Early short-term treatment with neutralizing human monoclonal antibodies halts SHIV infection in infant macaques

Preventing perinatal HIV acquisition; current gaps and future perspectives

PURPOSE OF REVIEW

Although current treatment could eradicate vertical transmission, in 2022, 130 000 infants acquired HIV globally. HIV suppression with antiretroviral therapy (ART) transforms survival for people living with HIV (PLWH), and prevents transmission, including vertical. International guidelines recommend lifelong ART for PLWH, consequently perinatal HIV acquisition reflects implementation gaps in the HIV care cascade. We summarize these gaps, exploring potential novel approaches and therapeutic innovations towards eliminating vertical HIV transmission.

RECENT FINDINGS

Multifactorial challenges continue to underpin gaps in the HIV care cascade, including accessibility, availability and sustainability of HIV testing, prevention and treatment, alongside stigma, gender-based violence and poverty. Long-acting ART may be important in preventing perinatal HIV acquisition, with early data demonstrating tolerability and efficacy of injectable ART throughout pregnancy, both as HIV treatment and prevention. Carefully selected long-acting broadly neutralizing antibodies (bNAbs) matching circulating, exposing viral envelope sequences have demonstrated safety, clinical trials are ongoing to demonstrate efficacy.

SUMMARY

Emerging clinical studies should prioritize pregnant/lactating people and infants to ensure such therapies are well tolerated and efficacious. Alongside therapeutic innovation, programmatic strategies must address social and economic challenges, ensuring sustainable HIV treatment/prevention programmes and facilitating global elimination of blood-borne viruses.

Engineered deletions of HIV replicate conditionally to reduce disease in nonhuman primates

Antiviral therapies with reduced frequencies of administration and high barriers to resistance remain a major goal. For HIV, theories have proposed that viral-deletion variants, which conditionally replicate with a basic reproductive ratio [R0] > 1 (termed "therapeutic interfering particles" or "TIPs"), could parasitize wild-type virus to constitute single-administration, escape-resistant antiviral therapies. We report the engineering of a TIP that, in rhesus macaques, reduces viremia of a highly pathogenic model of HIV by >3log10 following a single intravenous injection. Animal lifespan was significantly extended, TIPs conditionally replicated and were continually detected for >6 months, and sequencing data showed no evidence of viral escape. A single TIP injection also suppressed virus replication in humanized mice and cells from persons living with HIV. These data provide proof of concept for a potential new class of single-administration antiviral therapies.

Pediatric immunotherapy and HIV control

PURPOSE OF REVIEW

Highlighting opportunities/potential for immunotherapy by understanding dynamics of HIV control during pediatric HIV infection with and without antiretroviral therapy (ART), as modeled in Simian immunodeficiency virus (SIV) and Simian-human immunodeficiency virus (SHIV)-infected rhesus macaques and observed in clinical trials. This review outlines mode of transmission, pathogenesis of pediatric HIV, unique aspects of the infant immune system, infant macaque models and immunotherapies.

RECENT FINDINGS

During the earliest stages of perinatal HIV infection, the infant immune system is characterized by a unique environment defined by immune tolerance and lack of HIV-specific T cell responses which contribute to disease progression. Moreover, primary lymphoid organs such as the thymus appear to play a distinct role in HIV pathogenesis in children living with HIV (CLWH). Key components of the immune system determine the degree of viral control, targets for strategies to induce viral control, and the response to immunotherapy. The pursuit of highly potent broadly neutralizing antibodies (bNAbs) and T cell vaccines has revolutionized the approach to HIV cure. Administration of HIV-1-specific bNAbs, targeting the highly variable envelope improves humoral immunity, and T cell vaccines induce or improve T cell responses such as the cytotoxic effects of HIV-1-specific CD8+ T cells, both of which are promising options towards virologic control and ART-free remission as evidenced by completed and ongoing clinical trials.

SUMMARY

Understanding early events during HIV infection and disease progression in CLWH serves as a foundation for predicting or targeting later outcomes by harnessing the immune system's natural responses. The developing pediatric immune system offers multiple opportunities for specific long-term immunotherapies capable of improving quality of life during adolescence and adulthood.

Novel approaches to enable equitable access to monoclonal antibodies in low- and middle-income countries

Monoclonal antibodies (mAbs) are revolutionizing management of non-communicable diseases in high-income countries and are increasingly being advanced for a range of infectious diseases (IDs). However, access to existing mAbs is limited in low- and middle-income countries (LMICs), and investment in developing fit-for-purpose mAbs for IDs that disproportionately affect LMICs has been limited. Underlying these access barriers are systemic challenges, including a lack of commercial incentives to target LMIC markets and complexity in manufacturing and regulatory processes. Novel strategies are needed to overcome systemic access barriers for mAbs. We outline key areas where new approaches could address these barriers, based on a multistakeholder consultation in March 2023. Three disease-market archetypes are identified to guide thinking about business models tailored to different contexts. New business models are needed to incentivize development and manufacturing of ID mAbs and to ensure mAbs are optimized with a target product profile and cost of goods that enable use in diverse LMIC settings. Lessons can be applied from voluntary licensing strategies and product development partnerships that have shown success in catalysing development and affordable supply for a range of infectious diseases. Technology transfer will be key to expand LMIC research and manufacturing capacity and to enable sustainable and diversified supply. Improved market intelligence, demand aggregation mechanisms, and portfolio-based manufacturing models could be used to de-risk commercial investment and establish a sustainable manufacturing ecosystem for affordable mAbs. Novel regulatory approaches and robust technology transfer may reduce data requirements and timelines for biosimilar approvals. Trailblazer products, with coordinated "end-to-end" support from funders, can demonstrate proof of concept for pathways to accessible mAbs across a broader range of LMICs. Research funders; local, regional, global health agencies; and, private sector partners should commit to implementing innovative partnerships and end-to-end strategies that enable equitable access to mAbs for infectious diseases in LMICs.

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.

More than the Infinite Monkey Theorem: NHP Models in the Development of a Pediatric HIV Cure

PURPOSE OF REVIEW

An HIV cure that eliminates the viral reservoir or provides viral control without antiretroviral therapy (ART) is an urgent need in children as they face unique challenges, including lifelong ART adherence and the deleterious effects of chronic immune activation. This review highlights the importance of nonhuman primate (NHP) models in developing an HIV cure for children as these models recapitulate the viral pathogenesis and persistence.

RECENT FINDINGS

Several cure approaches have been explored in infant NHPs, although knowledge gaps remain. Broadly neutralizing antibodies (bNAbs) show promise for controlling viremia and delaying viral rebound after ART interruption but face administration challenges. Adeno-associated virus (AAV) vectors hold the potential for sustained bNAb expression. Therapeutic vaccination induces immune responses against simian retroviruses but has yet to impact the viral reservoir. Combining immunotherapies with latency reversal agents (LRAs) that enhance viral antigen expression should be explored. Current and future cure approaches will require adaptation for the pediatric immune system and unique features of virus persistence, for which NHP models are fundamental to assess their efficacy.

