Human immunodeficiency virus type 1-specific cytotoxic T lymphocyte activity is inversely correlated with HIV type 1 viral load in HIV type 1-infected long-term survivors

Comparison of the Biological Basis for Non-HIV Transmission to HIV-Exposed Seronegative Individuals, Disease Non-Progression in HIV Long-Term Non-Progressors and Elite Controllers

HIV-exposed seronegative individuals (HESIs) are a small fraction of persons who are multiply exposed to human immunodeficiency virus (HIV), but do not exhibit serological or clinical evidence of HIV infection. In other words, they are groups of people maintaining an uninfected status for a long time, even after being exposed to HIV several times. The long-term non-progressors (LTNPs), on the other hand, are a group of HIV-infected individuals (approx. 5%) who remain clinically and immunologically stable for an extended number of years without combination antiretroviral therapy (cART). Meanwhile, elite controllers are comprise a much lower number (0.5%) of HIV-infected persons who spontaneously and durably control viremia to below levels of detection for at least 12 months, even when using the most sensitive assays, such as polymerase chain reaction (PCR) in the absence of cART. Despite the fact that there is no universal agreement regarding the mechanisms by which these groups of individuals are able to control HIV infection and/or disease progression, there is a general consensus that the mechanisms of protection are multifaceted and include genetic, immunological as well as viral factors. In this review, we analyze and compare the biological factors responsible for the control of HIV in these unique groups of individuals.

The CD8+ T Cell Noncytotoxic Antiviral Responses

The CD8+ T cell noncytotoxic antiviral response (CNAR) was discovered during studies of asymptomatic HIV-infected subjects more than 30 years ago. In contrast to CD8+ T cell cytotoxic lymphocyte (CTL) activity, CNAR suppresses HIV replication without target cell killing. This activity has characteristics of innate immunity: it acts on all retroviruses and thus is neither epitope specific nor HLA restricted. The HIV-associated CNAR does not affect other virus families. It is mediated, at least in part, by a CD8+ T cell antiviral factor (CAF) that blocks HIV transcription. A variety of assays used to measure CNAR/CAF and the effects on other retrovirus infections are described. Notably, CD8+ T cell noncytotoxic antiviral responses have now been observed with other virus families but are mediated by different cytokines. Characterizing the protein structure of CAF has been challenging despite many biologic, immunologic, and molecular studies. It represents a low-abundance protein that may be identified by future next-generation sequencing approaches. Since CNAR/CAF is a natural noncytotoxic activity, it could provide promising strategies for HIV/AIDS therapy, cure, and prevention.

Conserved HIV Epitopes for an Effective HIV Vaccine

Despite major advances in antiretroviral therapy against HIV-1, an effective HIV vaccine is urgently required to reduce the number of new cases of HIV infections in the world. Vaccines are the ultimate tool in the medical arsenal to control and prevent the spread of infectious diseases such as HIV/AIDS. Several failed phase-IIb to –III clinical vaccine trials against HIV-1 in the past generated a plethora of information that could be used for better designing of an effective HIV vaccine in the future. Most of the tested vaccine candidates produced strong humoral responses against the HIV proteins; however, failed to protect due to: 1) the low levels and the narrow breadth of the HIV-1 neutralizing antibodies and the HIV-specific antibody-dependent Fc-mediated effector activities, 2) the low levels and the poor quality of the anti-HIV T-cell responses, and 3) the excessive responses to immunodominant non-protective HIV epitopes, which in some cases blocked the protective immunity and/or enhanced HIV infection. The B-cell epitopes on HIV for producing broadly neutralizing antibodies (bNAbs) against HIV have been extensively characterized, and the next step is to develop bNAb epitope immunogen for HIV vaccine. The bNAb epitopes are often conformational epitopes and therefore more difficult to construct as vaccine immunogen and likely to include immunodominant non-protective HIV epitopes. In comparison, T-cell epitopes are short linear peptides which are easier to construct into vaccine immunogen free of immunodominant non-protective epitopes. However, its difficulty lies in identifying the T-cell epitopes conserved among HIV subtypes and induce long-lasting, potent polyfunctional T-cell and cytotoxic T lymphocyte (CTL) activities against HIV. In addition, these protective T-cell epitopes must be recognized by the HLA prevalent in the country(s) targeted for the vaccine trial. In conclusion, extending from the findings from previous vaccine trials, future vaccines should combine both T- and B-cell epitopes as vaccine immunogen to induce multitude of broad and potent immune effector activities required for sterilizing protection against global HIV subtypes.

Immunogenicity of virus-like Semliki Forest virus replicon particles expressing Indian HIV-1C gag, env and polRT genes

Development of a vaccine targeting human immunodeficiency virus-1 subtype C (HIV-1C) is an important public health priority in regions with a high prevalence of the clade C virus. The present study demonstrates the immunogenicity of recombinant Semliki Forest virus (SFV)-based virus-like replicon particles (VRPs) expressing Indian HIV-1C env/gag/polRT genes. Immunization of mice with recombinant VRPs in a homologous prime-boost protocol, either individually or in combination, elicited significant antigen-specific IFN-γ T cell responses as detected by the ELISPOT assay. Additionally, Gag-specific TNF-α secreting CD8⁺ and CD4⁺ T cells and Env-specific IL-2 secreting T cells were also elicited by mice immunized with Gag and Env constructs, respectively, as estimated by intracellular cytokine staining assay. Moreover, an HIV Pol-specific TNF-α response was elicited in mice immunized with a combination of the three VRP constructs. Furthermore, HIV-1C Gag and Env-specific binding antibodies were elicited as verified by gp120 ELISA and p24 Gag ELISA, respectively. The immunogenicity of VRPs was found to be higher as compared to that of RNA replicons and VRPs may therefore be promising preventive and therapeutic candidate vaccines for the control and management of HIV/AIDS.

RTS,S/AS01E Malaria Vaccine Induces Memory and Polyfunctional T Cell Responses in a Pediatric African Phase III Trial

Comprehensive assessment of cellular responses to the RTS,S/AS01E vaccine is needed to understand potential correlates and ultimately mechanisms of protection against malaria disease. Cellular responses recognizing the RTS,S/AS01E-containing circumsporozoite protein (CSP) and Hepatitis B surface antigen (HBsAg) were assessed before and 1 month after primary vaccination by intracellular cytokine staining and 16-color flow cytometry in 105 RTS,S/AS01-vaccinated and 74 rabies-vaccinated participants (controls) in a pediatric phase III trial in Africa. RTS,S/AS01E-vaccinated children had significantly higher frequencies of CSP- and HBsAg-specific CD4⁺ T cells producing IL-2, TNF-α, and CD40L and HBsAg-specific CD4⁺ T producing IFN-γ and IL-17 than baseline and the control group. Vaccine-induced responses were identified in both central and effector memory (EM) compartments. EM CD4⁺ T cells expressing IL-4 and IL-21 were detected recognizing both vaccine antigens. Consistently higher response rates to both antigens in RTS,S/AS01E-vaccinated than comparator-vaccinated children were observed. RTS,S/AS01E induced polyfunctional CSP- and HBsAg-specific CD4⁺ T cells, with a greater degree of polyfunctionality in HBsAg responses. In conclusion, RTS,S/AS01E vaccine induces T cells of higher functional heterogeneity and polyfunctionality than previously characterized. Responses detected in memory CD4⁺ T cell compartments may provide correlates of RTS,S/AS01-induced immunity and duration of protection in future correlates of immunity studies.

