Polyfunctional CD4+ T-cell induction in neutralizing antibody-triggered control of simian immunodeficiency virus infection

Fc-Dependent Immunomodulation Induced by Antiviral Therapeutic Antibodies: New Perspectives for Eliciting Protective Immune Responses

The multiple mechanisms of action of antiviral monoclonal antibodies (mAbs) have made these molecules a potential therapeutic alternative for treating severe viral infections. In addition to their direct effect on viral propagation, several studies have shown that mAbs are able to enhance the host's adaptive immune response and generate long-lasting protective immunity. Such immunomodulatory effects occur in an Fc-dependent manner and rely on Fc-FcγR interactions. It is noteworthy that several FcγR-expressing cells have been shown to play a key role in enhancing humoral and cellular immune responses (so-called "vaccinal effects") in different experimental settings. This review recalls recent findings concerning the vaccinal effects induced by antiviral mAbs, both in several preclinical animal models and in patients treated with mAbs. It summarizes the main cellular and molecular mechanisms involved in these immunomodulatory properties of antiviral mAbs identified in different pathological contexts. It also describes potential therapeutic interventions to enhance host immune responses that could guide the design of improved mAb-based immunotherapies.

Vectored antibody gene delivery restores host B and T cell control of persistent viral infection

Passive antibody therapy and vectored antibody gene delivery (VAGD) in particular offer an innovative approach to combat persistent viral diseases. Here, we exploit a small animal model to investigate synergies of VAGD with the host's endogenous immune defense for treating chronic viral infection. An adeno-associated virus (AAV) vector delivering the lymphocytic choriomeningitis virus (LCMV)-neutralizing antibody KL25 (AAV-KL25) establishes protective antibody titers for >200 days. When therapeutically administered to chronically infected immunocompetent wild-type mice, AAV-KL25 affords sustained viral load control. In contrast, viral mutational escape thwarts therapeutic AAV-KL25 effects when mice are unable to mount LCMV-specific antibody responses or lack CD8⁺ T cells. VAGD augments antiviral germinal center B cell and antibody-secreting cell responses and reduces inhibitory receptor expression on antiviral CD8⁺ T cells. These results indicate that VAGD fortifies host immune defense and synergizes with B cell and CD8 T cell responses to restore immune control of chronic viral infection.

Late-phase dominance of a single epitope-specific CD8+ T-cell response in passive neutralizing antibody-infused simian immunodeficiency virus controllers

OBJECTIVE

Analysis of the quantity and quality of epitope-specific CD8+ T-cell responses is crucial for understanding the mechanism of HIV/simian immunodeficiency virus (SIV) replication control. We have previously shown that acute-phase passive infusion of neutralizing antibodies (NAbs) results in augmented broad T-cell responses and robust SIVmac239 control in rhesus macaques. Analyzing long-term dynamics of CD8+ T-cell responses in these SIV controllers provides important insights into designing lasting anti-HIV immunity.

DESIGN

We analyzed dynamics and metabolic/functional profiles of SIV-specific CD8+ T-cell responses in rhesus macaques that controlled SIVmac239 replication following acute-phase passive NAb infusion.

METHODS

SIV epitope-specific CD8+ T-cell responses in peripheral blood at multiple chronic-phase time points were investigated in four passive NAb-infused SIV controllers. In particular, expression patterns of Eomesodermin (Eomes), phosphorylated AMP kinase (pAMPK), CD28 and programmed death-1 (PD-1) were examined.

RESULTS

In the NAb-infused SIV controllers, a single epitope-specific CD8+ T-cell response detected from acute infection and maintaining low levels up to year 1 showed a surge thereafter, up to year 2 postchallenge. Retention of an effector-skewed and unexhausted Eomes-high/pAMPK-low/CD28-negative/PD-1-low subpopulation in these epitope-specific CD8+ T cells implicated their front-line commitment in residual viral replication control.

CONCLUSION

In long-term SIV control following acute-phase passive NAb infusion, a single-epitope, high-quality CTL response was dominantly induced in the chronic phase. These results likely describe one favorable pattern of immunodominant epitope-specific CD8+ T-cell preservation and suggest the importance of incorporating metabolic marker signatures for understanding NAb/T-cell synergism-based HIV/SIV control.

Nef-specific CD107a+ CD4+ T-cell responses in a rhesus macaque (Macaca mulatta) showing partial simian immunodeficiency virus control following passive neutralizing antibody infusion

Acute-phase neutralizing antibody (NAb) passive immunization in simian immunodeficiency virus (SIV)-infected rhesus macaques (Macaca mulatta) can confer stringent viremia control with T-cell augmentation. In one NAb-infused SIV partial controller, we identify chronic-phase Nef-specific CD107a⁺ CD4⁺ T-cell response maintenance, implicating that NAb infusion modulates long-term T-cell responses even within viremic control.

Differential and sequential immunomodulatory role of neutrophils and Ly6Chi inflammatory monocytes during antiviral antibody therapy

Antiviral monoclonal antibodies (mAbs) can generate protective immunity through Fc-FcγRs interactions. We previously showed a role for immune complexes (ICs) in the enhancement of antiviral T-cell responses through FcγR-mediated activation of dendritic cells (DCs). Here we addressed how mAb therapy in retrovirus-infected mice affects the activation of neutrophils and inflammatory monocytes, two FcγR-expressing innate effector cells rapidly recruited to sites of infection. We found that both cell-types activated in vitro by viral ICs secreted chemokines able to recruit monocytes and neutrophils themselves. Moreover, inflammatory cytokines potentiated chemokines and cytokines release by IC-activated cells and induced FcγRIV upregulation. Similarly, infection and mAb-treatment upregulated FcγRIV on neutrophils and inflammatory monocytes and enhanced their cytokines/chemokines secretion. Notably, upon antibody therapy neutrophils and inflammatory monocytes displayed distinct functional activation states and sequentially modulated the antiviral immune response by secreting Th1-type polarizing cytokines and chemokines, which occurred in a FcγRIV-dependent manner. Consistently, FcγRIV- blocking in mAb-treated, infected mice led to reduced immune protection. Our work provides new findings on the immunomodulatory role of neutrophils and monocytes in the enhancement of immune responses upon antiviral mAb therapy.

