Comparison of human immunodeficiency virus (HIV)-specific infection-enhancing and -inhibiting antibodies in AIDS patients

Research progress in Fc-effector functions against SARS-CoV-2

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has caused more than 676 million cases in the global human population with approximately 7 million deaths and vaccination has been proved as the most effective countermeasure in reducing clinical complications and mortality rate of SARS-CoV-2 infection in people. However, the protective elements and correlation of protection induced by vaccination are still not completely understood. Various antibodies with multiple protective mechanisms can be induced simultaneously by vaccination in vivo, thereby complicating the identification and characterization of individual correlate of protection. Recently, an increasing body of observations suggests that antibody-induced Fc-effector functions play a crucial role in combating SARS-CoV-2 infections, including neutralizing antibodies-escaping variants. Here, we review the recent progress in understanding the impact of Fc-effector functions in broadly disarming SARS-CoV-2 infectivity and discuss various efforts in harnessing this conserved antibody function to develop an effective SARS-CoV-2 vaccine that can protect humans against infections by SARS-CoV-2 virus and its variants of concern.

Harnessing Antibody-Dependent Cellular Cytotoxicity To Control HIV-1 Infection

Passive administration of broadly neutralizing anti-human immunodeficiency virus type 1 (HIV-1) antibodies (bNAbs) has been recently suggested as a promising alternative therapeutic approach for HIV-1 infection. Although the success behind the studies that used this approach has been attributed to the potency and neutralization breadth of anti-HIV-1 antibodies, several lines of evidence support the idea that specific antibody-dependent effector functions, particularly antibody-dependent cellular cytotoxicity (ADCC), play a critical role in controlling HIV-1 infection. In this review, we showed that there is a direct association between the activation of ADCC and better clinical outcomes. This, in turn, suggests that ADCC could be harnessed to control HIV-1 infection. To this end, we addressed the passive administration of bNAbs capable of selectively activating ADCC responses to HIV-1 patients. Finally, we summarized the potential barriers that may impede the optimal activation of ADCC during HIV-1 infection and provided strategic solutions to overcome these barriers.

HIV/AIDS vaccines for Africa: scientific opportunities, challenges and strategies

More than decades have already elapsed since human immunodeficiency virus (HIV) was identified as the causative agent of acquired immunodeficiency syndrome (AIDS). The HIV has since spread to all parts of the world with devastating effects. In sub-saharan Africa, the HIV/AIDS epidemic has reached unprecedented proportions. Safe, effective and affordable HIV/AIDS vaccines for Africans are therefore urgently needed to contain this public health problem. Although, there are challenges, there are also scientific opportunities and strategies that can be exploited in the development of HIV/AIDS vaccines for Africa. The recent RV144 Phase III trial in Thailand has demonstrated that it is possible to develop a vaccine that can potentially elicit modest protective immunity against HIV infection. The main objective of this review is to outline the key scientific opportunities, challenges and strategies in HIV/AIDS vaccine development in Africa.

Mycobacterium tuberculosis infection interferes with HIV vaccination in mice

Tuberculosis (TB) has emerged as the most prominent bacterial disease found in human immunodeficiency virus (HIV)-positive individuals worldwide. Due to high prevalence of asymptomatic Mycobacterium tuberculosis (Mtb) infections, the future HIV vaccine in areas highly endemic for TB will often be administrated to individuals with an ongoing Mtb infection. The impact of concurrent Mtb infection on the immunogenicity of a HIV vaccine candidate, MultiHIV DNA/protein, was investigated in mice. We found that, depending on the vaccination route, mice infected with Mtb before the administration of the HIV vaccine showed impairment in both the magnitude and the quality of antibody and T cell responses to the vaccine components p24Gag and gp160Env. Mice infected with Mtb prior to intranasal HIV vaccination exhibited reduced p24Gag-specific serum IgG and IgA, and suppressed gp160Env-specific serum IgG as compared to respective titers in uninfected HIV-vaccinated controls. Importantly, in Mtb-infected mice that were HIV-vaccinated by the intramuscular route the virus neutralizing activity in serum was significantly decreased, relative to uninfected counterparts. In addition mice concurrently infected with Mtb had fewer p24Gag-specific IFN-γ-expressing T cells and multifunctional T cells in their spleens. These results suggest that Mtb infection might interfere with the outcome of prospective HIV vaccination in humans.

