Augmentation of HIV-1-specific T helper cell responses in chronic HIV-1 infection by therapeutic immunization

HIV-1 Immunogen: an overview of almost 30 years of clinical testing of a candidate therapeutic vaccine

INTRODUCTION

Although current antiretroviral therapy (ART) has transformed HIV infection into a chronic, manageable disease, ART does not cure HIV infection. Furthermore, the majority of the world's infected individuals live in resource-limited countries in which access to ART is limited. Thus, the development of an effective therapeutic HIV vaccine would be an invaluable treatment alternative.

AREAS COVERED

Developed by the late Dr. Jonas Salk, HIV-1 Immunogen (Remune®) is a candidate therapeutic vaccine that has been studied in thousands of HIV-infected individuals in more than a dozen clinical trials during almost three decades. This Drug Evaluation, which summarizes the results of these trials that have shown the vaccine to be safe and immunogenic, also discusses the contradictory and controversial conclusions drawn from the phases 2, 2/3 and 3 trials that assessed the clinical efficacy of this vaccine.

EXPERT OPINION

Given the lack of unequivocal clinical benefits of HIV-1 Immunogen despite almost 30 years of extensive testing, it does not appear, in our view, that this vaccine is a clinically effective immunotherapy. However, inclusion of this vaccine in the newly proposed 'Kick/Shock and Kill' strategy for HIV eradication, or use as a prophylactic vaccine, could be considered for future trials.

Multifarious immunotherapeutic approaches to cure HIV-1 infection

Immunotherapy in the context of treated HIV-1 infection aims to improve immune responses to achieve better control of the virus. To date, multifaceted immunotherapeutic approaches have been shown to reduce immune activation and increase CD4 T-lymphocyte counts, further to the effects of antiretroviral therapy alone, in addition to improving HIV-1-specific T-cell responses. While sterilizing cure of HIV-1 would involve elimination of all replication-competent virus, a functional cure in which the host has long-lasting control of viral replication may be more feasible. In this commentary, we discuss novel strategies aimed at targeting the latent viral reservoir with cure of HIV-1 infection being the ultimate goal, an achievement that would have considerable impact on worldwide HIV-1 infection.

Therapeutic immunisation plus cytokine and hormone therapy improves CD4 T-cell counts, restores anti-HIV-1 responses and reduces immune activation in treated chronic HIV-1 infection

BACKGROUND

This randomised, open label, phase I, immunotherapeutic study investigated the effects of interleukin (IL)-2, granulocyte-macrophage colony-stimulating factor (GM-CSF), recombinant human growth hormone (rhGH), and therapeutic immunisation (a Clade B DNA vaccine) on combination antiretroviral therapy (cART)-treated HIV-1-infected individuals, with the objective to reverse residual T-cell dysfunction.

METHODS

Twelve HIV-1(+) patients on suppressive cART with baseline CD4 T-cell counts >400 cells/mm(3) blood were randomised into one of three groups: (1) vaccine, IL-2, GM-CSF and rhGH (n=3); (2) vaccine alone (n=4); or (3) IL-2, GM-CSF and rhGH (n=5). Samples were collected at weeks 0, 1, 2, 4, 6, 8, 12, 16, 24 and 48. Interferon (IFN)-γ, IL-2, IL-4 and perforin ELISpot assays performed at each time point quantified functional responses to Gag p17/p24, Nef, Rev, and Tat peptides; and detailed T-cell immunophenotyping was undertaken by flow cytometry. Proviral DNA was also measured.

RESULTS

Median baseline CD4 T-cell count was 757 cells/mm(3) (interquartile range [IQR] 567-886 cells/mm(3)), median age 48 years (IQR 42-51 years), and plasma HIV-1-RNA <50 copies/ml for all subjects. Patients who received vaccine plus IL-2, GM-CSF and rhGH (group 1) showed the most marked changes. Assessing mean changes from baseline to week 48 revealed significantly elevated numbers of CD4 T cells (p=0.0083) and improved CD4/CD8 T-cell ratios (p=0.0033). This was accompanied by a significant reduction in expression of CD38 on CD4 T cells (p=0.0194), significantly increased IFN-γ and IL-2 production in response to Gag (p=0.0122) and elevated IFN-γ production in response to Tat (p=0.041) at week 48 compared to baseline. Subjects in all treatment groups showed significantly reduced PD-1 expression at week 48 compared to baseline, with some reductions in proviral DNA.

CONCLUSIONS

Multifarious immunotherapeutic approaches in the context of fully suppressive cART further reduce immune activation, and improve both CD4 T-lymphocyte counts and HIV-1-specific T-cell responses (NCT01130376).

CD4+ T-cell help enhances NK cell function following therapeutic HIV-1 vaccination

Increasing data suggest that NK cells can mediate antiviral activity in HIV-1-infected humans, and as such, novel approaches harnessing the anti-HIV-1 function of both T cells and NK cells represent attractive options to improve future HIV-1 immunotherapies. Chronic progressive HIV-1 infection has been associated with a loss of CD4(+) T helper cell function and with the accumulation of anergic NK cells. As several studies have suggested that cytokines produced by CD4(+) T cells are required to enhance NK cell function in various infection models, we hypothesized that reconstitution of HIV-1-specific CD4(+) T-cell responses by therapeutic immunization would restore NK cell activity in infected individuals. Using flow cytometry, we examined the function of CD4(+) T cells and NK cells in response to HIV-1 in subjects with treated chronic HIV-1 infection before and after immunization with an adjuvanted HIV-1 Gp120/NefTat subunit protein vaccine candidate provided by GlaxoSmithKline. Vaccination induced an increased expression of interleukin-2 (IL-2) by Gp120-specific CD4(+) T cells in response to HIV-1 peptides ex vivo, which was associated with enhanced production of gamma interferon (IFN-γ) by NK cells. Our data show that reconstitution of HIV-1-specific CD4(+) T-cell function by therapeutic immunization can enhance NK cell activity in HIV-1-infected individuals.