Immune activation and HIV-specific T cell responses are modulated by a cyclooxygenase-2 inhibitor in untreated HIV-infected individuals: An exploratory clinical trial

Pathologically elevated immune activation and inflammation contribute to HIV disease progression and immunodeficiency, potentially mediated by elevated levels of prostaglandin E₂, which suppress HIV-specific T cell responses. We have previously shown that a high dose of the cyclooxygenase-2 inhibitor celecoxib can reduce HIV-associated immune activation and improve IgG responses to T cell-dependent vaccines. In this follow-up study, we included 56 HIV-infected adults, 28 antiretroviral therapy (ART)-naïve and 28 on ART with undetectable plasma viremia but CD4 counts below 500 cells/μL. Patients in each of the two study groups were randomized to receive 90 mg qd of the cyclooxygenase-2 inhibitor etoricoxib for six months, two weeks or to a control arm, respectively. T cell activation status, HIV Gag-specific T cell responses and plasma inflammatory markers, tryptophan metabolism and thrombin generation were analyzed at baseline and after four months. In addition, patients received tetanus toxoid, conjugated pneumococcal and seasonal influenza vaccines, to which IgG responses were determined after four weeks. In ART-naïve patients, etoricoxib reduced the density of the activation marker CD38 in multiple CD8⁺ T cell subsets, improved Gag-specific T cell responses, and reduced in vitro plasma thrombin generation, while no effects were seen on plasma markers of inflammation or tryptophan metabolism. No significant immunological effects of etoricoxib were observed in ART-treated patients. Patients receiving long-term etoricoxib treatment had poorer tetanus toxoid and conjugated pneumococcal vaccine responses than those receiving short-course etoricoxib. Cyclooxygenase-2 inhibitors may attenuate harmful immune activation in HIV-infected patients without access to ART.

Indian Long-term Non-Progressors Show Broad ADCC Responses with Preferential Recognition of V3 Region of Envelope and a Region from Tat Protein

HIV-specific antibody-dependent cell cytotoxicity (ADCC) is likely to be important in governing protection from human immunodeficiency virus (HIV) and slowing disease progression. Little is known about the ADCC responses to HIV-1 subtype C. We characterized ADCC responses in HIV-1 subtype C-infected Indian subjects with slow disease progression and identified the dominant antigenic regions recognized by these antibodies. ADCC responses were measured in plasma from 34 long-term non-progressors (LTNPs), who were asymptomatic and maintained CD4 count above 500 cells/mm³ for the last 7 years in the absence of antiretroviral therapy (ART), and 58 ART naïve progressors with CD4 count <500 cells/mm³ against overlapping HIV-1 peptides using a flow cytometry-based antibody-dependent natural killer (NK) cell activation assay. The assay measured CD107a expression on NK cells as a marker of antibody-dependent NK cell activation and IFN-γ secretion by NK cells upon activation. The ADCC epitopes were mapped using the matrix of overlapping peptides. Indian LTNPs showed higher and broader ADCC responses compared to the progressors. The Env-C and Tat-specific ADCC responses were associated with lower plasma viral load, whereas the Env-C responses were also associated with higher CD4 counts. Five of 10 LTNP responders targeted epitopes in the V3 region (amino acids 288–330) of Env-C. Additionally, three Tat regions were targeted by ADCC antibodies from LTNPs. ADCC responses were associated with slow HIV progression in Indian subtype C-infected cohort. The frequently recognized peptides from the V3 loop of Env and the novel epitopes from Tat by the LTNPs warrants further study to understand the role of ADCC responses to these regions in control and prevention of HIV-1 infection.

Regulation of Gag- and Env-Specific CD8+ T Cell Responses in ART-Naïve HIV-Infected Patients: Potential Implications for Individualized Immunotherapy

Strategies to develop a functional cure for HIV infection will likely require boosting of effector T cell responses to eliminate reactivated, latently infected cells. We have recently explored an assay for assessing antigen-specific regulation of T cell proliferation, which was related to clinical progression in untreated patients and to vaccine efficacy in two trials of therapeutic Gag-based vaccines. We here expand the same assay to further investigate regulation mediated by various inhibitory pathways. Peripheral blood mononuclear cells from 26 asymptomatic HIV-infected, antiretroviral therapy-naïve patients were stimulated with Gag and Env overlapping peptide panels for 5 days. Monoclonal antibodies (mAbs) blocking inhibitory mediators interleukin (IL) 10, transforming growth factor (TGF) β, programmed death ligand (PD–L) 1 and herpes virus entry mediator (HVEM) were added to parallel cultures. Functional T cell regulation (FTR) was defined as the difference in proliferation between stimulated cultures with and without blocking mAbs. FTR was detected in 54% of patients. Blockade of IL-10/PD-L1 and IL10/TGF-β detected all cases with Gag- and Env-associated FTR, respectively. In accordance with previous findings, isolated Env FTR was associated with higher plasma HIV RNA and lower CD4 counts, while patients with both Gag and Env FTR also had higher Gag- and Env-specific proliferative CD8⁺ T cell responses. There was no association between FTR and frequencies of activated regulatory T cells. In conclusion, we observed substantial heterogeneity in FTR between patients, inhibitory pathways and HIV antigens. FTR may help to individualize immunomodulation and warrants further assessment in clinical immunotherapy trials.

HIV therapeutic vaccines: moving towards a functional cure

Anti-viral T-cell and B-cell responses play a crucial role in suppressing HIV and SIV replication during chronic infection. However, these infections are rarely controlled by the host immune response, and most infected individuals need lifelong antiretroviral therapy (ART). Recent advances in our understanding of how anti-HIV immune responses are elicited and regulated prompted a surge of interest in harnessing these responses to reduce the HIV 'residual disease' that is present in ART-treated HIV-infected individuals. Novel approaches that are currently explored include both conventional therapeutic vaccines (i.e., active immunization strategies using HIV-derived immunogens) as well as the use of checkpoint blockers such as anti-PD-1 antibodies. These approaches appear promising as key components of complex therapeutic strategies aimed at curing HIV infection.

