Forward and reverse translational approaches to predict efficacy of neutralizing respiratory syncytial virus (RSV) antibody prophylaxis

A Phase 2a, Randomized, Placebo-Controlled Human Challenge Trial to Evaluate the Efficacy and Safety of Molnupiravir in Healthy Participants Inoculated with Respiratory Syncytial Virus

INTRODUCTION

Human respiratory syncytial virus (RSV) infections can result in hospitalization and/or death among vulnerable populations. Molnupiravir is a prodrug of ß-D-N4-hydroxycytidine, which has broad-spectrum preclinical activity against RNA viruses. We conducted a pilot trial evaluating molnupiravir for RSV infection.

METHODS

Double-blind, placebo-controlled, phase 2a human challenge study in healthy adults (≥ 18 to ≤ 55 years old). Eligible participants were randomized 1:1:1 to molnupiravir prophylaxis (5 days, 800 mg twice daily; followed by placebo), molnupiravir treatment (5 days, 800 mg twice daily; started on day 5, unless triggered earlier by positive PCR test; preceded and followed by placebo), or placebo. Study intervention was administered for 11 days, from day -1 (evening), prior to inoculation with RSV on day 0 (morning). For 10 days, quarantined participants reported symptoms thrice daily and underwent nasal wash sample collection twice daily. Primary efficacy endpoints (assessed by quantitative viral culture on plaque assay) were peak viral load (PVL) in all participants (for prophylaxis) and area under the viral-load time curve (VL-AUC) in participants with confirmed infection (for treatment). Adverse events were assessed from day 0 to day 28.

RESULTS

Forty participants each were randomized to prophylaxis and placebo and 36 to treatment. Molnupiravir was not statistically significant from placebo in either primary endpoint: with prophylaxis, the difference in mean log10 PVL was - 0.29 plaque-forming units (PFU)/ml (90% CI - 1.16, 0.58; p = 0.578), and with treatment, the difference in mean log10 VL-AUC was - 2.69 day*PFU/ml (90% CI - 6.17, 0.79; p = 0.201). Molnupiravir treatment resulted in significantly faster symptom resolution: 6.0 days versus 8.5 days with placebo (hazard ratio: 2.24 [95% CI: 0.99, 5.07]; p = 0.0459). Adverse event rates were comparable between arms.

CONCLUSIONS

Although the primary endpoints were not met, modest, non-significant benefits with molnupiravir treatment were seen across virologic endpoints, along with significantly faster symptom resolution.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT05559905.

Efficacy of monoclonal antibodies and maternal vaccination for prophylaxis of respiratory syncytial virus disease

BACKGROUND

Respiratory syncytial virus (RSV) is a leading cause of respiratory tract infection in infants and young children. The level of serum neutralizing antibodies (SNAs) is often used as a measure of protection against respiratory syncytial virus (RSV) infection.

METHODS

A qualified, model-based, meta-analysis efficacy prediction framework was used to understand the maternal vaccination-induced fold-increase in SNA titers necessary to achieve, over several study observation periods and study populations, similar protection to that of the monoclonal antibody clesrovimab (MK-1654).

RESULTS

Simulations indicated that 3-month and 6-month efficacy comparable to that predicted for passive immunization (clesrovimab) would require a maternal vaccine to increase SNA titers by 30- and 60-fold, respectively, higher than observed increases reported to date. Efficacy of maternal vaccination was predicted (for vaccines similar to those with published data) to be substantially lower for preterm infants compared to full-term infants, and substantially less over 6 months than over 3 months. Efficacy of passive immunization was predicted to be similar or higher in preterm infants than full-term infants and was similar for 3- and 6-month observation periods.

CONCLUSIONS

Modeling can be used to reliably predict the efficacy of maternal vaccination for preventing RSV in infants. Passive immunization (e.g., with clesrovimab) is likely to provide more protection for preterm infants and for infants born outside the RSV season than that provided by current maternal vaccines. Maternal vaccination may provide partial protection from RSV disease to full-term infants born just prior to or during the RSV season.

Current antiviral therapies and promising drug candidates against respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is one of the most common viruses leading to lower respiratory tract infections (LRTIs) in children and elderly individuals worldwide. Although significant progress in the prevention and treatment of RSV infection was made in 2023, with two anti-RSV vaccines and one monoclonal antibody approved by the FDA, there is still a lack of postinfection therapeutic drugs in clinical practice, especially for the pediatric population. In recent years, with an increasing understanding of the pathogenic mechanisms of RSV, drugs and drug candidates, have shown great potential for clinical application. In this review, we categorize and discuss promising anti-RSV drug candidates that have been in preclinical or clinical development over the last five years.

Development of High-Titer Antidrug Antibodies in a Phase 1b/2a Infant Clesrovimab Trial Are Associated With RSV Exposure Beyond Day 150

BACKGROUND

Clesrovimab is a human half-life-extended monoclonal antibody in phase 3 evaluation for the prevention of respiratory syncytial virus (RSV) disease in infants. Antidrug antibodies (ADA) were observed at late time points in a phase 1b/2a study where clesrovimab was well tolerated with an extended half-life of approximately 45 days.

