An autoreactive antibody from an SLE/HIV-1 individual broadly neutralizes HIV-1

Natural Variation in HIV-1 Entry Kinetics Map to Specific Residues and Reveal an Interdependence Between Attachment and Fusion

HIV-1 entry kinetics reflect the fluid motion of the HIV envelope glycoprotein through at least three major structural configurations that drive virus-cell membrane fusion. The lifetime of each state is an important component of potency for inhibitors that target them. We used the time-of-addition inhibitor assay and a novel analytical strategy to define the kinetics of pre-hairpin exposure (using T20) and co-receptor engagement (via. maraviroc), through a characteristic delay metric, across a variety of naturally occurring HIV Env isolates. Among 257 distinct HIV-1 envelope isolates we found a remarkable breadth of T20 and maraviroc delays ranging from as early as 30 seconds to as late as 60 minutes. The most extreme delays were observed among transmission-linked clade C isolates. We identified four single-residue determinants of late T20 and maraviroc delays that are associated with either receptor engagement or gp41 function. Comparison of these delays with T20 sensitivity suggest co-receptor engagement and fusogenic activity in gp41 act cooperatively but sequentially to drive entry. Our findings support current models of entry where co-receptor engagement drives gp41 eclipse and have strong implications for the design of entry inhibitors and antibodies that target transient entry states.

Author Summary

The first step of HIV-1 infection is entry, where virus-cell membrane fusion is driven by the HIV-1 envelope glycoprotein through a series of conformational changes. Some of the most broadly active entry inhibitors work by binding conformations that exist only transiently during entry. The lifetimes of these states and the kinetics of entry are important elements of inhibitor activity for which little is known. We demonstrate a remarkable range of kinetics among 257 diverse HIV-1 isolates and find that this phenotype is highly flexible, with multiple single-residue determinants. Examination of the kinetics of two conformational landmarks shed light on novel kinetic features that offer new details about the role of co-receptor engagement and provide a framework to explain entry inhibitor synergy.

Preservation of memory B cell homeostasis in an individual producing broadly neutralising antibodies against HIV-1

Immunological determinants favouring emergence of broadly neutralising antibodies are crucial to the development of HIV-1 vaccination strategies. Here, we combined RNAseq and B cell cloning approaches to isolate a broadly neutralising antibody (bnAb) ELC07 from an individual living with untreated HIV-1. Using single particle cryogenic electron microscopy (cryo-EM), we show that the antibody recognises a conformational epitope at the gp120-gp41 interface. ELC07 binds the closed state of the viral glycoprotein causing considerable perturbations to the gp41 trimer core structure. Phenotypic analysis of memory B cell subsets from the ELC07 bnAb donor revealed a lack of expected HIV-1-associated dysfunction, specifically no increase in CD21-/CD27- cells was observed whilst the resting memory (CD21+/CD27+) population appeared preserved despite uncontrolled HIV-1 viraemia. Moreover, single cell transcriptomes of memory B cells from this bnAb donor showed a resting memory phenotype irrespective of the epitope they targeted or their ability to neutralise diverse strains of HIV-1. Strikingly, single memory B cells from the ELC07 bnAb donor were transcriptionally similar to memory B cells from HIV-negative individuals. Our results demonstrate that potent bnAbs can arise without the HIV-1-induced dysregulation of the memory B cell compartment and suggest that sufficient levels of antigenic stimulation with a strategically designed immunogen could be effective in HIV-negative vaccine recipients.

Peptide Triazole Inhibitors of HIV-1: Hijackers of Env Metastability

With 1.5 million new infections and 690,000 AIDS-related deaths globally each year, HIV- 1 remains a pathogen of significant public health concern. Although a wide array of effective antiretroviral drugs have been discovered, these largely target intracellular stages of the viral infectious cycle, and inhibitors that act at or before the point of viral entry still require further advancement. A unique class of HIV-1 entry inhibitors, called peptide triazoles (PTs), has been developed, which irreversibly inactivates Env trimers by exploiting the protein structure's innate metastable nature. PTs, and a related group of inhibitors called peptide triazole thiols (PTTs), are peptide compounds that dually engage the CD4 receptor and coreceptor binding sites of Env's gp120 subunit. This triggers dramatic conformational rearrangements of Env, including the shedding of gp120 (PTs and PTTs) and lytic transformation of the gp41 subunit to a post-fusion-like arrangement (PTTs). Due to the nature of their dual receptor site engagement, PT/PTT-induced conformational changes may elucidate mechanisms behind the native fusion program of Env trimers following receptor and coreceptor engagement, including the role of thiols in fusion. In addition to inactivating Env, PTT-induced structural transformation enhances the exposure of important and conserved neutralizable regions of gp41, such as the membrane proximal external region (MPER). PTT-transformed Env could present an intriguing potential vaccine immunogen prototype. In this review, we discuss the origins of the PT class of peptide inhibitors, our current understanding of PT/PTT-induced structural perturbations and viral inhibition, and prospects for using these antagonists for investigating Env structural mechanisms and for vaccine development.

A Zika virus-specific IgM elicited in pregnancy exhibits ultrapotent neutralization

Congenital Zika virus (ZIKV) infection results in neurodevelopmental deficits in up to 14% of infants born to ZIKV-infected mothers. Neutralizing antibodies are a critical component of protective immunity. Here, we demonstrate that plasma IgM contributes to ZIKV immunity in pregnancy, mediating neutralization up to 3 months post-symptoms. From a ZIKV-infected pregnant woman, we isolated a pentameric ZIKV-specific IgM (DH1017.IgM) that exhibited ultrapotent ZIKV neutralization dependent on the IgM isotype. DH1017.IgM targets an envelope dimer epitope within domain II. The epitope arrangement on the virion is compatible with concurrent engagement of all ten antigen-binding sites of DH1017.IgM, a solution not available to IgG. DH1017.IgM protected mice against viremia upon lethal ZIKV challenge more efficiently than when expressed as an IgG. Our findings identify a role for antibodies of the IgM isotype in protection against ZIKV and posit DH1017.IgM as a safe and effective candidate immunotherapeutic, particularly during pregnancy.

Autoreactivity and broad neutralization of antibodies against HIV-1 are governed by distinct mutations: Implications for vaccine design strategies

Many of the best HIV-1 broadly neutralizing antibodies (bnAbs) known have poly-/autoreactive features that disfavor normal B cell development and maturation, posing a major hurdle in developing an effective HIV-1 vaccine. Key to resolving this problem is to understand if, and to what extent, neutralization breadth-conferring mutations acquired by bnAbs contribute to their autoreactivity. Here, we back-mutated all known changes made by a prototype CD4 binding site-directed bnAb lineage, CH103-106, during its later maturation steps. Strikingly, of 29 mutations examined, only four were crucial for increased autoreactivity, with minimal or no impact on neutralization. Furthermore, three of these residues were clustered in the heavy chain complementarity-determining region 2 (HCDR2). Our results demonstrate that broad neutralization activity and autoreactivity in the CH103-106 bnAb lineage can be governed by a few, distinct mutations during maturation. This provides strong rationale for developing immunogens that favor bnAb lineages bearing "neutralization-only" mutations into current HIV-1 vaccine designs.

HIV-1 Env Does Not Enable the Development of Protective Broadly Neutralizing Antibodies in an Experimental Autoimmune Encephalomyelitis Mouse Model

Recent studies showed that immunological tolerance may restrict the development of Env-specific autoreactive broadly neutralizing antibodies. This evidence is consistent with the finding that Env immunization of a systemic lupus erythematosus (SLE) murine model produced antibodies that neutralize tier 2 HIV-1 strains. In this study, we address the possibility of eliciting neutralizing anti-Env antibodies in other autoimmune diseases such as multiple sclerosis (MS). While, as reported for SLE, we showed for the first time that a small number of HIV-1 negative, relapsing remitting MS patients exhibited antibodies with neutralizing properties, our attempts at inducing those antibodies in a EAE mouse model of MS failed. The success in eliciting Env-specific neutralizing antibodies might be related to the specific characteristics of the autoimmune disease, or it might rely in improving the vaccination design. Studies using mouse models are useful to gain insight in how HIV-specific neutralizing antibody responses are regulated in order to develop a protective HIV-1 vaccine.

