (Pol(476)) of 23 conserved epitopes. Neutralizing antibodies were induced only to the homologous isolate. These results indicate an A1D intersubtype recombination or transmission of a minor variant. Transient early antiretroviral therapy may have induced full HIV-1 control in this individual mediated by a narrow specific cytotoxic T lymphocyte and neutralizing antibody response and/or other factors yet to be characterized.

Superior control of HIV-1 replication by CD8+ T cells is reflected by their avidity, polyfunctionality, and clonal turnover

The key attributes of CD8⁺ T cell protective immunity in human immunodeficiency virus (HIV) infection remain unclear. We report that CD8⁺ T cell responses specific for Gag and, in particular, the immunodominant p24 epitope KK10 correlate with control of HIV-1 replication in human histocompatibility leukocyte antigen (HLA)–B27 patients. To understand further the nature of CD8⁺ T cell–mediated antiviral efficacy, we performed a comprehensive study of CD8⁺ T cells specific for the HLA-B27–restricted epitope KK10 in chronic HIV-1 infection based on the use of multiparametric flow cytometry together with molecular clonotypic analysis and viral sequencing. We show that B27-KK10–specific CD8⁺ T cells are characterized by polyfunctional capabilities, increased clonal turnover, and superior functional avidity. Such attributes are interlinked and constitute the basis for effective control of HIV-1 replication. These data on the features of effective CD8⁺ T cells in HIV infection may aid in the development of successful T cell vaccines.

Lentiviral Vectors Encoding HIV-1 Polyepitopes Induce Broad CTL Responses In Vivo

Lentiviral vectors have been tested as vaccination vectors in anti-tumoral and anti-viral models. They efficiently transduce dendritic cells and stimulate strong T-cell responses against the encoded antigen. However, their capacity to stimulate a cytotoxic T-lymphocyte (CTL) response against several antigens has not been evaluated. Broad anti-human immunodeficiency virus 1 (HIV-1) T-cell immune responses are important for the control of HIV replication. We evaluated the potential of polyepitope-encoding lentiviral vectors to induce broad anti-HIV CTL responses. We constructed two lentiviral vectors coding for an HLA-A2- or HLA-B7-restricted polyepitope and evaluated their immunogenicity by direct injection of vector particles in HLA-A2 or HLA-B7 transgenic mice. In vitro cytotoxicity assays showed that a single immunization induces a strong, diversified, and long-lasting CTL response in both mouse models. CTL responses were directed against all 13 epitopes in the HLA-A2 system and 8 out of 12 in the HLA-B7 system. A second immunization augmented the number of responding mice in the HLA-A2 system but not in the HLA-B7 system. HLA-B7-immunized mice mounted strong interferon-gamma (IFN-gamma)-secreting T-cell responses against a majority of the epitopes and lysed peptide-loaded target cells in vivo. CTL responses in HLA-B7 mice were only partially dependent on CD4 T-cell help. This work underlines the potential of lentiviral vectors as candidates for therapeutic vaccination against acquired immunodeficiency syndrome.

Sequence conservation of subdominant HLA-A2-binding CTL epitopes in HIV-1 clinical isolates and CD8+T-lymphocyte cross-recognition may explain the immune reaction in infected individuals

Cytotoxic T-lymphocytes (CTL) are critical for immune control of infection with human immunodeficiency virus type-1 (HIV-1) and searches for relevant CTL epitopes for immune therapy are ongoing. Recently, we identified 28 HLA-A2-binding HIV-1 CTL epitopes (1). In this follow-up study we fully genome sequenced HIV-1 from 11 HLA-A2(+) patients to examine the sequence variation of these natural epitopes and compared them with the patient's CD8(+) T-cell recall response. Often the epitope was conserved but only a few patients showed a CD8(+) T-cell recall response. This infrequent targeting may be explained by immune subdominance. CD8(+) T-cell recall response to a natural epitope could be measured despite sequence differences in the patient's virus. T-cell cross-reaction between such variants could be demonstrated in HLA-A2 transgenic mice. Nine infrequently targeted but conserved or cross-reacting epitopes were identified in seven HIV-1 proteins. More immunogenic anchor amino acid optimized immunogens were designed that induced T-cell cross-reaction with these natural epitopes. It is concluded that most of the new CTL epitopes are conserved but subdominant during the infection. It is suggested that T-cell promiscuity may explain the observed CD8(+) T-cell reaction to epitope variants and it may be possible to use the selected immune optimized epitope peptides for therapeutic vaccination.