METHODS

Serum samples at days 150, 365, and 545 postdose were assayed for ADA titers. Samples with high ADA titers were characterized for their binding specificity to the Fab or the YTE portion of clesrovimab. RSV serum neutralization (SNA) titers were also measured on ADA-positive and ADA-negative infants. Additionally, a D25 (site Ø) competitive enzyme-linked immunosorbent assay (ELISA) was performed on ADA-positive available samples to determine RSV exposure. Local surveillance data was used to ascertain RSV circulation during the trial.

RESULTS

High ADA titers were observed in a minority of infants at days 365 and 545 for all doses tested. Additionally, all high-titer ADA-positive infants had ADA directed towards the YTE epitope of clesrovimab. Moreover, these infants demonstrated robust RSV-SNA and had D25 competitive antibodies suggesting an RSV exposure after day 150, coinciding with the epidemiological data.

CONCLUSIONS

RSV exposure in infants beyond day 150 after dosing is associated with ADA development and high RSV-SNA titers with no impact on pharmacokinetics.

CLINICAL TRIALS REGISTRATION

NCT03524118.

A Phase 1b/2a Trial of a Half-life Extended Respiratory Syncytial Virus Neutralizing Antibody, Clesrovimab, in Healthy Preterm and Full-term Infants

BACKGROUND

Clesrovimab is an investigational monoclonal antibody with an extended half-life targeting site IV of the respiratory syncytial virus (RSV) fusion protein for the prevention of RSV disease in infants.

METHODS

In this phase 1b/2a, double-blind study, 183 healthy preterm and full-term infants 2 weeks to 8 months of age were randomized 4:1 within 5 panels (preterm 20, 50, 75, or 100 mg; full-term 100 mg) to receive 1 dose of clesrovimab or placebo. The objectives were to evaluate safety, pharmacokinetics, serum neutralizing antibodies (SNA), and antidrug antibodies (ADA). The incidence of RSV-associated end points (medically attended lower respiratory tract infection, hospitalization, and acute respiratory infection) were also evaluated through 150 days postdose.

RESULTS

The most common adverse event through day 14 was irritability; no treatment-related serious AEs were reported. Clesrovimab serum concentrations displayed a geometric mean apparent half-life of 44.9 days. Of participants receiving clesrovimab, 51 (36.7%) developed ADA with no apparent impact in pharmacokinetics. SNA titers increased in a dose-dependent manner at day 150. The incidences of RSV-associated end points were lower in infants treated with clesrovimab compared with placebo.

CONCLUSIONS

Clesrovimab was generally well tolerated and exhibited an extended half-life compared to typical IgG1 antibodies, supporting its ongoing development in late-stage trials. Clinical Trial Registration. NCT03524118.

Evaluation of a non-nucleoside inhibitor of the RSV RNA-dependent RNA polymerase in translatable animals models

Respiratory Syncytial Virus (RSV) causes severe respiratory infections and concomitant disease resulting in significant morbidity and mortality in infants, elderly, and immunocompromised adults. Vaccines, monoclonal antibodies, and small-molecule antivirals are now either available or in development to prevent and treat RSV infections. Although rodent and non-rodent preclinical animal models have been used to evaluate these emerging agents, there is still a need to improve our understanding of the pharmacokinetic (PK)-pharmacodynamic (PD) relationships within and between animal models to enable better design of human challenge studies and clinical trials. Herein, we report a PKPD evaluation of MRK-1, a novel small molecule non-nucleoside inhibitor of the RSV L polymerase protein, in the semi-permissive cotton rat and African green monkey models of RSV infection. These studies demonstrate a strong relationship between in vitro activity, in vivo drug exposure, and pharmacodynamic efficacy as well as revealing limitations of the cotton rat RSV model. Additionally, we report unexpected horizontal transmission of human RSV between co-housed African green monkeys, as well as a lack of drug specific resistant mutant generation. Taken together these studies further our understanding of these semi-permissive animal models and offer the potential for expansion of their preclinical utility in evaluating novel RSV therapeutic agents.

Improving precision of vaccine efficacy evaluation using immune correlate data in time-to-event models

Understanding potential differences in vaccine-induced protection between demographic subgroups is key for vaccine development. Vaccine efficacy evaluation across these subgroups in phase 2b or 3 clinical trials presents challenges due to lack of precision: such trials are typically designed to demonstrate overall efficacy rather than to differentiate its value between subgroups. This study proposes a method for estimating vaccine efficacy using immunogenicity (instead of vaccination status) as a predictor in time-to-event models. The method is applied to two datasets from immunogenicity sub-studies of vaccine phase 3 clinical trials for zoster and dengue vaccines. Results show that using immunogenicity-based estimation of efficacy in subgroups using time-to-event models is more precise than the standard estimation. Incorporating immune correlate data in time-to-event models improves precision in estimating efficacy (i.e., yields narrower confidence intervals), which can assist vaccine developers and public health authorities in making informed decisions.