Employing Broadly Neutralizing Antibodies as a Human Immunodeficiency Virus Prophylactic & Therapeutic Application

Despite the discovery that the human immunodeficiency virus 1 (HIV-1) is the pathogen of acquired immunodeficiency syndrome (AIDS) in 1983, there is still no effective anti-HIV-1 vaccine. The major obstacle to the development of HIV-1 vaccine is the extreme diversity of viral genome sequences. Nonetheless, a number of broadly neutralizing antibodies (bNAbs) against HIV-1 have been made and identified in this area. Novel strategies based on using these bNAbs as an efficacious preventive and/or therapeutic intervention have been applied in clinical. In this review, we summarize the recent development of bNAbs and its application in HIV-1 acquisition prevention as well as discuss the innovative approaches being used to try to convey protection within individuals at risk and being treated for HIV-1 infection.

Viral Infections and Systemic Lupus Erythematosus: New Players in an Old Story

A causal link between viral infections and autoimmunity has been studied for a long time and the role of some viruses in the induction or exacerbation of systemic lupus erythematosus (SLE) in genetically predisposed patients has been proved. The strength of the association between different viral agents and SLE is variable. Epstein-Barr virus (EBV), parvovirus B19 (B19V), and human endogenous retroviruses (HERVs) are involved in SLE pathogenesis, whereas other viruses such as Cytomegalovirus (CMV) probably play a less prominent role. However, the mechanisms of viral-host interactions and the impact of viruses on disease course have yet to be elucidated. In addition to classical mechanisms of viral-triggered autoimmunity, such as molecular mimicry and epitope spreading, there has been a growing appreciation of the role of direct activation of innate response by viral nucleic acids and epigenetic modulation of interferon-related immune response. The latter is especially important for HERVs, which may represent the molecular link between environmental triggers and critical immune genes. Virus-specific proteins modulating interaction with the host immune system have been characterized especially for Epstein-Barr virus and explain immune evasion, persistent infection and self-reactive B-cell "immortalization". Knowledge has also been expanding on key viral proteins of B19-V and CMV and their possible association with specific phenotypes such as antiphospholipid syndrome. This progress may pave the way to new therapeutic perspectives, including the use of known or new antiviral drugs, postviral immune response modulation and innate immunity inhibition. We herein describe the state-of-the-art knowledge on the role of viral infections in SLE, with a focus on their mechanisms of action and potential therapeutic targets.

Antibodies to an Epstein Barr Virus protein that cross-react with dsDNA have pathogenic potential

Pathogens such as the Epstein Barr virus (EBV) have long been implicated in the etiology of systemic lupus erythematosus (SLE). The Epstein Barr virus nuclear antigen I (EBNA-1) has been shown to play a role in the development of anti-nuclear antibodies characteristic of SLE. One mechanism by which EBV may play a role in SLE is molecular mimicry. We previously generated two monoclonal antibodies (mAbs) to EBNA-1 and demonstrated that they cross-react with double-stranded DNA (dsDNA). In the present study, we demonstrate that these mAbs have pathogenic potential. We show that they can bind to isolated rat glomeruli and that binding can be greatly diminished by pretreatment of glomeruli with DNase I, suggesting that these mAbs bind dsDNA in the kidney. We also demonstrate that these antibodies can deposit in the kidney when injected into mice and can induce proteinuria and elicit histopathological alterations consistent with glomerulonephritis. Finally, we show that these antibodies can cross-react with laminin and collagen IV in the extracellular matrix suggesting that direct binding to the glomerular basement membrane or mesangial matrix may also contribute to the antibody deposition in the kidney. In summary, our results indicate that EBNA-1 can elicit antibodies that cross-react with dsDNA, that can deposit in the kidney, and induce kidney damage. These results are significant because they support the role of a viral protein in SLE and lupus nephritis.

RAB11FIP5-Deficient Mice Exhibit Cytokine-Related Transcriptomic Signatures

Rab11 recycling endosomes are involved in immunological synaptic functions, but the roles of Rab11 family–interacting protein 5 (Rab11Fip5), one of the Rab11 effectors, in the immune system remain obscure. Our previous study demonstrated that RAB11FIP5 transcripts are significantly elevated in PBMCs from HIV-1–infected individuals, making broadly HIV-1–neutralizing Abs compared with those without broadly neutralizing Abs; however, the role of Rab11FiP5 in immune functions remains unclear. In this study, a RAB11FIP5 gene knockout (RAB11FIP5^−/−) mouse model was employed to study the role of Rab11Fip5 in immune responses. RAB11FIP5^−/− mice exhibited no perturbation in lymphoid tissue cell subsets, and Rab11Fip5 was not required for serum Ab induction following HIV-1 envelope immunization, Ab transcytosis to mucosal sites, or survival after influenza challenge. However, differences were observed in multiple transcripts, including cytokine genes, in lymphocyte subsets from envelope-immunized RAB11FIP5^−/− versus control mice. These included alterations in several genes in NK cells that mirrored observations in NKs from HIV-infected humans expressing less RAB11FIP5, although Rab11Fip5 was dispensable for NK cell cytolytic activity. Notably, immunized RAB11FIP5^−/− mice had lower IL4 expression in CD4⁺ T follicular helper cells and showed lower TNF expression in CD8⁺ T cells. Likewise, TNF-α production by human CD8⁺ T cells correlated with PBMC RAB11FIP5 expression. These observations in RAB11FIP5^−/− mice suggest a role for Rab11Fip5 in regulating cytokine responses.

Computationally Designed Cyclic Peptides Derived from an Antibody Loop Increase Breadth of Binding for Influenza Variants

The influenza hemagglutinin (HA) glycoprotein is the target of many broadly neutralizing antibodies. However, influenza viruses can rapidly escape antibody recognition by mutation of hypervariable regions of HA that overlap with the binding epitope. We hypothesized that by designing peptides to mimic antibody loops, we could enhance breadth of binding to HA antigenic variants by reducing contact with hypervariable residues on HA that mediate escape. We designed cyclic peptides that mimic the heavy-chain complementarity-determining region 3 (CDRH3) of anti-influenza broadly neutralizing antibody C05 and show that these peptides bound to HA molecules with <100 nM affinity, comparable with that of the full-length parental C05 IgG. In addition, these peptides exhibited increased breadth of recognition to influenza H4 and H7 subtypes by eliminating clashes between the hypervariable antigenic regions and the antibody CDRH1 loop. This approach can be used to generate antibody-derived peptides against a wide variety of targets.

Histone H2A-Reactive B Cells Are Functionally Anergic in Healthy Mice With Potential to Provide Humoral Protection Against HIV-1

Peripheral tolerance is essential for silencing weakly autoreactive B cells that have escaped central tolerance, but it is unclear why these potentially pathogenic B cells are retained rather than being eliminated entirely. Release from peripheral tolerance restraint can occur under certain circumstances (i.e., strong TLR stimulus), that are present during infection. In this regard, we hypothesized that autoreactive B cells could function as a reserve population that can be activated to contribute to the humoral immune response, particularly with pathogens, such as HIV-1, that exploit immune tolerance to avoid host defense. In this study, we identify a population of autoreactive B cells with the potential to neutralize HIV-1 and experimentally release them from the functional restrictions of peripheral tolerance. We have previously identified murine monoclonal antibodies that displayed autoreactivity against histone H2A and neutralized HIV-1 in vitro. Here, we identify additional H2A-reactive IgM monoclonal antibodies and demonstrate that they are both autoreactive and polyreactive with self and foreign antigens and are able to neutralize multiple clades of tier 2 HIV-1. Flow cytometric analysis of H2A-reactive B cells in naïve wildtype mice revealed that these B cells are present in peripheral B cell populations and we further document that murine H2A-reactive B cells are restrained by peripheral tolerance mechanisms. Specifically, we show endogenous H2A-reactive B cells display increased expression of the inhibitory mediators CD5 and phosphatase and tensin homolog (PTEN) phosphatase and fail to mobilize calcium upon immunoreceptor stimulation; all characterized markers of anergy. Moreover, we show that toll-like receptor stimulation or provision of CD4 T cell help induces the in vitro production of H2A-reactive antibodies, breaking tolerance. Thus, we have identified a novel poly/autoreactive B cell population that has the potential to neutralize HIV-1 but is silenced by immune tolerance.