IMPORTANCE

NK cells are effector cells of the innate immune system and are important in the control of viral infection. Recent studies have demonstrated the crucial role played by NK cells in controlling and/or limiting acquisition of HIV-1 infection. However, NK cell function is impaired during progressive HIV-1 infection. We recently showed that therapeutic immunization of treated HIV-1-infected individuals reconstituted strong T-cell responses, measured notably by their production of IL-2, a cytokine that can activate NK cells. The current study suggests that reconstitution of T-cell function by therapeutic vaccination can enhance NK cell activity in individuals with chronic HIV-1 infection. Our findings provide new insights into the interplay between adaptive and innate immune mechanisms involved in HIV-1 immunity and unveil opportunities to harness NK cell function in future therapeutic vaccine strategies to target HIV-1.

Immune interventions in HIV infection

Immune-based therapy (IBT) interventions have found a window of opportunity within some limitations of the otherwise successful combined antiretroviral therapy (cART). Two major paradigms drove immunotherapeutic research to combat human immunodeficiency virus (HIV) infection. First, IBTs were proposed either to help restore CD4(+) T-cell counts in cases of therapeutic failures with cytokines, interleukin-2 (IL-2) or IL-7, or to better control HIV and disease progression during treatment interruptions with anti-HIV therapeutic candidate vaccines. The most widely used candidates were HIV-recombinant live vector-based alone or combined with other vaccine compounds and dendritic cell (DC) therapies. A more recent and current paradigm aims at achieving HIV cure by combining IBT with cART using either cytokines to reactivate virus production in latently infected cells and/or therapeutic immunization to boost HIV-specific immunity in a 'shock and kill' strategy. This review summarizes the rationale, hopes, and mechanisms of successes and failures of these cytokine-based and vaccine-based immune interventions. Results from these first series of IBTs have been so far somewhat disappointing in terms of clinical relevance, but have provided lessons that are discussed in light of the future combined strategies to be developed toward an HIV cure.

Short communication: human immunodeficiency virus rebound in blood and seminal plasma following discontinuation of antiretroviral therapy

Although there is discordance between human immunodeficiency virus (HIV) blood plasma and seminal plasma viral loads (VL), little is known about the dynamics of VL rebound in these compartments upon discontinuation of highly active antiretroviral therapy (HAART). Therefore, we sought to examine the relationship between blood and semen VL rebound after discontinuation of HAART. Participants in this substudy were men enrolled from two centers of a multicenter, placebo-controlled randomized trial of HIV therapeutic vaccination using ALVAC with or without Remune. With at least 2 years of sustained virologic suppression and following a 20-week vaccination course, subjects underwent structured HAART interruption. Fourteen men provided semen samples. Seven to 12 weeks after HAART interruption, all 14 men had detectable blood VLs whereas 8 of 14 had detectable seminal VLs. There was a significant correlation between blood and seminal VLs (Spearman r=0.58, p=0.03) at the time of semen collection. An earlier time to detectable blood VL after HAART interruption was associated with higher seminal VL (Spearman r=-0.64, p=0.02). These findings support the compartmentalization of HIV and underscore the importance of understanding the genital tract as an HIV reservoir in the quest to minimize HIV transmission.

Therapeutic vaccines against HIV infection

Resistance to medication, adverse effects in the medium-to-long-term and cost all place important limitations on lifelong adherence to combined antiretroviral therapy (cART). In this context, new therapeutic alternatives to 'cART for life' in HIV-infected patients merit investigation. Some data suggest that strong T cell-mediated immunity to HIV can indeed limit virus replication and protect against CD4 depletion and disease progression. The combination of cART with immune therapy to restore and/or boost immune-specific responses to HIV has been proposed, the ultimate aim being to achieve a 'functional cure'. In this scenario, new, induced, HIV-specific immune responses would be able to control viral replication to undetectable levels, mimicking the situation of the minority of patients who control viral replication without treatment and do not progress to AIDS. Classical approaches such as whole inactivated virus or recombinant protein initially proved useful as therapeutic vaccines. Overall, however, the ability of these early vaccines to increase HIV-specific responses was very limited and study results were discouraging, as no consistent immunogenicity was demonstrated and there was no clear impact on viral load. Recent years have seen the development of new approaches based on more innovative vectors such as DNA, recombinant virus or dendritic cells. Most clinical trials of these new vectors have demonstrated their ability to induce HIV-specific immune responses, although they show very limited efficacy in terms of controlling viral replication. However, some preliminary results suggest that dendritic cell-based vaccines are the most promising candidates. To improve the effectiveness of these vaccines, a better understanding of the mechanisms of protection, virological control and immune deterioration is required; without this knowledge, an efficacious therapeutic vaccine will remain elusive.

