Use of broadly neutralizing antibodies for HIV-1 prevention

HIV Vaccine Development at a Crossroads: New B and T Cell Approaches

Despite rigorous scientific efforts over the forty years since the onset of the global HIV pandemic, a safe and effective HIV-1 vaccine remains elusive. The challenges of HIV vaccine development have proven immense, in large part due to the tremendous sequence diversity of HIV and its ability to escape from antiviral adaptive immune responses. In recent years, several phase 3 efficacy trials have been conducted, testing a similar hypothesis, e.g., that non-neutralizing antibodies and classical cellular immune responses could prevent HIV-1 acquisition. These studies were not successful. As a result, the field has now pivoted to bold novel approaches, including sequential immunization strategies to drive the generation of broadly neutralizing antibodies and human CMV-vectored vaccines to elicit MHC-E-restricted CD8+ T cell responses. Many of these vaccine candidates are now in phase 1 trials, with early promising results.

Broadly neutralizing antibodies for HIV prevention: a comprehensive review and future perspectives

SUMMARYThe human immunodeficiency virus (HIV) epidemic remains a formidable global health concern, with 39 million people living with the virus and 1.3 million new infections reported in 2022. Despite anti-retroviral therapy's effectiveness in pre-exposure prophylaxis, its global adoption is limited. Broadly neutralizing antibodies (bNAbs) offer an alternative strategy for HIV prevention through passive immunization. Historically, passive immunization has been efficacious in the treatment of various diseases ranging from oncology to infectious diseases. Early clinical trials suggest bNAbs are safe, tolerable, and capable of reducing HIV RNA levels. Although challenges such as bNAb resistance have been noted in phase I trials, ongoing research aims to assess the additive or synergistic benefits of combining multiple bNAbs. Researchers are exploring bispecific and trispecific antibodies, and fragment crystallizable region modifications to augment antibody efficacy and half-life. Moreover, the potential of other antibody isotypes like IgG3 and IgA is under investigation. While promising, the application of bNAbs faces economic and logistical barriers. High manufacturing costs, particularly in resource-limited settings, and logistical challenges like cold-chain requirements pose obstacles. Preliminary studies suggest cost-effectiveness, although this is contingent on various factors like efficacy and distribution. Technological advancements and strategic partnerships may mitigate some challenges, but issues like molecular aggregation remain. The World Health Organization has provided preferred product characteristics for bNAbs, focusing on optimizing their efficacy, safety, and accessibility. The integration of bNAbs in HIV prophylaxis necessitates a multi-faceted approach, considering economic, logistical, and scientific variables. This review comprehensively covers the historical context, current advancements, and future avenues of bNAbs in HIV prevention.

High monoclonal neutralization titers reduced breakthrough HIV-1 viral loads in the Antibody Mediated Prevention trials

The Antibody Mediated Prevention (AMP) trials (NCT02716675 and NCT02568215) demonstrated that passive administration of the broadly neutralizing monoclonal antibody VRC01 could prevent some HIV-1 acquisition events. Here, we use mathematical modeling in a post hoc analysis to demonstrate that VRC01 influenced viral loads in AMP participants who acquired HIV. Instantaneous inhibitory potential (IIP), which integrates VRC01 serum concentration and VRC01 sensitivity of acquired viruses in terms of both IC50 and IC80, follows a dose-response relationship with first positive viral load (p = 0.03), which is particularly strong above a threshold of IIP = 1.6 (r = -0.6, p = 2e-4). Mathematical modeling reveals that VRC01 activity predicted from in vitro IC80s and serum VRC01 concentrations overestimates in vivo neutralization by 600-fold (95% CI: 300-1200). The trained model projects that even if future therapeutic HIV trials of combination monoclonal antibodies do not always prevent acquisition, reductions in viremia and reservoir size could be expected.

Conjugation of HIV-1 envelope to hepatitis B surface antigen alters vaccine responses in rhesus macaques

An effective HIV-1 vaccine remains a critical unmet need for ending the AIDS epidemic. Vaccine trials conducted to date have suggested the need to increase the durability and functionality of vaccine-elicited antibodies to improve efficacy. We hypothesized that a conjugate vaccine based on the learned response to immunization with hepatitis B virus could be utilized to expand T cell help and improve antibody production against HIV-1. To test this, we developed an innovative conjugate vaccine regimen that used a modified vaccinia virus Ankara (MVA) co-expressing HIV-1 envelope (Env) and the hepatitis B virus surface antigen (HBsAg) as a prime, followed by two Env-HBsAg conjugate protein boosts. We compared the immunogenicity of this conjugate regimen to matched HIV-1 Env-only vaccines in two groups of 5 juvenile rhesus macaques previously immunized with hepatitis B vaccines in infancy. We found expansion of both HIV-1 and HBsAg-specific circulating T follicular helper cells and elevated serum levels of CXCL13, a marker for germinal center activity, after boosting with HBsAg-Env conjugate antigens in comparison to Env alone. The conjugate vaccine elicited higher levels of antibodies binding to select HIV Env antigens, but we did not observe significant improvement in antibody functionality, durability, maturation, or B cell clonal expansion. These data suggests that conjugate vaccination can engage both HIV-1 Env and HBsAg specific T cell help and modify antibody responses at early time points, but more research is needed to understand how to leverage this strategy to improve the durability and efficacy of next-generation HIV vaccines.

Broadly neutralizing antibody epitopes on HIV-1 particles are exposed after virus interaction with host cells

The envelope (Env) glycoproteins on HIV-1 virions are the sole target of broadly neutralizing antibodies (bNAbs) and the focus of vaccines. However, many cross-reactive conserved epitopes are often occluded on virus particles, contributing to the evasion of humoral immunity. This study aimed to identify the Env epitopes that are exposed/occluded on HIV-1 particles and to investigate the mechanisms contributing to their masking. Using a flow cytometry-based assay, three HIV-1 isolates, and a panel of antibodies, we show that only select epitopes, including V2i, the gp120-g41 interface, and gp41-MPER, are accessible on HIV-1 particles, while V3, V2q, and select CD4bs epitopes are masked. These epitopes become accessible after allosteric conformational changes are induced by the pre-binding of select Abs, prompting us to test if similar conformational changes are required for these Abs to exhibit their neutralization capability. We tested HIV-1 neutralization where the virus-mAb mix was pre-incubated/not pre-incubated for 1 hour prior to adding the target cells. Similar levels of neutralization were observed under both assay conditions, suggesting that the interaction between virus and target cells sensitizes the virions for neutralization via bNAbs. We further show that lectin-glycan interactions can also expose these epitopes. However, this effect is dependent on the lectin specificity. Given that, bNAbs are ideal for providing sterilizing immunity and are the goal of current HIV-1 vaccine efforts, these data offer insight on how HIV-1 may occlude these vulnerable epitopes from the host immune response. In addition, the findings can guide the formulation of effective antibody combinations for therapeutic use. IMPORTANCE The human immunodeficiency virus (HIV-1) envelope (Env) glycoprotein mediates viral entry and is the sole target of neutralizing antibodies. Our data suggest that antibody epitopes including V2q (e.g., PG9, PGT145), CD4bs (e.g., VRC01, 3BNC117), and V3 (2219, 2557) are masked on HIV-1 particles. The PG9 and 2219 epitopes became accessible for binding after conformational unmasking was induced by the pre-binding of select mAbs. Attempts to understand the masking mechanism led to the revelation that interaction between virus and host cells is needed to sensitize the virions for neutralization by broadly neutralizing antibodies (bNAbs). These data provide insight on how bNAbs may gain access to these occluded epitopes to exert their neutralization effects and block HIV-1 infection. These findings have important implications for the way we evaluate the neutralizing efficacy of antibodies and can potentially guide vaccine design.

Application of the SLAPNAP statistical learning tool to broadly neutralizing antibody HIV prevention research

Combination monoclonal broadly neutralizing antibody (bnAb) regimens are in clinical development for HIV prevention, necessitating additional knowledge of bnAb neutralization potency/breadth against circulating viruses. Williamson et al. (2021) described a software tool, Super LeArner Prediction of NAb Panels (SLAPNAP), with application to any HIV bnAb regimen with sufficient neutralization data against a set of viruses in the Los Alamos National Laboratory's Compile, Neutralize, and Tally Nab Panels repository. SLAPNAP produces a proteomic antibody resistance (PAR) score for Env sequences based on predicted neutralization resistance and estimates variable importance of Env amino acid features. We apply SLAPNAP to compare HIV bnAb regimens undergoing clinical testing, finding improved power for downstream sieve analyses and increased precision for comparing neutralization potency/breadth of bnAb regimens due to the inclusion of PAR scores of Env sequences with much larger sample sizes available than for neutralization outcomes. SLAPNAP substantially improves bnAb regimen characterization, ranking, and down-selection.

