The protection receptor for IgG catabolism is the beta2-microglobulin-containing neonatal intestinal transport receptor

The influence of antibody engineering on Fc conformation and Fc receptor binding properties: Analysis of FcRn-binding engineered antibodies and an Fc fusion protein

Therapeutic immunoglobulin G (IgG) antibodies have comparatively long half-lives because the neonatal Fc receptor (FcRn) binds to the IgG Fc at acidic pH in the endosome and protects IgG from degradation. To further prolong the half-lives, amino acid-substituted antibodies having high affinity to FcRn are being developed, and one such therapeutic antibody (ravulizumab) has been approved. In this study, we investigated the binding property to FcγR and the conformation of seven FcRn affinity-modulated adalimumab variants to clarify the impact of the amino acid substitutions on the function and conformation of IgG Fc. The amino acid substitutions in T254-P261 caused a change in deuterium uptake into some regions of Fc in HDX-MS analysis, but those at T311, M432 and N438 did not cause such a change. The conformations around F245-L255 (FLFPPKPKDTL) were particularly influenced by the amino acid substitution in M256-P261, and the conformational changes of this region were correlated with the decrease of the affinity to FcγRIIIa. Additionally, we investigated the conformational difference of Fc between a Fc fusion protein (etanercept) and a native IgG (adalimumab). Although the Fc fusion proteins were expected to have similar FcRn affinity to IgGs, the affinity of etanercept to FcRn was lower than that of adalimumab, and its half-life was shorter than those of the IgG antibodies. Differences in deuterium uptakes were observed in the two regions where they were also detected in the adalimumab variants, and the conformational differences appeared to be an important factor for the low FcRn affinity of etanercept.

Model-Based Selection and Recommendation for Subcutaneous Abatacept Dose in Patients With Polyarticular Juvenile Idiopathic Arthritis

The selective T-cell costimulation modulator abatacept is approved for treatment of adult rheumatoid arthritis (RA) and polyarticular juvenile idiopathic arthritis (pJIA; 6-17 years [intravenous] and 2-17 years [subcutaneous]). An extrapolation approach was taken to determine subcutaneous weight-tiered doses of abatacept to evaluate in patients with pJIA. Population pharmacokinetic (PPK) and exposure-response (E-R) analyses were conducted to determine whether the weight-tiered subcutaneous regimen provides near-maximal efficacy and is therapeutically comparable to the intravenous regimen in patients with pJIA aged 2-17 years. Combined study data from intravenous or subcutaneous abatacept were used to assess clinically relevant exposure outcomes. The PPK model was developed with data from 13 phase 2/3 studies in RA and pJIA; the E-R model for the American College of Rheumatology pediatric scores (JIA-ACR 30/50/70/100 responses) in month 4 was developed with data from 2 phase 3 pJIA studies. Predefined covariates were investigated in both analyses. PPK model-predicted exposures were steady-state peak, trough (Cminss ), and time-averaged concentrations. Abatacept PK was characterized by a linear 2-compartment model (zero-order intravenous infusion, first-order subcutaneous absorption, first-order elimination); body weight was the only clinically relevant covariate. Cminss was the best exposure predictor for the JIA-ACR response: log odds for response increased in proportion to log-transformed Cminss ; JIA-ACR30 approached a plateau when Cminss ≥ 10 μg/mL. The PPK and E-R analyses demonstrated that the weight-tiered subcutaneous and intravenous abatacept dosing regimens provide near-maximal efficacy and are clinically comparable across children with pJIA who are > 2 years old.

Suppression of IgE-mediated anaphylaxis and food allergy with monovalent anti-FcεRIα mAbs

BACKGROUND

Mast cell and basophil activation by antigen cross-linking of FcεRI-bound IgE is central to allergy pathogenesis. We previously demonstrated global suppression of this process by rapid desensitization with anti-FcεRIα mAbs.

OBJECTIVES

We sought to determine whether use of monovalent (mv) anti-FcεRIα mAbs increases desensitization safety without loss of efficacy.

