Antibody-secreting B cells in HIV infection

Systems Biological Analysis of Immune Response to Influenza Vaccination

The last decade has witnessed tremendous progress in immunology and vaccinology, owing to several scientific and technological breakthroughs. Systems vaccinology is a field that has emerged at the forefront of vaccine research and development and provides a unique way to probe immune responses to vaccination in humans. The goals of systems vaccinology are to use systems-based approaches to define signatures that can be used to predict vaccine immunogenicity and efficacy and to delineate the molecular mechanisms driving protective immunity. The application of systems biological approaches in influenza vaccination studies has enabled the discovery of early signatures that predict immunogenicity to vaccination and yielded novel mechanistic insights about vaccine-induced immunity. Here we review the contributions of systems vaccinology to influenza vaccine development and critically examine the potential of systems vaccinology toward enabling the development of a universal influenza vaccine that provides robust and durable immunity against diverse influenza viruses.

Development of Antibodies with Broad Neutralization Specificities against HIV-1 after Long Term SHIV Infection in Macaques

Non-human primates (NHP) are the only animal model suitable to evaluate the protection efficacy of HIV-1 vaccines. It is important to understand how and when neutralizing antibodies (nAbs) with specificities similar to those of human broadly neutralizing antibodies (bnAbs) develop in NHPs. To address these questions, we determined plasma neutralization specificities in two macaques which developed neutralization breadth after long-term simian/human immunodeficiency virus (SHIV) infection and identified neutralization escape mutations by analyzing the env sequences from longitudinal plasma samples. Neutralization activities targeting V2, CD4bs, V3 and gp120-gp41 interface only became detectable in week 350 plasma from macaques G1015R and G1020R using 25710 env mutants. When mapped with CAP45 env mutants, only V2 specificity was detected at week 217 and persisted until week 350 in G1015R. Neutralization escape mutations were found in CD4bs and V2 regions. However, all of them were different from those resistant mutations identified for human bnAbs. These results show that nAbs with specificities similar to human bnAbs are only detectable after long-term SHIV infection and that neutralization escape mutations in macaques are different from those found in HIV-1-infected individuals. These findings can have important implications in the best utilization of the NHP model to evaluate HIV-1 vaccines.

Chronic virus infection compromises memory bystander T cell function in an IL-6/STAT1-dependent manner

Chronic viral infections are widespread among humans, with ∼8-12 chronic viral infections per individual, and there is epidemiological proof that these impair heterologous immunity. We studied the impact of chronic LCMV infection on the phenotype and function of memory bystander CD8⁺ T cells. Active chronic LCMV infection had a profound effect on total numbers, phenotype, and function of memory bystander T cells in mice. The phenotypic changes included up-regulation of markers commonly associated with effector and exhausted cells and were induced by IL-6 in a STAT1-dependent manner in the context of chronic virus infection. Furthermore, bystander CD8 T cell functions were reduced with respect to their ability to produce inflammatory cytokines and to undergo secondary expansion upon cognate antigen challenge with major cell-extrinsic contributions responsible for the diminished memory potential of bystander CD8⁺ T cells. These findings open new perspectives for immunity and vaccination during chronic viral infections.

Development of broad neutralization activity in simian/human immunodeficiency virus-infected rhesus macaques after long-term infection

OBJECTIVE

Nonhuman primates (NHPs) are the only animal model that can be used to evaluate protection efficacy of HIV-1 envelope vaccines. However, whether broadly neutralizing antibodies (bnAbs) can be elicited in NHPs infected with simian/human immunodeficiency virus (SHIV) has not been fully understood. The objective of this study is to investigate whether broad neutralization activities were developed in SHIV-infected macaques after long-term infection as in humans.

DESIGN

Neutralization breadth and specificities in plasmas from SHIV-infected macaques were determined by analyzing a panel of tier 2 viruses and their mutants.

METHODS

Forty-four Chinese macaques infected with SHIV1157ipd3N4, SHIVSF162P3 or SHIVCHN19P4 were followed for 54-321 weeks. Archived plasmas from 19 macaques were used to determine neutralization breadth and specificities against 17 tier 2 envelope-pseudoviruses.

RESULTS

Longitudinal plasma from three SHIVSF162P3-infected macaques and three SHIV1157ipd3N4-infected macaques rarely neutralized viruses (<25%) within 1 year of infection. The neutralization breadth in two SHIV1157ipd3N4-infected macaques significantly increased (≥65%) by year 6. Four of six SHIV1157ipd3N4-infected macaques could neutralize 50-75% viruses, whereas none of macaques infected with SHIVSF162P3 or SHIVCHN19P4 could neutralize more than 25% of viruses after 6 years of infection (P = 0.035). Neutralization specificity analysis showed mutations resistant to bnAbs in V2, V3 or CD4bs regions could abrogate neutralization by year-6 plasma from three SHIV1157ipd3N4-infected macaques.