RSV Neutralizing Antibodies Following Nirsevimab and Palivizumab Dosing

BACKGROUND

Data describing respiratory syncytial virus (RSV) neutralizing antibody (nAb) levels for nirsevimab, a recently approved, extended half-life, anti-RSV fusion protein (F protein) monoclonal antibody, relative to the previous standard of care, palivizumab, have not been reported.

METHODS

MEDLEY was a randomized, palivizumab-controlled, phase 2/3 study of nirsevimab during 2 RSV seasons (season 1 and 2) in infants born preterm (≤35 weeks' gestational age; dosed season 1 only) or with congenital heart disease or chronic lung disease of prematurity (dosed seasons 1 and 2). Participants were randomly assigned to receive a single dose of nirsevimab followed by 4 monthly placebo doses, or 5 once-monthly doses of palivizumab. Anti-RSV F protein serology (ie, levels of prefusion [pre-F]/postfusion [post-F] conformation antibodies), nirsevimab and palivizumab concentrations, and RSV nAbs were measured in participant serum collected at baseline (pre-dose) and days 31, 151, and 361.

RESULTS

Serologic data were similar in seasons 1 and 2. Nirsevimab predominately conferred pre-F antibodies, whereas palivizumab conferred pre-F and post-F antibodies. Nirsevimab and palivizumab serum concentrations highly correlated with nAb levels in both seasons. In season 1, nAb levels in nirsevimab recipients were highest in day 31 samples and gradually declined but remained 17-fold above baseline at day 361. nAb levels in palivizumab recipients increased incrementally with monthly doses to day 151. nAb levels followed similar patterns in season 2. nAb levels were ∼10-fold higher with nirsevimab compared with palivizumab across both seasons.

CONCLUSIONS

Nirsevimab prophylaxis confers ∼10-fold higher and more sustained RSV nAb levels relative to palivizumab.

A multi-center study on genetic variations in the fusion protein of respiratory syncytial virus from children with Acute Lower Respiratory Tract Infections in China during 2017-2021

Respiratory syncytial virus (RSV) is a significant cause of acute lower respiratory tract infection (ALRTI) in children under five years of age. Between 2017 and 2021, 396 complete sequences of the RSV F gene were obtained from 500 RSV-positive throat swabs collected from ten hospitals across nine provinces in China. In addition, 151 sequences from China were sourced from GenBank and GISAID, making a total of 549 RSV F gene sequences subjected to analysis. Phylogenetic and genetic diversity analyses revealed that the RSV F genes circulating in China from 2017 to 2021 have remained relatively conserved, although some amino acids (AAs) have undergone changes. AA mutations with frequencies ≥ 10% were identified at six sites and the p27 region: V384I (site I), N276S (site II), R213S (site Ø), and K124N (p27) for RSV A; F45L (site I), M152I/L172Q/S173 ​L/I185V/K191R (site V), and R202Q/I206M/Q209R (site Ø) for RSV B. Comparing mutational frequencies in RSV-F before and after 2020 revealed minor changes for RSV A, while the K191R, I206M, and Q209R frequencies increased by over 10% in RSV B. Notably, the nirsevimab-resistant mutation, S211N in RSV B, increased in frequency from 0% to 1.15%. Both representative strains aligned with the predicted RSV-F structures of their respective prototypes exhibited similar conformations, with low root-mean-square deviation values. These results could provide foundational data from China for the development of RSV mAbs and vaccines.

Respiratory Syncytial Virus: The Urgent Need for Innovative Preventive Strategies

Respiratory Syncytial Virus (RSV) is a medium-sized enveloped Pneumovirus belonging to the Paramyxoviridae family [...].

Virus neutralization assays for human respiratory syncytial virus using airway organoids

Neutralizing antibodies are considered a correlate of protection against severe human respiratory syncytial virus (HRSV) disease. Currently, HRSV neutralization assays are performed on immortalized cell lines like Vero or A549 cells. It is known that assays on these cell lines exclusively detect neutralizing antibodies (nAbs) directed to the fusion (F) protein. For the detection of nAbs directed to the glycoprotein (G), ciliated epithelial cells expressing the cellular receptor CX3CR1 are required, but generation of primary cell cultures is expensive and labor-intensive. Here, we developed a high-throughput neutralization assay based on the interaction between clinically relevant HRSV grown on primary cells with ciliated epithelial cells, and validated this assay using a panel of infant sera. To develop the high-throughput neutralization assay, we established a culture of differentiated apical-out airway organoids (Ap-O AO). CX3CR1 expression was confirmed, and both F- and G-specific monoclonal antibodies neutralized HRSV in the Ap-O AO. In a side-by-side neutralization assay on Vero cells and Ap-O AO, neutralizing antibody levels in sera from 125 infants correlated well, although titers on Ap-O AO were consistently lower. We speculate that these lower titers might be an actual reflection of the neutralizing antibody capacity in vivo. The organoid-based neutralization assay described here holds promise for further characterization of correlates of protection against HRSV disease.