Predictors of disease progression in HIV infection: a review

During the extended clinically latent period associated with Human Immunodeficiency Virus (HIV) infection the virus itself is far from latent. This phase of infection generally comes to an end with the development of symptomatic illness. Understanding the factors affecting disease progression can aid treatment commencement and therapeutic monitoring decisions. An example of this is the clear utility of CD4+ T-cell count and HIV-RNA for disease stage and progression assessment. Elements of the immune response such as the diversity of HIV-specific cytotoxic lymphocyte responses and cell-surface CD38 expression correlate significantly with the control of viral replication. However, the relationship between soluble markers of immune activation and disease progression remains inconclusive. In patients on treatment, sustained virological rebound to >10,000 copies/mL is associated with poor clinical outcome. However, the same is not true of transient elevations of HIV RNA (blips). Another virological factor, drug resistance, is becoming a growing problem around the globe and monitoring must play a part in the surveillance and control of the epidemic worldwide. The links between chemokine receptor tropism and rate of disease progression remain uncertain and the clinical utility of monitoring viral strain is yet to be determined. The large number of confounding factors has made investigation of the roles of race and viral subtype difficult, and further research is needed to elucidate their significance. Host factors such as age, HLA and CYP polymorphisms and psychosocial factors remain important, though often unalterable, predictors of disease progression. Although gender and mode of transmission have a lesser role in disease progression, they may impact other markers such as viral load. Finally, readily measurable markers of disease such as total lymphocyte count, haemoglobin, body mass index and delayed type hypersensitivity may come into favour as ART becomes increasingly available in resource-limited parts of the world. The influence of these, and other factors, on the clinical progression of HIV infection are reviewed in detail, both preceding and following treatment initiation.

Stable pattern of HIV-1 subtype C Gag-specific T-cell responses coincides with slow rate of CD4 T-cell decline in HIV-infected Ethiopians

We studied HIV-1 clade C Gag-specific T-cell responses in five HIV-infected Ethiopians with a relatively slow (< 15 cells/microl per year) and five with a fast (> 45 cells/microl per year) CD4 T-cell decline longitudinally. Six study subjects had T-cell responses directed to one or more HIV-1 Gag peptides. The persistence of strong and broad anti-Gag cytotoxic T-lymphocyte responses was associated with a slow rate of CD4 T-cell decline and with human leukocyte antigen alleles from the B27 supertype.

Not all cytokine-producing CD8+ T cells suppress simian immunodeficiency virus replication

Current assays of CD8+ T-lymphocyte function measure cytokine production rather than the ability of these lymphocytes to suppress viral replication. Here we show that CD8+ T-cell clones recognizing the same epitope vary enormously in the ability to suppress simian immunodeficiency virus SIVmac239 replication in an in vitro suppression assay. However, all Nef(165-173)IW9- and Vif(66-73)HW8-specific clones from elite controllers effectively suppressed SIV replication. Interestingly, in vitro suppression efficacy was not always associated with the ability to produce gamma interferon, tumor necrosis factor alpha, or interleukin-2.

Expression of human immunodeficiency virus type 1 tat from a replication-deficient herpes simplex type 1 vector induces antigen-specific T cell responses

Herpes simplex type-1 virus (HSV-1) based vectors have been widely used in different gene therapy approaches and also as experimental vaccines against HSV-1 infection. Recent advances in the HSV-1 technology do support the use of replication defective HSV-1 as vaccine vectors for delivery of foreign antigens. We have examined the ability of a recombinant replication-defective HSV-1 vector expressing the HIV-1 Tat protein to induce long-term Tat-specific immune responses in the Balb/c murine model. The results showed that vector administration by the subcutaneous route elicits anti-Tat specific T-cell mediated immune responses in mice characterized by the presence of the Tat-specific cytotoxic activity and production of high levels of IFN-gamma.