Optimize Prime/Boost Vaccine Strategies: Trained Immunity as a New Player in the Game

Most vaccines require multiple doses to induce long-lasting protective immunity in a high frequency of vaccines, and to ensure strong both individual and herd immunity. Repetitive immunogenic stimulations not only increase the intensity and durability of adaptive immunity, but also influence its quality. Several vaccine parameters are known to influence adaptive immune responses, including notably the number of immunizations, the delay between them, and the delivery sequence of different recombinant vaccine vectors. Furthermore, the initial effector innate immune response is key to activate and modulate B and T cell responses. Optimization of homologous and heterologous prime/boost vaccination strategies requires a thorough understanding of how vaccination history affects memory B and T cell characteristics. This requires deeper knowledge of how innate cells respond to multiple vaccine encounters. Here, we review how innate cells, more particularly those of the myeloid lineage, sense and respond differently to a 1st and a 2nd vaccine dose, both in an extrinsic and intrinsic manner. On one hand, the presence of primary specific antibodies and memory T cells, whose critical properties change with time after priming, provides a distinct environment for innate cells at the time of re-vaccination. On the other hand, innate cells themselves can exert enhanced intrinsic antimicrobial functions, long after initial stimulation, which is referred to as trained immunity. We discuss the potential of trained innate cells to be game-changers in prime/boost vaccine strategies. Their increased functionality in antigen uptake, antigen presentation, migration, and as cytokine producers, could indeed improve the restimulation of primary memory B and T cells and their differentiation into potent secondary memory cells in response to the boost. A better understanding of trained immunity mechanisms will be highly valuable for harnessing the full potential of trained innate cells, to optimize immunization strategies.

Immunotherapeutic strategies to target vulnerabilities in the Ebolavirus glycoprotein

The 2014 Ebola virus disease (EVD) outbreak in West Africa and the subsequent outbreaks of 2018-2020 in Equator and North Kivu provinces of the Democratic Republic of the Congo illustrate the public health challenges of emerging and reemerging viruses. EVD has a high case fatality rate with a rapidly progressing syndrome of fever, rash, vomiting, diarrhea, and bleeding diathesis. Recently, two monoclonal-antibody-based therapies received United States Food and Drug Administration (FDA) approval, and there are several other passive immunotherapies that hold promise as therapeutics against other species of Ebolavirus. Here, we review concepts needed to understand mechanisms of action, present an expanded schema to define additional sites of vulnerability on the viral glycoprotein, and review current antibody-based therapeutics. The concepts described are used to gain insights into the key characteristics that represent functional targets for immunotherapies against Zaire Ebolavirus and other emerging viruses within the Ebolavirus genus.

[In vivo protective mechanisms of neutralizing antibodies against simian immunodeficiency virus replicatio]

Identifying protective adaptive immune responses against human immunodeficiency virus type 1 (HIV-1), mainly comprising CD8+ cytotoxic T lymphocyte (CTL) and neutralizing antibody (NAb) responses, is crucial for understanding in vivo mechanisms of viral persistence and developing prophylactic/intervention strategies. In HIV-1 and pathogenic simian immunodeficiency virus (SIV) infections, CTL responses play the canonical role in primary viral replication control, whereas NAb responses are impaired. This NAb impairment in early infection conversely highlights the necessity of elucidating anti-HIV/SIV antibody defense/induction mechanisms, and one approach to analyze the impact of NAbs on HIV/SIV infection is passive immunization. We have analyzed a simian AIDS model of highly pathogenic SIVmac239-infected rhesus macaques, and characterized that a single acute-phase passive infusion of SIV-specific polyclonal NAbs drives a synergistic qualitative boosting of virus-specific T-cell responses, resulting in sustained SIV replication control. This in vivo functional augmentation of virus-specific T cells by NAbs in the SIV model provides insights into the design of protective immunity against HIV-1 infection.

Vaccinal effect of HIV-1 antibody therapy

PURPOSE OF REVIEW

The review recalls recent findings regarding the induction of vaccinal effects by HIV-1 broadly neutralizing antibodies (bNAbs) and highlights potential therapeutic strategies to exploit such immunomodulatory properties.

RECENT FINDINGS

Studies in different animal models have shown that mAbs can generate long-lasting protective immunity. Induction of this vaccinal effect by HIV-1 bNAbs has also been more recently reported in animal models of HIV-1 infection. Notably, bNAbs treatment of macaques infected with the chimeric simian-human immunodeficiency virus (SHIV) improved both humoral and cellular adaptive immune responses that contributed to disease control. Importantly, this concept has been extended to HIV-1-infected patients as enhancement of humoral responses was recently reported in HIV-1 patients treated with bNAbs. Studies aiming at elucidating the mechanisms underlying these immunomodulatory properties of bNAbs have identified a role for immune complexes in shaping immune responses against HIV-1. They also highlight different Fc (fragment crystallizable) region effector functions that might be required for the enhancement of HIV-1 immune responses upon bNAbs treatment.

SUMMARY

HIV-1 bNAbs can elicit protective adaptive immune responses through mechanisms involving multiple cellular and molecular actors of the immune system. Harnessing these mechanisms will be crucial to achieve protective immunity against HIV-1 infection by bNAbs.