Positioning of APOBEC3G/F mutational hotspots in the human immunodeficiency virus genome favors reduced recognition by CD8+ T cells

Due to constitutive expression in cells targeted by human immunodeficiency virus (HIV), and immediate mode of viral restriction upon HIV entry into the host cell, APOBEC3G (A3G) and APOBEC3F (A3F) have been considered primarily as agents of innate immunity. Recent bioinformatic and mouse model studies hint at the possibility that mutation of the HIV genome by these enzymes may also affect adaptive immunity but whether this occurs in HIV-infected individuals has not been examined. We evaluated whether APOBEC-mediated mutations within common HIV CD8⁺ T cell epitopes can potentially enhance or diminish activation of HIV-specific CD8⁺ T cells from infected individuals. We compared ex vivo activation of CD8⁺ T lymphocytes from HIV-infected individuals by wild type HIV peptide epitopes and synthetic variants bearing simulated A3G/F-induced mutations by measuring interferon-γ (IFN-γ) production. We found that A3G/F-induced mutations consistently diminished HIV-specific CD8⁺ T cell responses against the common epitopes we tested. If this reflects a significant trend in vivo, then adaptation by HIV to enrich sequences that are favored for mutation by A3G/F (A3G/F hotspots) in portions of its genome that encode immunogenic CD8⁺ T cell epitopes would favor CTL escape. Indeed, we found the most frequently mutated A3G motif (CCC) is enriched up to 6-fold within viral genomic sequences encoding immunodominant CD8⁺ T cell epitopes in Gag, Pol and Nef. Within each gene, A3G/F hotspots are more abundant in sequences encoding epitopes that are commonly recognized due to their HLA restriction. Thus, in our system, mutations of the HIV genome, mimicking A3G/F activity, appeared to abrogate or severely reduce CTL recognition. We suggest that the physiological significance of this potential effect in facilitating CTL escape is echoed in the adaptation of the HIV genome to enrich A3G/F hotspots in sequences encoding CTL epitopes that are more immunogenic at the population level.

The Significance of Interferon-γ in HIV-1 Pathogenesis, Therapy, and Prophylaxis

Interferon-γ (IFNγ) plays various roles in the pathogenesis of HIV/AIDS. In an HIV-1 infected individual, the production of IFNγ is detected as early as the acute phase and continually detected throughout the course of infection. Initially produced to clear the primary infection, IFNγ together with other inflammatory cytokines are involved in establishing a chronic immune activation that exacerbates clinical diseases associated with AIDS. Unlike Type 1 IFNs, IFNγ has no direct antiviral activity against HIV-1 in primary cultures, as supported by the in vivo findings of IFNγ therapy in infected subjects. Results from both in vitro and ex vivo studies show that IFNγ can instead enhance HIV-1 replication and its associated diseases, and therapies aimed at decreasing its production are under consideration. On the other hand, IFNγ has been shown to enhance cytotoxic T lymphocytes and NK cell activities against HIV-1 infected cells. These activities are important in controlling HIV-1 replication in an individual and will most likely play a role in the prophylaxis of an effective vaccine against HIV-1. Additionally, IFNγ has been used in combination with HIV-1 vaccine to augment antiviral immunity. Technological advancements have focused on using IFNγ as a biological marker to analyze the type(s) of immunity generated by candidate HIV vaccines and the levels of immunity restored by anti-retroviral drug therapies or novel immunotherapies. Hence, in addition to its valuable ancillary role as a biological marker for the development of effective HIV-1 prophylactic and therapeutic strategies, IFNγ has a vital role in promoting the pathogenesis of HIV.

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.

Immune activation and collateral damage in AIDS pathogenesis

In the past decade, evidence has accumulated that human immunodeficiency virus (HIV)-induced chronic immune activation drives progression to AIDS. Studies among different monkey species have shown that the difference between pathological and non-pathological infection is determined by the response of the immune system to the virus, rather than its cytopathicity. Here we review the current understanding of the various mechanisms driving chronic immune activation in HIV infection, the cell types involved, its effects on HIV-specific immunity, and how persistent inflammation may cause AIDS and the wide spectrum of non-AIDS related pathology. We argue that therapeutic relief of inflammation may be beneficial to delay HIV-disease progression and to reduce non-AIDS related pathological side effects of HIV-induced chronic immune stimulation.

HIV-1-infected individuals in antiretroviral therapy react specifically with polyfunctional T-cell responses to Gag p24

BACKGROUND

Still no effective HIV-1 prophylactic or therapeutic vaccines are available. However, as the proportion of HIV-1-infected individuals on antiretroviral treatment is increasing, knowledge about the residual immune response is important for the possible development of an HIV-1 vaccine.

METHODS

In this study, the magnitude, breadth, and quality of the HIV-1-specific T-cell response in HIV-1-infected viremic individuals (n = 19) and individuals on highly active antiretroviral treatment (HAART) (n = 14) using multicolor flow cytometry were determined.

RESULTS

We found that magnitude and breadth of the CD8 T-cell response were significantly higher in viremic individuals than individuals on HAART (P < 0.0001 and P < 0.0001, respectively) and that the functionality of the overall HIV-1-specific response was significantly different in individuals on HAART and viremic individuals (P = 0.0020). In individuals on HAART, the remaining responses were primarily detected upon stimulation with overlapping peptides from Gag p24, integrase, and Nef. The Gag p24 response was more polyfunctional than corresponding responses observed in viremic individuals.

CONCLUSIONS

Identification of highly immunogenic regions also recognized by individuals on HAART may be important for HIV-1 vaccine development. Irrespective of HLA haplotype, specific regions within the HIV-1 genome that is targeted more frequently in individuals on HAART have been identified. However, further studies are required to establish if these particular regions could be interesting for a future vaccine that might limit the time and opportunity for escape mutations.

Evolutionarily conserved epitopes on human immunodeficiency virus type 1 (HIV-1) and feline immunodeficiency virus reverse transcriptases detected by HIV-1-infected subjects

Anti-human immunodeficiency virus (HIV) cytotoxic T lymphocyte (CTL)-associated epitopes, evolutionarily conserved on both HIV type 1 (HIV-1) and feline immunodeficiency virus (FIV) reverse transcriptases (RT), were identified using gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) and carboxyfluorescein diacetate succinimide ester (CFSE) proliferation assays followed by CTL-associated cytotoxin analysis. The peripheral blood mononuclear cells (PBMC) or T cells from HIV-1-seropositive (HIV(+)) subjects were stimulated with overlapping RT peptide pools. The PBMC from the HIV(+) subjects had more robust IFN-γ responses to the HIV-1 peptide pools than to the FIV peptide pools, except for peptide-pool F3. In contrast, much higher and more frequent CD8(+) T-cell proliferation responses were observed with the FIV peptide pools than with the HIV peptide pools. HIV-1-seronegative subjects had no proliferation or IFN-γ responses to the HIV and FIV peptide pools. A total of 24% (40 of 166) of the IFN-γ responses to HIV pools and 43% (23 of 53) of the CD8(+) T-cell proliferation responses also correlated to responses to their counterpart FIV pools. Thus, more evolutionarily conserved functional epitopes were identified by T-cell proliferation than by IFN-γ responses. In the HIV(+) subjects, peptide-pool F3, but not the HIV H3 counterpart, induced the most IFN-γ and proliferation responses. These reactions to peptide-pool F3 were highly reproducible and persisted over the 1 to 2 years of testing. All five individual peptides and epitopes of peptide-pool F3 induced IFN-γ and/or proliferation responses in addition to inducing CTL-associated cytotoxin responses (perforin, granzyme A, granzyme B). The epitopes inducing polyfunctional T-cell activities were highly conserved among human, simian, feline, and ungulate lentiviruses, which indicated that these epitopes are evolutionarily conserved. These results suggest that FIV peptides could be used in an HIV-1 vaccine.