HIV and systemic lupus erythematosus: where immunodeficiency meets autoimmunity

We report a case of a new diagnosis of systemic lupus erythematosus (SLE) in a patient with HIV who presented to the outpatient department with a fever, headache and lymphadenopathy. Cerebrospinal fluid analysis showed lymphocytic pleocytosis. Initial concerns were for an infectious process, and investigations for systemic and central nervous system infection were negative. Serum testing for ANA, dsDNA, nucleosome, anti-histone and ribosomal-P antibodies was positive. A magnetic brain imaging scan of the brain showed a well-circumscribed lesion in the right cerebellar peduncle on T2/FLAIR. The patient was commenced on prednisolone and rituximab, and had a good clinical response. The cerebellar lesion resolved and has not recurred with sequential imaging. SLE and HIV are both multi-systemic diseases which rarely co-occur. Autoimmune processes should be considered in HIV patients with multi-systemic symptoms and signs.

HIV-1 Envelope Recognition by Polyreactive and Cross-Reactive Intestinal B Cells

Mucosal immune responses to HIV-1 involve the recognition of the viral envelope glycoprotein (gp)160 by tissue-resident B cells and subsequent secretion of antibodies. To characterize the B cells “sensing” HIV-1 in the gut of infected individuals, we probed monoclonal antibodies produced from single intestinal B cells binding to recombinant gp140 trimers. A large fraction of mucosal B cell antibodies were polyreactive and showed only low affinity to HIV-1 envelope glycoproteins, particularly the gp41 moiety. A few high-affinity gp140 antibodies were isolated but lacked neutralizing, potent ADCC, and transcytosis-blocking capacities. Instead, they displayed cross-reactivity with defined self-antigens. Specifically, intestinal HIV-1 gp41 antibodies targeting the heptad repeat 2 region (HR2) cluster II cross-reacted with the p38α mitogen-activated protein kinase 14 (MAPK14). Hence, physiologic polyreactivity of intestinal B cells and molecular mimicry-based self-reactivity of HIV-1 antibodies are two independent phenomena, possibly diverting and/or impairing mucosal humoral immunity to HIV-1.

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Polyreactive B cells in HIV-1⁺ intestinal mucosa interact with HIV-1 Env proteins

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High-affinity intestinal HIV-1 gp140 antibodies display poor antiviral activities

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Antibodies targeting the gp41 cluster II region cross-react with MAPK14

Germinal centers B-cell reaction and T follicular helper cells in response to HIV-1 infection

PURPOSE OF REVIEW

This review aims to summarize the recent findings on germinal center B-cell reaction and Tfh cells in HIV-1 infection, with particular emphasis on the spatial organization of the germinal center, follicular cell regulation, and cellular alterations resulting from HIV infection.

RECENT FINDINGS

HIV-specific bNAbs are generated by iterative cycles of B-cell maturation supported by GC environment. Recent observations underline that germinal center structural alterations at the earliest stages of HIV infection could impact Tfh cell and germinal center B-cell homeostasis, thus preventing the rise of efficient humoral immunity. Moreover, despite ART treatment, HIV-derived antigens persist, particularly in follicular CD4+ T cells. Antigenic persistence and variability lead to unregulated chronic stimulation. In this context, regulation of the germinal center appears of special interest. In addition to follicular T-regulatory cells (Tfr), new potent regulators of germinal center reaction, such as follicular CD8 T and NK cells have been recently identified.

SUMMARY

Altogether these new data provide a better understanding on how HIV infection severely impacts germinal center reaction. Here we propose several therapeutic approaches to promote the bNAb development in HIV-infected patients by improving the preservation of germinal center architecture and its regulation.

Retroviruses in the pathogenesis of systemic lupus erythematosus: Are they potential therapeutic targets?

The pathogenesis of systemic lupus erythematosus (SLE) is characterised by the hyper-activation of immunologic pathways related to the antiviral response. Exogenous and endogenous retroviruses, by integrating their DNA templates in the host cell genome, may epigenetically control the transcription of genes involved in the immune response. Furthermore, their nucleic acids or neo-synthesized proteins could stimulate the sensor molecules placed upstream the inflammatory cascade. Exogenous retroviruses, like human immunodeficiency virus, have been associated to SLE-like manifestations or to a fair SLE diagnosis. In addition, there is some evidence confirming a pathogenic role of human endogenous retroviruses in SLE. In line with these data, the use of antiretroviral agents could represent an attractive opportunity in the future therapeutic algorithms of this disease, but studies are still missing.

Effects of Early and Delayed Antiretroviral Therapy on Plasma Anti-CD4 Autoreactive IgG and Its Association With CD4+ T-Cell Recovery in Acute HIV-Infected Individuals

Background

Plasma levels of anti-CD4 autoantibodies are increased in chronically HIV-infected patients and inversely correlated with CD4⁺ T-cell recovery under viral-suppressive antiretroviral therapy (ART). However, it remains unknown the effect of early ART on plasma anti-CD4 autoantibody levels in acute HIV infection (AHI).

Methods

In this cohort study, we evaluated the effect of early and delayed initiation of ART on plasma anti-CD4 autoantibody levels in AHI individuals (n = 90). Blood samples were collected from men who had sex with men (MSM) with acute infection, pre-ART, and 4, 24, 48, and 96 weeks after ART. Plasma levels of anti-CD4 immunoglobulin G (IgG) were measured by ELISA.

Results

We found that plasma anti-CD4 IgG levels were significantly increased in AHI individuals compared with healthy controls (HCs) prior to ART. Notably, early ART decreased plasma anti-CD4 IgG to the levels similar to HCs starting at 24 weeks (W). However, delayed initiation of ART did not significantly reduce plasma anti-CD4 IgG levels in AHI individuals. Moreover, the peripheral CD4⁺ T-cell counts were inversely correlated with plasma anti-CD4 IgG levels in AHI individuals at 48 and 96 W after early ART but not after delayed ART.

Conclusions

Taken together, our findings demonstrate for the first time that early ART, but not delayed initiation of ART, is effective in influencing anti-CD4 autoantibody production and recovering CD4⁺ T-cell counts in AHI individuals.

Conditional antibody expression to avoid central B cell deletion in humanized HIV-1 vaccine mouse models

HIV-1 vaccine development aims to elicit broadly neutralizing antibodies (bnAbs) against diverse viral strains. In some HIV-1-infected individuals, bnAbs evolved from precursor antibodies through affinity maturation. To induce bnAbs, a vaccine must mediate a similar antibody maturation process. One way to test a vaccine is to immunize mouse models that express human bnAb precursors and assess whether the vaccine can convert precursor antibodies into bnAbs. A major problem with such mouse models is that bnAb expression often hinders B cell development. Such developmental blocks may be attributed to the unusual properties of bnAb variable regions, such as poly-reactivity and long antigen-binding loops, which are usually under negative selection during primary B cell development. To address this problem, we devised a method to circumvent such B cell developmental blocks by expressing bnAbs conditionally in mature B cells. We validated this method by expressing the unmutated common ancestor (UCA) of the human VRC26 bnAb in transgenic mice. Constitutive expression of the VRC26UCA led to developmental arrest of B cell progenitors in bone marrow; poly-reactivity of the VRC26UCA and poor pairing of the VRC26UCA heavy chain with the mouse surrogate light chain may contribute to this phenotype. The conditional expression strategy bypassed the impediment to VRC26UCA B cell development, enabling the expression of VRC26UCA in mature B cells. This approach should be generally applicable for expressing other bnAbs that are under negative selection during B cell development.

Pathways towards human immunodeficiency virus elimination

Antiretroviral therapy (ART) suppresses human immunodeficiency virus (HIV) infection. Research seeking to transform viral suppression into elimination has generated novel immune, chemical and molecular antiviral agents. However, none, to date, have excised latent integrated proviral DNA or removed infected cells from infected persons. These efforts included, but are not limited to, broadly neutralizing antibodies, "shock" and "kill" latency-reversing agents, innate immune regulators, and sequential long-acting antiretroviral nanoformulated prodrugs and CRISPR-Cas9 gene editing. While, the latter, enabled the complete excision of latent HIV-1 from the host genome success was so far limited. We contend that improvements in antiretroviral delivery, potency, agent specificity, or combinatorial therapies can provide a pathway towards complete HIV elimination.