Impact of Early Antiretroviral Therapy Initiation on HIV-Specific CD4 and CD8 T Cell Function in Perinatally Infected Children

Early initiation of antiretroviral therapy (ART) in vertically HIV-infected children limits the size of the virus reservoir, but whether the time of treatment initiation (TI) can durably impact host immune responses associated with HIV infection is still unknown. This study was conducted in PBMC of 20 HIV-infected virally suppressed children on ART (mean age 9.4 y), classified as early treated (ET; age at ART initiation ≤0.5 y, n = 14) or late treated (LT; age at ART initiation 1-10 y, n = 6). Frequencies and functions of Ag-specific CD4 (CD40L⁺) and CD8 (CD69⁺) T cells were evaluated by intracellular IL-2, IFN-γ, and TNF-α production with IL-21 in CD4 or CD107a, granzyme B and perforin in CD8 T cells following stimulation with HIV gp140 protein (ENV) or GAG peptides by multiparameter flow cytometry. ET showed a higher proportion of cytokine-producing ENV- and GAG-specific CD4 and CD8 T cells compared with LT. In particular, ET were enriched in polyfunctional T cells. RNA sequencing analysis showed upregulation of immune activation pathways in LT compared with ET. Our results suggest that timing of TI in HIV-infected children has a long-term and measurable impact on the quality of the HIV-specific T cell immune responses and transcriptional profiles of PBMC, reinforcing the importance of early TI.

Association of dengue virus-specific polyfunctional T-cell responses with clinical disease severity in acute dengue infection

INTRODUCTION

Although the role of dengue virus (DENV)-specific T cells in the pathogenesis of acute dengue infection is emerging, the functionality of virus-specific T cells associated with milder clinical disease has not been well studied. We sought to investigate how the functionality of DENV-NS3 and DENV-NS5 protein-specific T cells differ in patients with dengue fever (DF) and dengue hemorrhagic fever (DHF).

METHODS

Using intracellular cytokine assays, we assessed the production of interferon γ (IFNγ), tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-1β (MIP-1β), and CD107a expression in adult patients with acute DF (n = 21) and DHF (n = 22).

RESULTS

Quadruple cytokine-producing, polyfunctional DENV-NS3- and DENV-NS5-specific T cells were more frequent in those with DF when compared to those with DHF. While DENV-NS3- and DENV-NS5-specific T cells in patients with DF expressed IFNγ > TNF-α > MIP-β > CD107a, T cells of those with DHF predominantly expressed CD107a > MIP-1β > IFNγ > TNF-α. Overall production of IFNγ or TNF-α by DENV-NS3- and DENV-NS5-specific T cells was significantly higher in patients with DF. The majority of NS3-specific T cells in patients with DF (78.6%) and DHF (68.9%) were single-cytokine producers; 76.6% of DENV-NS5-specific T cells in those with DF and 77.1% of those with DHF, produced only a single cytokine. However, no significant association was found with polyfunctional T-cell responses and the degree of viraemia.

CONCLUSIONS

Our results suggest that the functional phenotype of DENV-specific T cells are likely to associate with clinical disease severity.

Antibody-mediated prevention and treatment of HIV-1 infection

Novel broadly neutralizing antibodies targeting HIV-1 hold promise for their use in the prevention and treatment of HIV-1 infection. Pre-clinical results have encouraged the evaluation of these antibodies in healthy and HIV-1-infected humans. In first clinical trials, highly potent broadly neutralizing antibodies have demonstrated their safety and significant antiviral activity by reducing viremia and delaying the time to viral rebound in individuals interrupting antiretroviral therapy. While emerging antibody-resistant viral variants have indicated limitations of antibody monotherapy, strategies to enhance the efficacy of broadly neutralizing antibodies in humans are under investigation. These include the use of antibody combinations to prevent viral escape, antibody modifications to increase the half-life and the co-administration of latency-reversing agents to target the cellular reservoir of HIV-1. We provide an overview of the results of pre-clinical and clinical studies of broadly HIV-1 neutralizing antibodies, discuss their implications and highlight approaches for the ongoing advancement into humans.

Of Mice, Macaques, and Men: Broadly Neutralizing Antibody Immunotherapy for HIV-1

The neutralizing antibodies targeting the HIV-1 envelope protein have been a major focus for HIV therapy. Early studies with anti-HIV-1 neutralizing monoclonal antibodies (mAbs) administered to infected individuals showed some promise, as they resulted in transient reductions in plasma viremia in some recipients. However, resistant viral variants rapidly emerged. A major development during the past 6 to 7 years has been the isolation and characterization of highly potent and broadly neutralizing mAbs (bNAbs) from infected individuals known as "elite neutralizers." These "next-generation" bNAbs have been tested in animal model systems and shown to effectively control virus replication, particularly following combination immunotherapy. The success of these preclinical animal studies has led to human clinical trials using an individual bNAb for therapy. This review examines recent findings from animal models and human clinical trials and discusses the future use of bNAbs for HIV-1 treatment.

Antiviral Functions of Human Immunodeficiency Virus Type 1 (HIV-1)-Specific IgG Antibodies: Effects of Antiretroviral Therapy and Implications for Therapeutic HIV-1 Vaccine Design

Contemporary antiretroviral therapy (ART) is effective and tolerable for long periods of time but cannot eradicate human immunodeficiency virus type 1 (HIV-1) infection by either elimination of viral reservoirs or enhancement of HIV-1-specific immune responses. Boosting "protective" HIV-1-specific immune responses by active or passive immunization will therefore be necessary to control or eradicate HIV-1 infection and is currently the topic of intense investigation. Recently reported studies conducted in HIV patients and non-human primate (NHP) models of HIV-1 infection suggest that HIV-1-specific IgG antibody responses may contribute to the control of HIV-1 infection. However, production of IgG antibodies with virus neutralizing activity by vaccination remains problematic and while vaccine-induced natural killer cell-activating IgG antibodies have been shown to prevent the acquisition of HIV-1 infection, they may not be sufficient to control or eradicate established HIV-1 infection. It is, therefore, important to consider other functional characteristics of IgG antibody responses. IgG antibodies to viruses also mediate opsonophagocytic antibody responses against virions and capsids that enhance the function of phagocytic cells playing critical roles in antiviral immune responses, particularly conventional dendritic cells and plasmacytoid dendritic cells. Emerging evidence suggests that these antibody functions might contribute to the control of HIV-1 infection. In addition, IgG antibodies contribute to the intracellular degradation of viruses via binding to the cytosolic fragment crystallizable (Fc) receptor tripartite motif containing-21 (TRIM21). The functional activity of an IgG antibody response is influenced by the IgG subclass content, which affects binding to antigens and to Fcγ receptors on phagocytic cells and to TRIM21. The IgG subclass content and avidity of IgG antibodies is determined by germinal center (GC) reactions in follicles of lymphoid tissue. As HIV-1 infects cells in GCs and induces GC dysfunction, which may persist during ART, strategies for boosting HIV-1-specific IgG antibody responses should include early commencement of ART and possibly the use of particular antiretroviral drugs to optimize drug levels in lymphoid follicles. Finally, enhancing particular functions of HIV-1-specific IgG antibody responses by using adjuvants or cytokines to modulate the IgG subclass content of the antibody response might be investigated in NHP models of HIV-1 infection and during trials of therapeutic vaccines in HIV patients.