A molecular perspective for the development of antibodies against the human respiratory syncytial virus

The human respiratory syncytial virus (hRSV) is the leading etiologic agent causing respiratory infections in infants, children, older adults, and patients with comorbidities. Sixty-seven years have passed since the discovery of hRSV, and only a few successful mitigation or treatment tools have been developed against this virus. One of these is immunotherapy with monoclonal antibodies against structural proteins of the virus, such as Palivizumab, the first prophylactic approach approved by the Food and Drug Administration (FDA) of the USA. In this article, we discuss different strategies for the prevention and treatment of hRSV infection, focusing on the molecular mechanisms against each target that underly the rational design of antibodies against hRSV. At the same time, we describe the latest results regarding currently approved therapies against hRSV and the challenges associated with developing new candidates.

Current state and challenges in respiratory syncytial virus drug discovery and development

Human respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections (LRTI) in young children and elderly people worldwide. Recent significant progress in our understanding of the structure and function of RSV proteins has led to the discovery of several clinical candidates targeting RSV fusion and replication. These include both the development of novel small molecule interventions and the isolation of potent monoclonal antibodies. In this review, we summarize the state-of-the-art of RSV drug discovery, with a focus on the characteristics of the candidates that reached the clinical stage of development. We also discuss the lessons learned from failed and discontinued clinical developments and highlight the challenges that remain for development of RSV therapies.

A Quantitative Clinical Pharmacology-Based Framework For Model-Informed Vaccine Development

Historically, vaccine development and dose optimization have followed mostly empirical approaches without clinical pharmacology and model-informed approaches playing a major role, in contrast to conventional drug development. This is attributed to the complex cascade of immunobiological mechanisms associated with vaccines and a lack of quantitative frameworks for extracting dose-exposure-efficacy-toxicity relationships. However, the Covid-19 pandemic highlighted the lack of sufficient immunogenicity due to suboptimal vaccine dosing regimens and the need for well-designed, model-informed clinical trials which enhance the probability of selection of optimal vaccine dosing regimens. In this perspective, we attempt to develop a quantitative clinical pharmacology-based approach that integrates vaccine dose-efficacy-toxicity across various stages of vaccine development into a unified framework that we term as model-informed vaccine dose-optimization and development (MIVD). We highlight scenarios where the adoption of MIVD approaches may have a strategic advantage compared to conventional practices for vaccines.

Quantification of clesrovimab, an investigational, half-life extended, anti-respiratory syncytial virus protein F human monoclonal antibody in the nasal epithelial lining fluid of healthy adults

BACKGROUND

Clesrovimab (MK-1654) is an investigational, half-life extended human monoclonal antibody (mAb) against RSV F glycoprotein in clinical trials as a prophylactic agent against RSV infection for infants.

METHODS

This adult study measured clesrovimab concentrations in the serum and nasal epithelial lining fluid (ELF) to establish the partitioning of the antibody after dosing. Clesrovimab concentrations in the nasal ELF were normalized for sampling dilution using urea concentrations from ELF and serum. Furthermore, in vitro RSV neutralization of human nasal ELF following dosing was also measured to examine the activity of clesrovimab in the nasal compartment.

FINDINGS

mAbs with YTE mutations are reported in literature to partition ∼1-2 % of serum antibodies into nasal mucosa. Nasal: serum ratios of 1:69-1:30 were observed for clesrovimab in two separate adult human trials after urea normalization, translating to 1.4-3.3 % of serum concentrations. The nasal PK and estimates of peripheral volume of distribution correlated with higher extravascular distribution of clesrovimab. These higher concentration of the antibody in the nasal ELF corroborated with the nasal sample's ability to neutralize RSV ex vivo. An overall trend of decreased viral plaque AUC was also noted with increasing availability of clesrovimab in the nasal ELF from a human RSV challenge study.

INTERPRETATION

Along with its extended half-life, the higher penetration of clesrovimab into the nasal epithelial lining fluid and the associated local increase in RSV neutralization activity could offer infants better protection against RSV infection.

Evaluation of a stabilized RSV pre-fusion F mRNA vaccine: Preclinical studies and Phase 1 clinical testing in healthy adults