Immune checkpoint modulation enhances HIV-1 antibody induction

Eliciting protective titers of HIV-1 broadly neutralizing antibodies (bnAbs) is a goal of HIV-1 vaccine development, but current vaccine strategies have yet to induce bnAbs in humans. Many bnAbs isolated from HIV-1-infected individuals are encoded by immunoglobulin gene rearrangments with infrequent naive B cell precursors and with unusual genetic features that may be subject to host regulatory control. Here, we administer antibodies targeting immune cell regulatory receptors CTLA-4, PD-1 or OX40 along with HIV envelope (Env) vaccines to rhesus macaques and bnAb immunoglobulin knock-in (KI) mice expressing diverse precursors of CD4 binding site HIV-1 bnAbs. CTLA-4 blockade augments HIV-1 Env antibody responses in macaques, and in a bnAb-precursor mouse model, CTLA-4 blocking or OX40 agonist antibodies increase germinal center B and T follicular helper cells and plasma neutralizing antibodies. Thus, modulation of CTLA-4 or OX40 immune checkpoints during vaccination can promote germinal center activity and enhance HIV-1 Env antibody responses.

Elucidation of broadly neutralizing antibodies (bnAb) is a goal in HIV vaccine development. Here, Bradley et al. show that administration of CTLA-4 blocking antibody with vaccine antigens increases HIV-1 envelope antibody responses in macaques and a bnAb precursor mouse model.

Neonatal Rhesus Macaques Have Distinct Immune Cell Transcriptional Profiles following HIV Envelope Immunization

HIV-1-infected infants develop broadly neutralizing antibodies (bnAbs) more rapidly than adults, suggesting differences in the neonatal versus adult responses to the HIV-1 envelope (Env). Here, trimeric forms of HIV-1 Env immunogens elicit increased gp120- and gp41-specific antibodies more rapidly in neonatal macaques than adult macaques. Transcriptome analyses of neonatal versus adult immune cells after Env vaccination reveal that neonatal macaques have higher levels of the apoptosis regulator BCL2 in T cells and lower levels of the immunosuppressive interleukin-10 (IL-10) receptor alpha (IL10RA) mRNA transcripts in T cells, B cells, natural killer (NK) cells, and monocytes. In addition, immunized neonatal macaques exhibit increased frequencies of activated blood T follicular helper-like (Tfh) cells compared to adults. Thus, neonatal macaques have transcriptome signatures of decreased immunosuppression and apoptosis compared with adult macaques, providing an immune landscape conducive to early-life immunization prior to sexual debut.

Cross-Reactivity with Self-Antigen Tunes the Functional Potential of Naive B Cells Specific for Foreign Antigens

Upon Ag exposure, naive B cells expressing BCR able to bind Ag can undergo robust proliferation and differentiation that can result in the production of Ab-secreting and memory B cells. The factors determining whether an individual naive B cell will proliferate following Ag encounter remains unclear. In this study, we found that polyclonal naive murine B cell populations specific for a variety of foreign Ags express high levels of the orphan nuclear receptor Nur77, which is known to be upregulated downstream of BCR signaling as a result of cross-reactivity with self-antigens in vivo. Similarly, a fraction of naive human B cells specific for clinically-relevant Ags derived from respiratory syncytial virus and HIV-1 also exhibited an IgMLOW IgD+ phenotype, which is associated with self-antigen cross-reactivity. Functionally, naive B cells expressing moderate levels of Nur77 are most likely to proliferate in vivo following Ag injection. Together, our data indicate that BCR cross-reactivity with self-antigen is a common feature of populations of naive B cells specific for foreign Ags and a moderate level of cross-reactivity primes individual cells for optimal proliferative responses following Ag exposure.

Minding the gap: The impact of B-cell tolerance on the microbial antibody repertoire

B lymphocytes must respond to vast numbers of foreign antigens, including those of microbial pathogens. To do so, developing B cells use combinatorial joining of V-, D-, and J-gene segments to generate an extraordinarily diverse repertoire of B-cell antigen receptors (BCRs). Unsurprisingly, a large fraction of this initial BCR repertoire reacts to self-antigens, and these "forbidden" B cells are culled by immunological tolerance from mature B-cell populations. While culling of autoreactive BCRs mitigates the risk of autoimmunity, it also opens gaps in the BCR repertoire, which are exploited by pathogens that mimic the forbidden self-epitopes. Consequently, immunological tolerance, necessary for averting autoimmune disease, also acts to limit effective microbial immunity. In this brief review, we recount the evidence for the linkage of tolerance and impaired microbial immunity, consider the implications of this linkage for vaccine development, and discuss modulating tolerance as a potential strategy for strengthening humoral immune responses.

Self-tolerance curtails the B cell repertoire to microbial epitopes

Immunological tolerance removes or inactivates self-reactive B cells, including those that also recognize cross-reactive foreign antigens. Whereas a few microbial pathogens exploit these "holes" in the B cell repertoire by mimicking host antigens to evade immune surveillance, the extent to which tolerance reduces the B cell repertoire to foreign antigens is unknown. Here, we use single-cell cultures to determine the repertoires of human B cell antigen receptors (BCRs) before (transitional B cells) and after (mature B cells) the second B cell tolerance checkpoint in both healthy donors and in patients with systemic lupus erythematosus (SLE) . In healthy donors, the majority (~70%) of transitional B cells that recognize foreign antigens also bind human self-antigens (foreign+self), and peripheral tolerance halves the frequency of foreign+self-reactive mature B cells. In contrast, in SLE patients who are defective in the second tolerance checkpoint, frequencies of foreign+self-reactive B cells remain unchanged during maturation of transitional to mature B cells. Patterns of foreign+self-reactivity among mature B cells from healthy donors differ from those of SLE patients. We propose that immune tolerance significantly reduces the scope of the BCR repertoire to microbial pathogens and that cross-reactivity between foreign and self epitopes may be more common than previously appreciated.

Antigen-specific antibody Fc glycosylation enhances humoral immunity via the recruitment of complement

HIV-specific broadly neutralizing antibodies (bNAbs) confer protection after passive immunization, but the immunological mechanisms that drive their development are poorly understood. Structural features of bNAbs indicate that they originate from extensive germinal center (GC) selection, which relies on persistent GC activity. However, why a fraction of infected individuals are able to successfully drive more effective affinity maturation is unclear. Delivery of antigens in the form of antibody-immune complexes (ICs), which bind to complement receptors (CRs) or Fc receptors (FcRs) on follicular dendritic cells, represents an effective mechanism for antigen delivery to the GC. We sought to define whether IC-FcR or CR interactions differ among individuals who develop bNAb responses to HIV. Enhanced Fc effector functions and FcR/CR interactions, via altered Fc glycosylation profiles, were observed among individuals with neutralizing antibody responses to HIV compared with those without neutralizing antibody activity. Moreover, both polyclonal neutralizer ICs and monoclonal IC mimics of neutralizer antibodies induced higher antibody titers, higher-avidity antibodies, and expanded GC B cell reactions after immunization of mice via accelerated antigen deposition within B cell follicles in a complement-dependent manner. Thus, these data point to a direct role for altered Fc profile/complement interactions in shaping the maturation of the humoral immune response, providing insights into how GC activity may be enhanced to drive affinity maturation in next-generation vaccine approaches.

