M281, an anti-FcRn antibody, inhibits IgG transfer in a human ex vivo placental perfusion model

Novel therapies in CIDP

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a heterogeneous but clinically well-described disease within circumscribed parameters. It is immunologically mediated through several poorly understood mechanisms. First-line therapies with steroids, intravenous immunoglobulin (IVIG) or plasma exchange are each effective in about two-thirds of patients. These treatments are seldom associated with complete resolution or cure, and often pose considerable practical, financial and medical implications.Our understanding of many of the key pathological processes in autoimmune diseases is expanding, and novel targeted therapeutics are being developed with promise in several autoimmune neurological disorders.This narrative review looks first at detailing key pathogenic mechanisms of disease in CIDP, followed by an in-depth description of potential novel therapies and the current evidence of their application in clinical practice.

Design of a Phase 3, Global, Multicenter, Randomized, Placebo-Controlled, Double-Blind Study of Nipocalimab in Pregnancies at Risk for Severe Hemolytic Disease of the Fetus and Newborn

OBJECTIVE

 Nipocalimab is a neonatal fragment crystallizable (Fc) receptor (FcRn)-blocking monoclonal antibody that inhibits placental immunoglobulin G (IgG) transfer and lowers circulating maternal IgG levels. In an open-label, single-arm, phase 2 study, nipocalimab demonstrated evidence of safety and efficacy that support further investigation in a pivotal phase 3 trial of recurrent hemolytic disease of the fetus and newborn (HDFN). The phase 3 AZALEA study aims to evaluate the efficacy and safety of nipocalimab in a larger population at risk for severe HDFN, defined as HDFN associated with poor fetal outcomes or neonatal death.

STUDY DESIGN

 AZALEA is a multicenter, randomized, placebo-controlled, double-blind, phase 3 study enrolling alloimmunized pregnant individuals (N ≈ 120) at risk for severe HDFN based on obstetric history. Participants are randomized 2:1 to receive intravenous 45 mg/kg nipocalimab or placebo weekly from 13-16 to 35 weeks gestational age (GA). During the double-blind treatment period, participants receive standard-of-care weekly monitoring for fetal anemia until planned delivery at 37 to 38 weeks of GA. Postnatal follow-up periods are 24 weeks for maternal participants and 104 weeks for neonates/infants.

RESULTS

 The primary endpoint is the proportion of pregnancies that do not result in intrauterine transfusion (IUT), hydrops fetalis, or fetal loss/neonatal death from all causes. Key secondary endpoints include the severity of HDFN as measured by a composite HDFN severity index, the earliest time to occurrence of IUT or hydrops fetalis, the modified neonatal mortality and morbidity index in liveborn neonates, and the number of IUTs received. Other endpoints are safety, patient- and caregiver-reported outcomes, pharmacokinetics, pharmacodynamics (e.g., IgG, FcRn receptor occupancy), and immunogenicity of nipocalimab.

CONCLUSION

 AZALEA, the first placebo-controlled, randomized, multicenter, prospective trial in severe HDFN, is designed to evaluate the safety and efficacy of nipocalimab, a potential preventive and noninvasive intervention, in at-risk HDFN pregnancies.

KEY POINTS

· Severe HDFN leads to poor fetal/neonatal outcomes.. · IUTs are associated with complications and fetal loss.. · Nipocalimab blocks IgG recycling and placental transfer.. · Nipocalimab reduces fetal anemia and IUTs in early-onset severe HDFN.. · The phase 3 AZALEA study evaluates nipocalimab in severe HDFN..

Nipocalimab in Early-Onset Severe Hemolytic Disease of the Fetus and Newborn

BACKGROUND

In early-onset severe hemolytic disease of the fetus and newborn (HDFN), transplacental transfer of maternal antierythrocyte IgG alloantibodies causes fetal anemia that leads to the use of high-risk intrauterine transfusions in order to avoid fetal hydrops and fetal death. Nipocalimab, an anti-neonatal Fc receptor blocker, inhibits transplacental IgG transfer and lowers maternal IgG levels.

METHODS

In an international, open-label, single-group, phase 2 study, we assessed treatment with intravenous nipocalimab (30 or 45 mg per kilogram of body weight per week) administered from 14 to 35 weeks' gestation in participants with pregnancies at high risk for recurrent early-onset severe HDFN. The primary end point was live birth at 32 weeks' gestation or later without intrauterine transfusions as assessed against a historical benchmark (0%; clinically meaningful difference, 10%).

RESULTS

Live birth at 32 weeks' gestation or later without intrauterine transfusions occurred in 7 of 13 pregnancies (54%; 95% confidence interval, 25 to 81) in the study. No cases of fetal hydrops occurred, and 6 participants (46%) did not receive any antenatal or neonatal transfusions. Six fetuses received an intrauterine transfusion: five fetuses at 24 weeks' gestation or later and one fetus before fetal loss at 22 weeks and 5 days' gestation. Live birth occurred in 12 pregnancies. The median gestational age at delivery was 36 weeks and 4 days. Of the 12 live-born infants, 1 received one exchange transfusion and one simple transfusion and 5 received only simple transfusions. Treatment-related decreases in the alloantibody titer and IgG level were observed in maternal samples and cord blood. No unusual maternal or pediatric infections were observed. Serious adverse events were consistent with HDFN, pregnancy, or prematurity.

CONCLUSIONS

Nipocalimab treatment delayed or prevented fetal anemia or intrauterine transfusions, as compared with the historical benchmark, in pregnancies at high risk for early-onset severe HDFN. (Funded by Janssen Research and Development; UNITY ClinicalTrials.gov number, NCT03842189.).