Extended safety and tolerability of subcutaneous CAP256V2LS and VRC07-523LS in HIV-negative women: study protocol for the randomised, placebo-controlled double-blinded, phase 2 CAPRISA 012C trial

INTRODUCTION

Women-controlled HIV prevention technologies that overcome adherence challenges of available daily oral pre-exposure prophylaxis and give women a choice of options are urgently needed. Broadly neutralising monoclonal antibodies (bnAbs) administered passively may offer a valuable non-antiretroviral biological intervention for HIV prevention. Animal and human studies have demonstrated that bnAbs which neutralise HIV can prevent infection. The optimal plasma antibody concentrations to confer protection against HIV infection in humans is under intense study. The Centre for the AIDS Programme of Research in South Africa (CAPRISA) 012C trial will evaluate extended safety and pharmacokinetics of CAP256V2LS and VRC07-523LS among young HIV-negative South African and Zambian women. The study design also allows for an evaluation of a signal of HIV prevention efficacy.

METHODS AND ANALYSIS

CAPRISA 012 is a series of trials with three distinct protocols. The completed CAPRISA 012A and 012B phase 1 trials provided critical data for the CAPRISA 012C trial, which is divided into parts A and B. In part A, 90 participants were randomised to receive both CAP256V2LS and VRC07-523LS at 20 mg/kg or placebo, subcutaneously every 16 or 24 weeks. Part B will enrol 900 participants in South Africa and Zambia who will be randomised in a 1:1 ratio and receive an initial loading dose of 1.2 g of CAP256V2LS and VRC07-523LS or placebo followed by 600 mg of CAP256V2LS and 1.2 g of VRC07-523LS or placebo subcutaneously every 6 months. Safety will be assessed by frequency and severity of reactogenicity and other related adverse events. Pharmacokinetics of both antibodies will be measured in systemic and mucosal compartments over time, while participants will be monitored for breakthrough HIV infections.

ETHICS AND DISSEMINATION OF STUDY FINDINGS

The University of KwaZulu-Natal Biomedical Research Ethics Committee and South African Health Products Regulatory Authority have approved the trial (BREC/00002492/2021, SAHPRA20210317). Results will be disseminated through conference presentations, peer-reviewed publications and the clinical trial registry.

TRIAL REGISTRATION NUMBER

PACTR202112683307570.

Construction and Applications of Mammalian Cell-Based DNA-Encoded Peptide/Protein Libraries

DNA-encoded peptide/protein libraries are the starting point for protein evolutionary modification and functional peptide/antibody selection. Different display technologies, protein directed evolution, and deep mutational scanning (DMS) experiments employ DNA-encoded libraries to provide sequence variations for downstream affinity- or function-based selections. Mammalian cells promise the inherent post-translational modification and near-to-natural conformation of exogenously expressed mammalian proteins and thus are the best platform for studying transmembrane proteins or human disease-related proteins. However, due to the current technical bottlenecks of constructing mammalian cell-based large size DNA-encoded libraries, the advantages of mammalian cells as screening platforms have not been fully exploited. In this review, we summarize the current efforts in constructing DNA-encoded libraries in mammalian cells and the existing applications of these libraries in different fields.

Multivalent display of engineered HIV-1 envelope trimers on silica nanoparticles for targeting and in vitro activation of germline VRC01 B cells

Selective targeting of germline B cells with specifically designed germline-targeting HIV-1 envelope immunogens (GT-Env) is considered a feasible vaccination strategy to elicit broadly neutralizing antibodies (bnAbs). BnAbs are extremely valuable because they neutralize genetically distant viral strains at the same time. To overcome its inherently low affinity to germline B cells, the aim of the study was to present GT-Env via different immobilization strategies densely arrayed on the surface of nanoparticles. We engineered a prefusion-stabilized GT-Env trimer with affinity to VRC01 germline B cells using a bioinformatics-supported design approach. Distinct glycan modifications and amino acid substitutions yielded a GT-Env trimer which bound to the receptor with a K_D of 11.5 µM. Silica nanoparticles with 200 nm diameter (SiNPs) were used for the multivalent display of the novel GT-Env with a 15 nm mean centre-to-centre spacing either by site-specific, covalent conjugation or at random, non-specific adsorption. Oriented, covalent GT-Env conjugation revealed better binding of structure dependent bnAbs as compared to non-specifically adsorbed GT-Env. In addition, GT-Env covalently attached activated a B cell line expressing the germline VRC01 receptor at an EC₅₀ value in the nanomolar range (4 nM), while soluble GT-Env required 1,000-fold higher concentrations to induce signalling. The significantly lower GT-Env concentration was likely required due to avidity effects, which were in the picomolar range. Thus, low affinity antigens may particularly benefit from a particulate and multivalent delivery. In future, SiNPs are ideal to be modified in a modular design with various GT-Env variants that target different stages of germline and bnAb precursor B cells.

Human immunoglobulin repertoire analysis guides design of vaccine priming immunogens targeting HIV V2-apex broadly neutralizing antibody precursors

Broadly neutralizing antibodies (bnAbs) to the HIV envelope (Env) V2-apex region are important leads for HIV vaccine design. Most V2-apex bnAbs engage Env with an uncommonly long heavy-chain complementarity-determining region 3 (HCDR3), suggesting that the rarity of bnAb precursors poses a challenge for vaccine priming. We created precursor sequence definitions for V2-apex HCDR3-dependent bnAbs and searched for related precursors in human antibody heavy-chain ultradeep sequencing data from 14 HIV-unexposed donors. We found potential precursors in a majority of donors for only two long-HCDR3 V2-apex bnAbs, PCT64 and PG9, identifying these bnAbs as priority vaccine targets. We then engineered ApexGT Env trimers that bound inferred germlines for PCT64 and PG9 and had higher affinities for bnAbs, determined cryo-EM structures of ApexGT trimers complexed with inferred-germline and bnAb forms of PCT64 and PG9, and developed an mRNA-encoded cell-surface ApexGT trimer. These methods and immunogens have promise to assist HIV vaccine development.

Long-acting HIV Pre-exposure Prophylaxis (PrEP) approaches: Recent advances, emerging technologies and development challenges

Introduction:

Poor or inconsistent adherence to daily oral pre-exposure prophylaxis (PrEP) has emerged as a key barrier to effective HIV prevention. The advent of potent long-acting (LA) antiretrovirals (ARVs) in conjunction with advances in controlled release technologies has enabled LA ARV drug delivery systems (DDS) capable of providing extended dosing intervals and overcome the challenge of suboptimal drug adherence with daily oral dosing.

Areas covered:

This review discusses the current state of the LA PrEP field, recent advances, and emerging technologies, including ARV prodrug modifications and new DDS. Technological challenges, knowledge gaps, preclinical testing considerations, and future directions important in the context of clinical translation and implementation of LA HIV PrEP are discussed.

Expert opinion:

The HIV prevention field is evolving faster than ever and the bar for developing next-generation LA HIV prevention options continues to rise. The requirements for viable LA PrEP products to be implemented in resource-limited settings are challenging, necessitating proactive consideration and product modifications during the design and testing of promising new candidates. If successfully translated, next-generation LA PrEP that are safe, affordable, highly effective, and accepted by both end-users and key stakeholders will offer significant potential to curb the HIV pandemic.

Recent Progress in the Discovery and Development of Monoclonal Antibodies against Viral Infections

Monoclonal antibodies (mAbs), the new revolutionary class of medications, are fast becoming tools against various diseases thanks to a unique structure and function that allow them to bind highly specific targets or receptors. These specialized proteins can be produced in large quantities via the hybridoma technique introduced in 1975 or by means of modern technologies. Additional methods have been developed to generate mAbs with new biological properties such as humanized, chimeric, or murine. The inclusion of mAbs in therapeutic regimens is a major medical advance and will hopefully lead to significant improvements in infectious disease management. Since the first therapeutic mAb, muromonab-CD3, was approved by the U.S. Food and Drug Administration (FDA) in 1986, the list of approved mAbs and their clinical indications and applications have been proliferating. New technologies have been developed to modify the structure of mAbs, thereby increasing efficacy and improving delivery routes. Gene delivery technologies, such as non-viral synthetic plasmid DNA and messenger RNA vectors (DMabs or mRNA-encoded mAbs), built to express tailored mAb genes, might help overcome some of the challenges of mAb therapy, including production restrictions, cold-chain storage, transportation requirements, and expensive manufacturing and distribution processes. This paper reviews some of the recent developments in mAb discovery against viral infections and illustrates how mAbs can help to combat viral diseases and outbreaks.