Characterization of HIV-1 Nucleoside-Modified mRNA Vaccines in Rabbits and Rhesus Macaques

Despite the enormous effort in the development of effective vaccines against HIV-1, no vaccine candidate has elicited broadly neutralizing antibodies in humans. Thus, generation of more effective anti-HIV vaccines is critically needed. Here we characterize the immune responses induced by nucleoside-modified and purified mRNA-lipid nanoparticle (mRNA-LNP) vaccines encoding the clade C transmitted/founder HIV-1 envelope (Env) 1086C. Intradermal vaccination with nucleoside-modified 1086C Env mRNA-LNPs elicited high levels of gp120-specific antibodies in rabbits and rhesus macaques. Antibodies generated in rabbits neutralized a tier 1 virus, but no tier 2 neutralization activity could be measured. Importantly, three of six non-human primates developed antibodies that neutralized the autologous tier 2 strain. Despite stable anti-gp120 immunoglobulin G (IgG) levels, tier 2 neutralization titers started to drop 4 weeks after booster immunizations. Serum from both immunized rabbits and non-human primates demonstrated antibody-dependent cellular cytotoxicity activity. Collectively, these results are supportive of continued development of nucleoside-modified and purified mRNA-LNP vaccines for HIV. Optimization of Env immunogens and vaccination protocols are needed to increase antibody neutralization breadth and durability.

Human Immunodeficiency Virus Infection: Spectrum of Rheumatic Manifestations

Emerging and reemerging viral infections have been a characteristic feature of the past several decades, with HIV infection being the most important example of an emergent viral infection. To date, the status of a considerable proportion of HIV/AIDS patients has changed from a near-fatal disorder secondary to opportunistic infections to a chronic disease in which a variety of co-morbid conditions have become prevalent and relevant. Arthralgia and myalgias are the most common symptoms. The rate of spondyloarthritis varies according to the geographic area, genetic and mode of transmission. Most RA and SLE patients might go into remission after the development of AIDS, but also there are patients that continue with active disease. Prevalence of DILS is highest among African Americans in less advanced stages. PAN is clinically less aggressive and peripheral neuropathy is the most common clinical manifestation. Anti-phospholipid syndrome (APS), systemic sclerosis and poly-dermatomyositis are uncommon. After the introduction of combination antiretroviral therapy (cART), a decline of spondyloarthritis disorders and of DILS and development of new syndromes such as IRIS, osteoporosis and avascular bone necrosis have occurred. The treatment of patients with rheumatic diseases and HIV infection remains a challenge.

Inference of the HIV-1 VRC01 Antibody Lineage Unmutated Common Ancestor Reveals Alternative Pathways to Overcome a Key Glycan Barrier

Elicitation of VRC01-class broadly neutralizing antibodies (bnAbs) is an appealing approach for a preventative HIV-1 vaccine. Despite extensive investigations, strategies to induce VRC01-class bnAbs and overcome the barrier posed by the envelope N276 glycan have not been successful. Here, we inferred a high-probability unmutated common ancestor (UCA) of the VRC01 lineage and reconstructed the stages of lineage maturation. Env immunogens designed on reverted VRC01-class bnAbs bound to VRC01 UCA with affinity sufficient to activate naive B cells. Early mutations defined maturation pathways toward limited or broad neutralization, suggesting that focusing the immune response is likely required to steer B cell maturation toward the development of neutralization breadth. Finally, VRC01 lineage bnAbs with long CDR H3s overcame the HIV-1 N276 glycan barrier without shortening their CDR L1, revealing a solution for broad neutralization in which the heavy chain, not CDR L1, is the determinant to accommodate the N276 glycan.

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A high-probability VRC01 lineage UCA was inferred and CDRH3 evolution defined

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Env immunogens bind to VRC01 UCA with affinity sufficient to activate naive B cells

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Early mutations defined maturation pathways toward limited or broad neutralization

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Antibodies with long CDRH3s achieved neutralization breadth without shortening CDRL1s

Sera of patients with systemic lupus erythematosus cross-neutralizes dengue viruses

Dengue is the most prevalent mosquito-borne disease in Southeast Asia, where the incidence of systemic lupus erythematosus (SLE) is approximately 30 to 53 per 100,000. Severe dengue, however, is rarely reported among individuals with SLE. Here, whether sera of patients with SLE cross-neutralize dengue virus (DENV) was investigated. Serum samples were obtained from individuals with SLE who were dengue IgG and IgM serology negative. Neutralization assays were performed against the three major DENV serotypes. Of the dengue serology negative sera of individuals with SLE, 60%, 61% and 52% of the sera at 1/320 dilution showed more than 50% inhibition against dengue type-1 virus (DENV-1), DENV-2 and DENV-3, respectively. The neutralizing capacity of the sera was significantly greater against DENV-1 (P < 0.001) and DENV-3 (P < 0.01) than against DENV-2 (P < 0.05). Neutralization against the DENV correlated with dengue-specific IgG serum titers below the cut-off point for dengue positivity. Depletion of total IgG from the sera of patients with SLE resulted in significant decreases of up to 80% in DENV inhibition, suggesting that IgG plays an important role. However, some of the SLE sera was still able to neutralize DENV, even with IgG titers <0.1 OD absorbance. Our findings suggest that sera of patients with SLE contain IgG, and possibly other type of antibodies, that can cross-neutralize DENV, which may explain the rarity of severe dengue in individuals with SLE. Further studies, are needed to further substantiate this finding and to elucidate the specific neutralizing epitopes recognized by the sera of individuals with SLE.

RAB11FIP5 Expression and Altered Natural Killer Cell Function Are Associated with Induction of HIV Broadly Neutralizing Antibody Responses

HIV-1 broadly neutralizing antibodies (bnAbs) are difficult to induce with vaccines but are generated in ∼50% of HIV-1-infected individuals. Understanding the molecular mechanisms of host control of bnAb induction is critical to vaccine design. Here, we performed a transcriptome analysis of blood mononuclear cells from 47 HIV-1-infected individuals who made bnAbs and 46 HIV-1-infected individuals who did not and identified in bnAb individuals upregulation of RAB11FIP5, encoding a Rab effector protein associated with recycling endosomes. Natural killer (NK) cells had the highest differential expression of RAB11FIP5, which was associated with greater dysregulation of NK cell subsets in bnAb subjects. NK cells from bnAb individuals had a more adaptive/dysfunctional phenotype and exhibited impaired degranulation and cytokine production that correlated with RAB11FIP5 transcript levels. Moreover, RAB11FIP5 overexpression modulated the function of NK cells. These data suggest that NK cells and Rab11 recycling endosomal transport are involved in regulation of HIV-1 bnAb development.

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Elevated RAB11FIP5 expression is associated with HIV-1 bnAb induction

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NK cells show the highest differential RAB11FIP5 expression

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NK cell subsets are more dysregulated in individuals developing bnAbs

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Rab11Fip5 regulates NK cell function

High-Frequency, Functional HIV-Specific T-Follicular Helper and Regulatory Cells Are Present Within Germinal Centers in Children but Not Adults

Broadly neutralizing antibodies (bnAbs) against HIV-1 are an effective means of preventing transmission. To better understand the mechanisms by which HIV-specific bnAbs naturally develop, we investigated blood and lymphoid tissue in pediatric infection, since potent bnAbs develop with greater frequency in children than adults. As in adults, the frequency of circulating effector T-follicular helper cells (TFH) in HIV infected, treatment naïve children correlates with neutralization breadth. However, major differences between children and adults were also observed both in circulation, and in a small number of tonsil samples. In children, TFH cells are significantly more abundant, both in blood and in lymphoid tissue germinal centers, than in adults. Second, HIV-specific TFH cells are more frequent in pediatric than in adult lymphoid tissue and secrete the signature cytokine IL-21, which HIV-infected adults do not. Third, the enrichment of IL-21-secreting HIV-specific TFH in pediatric lymphoid tissue is accompanied by increased TFH regulation via more abundant regulatory follicular T-cells and HIV-specific CXCR5+ CD8 T-cells compared to adults. The relationship between regulation and neutralization breadth is also observed in the pediatric PBMC samples and correlates with neutralization breadth. Matching neutralization data from lymphoid tissue samples is not available. However, the distinction between infected children and adults in the magnitude, quality and regulation of HIV-specific TFH responses is consistent with the superior ability of children to develop high-frequency, potent bnAbs. These findings suggest the possibility that the optimal timing for next generation vaccine strategies designed to induce high-frequency, potent bnAbs to prevent HIV infection in adults would be in childhood.