Cost-effectiveness of broadly neutralizing antibodies for infant HIV prophylaxis in settings with high HIV burdens: a simulation modeling study

Introduction

Approximately 130 000 infants acquire HIV annually despite global maternal antiretroviral therapy scale-up. We evaluated the potential clinical impact and cost-effectiveness of offering long-acting, anti-HIV broadly neutralizing antibody (bNAb) prophylaxis to infants in three distinct settings.

Methods

We simulated infants in Côte d'Ivoire, South Africa, and Zimbabwe using the Cost-Effectiveness of Preventing AIDS Complications-Pediatric (CEPAC-P) model. We modeled strategies offering a three-bNAb combination in addition to WHO-recommended standard-of-care oral prophylaxis to infants: a) with known, WHO-defined high-risk HIV exposure at birth (HR-HIVE); b) with known HIV exposure at birth (HIVE); or c) with or without known HIV exposure (ALL). Modeled infants received 1-dose, 2-doses, or Extended (every 3 months through 18 months) bNAb dosing. Base case model inputs included 70% bNAb efficacy (sensitivity analysis range: 10-100%), 3-month efficacy duration/dosing interval (1-6 months), and $20/dose cost ($5-$100/dose). Outcomes included pediatric HIV infections, life expectancy, lifetime HIV-related costs, and incremental cost-effectiveness ratios (ICERs, in US$/year-of-life-saved [YLS], assuming a ≤50% GDP per capita cost-effectiveness threshold).

Results

The base case model projects that bNAb strategies targeting HIVE and ALL infants would prevent 7-26% and 10-42% additional pediatric HIV infections, respectively, compared to standard-of-care alone, ranging by dosing approach. HIVE-Extended would be cost-effective (cost-saving compared to standard-of-care) in Côte d'Ivoire and Zimbabwe; ALL-Extended would be cost-effective in South Africa (ICER: $882/YLS). BNAb strategies targeting HR-HIVE infants would result in greater lifetime costs and smaller life expectancy gains than HIVE-Extended. Throughout most bNAb efficacies and costs evaluated in sensitivity analyses, targeting HIVE infants would be cost-effective in Côte d'Ivoire and Zimbabwe, and targeting ALL infants would be cost-effective in South Africa.

Discussion

Adding long-acting bNAbs to current standard-of-care prophylaxis would be cost-effective, assuming plausible efficacies and costs. The cost-effective target population would vary by setting, largely driven by maternal antenatal HIV prevalence and postpartum incidence.

Evidence for the Role of a Second Fc-Binding Receptor in Placental IgG Transfer in Nonhuman Primates

Transplacental transfer of maternal antibodies provides the fetus and newborn with passive protection against infectious diseases. While the role of the highly conserved neonatal Fc receptor (FcRn) in transfer of IgG in mammals is undisputed, recent reports have suggested that a second receptor may contribute to transport in humans. We report poor transfer efficiency of plant-expressed recombinant HIV-specific antibodies, including engineered variants with high FcRn affinity, following subcutaneous infusion into rhesus macaques close to parturition. Unexpectedly, unlike those derived from mammalian tissue culture, plant-derived antibodies were essentially unable to cross macaque placentas. This defect was associated with poor Fcγ receptor binding and altered Fc glycans and was not recapitulated in mice. These results suggest that maternal-fetal transfer of IgG across the three-layer primate placenta may require a second receptor and suggest a means of providing maternal antibody treatments during pregnancy while avoiding fetal harm. IMPORTANCE This study compared the ability of several human HIV envelope-directed monoclonal antibodies produced in plants with the same antibodies produced in mammalian cells for their ability to cross monkey and mouse placentas. We found that the two types of antibodies have comparable transfer efficiencies in mice, but they are differentially transferred across macaque placentas, consistent with a two-receptor IgG transport model in primates. Importantly, plant-produced monoclonal antibodies have excellent binding characteristics for human FcRn receptors, permitting desirable pharmacokinetics in humans. The lack of efficient transfer across the primate placenta suggests that therapeutic plant-based antibody treatments against autoimmune diseases and cancer could be provided to the mother while avoiding transfer and preventing harm to the fetus.

Cost-effectiveness of broadly neutralizing antibody prophylaxis for HIV-exposed infants in sub-Saharan African settings

INTRODUCTION

Infant HIV prophylaxis with broadly neutralizing anti-HIV antibodies (bNAbs) could provide long-acting protection against vertical transmission. We sought to estimate the potential clinical impact and cost-effectiveness of hypothetical bNAb prophylaxis programmes for children known to be HIV exposed at birth in three sub-Saharan African settings.

METHODS

We conducted a cost-effectiveness analysis using the CEPAC-Pediatric model, simulating cohorts of infants from birth through death in Côte d'Ivoire, South Africa and Zimbabwe. These settings were selected to reflect a broad range of HIV care cascade characteristics, antenatal HIV prevalence and budgetary constraints. We modelled strategies targeting bNAbs to only WHO-designated "high-risk" HIV-exposed infants (HR-HIVE) or to all HIV-exposed infants (HIVE). We compared four prophylaxis approaches within each target population: standard of care oral antiretroviral prophylaxis (SOC), and SOC plus bNAbs at birth (1-dose), at birth and 3 months (2-doses), or every 3 months throughout breastfeeding (Extended). Base-case model inputs included bNAb efficacy (60%/dose), effect duration (3 months/dose) and costs ($60/dose), based on published literature. Outcomes included paediatric HIV incidence and incremental cost-effectiveness ratios (ICERs) calculated from discounted life expectancy and lifetime HIV-related costs.

RESULTS

The model projects that bNAbs would reduce absolute infant HIV incidence by 0.3-2.2% (9.6-34.9% relative reduction), varying by country, prophylaxis approach and target population. In all three settings, HR-HIVE-1-dose would be cost-saving compared to SOC. Using a 50% GDP per capita ICER threshold, HIVE-Extended would be cost-effective in all three settings with ICERs of $497/YLS in Côte d'Ivoire, $464/YLS in South Africa and $455/YLS in Zimbabwe. In all three settings, bNAb strategies would remain cost-effective at costs up to $200/dose if efficacy is ≥30%. If the bNAb effect duration were reduced to 1 month, the cost-effective strategy would become HR-HIVE-1-dose in Côte d'Ivoire and Zimbabwe and HR-HIVE-2-doses in South Africa. Findings regarding the cost-effectiveness of bNAb implementation strategies remained robust in sensitivity analyses regarding breastfeeding duration, maternal engagement in postpartum care, early infant diagnosis uptake and antiretroviral treatment costs.

CONCLUSIONS

At current efficacy and cost estimates, bNAb prophylaxis for HIV-exposed children in sub-Saharan African settings would be a cost-effective intervention to reduce vertical HIV transmission.

Monoclonal Antibodies as Long-Acting Products: What Are We Learning From Human Immunodeficiency Virus (HIV) and Coronavirus Disease 2019 (COVID-19)?