Therapeutic immunization in HIV infected Ugandans receiving stable antiretroviral treatment: a Phase I safety study

Therapeutic immunizations in HIV infection may boost immunity during antiretroviral treatment. We report on the first therapeutic vaccine trial in Uganda, Africa. This open label Phase I trial was designed to assess the safety, tolerability and immunogenicity of a therapeutic HIV-1 vaccine candidate. Thirty HIV positive volunteers receiving a stable regimen of antiretroviral therapy with CD4 counts >400 were recruited for the safety evaluation of LFn-p24C, a detoxified anthrax-derived polypeptide fused to the subtype C HIV gag protein p24. The vaccine was well tolerated and HIV RNA levels remained undetectable following three immunizations. CD4 counts in vaccine recipients were significantly higher compared to the control individuals after 12 months. HIV-specific responses were associated with higher gain in CD4 counts following LFn-p24C immunizations. Volunteers were subsequently asked to undergo a 30-day period of observed treatment interruption. 8/24 (30%) individuals showed no evidence of viral rebound during treatment interruption. All demonstrated prompt suppression of viral load following resumption of ART. Our data demonstrate the safety of LFn-p24C and suggest that adjunct therapeutic immunization may benefit select individuals in further boosting an immune response.

Phase 1 trial of malaria transmission blocking vaccine candidates Pfs25 and Pvs25 formulated with montanide ISA 51

Background

Pfs25 and Pvs25, surface proteins of mosquito stage of the malaria parasites P. falciparum and P. vivax, respectively, are leading candidates for vaccines preventing malaria transmission by mosquitoes. This single blinded, dose escalating, controlled Phase 1 study assessed the safety and immunogenicity of recombinant Pfs25 and Pvs25 formulated with Montanide ISA 51, a water-in-oil emulsion.

Methodology/Principal Findings

The trial was conducted at The Johns Hopkins Center for Immunization Research, Washington DC, USA, between May 16, 2005–April 30, 2007. The trial was designed to enroll 72 healthy male and non-pregnant female volunteers into 1 group to receive adjuvant control and 6 groups to receive escalating doses of the vaccines. Due to unexpected reactogenicity, the vaccination was halted and only 36 volunteers were enrolled into 4 groups: 3 groups of 10 volunteers each were immunized with 5 µg of Pfs25/ISA 51, 5 µg of Pvs25/ISA 51, or 20 µg of Pvs25/ISA 51, respectively. A fourth group of 6 volunteers received adjuvant control (PBS/ISA 51). Frequent local reactogenicity was observed. Systemic adverse events included two cases of erythema nodosum considered to be probably related to the combination of the antigen and the adjuvant. Significant antibody responses were detected in volunteers who completed the lowest scheduled doses of Pfs25/ISA 51. Serum anti-Pfs25 levels correlated with transmission blocking activity.

Conclusion/Significance

It is feasible to induce transmission blocking immunity in humans using the Pfs25/ISA 51 vaccine, but these vaccines are unexpectedly reactogenic for further development. This is the first report that the formulation is associated with systemic adverse events including erythema nodosum.

Trial Registration

ClinicalTrials.gov NCT00295581

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.

Immunological responses and long-term treatment interruption after human immunodeficiency virus type 1 (HIV-1) lipopeptide immunization of HIV-1-infected patients: the LIPTHERA study

We studied the time course of immunological and virological markers after highly active antiretroviral therapy (HAART) interruption in chronically human immunodeficiency virus type 1 (HIV-1)-infected patients immunized with an HIV lipopeptide preparation. In a prospective open pilot study, 24 HIV-1-infected HAART-treated patients with undetectable plasma viral loads (pVLs) and CD4(+) T-cell counts above 350/mm(3) were immunized at weeks 0, 3, and 6 with a candidate vaccine consisting of six HIV lipopeptides. At week 24, patients with pVLs of <1.7 log(10) copies/ml were invited to stop taking HAART. Antiretroviral therapy was resumed if the pVL rose above 4.47 log(10) copies/ml and/or if the CD4(+) cell count fell below 250/mm(3). Immunological and virologic parameters were studied before and after HAART interruption. The median baseline and nadir CD4(+) cell counts were 482 (interquartile range [IQR], 195 to 826) and 313 (IQR, 1 to 481)/mm(3), respectively. New specific CD8(+) cell responses to HIV-1 epitopes were detected after immunization in 13 (57%) of 23 assessable patients. Twenty-one patients were evaluated 96 weeks after HAART interruption. The median time to pVL rebound was 4 weeks (IQR, 2 to 6), and the median peak pVL was 4.26 (IQR, 3 to 5) log(10) copies/ml. Thirteen of these 21 patients resumed HAART a median of 60 weeks after immunization (IQR, 9.2 to 68.4 weeks), when the median pVL was 4.8 (IQR, 2.9 to 5.7) log(10) copies/ml and the median CD4(+) cell count was 551 (IQR, 156 to 778)/mm(3). Eight patients were still off therapy at 96 weeks, with a median pVL of 4 (IQR, 1.7 to 4.6) log(10) copies/ml and a median CD4(+) cell count of 412 (IQR, 299 to 832)/mm(3). No clinical disease progression had occurred. Despite the lack of a control arm, these findings warrant a randomized study of therapeutic vaccination with HIV lipopeptides followed by long-term HAART interruption in AIDS-free chronically infected patients.