Distinct systemic microbiome and microbial translocation are associated with plasma level of anti-CD4 autoantibody in HIV infection

Microbial signals have been linked to autoantibody induction. Recently, we found that purified anti-CD4 autoantibodies from the plasma of chronic HIV-1-infected patients under viral-suppressed antiretroviral therapy (ART) play a pathologic role in poor CD4+ T cell recovery. The purpose of the study was to investigate the association of systemic microbiome and anti-CD4 autoantibody production in HIV. Plasma microbiome from 12 healthy controls and 22 HIV-infected subjects under viral-suppressed ART were analyzed by MiSeq sequencing. Plasma level of autoantibodies and microbial translocation (LPS, total bacterial 16S rDNA, soluble CD14, and LPS binding protein) were analyzed by ELISA, limulus amebocyte assay, and qPCR. We found that plasma level of anti-CD4 IgGs but not anti-CD8 IgGs was increased in HIV+ subjects compared to healthy controls. HIV+ subjects with plasma anti-CD4 IgG > 50 ng/mL (high) had reduced microbial diversity compared to HIV+ subjects with anti-CD4 IgG ≤ 50 ng/mL (low). Moreover, plasma anti-CD4 IgG level was associated with elevated microbial translocation and reduced microbial diversity in HIV+ subjects. The Alphaproteobacteria class was significantly enriched in HIV+ subjects with low anti-CD4 IgG compared to patients with high anti-CD4 IgG even after controlling for false discovery rate (FDR). The microbial components were different from the phylum to genus level in HIV+ subjects with high anti-CD4 IgGs compared to the other two groups, but these differences were not significant after controlling for FDR. These results suggest that systemic microbial translocation and microbiome may associate with anti-CD4 autoantibody production in ART-treated HIV disease.

Poly- and autoreactivity of HIV-1 bNAbs: implications for vaccine design

A central puzzle in HIV-1 research is the inability of vaccination or even infection to reliably elicit humoral responses against broadly neutralizing epitopes in the HIV-1 envelope protein. In infected individuals, broadly neutralizing antibodies (bNAbs) do arise in a substantial minority, but only after 2 or more years of chronic infection. All known bNAbs possess at least one of three traits: a high frequency of somatic hypermutation, a long third complementarity determining region in the antibody heavy chain (HCDR3), or significant poly- or autoreactivity. Collectively, these observations suggest a plausible explanation for the rarity of many types of bNAbs: namely, that their generation is blocked by immunological tolerance or immune response checkpoints, thereby mandating that B cells take a tortuous path of somatic evolution over several years to achieve broadly neutralizing activity. In this brief review, we discuss the evidence for this tolerance hypothesis, its implications for HIV-1 vaccine design, and potential ways to access normally forbidden compartments of the antibody repertoire by modulating or circumventing tolerance controls.

Cross-reactivity of HIV vaccine responses and the microbiome

PURPOSE OF REVIEW

A successful human immunodeficiency virus-type 1 (HIV-1) vaccine will require immunogens that induce protective immune responses. However, recent studies suggest that the response to HIV-1 and perhaps other viruses may be altered by immune system exposure to intestinal microbiota-antigens. This review will discuss select aspects of these studies.

RECENT FINDINGS

Naïve CD4 T and B cell repertoires can be imprinted by intestinal microbiota-antigens to respond to virus epitopes prior to virus infection. A multiclade envelope (Env) gp145 DNA prime, recombinant adenovirus type 5 boost vaccine tested in a HIV Vaccine Trials Network (HVTN) phase IIb human vaccine efficacy trial (HVTN 505) induced a dominant gp41-reactive antibody response that was non-neutralizing and cross-reactive with intestinal microbiota. This vaccine regimen also induced a dominant gp41-reactive, intestinal microbiota-cross-reactive gp41 antibody response in neonatal and adult Rhesus macaques. Studies of naïve CD4 T cells have demonstrated cross-reactivity to both HIV-1 and influenza peptides.

SUMMARY

HIV-1 Env vaccine-induced CD4 T and B cell responses can originate from a pool of intestinal microbiota-cross-reactive immune cells. Moreover, intestinal microbiota-cross-reactive HIV-1 Env antibodies are ineffective in protection against HIV-1 infection. Thus, intestinal microbiota-imprinting of the B cell repertoire may be one of several roadblocks to the induction of protective HIV-1 antibodies.

What Are the Primary Limitations in B-Cell Affinity Maturation, and How Much Affinity Maturation Can We Drive with Vaccination? Breaking through Immunity's Glass Ceiling

A key goal of HIV-1 vaccine development is the induction of broadly neutralizing antibodies (bnAbs) targeted to the vulnerable regions of the HIV envelope. BnAbs develop over time in ∼50% of HIV-1-infected individuals. However, to date, no vaccines have induced bnAbs and few or none of these vaccine-elicited HIV-1 antibodies carry the high frequencies of V(D)J mutations characteristic of bnAbs. Do the high frequencies of mutations characteristic of naturally induced bnAbs represent a fundamental barrier to the induction of bnAbs by vaccines? Recent studies suggest that high frequencies of V(D)J mutations can be achieved by serial vaccination strategies. Rather, it appears that, in the absence of HIV-1 infection, physiologic immune tolerance controls, including a germinal center process termed affinity reversion, may limit vaccine-driven bnAb development by clonal elimination or selecting for mutations incompatible with bnAb activity.

Altered Ratio of T Follicular Helper Cells to T Follicular Regulatory Cells Correlates with Autoreactive Antibody Response in Simian Immunodeficiency Virus-Infected Rhesus Macaques

Individuals with chronic HIV-1 infection have an increased prevalence of autoreactive Abs. Many of the isolated HIV broadly neutralizing Abs from these individuals are also autoreactive. However, the underlying mechanism(s) that produce these autoreactive broadly neutralizing Abs remains largely unknown. The highly regulated coordination among B cells, T follicular helper (T_FH) cells, and T follicular regulatory (T_FR) cells in germinal centers (GCs) of peripheral lymphatic tissues (LTs) is essential for defense against pathogens while also restricting autoreactive responses. We hypothesized that an altered ratio of T_FH/T_FR cells in the GC contributes to the increased prevalence of autoreactive Abs in chronic HIV infection. We tested this hypothesis using a rhesus macaque (RM) SIV model. We measured the frequency of T_FH cells, T_FR cells, and GC B cells in LTs and anti-dsDNA and anti-phospholipid Abs from Indian RMs, with and without SIV infection. We found that the frequency of anti-dsDNA and anti-phospholipid Abs was much higher in chronically infected RMs (83.3% [5/6] and 66.7% [4/6]) than in acutely infected RMs (33.3% [2/6] and 18.6% [1/6]) and uninfected RMs (0% [0/6] and 18.6% [1/6]). The increased ratio of T_FH/T_FR cells in SIV infection correlated with anti-dsDNA and anti-phospholipid autoreactive Ab levels, whereas the frequency of T_FR cells alone did not correlate with the levels of autoreactive Abs. Our results provide direct evidence that the ratio of T_FH/T_FR cells in LTs is critical for regulating autoreactive Ab production in chronic SIV infection and possibly, by extension, in chronic HIV-1 infection.

Advances in HIV-1 Vaccine Development

An efficacious HIV-1 vaccine is regarded as the best way to halt the ongoing HIV-1 epidemic. However, despite significant efforts to develop a safe and effective vaccine, the modestly protective RV144 trial remains the only efficacy trial to provide some level of protection against HIV-1 acquisition. This review will outline the history of HIV vaccine development, novel technologies being applied to HIV vaccinology and immunogen design, as well as the studies that are ongoing to advance our understanding of vaccine-induced immune correlates of protection.

Fine epitope signature of antibody neutralization breadth at the HIV-1 envelope CD4-binding site

Major advances in donor identification, antigen probe design, and experimental methods to clone pathogen-specific antibodies have led to an exponential growth in the number of newly characterized broadly neutralizing antibodies (bnAbs) that recognize the HIV-1 envelope glycoprotein. Characterization of these bnAbs has defined new epitopes and novel modes of recognition that can result in potent neutralization of HIV-1. However, the translation of envelope recognition profiles in biophysical assays into an understanding of in vivo activity has lagged behind, and identification of subjects and mAbs with potent antiviral activity has remained reliant on empirical evaluation of neutralization potency and breadth. To begin to address this discrepancy between recombinant protein recognition and virus neutralization, we studied the fine epitope specificity of a panel of CD4-binding site (CD4bs) antibodies to define the molecular recognition features of functionally potent humoral responses targeting the HIV-1 envelope site bound by CD4. Whereas previous studies have used neutralization data and machine-learning methods to provide epitope maps, here, this approach was reversed, demonstrating that simple binding assays of fine epitope specificity can prospectively identify broadly neutralizing CD4bs-specific mAbs. Building on this result, we show that epitope mapping and prediction of neutralization breadth can also be accomplished in the assessment of polyclonal serum responses. Thus, this study identifies a set of CD4bs bnAb signature amino acid residues and demonstrates that sensitivity to mutations at signature positions is sufficient to predict neutralization breadth of polyclonal sera with a high degree of accuracy across cohorts and across clades.