How could HIV-1 drug resistance impact preexposure prophylaxis for HIV prevention?

PURPOSE OF REVIEW

To review current laboratory and clinical data on the frequency and relative risk of drug resistance and range of mutations selected from approved and investigational antiretroviral agents used for preexposure prophylaxis (PrEP) of HIV-1 infection, including tenofovir disproxil fumarate (TDF)-based oral PrEP, dapivirine ring, injectable cabotegravir (CAB), islatravir, lenacapavir and broadly neutralizing antibodies (bNAbs).

RECENT FINDINGS

The greatest risk of HIV-1 resistance from PrEP with oral TDF/emtricitabine (FTC) or injectable CAB is from starting or continuing PrEP after undiagnosed acute HIV infection. By contrast, the dapivirine intravaginal ring does not appear to select nonnucleoside reverse transcriptase inhibitor resistance in clinical trial settings. Investigational inhibitors including islatravir, lenacapavir, and bNAbs are promising for use as PrEP due to their potential for sustained delivery and low risk of cross-resistance to currently used antiretrovirals, but surveillance for emergence of resistance mutations in more HIV-1 gene regions (gag, env) will be important as the same drugs are being developed for HIV therapy.

SUMMARY

PrEP is highly effective in preventing HIV infection. Although HIV drug resistance from PrEP use could impact future options in individuals who seroconvert on PrEP, the current risk is low and continued monitoring for the emergence of resistance and cross-resistance during product development, clinical studies, and product roll-out is advised to preserve antiretroviral efficacy for both treatment and prevention.

Development of Neutralization Breadth against Diverse HIV-1 by Increasing Ab-Ag Interface on V2

Understanding maturation pathways of broadly neutralizing antibodies (bnAbs) against HIV-1 can be highly informative for HIV-1 vaccine development. A lineage of J038 bnAbs is now obtained from a long-term SHIV-infected macaque. J038 neutralizes 54% of global circulating HIV-1 strains. Its binding induces a unique "up" conformation for one of the V2 loops in the trimeric envelope glycoprotein and is heavily dependent on glycan, which provides nearly half of the binding surface. Their unmutated common ancestor neutralizes the autologous virus. Continuous maturation enhances neutralization potency and breadth of J038 lineage antibodies via expanding antibody-Env contact areas surrounding the core region contacted by germline-encoded residues. Developmental details and recognition features of J038 lineage antibodies revealed here provide a new pathway for elicitation and maturation of V2-targeting bnAbs.

Vaccine with bacterium-like particles displaying HIV-1 gp120 trimer elicits specific mucosal responses and neutralizing antibodies in rhesus macaques

Preclinical studies have shown that the induction of secretory IgA (sIgA) in mucosa and neutralizing antibodies (NAbs) in sera is essential for designing vaccines that can effectively block the transmission of HIV-1. We previously showed that a vaccine consisting of bacterium-like particles (BLPs) displaying Protan-gp120AE-MTQ (PAM) could induce mucosal immune responses through intranasal (IN) immunization in mice and NAbs through intramuscular (IM) immunization in guinea pigs. Here, we evaluated the ability of this vaccine BLP-PAM to elicit HIV-1-specific mucosal and systemic immune responses through IN and IM immunization combination strategies in rhesus macaques. First, the morphology, antigenicity and epitope accessibility of the vaccine were analysed by transmission electron microscopy, bio-layer interferometry and ELISA. In BLP-PAM-immunized macaques, HIV-1-specific sIgA were rapidly induced through IN immunization in situ and distant mucosal sites, although the immune responses are relatively weak. Furthermore, the HIV-1-specific IgG and IgA antibody levels in mucosal secretions were enhanced and maintained, while production of serum NAbs against heterologous HIV-1 tier 1 and 2 pseudoviruses was elicited after IM boost. Additionally, situ mucosal responses and systemic T cell immune responses were improved by rAd2-gp120AE boost immunization via the IN and IM routes. These results suggested that BLP-based delivery in combination with the IN and IM immunization approach represents a potential vaccine strategy against HIV-1.

Estimation of the in vivo neutralization potency of eCD4Ig and conditions for AAV-mediated production for SHIV long-term remission

The engineered protein eCD4Ig has emerged as a promising approach to achieve HIV remission in the absence of antiviral therapy. eCD4Ig neutralizes nearly all HIV-1 isolates and induces antibody-dependent cell-mediated cytotoxicity (ADCC) in vitro. To characterize the in vivo antiviral neutralization and possible ADCC effects of eCD4Ig, we fit mathematical models to eCD4Ig, anti–eCD4Ig-drug antibody (ADA), and viral load kinetics from healthy and simian-human immunodeficiency virus AD8 (SHIV-AD8) infected nonhuman primates that were treated with single or sequentially dosed eCD4Ig passive administrations. Our model predicts that eCD4Ig transiently decreases SHIV viral loads due to neutralization only with an in vivo IC₅₀ of ~25 μg/ml but with limited effect due to ADA. Simulations suggest that endogenous, continuous expression of eCD4Ig at levels greater than 10⁵ μg/day, as is possible with Adeno-associated virus (AAV) vector-based production, could overcome the diminishing effects of ADA and allow for long-term remission of SHIV viremia in nonhuman primates.

Potent anti-viral activity of a trispecific HIV neutralizing antibody in SHIV-infected monkeys

Broadly neutralizing antibodies (bNAbs) represent an alternative to drug therapy for the treatment of HIV-1 infection. Immunotherapy with single bNAbs often leads to emergence of escape variants, suggesting a potential benefit of combination bNAb therapy. Here, a trispecific bNAb reduces viremia 100- to 1000-fold in viremic SHIV-infected macaques. After treatment discontinuation, viremia rebounds transiently and returns to low levels, through CD8-mediated immune control. These viruses remain sensitive to the trispecific antibody, despite loss of sensitivity to one of the parental bNAbs. Similarly, the trispecific bNAb suppresses the emergence of resistance in viruses derived from HIV-1-infected subjects, in contrast to parental bNAbs. Trispecific HIV-1 neutralizing antibodies, therefore, mediate potent antiviral activity in vivo and may minimize the potential for immune escape.

Bispecific Antibodies for IFN-β Delivery to ErbB2+ Tumors

The main aim of our work was to create a full-length bispecific antibody (BsAb) as a vehicle for the targeted delivery of interferon-beta (IFN-β) to ErbB2+ tumor cells in the form of non-covalent complex of BsAb and IFN-β. Such a construct is a CrossMab-type BsAb, consisting of an ErbB2-recognizing trastuzumab moiety, a part of chimeric antibody to IFN-β, and human IgG1 Fc domain carrying knob-into-hole amino acid substitutions necessary for the proper assembly of bispecific molecules. The IFN-β- recognizing arm of BsAb not only forms a complex with the cytokine but neutralizes its activity, thus providing a mechanism to avoid the side effects of the systemic action of IFN-β by blocking IFN-β Interaction with cell receptors in the process of cytokine delivery to tumor sites. Enzyme sandwich immunoassay confirmed the ability of BsAb to bind to human IFN-β comparable to that of the parental chimeric mAb. The BsAb binds to the recombinant ErbB2 receptor, as well as to lysates of ErbB2+ tumor cell lines. The inhibition of the antiproliferative effect of IFN-β by BsAb (IC50 = 49,3 µg/mL) was demonstrated on the HT29 cell line. It can be proposed that the BsAb obtained can serve as a component of the immunocytokine complex for the delivery of IFN-β to ErbB2-associated tumor cells.

Clinical Trials of Broadly Neutralizing Monoclonal Antibodies for Human Immunodeficiency Virus Prevention: A Review

Passive immunization with broadly neutralizing antibodies (bnAbs) is a promising approach to reduce the 1.7 million annual human immunodeficiency virus (HIV) infections globally. Early studies on bnAbs showed safety in humans, but short elimination half-lives and low potency and breadth. Since 2010, several new highly potent bnAbs have been assessed in clinical trials alone or in combination for HIV prevention. Published data indicate that these bnAbs are safe and have a half-life ranging from 15 to 71 days. Only intravenous VRC01 has advanced to an efficacy trial, with results expected in late 2020. If bnAbs are shown to be effective in preventing HIV infection, they could fast-track vaccine development as correlates of protection, and contribute as passive immunization to achieving the goal of epidemic control. The purpose of the current review is to describe the current status and provide a synopsis of the available data on bnAbs in clinical trials for HIV prevention.