Human respiratory syncytial virus (RSV) causes a substantial proportion of respiratory tract infections worldwide. Although RSV reinfections occur throughout life, older adults, particularly those with underlying comorbidities, are at risk for severe complications from RSV. There is no RSV vaccine available to date, and treatment of RSV in adults is largely supportive. A correlate of protection for RSV has not yet been established, but antibodies targeting the pre-fusion conformation of the RSV F glycoprotein play an important role in RSV neutralization. We previously reported a Phase 1 study of an mRNA-based vaccine (V171) expressing a pre-fusion-stabilized RSV F protein (mDS-Cav1) in healthy adults. Here, we evaluated an mRNA-based vaccine (V172) expressing a further stabilized RSV pre-fusion F protein (mVRC1). mVRC1 is a single chain version of RSV F with interprotomer disulfides in addition to the stabilizing mutations present in the mDS-Cav1 antigen. The immunogenicity of the two mRNA-based vaccines encoding mVRC1 (V172) or a sequence-optimized version of mDS-Cav1 to improve transcriptional fidelity (V171.2) were compared in RSV-naïve and RSV-experienced African green monkeys (AGMs). V172 induced higher neutralizing antibody titers than V171.2 and demonstrated protection in the AGM challenge model. We conducted a Phase 1, randomized, placebo-controlled, clinical trial of 25 μg, 100 μg, 200 μg, or 300 μg of V172 in healthy older adults (60-79 years old; N = 112) and 100 μg, 200 μg, or 300 μg of V172 in healthy younger adults (18-49 years old; N = 48). The primary clinical objectives were to evaluate the safety and tolerability of V172, and the secondary objective was to evaluate RSV serum neutralization titers. The most commonly reported solicited adverse events were injection-site pain, injection-site swelling, headache, and tiredness. V172 was generally well tolerated in older and younger adults and increased serum neutralizing antibody titers, pre-fusion F-specific competing antibody titers, and RSV F-specific T-cell responses.

Breakthrough SARS-CoV-2 Infections in the PROVENT Prevention Trial Were Not Associated With AZD7442 (Tixagevimab/Cilgavimab) Resistant Variants

BACKGROUND

We report spike protein-based lineage and AZD7442 (tixagevimab/cilgavimab) neutralizing activity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants identified from breakthrough infections in the PROVENT preexposure prophylaxis trial.

METHODS

Variants identified from PROVENT participants with reverse-transcription polymerase chain reaction-positive symptomatic illness were phenotypically assessed to determine neutralization susceptibility of variant-specific pseudotyped virus-like particles.

RESULTS

At completion of 6 months' follow-up, no AZD7442-resistant variants were observed in breakthrough coronavirus disease 2019 (COVID-19) cases. SARS-CoV-2 neutralizing antibody titers were similar in breakthrough and nonbreakthrough cases.

CONCLUSIONS

Symptomatic COVID-19 breakthrough cases in PROVENT were not due to resistance-associated substitutions in AZD7442 binding sites or lack of AZD7442 exposure.

CLINICAL TRIALS REGISTRATION

NCT04625725.

The road to approved vaccines for respiratory syncytial virus

After decades of work, several interventions to prevent severe respiratory syncytial virus (RSV) disease in high-risk infant and older adult populations have finally been approved. There were many setbacks along the road to victory. In this review, I will discuss the impact of RSV on human health and how structure-based vaccine design set the stage for numerous RSV countermeasures to advance through late phase clinical evaluation. While there are still many RSV countermeasures in preclinical and early-stage clinical trials, this review will focus on products yielding long-awaited efficacy results. Finally, I will discuss some challenges and next steps needed to declare a global victory against RSV.

Review of the Safety, Efficacy and Tolerability of Palivizumab in the Prevention of Severe Respiratory Syncytial Virus (RSV) Disease

Respiratory Syncytial Virus (RSV) is a major global cause of childhood morbidity and mortality. Palivizumab, a monoclonal antibody that provides passive immunity against RSV, is currently licensed for prophylactic use in specific "high-risk" populations, including congenital heart disease, bronchopulmonary dysplasia and prematurity. Available research suggests palivizumab use in these high-risk populations can lead to a reduction in RSV-related hospitalization. However, palivizumab has not been demonstrated to reduce mortality, adverse events or length of hospital stay related to RSV. In this article, we review the management of RSV, indications for palivizumab prophylaxis, the safety, cost-effectiveness and efficacy of this preventative medication, and emerging therapeutics that could revolutionize future prevention of this significant pathogen.

Risk of RSV-related hospitalization is associated with gestational age in preterm (born at 29-34 wGA) infants without outpatient palivizumab administration

Palivizumab has been shown to decrease RSV-related hospitalization (RSVH) risk and reduce RSVH severity. American Academy of Pediatrics (AAP) guidance on administration of palivizumab has changed over time; in 2014, palivizumab was no longer recommended in preterm infants born at 29 weeks gestational age (wGA) or later. This study's objective was to describe RSVH risk and severity in preterm infants (29-34 wGA) without comorbidities relative to healthy term infants and to each other by gestational age. Using the MarketScan Multi-State Medicaid and Commercial Databases, infants born from July 1, 2014 to June 30, 2019, at 29-34 wGA (preterm) and >37 wGA (term) were identified. During RSV seasons (November to March) from 2014 to 2020, claims incurred by infants while they were <6 months old were evaluated for RSVH and RSVH characteristics. This study included 63,351 preterm infants and 1,076,389 term infants without outpatient palivizumab administration. Rate of RSVH was higher in infants with lower wGA at birth and ranged 3.32-5.72 per 100 infant-seasons in Medicaid-insured infants and 3.21-4.84 in commercially insured infants. Relative risk of RSVH was 5-8 times higher in Medicaid-insured preterm infants and 3-5 times higher in commercially insured preterm infants compared to term infants. ICU admissions and mechanical ventilation were more common during RSVH in preterm infants relative to term infants. RSV-related outpatient healthcare utilization was also 2-3 times higher in preterm infants born at 31-34 wGA. Increased utilization of palivizumab among infants born at 29-34 wGA may decrease RSVH rates and result in less severe course in preterm infants with RSVH.