B-Cell-Activating Factor and the B-Cell Compartment in HIV/SIV Infection

With the goal to design effective HIV vaccines, intensive studies focused on broadly neutralizing antibodies, which arise in a fraction of HIV-infected people. Apart from identifying new vulnerability sites in the viral envelope proteins, these studies have shown that a fraction of these antibodies are produced by self/poly-reactive B-cells. These findings prompted us to revisit the B-cell differentiation and selection process during HIV/SIV infection and to consider B-cells as active players possibly shaping the helper T-cell program within germinal centers (GCs). In this context, we paid a particular attention to B-cell-activating factor (BAFF), a key cytokine in B-cell development and immune response that is overproduced during HIV/SIV infection. As it does in autoimmune diseases, BAFF excess might contribute to the abnormal rescue of self-reactive B-cells at several checkpoints of the B-cell development and impair memory B-cell generation and functions. In this review, we first point out what is known about the functions of BAFF/a proliferation-inducing ligand and their receptors [B-cell maturation, transmembrane activator and CAML interactor (TACI), and BAFF-R], in physiological and pathophysiological settings, in mice and humans. In particular, we highlight recent results on the previously underappreciated regulatory functions of TACI and on the highly regulated production of soluble TACI and BAFF-R that act as decoy receptors. In light of recent data on BAFF, TACI, and BAFF-R, we then revisit the altered phenotypes and functions of B-cell subsets during the acute and chronic phase of HIV/SIV infection. Given the atypical phenotype and reduced functions of memory B-cells in HIV/SIV infection, we particularly discuss the GC reaction, a key checkpoint where self-reactive B-cells are eliminated and pathogen-specific memory B-cells and plasmablasts/cells are generated in physiological settings. Through its capacity to differentially bind and process BAFF-R and TACI on GC B-cells and possibly on follicular helper T-cells, BAFF appears as a key regulator of the physiological GC reaction. Its local excess during HIV/SIV infection could play a key role in B-cell dysregulations.

Pathological Role of Anti-CD4 Antibodies in HIV-Infected Immunologic Nonresponders Receiving Virus-Suppressive Antiretroviral Therapy

Increased mortality and morbidity occur among human immunodeficiency virus (HIV)-infected patients in whom CD4+ T-cell counts do not increase despite viral suppression with antiretroviral therapy (ART). Here we identified an underlying mechanism. Significantly elevated plasma levels of anti-CD4 immunoglobulin G (IgG) were found in HIV-positive immunologic nonresponders (ie, HIV-positive individuals with CD4+ T-cell counts of ≤350 cells/μL), compared with levels in HIV-positive immunologic responders (ie, HIV-positive individuals with CD4+ T-cell counts of ≥500 cells/μL) and healthy controls. Higher plasma level of anti-CD4 IgG correlated with blunted CD4+ T-cell recovery. Furthermore, purified anti-CD4 IgG from HIV-positive immunologic nonresponders induced natural killer (NK) cell-dependent CD4+ T-cell cytolysis and apoptosis through antibody-dependent cell-mediated cytotoxicity (ADCC) in vitro. We also found that anti-CD4 IgG-mediated ADCC exerts greater apoptosis of naive CD4+ T cells relative to memory CD4+ T cells. Consistently, increased frequencies of CD107a+ NK cells and profound decreases of naive CD4+ T cells were observed in immunologic nonresponders as compared to responders and healthy controls ex vivo. These data indicate that autoreactive anti-CD4 IgG may play an important role in blunted CD4+ T-cell reconstitution despite effective ART.

Immunologic characteristics of HIV-infected individuals who make broadly neutralizing antibodies

Induction of broadly neutralizing antibodies (bnAbs) capable of inhibiting infection with diverse variants of human immunodeficiency virus type 1 (HIV‐1) is a key, as‐yet‐unachieved goal of prophylactic HIV‐1 vaccine strategies. However, some HIV‐infected individuals develop bnAbs after approximately 2‐4 years of infection, enabling analysis of features of these antibodies and the immunological environment that enables their induction. Distinct subsets of CD4⁺ T cells play opposing roles in the regulation of humoral responses: T follicular helper (Tfh) cells support germinal center formation and provide help for affinity maturation and the development of memory B cells and plasma cells, while regulatory CD4⁺ (Treg) cells including T follicular regulatory (Tfr) cells inhibit the germinal center reaction to limit autoantibody production. BnAbs exhibit high somatic mutation frequencies, long third heavy‐chain complementarity determining regions, and/or autoreactivity, suggesting that bnAb generation is likely to be highly dependent on the activity of CD4⁺ Tfh cells, and may be constrained by host tolerance controls. This review discusses what is known about the immunological environment during HIV‐1 infection, in particular alterations in CD4⁺ Tfh, Treg, and Tfr populations and autoantibody generation, and how this is related to bnAb development, and considers the implications for HIV‐1 vaccine design.

Antibody-virus co-evolution in HIV infection: paths for HIV vaccine development

Induction of HIV-1 broadly neutralizing antibodies (bnAbs) to date has only been observed in the setting of HIV-1 infection, and then only years after HIV transmission. Thus, the concept has emerged that one path to induction of bnAbs is to define the viral and immunologic events that occur during HIV-1 infection, and then to mimic those events with a vaccine formulation. This concept has led to efforts to map both virus and antibody events that occur from the time of HIV-1 transmission to development of bnAbs. This work has revealed that a virus-antibody "arms race" occurs in which a HIV-1 transmitted/founder (TF) Env induces autologous neutralizing antibodies that can not only neutralize the TF virus but also can select virus escape mutants that in turn select affinity-matured neutralizing antibodies. From these studies has come a picture of bnAb development that has led to new insights in host-pathogen interactions and, as well, led to insight into immunologic mechanisms of control of bnAb development. Here, we review the progress to date in elucidating bnAb B cell lineages in HIV-1 infection, discuss new research leading to understanding the immunologic mechanisms of bnAb induction, and address issues relevant to the use of this information for the design of new HIV-1 sequential envelope vaccine candidates.

HIV-1 Consensus Envelope-Induced Broadly Binding Antibodies

Antibodies that cross-react with multiple HIV-1 envelopes (Envs) are useful reagents for characterizing Env proteins and for soluble Env capture and purification assays. We previously reported 10 murine monoclonal antibodies induced by group M consensus Env, CON-6 immunization. Each demonstrated broad cross-reactivity to recombinant Envs. Here we characterized the Env epitopes to which they bind. Seven mapped to linear epitopes in gp120, five at the Env N-terminus, and two at the Env C-terminus. One antibody, 13D7, bound at the gp120 N-terminus (aa 30-42), reacted with HIV-1-infected CD4+ T cells, and when expressed in a human IgG1 backbone, mediated antibody-dependent cellular cytotoxicity. Antibody 18F11 bound at the gp120 C-terminus (aa 445-459) and reactivity was glycan dependent. Antibodies 13D7, 3B3, and 16H3 bound to 100 percent of HIV-1 Envs tested in ELISA and sodium dodecyl sulfate/polyacrylamide gel electrophoresis/western blot analysis. These data define the epitopes of monoclonal antibody reagents for characterization of recombinant Envs, one epitope of which is also expressed on the surface of HIV-1-infected CD4+ T cells.