Pharmacokinetics and Pharmacodynamics of Nipocalimab, a Neonatal Fc Receptor Blocker, in Healthy Japanese Volunteers

BACKGROUND AND OBJECTIVES

Nipocalimab is a high-affinity, fully human, effectorless immunoglobulin G1 monoclonal antibody targeting the neonatal Fc receptor and is currently under evaluation for the treatment of rare and prevalent immunoglobulin G autoantibody-mediated and alloantibody-mediated diseases. This phase I, randomized, double-blind, placebo-controlled, single-dose escalation study in healthy Japanese volunteers (N = 24) assessed the safety, pharmacokinetics, and effect on the serum immunoglobulin G level of single doses of nipocalimab.

METHODS

Volunteers were grouped into three cohorts and received intravenous nipocalimab at 10, 30, or 60 mg/kg or placebo. To complement the study, genetic variation in the Fcγ receptor and transporter subunit of the neonatal Fc receptor was analyzed in Japanese and diverse populations.

RESULTS

Nipocalimab was generally safe and well tolerated at all dose levels, with three (12.5% [3/24]) volunteers experiencing treatment-emergent adverse events across all nipocalimab doses. Mean serum immunoglobulin G levels decreased in a dose-dependent manner from baseline with nipocalimab treatment compared with placebo. Maximum serum nipocalimab concentrations demonstrated proportional increases with dose, while the area under the concentration-time curve was dose dependent and demonstrated non-linear increases with dose. Mean observed half-life was longer as the dose increased. Analysis of genetic variation in Fcγ receptor and transporter identified no unique Japanese variants or variants that alter amino acid sequences in or near the neonatal Fc receptor immunoglobulin G binding site targeted by nipocalimab.

CONCLUSIONS

The comparable pharmacokinetic/pharmacodynamic profiles and highly conserved neonatal Fc receptor structure among diverse populations further support the clinical development of nipocalimab for the treatment of various immunoglobulin G autoantibody-mediated and alloantibody-mediated diseases across global sites and populations, including the Japanese population.

Development and validation of HPLC-ultraviolet method for quantitative determination of pritelivir in human placental perfusion medium

A simple and reliable HPLC-ultraviolet (HPLC-UV) method was developed and validated for the quantification of pritelivir in the samples of medium from the experiments utilizing the ex vivo technique of dual perfusion of the human placental lobule. Phenacetin was used as an internal standard (IS) in our HPLC-UV method. Chromatographic separation of pritelivir and phenacetin was achieved on a Waters Symmetry C18 HPLC column (100 × 2.1 mm, 3.5 μm) at ambient temperature (22-25°C). The mobile phase was composed of 50% methanol in deionized water (v/v), the flow rate for isocratic elution was established at 0.25 mL/min, and the detection wavelength for pritelivir and IS was set at 254 nm. Pritelivir and IS were extracted with the protein precipitation method using methanol as a solvent. The calibration curve for pritelivir exhibited linearity (r2 > 0.99) within the concentration range from 0.155 to 6.62 μg/mL. Within- and between-day accuracy ranged from 97% to 110% with relative standard deviation (RSD) values not exceeding 10%. The extraction recovery of pritelivir and IS ranged from 89% to 91% with RSD not exceeding 7%. Pritelivir was stable under the storage and sample handling conditions. This validated HPLC-UV method was utilized to quantify pritelivir in the placental perfusion medium samples, and the resulting concentrations were authenticated with incurred sample reanalysis to confirm the reliability of the method.

Severity of haemolytic disease of the fetus and newborn in patients with a history of intrauterine transfusions in a previous pregnancy: A nationwide retrospective cohort study

OBJECTIVE

Pregnant women who received at least one intrauterine transfusion (IUT) for haemolytic disease of the fetus and newborn (HDFN) in the preceding pregnancy are presumed to have a high likelihood of requiring IUTs again, often starting at an earlier gestational age. Our aim was to quantify these risks in a large national cohort.

DESIGN

Retrospective cohort study of a nationwide Dutch database.

SETTING

The Netherlands.

POPULATION

All women treated in The Netherlands with IUTs for Rhesus D (RhD)- or Kell-mediated HDFN between 1999 and 2017 and their follow-up pregnancies were included. Pregnancies with an antigen-negative fetus were excluded.

METHODS

Electronic patient files were searched for the number and gestational age of each IUT, and analysed using descriptive statistics and linear regression.

MAIN OUTCOME MEASURES

Percentage of women requiring one or more IUTs again in the subsequent pregnancy, and gestational age at first IUT in both pregnancies.

RESULTS

Of the 321 women in our study population, 21% (69) had a subsequent ongoing pregnancy at risk. IUTs were administered in 86% (59/69) of cases. In subsequent pregnancies, the median gestational age at first IUT was 3 weeks earlier (interquartile range -6.8 to 0.4) than in the preceding pregnancy.

CONCLUSIONS

Our study shows that pregnant women with a history of IUTs in the previous pregnancy are highly likely to require IUTs again, and on average 3 weeks earlier. Clinicians need to be aware of these risks and ensure timely referral, and close surveillance from early pregnancy onwards. Additionally, for women with a history of IUT and their caregivers, this information is essential to enable adequate preconception counselling.

Transient Neonatal Myasthenia Gravis as a Common Complication of a Rare Disease: A Systematic Review

Myasthenia gravis (MG) is a rare autoimmune disease. Transient neonatal myasthenia gravis (TNMG) is caused by pathogenic maternal autoantibodies that cross the placenta and disrupt signaling at the neuromuscular junction. This is a systematic review of this transient immunoglobulin G (IgG)-mediated disease. TNMG affects 10-20% of children born to mothers with MG. The severity of symptoms ranges from minor feeding difficulties to life-threatening respiratory weakness. Minor symptoms might go unnoticed but can still interfere with breastfeeding. Acetylcholine-esterase inhibitors and antibody-clearing therapies such as immunoglobulins can be used to treat TNMG, but most children do well with observation only. TNMG is self-limiting within weeks as circulating antibodies are naturally cleared from the blood. In rare cases, TNMG is associated with permanent skeletal malformations or permanent myopathy. The mother's antibodies can also lead to spontaneous abortions. All healthcare professionals meeting pregnant or birthing women with MG or their neonates should be aware of TNMG. TNMG is hard to predict. Reoccurrence is common among siblings. Pre-pregnancy thymectomy and intravenous immunoglobulins during pregnancy reduce the risk. Neonatal fragment crystallizable receptor (FcRn) blocking drugs for MG might reduce TNMG risk.