SIV escape mutants in rhesus macaques vaccinated with NEF-derived lipopeptides and challenged with pathogenic SIVmac251

BACKGROUND

Emergence of viral variants that escape CTL control is a major hurdle in HIV vaccination unless such variants affect gene regions that are essential for virus replication. Vaccine-induced multispecific CTL could also be able to control viral variants replication. To explore these possibilities, we extensively characterized CTL responses following vaccination with an epitope-based lipopeptide vaccine and challenge with pathogenic SIVmac251. The viral sequences corresponding to the epitopes present in the vaccine as well as the viral loads were then determined in every macaque following SIV inoculation.

RESULTS

In most cases, the emergence of several viral variants or mutants within vaccine CTL epitopes after SIV challenge resulted in increased viral loads except for a single macaque, which showed a single escape viral variant within its 6 vaccine-induced CTL epitopes.

CONCLUSION

These findings provide a better understanding of the evolution of CD8+ epitope variations after vaccination-induced CTL expansion and might provide new insight for the development of an effective HIV vaccine.

Role of avidity and breadth of the CD4 T cell response in progression to AIDS

The great variability in the time between infection with HIV and the onset of AIDS has been the object of intense study. In the current work, we examine a mathematical model that focuses on the role of immune response variability between patients. We study the effect of variation in both the avidity and the breadth of the immune response on within-patient disease dynamics, viral setpoint and time to AIDS. We conclude that immune response variability can explain the observed variability in disease progression to a large extent. It turns out that the avidity, more than the breadth of the immune response, determines disease progression, and that the average avidity of the five best clones is a much better correlate for disease progression than the total number of clones responding. For the design of vaccines, this would suggest that, if given the choice between stimulating a broader, but average avidity response or a narrower high-avidity response, the latter option would yield better control of virus load and consequently slow down disease progression.

Dendritic cell-lysosomal-associated membrane protein (LAMP) and LAMP-1-HIV-1 gag chimeras have distinct cellular trafficking pathways and prime T and B cell responses to a diverse repertoire of epitopes

Ag processing is a critical step in defining the repertoire of epitope-specific immune responses. In the present study, HIV-1 p55Gag Ag was synthesized as a DNA plasmid with either lysosomal-associated membrane protein-1 (LAMP/gag) or human dendritic cell-LAMP (DC-LAMP/gag) and used to immunize mice. Analysis of the cellular trafficking of these two chimeras demonstrated that both molecules colocalized with MHC class II molecules but differed in their overall trafficking to endosomal/lysosomal compartments. Following DNA immunization, both chimeras elicited potent Gag-specific T and B cell immune responses in mice but differ markedly in their IL-4 and IgG1/IgG2a responses. The DC-LAMP chimera induced a stronger Th type 1 response. ELISPOT analysis of T cell responses to 122 individual peptides encompassing the entire p55gag sequence (15-aa peptides overlapping by 11 residues) showed that DNA immunization with native gag, LAMP/gag, or DC-LAMP/gag induced responses to identical immunodominant CD4+ and CD8+ peptides. However, LAMP/gag and DC-LAMP/gag plasmids also elicited significant responses to 23 additional cryptic epitopes that were not recognized after immunization with native gag DNA. The three plasmids induced T cell responses to a total of 39 distinct peptide sequences, 13 of which were induced by all three DNA constructs. Individually, DC-LAMP/gag elicited the most diverse response, with a specific T cell response against 35 peptides. In addition, immunization with LAMP/gag and DC-LAMP/gag chimeras also promoted Ab secretion to an increased number of epitopes. These data indicate that LAMP-1 and DC-LAMP Ag chimeras follow different trafficking pathways, induce distinct modulatory immune responses, and are able to present cryptic epitopes.