Broadly neutralizing antibodies directed against human immunodeficiency virus (HIV) offer promise as long-acting agents for prevention and treatment of HIV. Progress and challenges are discussed. Lessons may be learned from the development of monoclonal antibodies to treat and prevent COVID-19.

HIV-1 Vpu restricts Fc-mediated effector functions in vivo

Non-neutralizing antibodies (nnAbs) can eliminate HIV-1-infected cells via antibody-dependent cellular cytotoxicity (ADCC) and were identified as a correlate of protection in the RV144 vaccine trial. Fc-mediated effector functions of nnAbs were recently shown to alter the course of HIV-1 infection in vivo using a vpu-defective virus. Since Vpu is known to downregulate cell-surface CD4, which triggers conformational changes in the viral envelope glycoprotein (Env), we ask whether the lack of Vpu expression was linked to the observed nnAbs activity. We find that restoring Vpu expression greatly reduces nnAb recognition of infected cells, rendering them resistant to ADCC. Moreover, administration of nnAbs in humanized mice reduces viral loads only in animals infected with a vpu-defective but not with a wild-type virus. CD4-mimetics administration, known to "open" Env and expose nnAb epitopes, renders wild-type viruses sensitive to nnAbs Fc-effector functions. This work highlights the importance of Vpu-mediated evasion of humoral responses.

Antibody class-switching as a strategy to improve HIV-1 neutralization

Broadly neutralizing antibodies (bNAbs), when administered through passive immunization, are protective against HIV-1 infection. Current HIV-1 vaccine strategies are aimed at guiding the immune system to make bNAbs by mimicking their development during infection. Somatic hypermutation of the variable region is known to be crucial for the development of bNAbs. More recently, however, studies have shown how class-switch recombination (CSR) resulting in the generation of different antibody isotypes may serve as an additional mechanism through which antibodies can gain neutralization breadth and potency. In this review, we discuss the importance of different antibody isotypes for HIV-1 neutralization breadth and potency and how this information can be leveraged to improve passive and active immunization against HIV-1.

Early treatment regimens achieve sustained virologic remission in infant macaques infected with SIV at birth

Early antiretroviral therapy (ART) in HIV-infected infants generally fails to achieve a sustained state of ART-free virologic remission, even after years of treatment. Our studies show that viral reservoir seeding is different in neonatal macaques intravenously exposed to SIV at birth, in contrast to adults. Furthermore, one month of ART including an integrase inhibitor, initiated at day 3, but not day 4 or 5 post infection, efficiently and rapidly suppresses viremia to undetectable levels. Intervention initiated at day 3 post infection and continued for 9 months achieves a sustained virologic remission in 4 of 5 infants. Collectively, an early intervention strategy within a key timeframe and regimen may result in viral remission or successful post-exposure prophylaxis for neonatal SIV infection, which may be clinically relevant for optimizing treatment strategies for HIV-infected or exposed infants.

Challenges and Opportunities of Therapies Targeting Early Life Immunity for Pediatric HIV Cure

Early initiation of antiretroviral therapy (ART) significantly improves clinical outcomes and reduces mortality of infants/children living with HIV. However, the ability of infected cells to establish latent viral reservoirs shortly after infection and to persist during long-term ART remains a major barrier to cure. In addition, while early ART treatment of infants living with HIV can limit the size of the virus reservoir, it can also blunt HIV-specific immune responses and does not mediate clearance of latently infected viral reservoirs. Thus, adjunctive immune-based therapies that are geared towards limiting the establishment of the virus reservoir and/or mediating the clearance of persistent reservoirs are of interest for their potential to achieve viral remission in the setting of pediatric HIV. Because of the differences between the early life and adult immune systems, these interventions may need to be tailored to the pediatric settings. Understanding the attributes and specificities of the early life immune milieu that are likely to impact the virus reservoir is important to guide the development of pediatric-specific immune-based interventions towards viral remission and cure. In this review, we compare the immune profiles of pediatric and adult HIV elite controllers, discuss the characteristics of cellular and anatomic HIV reservoirs in pediatric populations, and highlight the potential values of current cure strategies using immune-based therapies for long-term viral remission in the absence of ART in children living with HIV.

Optimizing clinical dosing of combination broadly neutralizing antibodies for HIV prevention

Broadly neutralizing antibodies (bNAbs) are promising agents to prevent HIV infection and achieve HIV remission without antiretroviral therapy (ART). As with ART, bNAb combinations are likely needed to cover HIV's extensive diversity. Not all bNAbs are identical in terms of their breadth, potency, and in vivo longevity (half-life). Given these differences, it is important to optimally select the composition, or dose ratio, of combination bNAb therapies for future clinical studies. We developed a model that synthesizes 1) pharmacokinetics, 2) potency against a wide HIV diversity, 3) interaction models for how drugs work together, and 4) correlates that translate in vitro potency to clinical protection. We found optimization requires drug-specific balances between potency, longevity, and interaction type. As an example, tradeoffs between longevity and potency are shown by comparing a combination therapy to a bi-specific antibody (a single protein merging both bNAbs) that takes the better potency but the worse longevity of the two components. Then, we illustrate a realistic dose ratio optimization of a triple combination of VRC07, 3BNC117, and 10-1074 bNAbs. We apply protection estimates derived from both a non-human primate (NHP) challenge study meta-analysis and the human antibody mediated prevention (AMP) trials. In both cases, we find a 2:1:1 dose emphasizing VRC07 is nearly optimal. Our approach can be immediately applied to optimize the next generation of combination antibody prevention and cure studies.

Vaccine-Induced, High-Magnitude HIV Env-Specific Antibodies with Fc-Mediated Effector Functions Are Insufficient to Protect Infant Rhesus Macaques against Oral SHIV Infection

Improved access to antiretroviral therapy (ART) and antenatal care has significantly reduced in utero and peripartum mother-to-child human immunodeficiency virus (HIV) transmission. However, as breast milk transmission of HIV still occurs at an unacceptable rate, there remains a need to develop an effective vaccine for the pediatric population. Previously, we compared different HIV vaccine strategies, intervals, and adjuvants in infant rhesus macaques to optimize the induction of HIV envelope (Env)-specific antibodies with Fc-mediated effector function. In this study, we tested the efficacy of an optimized vaccine regimen against oral simian-human immunodeficiency virus (SHIV) acquisition in infant macaques. Twelve animals were immunized with 1086.c gp120 protein adjuvanted with 3M-052 in stable emulsion and modified vaccinia Ankara (MVA) virus expressing 1086.c HIV Env. Twelve control animals were immunized with empty MVA. The vaccine prime was given within 10 days of birth, with booster doses being administered at weeks 6 and 12. The vaccine regimen induced Env-specific plasma IgG antibodies capable of antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP). Beginning at week 15, infants were exposed orally to escalating doses of heterologous SHIV-1157(QNE)Y173H once a week until infected. Despite the induction of strong Fc-mediated antibody responses, the vaccine regimen did not reduce the risk of infection or time to acquisition compared to controls. However, among vaccinated animals, ADCC postvaccination and postinfection was associated with reduced peak viremia. Thus, nonneutralizing Env-specific antibodies with Fc effector function elicited by this vaccine regimen were insufficient for protection against heterologous oral SHIV infection shortly after the final immunization but may have contributed to control of viremia. IMPORTANCE Women of childbearing age are three times more likely to contract HIV infection than their male counterparts. Poor HIV testing rates coupled with low adherence to antiretroviral therapy (ART) result in a high risk of mother-to-infant HIV transmission, especially during the breastfeeding period. A preventative vaccine could curb pediatric HIV infections, reduce potential health sequalae, and prevent the need for lifelong ART in this population. The results of the current study imply that the HIV Env-specific IgG antibodies elicited by this candidate vaccine regimen, despite a high magnitude of Fc-mediated effector function but a lack of neutralizing antibodies and polyfunctional T cell responses, were insufficient to protect infant rhesus macaques against oral virus acquisition.