CONCLUSION

These results demonstrate that bnAbs targeting common HIV-1 epitopes can be elicited in SHIV1157ipd3N4-infected macaques as in humans after 4-6 years of infection, and SHIV/NHP can serve as an ideal model to study bnAb maturation.

Broadly neutralizing antibody specificities detected in the genital tract of HIV-1 infected women

BACKGROUND

Broadly neutralizing antibodies (bNAbs) targeting conserved epitopes on the HIV envelope glycoprotein have been identified in blood from HIV-1 infected women. We investigated whether antibodies in the genital tract from these women share similar epitope specificities and functional profiles as those in blood.

METHODS

Immunoglobulin (Ig)G and IgA antibodies were isolated from cervicovaginal lavages or Softcups from 13 HIV-infected women in the CAPRISA cohort using Protein G and Peptide M, respectively. Binding antibodies to envelope antigens were quantified by ELISA and binding antibody multiplex assay. Neutralizing antibody titers and epitope targets were measured using the TZM-bl assay with Env-pseudotyped wild-type and mutated viruses.

RESULTS

HIV-specific IgG, but not IgA, was detected in genital secretions and the ratio of total IgG to HIV-specific IgG was similar to plasma. HIV-specific IgG reacted with multiple envelope antigens, including V1V2, gp120, gp140 and gp41. Two women had high plasma titers of HIV-specific IgG3 which was also detected in their genital tract samples. IgG from the genital tract had neutralizing activity against both Tier 1 and Tier 2 primary HIV-isolates. Antibodies targeting well known glycan epitopes and the membrane proximal region of gp41 were detected in genital secretions, and matched specificities in plasma.

CONCLUSIONS

Women with plasma bNAbs have overlapping specificities in their genital secretions, indicating that these predominantly IgG isotype antibodies may transudate from blood to the genital tract. These data provide evidence that induction of systemic HIV-specific bNAbs can lead to antiviral immunity at the portal of entry.

Bactericidal Immunity to Salmonella in Africans and Mechanisms Causing Its Failure in HIV Infection

Background

Nontyphoidal strains of Salmonella are a leading cause of death among HIV-infected Africans. Antibody-induced complement-mediated killing protects healthy Africans against Salmonella, but increased levels of anti-lipopolysaccharide (LPS) antibodies in some HIV-infected African adults block this killing. The objective was to understand how these high levels of anti-LPS antibodies interfere with the killing of Salmonella.

Methodology/Principal Findings

Sera and affinity-purified antibodies from African HIV-infected adults that failed to kill invasive S. Typhimurium D23580 were compared to sera from HIV-uninfected and HIV-infected subjects with bactericidal activity. The failure of sera from certain HIV-infected subjects to kill Salmonella was found to be due to an inherent inhibitory effect of anti-LPS antibodies. This inhibition was concentration-dependent and strongly associated with IgA and IgG2 anti-LPS antibodies (p<0.0001 for both). IgG anti-LPS antibodies, from sera of HIV-infected individuals that inhibit killing at high concentration, induced killing when diluted. Conversely, IgG, from sera of HIV-uninfected adults that induce killing, inhibited killing when concentrated. IgM anti-LPS antibodies from all subjects also induced Salmonella killing. Finally, the inhibitory effect of high concentrations of anti-LPS antibodies is seen with IgM as well as IgG and IgA. No correlation was found between affinity or avidity, or complement deposition or consumption, and inhibition of killing.

Conclusion/Significance

IgG and IgM classes of anti-S. Typhimurium LPS antibodies from HIV-infected and HIV-uninfected individuals are bactericidal, while at very high concentrations, anti-LPS antibodies of all classes inhibit in vitro killing of Salmonella. This could be due to a variety of mechanisms relating to the poor ability of IgA and IgG2 to activate complement, and deposition of complement at sites where it cannot insert in the bacterial membrane. Vaccine trials are required to understand the significance of lack of in vitro killing by anti-LPS antibodies from a minority of HIV-infected individuals with impaired immune homeostasis.