METHODS

mv anti-human (hu) FcεRIα mAbs were produced with mouse-derived immunoglobulin variable regions and huIgG1 or huIgG4 C regions and were used to suppress murine IgE-mediated anaphylaxis and food allergy. mAbs were administered as a single dose or as serially increasing doses to mice that express hu instead of mouse FcεRIα; mice that additionally have an allergy-promoting IL-4Rα mutation; and hu cord blood-reconstituted immunodeficient, hu cytokine-secreting, mice that have large numbers of activated hu mast cells. Anaphylaxis susceptibility was sometimes increased by treatment with IL-4 or a β-adrenergic receptor antagonist.

RESULTS

mv anti-hu FcεRIα mAbs are considerably less able than divalent mAbs are to induce anaphylaxis and deplete mast cell and basophil IgE, but mv mAbs still strongly suppress IgE-mediated disease. The mv mAbs can be safely administered as a single large dose to mice with typical susceptibility to anaphylaxis, while a rapid desensitization approach safely suppresses disease in mice with increased susceptibility. Our huIgG4 variant of mv anti-huFcεRIα mAb is safer than our huIgG1 variant is, apparently because reduced interactions with FcεRs decrease ability to indirectly cross-link FcεRI.

CONCLUSIONS

mv anti-FcεRIα mAbs more safely suppress IgE-mediated anaphylaxis and food allergy than divalent variants of the same mAbs do. These mv mAbs may be useful for suppression of huIgE-mediated disease.

FcRn is not the receptor mediating the transfer of serum IgG to colostrum in pigs

In contrast to humans or rabbits, in which maternal IgG is transmitted to offspring prenatally via the placenta or the yolk sac, large domestic animals such as pigs, cows and sheep transmit IgG exclusively through colostrum feeding after delivery. The extremely high IgG content in colostrum is absorbed by newborns via the small intestine. Although it is widely accepted that the neonatal Fc receptor, FcRn, is the receptor mediating IgG transfer across both the placenta and small intestine, it remains unclear whether FcRn also mediates serum IgG transfer across the mammary barrier to colostrum/milk, especially in large domestic animals. In this study, using a FcRn knockout pig model generated with a CRISPR-Cas9-based approach, we clearly demonstrate that FcRn is not responsible for the IgG transfer from serum to colostrum in pigs, although like in other mammals, it is involved in IgG homeostasis and mediates IgG absorption in the small intestine of newborns.

Involved free light chain: an early independent predictor of response and progression in multiple myeloma

Serum and urine protein electrophoresis (sPEP/uPEP) are the standard methods for monitoring of multiple myeloma (MM). However, a method of detection with shorter half-life, such as serum-free light chain (FLC), could detect the response or progression earlier. In total, 450 MM patients were assessed in first, second, and third line. Response and progression were classified according to International myeloma working group guidelines. The overall median time to partial response or better was detectable significantly earlier with involved free light chain (iFLC) 1.94 months (IQR: 1.61-2.23) compared to sPEP 5.39 months (IQR: 3.88-7.00). In first line, iFLC detected progression earlier compared to sPEP, particularly in patients with progression more than 18 months after best response. In conclusion, a response observed by iFLC occurs at least a median of 3 months before response is detected by sPEP/uPEP.

Lack of neonatal Fc receptor does not diminish the efficacy of the HSV-1 0ΔNLS vaccine against ocular HSV-1 challenge