Immunological tolerance as a barrier to protective HIV humoral immunity

HIV-1 infection typically eludes antibody control by our immune system and is not yet prevented by a vaccine. While many viral features contribute to this immune evasion, broadly neutralizing antibodies (bnAbs) against HIV-1 are often autoreactive and it has been suggested that immunological tolerance may restrict a neutralizing antibody response. Indeed, recent Ig knockin mouse studies have shown that bnAb-expressing B cells are largely censored by central tolerance in the bone marrow. However, the contribution of peripheral tolerance in limiting the HIV antibody response by anergic and potentially protective B cells is poorly understood. Studies using mouse models to elucidate how anergic B cells are regulated and can be recruited into HIV-specific neutralizing antibody responses may provide insight into the development of a protective HIV-1 vaccine.

Breaching peripheral tolerance promotes the production of HIV-1-neutralizing antibodies

Schroeder et al. demonstrate that when peripheral tolerance is relaxed, tier 2 HIV-1–neutralizing antibodies can be elicited and identify new autoreactive antibody specificities against histone H2A capable of neutralizing tier 2 HIV-1.

A subset of characterized HIV-1 broadly neutralizing antibodies (bnAbs) are polyreactive with additional specificities for self-antigens and it has been proposed immunological tolerance may present a barrier to their participation in protective humoral immunity. We address this hypothesis by immunizing autoimmune-prone mice with HIV-1 Envelope (Env) and characterizing the primary antibody response for HIV-1 neutralization. We find autoimmune mice generate neutralizing antibody responses to tier 2 HIV-1 strains with alum treatment alone in the absence of Env. Importantly, experimentally breaching immunological tolerance in wild-type mice also leads to the production of tier 2 HIV-1–neutralizing antibodies, which increase in breadth and potency following Env immunization. In both genetically prone and experimentally induced mouse models of autoimmunity, increased serum levels of IgM anti-histone H2A autoantibodies significantly correlated with tier 2 HIV-1 neutralization, and anti-H2A antibody clones were found to neutralize HIV-1. These data demonstrate that breaching peripheral tolerance permits a cross-reactive HIV-1 autoantibody response able to neutralize HIV-1.

Nonorgan-specific autoantibodies in HIV-infected patients in the HAART era

Nonorgan-specific autoantibodies (AAbs) are used for diagnosing autoimmune diseases but can also be detected in other conditions. We carried out a cross-sectional study with the aim to screen HIV1-infected patients in the era of highly active antiretroviral therapy (HAART) for AAbs and to analyze the association of their presence with hypergammaglobulinemia and immunovirological status.Blood samples from HIV1-infected patients without major concomitant illnesses followed in 2 hospitals in Paris, France were tested for immunovirological status, serum immunoglobulin G (IgG) level, antinuclear antibodies (ANAs), anti-double-stranded DNA (anti-dsDNA), anti-extractable nuclear antigens (anti-ENAs), anticardiolipin (aCL), anti-β2glycoprotein1 (anti-β2GP1), and antineutrophil cytoplasmic antibodies (ANCAs). Clinically relevant AAbs were defined as ANAs with titers ≥1:160, anti-dsDNA or anti-ENA antibodies; aCL or anti-β2GP1 antibodies with a level ≥40 U/ml; and ANCAs reacting with proteinase 3 or myeloperoxidase.We included 92 patients (mean age 47 years, men 55%, sub-Saharan African background 55%, HAART 85%, mean CD4 lymphocyte count 611/mm, viral load < 40 copies/mL 74%). At least 1 AAb was detected in 45% of patients, mostly ANAs (33%) and ANCAs (13%); 12% had ≥1 clinically relevant AAb. Above-normal IgG levels were found in 71% of patients. We found an inverse association between the presence of ≥1 AAb and CD4 lymphocyte count (P = 0.03) and between above-normal IgG levels and duration of virological control (P = 0.02) and non-sub-Saharan African background (P = 0.001).In sum, in HIV1-infected patients without any major concomitant illness in the HAART era, the prevalence of AAbs remains high but AAb patterns leading to high suspicion of autoimmune diseases are rather uncommon. AAb presence is associated with reduced CD4 lymphocyte count but not hypergammaglobulinemia.

Boosting of HIV envelope CD4 binding site antibodies with long variable heavy third complementarity determining region in the randomized double blind RV305 HIV-1 vaccine trial

The canary pox vector and gp120 vaccine (ALVAC-HIV and AIDSVAX B/E gp120) in the RV144 HIV-1 vaccine trial conferred an estimated 31% vaccine efficacy. Although the vaccine Env AE.A244 gp120 is antigenic for the unmutated common ancestor of V1V2 broadly neutralizing antibody (bnAbs), no plasma bnAb activity was induced. The RV305 (NCT01435135) HIV-1 clinical trial was a placebo-controlled randomized double-blinded study that assessed the safety and efficacy of vaccine boosting on B cell repertoires. HIV-1-uninfected RV144 vaccine recipients were reimmunized 6–8 years later with AIDSVAX B/E gp120 alone, ALVAC-HIV alone, or a combination of ALVAC-HIV and AIDSVAX B/E gp120 in the RV305 trial. Env-specific post-RV144 and RV305 boost memory B cell V_H mutation frequencies increased from 2.9% post-RV144 to 6.7% post-RV305. The vaccine was well tolerated with no adverse events reports. While post-boost plasma did not have bnAb activity, the vaccine boosts expanded a pool of envelope CD4 binding site (bs)-reactive memory B cells with long third heavy chain complementarity determining regions (HCDR3) whose germline precursors and affinity matured B cell clonal lineage members neutralized the HIV-1 CRF01 AE tier 2 (difficult to neutralize) primary isolate, CNE8. Electron microscopy of two of these antibodies bound with near-native gp140 trimers showed that they recognized an open conformation of the Env trimer. Although late boosting of RV144 vaccinees expanded a novel pool of neutralizing B cell clonal lineages, we hypothesize that boosts with stably closed trimers would be necessary to elicit antibodies with greater breadth of tier 2 HIV-1 strains.

Trial Registration: ClinicalTrials.gov NCT01435135

Developing a successful HIV-1 vaccine remains a high global health priority. Several HIV-1 vaccine trials have been performed with only the RV144 vaccine trial showing vaccine efficacy, albeit modest. No broadly neutralizing antibody activity was identified in RV144 and inducing sterilizing immunity against a complex pathogen like HIV-1 remains a major challenge. Here we characterize the B cell responses after RV144 vaccine-recipients received two additional boosts severals years after the conclusion of the RV144 vaccine trial. Delayed and repetitive boosting of RV144 vaccine-recipients was capable of increasing somatic hypermutation of the Env-reactive antibodies and expanding subdominant pools of neutralizing B cell clonal lineages. These data are pertinent to HIV-1 vaccine-regimen design.

Humanized Immunoglobulin Mice: Models for HIV Vaccine Testing and Studying the Broadly Neutralizing Antibody Problem

A vaccine that can effectively prevent HIV-1 transmission remains paramount to ending the HIV pandemic, but to do so, will likely need to induce broadly neutralizing antibody (bnAb) responses. A major technical hurdle toward achieving this goal has been a shortage of animal models with the ability to systematically pinpoint roadblocks to bnAb induction and to rank vaccine strategies based on their ability to stimulate bnAb development. Over the past 6 years, immunoglobulin (Ig) knock-in (KI) technology has been leveraged to express bnAbs in mice, an approach that has enabled elucidation of various B-cell tolerance mechanisms limiting bnAb production and evaluation of strategies to circumvent such processes. From these studies, in conjunction with the wealth of information recently obtained regarding the evolutionary pathways and paratopes/epitopes of multiple bnAbs, it has become clear that the very features of bnAbs desired for their function will be problematic to elicit by traditional vaccine paradigms, necessitating more iterative testing of new vaccine concepts. To meet this need, novel bnAb KI models have now been engineered to express either inferred prerearranged V(D)J exons (or unrearranged germline V, D, or J segments that can be assembled into functional rearranged V(D)J exons) encoding predecessors of mature bnAbs. One encouraging approach that has materialized from studies using such newer models is sequential administration of immunogens designed to bind progressively more mature bnAb predecessors. In this review, insights into the regulation and induction of bnAbs based on the use of KI models will be discussed, as will new Ig KI approaches for higher-throughput production and/or altering expression of bnAbs in vivo, so as to further enable vaccine-guided bnAb induction studies.