Incorporating the Cluster A and V1V2 Targets into a Minimal Structural Unit of the HIV-1 Envelope to Elicit a Cross-Clade Response with Potent Fc-Effector Functions

The generation of a potent vaccine for the prevention and/or control of HIV-1 has been unsuccessful to date, despite decades of research. Existing evidence from both infected individuals and clinical trials support a role for non-neutralizing or weakly neutralizing antibodies with potent Fc-effector functions in the prevention and control of HIV-1 infection. Vaccination strategies that induce such antibodies have proven partially successful in preventing HIV-1 infection. This is largely thought to be due to the polyclonal response that is induced in a vaccine setting, as opposed to the infusion of a single therapeutic antibody, which is capable of diverse Fc-effector functions and targets multiple but highly conserved epitopes. Here, we build on the success of our inner domain antigen, ID2, which incorporates conformational CD4-inducible (CD4i) epitopes of constant region 1 and 2 (C1C2 or Cluster A), in the absence of neutralizing antibody epitopes, into a minimal structural unit of gp120. ID2 has been shown to induce Cluster A-specific antibodies in a BALB/c mouse model with Fc-effector functions against CD4i targets. In order to generate an immunogen that incorporates both epitope targets implicated in the protective Fc-effector functions of antibodies from the only partially successful human vaccine trial, RV144, we incorporated the V1V2 domain into our ID2 antigen generating ID2-V1V2, which we used to immunize in combination with ID2. Immunized BALB/c mice generated both Cluster A- and V1V2-specific antibodies, which synergized to significantly improve the Fc-mediated effector functions compared to mice immunized with ID2 alone. The sera were able to mediate both antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). We therefore conclude that ID2-V1V2 + ID2 represents a promising vaccine immunogen candidate for the induction of antibodies with optimal Fc-mediated effector functions against HIV-1.

Rectal tissue and vaginal tissue from intravenous VRC01 recipients show protection against ex vivo HIV-1 challenge

BackgroundVRC01, a potent, broadly neutralizing monoclonal antibody, inhibits simian-HIV infection in animal models. The HVTN 104 study assessed the safety and pharmacokinetics of VRC01 in humans. We extend the clinical evaluation to determine intravenously infused VRC01 distribution and protective function at mucosal sites of HIV-1 entry.MethodsHealthy, HIV-1-uninfected men (n = 7) and women (n = 5) receiving VRC01 every 2 months provided mucosal and serum samples once, 4-13 days after infusion. Eleven male and 8 female HIV-seronegative volunteers provided untreated control samples. VRC01 levels were measured in serum, secretions, and tissue, and HIV-1 inhibition was determined in tissue explants.ResultsMedian VRC01 levels were quantifiable in serum (96.2 μg/mL or 1.3 pg/ng protein), rectal tissue (0.11 pg/ng protein), rectal secretions (0.13 pg/ng protein), vaginal tissue (0.1 pg/ng protein), and cervical secretions (0.44 pg/ng protein) from all recipients. VRC01/IgG ratios in male serum correlated with those in paired rectal tissue (r = 0.893, P = 0.012) and rectal secretions (r = 0.9643, P = 0.003). Ex vivo HIV-1Bal26 challenge infected 4 of 21 rectal explants from VRC01 recipients versus 20 of 22 from controls (P = 0.005); HIV-1Du422.1 infected 20 of 21 rectal explants from VRC01 recipients and 12 of 12 from controls (P = 0.639). HIV-1Bal26 infected 0 of 14 vaginal explants of VRC01 recipients compared with 23 of 28 control explants (P = 0.003).ConclusionIntravenous VRC01 distributes into the female genital and male rectal mucosa and retains anti-HIV-1 functionality, inhibiting a highly neutralization-sensitive but not a highly resistant HIV-1 strain in mucosal tissue. These findings lend insight into VRC01 mucosal infiltration and provide perspective on in vivo protective efficacy.FundingNational Institute of Allergy and Infectious Diseases and Bill & Melinda Gates Foundation.

Broadly neutralizing antibody-mediated protection of macaques against repeated intravenous exposures to simian-human immunodeficiency virus

OBJECTIVE

The opioid epidemic has increased parentally acquired HIV infection. To inform the development of a long-acting prevention strategy, we evaluated the protective efficacy of broadly neutralizing antibodies (bNAbs) against intravenous simian-human immunodeficiency virus (SHIV) infection in macaques.

DESIGN

Five cynomolgus macaques were injected once subcutaneously with 10-1074 and 3BNC117 (10 mg each kg-1) and were repeatedly challenged intravenously once weekly with SHIVAD8-EO (130 TCID50), until infection was confirmed via plasma viral load assay. Two control macaques, which received no antibody, were challenged identically.

METHODS

Plasma viremia was monitored via RT-qPCR assay. bNAb concentrations were determined longitudinally in plasma samples via TZM-bl neutralization assays using virions pseudotyped with 10-1074-sensitive (X2088_c9) or 3BNC117-sensitive (Q769.d22) HIV envelope proteins.

RESULTS

Passively immunized macaques were protected against a median of five weekly intravenous SHIV challenges, as compared to untreated controls, which were infected following a single challenge. Of the two bNAbs, 10-1074 exhibited relatively longer persistence in vivo. The median plasma level of 10-1074 at SHIV breakthrough was 1.1 μg ml-1 (range: 0.6-1.6 μg ml-1), whereas 3BNC117 was undetectable. Probit modeling estimated that 6.6 μg ml-1 of 10-1074 in plasma corresponded to a 99% reduction in per-challenge infection probability, as compared to controls.

CONCLUSIONS

Significant protection against repeated intravenous SHIV challenges was observed following administration of 10-1074 and 3BNC117 and was due primarily to 10-1074. Our findings extend preclinical studies of bNAb-mediated protection against mucosal SHIV acquisition and support the possibility that intermittent subcutaneous injections of 10-1074 could serve as long-acting preexposure prophylaxis for persons who inject drugs.

Predicting in vivo escape dynamics of HIV-1 from a broadly neutralizing antibody

Broadly neutralizing antibodies are promising candidates for treatment and prevention of HIV-1 infections. Such antibodies can temporarily suppress viral load in infected individuals; however, the virus often rebounds by escape mutants that have evolved resistance. In this paper, we map a fitness model of HIV-1 interacting with broadly neutralizing antibodies using in vivo data from a recent clinical trial. We identify two fitness factors, antibody dosage and viral load, that determine viral reproduction rates reproducibly across different hosts. The model successfully predicts the escape dynamics of HIV-1 in the course of an antibody treatment, including a characteristic frequency turnover between sensitive and resistant strains. This turnover is governed by a dosage-dependent fitness ranking, resulting from an evolutionary trade-off between antibody resistance and its collateral cost in drug-free growth. Our analysis suggests resistance-cost trade-off curves as a measure of antibody performance in the presence of resistance evolution.

Broadly Neutralizing Antibodies for HIV-1 Prevention

Given the absence of an effective vaccine for protection against HIV-1 infection, passive immunization strategies that utilize potent broadly neutralizing antibodies (bnAbs) to block acquisition of HIV-1 are being rigorously pursued in the clinical setting. bnAbs have demonstrated robust protection in preclinical animal models, and several leading bnAb candidates have shown favorable safety and pharmacokinetic profiles when tested individually or in combinations in early phase human clinical trials. Furthermore, passive administration of bnAbs in HIV-1 infected individuals has resulted in prolonged suppression of viral rebound following interruption of combination antiretroviral therapy, and robust antiviral activity when administered to viremic individuals. Recent results from the first efficacy trials testing repeated intravenous administrations of the anti-CD4 binding site bnAb VRC01 have demonstrated positive proof of concept that bnAb passive immunization can confer protection against HIV-1 infection in humans, but have also highlighted the considerable barriers that remain for such strategies to effectively contribute to control of the epidemic. In this review, we discuss the current status of clinical studies evaluating bnAbs for HIV-1 prevention, highlight lessons learned from the recent Antibody Mediated Prevention (AMP) efficacy trials, and provide an overview of strategies being employed to improve the breadth, potency, and durability of antiviral protection.