Phage-derived anti-idiotype and anti-YTE antibodies in development of MK-1654 pharmacokinetic and immune response assays

Background: MK-1654 is a fully human monoclonal antibody with YTE mutations currently in phase III clinical trials for prophylactic use in protecting infants from human respiratory syncytial virus infection. Materials & methods: We generated anti-idiotype (anti-ID) and anti-YTE antibodies against MK-1654 by panning with MorphoSys HuCal phage libraries, and used the antibodies in the development of MK-1654 pharmacokinetic (PK) and immune response (IR) assays. Results: Detection of MK-1654 in nonhuman primate and human nasal wash samples showed combined use of anti-ID and anti-YTE antibodies can deliver desired sensitivity and accuracy in PK studies. IR studies showed anti-ID can serve as suitable positive control in neutralizing antibody assays. Conclusion: Phage-derived anti-IDs and anti-YTEs are suitable for PK and IR assays.

Structural basis for respiratory syncytial virus and human metapneumovirus neutralization

Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) continue to be a global burden to infants, the elderly, and immunocompromised individuals. In the past ten years, there has been substantial progress in the development of new vaccine candidates and therapies against these viruses. These advancements were guided by the structural elucidation of the major surface glycoproteins for these viruses, the fusion (F) protein and attachment (G) protein. The identification of immunodominant epitopes on the RSV F and hMPV F proteins has expanded current knowledge on antibody-mediated immune responses, which has led to new approaches for vaccine and therapeutic development through the stabilization of pre-fusion constructs of the F protein and pre-fusion-specific monoclonal antibodies with high potency and efficacy. In this review, we describe structural characteristics of known antigenic sites on the RSV and hMPV proteins, their influence on the immune response, and current progress in vaccine and therapeutic development.

Molecular and phenotypic characteristics of RSV infections in infants during two nirsevimab randomized clinical trials

Nirsevimab is a monoclonal antibody that binds to the respiratory syncytial virus (RSV) fusion protein. During the Phase 2b (NCT02878330) and MELODY (NCT03979313) clinical trials, infants received one dose of nirsevimab or placebo before their first RSV season. In this pre-specified analysis, isolates from RSV infections were subtyped, sequenced and analyzed for nirsevimab binding site substitutions; subsequently, recombinant RSVs were engineered for microneutralization susceptibility testing. Here we show that the frequency of infections caused by subtypes A and B is similar across and within the two trials. In addition, RSV A had one and RSV B had 10 fusion protein substitutions occurring at >5% frequency. Notably, RSV B binding site substitutions were rare, except for the highly prevalent I206M:Q209R, which increases nirsevimab susceptibility; RSV B isolates from two participants had binding site substitutions that reduce nirsevimab susceptibility. Overall, >99% of isolates from the Phase 2b and MELODY trials retained susceptibility to nirsevimab.

Immunization with a mucosal, post-fusion F/G protein-based polyanhydride nanovaccine protects neonatal calves against BRSV infection

Human respiratory syncytial virus (HRSV) is a leading cause of death in young children and there are no FDA approved vaccines. Bovine RSV (BRSV) is antigenically similar to HRSV, and the neonatal calf model is useful for evaluation of HRSV vaccines. Here, we determined the efficacy of a polyanhydride-based nanovaccine encapsulating the BRSV post-fusion F and G glycoproteins and CpG, delivered prime-boost via heterologous (intranasal/subcutaneous) or homologous (intranasal/intranasal) immunization in the calf model. We compared the performance of the nanovaccine regimens to a modified-live BRSV vaccine, and to non-vaccinated calves. Calves receiving nanovaccine via either prime-boost regimen exhibited clinical and virological protection compared to non-vaccinated calves. The heterologous nanovaccine regimen induced both virus-specific cellular immunity and mucosal IgA, and induced similar clinical, virological and pathological protection as the commercial modified-live vaccine. Principal component analysis identified BRSV-specific humoral and cellular responses as important correlates of protection. The BRSV-F/G CpG nanovaccine is a promising candidate vaccine to reduce RSV disease burden in humans and animals.

Responding to Higher-Than-Expected Infant Mortality Rates from Respiratory Syncytial Virus (RSV): Improving Treatment and Reporting Strategies

Respiratory syncytial virus (RSV) has a major role in respiratory infections in young infants around the world. However, substantial progress has been made in recent years in the field of RSV. A wide variety of observational studies and clinical trials published in the past decade provide a thorough idea of the health and economic burden of RSV disease in the developing world. In this review, we discuss the impact of RSV burden of disease, major gaps in disease estimations, and challenges in generating new therapeutic options and an immune response against the virus, and briefly describe next generation technologies that are being evaluated.