The Efficacy and Safety of Different Targeted Drugs for the Treatment of Generalized Myasthenia Gravis: A Systematic Review and Bayesian Network Meta-analysis

BACKGROUND

The treatment of generalized myasthenia gravis (gMG) has been transformed by the development and approval of new targeted therapies. This analysis aimed to rank and compare the new therapies for gMG using efficacy and safety data from randomized controlled trials (RCTs).

METHODS

We searched PubMed, Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), and ClinicalTrials.gov (up to November 2022) for RCTs of targeted drugs for gMG. We used a Bayesian random-effects network meta-analysis (NMA) model and a Markov chain Monte Carlo (MCMC) model for statistical analysis. The primary outcome was the change in quantitative myasthenia gravis score (QMGS) from baseline, while the secondary outcome was the risk ratio (RR) of adverse events (AEs) during treatment. The surface under the cumulative ranking curve (SUCRA) was used to rank these targeted drugs, with higher SUCRA values indicating better efficacy or lower likelihood of AEs.

RESULTS

In total, 13 studies (872 subjects) were included in this analysis evaluating 10 targeted drugs (batoclimab, belimumab, CFZ533, eculizumab, efgartigimod, nipocalimab, rituximab, ravulizumab, rozanolixizumab, and zilucoplan). With regards to the primary outcome, batoclimab [standardized mean difference (SMD), - 1.61; 95% credible interval (CrI), - 2.78, - 0.43] significantly reduced QMGS in patients with gMG when compared with placebo and was ranked as the most efficacious drug. Ranked second and third were eculizumab (SMD, - 0.67; 95% CrI, 1.43, 0.01) and zilucoplan (SMD, - 0.54; 95% CrI, - 1.56, 0.46), respectively. Nipoclimab (SMD, - 0.02; 95% CrI, - 1.04, 1.00) had the worst efficacy and ranked last among all targeted drugs. In our study, except for batoclimab, there was no statistically significant difference in the reduction of patient QMGS for the remaining targeted agents compared with placebo. With regards to the secondary outcomes, only batoclimab (RR, 0.19; 95% CrI, 0, 0.97) led to a significant reduction in the incidence of AEs when compared with the placebo. Belimumab (RR, 0.85; 95% CrI, 0.57, 1.19), CFZ533 (RR, 0.95; 95% CrI, 0.72, 1.25), eculizumab (RR, 0.99; 95% CrI, 0.85, 1.21), and efgartigimod (RR, 0.93; 95% CrI, 0.76, 1.15) also led to a lower incidence of AEs, although these effects were not significantly different from the placebo.

CONCLUSIONS

Batoclimab had the best efficacy and safety for the treatment of gMG and was ranked first out of the 10 targeted drugs included in this study. Eculizumab was ranked second, and nipocalimab had the worst efficacy. With the exception of batoclimab, the incidence of AEs for the remaining drugs was not statistically significantly different from placebo. We note, however, that wide CrIs reflect the uncertainty in this analysis owing to the small number of available studies and low numbers of study participants; moreover, batoclimab had the widest CrI of all drugs in this analysis. More well-designed studies with long-term follow-up are needed to further evaluate and compare the efficacy and safety of these drugs in the future.

Safety and Efficacy of Nipocalimab in Patients With Generalized Myasthenia Gravis: Results From the Randomized Phase 2 Vivacity-MG Study

BACKGROUND AND OBJECTIVES

To evaluate in a phase 2 study the safety and efficacy of IV nipocalimab, a fully human, antineonatal Fc receptor monoclonal antibody, in patients with generalized myasthenia gravis (gMG).

METHODS

Patients with gMG with inadequate response to stable standard-of-care (SOC) therapy were randomized 1:1:1:1:1 to receive either IV placebo every 2 weeks (Q2W) or one of 4 IV nipocalimab treatments: 5 mg/kg once every 4 weeks (Q4W), 30 mg/kg Q4W, 60 mg/kg Q2W each for 8 weeks, or a 60 mg/kg single dose, in addition to their background SOC therapy. Infusions (placebo or nipocalimab) were Q2W in all groups to maintain blinding. The primary safety endpoint was incidence of treatment-emergent adverse events (TEAEs), including serious adverse events and adverse events of special interest. The primary efficacy endpoint was change from baseline to day 57 in Myasthenia Gravis-Activities of Daily Living (MG-ADL) total scores. Dose response of change at day 57 was analyzed with a linear trend test over the placebo, nipocalimab 5 mg/kg Q4W, nipocalimab 30 mg/kg Q4W, and nipocalimab 60 mg/kg Q2W groups.

RESULTS

Sixty-eight patients (nipocalimab: n = 54; placebo, n = 14) were randomized; 64 patients (94.1%) were positive for antiacetylcholine receptor autoantibodies, and 4 patients (6%) were positive for antimuscle-specific tyrosine kinase autoantibodies. Fifty-seven patients (83.8%) completed treatment through day 57. The combined nipocalimab group compared with the placebo group demonstrated similar incidences of TEAEs (83.3% vs 78.6%, respectively) and infections (33.3% vs 21.4%, respectively). No deaths or discontinuations due to TEAEs and no TEAEs of special interest (grade ≥3 infection or hypoalbuminemia) were observed with nipocalimab treatment. A statistically significant dose response was observed for change from baseline in MG-ADL at day 57 (p = 0.031, test of linear trend).