A phase I, randomized study of combined IL-2 and therapeutic immunisation with antiretroviral therapy

Background

Fully functional HIV-1-specific CD8 and CD4 effector T-cell responses are vital to the containment of viral activity and disease progression. These responses are lacking in HIV-1-infected patients with progressive disease. We attempted to augment fully functional HIV-1-specific CD8 and CD4 effector T-cell responses in patients with advanced chronic HIV-1 infection.

Design

Chronically infected patients with low CD4 counts T-cell counts who commenced antiretroviral therapy (ART) were subsequently treated with combined interleukin-2 and therapeutic vaccination.

Methods

Thirty six anti-retroviral naive patients were recruited and initiated on combination ART for 17 weeks before randomization to: A) ongoing ART alone; B) ART with IL-2 twice daily for 5 days every four weeks starting at week 17 for 3 cycles; C) ART with IL-2 as in group B and Remune HIV-1 vaccine administered once every 3 months, starting at week 17; and D) ART with Remune vaccine as in group C. Patients were studied for 65 weeks following commencement of ART, with an additional prior 6 week lead-in observation period. CD4 and CD8 T-cell counts, evaluations of HIV-1 RNA levels and proliferative responses to recall and HIV-1 antigens were complemented with assessment of IL-4-secretion alongside quantification of anti-HIV-1 CD8 T-cell responses and neutralizing antibody titres.

Results

Neither IL-2 nor Remune™ vaccination induced sustained HIV-1-specific T-cell responses. However, we report an inverse relationship between HIV-1-specific proliferative responses and IL-4 production which continuously increased in patients receiving immunotherapy, but not patients receiving ART alone.

Conclusion

Induction of HIV-1-specific cell-mediated responses is a major challenge in chronically HIV-1-infected patients even when combining immunisation with IL-2 therapy. An antigen-specific IL-4-associated suppressive response may play a role in attenuating HIV-specific responses.

Clinical experience with plasmid DNA- and modified vaccinia virus Ankara-vectored human immunodeficiency virus type 1 clade A vaccine focusing on T-cell induction

Candidate human immunodeficiency virus type 1 (HIV-1) vaccines focusing on T-cell induction, constructed as pTHr.HIVA DNA and modified vaccinia virus Ankara (MVA).HIVA, were delivered in a heterologous prime-boost regimen. The vaccines were tested in several hundred healthy or HIV-1-infected volunteers in Europe and Africa. Whilst larger trials of hundreds of volunteers suggested induction of HIV-1-specific T-cell responses in <15 % of healthy vaccinees, a series of small, rapid trials in 12-24 volunteers at a time with a more in-depth analysis of vaccine-elicited T-cell responses proved to be highly informative and provided more encouraging results. These trials demonstrated that the pTHr.HIVA vaccine alone primed consistently weak and mainly CD4(+), but also CD8(+) T-cell responses, and the MVA.HIVA vaccine delivered a consistent boost to both CD4(+) and CD8(+) T cells, which was particularly strong in HIV-1-infected patients. Thus, whilst the search is on for ways to enhance T-cell priming, MVA is a useful boosting vector for human subunit genetic vaccines.

Immunisation with recombinant modified vaccinia virus Ankara expressing HIV-1 gag in HIV-1-infected subjects stimulates broad functional CD4+ T cell responses

Virus-specific CD4+ T cells with IL-2-secreting and/or proliferative capacity are detected readily in HIV-1-infected long-term nonprogressors and rarely in persons with untreated progressive infection. The contribution of these cells to viraemia control is uncertain, but this question might be addressed in clinical therapeutic vaccination studies. However, the quality of T helper responses induced by currently available HIV-1 vaccine candidates has not been explored in depth. We determined the effect of vaccination with modified vaccinia virus Ankara (MVA) expressing HIV-1 gag p24/p17 (MVA.HIVA) on HIV-1-specific CD4+ T cell responses in 16 chronically infected, highly active antiretroviral therapy (HAART)-treated subjects using CD8-depleted IFN-gamma ELISPOT assays, intracellular cytokine staining assays for IL-2 and IFN-gamma, and a CFSE-based proliferation assay. Gag-specific CD4+ T cell responses were significantly increased in magnitude and breadth after vaccination and targeted both known and new epitopes, several of which were also recognised by healthy HIV-uninfected volunteers immunised with the same vaccines. The frequencies of CD4+ T cells expressing IL-2 or IFN-gamma, alone or simultaneously, were also augmented. These findings indicate that functional virus-specific T helper cells can be boosted by vaccination in chronic HIV-1 infection. Further evaluation of their role in viraemia control is warranted.