The neonatal Fc receptor (FcRn) is constitutively expressed in the cornea and is up-regulated in response to herpes simplex virus type 1 (HSV-1). Previously, we found targeting cornea FcRn expression by small interfering RNA-mediated knockdown reduced the local efficacy of HSV-1 0ΔNLS vaccinated C57BL/6 mice against ocular challenge with HSV-1. The current study was undertaken to evaluate the HSV-1 0ΔNLS vaccine efficacy in FcRn deficient (FcRn KO) mice challenged with HSV-1. Whereas there was little neutralizing antibody detected in the serum of HSV-1 0ΔNLS vaccinated FcRn KO mice, these mice exhibited the same degree of protection against ocular challenge with HSV-1 as wild type (WT) C57BL/6 mice as measured by cumulative survival, infectious virus shed or retained in tissue, and corneal pathology including opacity and neovascularization. Mock-vaccinated FcRn KO mice were found to be more sensitive to ocular HSV-1 infection compared to mock-vaccinated (WT) mice in terms of cumulative survival and virus shedding. In addition, the FcRn KO mice generated significantly fewer effector (CD3⁺CD44⁺CD62L^-) and central (CD3⁺CD44⁺CD62L⁺) memory CD8⁺ T cells compared to the WT mice 7 days post infection. Collectively, mock-vaccinated FcRn KO mice are susceptible to ocular HSV-1 infection but HSV-1 0ΔNLS vaccinated FcRn KO mice are resistant suggesting that in addition to the FcRn, other pathways are involved in mediating the protective effect of the HSV-1 0ΔNLS vaccine against subsequent HSV-1 challenge.

Antigen Mass May Influence Trastuzumab Concentrations in Cerebrospinal Fluid After Intrathecal Administration

Intravenous administration of monoclonal antibodies leads to low concentrations in the central nervous system, which is a serious concern in neuro-oncology, especially in leptomeningeal carcinomatosis of HER2-overexpressing breast cancer. Case reports of i.t. administrations of trastuzumab have shown promising results in these patients but dosing regimens are empirical in absence of pharmacokinetic (PK) study. With a population PK approach, we described the fate of trastuzumab after i.t. administration in 21 women included in a phase I-II clinical trial. Trastuzumab was administered by i.t. route every week for 8 weeks and both cerebrospinal fluid (CSF) and serum were sampled to measure trough concentrations. Some patients showed noticeable CSF concentration fluctuations predicted using a target-mediated drug disposition. This target was latent and produced with a delayed feedback. Apparent volumes of distribution were close to physiological volumes (V₁  = 3.25 L, V₂  = 0.644 L, for serum and CSF, respectively). Estimated (constant) transfer from serum to CSF was very slow (k₁₂  = 0.264 mg/day) whereas estimated half-life of transfer from CSF to serum was rapid (2.2 days). From the individual parameters of patients, a single i.t. administration of 150 mg of trastuzumab corresponded to median mean residence times of 3.8 days and 15.6 days in CSF and serum, respectively. Survival without neurological relapse was not related to trastuzumab exposure. This study confirms that transfer of trastuzumab from serum to CSF is very limited and that this monoclonal antibody, when administered by i.t. route, is rapidly transferred to the serum.

The Role of TNF-α and Anti-TNF-α Agents during Preconception, Pregnancy, and Breastfeeding

Tumor necrosis factor-alpha (TNF-α) is a multifunctional Th1 cytokine and one of the most important inflammatory cytokines. In pregnancy, TNF-α influences hormone synthesis, placental architecture, and embryonic development. It was also shown that increased levels of TNF-α are associated with pregnancy loss and preeclampsia. Increased TNF-α levels in complicated pregnancy draw attention to trophoblast biology, especially migratory activity, syncytialisation, and endocrine function. Additionally, elevated TNF-α levels may affect the maternal-fetal relationship by altering the secretory profile of placental immunomodulatory factors, which in turn affects maternal immune cells. There is growing evidence that metabolic/pro-inflammatory cytokines can program early placental functions and growth in the first trimester of pregnancy. Furthermore, early pregnancy placenta has a direct impact on fetal development and maternal immune system diseases that release inflammatory (e.g., TNF-α) and immunomodulatory factors, such as chronic inflammatory rheumatic, gastroenterological, or dermatological diseases, and may result in an abnormal release of cytokines and chemokines in syncytiotrophoblasts. Pregnancy poses a challenge in the treatment of chronic disease in patients who plan to have children. The activity of the disease, the impact of pregnancy on the course of the disease, and the safety of pharmacotherapy, including anti-rheumatic agents, in pregnancy should be considered.