DISCUSSION

Nipocalimab was generally safe, well-tolerated, and showed evidence of dose-dependent reduction in MG-ADL scores at day 57 in this phase 2 study. These results support further evaluation of nipocalimab for the treatment of gMG.

TRIAL REGISTRATION INFORMATION

Clinical Trials Registration: NCT03772587; first submitted December 10, 2018; EudraCT Number: 2018-002247-28; first submitted November 30, 2018; date of first patient dosed April 10, 2019.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that for patients with gMG, nipocalimab was well-tolerated, and it did not significantly improve MG-ADL at any individual dose but demonstrated a significant dose response for improved MG-ADL across doses.

Current Insights Into K-associated Fetal Anemia and Potential Treatment Strategies for Sensitized Pregnancies

K-associated anemic disease of the fetus and newborn (K-ADFN) is a rare but life-threatening disease in which maternal alloantibodies cross the placenta and can mediate an immune attack on fetal red blood cells expressing the K antigen. A considerably more common disease, D-associated hemolytic disease of the fetus and newborn (D-HDFN), can be prophylactically treated using polyclonal α-D antibody preparations. Currently, no such prophylactic treatment exists for K-associated fetal anemia, and disease is usually treated with intrauterine blood transfusions. Here we review current understanding of the biology of K-associated fetal anemia, how the maternal immune system is sensitized to fetal red blood cells, and what is understood about potential mechanisms of prophylactic HDFN interventions. Given the apparent challenges associated with preventing alloimmunization, we highlight novel strategies for treating sensitized mothers to prevent fetal anemia that may hold promise not only for K-mediated disease, but also for other pathogenic alloantibody responses.

Balance between maternal antiviral response and placental transfer of protection in gestational SARS-CoV-2 infection

The intricate interplay between maternal immune response to SARS-CoV-2 and the transfer of protective factors to the fetus remains unclear. By analyzing mother-neonate dyads from second and third trimester SARS-CoV-2 infections, our study shows that neutralizing antibodies (NAbs) are infrequently detected in cord blood. We uncovered that this is due to impaired IgG-NAb placental transfer in symptomatic infection and to the predominance of maternal SARS-CoV-2 NAbs of the IgA and IgM isotypes, which are prevented from crossing the placenta. Crucially, the balance between maternal antiviral response and transplacental transfer of IgG-NAbs appears to hinge on IL-6 and IL-10 produced in response to SARS-CoV-2 infection. In addition, asymptomatic maternal infection was associated with expansion of anti-SARS-CoV-2 IgM and NK cell frequency. Our findings identify a protective role for IgA/IgM-NAbs in gestational SARS-CoV-2 infection and open the possibility that the maternal immune response to SARS-CoV-2 infection might benefit the neonate in 2 ways, first by skewing maternal immune response toward immediate viral clearance, and second by endowing the neonate with protective mechanisms to curtail horizontal viral transmission in the critical postnatal period, via the priming of IgA/IgM-NAbs to be transferred by the breast milk and via NK cell expansion in the neonate.

FcRN receptor antagonists in the management of myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disorder characterized by autoantibodies specifically directed against proteins located within the postsynaptic membrane of the neuromuscular junction. These pathogenic autoantibodies can be reduced by therapies such as plasma exchange, IVIG infusions and other immunosuppressive agents. However, there are significant side effects associated with most of these therapies. Since there is a better understanding of the molecular structure and the biological properties of the neonatal Fc receptors (FcRn), it possesses an attractive profile in treating myasthenia gravis. FcRn receptors prevent the catabolism of IgG by impeding their lysosomal degradation and facilitating their extracellular release at physiological pH, consequently extending the IgG half-life. Thus, the catabolism of IgG can be enhanced by blocking the FcRn, leading to outcomes similar to those achieved through plasma exchange with no significant safety concerns. The available studies suggest that FcRn holds promise as a versatile therapeutic intervention, capable of delivering beneficial outcomes in patients with distinct characteristics and varying degrees of MG severity. Efgartigimod is already approved for the treatment of generalized MG, rozanolixizumab is under review by health authorities, and phase 3 trials of nipocalimab and batoclimab are underway. Here, we will review the available data on FcRn therapeutic agents in the management of MG.

The therapeutic age of the neonatal Fc receptor

IgGs are essential soluble components of the adaptive immune response that evolved to protect the body from infection. Compared with other immunoglobulins, the role of IgGs is distinguished and enhanced by their high circulating levels, long half-life and ability to transfer from mother to offspring, properties that are conferred by interactions with neonatal Fc receptor (FcRn). FcRn binds to the Fc portion of IgGs in a pH-dependent manner and protects them from intracellular degradation. It also allows their transport across polarized cells that separate tissue compartments, such as the endothelium and epithelium. Further, it is becoming apparent that FcRn functions to potentiate cellular immune responses when IgGs, bound to their antigens, form IgG immune complexes. Besides the protective role of IgG, IgG autoantibodies are associated with numerous pathological conditions. As such, FcRn blockade is a novel and effective strategy to reduce circulating levels of pathogenic IgG autoantibodies and curtail IgG-mediated diseases, with several FcRn-blocking strategies on the path to therapeutic use. Here, we describe the current state of knowledge of FcRn-IgG immunobiology, with an emphasis on the functional and pathological aspects, and an overview of FcRn-targeted therapy development.