Functional development of a V3/glycan-specific broadly neutralizing antibody isolated from a case of HIV superinfection

Stimulating broadly neutralizing antibodies (bnAbs) directly from germline remains a barrier for HIV vaccines. HIV superinfection elicits bnAbs more frequently than single infection, providing clues of how to elicit such responses. We used longitudinal antibody sequencing and structural studies to characterize bnAb development from a superinfection case. BnAb QA013.2 bound initial and superinfecting viral Env, despite its probable naive progenitor only recognizing the superinfecting strain, suggesting both viruses influenced this lineage. A 4.15 Å cryo-EM structure of QA013.2 bound to native-like trimer showed recognition of V3 signatures (N301/N332 and GDIR). QA013.2 relies less on CDRH3 and more on framework and CDRH1 for affinity and breadth compared to other V3/glycan-specific bnAbs. Antigenic profiling revealed that viral escape was achieved by changes in the structurally-defined epitope and by mutations in V1. These results highlight shared and novel properties of QA013.2 relative to other V3/glycan-specific bnAbs in the setting of sequential, diverse antigens.

Can Broadly Neutralizing HIV-1 Antibodies Help Achieve an ART-Free Remission?

Many broadly neutralizing antibodies (bnAbs) targeting the HIV-1 envelope glycoprotein are being assessed in clinical trials as strategies for HIV-1 prevention, treatment, and antiretroviral-free remission. BnAbs can neutralize HIV-1 and target infected cells for elimination. Concerns about HIV-1 resistance to single bnAbs have led to studies of bnAb combinations with non-overlapping resistance profiles. This review focuses on the potential for bnAbs to induce HIV-1 remission, either alone or in combination with latency reversing agents, therapeutic vaccines or other novel therapeutics. Key topics include preliminary activity of bnAbs in preclinical models and in human studies of HIV-1 remission, clinical trial designs, and antibody design strategies to optimize pharmacokinetics, coverage of rebound-competent virus, and enhancement of cellular immune functions.

Advancing HIV Broadly Neutralizing Antibodies: From Discovery to the Clinic

Despite substantial progress in confronting the global HIV-1 epidemic since its inception in the 1980s, better approaches for both treatment and prevention will be necessary to end the epidemic and remain a top public health priority. Antiretroviral therapy (ART) has been effective in extending lives, but at a cost of lifelong adherence to treatment. Broadly neutralizing antibodies (bNAbs) are directed to conserved regions of the HIV-1 envelope glycoprotein trimer (Env) and can block infection if present at the time of viral exposure. The therapeutic application of bNAbs holds great promise, and progress is being made toward their development for widespread clinical use. Compared to the current standard of care of small molecule-based ART, bNAbs offer: (1) reduced toxicity; (2) the advantages of extended half-lives that would bypass daily dosing requirements; and (3) the potential to incorporate a wider immune response through Fc signaling. Recent advances in discovery technology can enable system-wide mining of the immunoglobulin repertoire and will continue to accelerate isolation of next generation potent bNAbs. Passive transfer studies in pre-clinical models and clinical trials have demonstrated the utility of bNAbs in blocking or limiting transmission and achieving viral suppression. These studies have helped to define the window of opportunity for optimal intervention to achieve viral clearance, either using bNAbs alone or in combination with ART. None of these advances with bNAbs would be possible without technological advancements and expanding the cohorts of donor participation. Together these elements fueled the remarkable growth in bNAb development. Here, we review the development of bNAbs as therapies for HIV-1, exploring advances in discovery, insights from animal models and early clinical trials, and innovations to optimize their clinical potential through efforts to extend half-life, maximize the contribution of Fc effector functions, preclude escape through multiepitope targeting, and the potential for sustained delivery.

Feasibility and Successful Enrollment in a Proof-of-Concept HIV Prevention Trial of VRC01, a Broadly Neutralizing HIV-1 Monoclonal Antibody

BACKGROUND

The Antibody-Mediated Prevention trials (HVTN 704/HPTN 085 and HVTN 703/HPTN 081) are the first efficacy trials to evaluate whether VRC01, a broadly neutralizing monoclonal antibody targeting the CD4-binding site of the HIV envelope protein, prevents sexual transmission of HIV-1. HVTN 704/HPTN 085 enrolled 2701 cisgender men and transgender (TG) individuals who have sex with men at 26 sites in Brazil, Peru, Switzerland, and the United States.

METHODS

Participants were recruited and retained through early, extensive community engagement. Eligible participants were randomized 1:1:1 to 10 mg/kg or 30 mg/kg of VRC01 or saline placebo. Visits occurred monthly, with intravenous (IV) infusions every 8 weeks over 2 years, for a total of 10 infusions. Participants were followed for 104 weeks after first infusion.

RESULTS

The median HVTN 704/HPTN 085 participant age was 28 years; 99% were assigned male sex; 90% identified as cisgender men, 5% as TG women and the remaining as other genders. Thirty-two percent were White, 15% Black, and 57% Hispanic/Latinx. Twenty-eight percent had a sexually transmitted infection at enrollment. More than 23,000 infusions were administered with no serious IV administration complications. Overall, retention and adherence to the study schedule exceeded 90%, and the dropout rate was below 10% annually (7.3 per 100 person-years) through week 80, the last visit for the primary end point.

CONCLUSIONS

HVTN 704/HPTN 085 exceeded accrual and retention expectations. With exceptional safety of IV administration and operational feasibility, it paves the way for future large-scale monoclonal antibody trials for HIV prevention and/or treatment.

Immunization by exposure to live virus (SIVmne/HIV-2287) during antiretroviral drug prophylaxis may reduce risk of subsequent viral challenge

Rationale/Study design

A major challenge in the development of HIV vaccines is finding immunogens that elicit protection against a broad range of viral strains. Immunity to a narrow range of viral strains may protect infants of HIV-infected women or partners discordant for HIV. We hypothesized that immunization to the relevant viral variants could be achieved by exposure to infectious virus during prophylaxis with antiretroviral drugs. To explore this approach in an animal model, macaques were exposed to live virus (SIV_mne or HIV-2₂₈₇) during prophylaxis with parenteral tenofovir and humoral and cellular immune responses were quantified. Subsequently, experimental animals were challenged with homologous virus to evaluate protection from infection, and if infection occurred, the course of disease was compared to control animals. Experimental animals uninfected with SIV_mne were challenged with heterologous HIV-2₂₈₇ to assess resistance to retroviral infection.

Methodology/Principal findings

Juvenile female Macaca nemestrina (N = 8) were given ten weekly intravaginal exposures with either moderately (SIV_mne) or highly (HIV-2₂₈₇) pathogenic virus during tenofovir prophylaxis. Tenofovir protected all 8 experimental animals from infection, while all untreated control animals became infected. Specific non-neutralizing antibodies were elicited in blood and vaginal secretions of experimental animals, but no ELISPOT responses were detected. Six weeks following the cessation of tenofovir, intravaginal challenge with homologous virus infected 2/4 (50%) of the SIV_mne-immunized animals and 4/4 (100%) of the HIV-2₂₈₇-immunized animals. The two SIV_mne-infected and 3 (75%) HIV-2₂₈₇-infected had attenuated disease, suggesting partial protection.

Conclusions/Significance

Repeated exposure to SIV_mne or HIV-2₂₈₇, during antiretroviral prophylaxis that blocked infection, induced binding antibodies in the blood and mucosa, but not neutralizing antibodies or specific cellular immune responses. Studies to determine whether antibodies are similarly induced in breastfeeding infants and sexual partners discordant for HIV infection and receiving pre-exposure antiretroviral prophylaxis are warranted, including whether these antibodies appear to confer partial or complete protection from infection.

Mutations that confer resistance to broadly-neutralizing antibodies define HIV-1 variants of transmitting mothers from that of non-transmitting mothers

Despite considerable reduction of mother-to-child transmission (MTCT) of HIV through use of maternal and infant antiretroviral therapy (ART), over 150,000 infants continue to become infected with HIV annually, falling far short of the World Health Organization goal of reaching <20,000 annual pediatric HIV cases worldwide by 2020. Prior to the widespread use of ART in the setting of pregnancy, over half of infants born to HIV-infected mothers were protected against HIV acquisition. Yet, the role of maternal immune factors in this protection against vertical transmission is still unclear, hampering the development of synergistic strategies to further reduce MTCT. It has been established that infant transmitted/founder (T/F) viruses are often resistant to maternal plasma, yet it is unknown if the neutralization resistance profile of circulating viruses predicts the maternal risk of transmission to her infant. In this study, we amplified HIV-1 envelope genes (env) by single genome amplification and produced representative Env variants from plasma of 19 non-transmitting mothers from the U.S. Women Infant Transmission Study (WITS), enrolled in the pre-ART era. Maternal HIV Env variants from non-transmitting mothers had similar sensitivity to autologous plasma as observed for non-transmitting variants from transmitting mothers. In contrast, infant variants were on average 30% less sensitive to paired plasma neutralization compared to non-transmitted maternal variants from both transmitting and non-transmitting mothers (p = 0.015). Importantly, a signature sequence analysis revealed that motifs enriched in env sequences from transmitting mothers were associated with broadly neutralizing antibody (bnAb) resistance. Altogether, our findings suggest that circulating maternal virus resistance to bnAb-mediated neutralization, but not autologous plasma neutralization, near the time of delivery, predicts increased MTCT risk. These results caution that enhancement of maternal plasma neutralization through passive or active vaccination during pregnancy may potentially drive the evolution of variants fit for vertical transmission.