A New Adjuvant MTOM Mediates Mycobacterium tuberculosis Subunit Vaccine to Enhance Th1-Type T Cell Immune Responses and IL-2+ T Cells

The only licensed vaccine Mycobacterium bovis Bacillus Calmette–Guérin (BCG) cannot prevent the prevalence of tuberculosis (TB), which remains a major public health problem worldwide. A more effective TB vaccine than BCG is urgently needed. Subunit vaccine is a promising strategy, and suitable adjuvants will benefit the development of effective TB subunit vaccines. MTO, consisting of monophosphoryl lipid A (MPLA), trehalose-6,6′-dibehenate (TDB), and MF59, was developed as an adjuvant of TB vaccine because of its ability to evoke the Th1-type T cell responses, while it is insufficient to induce single and multifunctional IL-2⁺ T cells and has a limited ability to confer protection against Mycobacterium tuberculosis infection. Heat-killed Mycobacterium vaccae (Mv), which can evoke cytotoxic CD8⁺ and CD4⁺ T cell responses and has adjuvanticity, was, in this study, combined with MTO to produce a new adjuvant, called MTOM. The TB fusion protein Rv3407-PhoY2-Ag85A-Rv2626c-RpfB (WH121) was mixed with MTO, Mv, and MTOM to produce three subunit vaccines, and the protective efficacy and immune responses were compared in C57BL/6 mice. WH121/MTOM provided better protection against TB than the other two vaccines, matching the performance of BCG vaccine. MTOM showed stronger ability to increase single and multifunctional IL-2⁺ T cells and induce Th1-type responses than MTO or Mv. Therefore, MTOM might be a promising adjuvant that could contribute to the development of TB subunit vaccines.

Neutralizing Monoclonal Antibodies to Fight HIV-1: On the Threshold of Success

Anti-human immunodeficiency virus type-1 (anti-HIV-1) neutralizing monoclonal antibodies are broadening the spectrum of pre- and post-exposure treatment against HIV-1. A better understanding of how these antibodies develop and interact with particular regions of the viral envelope protein is guiding a more rational structure-based immunogen design. The aim of this article is to review the most recent advances in the field, from the development of these particular antibodies during natural HIV-1 infection, to their role preventing infection, boosting endogenous immune responses and clearing both free viral particles and persistently infected cells.

Mechanisms Underlying T Cell Immunosenescence: Aging and Cytomegalovirus Infection

The ability of the human immune system to protect against infectious disease declines with age and efficacy of vaccination reduces significantly in the elderly. Aging of the immune system, also termed as immunosenescence, involves many changes in human T cell immunity that is characterized by a loss in naïve T cell population and an increase in highly differentiated CD28- memory T cell subset. There is extensive data showing that latent persistent human cytomegalovirus (HCMV) infection is also associated with age-related immune dysfunction in the T cells, which might enhance immunosenescence. Understanding the molecular mechanisms underlying age-related and HCMV-related immunosenescence is critical for the development of effective age-targeted vaccines and immunotherapies. In this review, we will address the role of both aging and HCMV infection that contribute to the T cell senescence and discuss the potential molecular mechanisms in aged T cells.

Patterns of HIV/SIV Prevention and Control by Passive Antibody Immunization

Neutralizing antibody (NAb) responses are promising immune effectors for control of human immunodeficiency virus (HIV) infection. Protective activity and mechanisms of immunodeficiency virus-specific NAbs have been increasingly scrutinized in animals infected with simian immunodeficiency virus (SIV), chimeric simian/human immunodeficiency virus (SHIV) and related viruses. Studies on such models have unraveled a previously underscored protective potential against in vivo immunodeficiency virus replication. Pre-challenge NAb titers feasibly provide sterile protection from SIV/SHIV infection by purging the earliest onset of viral replication and likely modulate innate immune cell responses. Sufficient sub-sterile NAb titers after established infection also confer dose-dependent reduction of viremia, and in certain earlier time frames augment adaptive immune cell responses and even provide rebound-free viral control. Here, we provide an overview of the obtained patterns of SIV/SHIV protection and viral control by various types of NAb passive immunizations and discuss how these notions may be extrapolated to NAb-based clinical control of HIV infection.

Converting monoclonal antibody-based immunotherapies from passive to active: bringing immune complexes into play

Monoclonal antibodies (mAbs), which currently constitute the main class of biotherapeutics, are now recognized as major medical tools that are increasingly being considered to fight severe viral infections. Indeed, the number of antiviral mAbs developed in recent years has grown exponentially. Although their direct effects on viral blunting have been studied in detail, their potential immunomodulatory actions have been overlooked until recently. The ability of antiviral mAbs to modulate antiviral immune responses in infected organisms has recently been revealed. More specifically, upon recognition of their cognate antigens, mAbs form immune complexes (ICs) that can be recognized by the Fc receptors expressed on different immune cells of infected individuals. This binding may be followed by the modulation of the host immune responses. Harnessing this immunomodulatory property may facilitate improvements in the therapeutic potential of antiviral mAbs. This review focuses on the role of ICs formed with different viral determinants and mAbs in the induction of antiviral immune responses in the context of both passive immunotherapies and vaccination strategies. Potential deleterious effects of ICs on the host immune response are also discussed.