A review of ex vivo placental perfusion models: an underutilized but promising method to study maternal-fetal interactions

Studying the placenta can provide information about the mechanistic pathways of pregnancy disease. However, analyzing placental tissues and manipulating placental function in real-time during pregnancy is not feasible. The ex vivo placental perfusion model allows observing important aspects of the physiology and pathology of the placenta, while maintaining its viability and functional integrity, and without causing harm to mother or fetus. In this review, we describe and compare setups for this technically complex model and summarize outcomes from various published studies. We hope that our review will encourage wider use of ex vivo placental perfusion, which in turn would generate more knowledge to improve pregnancy outcomes.

Monoclonal Antibody Engineering and Design to Modulate FcRn Activities: A Comprehensive Review

Understanding the biological mechanisms underlying the pH-dependent nature of FcRn binding, as well as the various factors influencing the affinity to FcRn, was concurrent with the arrival of the first recombinant IgG monoclonal antibodies (mAbs) and IgG Fc-fusion proteins in clinical practice. IgG Fc–FcRn became a central subject of interest for the development of these drugs for the comfort of patients and good clinical responses. In this review, we describe (i) mAb mutations close to and outside the FcRn binding site, increasing the affinity for FcRn at acidic pH and leading to enhanced mAb half-life and biodistribution, and (ii) mAb mutations increasing the affinity for FcRn at acidic and neutral pH, blocking FcRn binding and resulting, in vivo, in endogenous IgG degradation. Mutations modifying FcRn binding are discussed in association with pH-dependent modulation of antigen binding and (iii) anti-FcRn mAbs, two of the latest innovations in anti-FcRn mAbs leading to endogenous IgG depletion. We discuss the pharmacological effects, the biological consequences, and advantages of targeting IgG–FcRn interactions and their application in human therapeutics.

Contribution of the ex vivo placental perfusion model in understanding transplacental immunoglobulin G transfer

INTRODUCTION

The acquisition of humoral immunity in utero is essential for the fetus. The crucial protein, which is responsible for this part of immunity, is immunoglobulin-G (IgG). Immune functions of IgGs are mediated via the interaction of the crystallizable fragment (Fc) region of IgG with specific Fc γ receptors (FcγRs). However, an atypical FcγR, the neonatal Fc receptor (FcRn), is a key regulator of IgG transfer across the human placenta. During the last four decades ex vivo placental perfusion studies have contributed significantly to the study of mechanisms of IgG transfer across the multicellular placental barrier.

METHOD

A PubMed search was conducted by using specific keywords: placenta, perfusion and IgG to review manuscripts using human placental perfusion to study the transplacental transfer of IgG. Relevant studies found in reference lists of these manuscripts were also added to the review, and references were included that supported or gave nuance to the discussion of the mechanisms of IgG kinetics in the placenta.

RESULTS AND DISCUSSION

We found twenty publications on the study of transplacental transfer of IgG using human ex vivo placental perfusion, by research groups with partly different settings. This review summarizes knowledge about placental IgG transfer, with a strong focus on the contributions from ex vivo placental perfusion studies.

Opportunities and Challenges for PBPK Model of mAbs in Paediatrics and Pregnancy

New drugs may in some cases need to be tested in paediatric and pregnant patients. However, it is difficult to recruit such patients and there are many ethical issues around their inclusion in clinical trials. Modelling and simulation can help to plan well-designed clinical trials with a reduced number of participants and to bridge gaps where recruitment is difficult. Physiologically based pharmacokinetic (PBPK) models for small molecule drugs have been used to aid study design and dose adjustments in paediatrics and pregnancy, with several publications in the literature. However, published PBPK models for monoclonal antibodies (mAb) in these populations are scarce. Here, the current status of mAb PBPK models in paediatrics and pregnancy is discussed. Seven mAb PBPK models published for paediatrics were found, which report good prediction accuracy across a wide age range. No mAb PBPK models for pregnant women have been published to date. Current challenges to the development of such PBPK models are discussed, including gaps in our knowledge of relevant physiological processes and availability of clinical data to verify models. As the availability of such data increases, it will help to improve our confidence in the PBPK model predictive ability. Advantages for using PBPK models to predict mAb PK in paediatrics and pregnancy are discussed. For example, the ability to incorporate ontogeny and gestational changes in physiology, prediction of maternal, placental and foetal exposure and the ability to make predictions from in vitro and preclinical data prior to clinical data being available.

Pharmacotherapy of Generalized Myasthenia Gravis with Special Emphasis on Newer Biologicals

Myasthenia gravis (MG) is a chronic, fluctuating, antibody-mediated autoimmune disorder directed against the post-synaptic neuromuscular junctions of skeletal muscles, resulting in a wide spectrum of manifestations ranging from mild to potentially fatal. Given its unique natural course, designing an ideal trial design for MG has been wrought with difficulties and evidence in favour of several of the conventional agents is weak as per current standards. Despite this, acetylcholinesterases and corticosteroids have remained the cornerstones of treatment for several decades with intravenous immunoglobulins (IVIG) and therapeutic plasma exchange (PLEX) offering rapid treatment response, especially in crises. However, the treatment of MG entails long-term immunosuppression and conventional agents are viable options but take longer to act and have a number of class-specific adverse effects. Advances in immunology, translational medicine and drug development have seen the emergence of several newer biological agents which offer selective, target-specific immunotherapy with fewer side effects and rapid onset of action. Eculizumab is one of the newer agents that belong to the class of complement inhibitors and has been approved for the treatment of refractory general MG. Zilucoplan and ravulizumab are other agents in this group in clinical trials. Neisseria meningitis is a concern with all complement inhibitors, mandating vaccination. Neonatal Fc receptor (FcRn) inhibitors prevent immunoglobulin recycling and cause rapid reduction in antibody levels. Efgartigimod is an FcRn inhibitor recently approved for MG treatment, and rozanolixizumab, nipocalimab and batoclimab are other agents in clinical trial development. Although lacking high quality evidence from randomized clinical trials, clinical experience with the use of anti-CD20 rituximab has led to its use in refractory MG. Among novel targets, interleukin 6 (IL6) inhibitors such as satralizumab are promising and currently undergoing evaluation. Cutting-edge therapies include genetically modifying T cells to recognise chimeric antigen receptors (CAR) and chimeric autoantibody receptors (CAAR). These may offer sustained and long-term remissions, but are still in very early stages of evaluation. Hematopoietic stem cell transplantation (HSCT) allows immune resetting and offers sustained remission, but the induction regimens often involve serious systemic toxicity. While MG treatment is moving beyond conventional agents towards target-specific biologicals, lack of knowledge as to the initiation, maintenance, switching, tapering and long-term safety profile necessitates further research. These concerns and the high financial burden of novel agents may hamper widespread clinical use in the near future.