Antibodies face the challenge against human respiratory syncytial virus

In the December 22 issue of Cell, Bartsch et al. describe functional profiling of the antibody response to respiratory syncytial virus in human adults vaccinated with an experimental adenovirus-based prefusion-stabilized HRSV-F vaccine and subsequently intranasally challenged with HRSV. The authors identified various antibody effector functions as humoral correlates of protection.

Respiratory syncytial virus prevention within reach: the vaccine and monoclonal antibody landscape

Respiratory syncytial virus is the second most common cause of infant mortality and a major cause of morbidity and mortality in older adults (aged >60 years). Efforts to develop a respiratory syncytial virus vaccine or immunoprophylaxis remain highly active. 33 respiratory syncytial virus prevention candidates are in clinical development using six different approaches: recombinant vector, subunit, particle-based, live attenuated, chimeric, and nucleic acid vaccines; and monoclonal antibodies. Nine candidates are in phase 3 clinical trials. Understanding the epitopes targeted by highly neutralising antibodies has resulted in a shift from empirical to rational and structure-based vaccine and monoclonal antibody design. An extended half-life monoclonal antibody for all infants is likely to be within 1 year of regulatory approval (from August, 2022) for high-income countries. Live-attenuated vaccines are in development for older infants (aged >6 months). Subunit vaccines are in late-stage trials for pregnant women to protect infants, whereas vector, subunit, and nucleic acid approaches are being developed for older adults. Urgent next steps include ensuring access and affordability of a respiratory syncytial virus vaccine globally. This review gives an overview of respiratory syncytial virus vaccines and monoclonal antibodies in clinical development highlighting different target populations, antigens, and trial results.

Accelerating model-informed decisions for COVID-19 vaccine candidates using a model-based meta-analysis approach

BACKGROUND

The COVID-19 pandemic has increased the need for innovative quantitative decision tools to support rapid development of safe and efficacious vaccines against SARS-CoV-2. To meet that need, we developed and applied a model-based meta-analysis (MBMA) approach integrating non-clinical and clinical immunogenicity and protection data.

METHODS

A systematic literature review identified studies of vaccines against SARS-CoV-2 in rhesus macaques (RM) and humans. Summary-level data of 13 RM and 8 clinical trials were used in the analysis. A RM MBMA model was developed to quantify the relationship between serum neutralizing (SN) titres after vaccination and peak viral load (VL) post-challenge in RM. The translation of the RM MBMA model to a clinical protection model was then carried out to predict clinical efficacies based on RM data alone. Subsequently, clinical SN and efficacy data were integrated to develop three predictive models of efficacy - a calibrated RM MBMA, a joint (RM-Clinical) MBMA, and the clinical MBMA model. The three models were leveraged to predict efficacies of vaccine candidates not included in the model and efficacies against newer strains of SARS-CoV-2.

FINDINGS

Clinical efficacies predicted based on RM data alone were in reasonable agreement with the reported data. The SN titre predicted to provide 50% efficacy was estimated to be about 21% of the mean human convalescent titre level, and that value was consistent across the three models. Clinical efficacies predicted from the MBMA models agreed with reported efficacies for two vaccine candidates (BBV152 and CoronaVac) not included in the modelling and for efficacies against delta variant.

INTERPRETATION

The three MBMA models are predictive of protection against SARS-CoV-2 and provide a translational framework to enable early Go/No-Go and study design decisions using non-clinical and/or limited clinical immunogenicity data in the development of novel SARS-CoV-2 vaccines.

FUNDING

This study was funded by Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.

Neutralization Activity of Anti-drug Antibodies Against a Biotherapeutic Can Be Predicted from a Comprehensive Pharmacokinetics, Pharmacodynamics, and Anti-drug Antibody Data Analysis

Historically, a neutralization antibody (NAb) assay is considered critical in immunogenicity assessment of biologic therapeutics, even with low anti-drug antibody (ADA) positive rates. In 2019, FDA new guidelines issued on immunogenicity testing acknowledged the possibility of using "a highly sensitive PD marker or an appropriately designed PK assay or both that generate data that inform clinical activity" to replace a NAb assay. In the current manuscript, we present data for PK, PD, and ADA assays which collectively succeed to replace the standalone NAb assay. The data include a total LC/MS-based PK assay, a serum neutralization antibody (SNA) assay that essentially measures pharmacodynamically functional PK and can detect NAb activity in the presence of 1:1 ratio of drug, and a highly drug-tolerant ADA assay. In addition, a model-based meta-analysis (MBMA) demonstrated that the ability of SNA assay to detect NAb at 1:1 ratio of drug is sensitive enough to monitor clinically meaningful efficacy change, which is 50% reduction of SNA titer. Our strategy of preparing a holistic data package discussed here may provide a roadmap to the community for alternatives in assaying neutralizing activity of ADA.