Immunotherapeutic approaches to HIV cure and remission

PURPOSE OF REVIEW

Despite improvements in the effectiveness of antiretroviral therapy (ART), there are still unmet needs for people living with HIV which drive the search for a cure for HIV infection. The goal of this review is to discuss the challenges and recent immunotherapeutic advances towards developing a safe, effective and durable cure strategy for HIV.

RECENT FINDINGS

In recent years, advances have been made in uncovering the mechanisms of persistence of latent HIV and in developing more accurate assays to measure the intact proviral reservoir. Broadly neutralising antibodies and modern techniques to enhance antibody responses have shown promising results. Other strategies including therapeutic vaccination, latency reversal agents, and immunomodulatory agents have shown limited success, but newer interventions including engineered T cells and other immunotherapies may be a potent and flexible strategy for achieving HIV cure.

SUMMARY

Although progress with newer cure strategies may be encouraging, challenges remain and it is essential to achieve a high threshold of safety and effectiveness in the era of safe and effective ART. It is likely that to achieve sustained HIV remission or cure, a multipronged approach involving a combination of enhancing both adaptive and innate immunity is required.

Single-chain variable fragments of broadly neutralizing antibodies prevent HIV cell-cell transmission

Broadly neutralizing antibodies (bNAbs) are able to prevent HIV infection following passive administration. Single-chain variable fragments (scFv) may have advantages over IgG as their smaller size permits improved diffusion into mucosal tissues. We have previously shown that scFv of bNAbs retain significant breadth and potency against cell-free viral transmission in a TZM-bl assay. However, scFv have not been tested for their ability to block cell-cell transmission, a model in which full-sized bNAbs lose potency. We tested 4 scFv (CAP256.25, PGT121, 3BNC117 and 10E8v4) compared to IgG, in free-virus and cell-cell neutralization assays in A3.01 cells, against a panel of seven heterologous viruses. We show that free-virus neutralization titers in the TZM-bl and A3.01 assays were not significantly different, and confirm that scFv show a 1 to 32-fold reduction in activity in the cell-free model, compared to IgG. However, whereas IgG show 3.4 to 19-fold geometric mean potency loss in cell-cell neutralization compared to free-virus transmission, scFv had more comparable activity in the two assays, with only a 1.3 to 2.3-fold reduction. Geometric mean IC₅₀ of scFv for cell-cell transmission ranged from 0.65 μg/ml (10E8v4) to 2.3 μg/ml (3BNC117) with IgG and scFv neutralization showing similar potency against cell-associated transmission. Therefore, despite the reduced activity of scFv in cell-free assays, their retention of activity in the cell-cell format may make scFv useful for the prevention of both modes of transmission in HIV prevention studies. Importance Broadly neutralizing antibodies (bNAbs) are a major focus for passive immunization against HIV, with the recently concluded HVTN AMP (Antibody Mediated Protection) trial providing proof of concept. Most studies focus on cell-free HIV, however cell-associated virus may play a significant role in HIV infection, pathogenesis and latency. Single-chain variable fragments (scFv) of antibodies may have increased tissue penetration, and reduced immunogenicity. We previously demonstrated that scFv of four HIV-directed bNAbs (CAP256-VRC26.25, PGT121, 3BNC117 and 10E8v4) retain significant potency and breadth against cell-free HIV. As some bNAbs have been shown to lose potency against cell-associated virus, we investigated the ability of bNAb scFv to neutralize this mode of transmission. We demonstrate that unlike IgG, scFv of bNAbs are able to neutralize cell-free and cell-associated virus with similar potency. These scFv, which show functional activity in the therapeutic range, may therefore be suitable for further development as passive immunity for HIV prevention.

Research priorities for an HIV cure: International AIDS Society Global Scientific Strategy 2021

Despite the success of antiretroviral therapy (ART) for people living with HIV, lifelong treatment is required and there is no cure. HIV can integrate in the host genome and persist for the life span of the infected cell. These latently infected cells are not recognized as foreign because they are largely transcriptionally silent, but contain replication-competent virus that drives resurgence of the infection once ART is stopped. With a combination of immune activators, neutralizing antibodies, and therapeutic vaccines, some nonhuman primate models have been cured, providing optimism for these approaches now being evaluated in human clinical trials. In vivo delivery of gene-editing tools to either target the virus, boost immunity or protect cells from infection, also holds promise for future HIV cure strategies. In this Review, we discuss advances related to HIV cure in the last 5 years, highlight remaining knowledge gaps and identify priority areas for research for the next 5 years.

Broadly neutralizing monoclonal antibodies for HIV prevention

INTRODUCTION

The last 12 years have seen remarkable progress in the isolation and characterization of at least five different epitope classes of HIV-specific broadly neutralizing antibodies (bnAbs). Detailed analyses of these bnAb lineages, maturation pathways and epitopes have created new opportunities for vaccine development. In addition, interest exists in passive administration of monoclonal antibodies as a viable option for HIV prevention.

DISCUSSION

Recently, two antibody-mediated prevention (AMP) trials of a passively administered monoclonal antibody targeting the HIV envelope CD4 binding site, called VRC01, provided proof-of-concept that monoclonal antibody infusion could offer protection against HIV acquisition. While the trials failed to show overall protection against HIV acquisition, sub-analyses revealed that VRC01 infusion provided a 75% prevention efficacy against HIV strains that were susceptible to the antibody. The study also demonstrated that in vitro neutralizing activity, measured by the TZM-bl/pseudovirus assay, was able to predict HIV prevention efficacy in humans. In addition, the AMP trials defined a threshold protective concentration, or neutralization titer, for the VRC01 class of bnAbs, explaining the observed low overall efficacy and serving as a benchmark for the clinical testing of new bnAbs, bnAb cocktails and neutralizing antibody-inducing vaccines. Newer bnAbs that exhibit greater potency and breadth of neutralization in vitro than VRC01 are available for clinical testing. Combinations of best-in-class bnAbs with complementary magnitude, breadth and extent of complete neutralization are predicted to far exceed the prevention efficacy of VRC01. Some engineered bi- and trispecific mAbs exhibit similar desirable neutralizing activity and afford advantages for manufacturing and delivery. Modifications that prolong the serum half-life and improve genital tissue persistence offer additional advantages.