HIV-1 Vaccine Trials: Evolving Concepts and Designs

An effective prophylactic HIV-1 vaccine is needed to eradicate the HIV/AIDS pandemic but designing such a vaccine is a challenge. Despite many advances in vaccine technology and approaches to generate both humoral and cellular immune responses, major phase-II and -III vaccine trials against HIV/AIDS have resulted in only moderate successes. The modest achievement of the phase-III RV144 prime-boost trial in Thailand re-emphasized the importance of generating robust humoral and cellular responses against HIV. While antibody-directed approaches are being pursued by some groups, others are attempting to develop vaccines targeting cell-mediated immunity, since evidence show CTLs to be important for the control of HIV replication. Phase-I and -IIa multi-epitope vaccine trials have already been conducted with vaccine immunogens consisting of known CTL epitopes conserved across HIV subtypes, but have so far fallen short of inducing robust and consistent anti-HIV CTL responses. The concepts leading to the development of T-cell epitope-based vaccines, the outcomes of related clinical vaccine trials and efforts to enhance the immunogenicity of cell-mediated approaches are summarized in this review. Moreover, we describe a novel approach based on the identification of SIV and FIV antigens which contain conserved HIV-specific T-cell epitopes and represent an alternative method for developing an effective HIV vaccine against global HIV isolates.

The expansion ability but not the quality of HIV-specific CD8(+) T cells is associated with protective human leucocyte antigen class I alleles in long-term non-progressors

Studies in long-term non-progressors (LTNP) have suggested that the quality of the CD8(+) response may involve protective human leucocyte antigen (HLA) class I alleles. However, studies examining the expansion ability of different functional CD8(+) T cells and their association with HLA class I alleles are lacking. LTNP, untreated typical progressors (TP) and patients successfully on highly active retroviral therapy (HAART) during 1 year (HP) were included. HLA class I typing was performed using a sequence-specific primer assay. Functional subsets of Gag- and Nef-specific CD8(+) cells were analysed based on the production of macrophage inflammatory protein (MIP)-1β, tumour necrosis factor (TNF)-α and interleukin (IL)-2. Their expansion abilities were evaluated after 10-day culture in the presence of Gag and Nef human immunodeficiency virus (HIV) peptides. No differences were seen when comparing quantitative and qualitative HIV-specific CD8(+) T cell responses according to the presence/absence of protective HLA alleles (B*58 and B*27 supertypes) in each group. However, LTNP with protective HLA alleles showed a higher expansion ability of Gag-specific MIP(+) TNF(+) IL-2(+) T cells and Nef-specific MIP(+) TNF(+) IL-2(+) . HLA-B*5701+LTNP displayed a higher expansion ability of Gag and Nef-specific MIP(+) TNF(-) IL-2(+) T cells than HLA-B*5701-LTNP. This was not so for HLA-B*2705. No differences were seen in the expansion ability according to the presence/absence of protective HLA alleles in TP and HP. The expansion ability of polyfunctional CD8(+) T cells is modulated by HLA class I alleles and targeted protein. LTNP with HLA class I protective alleles (mainly B*5701) display better expansion ability of polyfunctional HIV-specific CD8(+) T cells than the rest, suggesting that factors other than HLA-B*5701 must contribute to the control of viral replication in other LTNP. Furthermore, these attributes of HIV-specific CD8(+) T are not restored by HAART; thus, adjuvant therapies and vaccines that induce and/or normalize the expansion ability of HIV-specific T cells are required.

HIV-specific CD8+ T-cell proliferation is prospectively associated with delayed disease progression

Human immunodeficiency virus (HIV)-specific CD8(+) T-cell proliferation is consistently correlated with enhanced host HIV immune control, but whether proliferative responses are a cause or consequence of immune protection is unclear. We measured Env-specific CD8(+) T-cell proliferation and interferon (IFN)-γ secretion in HIV-infected participants with CD4 counts >200, who then completed 121 person-years of prospective follow-up to monitor HIV disease progression. In all, 13 of 31 participants (42%) reached end point during longitudinal follow-up. Strong Env-specific CD8(+) T-cell proliferation (>10% of CD8(+) T cells) was observed in 14/31 participants at baseline, and this was associated with a longer time to HIV disease progression end point, stratified baseline CD4 count (P=0.016). No associations were observed for IFN-γ ELISPOT responses and progression (P>0.2). Strong proliferation remained significant in multivariate Cox regression analyses (P=0.044) as an independent predictor of delayed HIV disease progression, along with baseline CD4 count (P=0.04). Duration of HIV infection was associated with more rapid progression in univariate, but not multivariate, analysis (P=0.112). Age and baseline viral load were not predictive of progression. HIV-specific CD8(+) T-cell proliferation was a correlate of protective immunity in this prospective study; such responses may be important for HIV vaccine protection.

Human immunodeficiency virus type 1 long-term non-progressors: the viral, genetic and immunological basis for disease non-progression

A small subset of human immunodeficiency virus type 1 (HIV-1)-infected, therapy-naive individuals--referred to as long-term non-progressors (LTNPs)--maintain a favourable course of infection, often being asymptomatic for many years with high CD4(+) and CD8(+) T-cell counts (>500 cells  μl(-1)) and low plasma HIV-RNA levels (<10 ,000 copies ml(-1)). Research in the field has undergone considerable development in recent years and LTNPs offer a piece of the puzzle in understanding the ways that persons can naturally control HIV-1 infection. Their method of control is based on viral, genetic and immunological components. With respect to virological features, genomic sequencing has shown that some LTNPs are infected with attenuated strains of HIV-1 and harbour mutant nef, vpr, vif or rev genes that contain single nuclear polymorphisms, or less frequently, large deletions, in conserved domains. Studies have also shown that some LTNPs have unique genetic advantages, including heterozygosity for the CCR5-Δ32 polymorphism, and have been found with excitatory mutations that upregulate the production of the chemokines that competitively inhibit HIV-1 binding to CCR5 or CXCR4. Lastly, immunological factors are crucial for providing LTNPs with a natural form of control, the most important being robust HIV-specific CD4(+) and CD8(+) T-cell responses that correlate with lower viral loads. Many LTNPs carry the HLA class I B57 allele that enhances presentation of antigenic peptides on the surface of infected CD4(+) cells to cytotoxic CD8(+) T cells. For these reasons, LTNPs serve as an ideal model for HIV-1 vaccine development due to their natural control of HIV-1 infection.