Expansion and diversification of virus-specific T cells following immunization of human immunodeficiency virus type 1 (HIV-1)-infected individuals with a recombinant modified vaccinia virus Ankara/HIV-1 Gag vaccine

Affordable therapeutic strategies that induce sustained control of human immunodeficiency virus type 1 (HIV-1) replication and are tailored to the developing world are urgently needed. Since CD8(+) and CD4(+) T cells are crucial to HIV-1 control, stimulation of potent cellular responses by therapeutic vaccination might be exploited to reduce antiretroviral drug exposure. However, therapeutic vaccines tested to date have shown modest immunogenicity. In this study, we performed a comprehensive analysis of the changes in virus-specific CD8(+) and CD4(+) T-cell responses occurring after vaccination of 16 HIV-1-infected individuals with a recombinant modified vaccinia virus Ankara-vectored vaccine expressing the consensus HIV-1 clade A Gag p24/p17 sequences and multiple CD8(+) T-cell epitopes during highly active antiretroviral therapy. We observed significant amplification and broadening of CD8(+) and CD4(+) gamma interferon responses to vaccine-derived epitopes in the vaccinees, without rebound viremia, but not in two unvaccinated controls followed simultaneously. Vaccine-driven CD8(+) T-cell expansions were also detected by tetramer reactivity, predominantly in the CD45RA(-) CCR7(+) or CD45RA(-) CCR7(-) compartments, and persisted for at least 1 year. Expansion was associated with a marked but transient up-regulation of CD38 and perforin within days of vaccination. Gag-specific CD8(+) and CD4(+) T-cell proliferation also increased postvaccination. These data suggest that immunization with MVA.HIVA is a feasible strategy to enhance potentially protective T-cell responses in individuals with chronic HIV-1 infection.

Therapeutic immunization strategies for the control of HIV-1

Highly active antiretroviral therapy (HAART) is currently the only means to halt or prevent progression to AIDS. However, lack of access to medications for the vast majority of HIV-1-infected individuals in immediate need, together with the requirement for lifelong adherence and potential for serious toxicity, are significant limitations which have yet to be overcome. Augmentation of HIV-specific immunity by therapeutic vaccination is being explored as a possible alternative to continuous HAART. A few candidate HIV-1 vaccines have entered clinical trials involving an assessment of viremia control during an analytic therapy interruption, but even the most promising of these achieve a short-lived suppression of HIV-1 without HAART. Nevertheless, these studies are guiding the development of better immune augmentation strategies, which could extend the time off therapy and will also contribute to a better understanding of the immune correlates of protection against AIDS. The status of therapeutic vaccines that are currently undergoing preclinical and clinical evaluation is reviewed.

Therapeutic immunization with a human immunodeficiency virus (HIV) type 1-recombinant canarypox vaccine in chronically HIV-infected patients: The Vacciter Study (ANRS 094)

This open single-arm study evaluated whether the administration of an HIV-recombinant canarypox vaccine (vCP1433) in highly active antiretroviral therapy (HAART)-treated patients chronically infected with HIV was safe, immunogenic and associated with prolongation of treatment discontinuation: 48 patients received four monthly vCP1433 injections and stopped HAART. Immunization was safe. HIV-p24-specific lymphoproliferative responses (LPR), significantly increased in the whole group after two injections but decreased thereafter, HIV-gag-specific CD8 T cells were boosted in 55% patients tested. Altogether, 11% patients with at least one HIV-specific LPR during immunization remained off therapy after 44 weeks of interruption. Detection of such LPR response at the time of treatment interruption was significantly associated with the probability of remaining off therapy. These results provide rationale for future randomized trials exploring this strategy.

Loss of reactivity of vaccine-induced CD4 T cells in immunized monkeys after SIV/HIV challenge

BACKGROUND

Immunization protocols involving priming with DNA and boosting with recombinant live virus vectors such as recombinant modified Vaccinia Ankara (rMVA) are considered as vaccine candidates against HIV. Such protocols improve the outcome of simian/human immunodeficiency virus (SHIV) pathogenic challenge in Rhesus monkeys.

OBJECTIVES

To investigate the fate of vaccine-induced T cells after a mucosal SHIV challenge.

METHODS

We immunized Rhesus monkeys (Macaca mulatta) by DNA priming followed by rMVA boost. After intrarectal challenge with SHIV 89.6P, immunized animals demonstrated early control of viral replication and stable CD4 T-cell counts. We monitored T-cell responses by measuring IFN-gamma secretion and proliferation.

RESULTS

Immunization induced strong and sustained SHIV-specific CD4 and CD8 T-cell responses. CD8 T-cell responses were recalled during acute infection, whereas none of the vaccine-induced SHIV-specific CD4 T-cell responses were recalled. Moreover, most of the CD4 T-cell responses became undetectable in peripheral blood or lymph nodes even after in-vitro peptide stimulation. In contrast, we persistently detected CD4 T-cell responses specific for control recall antigens in infected animals.

CONCLUSION

SHIV 89.6P challenge results in a lack of reactivity of vaccine-induced SHIV-specific CD4 T cells. These results may have important implications in the AIDS vaccine field, especially for the evaluation of new vaccine candidates, both in preventive and therapeutic trials.

Enhanced HIV-1 specific immune response by CpG ODN and HIV-1 immunogen-pulsed dendritic cells confers protection in the Trimera murine model of HIV-1 infection

We have recently developed a novel small animal model for HIV-1 infection (Ayash-Rashkovsky et al., http://www.fasebj.org/cgi/doi/10.1096/fj.04-3184fje; doi:10.1096/fj.04-3184fje). The mice were successfully infected with HIV-1 for 4-6 wk with different clades of either T- or M-tropic isolates. HIV-1 infection was accompanied by rapid loss of human CD4+ T cells, decrease in CD4/CD8 ratio, and increased T cell activation. HIV specific human humoral and cellular immune responses were observed in all HIV-1 infected animals. In the present study, HIV specific human immune responses, both humoral and cellular, were generated in noninfected Trimera mice, after their immunization with gp120-depleted HIV-1 antigen, presented by autologous human dendritic cells. Addition of CpG ODN to the antigen-pulsed DCs significantly enhanced (by 2- to 30-fold) the humoral and cellular HIV-1 specific immune responses. Only mice immunized with the HIV-1 immunogen and CpG were completely protected from infection with HIV-1 after challenge with high infection titers of the virus. This novel small animal model for HIV-1 infection may thus serve as an attractive platform for rapid testing of candidate HIV-1 vaccines and of adjuvants and may shorten the time needed for the development and final assessment of protective HIV-1 vaccines in human trials.