Biphasic CD8+ T-Cell Defense in Simian Immunodeficiency Virus Control by Acute-Phase Passive Neutralizing Antibody Immunization

Identifying human immunodeficiency virus type 1 (HIV-1) control mechanisms by neutralizing antibodies (NAbs) is critical for anti-HIV-1 strategies. Recent in vivo studies on animals infected with simian immunodeficiency virus (SIV) and related viruses have shown the efficacy of postinfection NAb passive immunization for viremia reduction, and one suggested mechanism is its occurrence through modulation of cellular immune responses. Here, we describe SIV control in macaques showing biphasic CD8(+) cytotoxic T lymphocyte (CTL) responses following acute-phase NAb passive immunization. Analysis of four SIVmac239-infected rhesus macaque pairs matched with major histocompatibility complex class I haplotypes found that counterparts receiving day 7 anti-SIV polyclonal NAb infusion all suppressed viremia for up to 2 years without accumulating viral CTL escape mutations. In the first phase of primary viremia control attainment, CD8(+) cells had high capacities to suppress SIVs carrying CTL escape mutations. Conversely, in the second, sustained phase of SIV control, CTL responses converged on a pattern of immunodominant CTL preservation. During this sustained phase of viral control, SIV epitope-specific CTLs showed retention of phosphorylated extracellular signal-related kinase (ERK)(hi)/phosphorylated AMP-activated protein kinase (AMPK)(lo) subpopulations, implying their correlation with SIV control. The results suggest that virus-specific CTLs functionally boosted by acute-phase NAbs may drive robust AIDS virus control.

IMPORTANCE

In early HIV infection, NAb responses are lacking and CTL responses are insufficient, which leads to viral persistence. Hence, it is important to identify immune responses that can successfully control such HIV replication. Here, we show that monkeys receiving NAb passive immunization in early SIV infection strictly control viral replication for years. Passive infusion of NAbs with CTL cross-priming capacity resulted in induction of functionally boosted early CTL responses showing enhanced suppression of CTL escape mutant virus replication. Accordingly, the NAb-infused animals did not show accumulation of viral CTL escape mutations during sustained SIV control, and immunodominant CTL responses were preserved. This early functional augmentation of CTLs by NAbs provides key insights into the design of lasting and viral escape mutation-free protective immunity against HIV-1 infection.

Antiviral Monoclonal Antibodies: Can They Be More Than Simple Neutralizing Agents?

Monoclonal antibodies (mAbs) are increasingly being considered as agents to fight severe viral diseases. So far, they have essentially been selected and used on the basis of their virus-neutralizing activity and/or cell-killing activity to blunt viral propagation via direct mechanisms. There is, however, accumulating evidence that they can also induce long-lasting protective antiviral immunity by recruiting the endogenous immune system of infected individuals during the period of immunotherapy. Exploiting this property may revolutionize antiviral mAb-based immunotherapies, with benefits for both patients and healthcare systems.

Antiviral monoclonal antibodies (mAbs) are promising, high-added-value biotherapeutics. During recent years, the number of antiviral mAbs developed against both acute and chronic viruses has grown exponentially, some of them being currently tested in clinical trials.

Antiviral mAbs can be used to blunt viral propagation through direct effects. They can also engage the host's immune system, leading to the induction of long-lasting protective vaccine-like effects.

The assessment of mechanisms at play in the induction of vaccine-like effects by antiviral mAbs will help in improving antiviral treatments.

Exploiting this effect will translate into therapeutic benefit for patients. The benefit will also help healthcare systems through the reduction of treatment costs.

Functionality of dengue virus specific memory T cell responses in individuals who were hospitalized or who had mild or subclinical dengue infection

Background

Although antibody responses to dengue virus (DENV) in naturally infected individuals have been extensively studied, the functionality of DENV specific memory T cell responses in relation to clinical disease severity is incompletely understood.

Methodology/Principal findings

Using ex vivo IFNγ ELISpot assays, and by determining cytokines produced in ELISpot supernatants, we investigated the functionality of DENV-specific memory T cell responses in a large cohort of individuals from Sri Lanka (n=338), who were naturally infected and were either hospitalized due to dengue or had mild or sub clinical dengue infection. We found that T cells of individuals with both past mild or sub clinical dengue infection and who were hospitalized produced multiple cytokines when stimulated with DENV-NS3 peptides. However, while DENV-NS3 specific T cells of those with mild/sub clinical dengue infection were more likely to produce only granzyme B (p=0.02), those who were hospitalized were more likely to produce both TNFα and IFNγ (p=0.03) or TNFα alone.

We have also investigated the usefulness of a novel T cell based assay, which can be used to determine the past infecting DENV serotype. 92.4% of DENV seropositive individuals responded to at least one DENV serotype of this assay and none of the seronegatives responded. Individuals who were seronegative, but had received the Japanese encephalitis vaccine too made no responses, suggesting that the peptides used in this assay did not cross react with the Japanese encephalitis virus.

Conclusions/significance

The types of cytokines produced by DENV-specific memory T cells appear to influence the outcome of clinical disease severity. The novel T cell based assay, is likely to be useful in determining the past infecting DENV serotype in immune-epidemiological studies and also in dengue vaccine trials.

Although dengue viral infections cause severe clinical disease, the majority of individuals infected with the dengue virus (DENV) develop asymptomatic infection. The function of DENV specific memory T cells in relation to past clinical disease severity is incompletely understood. In this study, we sought to investigate the function of DENV specific memory T cell responses in a large cohort (n = 338) of individuals who were naturally infected with the DENV but developed varying severity of clinical disease. We found that T cells of individuals who were hospitalized due to dengue and those with mild/sub clinical dengue infection produced multiple cytokines when stimulated with DENV-NS3 peptides. In addition, we have also validated a novel T cell based assay, which can be used to determine the past infecting DENV serotype. We found that 92.4% of DENV seropositive individuals responded to at least one DENV serotype of this assay and none of the seronegatives responded. Moreover, the peptides used in this assay did not cross react with Japanese encephalitis virus. Therefore, this assay is likely to be useful in determining the past infecting DENV serotype in immune-epidemiological studies and also in dengue vaccine trials.