Synthesis of Disulfide-Bridging Trehalose Polymers for Antibody and Fab Conjugation Using a Bis-Sulfone ATRP Initiator

Antibodies and antigen binding fragments (FABs) are widely used as therapeutics and conjugated polymers can enhance the properties of these important biomolecules. However, limitations to the selectivity and stability of current conjugation methodologies can inhibit the exploration of new antibody-polymer conjugates. Herein, we describe a new strategy for the synthesis of these conjugates that forms a stable thioether bond and can be directly incorporated into an atom transfer radical polymerization (ATRP) initiator. Specifically, a bis-sulfone alkyl bromide initiator was synthesized and utilized in the activators generated by electron transfer (AGET) ATRP of ethylene glycol methacrylate and trehalose methacrylate to form the respective polymers. The trehalose polymer was then irreversibly inserted into the disulfide bonds of Herceptin and Herceptin FAB after mild reduction to form the conjugates with quantitative conversions as verified by Western Blot and mass spectrometry after cleavage of the polymer. The binding of the Herceptin and Herceptin Fab conjugates to the receptor was investigated by indirect ELISA (enzyme-linked immunosorbent assay) and the EC50's were 0.90 and 2.74 nM, respectively, compared to Herceptin (0.26 nM) and the Fab (0.56 nM). The conjugates were subjected to heating studies at a constant 75 °C, the temperature determined in a heat ramp to be the threshold of stability for the antibody and FAB; the trehalose polymer was found to considerably increase the thermal stability of both Herceptin and Herceptin Fab. This work provides a new way to prepare polymer-antibody/Fab conjugates utilizing bis-sulfone end groups installed by atom transfer radical polymerization of the functionalized initiators and a way to stabilize these important molecules by conjugation to trehalose polymers.

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.

Humanized Mouse Models to Evaluate Cancer Immunotherapeutics

Immunotherapy is at the forefront of cancer treatment. The advent of numerous novel approaches to cancer immunotherapy, including immune checkpoint antibodies, adoptive transfer of CAR (chimeric antigen receptor) T cells and TCR (T cell receptor) T cells, NK (natural killer) cells, T cell engagers, oncolytic viruses, and vaccines, is revolutionizing the treatment for different tumor types. Some are already in the clinic, and many others are underway. However, not all patients respond, resistance develops, and as available therapies multiply there is a need to further understand how they work, how to prioritize their clinical evaluation, and how to combine them. For this, animal models have been highly instrumental, and humanized mice models (i.e., immunodeficient mice engrafted with human immune and cancer cells) represent a step forward, although they have several limitations. Here, we review the different humanized models available today, the approaches to overcome their flaws, their use for the evaluation of cancer immunotherapies, and their anticipated evolution as tools to help personalized clinical decision-making.

Biologics During Pregnancy and Breastfeeding Among Women With Rheumatic Diseases: Safety Clinical Evidence on the Road

Females are generally more affected by autoimmune diseases, a fact that underlines the relationship with pregnancy and the safety of anti-rheumatic drugs in pregnancy and lactation. Biologic therapies are increasingly prescribed to treat and maintain remission in a significant number of systemic autoimmune rheumatic diseases. The experience with the use of biologics during gestation is extremely lacking because of the observational nature of the available studies and the difficulty in designing proper clinical trials in pregnancy. Among the studied biologics, more information was published on TNFα inhibitors and, in particular, on their potential passage through the placenta and impact on the fetus. Currently, a fragment of anti-TNFα monoclonal IgG, certolizumab pegol, is considered safe with almost no placental transfer. Subsequent observations are suggesting a comparable safety for the soluble TNFα receptor etanercept. Another biologic, eculizumab, the anti-C5a antibody used to treat complement-mediated microangiopathies, is also considered safe due to the unique engineered IgG2/4κ formulation that limits its passage through the placental barrier. Still, long-term data about children born to women treated with biologics in pregnancy are not attainable. Data on breastfeeding are currently available for several biologics. This article reviews the literature available about which drugs are considered safe during pregnancy and lactation, which are not, and on future prospects.