Despite widespread, effective use of ART among HIV infected pregnant women, new pediatric HIV infections increase by about 150,000 every year. Thus, alternative strategies will be required to reduce MTCT and eliminate pediatric HIV infections. Interestingly, in the absence of ART, less than half of HIV-infected pregnant women will transmit HIV, suggesting natural immune protection of infants from virus acquisition. To understand the impact of maternal plasma autologous virus neutralization responses on MTCT, we compared the plasma and bnAb neutralization sensitivity of the circulating viral population present at the time of delivery in untreated, HIV-infected transmitting and non-transmitting mothers. While there was no significant difference in the ability of transmitting and non-transmitting women to neutralize their own circulating virus strains, specific genetic motifs enriched in variants from transmitting mothers were associated with resistance to bnAbs, suggesting that acquired bnAb resistance is a common feature of vertically-transmitted variants. This work suggests that enhancement of plasma neutralization responses in HIV-infected mothers through passive or active vaccination could further drive selection of variants that could be vertically transmitted, and cautions the use of passive bnAbs for HIV-1 prophylaxis or therapy during pregnancy.

Neutralizing monoclonal antibodies for COVID-19 treatment and prevention

The SARS-CoV-2 pandemic has caused unprecedented global health and economic crises. Several vaccine approaches and repurposed drugs are currently under evaluation for safety and efficacy. However, none of them have been approved for COVID-19 yet. Meanwhile, several nMAbs targeting SARS-CoV-2 spike glycoprotein are in different stages of development and clinical testing. Preclinical studies have shown that cocktails of potent nMAbs targeting the receptor binding site of SARS-CoV-2, as well as broad-nMAbs targeting conserved regions within the virus spike, might be effective for the treatment and prophylaxis of COVID-19. Currently, several clinical trials have started to test safety, tolerability, PKs and efficacy of these nMAbs. One paramount limitation for the use of nMAbs in clinical settings is the production of large amounts of MAbs and the high costs related to it. Cooperation among public and private institutions coupled with speed of development, rapid safety evaluation and efficacy, and early planning for scale-up and manufacture will be critical for the control of COVID-19 pandemic.

Parainfluenza Virus 5 Priming Followed by SIV/HIV Virus-Like-Particle Boosting Induces Potent and Durable Immune Responses in Nonhuman Primates

The search for a preventive vaccine against HIV infection remains an ongoing challenge, indicating the need for novel approaches. Parainfluenza virus 5 (PIV5) is a paramyxovirus replicating in the upper airways that is not associated with any animal or human pathology. In animal models, PIV5-vectored vaccines have shown protection against influenza, RSV, and other human pathogens. Here, we generated PIV5 vaccines expressing HIV envelope (Env) and SIV Gag and administered them intranasally to macaques, followed by boosting with virus-like particles (VLPs) containing trimeric HIV Env. Moreover, we compared the immune responses generated by PIV5-SHIV prime/VLPs boost regimen in naïve vs a control group in which pre-existing immunity to the PIV5 vector was established. We demonstrate for the first time that intranasal administration of PIV5-based HIV vaccines is safe, well-tolerated and immunogenic, and that boosting with adjuvanted trimeric Env VLPs enhances humoral and cellular immune responses. The PIV5 prime/VLPs boost regimen induced robust and durable systemic and mucosal Env-specific antibody titers with functional activities including ADCC and neutralization. This regimen also induced highly polyfunctional antigen-specific T cell responses. Importantly, we show that diminished responses due to PIV5 pre-existing immunity can be overcome in part with VLP protein boosts. Overall, these results establish that PIV5-based HIV vaccine candidates are promising and warrant further investigation including moving on to primate challenge studies.

Extremely potent human monoclonal antibodies from COVID-19 convalescent patients

Human monoclonal antibodies are safe, preventive, and therapeutic tools that can be rapidly developed to help restore the massive health and economic disruption caused by the coronavirus disease 2019 (COVID-19) pandemic. By single-cell sorting 4,277 SARS-CoV-2 spike protein-specific memory B cells from 14 COVID-19 survivors, 453 neutralizing antibodies were identified. The most potent neutralizing antibodies recognized the spike protein receptor-binding domain, followed in potency by antibodies that recognize the S1 domain, the spike protein trimer, and the S2 subunit. Only 1.4% of them neutralized the authentic virus with a potency of 1–10 ng/mL. The most potent monoclonal antibody, engineered to reduce the risk of antibody-dependent enhancement and prolong half-life, neutralized the authentic wild-type virus and emerging variants containing D614G, E484K, and N501Y substitutions. Prophylactic and therapeutic efficacy in the hamster model was observed at 0.25 and 4 mg/kg respectively in absence of Fc functions.

Modified Adenovirus Prime-Protein Boost Clade C HIV Vaccine Strategy Results in Reduced Viral DNA in Blood and Tissues Following Tier 2 SHIV Challenge

Designing immunogens and improving delivery methods eliciting protective immunity is a paramount goal of HIV vaccine development. A comparative vaccine challenge study was performed in rhesus macaques using clade C HIV Envelope (Env) and SIV Gag antigens. One group was vaccinated using co-immunization with DNA Gag and Env expression plasmids cloned from a single timepoint and trimeric Env gp140 glycoprotein from one of these clones (DNA+Protein). The other group was a prime-boost regimen composed of two replicating simian (SAd7) adenovirus-vectored vaccines expressing Gag and one Env clone from the same timepoint as the DNA+Protein group paired with the same Env gp140 trimer (SAd7+Protein). The env genes were isolated from a single pre-peak neutralization timepoint approximately 1 year post infection in CAP257, an individual with a high degree of neutralization breadth. Both DNA+Protein and SAd7+Protein vaccine strategies elicited significant Env-specific T cell responses, lesser Gag-specific responses, and moderate frequencies of Env-specific T_FH cells. Both vaccine modalities readily elicited systemic and mucosal Env-specific IgG but not IgA. There was a higher frequency and magnitude of ADCC activity in the SAd7+Protein than the DNA+Protein arm. All macaques developed moderate Tier 1 heterologous neutralizing antibodies, while neutralization of Tier 1B or Tier 2 viruses was sporadic and found primarily in macaques in the SAd7+Protein group. Neither vaccine approach provided significant protection from viral acquisition against repeated titered mucosal challenges with a heterologous Tier 2 clade C SHIV. However, lymphoid and gut tissues collected at necropsy showed that animals in both vaccine groups each had significantly lower copies of viral DNA in individual tissues compared to levels in controls. In the SAd7+Protein-vaccinated macaques, total and peak PBMC viral DNA were significantly lower compared with controls. Taken together, this heterologous Tier 2 SHIV challenge study shows that combination vaccination with SAd7+Protein was superior to combination DNA+Protein in reducing viral seeding in tissues in the absence of protection from infection, thus emphasizing the priming role of replication-competent SAd7 vector. Despite the absence of correlates of protection, because antibody responses were significantly higher in this vaccine group, we hypothesize that vaccine-elicited antibodies contribute to limiting tissue viral seeding.

Pharmacokinetics and predicted neutralisation coverage of VRC01 in HIV-uninfected participants of the Antibody Mediated Prevention (AMP) trials

The phase 2b AMP trials are testing whether the broadly neutralising antibody VRC01 prevents HIV-1 infection in two cohorts: women in sub-Saharan Africa, and men and transgender persons who have sex with men (MSM/TG) in the Americas and Switzerland. We used nonlinear mixed effects modelling of longitudinal serum VRC01 concentrations to characterise pharmacokinetics and predict HIV-1 neutralisation coverage. We found that body weight significantly influenced clearance, and that the mean peripheral volume of distribution, steady state volume of distribution, elimination half-life, and accumulation ratio were significantly higher in MSM/TG than in women. Neutralisation coverage was predicted to be higher in the first (versus second) half of a given 8-week infusion interval, and appeared to be higher in MSM/TG than in women overall. Study cohort differences in pharmacokinetics and neutralisation coverage provide insights for interpreting the AMP results and for investigating how VRC01 concentration and neutralisation correlate with HIV incidence.