CONCLUSIONS

Iterative phase 1 trials are acquiring safety and pharmacokinetic data on dual and triple bnAbs and bi- and trispecific antibodies in preparation for future AMP studies that seek to translate findings from the VRC01 efficacy trials and achieve acceptable levels of overall prevention efficacy.

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.

Eliminating HIV transmission through breast milk from women taking antiretroviral drugs

Ameena Goga and colleagues argue that frequent testing of maternal viral load is needed to eliminate HIV transmission through breast milk in low and middle income settings

Preventive HIV Vaccines-Leveraging on Lessons from the Past to Pave the Way Forward

Almost four decades on, since the 1980’s, with hundreds of HIV vaccine candidates tested in both non-human primates and humans, and several HIV vaccines trials later, an efficacious HIV vaccine continues to evade us. The enormous worldwide genetic diversity of HIV, combined with HIV’s inherent recombination and high mutation rates, has hampered the development of an effective vaccine. Despite the advent of antiretrovirals as pre-exposure prophylaxis and preventative treatment, which have shown to be effective, HIV infections continue to proliferate, highlighting the great need for a vaccine. Here, we provide a brief history for the HIV vaccine field, with the most recent disappointments and advancements. We also provide an update on current passive immunity trials, testing proof of the concept of the most clinically advanced broadly neutralizing monoclonal antibodies for HIV prevention. Finally, we include mucosal immunity, the importance of vaccine-elicited immune responses and the challenges thereof in the most vulnerable environment–the female genital tract and the rectal surfaces of the gastrointestinal tract for heterosexual and men who have sex with men transmissions, respectively.

Concordance of immunological events between intrarectal and intravenous SHIVAD8-EO infection when assessed by Fiebig-equivalent staging

Primary HIV-1 infection can be classified into six Fiebig stages based on virological and serological laboratory testing, whereas simian-HIV (SHIV) infection in nonhuman primates (NHPs) is defined in time post-infection, making it difficult to extrapolate NHP experiments to the clinics. We identified and extensively characterized the Fiebig-equivalent stages in NHPs challenged intrarectally or intravenously with SHIVAD8-EO. During the first month post-challenge, intrarectally challenged monkeys were up to 1 week delayed in progression through stages. However, regardless of the challenge route, stages I-II predominated before, and stages V-VI predominated after, peak viremia. Decrease in lymph node (LN) CD4+ T cell frequency and rise in CD8+ T cells occurred at stage V. LN virus-specific CD8+ T cell responses, dominated by degranulation and TNF, were first detected at stage V and increased at stage VI. A similar late elevation in follicular CXCR5+ CD8+ T cells occurred, consistent with higher plasma CXCL13 levels at these stages. LN SHIVAD8-EO RNA+ cells were present at stage II, but appeared to decline at stage VI when virions accumulated in follicles. Fiebig-equivalent staging of SHIVAD8-EO infection revealed concordance of immunological events between intrarectal and intravenous infection despite different infection progressions, and can inform comparisons of NHP studies with clinical data.

Immunotherapy during the acute SHIV infection of macaques confers long-term suppression of viremia

We report that combination bNAb immunotherapy initiated on day 3 post-infection (PI) maintained durable CD8+ T cell-mediated suppression of SHIVAD8 viremia and preinoculation levels of CD4+ T cells in 9 of 13 treated monkeys during nearly 6 yr of observation, as assessed by successive CD8+ T cell-depletion experiments. In an extension of that study, two treatment interventions (bNAbs alone or cART plus bNAbs) beginning on week 2 PI were conducted and conferred controller status to 7 of 12 monkeys that was also dependent on control mediated by CD8+ cells. However, the median time to suppression of plasma viremia following intervention on week 2 was markedly delayed (85 wk) compared with combination bNAb immunotherapy initiated on day 3 (39 wk). In both cases, the principal correlate of virus control was the induction of CD8+ T cellular immunity.

Protection of Newborn Macaques by Plant-Derived HIV Broadly Neutralizing Antibodies: a Model for Passive Immunotherapy during Breastfeeding

Preventing human immunodeficiency virus (HIV) infection in newborns by vertical transmission remains an important unmet medical need in resource-poor areas where antiretroviral therapy (ART) is not available and mothers and infants cannot be treated prepartum or during the breastfeeding period. In the present study, the protective efficacy of the potent HIV-neutralizing antibodies PGT121 and VRC07-523, both produced in plants, were assessed in a multiple-SHIV (simian-human immunodeficiency virus)-challenge breastfeeding macaque model. Newborn macaques received either six weekly subcutaneous injections with PGT121 alone or as a cocktail of PGT121-LS plus VRC07-523-LS injected three times every 2 weeks. Viral challenge with SHIVSF162P3 was twice weekly over 5.5 weeks using 11 exposures. Despite the transient presence of plasma viral RNA either immediately after the first challenge or as single-point blips, the antibodies prevented a productive infection in all babies with no sustained plasma viremia, compared to viral loads ranging from 103 to 5 × 108 virions/ml in four untreated controls. No virus was detected in peripheral blood mononuclear cells (PBMCs), and only 3 of 159 tissue samples were weakly positive in the treated babies. Newborn macaques proved to be immunocompetent, producing transient anti-Env antibodies and anti-drug antibody (ADA), which were maintained in the circulation after passive broadly neutralizing antibody clearance. ADA responses were directed to the IgG1 Fc CH2-CH3 domains, which has not been observed to date in adult monkeys passively treated with PGT121 or VRC01. In addition, high levels of VRC07-523 anti-idiotypic antibodies in the circulation of one newborn was concomitant with the rapid elimination of VRC07. Plant-expressed antibodies show promise as passive immunoprophylaxis in a breastfeeding model in newborns. IMPORTANCE Plant-produced human neutralizing antibody prophylaxis is highly effective in preventing infection in newborn monkeys during repeated oral exposure, modeling virus in breastmilk, and offers advantages in cost of production and safety. These findings raise the possibility that anti-Env antibodies may contribute to the control of viral replication in this newborn model and that the observed immune responsiveness may be driven by the long-lived presence of immune complexes.