Highly avid, oligoclonal, early-differentiated antigen-specific CD8+ T cells in chronic HIV-2 infection

HIV-1-specific CD8(+) T cells are present in most HIV-1-infected people and play an important role in controlling viral replication, but the characteristics of an effective HIV-specific T-cell response are largely unknown. The majority of HIV-2-infected people behave as long-term non-progressors while those who progress to AIDS do so in a manner indistinguishable from HIV-1. A detailed study of HIV-2 infection may identify protective immune responses. Robust gag p26-specific T-cell responses are elicited during HIV-2 infection and correlate with control of viremia. In this study, we analyzed features of an HLA-B 3501-restricted T-cell response to HIV-2 p26 that may contribute to virus control. In contrast to HIV-1, HIV-2-specific T cells are at an early stage of differentiation (CD27(+)CD28(+)), a finding that relates directly to CD4(+) T-cell levels and inversely to immune activation. The cells demonstrate IFN-gamma secretion, oligoclonal T-cell receptor Vbeta gene segment usage, exceptional avidity and secretion of pro-inflammatory cytokines. Despite the potentially strong selection pressure imposed on the virus by these cells, there was no evidence of HIV-2 sequence evolution. We propose that in chronic HIV-2 infection, the maintenance of early-differentiated, highly avid CD8(+) T cells could account for the non-progressive course of disease. Such responses may be desirable from an HIV vaccine.

Quality assurance of intracellular cytokine staining assays: analysis of multiple rounds of proficiency testing

When evaluating candidate prophylactic HIV and cancer vaccines, intracellular cytokine staining (ICS) assays that measure the frequency and magnitude of antigen-specific T-cell subsets are one tool to monitor immunogen performance and make product advancement decisions. To assess the inter-laboratory assay variation among multiple laboratories testing vaccine candidates, the NIH/NIAID/DAIDS in collaboration with BD Biosciences implemented an ICS Quality Assurance Program (QAP). Seven rounds of testing have been conducted in which 16 laboratories worldwide participated. In each round, IFN-γ, IL-2 and/or TNF-α responses in CD4+ and CD8+ T-cells to CEF or CMV pp65 peptide mixes were tested using cryopreserved peripheral blood mononuclear cells (PBMC) from CMV seropositive donors. We found that for responses measured above 0.2%, inter-laboratory %CVs were, on average, 35%. No differences in inter-laboratory variation were observed if a 4-color antibody cocktail or a 7-color combination was used. Moreover, the data allowed identification of important sources of variability for flow cytometry-based assays, including: number of collected events, gating strategy and instrument setup and performance. As a consequence, in this multi-site study we were able to define pass and fail criteria for ICS assays, which will be adopted in the subsequent rounds of testing and could be easily extrapolated to QAP for other flow cytometry-based assays.

Preclinical evaluation of the immunogenicity of C-type HIV-1-based DNA and NYVAC vaccines in the Balb/C mouse model

As part of a European initiative (EuroVacc), we report the design, construction, and immunogenicity of two HIV-1 vaccine candidates based on a clade C virus strain (CN54) representing the current major epidemic in Asia and parts of Africa. Open reading frames encoding an artificial 160-kDa GagPolNef (GPN) polyprotein and the external glycoprotein gp120 were fully RNA and codon optimized. A DNA vaccine (DNA-GPN and DNA-gp120, referred to as DNA-C), and a replication-deficient vaccinia virus encoding both reading frames (NYVAC-C), were assessed regarding immunogenicity in Balb/C mice. The intramuscular administration of both plasmid DNA constructs, followed by two booster DNA immunizations, induced substantial T-cell responses against both antigens as well as Env-specific antibodies. Whereas low doses of NYVAC-C failed to induce specific CTL or antibodies, high doses generated cellular as well as humoral immune responses, but these did not reach the levels seen following DNA vaccination. The most potent immune responses were detectable using prime:boost protocols, regardless of whether DNA-C or NYVAC-C was used as the priming or boosting agent. These preclinical findings revealed the immunogenic response triggered by DNA-C and its enhancement by combining it with NYVAC-C, thus complementing the macaque preclinical and human phase I clinical studies of EuroVacc.

Plasmid-encoded interleukin-15 receptor alpha enhances specific immune responses induced by a DNA vaccine in vivo

Plasmid-encoded DNA vaccines appear to be a safe and effective method for delivering antigen; however, the immunogenicity of such vaccines is often suboptimal. Cytokine adjuvants including interleukin (IL)-12, RANTES, granulocyte-macrophage colony-stimulating factor, IL-15, and others have been used to augment the immune response against DNA vaccines. In particular, IL-15 binds to a unique high-affinity receptor, IL-15R alpha; is trans-presented to CD8(+) T cells expressing the common betagamma chain; and has been shown to play a role in the generation, maintenance, and proliferation of antigen-specific CD8(+) T cells. In this study, we took the unique approach of using both a cytokine and its receptor as an adjuvant in an HIV-1 vaccine strategy. To study IL-15R alpha expression, a unique monoclonal antibody (KK1.23) was generated to confirm receptor expression in vitro. Coimmunization of IL-15 and IL-15R alpha plasmids with HIV-1 antigenic plasmids in mice enhanced the antigen-specific immune response 2-fold over IL-15 immunoadjuvant alone. Furthermore, plasmid-encoded IL-15R alpha augments immune responses in the absence of IL-15, suggesting its role as a novel adjuvant. Moreover, pIL-15R alpha enhanced the cellular, but not the humoral, immune response as measured by antigen-specific IgG antibody. This is the first report describing that IL-15R alpha itself can act as an adjuvant by enhancing an antigen-specific T cell response. Uniquely, pIL-15 and pIL-15R alpha adjuvants combined, but not the receptor alpha chain alone, may be useful as a strategy for generating and maintaining memory CD8(+) T cells in a DNA vaccine.

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.

HIV/AIDS vaccines: a need for new concepts?

HIV vaccine research is at a crossroads carefully contemplating on the next path. The unexpected results of the Merck vaccine trial, while providing a stunning blow to a field in dire need of a protective vaccine, has also raised several fundamental questions regarding the candidate immunogen itself, preexisting immunity to vaccine vectors, surrogate assays and animal models used for assessing preclinical protective responses, as well as relevant endpoints to be measured in a clinical trial. As a result, the research community is faced with the daunting task of identifying novel vaccine concepts and products to continue the search. This review highlights and addresses some of the scientific and practical concerns.