Enhanced protective efficacy against Mycobacterium tuberculosis afforded by BCG prime-DNA boost regimen in an early challenge mouse model is associated with increased splenic interleukin-2-producing CD4 T-cell frequency post-vaccination

The development of improved vaccines and vaccination strategies against Mycobacterium tuberculosis has been hindered by a limited understanding of the immune correlates of anti-tuberculosis protective immunity. Simple measurement of interferon-γ frequency or production per se does not provide adequate prediction of immune protection. In this study, we examined the relationship between T-cell immune responses and protective efficacy conferred by the heterologous vaccination strategy, bacillus Calmette-Guérin (BCG) prime-Ag85A DNA boost (B/D), in an early challenge mouse model of pulmonary tuberculosis. The results demonstrated that mice vaccinated with the B/D regimen had a significantly reduced bacillary load compared with BCG-vaccinated mice, and the reduction in colony-forming units was associated with decreased pathology and lower levels of inflammatory cytokines in the infected lungs. Further analysis of immunogenicity showed that the superior protection afforded by the B/D regimen was associated with significantly increased frequency of splenic interleukin-2 (IL-2) -producing CD4 T cells and increased IL-2 production when measured as integrated mean fluorescence intensity post-vaccination as well. These data suggest that measurement of elevated frequency of IL-2-producing CD4 T cells or IL-2 production in the spleens of vaccinated mice can predict vaccine efficacy, at least in the B/D strategy, and add to the accumulating body of evidence suggesting that BCG prime-boost strategies may be a useful approach to the control of M. tuberculosis infection.

Vaccine-induced CD107a+ CD4+ T cells are resistant to depletion following AIDS virus infection

CD4(+) T-cell responses are crucial for effective antibody and CD8(+) T-cell induction following virus infection. However, virus-specific CD4(+) T cells can be preferential targets for human immunodeficiency virus (HIV) infection. HIV-specific CD4(+) T-cell induction by vaccination may thus result in enhancement of virus replication following infection. In the present study, we show that vaccine-elicited CD4(+) T cells expressing CD107a are relatively resistant to depletion in a macaque AIDS model. Comparison of virus-specific CD107a, macrophage inflammatory protein-1β, gamma interferon, tumor necrosis factor alpha, and interleukin-2 responses in CD4(+) T cells of vaccinated macaques prechallenge and 1 week postchallenge showed a significant reduction in the CD107a(-) but not the CD107a(+) subset after virus exposure. Those vaccinees that failed to control viremia showed a more marked reduction and exhibited significantly higher viral loads at week 1 than unvaccinated animals. Our results indicate that vaccine-induced CD107a(-) CD4(+) T cells are depleted following virus infection, suggesting a rationale for avoiding virus-specific CD107a(-) CD4(+) T-cell induction in HIV vaccine design.

IMPORTANCE

Induction of effective antibody and/or CD8(+) T-cell responses is a principal vaccine strategy against human immunodeficiency virus (HIV) infection. CD4(+) T-cell responses are crucial for effective antibody and CD8(+) T-cell induction. However, virus-specific CD4(+) T cells can be preferential targets for HIV infection. Here, we show that vaccine-induced virus-specific CD107a(-) CD4(+) T cells are largely depleted following infection in a macaque AIDS model. While CD4(+) T-cell responses are important in viral control, our results indicate that virus-specific CD107a(-) CD4(+) T-cell induction by vaccination may not lead to efficient CD4(+) T-cell responses following infection but rather be detrimental and accelerate viral replication in the acute phase. This suggests that HIV vaccine design should avoid virus-specific CD107a(-) CD4(+) T-cell induction. Conversely, this study found that vaccine-induced CD107a(+) CD4(+) T cells are relatively resistant to depletion following virus challenge, implying that induction of these cells may be an alternative approach toward HIV control.

Current understanding of HIV-1 and T-cell adaptive immunity: progress to date

The cellular immune response to human immunodeficiency virus (HIV) has different components originating from both the adaptive and innate immune systems. HIV cleverly utilizes the host machinery to survive by its intricate nature of interaction with the host immune system. HIV evades the host immune system at innate ad adaptive, allows the pathogen to replicate and transmit from one host to another. Researchers have shown that HIV has multipronged effects especially on the adaptive immunity, with CD4(+) cells being the worst effect T-cell populations. Various analyses have revealed that, the exposure to HIV results in clonal expansion and excessive activation of the immune system. Also, an abnormal process of differentiation has been observed suggestive of an alteration and blocks in the maturation of various T-cell subsets. Additionally, HIV has shown to accelerate immunosenescence and exhaustion of the overtly activated T-cells. Apart from causing phenotypic changes, HIV has adverse effects on the functional aspect of the immune system, with evidences implicating it in the loss of the capacity of T-cells to secrete various antiviral cytokines and chemokines. However, there continues to be many aspects of the immune- pathogenesis of HIV that are still unknown and thus required further research in order to convert the malaise of HIV into a manageable epidemic.

Limited impact of passive non-neutralizing antibody immunization in acute SIV infection on viremia control in rhesus macaques

Background

Antiviral antibodies, especially those with neutralizing activity against the incoming strain, are potentially important immunological effectors to control human immunodeficiency virus (HIV) infection. While neutralizing activity appears to be central in sterile protection against HIV infection, the entity of inhibitory mechanisms via HIV and simian immunodeficiency virus (SIV)-specific antibodies remains elusive. The recent HIV vaccine trial RV144 and studies in nonhuman primate models have indicated controversial protective efficacy of HIV/SIV-specific non-neutralizing binding antibodies (non-NAbs). While reports on HIV-specific non-NAbs have demonstrated virus inhibitory activity in vitro, whether non-NAbs could also alter the pathogenic course of established SIV replication in vivo, likewise via neutralizing antibody (NAb) administration, has been unclear. Here, we performed post-infection passive immunization of SIV-infected rhesus macaques with polyclonal SIV-specific, antibody-dependent cell-mediated viral inhibition (ADCVI)-competent non-NAbs.