Tandem bispecific antibody prevents pathogenic SHIVSF162P3CN infection and disease progression

Although progress has been made on constructing potent bi-specific broadly neutralizing antibody (bi-bNAb), few bi-bNAbs have been evaluated against HIV-1/AIDS in non-human primates (NHPs). Here, we report the efficacy of a tandem bi-bNAb, namely BiIA-SG, in Chinese-origin rhesus macaques (CRM) against the CRM-adapted R5-tropic pathogenic SHIV_SF162P3CN challenge. Pre-exposure BiIA-SG injection prevents productive viral infection in 6 of 6 CRMs with unmeasurable proviral load, T cell responses, and seroconversion. Single BiIA-SG injection, at day 1 or 3 post viral challenge, significantly reduces peak viremia, achieves undetectable setpoint viremia in 8 of 13 CRMs, and delays disease progression for years in treated CRMs. In contrast, 6 of 8 untreated CRMs develop simian AIDS within 2 years. BiIA-SG-induced long-term protection is associated with CD8⁺ T cells as determined by anti-CD8β antibody depletion experiments. Our findings provide a proof-of-concept that bi-bNAb treatment elicits T cell immunity in NHPs, which warrant the clinical development of BiIA-SG for HIV-1 prevention and immunotherapy.

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.

CD8 Effector T Cells Function Synergistically With Broadly Neutralizing Antibodies to Enhance Suppression of HIV Infection

HIV-specific CD8 T cells and broadly neutralizing antibodies (bNAbs) both contribute to the control of viremia, but in most cases, neither can completely suppress viral replication. To date, therapeutic vaccines have not been successful in eliciting HIV-specific CD8 T cell or bNAb responses that are capable of preventing long-term viral rebound upon ART cessation. These challenges suggest that a combinatorial approach that harnesses both bNAbs and CD8 T cell responses may be necessary for long term control of viral replication. In this study we demonstrate a synergistic interaction between CD8 T cells and bNAbs using an in vitro model. Our data suggest that this combinatorial approach is very effective at suppressing viral replication in vitro and should be considered in future therapeutic studies.

Improved delivery of broadly neutralizing antibodies by nanocapsules suppresses SHIV infection in the CNS of infant rhesus macaques

Broadly neutralizing antibodies (bNAbs) directed to HIV-1 have shown promise at suppressing viremia in animal models. However, the use of bNAbs for the central nervous system (CNS) infection is confounded by poor penetration of the blood brain barrier (BBB). Typically, antibody concentrations in the CNS are extremely low; with levels in cerebrospinal fluid (CSF) only 0.1% of blood concentrations. Using a novel nanotechnology platform, which we term nanocapsules, we show effective transportation of the human bNAb PGT121 across the BBB in infant rhesus macaques upon systemic administration up to 1.6% of plasma concentration. We demonstrate that a single dose of PGT121 encased in nanocapsules when delivered at 48h post-infection delays early acute infection with SHIV_SF162P3 in infants, with one of four animals demonstrating viral clearance. Importantly, the nanocapsule delivery of PGT121 improves suppression of SHIV infection in the CNS relative to controls.

In patients where HIV-1 is fully suppressed by antiretroviral drugs, HIV-1 still persists in reservoirs. If antiretroviral drugs are stopped, the virus will emerge from these reservoirs and re-seeds systemically. The central nervous system (CNS) is proposed to be a tissue compartment that harbors other HIV-1 reservoirs. A key obstacle that constrains the treatment for the CNS infection is the blood–brain barrier (BBB), a highly restrictive barrier separating the circulating blood from the brain and extracellular fluid in the CNS, which impedes ~98% of the small molecule therapeutics and almost all macromolecules including broadly neutralizing antibodies (bNAbs) directed to HIV-1. Our “nanocapsule” strategy is based on a nanotechnology wherein bNAb molecules are encapsulated within nanocapsules of which the surface contains abundant choline and acetylcholine analogues. This design allows the nanocapsules to effectively cross the BBB to deliver bNAbs into the CNS upon systemic administration and show an impact of bNAb on CNS reservoirs in SHIV infected infant macaques.

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.

Non-human Primate Models to Investigate Mechanisms of Infection-Associated Fetal and Pediatric Injury, Teratogenesis and Stillbirth

A wide array of pathogens has the potential to injure the fetus and induce teratogenesis, the process by which mutations in fetal somatic cells lead to congenital malformations. Rubella virus was the first infectious disease to be linked to congenital malformations due to an infection in pregnancy, which can include congenital cataracts, microcephaly, hearing impairment and congenital heart disease. Currently, human cytomegalovirus (HCMV) is the leading infectious cause of congenital malformations globally, affecting 1 in every 200 infants. However, our knowledge of teratogenic viruses and pathogens is far from complete. New emerging infectious diseases may induce teratogenesis, similar to Zika virus (ZIKV) that caused a global pandemic in 2016-2017; thousands of neonates were born with congenital microcephaly due to ZIKV exposure in utero, which also included a spectrum of injuries to the brain, eyes and spinal cord. In addition to congenital anomalies, permanent injury to fetal and neonatal organs, preterm birth, stillbirth and spontaneous abortion are known consequences of a broader group of infectious diseases including group B streptococcus (GBS), Listeria monocytogenes, Influenza A virus (IAV), and Human Immunodeficiency Virus (HIV). Animal models are crucial for determining the mechanism of how these various infectious diseases induce teratogenesis or organ injury, as well as testing novel therapeutics for fetal or neonatal protection. Other mammalian models differ in many respects from human pregnancy including placentation, labor physiology, reproductive tract anatomy, timeline of fetal development and reproductive toxicology. In contrast, non-human primates (NHP) most closely resemble human pregnancy and exhibit key similarities that make them ideal for research to discover the mechanisms of injury and for testing vaccines and therapeutics to prevent teratogenesis, fetal and neonatal injury and adverse pregnancy outcomes (e.g., stillbirth or spontaneous abortion). In this review, we emphasize key contributions of the NHP model pre-clinical research for ZIKV, HCMV, HIV, IAV, L. monocytogenes, Ureaplasma species, and GBS. This work represents the foundation for development and testing of preventative and therapeutic strategies to inhibit infectious injury of human fetuses and neonates.

The current and future role of nanovaccines in HIV-1 vaccine development

Introduction: An efficacious vaccine for HIV-1 has been sought for over 30 years to eliminate the virus from the human population. Many challenges have occurred in the attempt to produce a successful immunogen, mainly caused by the basic biology of the virus. Immunogens have been developed focusing on inducing one or more of the following types of immune responses; neutralizing antibodies, non-neutralizing antibodies, and T-cell mediated responses. One way to better present and develop an immunogen for HIV-1 is through the use of nanotechnology and nanoparticles.Areas covered: This article gives a basic overview of the HIV-1 vaccine field, as well as nanotechnology, specifically nanovaccines. It then covers the application of nanovaccines made from biological macromolecules to HIV-1 vaccine development for neutralizing antibodies, non-neutralizing antibodies, and T-cell-mediated responses.Expert opinion: Nanovaccines are an area that is ripe for further exploration in HIV-1 vaccine field. Not only are nanovaccines capable of carrying and presenting antigens in native-like conformations, but they have also repeatedly been shown to increase immunogenicity over recombinant antigens alone. Only through further research can the true role of nanovaccines in the development of an efficacious HIV-1 vaccine be established.