Virus reduction neutralization test and LI-COR microneutralization assay bridging and WHO international standard calibration studies for respiratory syncytial virus

Background: Respiratory syncytial virus (RSV) vaccine is an unmet medical need. The virus reduction neutralization test (VRNT) was developed to replace the LI-COR microneutralization assay to measure RSV neutralization titers. Methods: A bridging study using selected V171 phase I samples and calibration studies using the WHO international standard antiserum to RSV were performed to compare VRNT and LI-COR. Results: From the bridging study, we showed good concordance between VRNT and LI-COR titers, and similar post-/pre-vaccination titer ratios. From the calibration studies, we can convert VRNT and LI-COR titers into similar IU/ml. Conclusion: The VRNT and LI-COR microneutralization assay correlate well and the titers can be standardized as similar IU/ml, enabling direct comparison of titers from different assays.

Monoclonal antibodies for prophylaxis and treatment of respiratory viral infections

PURPOSE OF REVIEW

Monoclonal antibody (mAb) administration represents an important strategy for preventing and treating respiratory viral infections in vulnerable populations, including immunocompromised individuals. The purpose of this review is to provide an overview of mAbs in clinical use against respiratory viruses, highlight factors that modulate mAb clinical efficacy, and provide a perspective on future innovations in the field. This review focuses on publications from the last year.

RECENT FINDINGS

Historically, clinical development of a single mAb has taken over a decade. The COVID-19 pandemic has demonstrated that this timeframe can be reduced to less than a year and has catalyzed rapid innovations in the field. Several novel mAbs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have received emergency use authorization by the Food and Drug Administration (FDA) for the early treatment of mild to moderate COVID-19. However, the majority of these mAbs have ultimately failed due to the emergence of variants, highlighting an important lesson about predicting and countering resistance. Novel mAbs are also in clinical use or in late-stage development for the prevention of infection by SARS-CoV-2 and respiratory syncytial virus (RSV) in vulnerable populations. Several factors can be modulated to improve the clinical efficacy of mAbs. For example, Fc modifications can extend mAb half-life and increase respiratory tract bioavailability, both of which are attractive properties for achieving protection against respiratory viruses.

SUMMARY

The mAb landscape is rapidly evolving with numerous examples of success and failure. The armamentarium of clinically-available mAbs to protect vulnerable populations is expected to undergo continued growth.

A Phase 1 Study to Evaluate Safety, Pharmacokinetics, and Pharmacodynamics of Respiratory Syncytial Virus (RSV) Neutralizing Monoclonal Antibody MK-1654 in Healthy Japanese Adults

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection among all infants worldwide and remains a significant cause of morbidity and mortality. To address this unmet medical need, MK‐1654, a half‐life extended RSV neutralizing monoclonal antibody, is in clinical development for the prevention of RSV disease in infants. This was a phase I, randomized, placebo‐controlled, single‐site, double‐blind trial of MK‐1654 in 44 healthy Japanese adults. The safety, tolerability, pharmacokinetics, antidrug antibodies (ADAs), and serum neutralizing antibody (SNA) titers against RSV were evaluated for 1 year after a single intramuscular (i.m.) or intravenous (i.v.) dose of MK‐1654 or placebo in five groups (100 mg i.m., 300 mg i.m., 300 mg i.v., 1000 mg i.v., or placebo). MK‐1654 was generally well‐tolerated in Japanese adults. There were no serious drug‐related adverse events (AEs) reported in any MK‐1654 recipient and no discontinuations due to any AEs in the study. The half‐life of MK‐1654 ranged from 76 to 91 days across dosing groups. Estimated bioavailability was 86% for 100 mg i.m. and 77% for 300 mg i.m. One participant out of 33 (3.0%) developed detectable ADA with no apparent associated AEs. The RSV SNA titers increased in a dose‐dependent manner among participants who received MK‐1654. These data support the development of MK‐1654 for use in Japanese infants.

Location matters in RSV protection

In this issue of Cell Host & Microbe, Zohar et al., 2022 show that immunization of non-human primates with six different candidate respiratory syncytial virus vaccines resulted in distinct antibody profiles and variable levels of protection. Using a systems serology approach, they identified compartment-specific antibody-mediated correlates of protection.

Upper and lower respiratory tract correlates of protection against respiratory syncytial virus following vaccination of nonhuman primates

Respiratory syncytial virus (RSV) infection is a major cause of respiratory illness in infants and the elderly. Although several vaccines have been developed, none have succeeded in part due to our incomplete understanding of the correlates of immune protection. While both T cells and antibodies play a role, emerging data suggest that antibody-mediated mechanisms alone may be sufficient to provide protection. Therefore, to map the humoral correlates of immunity against RSV, antibody responses across six different vaccines were profiled in a highly controlled nonhuman primate-challenge model. Viral loads were monitored in both the upper and lower respiratory tracts, and machine learning was used to determine the vaccine platform-agnostic antibody features associated with protection. Upper respiratory control was associated with virus-specific IgA levels, neutralization, and complement activity, whereas lower respiratory control was associated with Fc-mediated effector mechanisms. These findings provide critical compartment-specific insights toward the rational development of future vaccines.