Poor recognition of HIV-1 Nef protein by CD8 T cells from HIV-1-infected children: impact of age

Recognition of various HIV proteins by CD8 T cells from HIV-infected children was determined by two functional assays. First, using an Elispot assay, we show that 80% of patients recognized Gag, 77% recognized Pol, 61% recognized Env, 44% recognized Nef and 29% recognized Vif. Frequencies of Gag-, Pol-, and Env-specific IFN-gamma producing CD8 T cells were higher than frequencies of Nef and Vif-specific CD8 T cells. The poor recognition of Nef by ex vivo CD8 T cells was confirmed by CTL assays performed in HAART naïve children: 25% of children had positive response against Nef versus 44, 63 and 62% for Env, Gag, and Pol, respectively. Memory Gag-specific CTL were positively correlated with age, whereas Nef-specific CTL were negatively correlated with age. The poor Nef-specific CD8 T cell response in HIV-infected children contrasts with dominance of Nef-specific responses in infected adults.

Immune responses of a designed HIV-1 DNA vaccine on rhesus monkeys

An effective HIV-1 vaccine will be the ultimate solution for the prevention of HIV/AIDS, though HAART plays important roles in treating the disease. In this study, a large-scale recombinant DNA plasmid containing a designed HIV-1 multi-epitope-p24 chimeric gene was prepared and purified. Rhesus monkeys were then inoculated muscularly with the plasmid for four times in week 0, 4, 8 and 18. Whole blood was collected two weeks after the third and fourth inoculation, followed by serum and peripheral blood mononuclear cell (PBMC) separation. The CTL activity and proliferation of PBMCs stimulated by macaque MHC-I-restricted HIV-1 CTL epitope peptide were analyzed by MTT and LDH release assay, respectively. Th1 cytokines in supernatant of cultured PBMC stimulated by HIV-1 CTL epitope peptide and anti-HIV-1 antibody in serum were assayed by ELISA. The results showed that increased CTL target-killing activity, higher secretion of Th1 cytokines (IFN-γ and IL-2) and promoted proliferative reaction of monkey PBMCs stimulated by HIV-1 CTL epitope peptide were detected in the immunization group inoculated by the recombinant DNA vaccine for three times, which were further enhanced by the fourth inoculation. At the same time, HIV-1 specific antibody in serum of immunized monkeys was higher than that in controls. We concluded that the designed HIV-1 DNA vaccine may induce HIV-1 specific cellular and humoral immunity on monkeys.

Capric acid and hydroxypropylmethylcellulose increase the immunogenicity of nasally administered peptide vaccines

Immunization by the nasal route is an established method for the induction of mucosal and systemic humoral and cell-mediated antigen-specific responses. However, the effectiveness of nasal immunization is often hampered by the need for increased doses of antigen. Bioadhesives and absorption enhancers were investigated for their ability to enhance immune responses in mice after nasal immunization with model HIV-1 peptide and protein immunogens. Two additives, hydroxypropylmethylcellulose (HPMC) and capric acid, consistently enhanced antigen-specific serum IgG endpoint titers under conditions in which antigen dose was limiting. Nasal immunization of mice with 20 microg of an HIV-1 peptide immunogen plus cholera toxin (CT) as adjuvant induced serum antipeptide IgG titers of 1:9.5log2 after four immunizations while the addition of CA or HPMC to the vaccine formulation increased serum antipeptide IgG titers to 1:15.4log2 and 1:17.6log2, respectively. When 5 microg recombinant HIV-1 gp41 was used as the immunogen, the addition of CA or HPMC to the vaccine formulation increased serum anti-gp41 IgG titers to 1:11.6log2 and 1:8.8log2, respectively, compared to 1:5.2log2 after three nasal immunizations with 5 microg gp41 + CT alone. Thus, HPMC and capric acid may be useful additives that increase the immunogenicity of nasally administered vaccines and permit less antigen to be used with each immunization.

Virus fitness: concept, quantification, and application to HIV population dynamics

Viral fitness has been broadly studied during the past three decades, mainly to test evolutionary models and population theories difficult to analyze and interpret with more complex organisms. More recent studies, however, are focused in the role of fitness on viral transmission, pathogenesis, and drug resistance. Here, we used human immunodeficiency virus (HIV) as one of the most relevant models to evaluate the importance of viral quasispecies and fitness in HIV evolution, population dynamics, disease progression, and potential clinical implications.

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.