Methods and Findings

Ten lots of polyclonal immunoglobulin G (IgG) were prepared from plasma of ten chronically SIV_mac239-infected, NAb-negative rhesus macaques, respectively. Their binding capacity to whole SIV_mac239 virions showed a propensity similar to ADCVI activity. A cocktail of three non-NAb lots showing high virion-binding capacity and ADCVI activity was administered to rhesus macaques at day 7 post-SIV_mac239 challenge. This resulted in an infection course comparable with control animals, with no significant difference in set point plasma viral loads or immune parameters.

Conclusions

Despite virus-specific suppressive activity of the non-NAbs having been observed in vitro, their passive immunization post-infection did not result in SIV control in vivo. Virion binding and ADCVI activity with lack of virus neutralizing activity were indicated to be insufficient for antibody-triggered non-sterile SIV control. More diverse effector functions or sophisticated localization may be required for non-NAbs to impact HIV/SIV replication in vivo.

Neutralizing polyclonal IgG present during acute infection prevents rapid disease onset in simian-human immunodeficiency virus SHIVSF162P3-infected infant rhesus macaques

Simian-human immunodeficiency virus (SHIV) models for human immunodeficiency virus (HIV) infection have been widely used in passive studies with HIV neutralizing antibodies (NAbs) to test for protection against infection. However, because SHIV-infected adult macaques often rapidly control plasma viremia and any resulting pathogenesis is minor, the model has been unsuitable for studying the impact of antibodies on pathogenesis in infected animals. We found that SHIVSF162P3 infection in 1-month-old rhesus macaques not only results in high persistent plasma viremia but also leads to very rapid disease progression within 12 to 16 weeks. In this model, passive transfer of high doses of neutralizing IgG (SHIVIG) prevents infection. Here, we show that at lower doses, SHIVIG reduces both plasma and peripheral blood mononuclear cell (PBMC)-associated viremia and mitigates pathogenesis in infected animals. Moreover, production of endogenous NAbs correlated with lower set-point viremia and 100% survival of infected animals. New SHIV models are needed to investigate whether passively transferred antibodies or antibodies elicited by vaccination that fall short of providing sterilizing immunity impact disease progression or influence immune responses. The 1-month-old rhesus macaque SHIV model of infection provides a new tool to investigate the effects of antibodies on viral replication and clearance, mechanisms of B cell maintenance, and the induction of adaptive immunity in disease progression.

[Analytic and integrative perspectives for HIV vaccine design]

Prophylactic AIDS vaccines are required to optimally load adaptive immune responses against a virus optimally designed to impair those responses and induce persistent infection. This inevitably may necessitate atypical induction patterns that are distinct from well-balanced responses deriving from the inherent immunological framework. This review discusses how the diverse features of pathologic context-dependent T-cell (CTL/Th) and B-cell (neutralizing antibody) responses may be incorporated into vaccine-induced immunity to achieve HIV control in vivo.

Association of major histocompatibility complex class I haplotypes with disease progression after simian immunodeficiency virus challenge in burmese rhesus macaques

Nonhuman primate AIDS models are essential for the analysis of AIDS pathogenesis and the evaluation of vaccine efficacy. Multiple studies on human immunodeficiency virus and simian immunodeficiency virus (SIV) infection have indicated the association of major histocompatibility complex class I (MHC-I) genotypes with rapid or slow AIDS progression. The accumulation of macaque groups that share not only a single MHC-I allele but also an MHC-I haplotype consisting of multiple polymorphic MHC-I loci would greatly contribute to the progress of AIDS research. Here, we investigated SIVmac239 infections in four groups of Burmese rhesus macaques sharing individual MHC-I haplotypes, referred to as A, E, B, and J. Out of 20 macaques belonging to A(+) (n = 6), E(+) (n = 6), B(+) (n = 4), and J(+) (n = 4) groups, 18 showed persistent viremia. Fifteen of them developed AIDS in 0.5 to 4 years, with the remaining three at 1 or 2 years under observation. A(+) animals, including two controllers, showed slower disease progression, whereas J(+) animals exhibited rapid progression. E(+) and B(+) animals showed intermediate plasma viral loads and survival periods. Gag-specific CD8(+) T-cell responses were efficiently induced in A(+) animals, while Nef-specific CD8(+) T-cell responses were in A(+), E(+), and B(+) animals. Multiple comparisons among these groups revealed significant differences in survival periods, peripheral CD4(+) T-cell decline, and SIV-specific CD4(+) T-cell polyfunctionality in the chronic phase. This study indicates the association of MHC-I haplotypes with AIDS progression and presents an AIDS model facilitating the analysis of virus-host immune interaction.

Immunodeficiency lentiviral infections in natural and non-natural hosts

The host immune system is profoundly affected during the acute phase of progressive immunodeficiency lentiviral infections. Studies of these alterations have been quite restricted in humans because of the limited availability of samples from acutely HIV-infected persons. Therefore, numerous studies have turned attention to nonhuman primate models. Specifically, SIV-infected rhesus macaques (RMs) have been informative for understanding the pathogenesis of HIV infection in humans. Indeed, advantages of the nonhuman primate model include the ability to study the very early events after infection and the ability to retrieve copious amounts of tissues. In addition, nonhuman primates allow for comparative studies between non-natural and natural hosts for SIV, in which SIV infection results in progression, or not, to AIDS, respectively. Although SIV infection of RM is the best model for HIV infection, the immunologic and/or virologic phenomena in SIV-infected RM do not always reflect those seen in HIV-infected humans. Here virologic and immunologic aspects of acute HIV infection of humans and SIV infection of Asian and African nonhuman primates are discussed and compared in relation to how these aspects relate to disease progression.