Deployment of the human immunodeficiency virus type 1 protein arsenal: combating the host to enhance viral transcription and providing targets for therapeutic development

Despite the success of highly active antiretroviral therapy in combating human immunodeficiency virus type 1 (HIV-1) infection, the virus still persists in viral reservoirs, often in a state of transcriptional silence. This review focuses on the HIV-1 protein and regulatory machinery and how expanding knowledge of the function of individual HIV-1-coded proteins has provided valuable insights into understanding HIV transcriptional regulation in selected susceptible cell types. Historically, Tat has been the most studied primary transactivator protein, but emerging knowledge of HIV-1 transcriptional regulation in cells of the monocyte-macrophage lineage has more recently established that a number of the HIV-1 accessory proteins like Vpr may directly or indirectly regulate the transcriptional process. The viral proteins Nef and matrix play important roles in modulating the cellular activation pathways to facilitate viral replication. These observations highlight the cross talk between the HIV-1 transcriptional machinery and cellular activation pathways. The review also discusses the proposed transcriptional regulation mechanisms that intersect with the pathways regulated by microRNAs and how development of the knowledge of chromatin biology has enhanced our understanding of key protein-protein and protein-DNA interactions that form the HIV-1 transcriptome. Finally, we discuss the potential pharmacological approaches to target viral persistence and enhance effective transcription to purge the virus in cellular reservoirs, especially within the central nervous system, and the novel therapeutics that are currently in various stages of development to achieve a much superior prognosis for the HIV-1-infected population.

Association of HIV neutralizing antibody with lower viral load after treatment interruption in a prospective trial (A5170)

OBJECTIVE

We investigated the impact of neutralizing antibodies (NAbs) on CD4 T-cell count and viral load in a cohort of HAART recipients who underwent extended structured treatment interruption.

DESIGN

Substudy of NAb in the AIDS Clinical Trials Group 5170 trial.

METHODS

Early plasma samples from 50 volunteers who discontinued HAART were evaluated in a peripheral blood mononuclear cell-based neutralization assay against a panel of four subtype B primary isolates.

RESULTS

We found that high-titer (90% inhibitory dose > 500) NAb against two or more isolates was associated with reduced viral load (P = 0.003 at 12-week posttreatment interruption). This effect faded with time, losing significance (P = 0.161) by study conclusion. Participants possessing the highest NAb levels against individual isolates appeared more likely to have lower viral loads with the association gaining significance against the R5-tropic primary isolate US1 (P = 0.005). There was no association between broader neutralization and CD4 T-cell slope over time.

CONCLUSION

The data suggest that high-titer NAb responses at the time of treatment interruption are associated with reduced viral load over time, but not CD4(+) T-cell decline.

Dengue virus pathogenesis: an integrated view

Much remains to be learned about the pathogenesis of the different manifestations of dengue virus (DENV) infections in humans. They may range from subclinical infection to dengue fever, dengue hemorrhagic fever (DHF), and eventually dengue shock syndrome (DSS). As both cell tropism and tissue tropism of DENV are considered major determinants in the pathogenesis of dengue, there is a critical need for adequate tropism assays, animal models, and human autopsy data. More than 50 years of research on dengue has resulted in a host of literature, which strongly suggests that the pathogenesis of DHF and DSS involves viral virulence factors and detrimental host responses, collectively resulting in abnormal hemostasis and increased vascular permeability. Differential targeting of specific vascular beds is likely to trigger the localized vascular hyperpermeability underlying DSS. A personalized approach to the study of pathogenesis will elucidate the basis of individual risk for development of DHF and DSS as well as identify the genetic and environmental bases for differences in risk for development of severe disease.

Exploring peptide mimics for the production of antibodies against discontinuous protein epitopes

Peptide "mimics" (mimotopes) of linear protein epitopes and carbohydrate epitopes have been successfully used as immunogens to elicit cross-reactive antibodies against their cognate epitopes; however, immunogenic mimicry has been difficult to achieve for discontinuous protein epitopes. To explore this, we developed from phage-displayed peptide libraries optimized peptide mimics for three well-characterized discontinuous epitopes on hen egg lysozyme and horse cytochrome c. The peptides competed with their cognate antigens for antibody binding, displayed affinities in the nM range, and shared critical binding residues with their native epitopes. Yet, while immunogenic, none of the peptides elicited antibodies that cross-reacted with their cognate antigens. We analyzed the 3-D structure of the site within each discontinuous epitope that shared critical binding residues with its peptide mimic, and observed that in each case it formed a ridge-like patch on the epitope; in no case did it cover most or all of the epitope. Thus, the peptides' lack of immunogenic mimicry could be attributed to their inability to recapitulate the topological features of their cognate epitopes. Our results suggest that direct peptide immunizations are not a practical strategy for generating targeted antibody responses against discontinuous epitopes.