Development of antibody-dependent cell cytotoxicity function in HIV-1 antibodies

A prerequisite for the design of an HIV vaccine that elicits protective antibodies is understanding the developmental pathways that result in desirable antibody features. The development of antibodies that mediate antibody-dependent cellular cytotoxicity (ADCC) is particularly relevant because such antibodies have been associated with HIV protection in humans. We reconstructed the developmental pathways of six human HIV-specific ADCC antibodies using longitudinal antibody sequencing data. Most of the inferred naive antibodies did not mediate detectable ADCC. Gain of antigen binding and ADCC function typically required mutations in complementarity determining regions of one or both chains. Enhancement of ADCC potency often required additional mutations in framework regions. Antigen binding affinity and ADCC activity were correlated, but affinity alone was not sufficient to predict ADCC potency. Thus, elicitation of broadly active ADCC antibodies may require mutations that enable high-affinity antigen recognition along with mutations that optimize factors contributing to functional ADCC activity.

A matrix of structure-based designs yields improved VRC01-class antibodies for HIV-1 therapy and prevention

Passive transfer of broadly neutralizing antibodies is showing promise in the treatment and prevention of HIV-1. One class of antibodies, the VRC01 class, appears especially promising. To improve VRC01-class antibodies, we combined structure-based design with a matrix-based approach to generate VRC01-class variants that filled an interfacial cavity, used diverse third-complementarity-determining regions, reduced potential steric clashes, or exploited extended contacts to a neighboring protomer within the envelope trimer. On a 208-strain panel, variant VRC01.23LS neutralized 90% of the panel at a geometric mean IC80 less than 1 μg/ml, and in transgenic mice with human neonatal-Fc receptor, the serum half-life of VRC01.23LS was indistinguishable from that of the parent VRC01LS, which has a half-life of 71 d in humans. A cryo-electron microscopy structure of VRC01.23 Fab in complex with BG505 DS-SOSIP.664 Env trimer determined at 3.4-Å resolution confirmed the structural basis for its ~10-fold improved potency relative to VRC01. Another variant, VRC07-523-F54-LS.v3, neutralized 95% of the 208-isolated panel at a geometric mean IC80 of less than 1 μg/ml, with a half-life comparable to that of the parental VRC07-523LS. Our matrix-based structural approach thus enables the engineering of VRC01 variants for HIV-1 therapy and prevention with improved potency, breadth, and pharmacokinetics.

Assessing the safety and pharmacokinetics of the anti-HIV monoclonal antibody CAP256V2LS alone and in combination with VRC07-523LS and PGT121 in South African women: study protocol for the first-in-human CAPRISA 012B phase I clinical trial

INTRODUCTION

New HIV prevention strategies are urgently required. The discovery of broadly neutralising antibodies (bNAbs) has provided the opportunity to evaluate passive immunisation as a potential prevention strategy and facilitate vaccine development. Since 2014, several bNAbs have been isolated from a clade C-infected South African donor, CAPRISA 256. One particular bNAb, CAP256-VRC26.25, was found to be extremely potent, with good coverage against clade C viruses, the dominant HIV clade in sub-Saharan Africa. Challenge studies in non-human primates demonstrated that this antibody was fully protective even at extremely low doses. This bNAb was subsequently structurally engineered and the clinical variant is now referred to as CAP256V2LS.

METHODS AND ANALYSIS

CAPRISA 012B is the second of three trials in the CAPRISA 012 bNAb trial programme. It is a first-in-human, phase I study to assess the safety and pharmacokinetics of CAP256V2LS. The study is divided into four groups. Group 1 is a dose escalation of CAP256V2LS administered intravenously to HIV-negative and HIV-positive women. Group 2 is a dose escalation of CAP256V2LS administered subcutaneously (SC), with and without the dispersing agent recombinant human hyaluronidase (rHuPH20) as single or repeat doses in HIV-negative women. Groups 3 and 4 are randomised placebo controlled to assess two (CAP256V2LS+VRC07-523LS; CAP256V2LS+PGT121) and three (CAP256V2LS+VRC07-523LS+PGT121) bNAb combinations administered SC to HIV-negative women. Safety will be assessed by the frequency of reactogenicity and adverse events related to the study product. Pharmacokinetic disposition of CAP256V2LS alone and in combination with VRC07-523LS and PGT121 will be assessed via dose subgroups and route of administration.

ETHICS AND DISSEMINATION

The University of KwaZulu-Natal Biomedical Research Ethics Committee (BREC) and the South African Health Products Regulatory Authority (SAHPRA) have granted regulatory approval (trial reference numbers: BREC00000857/2019 and SAHPRA 20200123). Trial results will be disseminated through conference presentations, peer-reviewed publications and the clinical trial registry.

TRIAL REGISTRATION NUMBER

PACTR202003767867253; Pre-results.

Broadly Neutralizing Antibodies for HIV Prevention

In the last decade, over a dozen potent broadly neutralizing antibodies (bnAbs) to several HIV envelope protein epitopes have been identified, and their in vitro neutralization profiles have been defined. Many have demonstrated prevention efficacy in preclinical trials and favorable safety and pharmacokinetic profiles in early human clinical trials. The first human prevention efficacy trials using 10 sequential, every-two-month administrations of a single anti-HIV bnAb are anticipated to conclude in 2020. Combinations of complementary bnAbs and multi-specific bnAbs exhibit improved breadth and potency over most individual antibodies and are entering advanced clinical development. Genetic engineering of the Fc regions has markedly improved bnAb half-life, increased mucosal tissue concentrations of antibodies (especially in the genital tract), and enhanced immunomodulatory and Fc effector functionality, all of which improve antibodies' preventative and therapeutic potential. Human-derived monoclonal antibodies are likely to enter the realm of primary care prevention and therapy for viral infections in the near future.

Major Scientific Hurdles in HIV Vaccine Development: Historical Perspective and Future Directions

Following the discovery of HIV as a causative agent of AIDS, the expectation was to rapidly develop a vaccine; but thirty years later, we still do not have a licensed vaccine. Progress has been hindered by the extensive genetic variability of HIV and our limited understanding of immune responses required to protect against HIV acquisition. Nonetheless, valuable knowledge accrued from numerous basic and translational science research studies and vaccine trials has provided insight into the structural biology of the virus, immunogen design and novel vaccine delivery systems that will likely constitute an effective vaccine. Furthermore, stakeholders now appreciate the daunting scientific challenges of developing an effective HIV vaccine, hence the increased advocacy for collaborative efforts among academic research scientists, governments, pharmaceutical industry, philanthropy, and regulatory entities. In this review, we highlight the history of HIV vaccine development efforts, highlighting major challenges and future directions.

Pediatric HIV: the Potential of Immune Therapeutics to Achieve Viral Remission and Functional Cure

PURPOSE OF REVIEW

In the absence of antiretroviral therapy (ART), more than 50% of perinatally HIV-infected children die by 2 years of age. Early ART from infancy is therefore a global recommendation and significantly improves immune health, child survival, and disease outcome. However, even early treatment does not prevent or eradicate the latent reservoir necessitating life-long ART. Adherence to life-long ART is challenging for children and longstanding ART during chronic HIV infection led to higher risks of non-AIDS co-morbidities and virologic failure in infected children. Thus, HIV-infected children are an important population for consideration for immune-based interventions to achieve ART-free remission and functional cure. This review summarizes how the uniqueness of the early life immune system can be harnessed for the development of ART-free remission and functional cure, which means complete virus control in absence of ART. In addition, recent advances in therapeutics in the HIV cure field and their potential for the treatment of pediatric HIV infections are discussed.

RECENT FINDINGS

Preclinical studies and clinical trials demonstrated that immune-based interventions target HIV replication, limit size of virus reservoir, maintain virus suppression, and delay time to virus rebound. However, these studies have been performed so far only in carefully selected HIV-infected adults, highlighting the need to evaluate the efficacy of immune-based therapeutics in HIV-infected children and to design interventions tailored to the early life maturing immune system. Immune-based therapeutics alone or in combination with ART should be actively explored as potential strategies to achieve viral remission and functional cure in HIV-infected pediatric populations.