A DNA vaccine encoding multiple HIV CD4 epitopes elicits vigorous polyfunctional, long-lived CD4+ and CD8+ T cell responses

T-cell based vaccines against HIV have the goal of limiting both transmission and disease progression by inducing broad and functionally relevant T cell responses. Moreover, polyfunctional and long-lived specific memory T cells have been associated to vaccine-induced protection. CD4⁺ T cells are important for the generation and maintenance of functional CD8⁺ cytotoxic T cells. We have recently developed a DNA vaccine encoding 18 conserved multiple HLA-DR-binding HIV-1 CD4 epitopes (HIVBr18), capable of eliciting broad CD4⁺ T cell responses in multiple HLA class II transgenic mice. Here, we evaluated the breadth and functional profile of HIVBr18-induced immune responses in BALB/c mice. Immunized mice displayed high-magnitude, broad CD4⁺/CD8⁺ T cell responses, and 8/18 vaccine-encoded peptides were recognized. In addition, HIVBr18 immunization was able to induce polyfunctional CD4⁺ and CD8⁺ T cells that proliferate and produce any two cytokines (IFNγ/TNFα, IFNγ/IL-2 or TNFα/IL-2) simultaneously in response to HIV-1 peptides. For CD4⁺ T cells exclusively, we also detected cells that proliferate and produce all three tested cytokines simultaneously (IFNγ/TNFα/IL-2). The vaccine also generated long-lived central and effector memory CD4⁺ T cells, a desirable feature for T-cell based vaccines. By virtue of inducing broad, polyfunctional and long-lived T cell responses against conserved CD4⁺ T cell epitopes, combined administration of this vaccine concept may provide sustained help for CD8⁺ T cells and antibody responses- elicited by other HIV immunogens.

Broadening of CD8+ cell responses in vaccine-based simian immunodeficiency virus controllers

OBJECTIVE

In our prior study on a prophylactic T-cell-based vaccine, some vaccinated macaques controlled a simian immunodeficiency virus (SIV) challenge. These animals allowed viremia in the acute phase but showed persistent viral control after the setpoint. Here, we examined the breadth of postchallenge virus-specific cellular immune responses in these SIV controllers.

DESIGN

We previously reported that in a group of Burmese rhesus macaques possessing the MHC haplotype 90-120-Ia, immunization with a Gag-expressing vaccine results in nonsterile control of a challenge with SIVmac239 but not a mutant SIV carrying multiple cytotoxic T lymphocyte (CTL) escape gag mutations. In the present study, we investigated whether broader cellular immune responses effective against the mutant SIV replication are induced after challenge in those vaccinees that maintained wild-type SIVmac239 control.

METHODS

We analyzed cellular immune responses in these SIV controllers (n = 8).

RESULTS

These controllers elicited CTL responses directed against SIV non-Gag antigens as well as Gag in the chronic phase. Postvaccinated, prechallenge CD8(+) cells obtained from these animals suppressed wild-type SIV replication in vitro, but mostly had no suppressive effect on the mutant SIV replication, whereas CD8(+) cells in the chronic phase after challenge showed efficient antimutant SIV efficacy. The levels of in-vitro antimutant SIV efficacy of CD8(+) cells correlated with Vif-specific CD8(+) T-cell frequencies. Plasma viremia was kept undetectable even after the mutant SIV superchallenge in the chronic phase.

CONCLUSION

These results suggest that vaccine-based wild-type SIV controllers can acquire CD8(+) cells with the potential to suppress replication of SIV variants carrying CTL escape mutations.

Neutralizing antibodies in SIV control: co-impact with T cells

Human immunodeficiency virus type 1 (HIV-1) and pathogenic simian immunodeficiency virus (SIV)-infected naïve hosts experience a characteristic absence of early and potent virus-specific neutralizing antibody (NAb) responses preceding establishment of persistent infection. Yet conversely, we have recently shown that NAbs passively immunized in rhesus macaques at early post-SIV challenge are capable of playing a critical role in non-sterile viremia control with implications of antibody-enhanced antigen presentation. In a current follow-up study we have further reported that NAbs mediate rapid elicitation of polyfunctional virus-specific CD4+ T-cells in vivo. The NAb-immunized macaques mounting these responses exhibited sustained viremia control for over 1 year, accompanied with robust anti-SIV cellular immunity. Perspectives obtained from the results are discussed.

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

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

[Theory for prophylactic AIDS vaccine development]

In the natural courses of human immunodeficiency virus (HIV) infections, host immune responses fail to contain the virus and allow persistent HIV replication, leading to AIDS progression. For development of an effective vaccine against those viral infections which do not show spontaneous remission, it is important to elucidate which immune responses to be induced for viral control. This review focuses on antibodies and cytotoxic T lymphocytes, key adaptive immune effectors, and discusses possible mechanisms for HIV control by vaccine-induced antibody, memory B lymphocyte, and (effector and central) memory T lymphocyte responses. Finally, we mention the ongoing international project for a clinical trial of our Sendai virus vector-based AIDS vaccine.

HIV-1 Gag-specific immunity induced by a lentivector-based vaccine directed to dendritic cells

Lentivectors (LVs) have attracted considerable interest for their potential as a vaccine delivery vehicle. In this study, we evaluate in mice a dendritic cell (DC)-directed LV system encoding the Gag protein of human immunodeficiency virus (HIV) (LV-Gag) as a potential vaccine for inducing an anti-HIV immune response. The DC-directed specificity is achieved through pseudotyping the vector with an engineered Sindbis virus glycoprotein capable of selectively binding to the DC-SIGN protein. A single immunization by this vector induces a durable HIV Gag-specific immune response. We investigated the antigen-specific immunity and T-cell memory generated by a prime/boost vaccine regimen delivered by either successive LV-Gag injections or a DNA prime/LV-Gag boost protocol. We found that both prime/boost regimens significantly enhance cellular and humoral immune responses. Importantly, a heterologous DNA prime/LV-Gag boost regimen results in superior Gag-specific T-cell responses as compared with a DNA prime/adenovector boost immunization. It induces not only a higher magnitude response, as measured by Gag-specific tetramer analysis and intracellular IFN-gamma staining, but also a better quality of response evidenced by a wider mix of cytokines produced by the Gag-specific CD8(+) and CD4(+) T cells. A boosting immunization with LV-Gag also generates T cells reactive to a broader range of Gag-derived epitopes. These results demonstrate that this DC-directed LV immunization is a potent modality for eliciting anti-HIV immune responses.