Bacteremia caused by nontyphoidal Salmonellae are a major health burden in Africa. While antibody-induced complement-mediated killing protects healthy Africans against Salmonella, increased levels of anti-LPS antibodies in some HIV-infected Africans block this killing. Little is known about the mechanism of the interference of killing by these antibodies. Here, we compared sera and affinity-purified antibodies from African HIV-infected adults that are unable to kill invasive S. Typhimurium D23580, with sera from HIV-uninfected and HIV-infected subjects with bactericidal activity. We found that the blocking effect of anti-LPS antibodies is a factor of antibody concentration, rather than antibody structure or specificity. While all three isotypes (IgG, IgA and IgM) can inhibit killing of Salmonella at grossly high concentrations, the IgG and IgM isotypes of the anti-LPS antibodies have in vitro bactericidal activity against invasive African S. Typhimurium. Inhibition of killing did not associate with antibody affinity or avidity, or complement deposition or consumption. It is possible that a LPS-based vaccine would induce antibodies at bactericidal rather than inhibitory concentrations in HIV-uninfected individuals. In HIV-infected individuals, it is uncertain whether vaccination will induce a protective response or a dysregulated excess of anti-LPS antibodies that impairs serum killing of Salmonella.

Reverse vaccinology 2.0: Human immunology instructs vaccine antigen design

Traditionally, vaccines have been developed by cultivating infectious agents and isolating the inactivated whole pathogen or some of its purified components. 20 years ago, reverse vaccinology enabled vaccine discovery and design based on information deriving from the sequence of microbial genomes rather than via the growth of pathogens. Today, the high throughput discovery of protective human antibodies, sequencing of the B cell repertoire, and the increasing structural characterization of protective antigens and epitopes provide the molecular and mechanistic understanding to drive the discovery of novel vaccines that were previously impossible. We are entering a "reverse vaccinology 2.0" era.

Oligoclonal Bands of Immunoglobulins in Serum Leading to Diagnosis of Human Immunodeficiency Virus 1 Infection

OBJECTIVES

To present a unique case where detection of oligoclonal bands in serum led to the diagnosis of human immunodeficiency virus (HIV) infection.

METHODS

A 64-year-old man treated for hypertension for 11 years had laboratory tests ordered by his primary care physician, including serum protein electrophoresis (SPE) and serum immunofixation electrophoresis.

RESULTS

The total protein serum protein concentration was elevated at 9.6 g/dL. The SPE showed an oligoclonal pattern of multiple discrete bands in the γ region; the concentration of one band was approximately 1 g/dL and that of two bands was approximately 0.5 g/dL each, with multiple smaller overlapping bands at approximately 0.1 g/dL each. All fractions by SPE were within reference intervals except for the γ fraction, which was elevated at 3.4 g/dL. The IFE demonstrated that this oligoclonal pattern was a mixture of multiple bands of immunoglobulin G (IgG)-λ and IgG-κ. The patient's HIV-1 antibody screen and HIV-1 Western blot were positive on three subsequent visits with strongly positive HIV-1 antibody index values of more than 50 (cutoff value of 1.0 for reactivity).

CONCLUSIONS

The etiology of HIV-associated clonal immunoglobulin bands is hypothesized to result from chronic antigenic stimulation leading to B-cell hyperplasia. In this regard, hypergammaglobulinemia is a well-known consequence of HIV infection due to B-cell activation, associated with paraproteins, and can be seen at any stage of the disease.

Evolution of the Humoral Response during HCV Infection: Theories on the Origin of Broadly Neutralizing Antibodies and Implications for Vaccine Design

Similar to human immunodeficiency virus (HIV)-1, vaccine-induced elicitation of broadly neutralizing (bNt) antibodies (Abs) is gaining traction as a key goal toward the eradication of the hepatitis C virus (HCV) pandemic. Previously, the significance of the Ab response against HCV was underappreciated given the prevailing evidence advancing the role of the cellular immune response in clearance and overall control of the infection. However, recent findings have driven growing interest in the humoral arm of the immune response and in particular the role of bNt responses due to their ability to confer protective immunity upon passive transfer in animal models. Nevertheless, the origin and development of bNt Abs is poorly understood and their occurrence is rare as well as delayed with emergence only observed in the chronic phase of infection. In this review, we characterize the interplay between the host immune response and HCV as it progresses from the acute to chronic phase of infection. In addition, we place these events in the context of current hypotheses on the origin of bNt Abs against the HIV-1, whose humoral immune response is better characterized. Based on the increasing significance of the humoral immune response against HCV, characterization of these events may be critical in understanding the development of the bNt responses and, thus, provide strategies toward effective vaccine design.

Compartmentalized intrathecal immunoglobulin synthesis during HIV infection - a model of chronic CNS inflammation?