SARS-CoV-2 Portrayed against HIV: Contrary Viral Strategies in Similar Disguise

SARS-CoV-2 and HIV are zoonotic viruses that rapidly reached pandemic scale, causing global losses and fear. The COVID-19 and AIDS pandemics ignited massive efforts worldwide to develop antiviral strategies and characterize viral architectures, biological and immunological properties, and clinical outcomes. Although both viruses have a comparable appearance as enveloped viruses with positive-stranded RNA and envelope spikes mediating cellular entry, the entry process, downstream biological and immunological pathways, clinical outcomes, and disease courses are strikingly different. This review provides a systemic comparison of both viruses' structural and functional characteristics, delineating their distinct strategies for efficient spread.

Anatomic Distribution of Intravenously Injected IgG Takes Approximately 1 Week to Achieve Stratum Corneum Saturation in Vaginal Tissues

i.v. injected Abs have demonstrated protection against simian HIV infection in rhesus macaques, paving the way for the Antibody Mediated Prevention trial in which at-risk individuals for HIV received an i.v. infusion of the HIV broadly neutralizing Ab VRC01. However, the time needed for these Abs to fully distribute and elicit protection at mucosal sites is still unknown. In this study, we interrogate how long it takes for Abs to achieve peak anatomical levels at the vaginal surface following i.v. injection. Fluorescently labeled VRC01 and/or Gamunex-C were i.v. injected into 24 female rhesus macaques (Macaca mulatta) with vaginal tissues and plasma acquired up to 2 wk postinjection. We found that Ab delivery to the vaginal mucosa occurs in two phases. The first phase involves delivery to the submucosa, occurring within 24 h and persisting beyond 1 wk. The second phase is the delivery through the stratified squamous epithelium, needing ∼1 wk to saturate the stratum corneum. This study has important implications for the efficacy of immunoprophylaxis targeting pathogens at the mucosa.

Timing HIV infection with a simple and accurate population viral dynamics model

Clinical trials for HIV prevention can require knowledge of infection times to subsequently determine protective drug levels. Yet, infection timing is difficult when study visits are sparse. Using population nonlinear mixed-effects (pNLME) statistical inference and viral loads from 46 RV217 study participants, we developed a relatively simple HIV primary infection model that achieved an excellent fit to all data. We also discovered that Aptima assay values from the study strongly correlated with viral loads, enabling imputation of very early viral loads for 28/46 participants. Estimated times between infecting exposures and first positives were generally longer than prior estimates (average of two weeks) and were robust to missing viral upslope data. On simulated data, we found that tighter sampling before diagnosis improved estimation more than tighter sampling after diagnosis. Sampling weekly before and monthly after diagnosis was a pragmatic design for good timing accuracy. Our pNLME timing approach is widely applicable to other infections with existing mathematical models. The present model could be used to simulate future HIV trials and may help estimate protective thresholds from the recently completed antibody-mediated prevention trials.

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.

Safety, Tolerability, and Pharmacokinetics of a Long-Acting Broadly Neutralizing HIV-1 Monoclonal Antibody VRC01LS in HIV-1-Exposed Newborn Infants

BACKGROUND

Perinatal HIV-1 continues to occur due to barriers to effective antiretroviral prevention that might be mitigated by long-acting broadly neutralizing monoclonal antibodies (bNAbs).

METHODS

Extended half-life bNAb, VRC01LS, was administered subcutaneously (SC) at 80 mg/dose after birth to HIV-1-exposed, non-breastfed (Cohort 1, n=10) and breastfed (Cohort 2, n=11) infants. Cohort 2 received a second dose (100mg) at 12 weeks. All received antiretroviral prophylaxis. VRC01LS levels were compared to VRC01 levels determined in a prior cohort.

RESULTS

Local reactions (all Grade <2) occurred in 67% and 20% after Dose 1 and Dose 2, respectively. The weight-banded dose (mean 28.8 mg/kg) of VRC01LS administrated SC achieved a mean +SD plasma level of 222.3 + 71.6 mcg/mL by 24 hours and 44.0 + 11.6 mcg/mL at week 12, prior to Dose 2. The pre-established target of > 50 mcg/mL was attained in 95% and 32% at week 8 and 12, respectively. The terminal half-life was 37-41 days. VRC01LS level after one dose was significantly greater (p=<0.002) than after a VRC01 dose (20mg/kg). No infants acquired HIV-1.

CONCLUSIONS

VRC01LS was well tolerated with pharmacokinetics that support further studies of more potent long-acting bNAbs as adjunct treatment with ARVs to prevent infant HIV-1 transmission.

Maternal Intervention to Prevent Mother-to-Child Transmission of HIV: Moving Beyond Antiretroviral Therapy

Widespread availability of antiretroviral therapy among pregnant women living with HIV has greatly reduced the rate of mother-to-child transmission (MTCT) of HIV across the globe. However, while Joint United Nations Programme on HIV/AIDS has set targets to reduce the annual number of new pediatric HIV infections to fewer than 40,000 in 2018 and fewer than 20,000 in 2020, progress towards these targets has plateaued at an unacceptably high global estimate of greater than 160,000 children newly infected with HIV in 2018. Moreover, it has become clear that expansion of maternal antiretroviral therapy alone will not be sufficient to close the remaining gap and eliminate MTCT of HIV. Additional strategies such as maternal or infant passive and/or active immunization that synergize with maternal antiretroviral therapy will be required to end the pediatric HIV epidemic. In this review, we outline the landscape of existing maternal interventions and emerging maternal immune-based approaches to prevent MTCT of HIV.

Eliminating postnatal HIV transmission in high incidence areas: need for complementary biomedical interventions

The rate of mother-to-child transmission (MTCT) of HIV from breastfeeding is increasing relative to other causes of MTCT. Early effective preconception and antenatal antiretroviral therapy (ART) reduces intrauterine and intrapartum MTCT, whereas maternal post-partum HIV acquisition, untreated maternal HIV, and suboptimal postnatal maternal ART adherence increase the risk of MTCT through breastfeeding. Although the absolute number of cases of MTCT acquired through breastfeeding is decreasing, the rate of decrease is less than the decrease in intrauterine and intrapartum MTCT. Unless current strategies are universally applied, they might not be sufficient to eliminate MTCT due to breastfeeding. Urgent action is needed to evaluate and implement additional preventive biomedical strategies in high HIV prevalence and incidence settings to eliminate MTCT from breastfeeding. Preventive strategies include: pre-exposure prophylaxis in breastfeeding women who have an increased risk of acquiring HIV; postnatal reinforcement strategies, such as maternal retesting for HIV, maternal care reinforcement, and prophylaxis in infants exposed to HIV via breastmilk; and active (vaccine) or passive immunoprophylaxis with long-acting broadly neutralising antibodies.

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.