Killer immunoglobulin-like receptors and HLA act both independently and synergistically to modify HIV disease progression

Variation in the host response to infection by pathogens including HIV-1 may be conferred by polymorphic genetic factors such as HLA and killer immunoglobulin-like receptors (KIR) genes. Here, we examined KIR and HLA genotype effects on pretreatment viral load, rate of CD4(+) T-cell decline and progression to AIDS among adult HIV-1-infected patients within the Western Australian HIV Study Cohort. In this study, carriage of KIR genes within the 'B' haplotype (eg KIR2DS2) was specifically associated with a more rapid CD4(+) T-cell decline over time and progression to AIDS. In contrast, KIR gene repertoire had no effect on pretreatment viral load while selected HLA alleles (eg HLA-B*5701, HLA-B*2705) demonstrated significant protective effects on viremia. Furthermore, interactions between specific HLA and KIR genes did appear to influence HIV disease progression. The results suggest that host genetic variation within the HLA and KIR gene complexes have clinically relevant effects on the course of HIV-1/AIDS, acting independently as well as synergistically to modify disease progression at multiple levels.

Screening for CD8 cytotoxic T lymphocytes specific for Gag of human immunodeficiency virus type 1 subtype B′ Henan isolate from China and identification of novel epitopes restricted by the HLA-A2 and HLA-A11 alleles

The human immunodeficiency virus type 1 (HIV-1) epidemic in China is increasing rapidly at an irrepressible rate. It is caused by HIV-1 subtype B′ in central China. After the full-length genome sequencing of the Henan isolate was performed, the definition of optimal cytotoxic T-lymphocyte (CTL) epitopes across the Henan isolate genome has become crucial for vaccine design. In this study, by using ELISPOT assays with synthetic peptides corresponding to the sequence of the Henan isolate, the identification and analysis of Gag-specific CTL responses among 28 treated and 26 untreated infected paid blood donors (PBDs) from the Henan and Hubei provinces of China are presented. These studies focused on CTL responses restricted by the human leukocyte antigen (HLA)-A2 and -A11 molecules, two of the most prominent HLA-A alleles in the Chinese population. The results suggested that, in the subgroup analysis, the magnitude of response in the infected treated subgroup [median, 93 spot-forming cells (SFCs) per 106 peripheral blood mononuclear cells (PBMCs)] was significantly lower than that in the chronically infected untreated subgroup (median, 221 SFCs per 106 PBMCs), and HLA-A2-restricted treated PBDs had a response of a much higher frequency and magnitude than that of HLA-A11-restricted treated PBDs. Moreover, some novel peptides restricted by the HLA-A2 and -A11 molecules were identified.

Basics of the virology of HIV-1 and its replication

Human immunodeficiency virus is undoubtedly the causative agent of AIDS. The understanding of HIV-1 pathogenesis is essential to develop and maintain antiretroviral treatment and vaccination. Since the first isolation of HIV-1 in cell culture, thousands of publications dealing with HIV and/or AIDS per year were released. In this review we give a basic overview of the virology of HIV-1 including the functions of the different HIV-1 proteins required for effective viral replication. Moreover, we summarize the interactive processes between HIV-1 and its target cells. Finally, the HIV-1 specific immune response and the current status of antiretroviral therapy are briefly described in this review.

Longitudinal assessment of human immunodeficiency virus type 1 (HIV-1)-specific gamma interferon responses during the first year of life in HIV-1-infected infants

Human immunodeficiency virus type 1 (HIV-1) infection results in different patterns of viral replication in pediatric compared to adult populations. The role of early HIV-1-specific responses in viral control has not been well defined, because most studies of HIV-1-infected infants have been retrospective or cross-sectional. We evaluated the association between HIV-1-specific gamma interferon (IFN-gamma) release from the cells of infants of 1 to 3 months of age and peak viral loads and mortality in the first year of life among 61 Kenyan HIV-1-infected infants. At 1 month, responses were detected in 7/12 (58%) and 6/21 (29%) of infants infected in utero and peripartum, respectively (P = 0.09), and in approximately 50% of infants thereafter. Peaks of HIV-specific spot-forming units (SFU) increased significantly with age in all infants, from 251/10(6) peripheral blood mononuclear cells (PBMC) at 1 month of age to 501/10(6) PBMC at 12 months of age (P = 0.03), although when limited to infants who survived to 1 year, the increase in peak HIV-specific SFU was no longer significant (P = 0.18). Over the first year of life, infants with IFN-gamma responses at 1 month had peak plasma viral loads, rates of decline of viral load, and mortality risk similar to those of infants who lacked responses at 1 month. The strength and breadth of IFN-gamma responses at 1 month were not significantly associated with viral containment or mortality. These results suggest that, in contrast to HIV-1-infected adults, in whom strong cytotoxic T lymphocyte responses in primary infection are associated with reductions in viremia, HIV-1-infected neonates generate HIV-1-specific CD8+-T-cell responses early in life that are not clearly associated with improved clinical outcomes.