A novel approach to inhibit HIV-1 infection and enhance lysis of HIV by a targeted activator of complement

Background

The complement system is one of the most potent weapons of innate immunity. It is not only a mechanism for direct protection against invading pathogens but it also interacts with the adaptive immunity to optimize the pathogen-specific humoral and cellular defense cascades in the body. Complement-mediated lysis of HIV is inefficient but the presence of HIV particles results in complement activation by the generation of many C3-fragments, such as C3dg and C3d. It has been demonstrated that activation of complement can enhance HIV infection through the binding of special complement receptor type 2 expression on the surface of mature B cells and follicular dendritic cells.

Presentation of the hypothesis

Previous studies have proven that the complement-mediated antibody-dependent enhancement of HIV infection is mediated by the association of complement receptor type 2 bound to the C3 fragment and deposited on the surface of HIV virions. Thus, we hypothesize that a new activator of complement, consisting of a target domain (C3-binding region of complement receptor type 2) linked to a complement-activating human IgG1 Fc domain (CR2-Fc), can target and amplify complement deposition on HIV virions and enhance the efficiency of HIV lysis.

Testing the hypothesis

Our hypothesis was tested using cell-free HIV-1 virions cultivated in vitro and assessment of virus opsonization was performed by incubating appropriate dilutions of virus with medium containing normal human serum and purified CR2-Fc proteins. As a control group, viruses were incubated with normal human serum under the same conditions. Virus neutralization assays were used to estimate the degree of CR2-Fc-enhanced lysis of HIV compared to untreated virus.

Implications of the hypothesis

The targeted complement activator, CR2-Fc, can be used as a novel approach to HIV therapy by abrogating the complement-enhanced HIV infection of cells.

Humoral immunity to HIV-1: neutralisation and antibody effector functions

Several features of HIV have frustrated efforts to develop a vaccine able to induce broadly neutralising antibodies. The enormous genetic diversity of HIV is a major factor, accompanied by the camouflaged nature of the envelope spike, upon which HIV depends for cellular entry and to which antibodies must bind to neutralise. The picture is further complicated by the presence of nonfunctional envelope glycoproteins on the surface of HIV that are immunogenic. Consequently, HIV attracts antibodies that do not directly neutralise the virus but still activate complement and engage Fc receptors, which can both enhance and inhibit infection. The various effects that anti-envelope antibodies have on HIV infection will be reviewed here. Further research is needed to determine if these in vitro-characterised activities have relevance in vivo, and if some of the undesirable effects of non-neutralising antibodies can be avoided or the beneficial effects harnessed.

Traitors of the immune system-enhancing antibodies in HIV infection: their possible implication in HIV vaccine development

Considering recent HIV vaccine failures, the authors believe that it would be most important to find new targets for vaccine-induced immunity, and to analyze the data from previous trials, using an innovative approach. In their review article, the authors briefly summarize the significance of the antibody-dependent enhancement of infection in different viral diseases and discuss role of these types of antibodies as the obstacles for vaccine development. Findings which indicate that complement-mediated antibody-dependent enhancement (C-ADE) is present also in HIV-infected patients, are summarized. Previous results of the authors, suggesting that C-ADE plays a very important role in the progression of HIV infection are described. Data reflecting that enhancing antibodies may develop even in vaccinated animals and human volunteers, and may be responsible for the paradoxical results obtained in some subgroups of vaccinees are discussed. Finally, based on their hypothesis, the authors offer some suggestions for the future development of vaccines.

Humoral immunity to HIV-1: neutralization and beyond

Humoral immunity is considered a key component of effective vaccines against HIV-1. Hence, an enormous effort has been put into investigating the neutralizing antibody response to HIV-1 over the past 20 years which generated key information on epitope specificity, potency, breadth and in vivo activity of the neutralizing antibodies. Less clear is still the role of antibody-mediated effector functions (antibody-dependent cellular cytotoxicity, phagocytosis, complement system) and uncertainty prevails whether Fc-mediated mechanisms are largely beneficial or detrimental for the host. The current knowledge on the manifold functions of the humoral immune response in HIV infection, their underlying mechanisms and potential in vaccine-induced immunity will be discussed in this review.

Mechanism for complement-mediated, antibody-dependent enhancement of human immunodeficiency virus type 1 infection in MT2 cells is enhanced entry through CD4, CD21, and CXCR4 chemokine receptors

Some antibodies neutralize Human Immunodeficiency Virus (HIV). However, antibody to HIV and complement can enhance HIV replication if cells express both complement receptors and CD4, a phenomenon described as complement-mediated, antibody-dependent enhancement (C'ADE). Although increased binding of opsonized virions has been reported, the mechanism by which C'ADE enhances HIV replication remains unproven. In this study, real-time polymerase chain reaction to detect HIV cDNA indicates that complement and anti-HIV antibodies enhance HIV entry 8- to 30- fold with similar increases in integrated provirus. Thus, complement increases HIV replication through a mechanism of enhanced entry. To further refine the mechanism of C'ADE, chemokine receptor antagonists were employed. JM2987, a CXCR4 chemokine receptor antagonist, blocked HIV infection and C'ADE; thus CD4, complement receptors, and CXCR4 chemokine receptors are required for enhanced entry of HIV into MT2 cells. Finally, anti-HIV immunoglobulin enhanced replication of not only group M clade B HIV but also group M clade D and group O isolates. These data demonstrate that antibodies mediating C'ADE of HIV infection are broadly reactive.