HIV infects the central nervous system (CNS) during primary infection and persists in resident macrophages. CNS infection initiates a strong local immune response that fails to control the virus but is responsible for by-stander lesions involved in neurocognitive disorders. Although highly active anti-retroviral therapy now offers an almost complete control of CNS viral proliferation, low-grade CNS inflammation persists. This review focuses on HIV-induced intrathecal immunoglobulin (Ig) synthesis. Intrathecal Ig synthesis early occurs in more than three-quarters of patients in response to viral infection of the CNS and persists throughout the course of the disease. Viral antigens are targeted but this specific response accounts for <5% of the whole intrathecal synthesis. Although the nature and mechanisms leading to non-specific synthesis are unknown, this prominent proportion is comparable to that observed in various CNS viral infections. Cerebrospinal fluid-floating antibody-secreting cells account for a minority of the whole synthesis, which mainly takes place in perivascular inflammatory infiltrates of the CNS parenchyma. B-cell traffic and lineage across the blood-brain-barrier have not yet been described. We review common technical pitfalls and update the pending questions in the field. Moreover, since HIV infection is associated with an intrathecal chronic oligoclonal (and mostly non-specific) Ig synthesis and associates with low-grade axonal lesions, this could be an interesting model of the chronic intrathecal synthesis occurring during multiple sclerosis.

Independent evolution of Fc- and Fab-mediated HIV-1-specific antiviral antibody activity following acute infection

Fc-related antibody activities, such as antibody-dependent cellular cytotoxicity (ADCC), or more broadly, antibody-mediated cellular viral inhibition (ADCVI), play a role in curbing early SIV viral replication, are enriched in human long-term infected nonprogressors, and could potentially contribute to protection from infection. However, little is known about the mechanism by which such humoral immune responses are naturally induced following infection. Here, we focused on the early evolution of the functional antibody response, largely driven by the Fc portion of the antibody, in the context of the evolving binding and neutralizing antibody response, which is driven mainly by the antibody-binding fragment (Fab). We show that ADCVI/ADCC-inducing responses in humans are rapidly generated following acute HIV-1 infection, peak at approximately 6 months postinfection, but decay rapidly in the setting of persistent immune activation, as Fab-related activities persistently increase. Moreover, the loss of Fc activity occurred in synchrony with a loss of HIV-specific IgG3 responses. Our data strongly suggest that Fc- and Fab-related antibody functions are modulated in a distinct manner following acute HIV infection. Vaccination strategies intended to optimally induce both sets of antiviral antibody activities may, therefore, require a fine tuning of the inflammatory response.

How can HIV-type-1-Env immunogenicity be improved to facilitate antibody-based vaccine development?

No vaccine candidate has induced antibodies (Abs) that efficiently neutralize multiple primary isolates of HIV-1. Preexisting high titers of neutralizing antibodies (NAbs) are essential, because the virus establishes infection before anamnestic responses could take effect. HIV-1 infection elicits Abs against Env, Gag, and other viral proteins, but of these only a subset of the anti-Env Abs can neutralize the virus. Whereas the corresponding proteins from other viruses form the basis of successful vaccines, multiple large doses of HIV-1 Env elicit low, transient titers of Abs that are not protective in humans. The inaccessibility of neutralization epitopes hinders NAb induction, but Env may also subvert the immune response by interacting with receptors on T cells, B cells, monocytes, macrophages, and dendritic cells. Here, we discuss evidence from immunizations of different species with various modified Env constructs. We also suggest how the divergent Ab responses to Gag and Env during infection may reflect differences in B cell regulation. Drawing on these analyses, we outline strategies for improving Env as a component of a vaccine aimed at inducing strong and sustained NAb responses.

Aging and HIV infection

INTRODUCTION

Population aging has become a global phenomenon, and HIV infection among older individuals is also increasing. Because age can affect the progression of HIV infection, we aimed to evaluate the present knowledge on HIV infection in older patients.

METHODS

Literature review of the last 20 years.

RESULTS

Older HIV-infected patients have lower CD4(+) T cell counts, higher viral load and are more frequently symptomatic at diagnosis. The infection progresses more rapidly, with higher morbidity and lethality rates. However, older patients are more compliant to antiretroviral treatment; they experience a better virologic response, and treatment represents a positive clinical impact. Aging affects the complex interaction between HIV infection and the immune system. Both conditions contribute to the dysfunction of immune cells, including a decrease in the phagocytes' microbicidal capability, natural killer cells' cytolytic function, expression of toll-like receptors and production of interleukin-12. Chronic immune activation responsible for the depletion of CD4(+) and CD8(+) T cells in HIV infection appears to worsen with senescence. Older patients also exhibit a less robust humoral response, with the production of less avid and specific antibodies.

CONCLUSION

Both HIV and aging contribute to immune dysfunction, morbidity and mortality. However, highly active antiretroviral therapy (HAART) is beneficial for older patients, and treatment of older patients should not be discouraged.