Viral load and clinical disease enhancement associated with a lentivirus cytotoxic T lymphocyte vaccine regimen

Effective DNA-based vaccines against lentiviruses will likely induce CTL against conserved viral proteins. Equine infectious anemia virus (EIAV) infects horses worldwide, and serves as a useful model for lentiviral immune control. Although attenuated live EIAV vaccines have induced protective immune responses, DNA-based vaccines have not. In particular, DNA-based vaccines have had limited success in inducing CTL responses against intracellular pathogens in the horse. We hypothesized that priming with a codon-optimized plasmid encoding EIAV Gag p15/p26 with co-administration of a plasmid encoding an equine IL-2/IgG fusion protein as a molecular adjuvant, followed by boosting with a vaccinia vector expressing Gag p15/p26, would induce protective Gag-specific CTL responses. Although the regimen induced Gag-specific CTL in four of seven vaccinated horses, CTL were not detected until after the vaccinia boost, and protective effects were not observed in EIAV challenged vaccinates. Unexpectedly, vaccinates had significantly higher viral loads and more severe clinical disease, associated with the presence of vaccine-induced CTL. It was concluded that (1) further optimization of the timing and route of DNA immunization was needed for efficient CTL priming in vivo, (2) co-administration of the IL-2/IgG plasmid did not enhance CTL priming by the Gag p15/p26 plasmid, (3) vaccinia vectors are useful for lentivirus-specific CTL induction in the horse, (4) Gag-specific CTL alone are either insufficient or a more robust Gag-specific CTL response is needed to limit EIAV viremia and clinical disease, and (5) CTL-inducing vaccines lacking envelope immunogens can result in lentiviral disease enhancement. Although the mechanisms for enhancement associated with this vaccine regimen remain to be elucidated, these results have important implications for development of lentivirus T cell vaccines.

Enhanced antibody responses elicited by a CpG adjuvant do not improve the protective effect of an aldrithiol-2-inactivated simian immunodeficiency virus therapeutic AIDS vaccine

The potential benefit of using unmethylated CpG oligoribodeoxynucleotides (ODN) as an adjuvant in a therapeutic simian immunodeficiency virus (SIV) vaccine consisting of AT2-inactivated SIVmac239 was evaluated in SIV-infected rhesus macaques receiving antiretroviral therapy (ART). We hypothesized that using CpG ODN as an adjuvant in therapeutic vaccination would enhance SIV-specific immune responses and suppress SIV replication after ART was stopped. To test our hypothesis, we immunized chronically SIV-infected rhesus macaques receiving ART with one of the following therapeutic vaccines: (i) AT2-inactivated SIVmac239, (ii) CpG10103 plus AT2-inactivated SIVmac239, (iii) CpG10103, and (iv) saline. While immunization with CpG plus AT2-SIVmac239 significantly increased SIV-specific immunoglobulin G (IgG) antibody titers, the mean plasma viral RNA (vRNA) level in these animals after ART did not differ from those of saline-treated animals. The AT2-inactivated SIVmac239-immunized animal group had a significantly higher mean SIV-specific gamma interferon T-cell response after three immunizations and lower plasma vRNA levels for 6 weeks after ART was withdrawn compared to the saline-treated animal group. Compared to the saline control group, the animal group treated with CpG alone had a significantly higher mean SIV-specific lymphocyte proliferation index and a higher rate of plasma vRNA rebound after ART. These results demonstrate that while the use of CpG as an adjuvant enhances SIV-specific antibody responses, this does not improve the control of SIV replication after ART is stopped. The lack of benefit may be related to the high levels of SIV-specific lymphocyte proliferation in the CpG adjuvant group.

No major differences in the functional profile of HIV Gag and Nef-specific CD8+ responses between long-term nonprogressors and typical progressors

The mechanism explaining the failure of HIV-specific CD8(+) T cell responses to successfully control HIV replication remains elusive. A total of 83 drug-naive HIV-infected individuals, 27 of whom were long-term nonprogressors (LTNP), was examined. The ability of CD8(+) T lymphocytes to produce three different cytokines (MIP-1beta, TNF-alpha, IL-2) in response to HIV Gag and Nef peptides and to polyclonal stimuli and the ability of HIV-specific CD8(+) T cells to expand in vitro were evaluated by multiparameter flow cytometry. In response to polyclonal stimulation, LTNP presented significantly higher levels of several CD8(+) T cell subsets than progressors. While most patients presented detectable Gag and Nef-specific CD8(+) responses, no significant differences in any of the CD8(+) functional T cell subsets were recognized when comparing LTNP and progressors. HIV responses were dominated by cells producing only MIP-1beta or TNF-alpha, being similar in LTNP and progressors. However, expansion of HIV-specific CD8(+) T cells was more frequent in LTNP than progressors, especially for cells producing MIP-1beta. LTNP show higher levels of CD8(+) responses against polyclonal stimuli than progressors. However, HIV-specific CD8(+) responses do not differ between them except for a more preserved ability of cells from LTNP to expand in vitro.

Host CCL3L1 gene copy number in relation to HIV-1-specific CD4+ and CD8+ T-cell responses and viral load in South African women

HIV-specific T-cell responses play an important role in control of infection. Because CCL3 has immune modulatory and antiviral activities, we hypothesized that host CCL3 genotype (CCL3L1 gene duplications) would influence the development of effective HIV-specific immune responses. Copy numbers of CCL3L1 were determined for 71 HIV-infected women, and HIV-specific CD4 and CD8 T-cell responses to overlapping peptide pools spanning the HIV-1 subtype C genome were simultaneously measured by an interferon-gamma and interleukin-2 whole-blood flow cytometric assay. Host CCL3L1 copy number correlated negatively with viral load (r=-0.239, P=0.045), as did magnitudes of Gag CD4 (r=-0.362, P=0.002) and CD8 (r=-0.261, P=0.028) T-cell responses. Patients with a Gag CD4 response (P=0.002) or dominant Gag CD8 (P=0.006) response had significantly lower viral loads than those whose dominant response targeted another region of the genome, whereas a dominant Nef-specific CD8 T-cell response was associated with higher HIV viral load. CCL3L1 copy number greater than or equal to the population median of 5 was significantly associated with increased magnitude of CD4 Gag responses (P=0.017), and women who had CD4 and CD8 Gag-specific responses had significantly lower viral loads (P=0.004) and higher CCL3L1 copy number (P=0.015) than those women with only CD8 Gag-specific responses.

HIV-1-specific T cell precursors with high proliferative capacity correlate with low viremia and high CD4 counts in untreated individuals

Evidences have recently suggested that the preservation of vaccine-induced memory rather than effector T cells is essential for better outcome and survival following pathogenic SIV challenge in macaques. However, an equivalent demonstration in humans is missing, and the immune correlates of HIV-1 control have been only partially characterized. We focused on the quantification of Ag-specific T cell precursors with high proliferative capacity (PHPC) using a peptide-based cultured IFN-gamma ELISPOT assay (PHPC assay), which has been shown to identify expandable memory T cells. To determine which responses correlate with viral suppression and positive immunologic outcome, PBMC from 32 chronically untreated HIV-1-infected individuals were evaluated in response to peptide pools, representing the complete HIV-1 Gag, Nef, and Rev proteins, by PHPC and IFN-gamma ELISPOT assay, which instead identifies effector T cells with low proliferative capacity. High magnitude of Gag-specific PHPC, but not ELISPOT, responses significantly correlated with low plasma viremia, due to responses directed toward p17 and p15 subunits. Only Gag p17-specific PHPC response significantly correlated with high CD4 counts. Analysis of 20 additional PBMC samples from an independent cohort of chronically untreated HIV-1-infected individuals confirmed the correlation between Gag p17-specific PHPC response and either plasma viremia (inverse correlation) or CD4 counts (direct correlation). Our results indicate that the PHPC assay is quantitatively and qualitatively different from the ELISPOT assay, supporting that different T cell populations are being evaluated. The PHPC assay might be an attractive option for individual patient management and for the design and testing of therapeutic and prophylactic vaccines.