Novel peptide-based HIV-1 immunotherapy

Therapeutic immunisation of human immunodeficiency virus type 1-infected individuals should be actively pursued in the first instance to augment highly active antiretroviral therapy regimens. Peptide-based immunotherapeutic strategies offer considerable advantages over conventional approaches, particularly regarding safety. Peptide design itself is becoming increasingly sophisticated, with the rapid evolution of bioinformatics tools that can analyse not only T cell epitopes, but also their potential for successful presentation on diverse human leukocyte antigen (HLA) class I or II following intracellular processing by antigen-presenting cells (APCs). By targeting conserved viral domains, peptides acquire improved reactivity to diverse viral strains. Dendritic cells represent a powerful route of administration, as they are the most potent APCs and can present exogenous peptides on both HLA class I and II through the process of cross-presentation. In this way, soluble peptides can thereby stimulate both CD4+ and CD8+ T cells.

Therapeutic HIV vaccines: An update

The goal of therapeutic immunization in HIV infection is to induce strong and sustained immune responses against HIV. Several arguments suggest that the immune system may contain HIV replication in the long term before declining. The potency on new antiviral regimens in clinic has provided an opportunity to improve the control of the virus replication by the immune system. In clinical terms, this might allow patients to delay or to stop antiviral therapy and to minimize the duration of the exposition to antiviral drugs.

Limited durability of viral control following treated acute HIV infection

BACKGROUND

Early treatment of acute HIV infection with highly active antiretroviral therapy, followed by supervised treatment interruption (STI), has been associated with at least transient control of viremia. However, the durability of such control remains unclear. Here we present longitudinal follow-up of a single-arm, open-label study assessing the impact of STI in the setting of acute HIV-1 infection.

METHODS AND FINDINGS

Fourteen patients were treated during acute HIV-1 infection and subsequently subjected to an STI protocol that required retreatment if viral load exceeded 50,000 RNA copies/ml plasma or remained above 5,000 copies/ml for more than three consecutive weeks. Eleven of 14 (79%) patients were able to achieve viral loads of less than 5,000 RNA copies/ml for at least 90 d following one, two, or three interruptions of treatment. However, a gradual increase in viremia and decline in CD4+ T cell counts was observed in most individuals. By an intention-to-treat analysis, eight (57%), six (43%), and three (21%) of 14 patients achieved a maximal period of control of 180, 360, and 720 d, respectively, despite augmentation of HIV-specific CD4+ and CD8+ T cell responses. The magnitude of HIV-1-specific cellular immune responses before treatment interruption did not predict duration of viremia control. The small sample size and lack of concurrent untreated controls preclude assessment of possible clinical benefit despite failure to control viremia by study criteria.

CONCLUSIONS

These data indicate that despite initial control of viremia, durable viral control to less than 5,000 RNA copies/ml plasma in patients following treated acute HIV-1 infection occurs infrequently. Determination of whether early treatment leads to overall clinical benefit will require a larger and randomized clinical trial. These data may be relevant to current efforts to develop an HIV-1 vaccine designed to retard disease progression rather than prevent infection since they indicate that durable maintenance of low-level viremia may be difficult to achieve.

The potential role of the HIV-1 immunogen (Remune) as a therapeutic vaccine in the treatment of HIV infection

Immune-based therapies, such as therapeutic vaccination, that might preserve, restore, enhance and induce new HIV-specific immunologic responses are currently being explored. HIV-specific immunotherapy with Remune (The Immune Response Corp.) offers the opportunity to boost immune responses against HIV-1. The clinical trial program in a wide range of subjects has established the efficacy of Remune in stimulating an appropriate immune response in HIV-positive individuals. Furthermore, a recent unblinded study conducted in Europe has documented a significant effect of Remune on viral load. Evidence regarding clinical end points is more difficult to collect. The same studies have revealed no serious safety issues in a total of more than 2000 Remune-treated patients. It is therefore reasonable to suggest that the risk-benefit ratio of Remune could be positive.

Autoimmunity induced by adjuvant hydrocarbon oil components of vaccine

Adjuvant oils such as Bayol F (Incomplete Freund's adjuvant: IFA) and squalene (MF59) have been used in human and veterinary vaccines despite poor understanding of their mechanisms of action. Several reports suggest an association of vaccination and various autoimmune diseases, however, few were confirmed epidemiologically and the risk of vaccination for autoimmune diseases has been considered minimal. Microbial components, not the adjuvant components, are considered to be of primary importance for adverse effects of vaccines. We have reported that a single intraperitoneal injection of the adjuvant oils pristane, IFA or squalene induces lupus-related autoantibodies to nRNP/Sm and -Su in non-autoimmune BALB/c mice. Induction of these autoantibodies appeared to be associated with the hydrocarbon's ability to induce IL-12, IL-6, and TNF-alpha, suggesting a relationship with hydrocarbon's adjuvanticity. Whether this is relevant in human vaccination is a difficult issue due to the complex effects of vaccines and the fact that immunotoxicological effects vary depending on species, route, dose, and duration of administration. Nevertheless, the potential of adjuvant hydrocarbon oils to induce autoimmunity has implications in the use of oil adjuvants in human and veterinary vaccines as well as basic research.