Development of New Drugs for Autoimmune Hemolytic Anemia

Autoimmune hemolytic anemia (AIHA) is a rare disorder characterized by the autoantibody-mediated destruction of red blood cells, and treatments for it still remain challenging. Traditional first-line immunosuppressive therapy, which includes corticosteroids and rituximab, is associated with adverse effects as well as treatment failures, and relapses are common. Subsequent lines of therapy are associated with higher rates of toxicity, and some patients remain refractory to currently available treatments. Novel therapies have become promising for this vulnerable population. In this review, we will discuss the mechanism of action, existing data, and ongoing clinical trials of current novel therapies for AIHA, including B-cell-directed therapy, phagocytosis inhibition, plasma cell-directed therapy, and complement inhibition.

Blocking Placental Class G Immunoglobulin Transfer Prevents NMDA Receptor Antibody Effects in Newborn Mice

BACKGROUND AND OBJECTIVES

To determine in a mouse model whether neonatal Fc receptor (FcRn) blockade prevents the placental transfer of class G immunoglobulin (IgG) derived from patients with anti-NMDA receptor (NMDAR) encephalitis and their pathogenic effects on the fetuses and offspring.

METHODS

Pregnant C57BL/6J mice were administered via tail vein FcRn antibody (FcRn-ab) or saline solution 6 hours before administration of patients' or controls' IgG on days 14, 15, and 16 of gestation. Three experimental groups were established: mice receiving controls' IgG, patients' IgG, or patients' IgG along with pretreatment with FcRn-ab. Immunohistochemical staining, confocal microscopy, hippocampal long-term potentiation, and standardized developmental and behavioral tasks were used to assess the efficacy of treatment with FcRn-ab.

RESULTS

In pregnant mice that received patients' IgG, treatment with FcRn-ab prevented the IgG from reaching the fetal brain, abrogating the decrease of NMDAR clusters and the reduction of cortical plate thickness that were observed in fetuses from untreated pregnant mice. Moreover, among the offspring of mothers that received patients' IgG, those whose mothers were treated with FcRn-ab did not develop the alterations that occurred in offspring of untreated mothers, including impairment in hippocampal plasticity, delay in innate reflexes, and visuospatial memory deficits.

DISCUSSION

FcRn blockade prevents placental transfer of IgG from patients with anti-NMDAR encephalitis and abrogates the synaptic and neurodevelopmental alterations caused by patients' antibodies. This model has potential therapeutic implications for other antibody-mediated diseases of the CNS during pregnancy.

"Ways in which the neonatal Fc-receptor is involved in autoimmunity"

Since the neonatal IgG Fc receptor (FcRn) was discovered, its role has evolved from immunoglobulin recycling and biodistribution to antigen presentation and immune complex routing, bringing it to the center of both humoral and cellular immune responses. FcRn is thus involved in the pathophysiology of immune-related diseases such as cancer, infection, and autoimmune disorders. This review focuses on the role of FcRn in autoimmunity, based on the available data from both animal models and human studies. The knowledge concerning ways in which FcRn is involved in autoimmune response has led to the development of inhibitors for the treatment of autoimmune diseases, also described here. Up to date, the literature remains scarce, shedding light on the need for further studies to fully understand the various pathophysiological roles of this unique receptor.

•

FcRn is an intracellular receptor with a key role in IgG and immune complex management.

•

FcRn-targeting therapies are a promising way of treatment in antibodies mediated diseases.

The Role of Fc Receptors on the Effectiveness of Therapeutic Monoclonal Antibodies

Since the approval of the first monoclonal antibody (mAb) in 1986, a huge effort has been made to guarantee safety and efficacy of therapeutic mAbs. As of July 2021, 118 mAbs are approved for the European market for a broad range of clinical indications. In order to ensure clinical efficacy and safety aspects, (pre-)clinical experimental approaches evaluate the respective modes of action (MoA). In addition to antigen-specificity including binding affinity and -avidity, MoA comprise Fc-mediated effector functions such as antibody dependent cellular cytotoxicity (ADCC) and the closely related antibody dependent cellular phagocytosis (ADCP). For this reason, a variety of cell-based assays have been established investigating effector functions of therapeutic mAbs with different effector/target-cell combinations and several readouts including Fcγ receptor (FcγR)-mediated lysis, fluorescence, or luminescence. Optimized FcγR-mediated effector functions regarding clinical safety and efficacy are addressed with modification strategies such as point mutations, altered glycosylation patterns, combination of different Fc subclasses (cross isotypes), and Fc-truncation of the mAb. These strategies opened the field for a next generation of therapeutic mAbs. In conclusion, it is of major importance to consider FcγR-mediated effector functions for the efficacy of therapeutic mAbs.

Inhibition of Maternal-to-Fetal Transfer of IgG Antibodies by FcRn Blockade in a Mouse Model of Arthrogryposis Multiplex Congenita

Objective

To determine whether blocking the neonatal Fc receptor (FcRn) during gestation with an anti-FcRn monoclonal antibody (mAb) reduces transfer of pathogenic maternal antibodies in utero and decreases the likelihood of maternal antibody-mediated neonatal disease in the offspring.