Immunization with an HIV-1 immunogen induces CD4+ and CD8+ HIV-1-specific polyfunctional responses in patients with chronic HIV-1 infection receiving antiretroviral therapy

Development of polyfunctional T lymphocyte responses is critical in the immunological response against HIV-1. Fifty-four HIV-1 infected patients receiving antiretroviral treatment (ART) and immunization with an HIV-1 immunogen or placebo, periodically every 3 months throughout a period of 36 months, were evaluated for the purposes of analysing the development of HIV-1-specific CD4+ and CD8+ responses. A significant increase of proliferating and IFN-gamma producing CD8+ HIV-1-specific T cells, of HIV-1-specific precursor frequencies for CD8+ and for CD4+ T cells and of Gag/pol-specific memory CTL precursors (CTLp) was observed in the immunogen group in comparison to placebo. IL-2 intracellular expression and IFN-gamma and TNF-alpha co-expression in HIV-1-specific CD8+ T cells were also substantially increased in the immunized group. A negative correlation between viral load and CD3+CD4+CFSElow HIV-1-specific lymphoproliferative response and frequency of Gag/pol-specific CTLp was solely observed in the HIV-1 immunogen group. Long-term immunization in patients receiving ART helps to develop HIV-1-specific polyfunctional T cell responses.

Failure of low-dose recombinant human IL-2 to support the survival of virus-specific CTL clones infused into severe combined immunodeficient foals: lack of correlation between in vitro activity and in vivo efficacy

Although CTL are important for control of lentiviruses, including equine infectious anemia virus (EIAV), it is not known if CTL can limit lentiviral replication in the absence of CD4 help and neutralizing antibody. Adoptive transfer of EIAV-specific CTL clones into severe combined immunodeficient (SCID) foals could resolve this issue, but it is not known whether exogenous IL-2 administration is sufficient to support the engraftment and proliferation of CTL clones infused into immunodeficient horses. To address this question we adoptively transferred EIAV Rev-specific CTL clones into four EIAV-challenged SCID foals, concurrent with low-dose aldesleukin (180,000U/m2), a modified recombinant human IL-2 (rhuIL-2) product. The dose was calculated based on the specific activity on equine PBMC in vitro, and resulted in plasma concentrations considered sufficient to saturate high affinity IL-2 receptors in humans. Despite specific activity on equine PBMC that was equivalent to recombinant equine IL-2 and another form of rhuIL-2, aldesleukin did not support the engraftment and expansion of infused CTL clones, and control of viral load and clinical disease did not occur. It was concluded that survival of Rev-specific CTL clones infused into EIAV-challenged SCID foals was not enhanced by aldesleukin at the doses used in this study, and that in vitro specific activity did not correlate with in vivo efficacy. Successful adoptive immunotherapy with CTL clones in immunodeficient horses will likely require higher doses of rhuIL-2, co-infusion of CD4+ T lymphocytes, or administration of equine IL-2.

Control of HIV-1 RNA load after HAART interruption: Relationship with CCR5 co-receptor density and proviral DNA load in HIV-infected patients

BACKGROUND

CCR5 co-receptor density has been reported to play a role in the level of HIV production. In addition, reports about the relationship between proviral DNA load and plasma HIV load are controversial.

OBJECTIVES

To analyse the role of CCR5 co-receptor density and proviral DNA load in the control of plasma HIV-viral load after HAART interruption, comparing patients whose plasma HIV load was persistently below 4log(10) RNA copies/mL, defined as "HIV controllers", with patients who showed a viral load higher than 4log(10) RNA copies/mL, defined as "non-controllers".

STUDY DESIGN

Proviral DNA load quantification (N=55) and CCR5 co-receptor density (N=29) were determined in HIV-infected patients on prolonged HAART interruption.

RESULTS

Twenty-three percent of our HAART interruption cohort were classified as HIV controllers, while 77% were classified as non-controllers. CCR5 co-receptor density was statistically higher in HIV controllers than in non-controllers, while proviral DNA load was not different between them. CCR5 co-receptor density in activated CD4 cells was independently associated with HIV plasma load after interruption.

CONCLUSIONS

The observation of a higher CCR5 co-receptor expression in HIV controllers suggests that HIV infection leads to the selection of CD4 cells with low CCR5 co-receptor density after HAART interruption.

Virus-specific T cell responses in macaques acutely infected with SHIV(sf162p3)

CD4(+) T helper and CD8(+) cytotoxic T lymphocyte responses are believed to play an important role in the control of primary HIV and SIV infection. However, the role of these cells in macaques acutely infected with SHIV(sf162p3) has not been well characterized. In this study, ten adult rhesus macaques were intravaginally infected with SHIV(sf162p3), and antigen-specific cytokine responses to SHIV-Tat, Nef, Gag and Env peptide pools were examined through 70 days post inoculation (p.i.) using ELISPOT and/or cytokine flow cytometry (CFC). Peak plasma viral replication occurred between 14 and 21 days p.i. followed by low to undetectable plasma viremia by 70 days of infection in most macaques. Although some animals had strong virus-specific cellular immune responses, many had weak or minimal responses that did not correlate with the post peak decline in plasma viremia.

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.

Lack of temporal structure in the short term HIV-1 evolution within asymptomatic naïve patients

HIV-1 evolution in the envelope gene (env) was analyzed in four asymptomatic antiretroviral therapy naïve patients with typical and slow disease progression rates. In typical progressors, viral populations were monophyletic and two distinct evolutionary patterns were observed. In one patient, HIV-1 evolution displayed a strong temporal structure similar to the consistent pattern previously described. In the other, viral evolution displayed a lack of temporal structure with no increase in genetic heterogeneity and divergence over time. In slow progressors, several clades were observed in viral populations. However, analysis within the major sub-population revealed the same two evolutionary patterns described for typical progressors. Synonymous and non-synonymous substitution rate analyses indicated that positive selection was the major force driving HIV-1 evolution in viral populations with temporal structure, while evolution in viral populations with an atemporal structure was dominated by genetic drift and purifying selection. These results support the existence of distinct patterns of env evolution in untreated HIV-1-infected patients.

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.