High specificity of V3 serotyping among human immunodeficiency virus type-1 subtype C infected patients with varying disease status and viral phenotype

V3 serotyping is a technique for determining HIV-1 genetic subtype based on the binding of antibodies from patient sera or plasma to synthetic V3 peptides derived from subtype consensus sequences. Variation in the performance of this assay has been attributed to V3 sequence heterogeneity, the degree of which varies with patient disease progression, virus co-receptor usage, and genetic subtype. This study assessed the performance of a competitive peptide enzyme immunoassay (cPEIA) in samples from HIV-1 subtype C infected patients with varying disease profiles, including those with syncytium (SI) and non-syncytium-inducing (NSI) viruses. Out of 90 sera tested, 94.4% reacted strongly against the subtype C peptide. There was no significant difference in assay sensitivity among samples from advanced AIDS patients in which humoral immune response may be lower, nor among SI viruses which carry changes in the V3 sequence. Four samples were found to be cross-reactive with other subtypes and one acutely infected patient sample was non-reactive due to low anti-gp120 antibody titers. A significantly higher number of samples showed secondary reactivity to subtype A, compared to other subtypes (P < 0.005). In conclusion, the assay was able to identify HIV-1 subtype C infection with a high level of sensitivity (94%) irrespective of the stage of disease and therefore provides a valuable resource for the large-scale epidemiological monitoring of the spread of HIV-1 subtypes in South Africa.

Immunoglobulin levels amongst persons with and without human immunodeficiency virus type 1 infection in Uganda and Norway

CD4+-cell count and viral load monitoring are expensive and unavailable to most human immunodeficiency virus (HIV)-infected people in Africa. In an attempt to evaluate alternative methods for monitoring antiretroviral (ARV) therapy, we measured concentrations of immunoglobulin (Ig)A, IgM, IgG and IgG1 amongst adults with and without HIV in Uganda and Norway. We adjusted for disease severity by stratifying HIV-positive subjects on CD4+-cell counts above and below 200 cells/ micro l. Median serum levels of IgG, IgG1 and IgA were significantly higher in HIV-positive persons compared with HIV-negative persons in both countries (P < 0.001 and P = 0.018 for IgA in Ugandan patients). Levels of IgA in Ugandan HIV-negative subjects were significantly lower than those in HIV-positive subjects with low CD4+ compared with those with high CD4+-cell counts (P < 0.001 and P = 0.069, respectively). IgM levels were different between the HIV-negative and the two HIV-positive groups in Norway (P < 0.001). The mean levels of IgM, IgG and IgG1 in HIV-negative and -positive African subjects were generally higher than those in comparable groups of Western subjects. Our results verify that levels of IgA, IgG and IgG1 vary between HIV-negative and -positive individuals in both study populations. Their determination may be useful in monitoring both disease progression and response to ARV therapy.

Significant decrease of the enhancement/neutralization index in HIV patients during highly active antiretroviral therapy (HAART)

Authors studied the effect of highly active antiretroviral therapy (HAART) on balance of the antibodies that enhance or neutralize growth of HIV-1(IIIB) strain in MT-4 cells in the presence or absence of human complement. Sequential serum samples were collected from 28 patients in advanced stage of HIV disease before and during HAART. The balance of the enhancing and neutralizing antibodies was expressed by an index value (E/N I). Samples with an E/N I of <0.5 (twofold decrease in virus production) were considered as neutralizing, whereas samples with an E/N I>2.0 (twofold increase in virus production) were considered as enhancing. At the beginning of HAART serum samples from eight patients enhanced, and samples from only two patients neutralized the virus in the presence of complement, median (25th-75th percentile) value of E/N I was 1.32 (0.79-2.29). E/N I significantly (P<0.0001) dropped to 0.37 (0.19-0.57) during the follow-up period of 18.5 (10.5-23.5) months under HAART. Similar changes were detected when serum samples were tested with no complement added. The E/N I values were also markedly decreased when cultures inoculated with mixtures of HIV and purified IgG prepared from serum pools taken before and during HAART, respectively, were compared. In the last samples of 20/28 patients, neutralization was measured even in the presence of complement while enhancement was found with none of these samples. These findings suggest that HAART results in disappearance of enhancing antibodies and switches the E/N I toward neutralization.