Methods

Using a previously established maternal-to-fetal transfer mouse model of arthrogryposis multiplex congenita (AMC), we assessed the effect of 4470, an anti-FcRn mAb, on the transfer of total human immunoglobulin G (IgG) and specific acetylcholine receptor (AChR)-antibodies from mother to fetus, as well as its effect on the prevention of neurodevelopmental abnormalities in the offspring.

Results

Offspring of pregnant dams treated with 4470 during gestation showed a substantial reduction in total human IgG and AChR antibody levels compared with those treated with the isotype mAb control. Treatment with 4470 was also associated with a significant reduction in AMC-IgG–induced deformities (limb or spinal curve malformations) when compared with mAb control–exposed embryos and a nonsignificant increase in the percentage of fetuses showing spontaneous movements. 4470 exposure during pregnancy was not associated with changes in general parameters of maternal well-being or fetal development; indeed, male neonates showed faster weight gain and shorter time to reach developmental milestones.

Conclusions

FcRn blockade is a promising therapeutic strategy to prevent the occurrence of AMC and other human maternal autoantibody-related diseases in the offspring.

Neonatal Fc receptor in human immunity: Function and role in therapeutic intervention

The humoral immune response provides specific, long-lived protection against invading pathogens, via immunoglobulin production and other memory functions. IgG, the most abundant immunoglobulin isotype, has the longest half-life and protects against bacterial and viral infections. The neonatal Fc receptor (FcRn) transports IgG across barriers, for example, the placenta, enhancing fetal humoral immunity to levels similar to their mothers'. Importantly, FcRn, by protecting IgG from intracellular degradation, results in an approximately 21-day circulating IgG half-life and high plasma levels; similarly, FcRn recycles albumin and is the portal of entry for enteric cytopathic human orphan (echo) virus infection. Dysregulated immune responses may lead to antibodies against self-antigens (autoantibodies), resulting in organ-specific or systemic autoimmune diseases. Autoantibody-mediated diseases have been treated by nonspecific immunoglobulin-lowering/modulating therapies, including immunoadsorption, plasma exchange, and high-dose intravenous immunoglobulin. However, targeting FcRn with specific inhibitors results in reduction in only IgG levels. The effectiveness of FcRn inhibitors in autoimmune diseases, including myasthenia gravis and immune thrombocytopenia, provides further evidence that IgG is a primary driver in these autoantibody-mediated diseases. We describe the role of FcRn in human biology, including insights that clinical testing of FcRn inhibitors have provided into FcRn biology and autoimmune disease mechanisms, allowing fact-based speculation on their therapeutic potential.

Targeting the neonatal Fc receptor (FcRn) to treat autoimmune diseases and maternal-fetal immune cytopenias

FcRn, a non-classical Fc gamma (γ) receptor (FcγR) with near ubiquitous expression, plays key roles in disease pathogenesis and progression though immunoglobulin G (IgG) transport, IgG recycling, and IgG-immune complex clearance. FcRn function can be inhibited using IgG-based and non-IgG-based antagonists, by exploiting the pH-dependent binding affinity of FcRn for the IgG Fc region. FcRn therapeutics have shown promise in murine models and human clinical trials for autoimmune diseases and maternal-fetal immune cytopenias; they appear safe, well-tolerated, and reduce circulating IgG levels. Compared to traditional therapeutics, inhibiting FcRn has fewer adverse side effects and represents a new approach that is less invasive, time-consuming, and costly.

Neonatal Fc receptor induces intravenous immunoglobulin growth suppression in Langerhans cell histiocytosis

The neonatal Fc receptor (FcRn) plays a role in trafficking IgG and albumin and is thought to mediate intravenous immunoglobulin (IVIG) therapy for certain diseases. IVIG can be used for the treatment of human Langerhans cell histiocytosis (LCH); however, the mechanism remains unclear. The expression and function of FcRn protein have not been studied in LCH, though the expression of FcRn messenger RNA (mRNA) have been reported. In this report, we confirmed the expression of FcRn in 26 of 30 pathological cases (86.7%) diagnosed immunohistochemically as LCH. The expression was independent of age, gender, location, multi‐ or single‐system, and the status of BRAFV600E immunostaining. We also confirmed the expression of FcRn mRNA and protein in the human LCH‐like cell line, ELD‐1. FcRn suppressed albumin consumption and growth of IVIG preparation‐treated ELD‐1 cells, but not of IVIG preparation‐untreated or FcRn‐knockdown ELD‐1 cells. In addition, FITC‐conjugated albumin was taken into Rab11‐positive recycle vesicles in mock ELD‐1 cells but not in FcRn‐knockdown ELD‐1 cells. IVIG preparation prolonged this status in mock ELD‐1 cells. Therefore, ELD‐1 recycled albumin via FcRn and albumin was not used for metabolism. Our results increase our understanding of the molecular mechanism of IVIG treatment of LCH.

The neonatal Fc receptor in mucosal immune regulation

The neonatal Fc receptor (FcRn) was first recognized for its role in transfer of maternal IgG to the foetus or newborn, providing passive immunity early in life. However, it has become clear that the receptor is versatile, widely expressed and plays an indispensable role in both immunological and non-immunological processes throughout life. The receptor rescues immunoglobulin G (IgG) and albumin from intracellular degradation and shuttles the ligands across polarized cell barriers, in all cases via a pH-dependent binding-and-release mechanism. These processes secure distribution and high levels of both IgG and albumin throughout the body. At mucosal sites, FcRn transports IgG across polarized epithelial cells where it retrieves IgG in complex with luminal antigens that is delivered to tissue-localized immune cells. In dendritic cells (DCs), FcRn orchestrates processing of IgG-opsonized immune complexes (ICs) in concert with classical Fcγ receptors, which results in antigen presentation and cross-presentation of antigenic peptides on MHC class II and I to CD4+ and CD8+ T cells, respectively. Hence, FcRn regulates transport of the ligands within and across different types of cells, but also processing of IgG-ICs by immune cells. As such, the receptor is involved in immune surveillance and protection against infections. In this brief review, we highlight how FcRn expressed by hematopoietic and non-hematopoietic cells contributes to immune regulation at mucosal barriers-biology that can be utilized in development of biologics and subunit vaccines for non-invasive delivery.