In vivo delivery of synthetic DNA-encoded antibodies induces broad HIV-1-neutralizing activity

Interventions to prevent HIV-1 infection and alternative tools in HIV cure therapy remain pressing goals. Recently, numerous broadly neutralizing HIV-1 monoclonal antibodies (bNAbs) have been developed that possess the characteristics necessary for potential prophylactic or therapeutic approaches. However, formulation complexities, especially for multiantibody deliveries, long infusion times, and production issues could limit the use of these bNAbs when deployed, globally affecting their potential application. Here, we describe an approach utilizing synthetic DNA-encoded monoclonal antibodies (dmAbs) for direct in vivo production of prespecified neutralizing activity. We designed 16 different bNAbs as dmAb cassettes and studied their activity in small and large animals. Sera from animals administered dmAbs neutralized multiple HIV-1 isolates with activity similar to that of their parental recombinant mAbs. Delivery of multiple dmAbs to a single animal led to increased neutralization breadth. Two dmAbs, PGDM1400 and PGT121, were advanced into nonhuman primates for study. High peak-circulating levels (between 6 and 34 μg/ml) of these dmAbs were measured, and the sera of all animals displayed broad neutralizing activity. The dmAb approach provides an important local delivery platform for the in vivo generation of HIV-1 bNAbs and for other infectious disease antibodies.

Networks of HIV-1 Envelope Glycans Maintain Antibody Epitopes in the Face of Glycan Additions and Deletions

Numerous broadly neutralizing antibodies (bnAbs) have been identified that target the glycans of the HIV-1 envelope spike. Neutralization breadth is notable given that glycan processing can be substantially influenced by the presence or absence of neighboring glycans. Here, using a stabilized recombinant envelope trimer, we investigate the degree to which mutations in the glycan network surrounding an epitope impact the fine glycan processing of antibody targets. Using cryo-electron microscopy and site-specific glycan analysis, we reveal the importance of glycans in the formation of the 2G12 bnAb epitope and show that the epitope is only subtly impacted by variations in the glycan network. In contrast, we show that the PG9 and PG16 glycan-based epitopes at the trimer apex are dependent on the presence of the highly conserved surrounding glycans. Glycan networks underpin the conservation of bnAb epitopes and are an important parameter in immunogen design.

Characterization of Co-Formulated High-Concentration Broadly Neutralizing Anti-HIV-1 Monoclonal Antibodies for Subcutaneous Administration

The discovery of numerous potent and broad neutralizing antibodies (bNAbs) against Human Immunodeficiency Virus type 1 (HIV-1) envelope glycoprotein has invigorated the potential of using them as an effective preventative and therapeutic agent. The majority of the anti-HIV-1 antibodies, currently under clinical investigation, are formulated singly for intra-venous (IV) infusion. However, due to the high degree of genetic variability in the case of HIV-1, a single broad neutralizing antibody will likely not be sufficient to protect against the broad range of viral isolates. To that end, delivery of two or more co-formulated bnAbs against HIV-1 in a single subcutaneous (SC) injection is highly desired. We, therefore, co-formulated two anti-HIV bnAbs, 3BNC117-LS and 10-1074-LS, to a total concentration of 150 mg/mL for SC administration and analyzed them using a panel of analytical techniques. Chromatographic based methods, such as RP-HPLC, CEX-HPLC, SEC-HPLC, were developed to ensure separation and detection of each antibody in the co-formulated sample. In addition, we used a panel of diverse pseudoviruses to detect the functionality of individual antibodies in the co-formulation. We also used these methods to test the stability of the co-formulated antibodies and believe that such an approach can support future efforts towards the formulation and characterization of multiple high-concentration antibodies for SC delivery.

Safety, Tolerability, and Pharmacokinetics of the Broadly Neutralizing Human Immunodeficiency Virus (HIV)-1 Monoclonal Antibody VRC01 in HIV-Exposed Newborn Infants

BACKGROUND

Although mother-to-child human immunodeficiency virus (HIV) transmission has dramatically decreased with maternal antiretroviral therapy, breast milk transmission accounts for most of the 180 000 new infant HIV infections annually. Broadly neutralizing antibodies (bNAb) may further reduce transmission.

METHODS

A Phase 1 safety and pharmacokinetic study was conducted: a single subcutaneous (SC) dose of 20 or 40 mg/kg (Dose Groups 1 and 2, respectively) of the bNAb VRC01 was administered to HIV-exposed infants soon after birth. Breastfeeding infants (Dose Group 3) received 40 mg/kg SC VRC01 after birth and then 20 mg/kg/dose SC monthly. All infants received appropriate antiretroviral prophylaxis.

RESULTS

Forty infants were enrolled (21 in the United States, 19 in Africa). Subcutaneous VRC01 was safe and well tolerated with only mild-to-moderate local reactions, primarily erythema, which rapidly resolved. For multiple-dose infants, local reactions decreased with subsequent injections. VRC01 was rapidly absorbed after administration, with peak concentrations 1-6 days postdose. The 40 mg/kg dose resulted in 13 of 14 infants achieving the serum 50 micrograms (mcg)/mL target at day 28. Dose Group 3 infants maintained concentrations greater than 50 mcg/mL throughout breastfeeding.

CONCLUSIONS

Subcutaneous VRC01 as single or multiple doses is safe and well tolerated in very young infants and is suitable for further study to prevent HIV transmission in infants.

HIV-1 antibodies in prevention of transmission

PURPOSE OF REVIEW

To present the data that suggest that antibodies to HIV may prevent HIV-1 infection.

RECENT FINDINGS

Many human monoclonal broadly neutralizing antibodies (bnAbs) have been isolated over the last decade. Numerous experiments of passive immunization in nonhuman primate models have allowed to accumulate strong evidences that bnAbs, opposed to nonneutralizing antibodies, are the best candidates to prevent HIV-1 infection. bnAbs counteract HIV-1 by both blocking the virus at the portal of entry and clearing rapidly viral foci established at distance after dissemination of the virus following infection. Cocktails of bnAbs or modified bi/trispecific antibodies will be necessary to counter the large and evolving antigenic diversity of the HIV-1 species. Two large multicenter phase IIb clinical trials have been initiated. Even if they are not conducted with the most recent and most potent bnAb, the results which are expected in 2022 will inform us on the real potency of bnAbs at preventing HIV-1 acquisition in the real life.

SUMMARY

If these trials demonstrate the efficacy of bnAbs, they will open the trail toward new strategies for preexposure prophylaxis, eventually postexposure prophylaxis and prevention of mother-to-child transmission.

Coevolution of HIV-1 and broadly neutralizing antibodies

PURPOSE OF REVIEW

Exploring the molecular details of the coevolution of HIV-1 Envelope with broadly neutralizing antibodies (bNAbs) in infected individuals over time provides insights for vaccine design. Since mid-2017, the number of individuals described in such publications has nearly tripled. New publications have extended such studies to new epitopes on Env and provided more detail on previously known sites.

RECENT FINDINGS

Studies of two donors - one of them an infant, the other with three lineages targeting the same site - has deepened our understanding of V3-glycan-directed lineages. A V2-apex-directed lineage showed remarkable similarity to a lineage from a previously described donor, revealing general principles for this class of bNAbs. Understanding development of CD4 binding site antibodies has been enriched by the study of a VRC01-class lineage. Finally, the membrane-proximal external region is a new addition to the set of epitopes studied in this manner, with early development events explored in a study of three lineages from a single donor.

SUMMARY

These studies provide templates for immunogen design to elicit bNAbs against a widened set of epitopes, generating new directions in the quest for an HIV vaccine.

Neutralizing antibodies for HIV-1 prevention

PURPOSE OF REVIEW

In the absence of a protective vaccine against HIV-1, passive immunization using novel broadly neutralizing antibodies (bNAbs) is an attractive concept for HIV-1 prevention. Here, we summarize the results of preclinical and clinical studies of bNAbs, discuss strategies for optimizing bNAb efficacy and lay out current pathways for the development of bNAbs as prophylaxis.

RECENT FINDINGS

Passive transfer of second-generation bNAbs results inpotent protection against infection in preclinical animal models. Furthermore, multiple bNAbs targeting different epitopes on the HIV-1 envelope trimer are in clinical evaluation and have demonstrated favorable safety profiles and robust antiviral activity in chronically infected individuals. The confirmation that passive immunization with bNAb(s) will prevent HIV-1 acquisition in humans is pending and the focus of ongoing investigations. Given the global diversity of HIV-1, bNAb combinations or multispecific antibodies will most likely be required to produce the necessary breadth for effective protection.

SUMMARY

Encouraging results from preclinical and clinical studies support the development of bNAbs for prevention and a number of antibodies with exceptional breadth and potency are available for clinical evaluation. Further optimization of viral coverage and antibody half-life will accelerate the clinical implementation of bNAbs as a critical tool for HIV-1 prevention strategies.