High levels of human immunodeficiency virus infection of CD8 lymphocytes expressing CD4 in vivo

Human immunodeficiency virus (HIV)-infected CD8 lymphocytes have been reported in vivo, but the mechanism of infection remains unclear. Experiments using the thy/hu mouse model support export of intrathymically infected CD8 precursors, while recent in vitro data suggest that mature CD8 lymphocytes upregulate CD4 upon activation (generating a CD8bright CD4dim phenotype) and are susceptible to HIV infection. To determine whether these mechanisms operate in vivo and to assess their relative importance in the generation of circulating HIV-infected CD8 lymphocytes, we quantified HIV long terminal repeat (LTR) DNA in CD8+ CD4- and CD8bright CD4dim lymphocytes isolated from HIV-infected individuals by fluorescence-activated cell sorting. HIV infection of CD8 lymphocytes was demonstrated in 17 of 19 subjects, with a significant inverse relationship between level of infection and CD4 lymphocyte count (R = -0.73; P < 0.001). The level of HIV infection of CD8bright CD4dim lymphocytes was significantly higher (median, 1,730 HIV LTR copies/10(6) cells; n = 9) than that of CD8+ CD4- lymphocytes (undetectable in seven of nine individuals; P < 0.01) and approached that of CD4 lymphocytes from the same individuals (median, 3,660 HIV LTR copies/10(6) cells). CD8bright CD4dim lymphocytes represented 0.8 to 3.3% of total CD8 lymphocytes and were most prevalent in the memory subset. Thus, HIV-infected CD8 lymphocytes commonly circulate in HIV-infected individuals and are generated through infection of activated CD8 lymphocytes rather than through export of intrathymically infected precursors. The high level of infection of CD8bright CD4dim lymphocytes could have a direct role in the decline in CD8 lymphocyte function that accompanies HIV disease progression.

HLA- and dose-dependent immunogenicity of a peptide-based HIV-1 immunotherapy candidate (Vacc-4x)

OBJECTIVE

The Vacc-4x immunotherapy candidate is composed of four modified peptides corresponding to conserved domains of the HIV-1 protein p24 that preferentially include HLA-A2 restricted elements. Dose-dependent safety and immunogenicity of Vacc-4x and the significance of a HLA-A2 haplotype were examined.

DESIGN

Non-AIDS, HIV-1 infected healthy patients (n = 40) stable on HAART with CD4 counts > 300 x 10 cells/l were randomized to receive either low-dose or high-dose Vacc-4x over 26 weeks in an open, prospective phase II clinical trial.

METHODS

Patients received a total of 10 intradermal injections, using recombinant granulocyte-macrophage colony stimulating factor as a local adjuvant. Vacc-4x-specific cellular responses were monitored in vivo by delayed-type hypersensitivity (DTH) skin test infiltrates and in vitro by both T-cell proliferation, and induction /secretion of cytokines.

RESULTS

Most patients developed Vacc-4x-specific DTHs (90%) and proliferative T-cell responses (80%) that were inter-related in magnitude. High-dose Vacc-4x generally induced stronger specific immune responses than low dose in terms of DTH areas and CD4 and CD8 T-cell proliferation. Only HLA-A2 negative patients had a definite dose advantage, and this subgroup had in fact the best overall DTH and proliferative responses. In contrast, no significant dose difference was observed for HLA-A2 positive patients. No serious adverse events were reported.

CONCLUSIONS

HIV-associated specific responses were safely induced in most patients by Vacc-4x in a dose-dependent manner and were also influenced by the HLA haplotype.

Loss of HIV-1-specific CD8+ T cell proliferation after acute HIV-1 infection and restoration by vaccine-induced HIV-1-specific CD4+ T cells

Virus-specific CD8(+) T cells are associated with declining viremia in acute human immunodeficiency virus (HIV)1 infection, but do not correlate with control of viremia in chronic infection, suggesting a progressive functional defect not measured by interferon gamma assays presently used. Here, we demonstrate that HIV-1-specific CD8(+) T cells proliferate rapidly upon encounter with cognate antigen in acute infection, but lose this capacity with ongoing viral replication. This functional defect can be induced in vitro by depletion of CD4(+) T cells or addition of interleukin 2-neutralizing antibodies, and can be corrected in chronic infection in vitro by addition of autologous CD4(+) T cells isolated during acute infection and in vivo by vaccine-mediated induction of HIV-1-specific CD4(+) T helper cell responses. These data demonstrate a loss of HIV-1-specific CD8(+) T cell function that not only correlates with progressive infection, but also can be restored in chronic infection by augmentation of HIV-1-specific T helper cell function. This identification of a reversible defect in cell-mediated immunity in chronic HIV-1 infection has important implications for immunotherapeutic interventions.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Therapeutic immunization with an inactivated HIV-1 Immunogen plus antiretrovirals versus antiretroviral therapy alone in asymptomatic HIV-infected subjects