Monoclonal Antibody-Based Therapies for Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune, neuromuscular disorder that produces disabling weakness through a compromise of neuromuscular transmission. The disease fulfills strict criteria of an antibody-mediated disease. Close to 90% of patients have antibodies directed towards the nicotinic acetylcholine receptor (AChR) on the post-synaptic surface of skeletal muscle and another 5% to the muscle-specific kinase, which is involved in concentrating the AChR to the muscle surface of the neuromuscular junction. Conventional treatments of intravenous immunoglobulin and plasma exchange reduce autoantibody levels to produce their therapeutic effect, while prednisone and immunosuppressives do so by moderating autoantibody production. None of these treatments were specifically developed for MG and have a range of adverse effects. The extensive advances in monoclonal antibody technology allowing specific modulation of biological pathways has led to a tremendous increase in the potential treatment options. For MG, monoclonal antibody therapeutics target the effector mechanism of complement inhibition and the reduction of antibody levels by FcRn inhibition. Antibodies directed against CD20 and signaling pathways, which support lymphocyte activity, have been used to reduce autoantibody production. Thus far, only eculizumab, an antibody against C5, has reached the clinic. We review the present status of monoclonal antibody-based treatments for MG that have entered human testing and offer the promise to transform treatment of MG.

Medical therapy to attenuate fetal anaemia in severe maternal red cell alloimmunisation

Haemolytic disease of the fetus and newborn (HDFN) remains an important cause of fetal mortality with potential neonatal and longer-term morbidity. HDFN is caused by maternal red cell alloimmunisation, with IgG antibodies crossing the placenta to destroy fetal erythroid cells expressing the involved antigen. Intrauterine fetal blood transfusion is the therapy of choice for severe fetal anaemia. Despite a strong evidence base and technical advances, invasive fetal therapy carries risk of miscarriage and preterm birth. Procedure-related risks are increased when invasive, in utero transfusion is instituted prior to 22 weeks to treat severe early-onset fetal anaemia. This review focuses upon this cohort of HDFN and discusses intravenous immunoglobin (IVIg) and novel monoclonal antibody (M281, nipocalimab) treatments which, if started at the end of the first trimester, may attenuate the transplacental passage and fetal effects of IgG antibodies. Such therapy has the ability to improve fetal survival in this severe presentation of HDFN when early in utero transfusion may be required and may have wider implications for the perinatal management in general.

Synthetic nanobodies as angiotensin receptor blockers

There is considerable interest in developing antibodies as functional modulators of G protein-coupled receptor (GPCR) signaling for both therapeutic and research applications. However, there are few antibody ligands targeting GPCRs outside of the chemokine receptor group. GPCRs are challenging targets for conventional antibody discovery methods, as many are highly conserved across species, are biochemically unstable upon purification, and possess deeply buried ligand-binding sites. Here, we describe a selection methodology to enrich for functionally modulatory antibodies using a yeast-displayed library of synthetic camelid antibody fragments called "nanobodies." Using this platform, we discovered multiple nanobodies that act as antagonists of the angiotensin II type 1 receptor (AT1R). Following angiotensin II infusion in mice, we found that an affinity matured nanobody antagonist has comparable antihypertensive activity to the angiotensin receptor blocker (ARB) losartan. The unique pharmacology and restricted biodistribution of nanobody antagonists may provide a path for treating hypertensive disorders when small-molecule drugs targeting the AT1R are contraindicated, for example, in pregnancy.

Red cell alloimmunization: A 2020 update

Management of maternal red cell alloimmunization has been revolutionized over the last 60 years. Advances in the prevention, screening, diagnosis, and treatment of alloimmune-induced fetal anemia make this condition an exemplar for contemporary practice in fetal therapy. Since survival is now an expectation, attention has turned to optimization of long-term outcomes following an alloimmunized pregnancy. In this review, the current management of red cell alloimmunization is described. Current research and future directions are discussed with particular emphasis on later life outcomes after alloimmune fetal anemia.

Antagonism of the Neonatal Fc Receptor as an Emerging Treatment for Myasthenia Gravis

Myasthenia gravis is an autoimmune disease in which immunoglobulin G (IgG) autoantibodies are formed against the nicotinic acetylcholine receptor (AChR) or other components of the neuromuscular junction. Though effective treatments are currently available, many commonly used therapies have important limitations and alternative therapeutic options are needed for patients. A novel treatment approach currently in clinical trials for myasthenia gravis targets the neonatal Fc receptor (FcRn). This receptor plays a central role in prolonging the half–life of IgG molecules. The primary function of FcRn is salvage of IgG and albumin from lysosomal degradation through the recycling and transcytosis of IgG within cells. Antagonism of this receptor causes IgG catabolism, resulting in reduced overall IgG and pathogenic autoantibody levels. This treatment approach is particularly intriguing as it does not result in widespread immune suppression, in contrast to many therapies in routine clinical use. Experience with plasma exchange and emerging phase 2 clinical trial data of FcRn antagonists provide proof of concept for IgG lowering in myasthenia gravis. Here we review the IgG lifecycle and the relevance of IgG lowering to myasthenia gravis treatment and summarize the available data on FcRn targeted therapeutics in clinical trials for myasthenia gravis.