Vaccination induces maturation in a mouse model of diverse unmutated VRC01-class precursors to HIV-neutralizing antibodies with >50% breadth

Vaccine elicitation of broadly neutralizing antibodies (bnAbs) is a key HIV-research goal. The VRC01 class of bnAbs targets the CD4-binding site on the HIV-envelope trimer and requires extensive somatic hypermutation (SHM) to neutralize effectively. Despite substantial progress, vaccine-induced VRC01-class antibodies starting from unmutated precursors have exhibited limited neutralization breadth, particularly against viruses bearing glycan on loop D residue N276 (glycan276), present on most circulating strains. Here, using sequential immunization of immunoglobulin (Ig)-humanized mice expressing diverse unmutated VRC01-class antibody precursors, we elicited serum responses capable of neutralizing viruses bearing glycan276 and isolated multiple lineages of VRC01-class bnAbs, including two with >50% breadth on a 208-strain panel. Crystal structures of representative bnAbs revealed the same mode of recognition as known VRC01-class bnAbs. Structure-function studies further pinpointed key mutations and correlated their induction with specific immunizations. VRC01-class bnAbs can thus be matured by sequential immunization from unmutated ancestors to >50% breadth, and we delineate immunogens and regimens inducing key SHM.

Systematic Assessment of Antiviral Potency, Breadth, and Synergy of Triple Broadly Neutralizing Antibody Combinations against Simian-Human Immunodeficiency Viruses

Daily burden and clinical toxicities associated with antiretroviral therapy (ART) emphasize the need for alternative strategies to induce long-term human immunodeficiency virus (HIV) remission upon ART cessation. Broadly neutralizing antibodies (bNAbs) can both neutralize free virions and mediate effector functions against infected cells and therefore represent a leading immunotherapeutic approach. To increase potency and breadth, as well as to limit the development of resistant virus strains, it is likely that bNAbs will need to be administered in combination. It is therefore critical to identify bNAb combinations that can achieve robust polyfunctional antiviral activity against a high number of HIV strains. In this study, we systematically assessed the abilities of single bNAbs and triple bNAb combinations to mediate robust polyfunctional antiviral activity against a large panel of cross-clade simian-human immunodeficiency viruses (SHIVs), which are commonly used as tools for validation of therapeutic strategies targeting the HIV envelope in nonhuman primate models. We demonstrate that most bNAbs are capable of mediating both neutralizing and nonneutralizing effector functions against cross-clade SHIVs, although the susceptibility to V3 glycan-specific bNAbs is highly strain dependent. Moreover, we observe a strong correlation between the neutralization potencies and nonneutralizing effector functions of bNAbs against the transmitted/founder SHIV CH505. Finally, we identify several triple bNAb combinations comprising of CD4 binding site-, V2-glycan-, and gp120-gp41 interface-targeting bNAbs that are capable of mediating synergistic polyfunctional antiviral activities against multiple clade A, B, C, and D SHIVs.IMPORTANCE Optimal bNAb immunotherapeutics will need to mediate multiple antiviral functions against a broad range of HIV strains. Our systematic assessment of triple bNAb combinations against SHIVs will identify bNAbs with synergistic, polyfunctional antiviral activity that will inform the selection of candidate bNAbs for optimal combination designs. The identified combinations can be validated in vivo in future passive immunization studies using the SHIV challenge model.

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

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

Simian-Human Immunodeficiency Virus SHIV.C.CH505 Persistence in ART-Suppressed Infant Macaques Is Characterized by Elevated SHIV RNA in the Gut and a High Abundance of Intact SHIV DNA in Naive CD4+ T Cells

Mother-to-child transmission of human immunodeficiency virus type 1 (HIV-1) continues to cause new pediatric cases of infection through breastfeeding, a setting where it is not always possible to initiate early antiretroviral therapy (ART). Without novel interventions that do not rely on daily ART, HIV-1-infected children face lifelong medications to control infection. A detailed analysis of virus persistence following breast milk transmission of HIV-1 and ART has not been performed. Here, we used infant rhesus macaques orally infected with simian/human immunodeficiency virus (SHIV) (SHIV.C.CH505) to identify cellular and anatomical sites of virus persistence under ART. Viral DNA was detected at similar levels in blood and tissue CD4+ T cells after a year on ART, with virus in blood and lymphoid organs confirmed to be replication competent. Viral RNA/DNA ratios were elevated in rectal CD4+ T cells compared to those of other sites (P ≤ 0.0001), suggesting that the gastrointestinal tract is an active site of virus transcription during ART-mediated suppression of viremia. SHIV.C.CH505 DNA was detected in multiple CD4+ T cell subsets, including cells with a naive phenotype (CD45RA+ CCR7+ CD95-). While the frequency of naive cells harboring intact provirus was lower than in memory cells, the high abundance of naive cells in the infant CD4+ T cell pool made them a substantial source of persistent viral DNA (approximately 50% of the total CD4+ T cell reservoir), with an estimated 1:2 ratio of intact provirus to total viral DNA. This viral reservoir profile broadens our understanding of virus persistence in a relevant infant macaque model and provides insight into targets for cure-directed approaches in the pediatric population.IMPORTANCE Uncovering the sanctuaries of the long-lived HIV-1 reservoir is crucial to develop cure strategies. Pediatric immunity is distinct from that of adults, which may alter where the reservoir is established in infancy. Thus, it is important to utilize pediatric models to inform cure-directed approaches for HIV-1-infected children. We used an infant rhesus macaque model of HIV-1 infection via breastfeeding to identify key sites of viral persistence under antiretroviral therapy (ART). The gastrointestinal tract was found to be a site for low-level viral transcription during ART. We also show that naive CD4+ T cells harbored intact provirus and were a major contributor to blood and lymphoid reservoir size. This is particularly striking, as memory CD4+ T cells are generally regarded as the main source of latent HIV/simian immunodeficiency virus (SIV) infection of adult humans and rhesus macaques. Our findings highlight unique features of reservoir composition in pediatric infection that should be considered for eradication efforts.

Vaccines for Perinatal and Congenital Infections-How Close Are We?

Congenital and perinatal infections are transmitted from mother to infant during pregnancy across the placenta or during delivery. These infections not only cause pregnancy complications and still birth, but also result in an array of pediatric morbidities caused by physical deformities, neurodevelopmental delays, and impaired vision, mobility and hearing. Due to the burden of these conditions, congenital and perinatal infections may result in lifelong disability and profoundly impact an individual's ability to live to their fullest capacity. While there are vaccines to prevent congenital and perinatal rubella, varicella, and hepatitis B infections, many more are currently in development at various stages of progress. The spectrum of our efforts to understand and address these infections includes observational studies of natural history of disease, epidemiological evaluation of risk factors, immunogen design, preclinical research of protective immunity in animal models, and evaluation of promising candidates in vaccine trials. In this review we summarize this progress in vaccine development research for Cytomegalovirus, Group B Streptococcus, Herpes simplex virus, Human Immunodeficiency Virus, Toxoplasma, Syphilis, and Zika virus congenital and perinatal infections. We then synthesize this evidence to examine how close we are to developing a vaccine for these infections, and highlight areas where research is still needed.

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.