To determine whether the addition of an inactivated-gp120-depleted HIV-1 Immunogen to antiretrovirals (ARTs) conferred a beneficial effect on delaying time to virologic failure relative to that obtained by ARTs alone, a phase II clinical trial was performed in 243 asymptomatic, ART naïve, HIV-1 seropositive adults. The Cox model showed that HIV-1 Immunogen treatment was associated with a 34% decrease in the risk of virologic failure (P = 0.056). When the analysis incorporated baseline HIV-RNA stratification the risk of virologic failure in the HIV-1 Immunogen Arm was significantly reduced a 37% compared to the IFA placebo Arm (P = 0.034). The data suggest that therapeutic immunization plus ARTs could influence virologic control.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Immune reconstitution following autologous transfers of CD3/CD28 stimulated CD4+ T cells to HIV-infected persons

We have previously shown that adoptive transfer of in vitro CD3/CD28 activated autologous CD4(+) T cells results in increased CD4 counts and CD4/CD8 ratios in HIV+ subjects. In this report, analysis of variable beta (Vbeta) chain T cell receptor (TCR) repertoire showed that CD3/CD28 stimulation was able to increase polyclonality within skewed spectra types in vitro. In vivo, two of eight subjects showed increase in TCR diversity and importantly, in no subject did a highly skewed in vivo repertoire emerge. Measurement of proliferative response to alloantigen showed increases following infusions. Response to pharmacological stimulus and lectin via Interferon-gamma ELISpot assay showed increases in a subset of subjects following infusions. However, interferon-gamma response to HIV antigens and peptides declined concurrent with stable or diminishing latent infectious viral load in CD4(+) T cells. These data provide further evidence that adoptive transfer of activated autologous CD4(+) T cells can augment the immune system.

Comprehensive analysis of human immunodeficiency virus type 1-specific CD4 responses reveals marked immunodominance of gag and nef and the presence of broadly recognized peptides

Increasing evidence suggests that human immunodeficiency virus type 1 (HIV-1)-specific CD4 T-cell responses contribute to effective immune control of HIV-1 infection. However, the breadths and specificities of these responses have not been defined. We screened fresh CD8-depleted peripheral blood mononuclear cells (PBMC) from 36 subjects at different stages of HIV-1 infection for virus-specific CD4 responses by gamma interferon enzyme-linked immunospot assay, using 410 overlapping peptides spanning all HIV-1 proteins (based on the clade B consensus sequence). HIV-1-specific CD4 responses were identified in 30 of the 36 individuals studied, with the strongest and broadest responses detected in persons treated in acute infection who underwent treatment interruption. In individuals with identified responses, the total number of recognized HIV-1 peptides ranged from 1 to 36 (median, 7) and the total magnitude of responses ranged from 80 to >14,600 (median, 990) spot-forming cells/10(6) CD8-depleted PBMC. Neither the total magnitude nor the number of responses correlated with viremia. The most frequent and robust responses were directed against epitopes within the Gag and Nef proteins. Peptides targeted by >/=25% of individuals were then tested for binding to a panel of common HLA-DR molecules. All bound broadly to at least four of the eight alleles tested, and two bound to all of the HLA-DR molecules studied. Fine mapping and HLA restriction of the responses against four of these peptides showed a combination of clustering of epitopes and promiscuous presentation of the same epitopes by different HLA class II alleles. These findings have implications for the design of immunotherapeutic strategies and for testing candidate HIV vaccines.

Proliferation responses to HIVp24 during antiretroviral therapy do not reflect improved immune phenotype or function

OBJECTIVE

To ascertain whether lymphoproliferation (LP) responses to HIVp24 in chronically infected patients treated with antiretroviral therapy (ART) predict an improved cytolytic T-cell phenotype or better in vivo immune function as measured by immunization responses.

METHODS

HIV-infected patients who started ART during chronic infection and who achieved viral suppression (HIV-RNA < 400 copies/ml for > 12 months) were grouped by the presence of strong [stimulation index (SI) > 10; n = 21] or absent (SI < 3; n = 18) LP to HIV-core antigen. The two groups were compared for functional immune responses to vaccination with diphtheria-toxoid, tetanus-toxoid and keyhole-limpet-hemocyanin, frequency of circulating naive and memory CD4+ and CD8+ T lymphocytes, maturation phenotype and expression of cytolytic molecules on total and HIV-specific CD8+ T cells, and frequency of memory CD4+ T cells with intracellular HIV-mRNA. Group comparisons were analyzed by non-parametric Mann-Whitney tests. Proportions were estimated by Pearson's chi analysis.

RESULTS

There were no differences between the groups in immune responses to vaccination or in the numbers or phenotype of circulating T cells. In a subgroup of HLA-A2+ or B8+ patients, HIV-reactive CD8+ T cells in both groups had similar expression of perforin, granzyme A and T-cell maturation markers (CD27, CD28, CCR7, CD62L). However, patients with SI > 10 in response to HIVp24 tended to more often have high levels of circulating CD4+ T cells with intracellular HIV-1 mRNA than did patients with SI < 3.

CONCLUSION

Following long-standing suppression of viral replication on ART, the presence of HIV-1 specific T-helper proliferation responses does not correlate with improved indices of immune phenotype or function but may reflect relatively higher levels of HIV-expression.