A single amino acid difference within the alpha-2 domain of two naturally occurring equine MHC class I molecules alters the recognition of Gag and Rev epitopes by equine infectious anemia virus-specific CTL

Although CTL are critical for control of lentiviruses, including equine infectious anemia virus, relatively little is known regarding the MHC class I molecules that present important epitopes to equine infectious anemia virus-specific CTL. The equine class I molecule 7-6 is associated with the equine leukocyte Ag (ELA)-A1 haplotype and presents the Env-RW12 and Gag-GW12 CTL epitopes. Some ELA-A1 target cells present both epitopes, whereas others are not recognized by Gag-GW12-specific CTL, suggesting that the ELA-A1 haplotype comprises functionally distinct alleles. The Rev-QW11 CTL epitope is also ELA-A1-restricted, but the molecule that presents Rev-QW11 is unknown. To determine whether functionally distinct class I molecules present ELA-A1-restricted CTL epitopes, we sequenced and expressed MHC class I genes from three ELA-A1 horses. Two horses had the 7-6 allele, which when expressed, presented Env-RW12, Gag-GW12, and Rev-QW11 to CTL. The other horse had a distinct allele, designated 141, encoding a molecule that differed from 7-6 by a single amino acid within the alpha-2 domain. This substitution did not affect recognition of Env-RW12, but resulted in more efficient recognition of Rev-QW11. Significantly, CTL recognition of Gag-GW12 was abrogated, despite Gag-GW12 binding to 141. Molecular modeling suggested that conformational changes in the 141/Gag-GW12 complex led to a loss of TCR recognition. These results confirmed that the ELA-A1 haplotype is comprised of functionally distinct alleles, and demonstrated for the first time that naturally occurring MHC class I molecules that vary by only a single amino acid can result in significantly different patterns of epitope recognition by lentivirus-specific CTL.

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.

Increased IFN-γ production by NK and CD3+/CD56+ cells in sexually HIV-1-exposed but uninfected individuals

The mechanisms involved in controlling the establishment of HIV-1 infection are not fully understood. In particular, the role of innate immunity in natural resistance exhibited by individuals who are continuously exposed to HIV-1 but remain seronegative (ESN) has not been thoroughly evaluated. We determined the frequency and function of peripheral blood innate immune cells (plasmacytoid and myeloid dendritic cells, monocytes, NK cells, CD3+/CD56+ cells and invariant NKT cells) in ESN, chronically HIV-1-infected and low-risk HIV-1 seronegative individuals. ESN demonstrated a similar frequency of innate immune cells in comparison to controls and a higher frequency of dendritic cells, NK and invariant NKT cells compared to HIV-1-infected subjects. Incubation of mononuclear cells with stimulatory CpG ODN induced CD86 and CD69 up-regulation to a similar degree on innate cells from the three study groups. CpG ODN-stimulated secretion of cytokines was also similar between ESN and controls, while secretion of IFN-alpha was significantly decreased in HIV-1+ individuals. Importantly, expression of IFN-gamma by PMA/Ionomycin-activated CD56(bright) NK cells and CD3+/CD56+ cells was significantly higher in ESN when compared with controls. The anti-viral effects of IFN-gamma are well established, and so our results suggest that IFN-gamma production by innate immune cells might be one of the multiple factors involved in controlling the establishment of sexually transmitted HIV-1 infection.

Induction of human immunodeficiency virus type-1-specific immunity with a novel gene transport unit (GTU)-MultiHIV DNA vaccine

A multiHIV fusion gene expressing an antigenic fusion protein composed of regulatory HIV-1 proteins Rev, Nef, and Tat, as well as Gag p17/p24 and a stretch of 11 cytotoxic T lymphocyte (CTL) epitope clusters from Pol and Env, was cloned into a novel DNA vector named the Gene Transport Unit (GTU). A mouse H-2(d)-restricted HIV-1 gp120 epitope (RGPGRAFVTI) was cloned into the fusion gene as well. In addition to the HIV- 1 genes the GTU codes for a nuclear anchoring protein (bovine papilloma virus E2), ensuring the long maintenance of the vector and a high expression level of the selected immunogens. BALB/c mice were immunized with the GTU-MultiHIV DNA construct by different routes and regimens of immunization to assess the immunogenicity of the DNA vaccine in vivo. Mice developed strong CD8(+) CTL responses to HIV-1 Env and Gag measured by an ELISPOT-IFN-gamma assay and chromium release assay. In addition, T cell responses to regulatory proteins Rev, Nef, and Tat were induced. Antibody responses were detected to each of the HIV antigens encoded by the DNA construct. Minimal doses of the GTU-MultiHIV DNA delivered by gene gun were potent in inducing significant HIV-specific CTL responses. The equivalent doses of the conventional plasmid expressing MultiHIV DNA delivered by gene gun failed to do so. An ideal DNA vaccine should yield high expression of the viral antigens for a prolonged period of time, and expression of the multiple viral antigens is probably required for the induction of a broad and protective immune response. The GTU-MultiHIV DNA vaccine described is a good vaccine candidate that meets the above criteria.

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.

Current advances and challenges in HIV-1 vaccines

Recent advances in science, which have aided HIV-1 vaccine development, include an improved understanding of HIV-1 envelope structure and function, expansion of the pipeline with innovative vaccine strategies, promising multi-gene and multi-clade vaccines that elicit cellular immunity, conduct of clinical trials in a global network, and development of validated techniques that enable simultaneous measurement of multiple T cell vaccine-induced immune responses in humans. A common feature of several preventive vaccine strategies now in early clinical trials is their ability in nonhuman primates to attenuate clinical disease rather than completely prevent HIV-1 infection. One vaccine concept has been tested in large-scale clinical trials, two are currently in efficacy trials, and one more is poised to enter efficacy trial in the next few years. Simultaneously, expanded efforts continue to identify new designs that induce mucosal immunity as well as broadly neutralizing antibodies.

HIV-specific IL-10-positive CD8+ T cells are increased in advanced disease and are associated with decreased HIV-specific cytolysis

IL-10-producing T cells have been shown to inhibit Ag-specific CD8+ T cell responses, and may play a role in the immune dysregulation observed in HIV-1 infection. We characterized the Gag-specific IL-10 responses by CD8+ T cells in HIV-1-positive volunteers from Uganda. HIV-specific IL-10 responses were detected in 32 of 61 (52.4%) antiretroviral naive and 2 of 15 (13.3%) volunteers with a complete virologic response on antiretroviral therapy (< 400 copies/ml). The frequency of HIV-specific IL-10-positive cells was significantly higher in volunteers with advanced disease (CD4+ T cell count <200 cells/mm3; p = 0.0004), and correlated positively with plasma HIV RNA (r = 0.43, p = 0.0004). Interestingly, the frequency of Gag-specific CD107a/b-, but not IFN-gamma-, positive cells was significantly lower in individuals with detectable IL-10-positive CD8+ T cells (p = 0.004). Gag-specific IL-10-positive CD8+ T cells demonstrated a pattern of surface memory marker expression that is distinct compared with CD107a/b- and IFN-gamma-positive CD8+ T cell populations (p < 0.0001). Our study describes a distinct population of IL-10-positive CD8+ T cells that may play a role in HIV-associated immune dysfunction.

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.