Antiretroviral therapy: when and what to start-- an American perspective

The major US treatment guidelines now recommend starting antiretroviral therapy (ART) later in the course of HIV infection because of an increasing awareness of the difficulties associated with these regimens. Most of the data to support this change come from observational cohort studies. When deciding to start ART, several patient-specific factors and other issues should be considered. Because of the many choices for initial ART, clinicians should individualize the choice, taking into account regimen antiretroviral potency, durability, side effects, toxicities, and convenience to ensure a sustained clinical benefit for the patient.

A vaccinia-based elispot assay for detection of CD8+ T cells from HIV-1 infected children

HIV-specific CD8+ T lymphocytes participate in the control of viral replication in infected patients. These responses are of low intensity in young infants and are decreased by antiretroviral therapy. In the present study, we report on a recombinant Vaccinia virus (rVV)-based Elispot assay for the detection of HIV-specific CD8+ T cells immediately after isolation of peripheral blood mononuclear cells (PBMC). The rVV-based assay was highly sensitive; 48 out of 50 children had a positive response against the rVV encoding HIV Env-Gag-Pol antigen. Interferon-gamma was produced by CD8+ T cells, and CD14+/15+ cells were the main cell subset presenting antigens expressed by rVV. We observed that the cell input per well had a critical influence on the sensitivity of the assay. Results from the ex vivo Elispot assay correlated poorly with those of the 51Cr release assay performed after expansion of PBMC in vitro; thus, both assays gave information on different subsets and/or functions of the HIV-specific T cell response.

Not All Tetramer Binding CD8+ T Cells Can Produce Cytokines and Chemokines Involved in the Effector Functions of Virus-Specific CD8+ T Lymphocytes in HIV-1 Infected Children

In the pediatric human immunodeficiency virus type-1 (HIV-1) infection, the presence of cytotoxic T lymphocytes (CTL) is associated with a slow progression to AIDS. The secretion of cytokines by CTLs may be critical in the control of viral infection. We used the combination of cell surface and intracellular staining to study the functionality of tetramer binding CD8+ T cells recognizing two HIV-1 immunodominant epitopes, in peripheral blood mononuclear cells from HIV-1-infected children. A fraction of tetramer positive CD8+ T cells produce cytokines (IFN-gamma, TNF-alpha) or chemokines (CCL4, CCL5) after ex vivo stimulation with the cognate peptide. There was a negative correlation between the plasma viral load and the percentage of CD8+ Tetramer Gag+ T cells secreting IFN-gamma. This is the first report in the context of pediatric HIV-1 infection showing that only a fraction of HIV-1-specific CD8+ T cells have the capacity to produce cytokines and chemokines implicated in their antiviral functions.

A dominant role for CD8+-T-lymphocyte selection in simian immunodeficiency virus sequence variation

CD8(+) T lymphocytes (CD8-TL) select viral escape variants in both human immunodeficiency virus and simian immunodeficiency virus (SIV) infections. The frequency of CD8-TL viral escape as well as the contribution of escape to overall virus diversification has not been assessed. We quantified CD8-TL selection in SIV infections by sequencing viral genomes from 35 SIVmac239-infected animals at the time of euthanasia. Here we show that positive selection for sequences encoding 46 known CD8-TL epitopes is comparable to the positive selection observed for the variable loops of env. We also found that >60% of viral variation outside of the viral envelope occurs within recognized CD8-TL epitopes. Therefore, we conclude that CD8-TL selection is the dominant cause of SIV diversification outside of the envelope.