FcRn augments induction of tissue factor activity by IgG-containing immune complexes

Thromboembolism complicates disorders caused by immunoglobulin G (IgG)-containing immune complexes (ICs), but the underlying mechanisms are incompletely understood. Prior evidence indicates that induction of tissue factor (TF) on monocytes, a pivotal step in the initiation, localization, and propagation of coagulation by ICs, is mediated through Fcγ receptor IIa (FcγRIIa); however, the involvement of other receptors has not been investigated in detail. The neonatal Fc receptor (FcRn) that mediates IgG and albumin recycling also participates in cellular responses to IgG-containing ICs. Here we asked whether FcRn is also involved in the induction of TF-dependent factor Xa (FXa) activity by IgG-containing ICs by THP-1 monocytic cells and human monocytes. Induction of FXa activity by ICs containing IgG antibodies to platelet factor 4 (PF4) involved in heparin-induced thrombocytopenia (HIT), β-2-glycoprotein-1 implicated in antiphospholipid syndrome, or red blood cells coated with anti-(α)-Rh(D) antibodies that mediate hemolysis in vivo was inhibited by a humanized monoclonal antibody (mAb) that blocks IgG binding to human FcRn. IgG-containing ICs that bind to FcγR and FcRn induced FXa activity, whereas IgG-containing ICs with an Fc engineered to be unable to engage FcRn did not. Infusion of an α-FcRn mAb prevented fibrin deposition after microvascular injury in a murine model of HIT in which human FcγRIIa was expressed as a transgene. These data implicate FcRn in TF-dependent FXa activity induced by soluble and cell-associated IgG-containing ICs. Antibodies to FcRn, now in clinical trials in warm autoimmune hemolytic anemia to lower IgG antibodies and IgG containing ICs may also reduce the risk of venous thromboembolism.

Personalized Medicine of Monoclonal Antibodies in Inflammatory Bowel Disease: Pharmacogenetics, Therapeutic Drug Monitoring, and Beyond

The pharmacotherapy of inflammatory bowel diseases (Crohn’s disease and ulcerative colitis) has experienced significant progress with the advent of monoclonal antibodies (mABs). As therapeutic proteins, mABs display peculiar pharmacokinetic characteristics that differentiate them from chemical drugs, such as aminosalicylates, antimetabolites (i.e., azathioprine, 6-mercaptopurine, and methotrexate), and immunosuppressants (corticosteroids and cyclosporine). However, clinical trials have demonstrated that biologic agents may suffer from a pharmacokinetic variability that could influence the desired clinical outcome, beyond primary resistance phenomena. Therefore, therapeutic drug monitoring (TDM) protocols have been elaborated and applied to adaptation drug doses according to the desired plasma concentrations of mABs. This activity is aimed at maximizing the beneficial effects of mABs while sparing patients from toxicities. However, some aspects of TDM are still under discussion, including time-changing therapeutic ranges, proactive and reactive approaches, the performance and availability of instrumental platforms, the widely varying individual characteristics of patients, the severity of the disease, and the coadministration of immunomodulatory drugs. Facing these issues, personalized medicine in IBD may benefit from a combined approach, made by TDM protocols and pharmacogenetic analyses in a timeline that necessarily considers the frailty of patients, the chronic administration of drugs, and the possible worsening of the disease. Therefore, the present review presents and discusses the activities of TDM protocols using mABs in light of the most recent results, with special attention on the integration of other actions aimed at exploiting the most effective and safe therapeutic effects of drugs prescribed in IBD patients.

Fc Engineering Strategies to Advance IgA Antibodies as Therapeutic Agents

In the past three decades, a great interest has arisen in the use of immunoglobulins as therapeutic agents. In particular, since the approval of the first monoclonal antibody Rituximab for B cell malignancies, the progress in the antibody-related therapeutic agents has been incremental. Therapeutic antibodies can be applied in a variety of diseases, ranging from cancer to autoimmunity and allergy. All current therapeutic monoclonal antibodies used in the clinic are of the IgG isotype. IgG antibodies can induce the killing of cancer cells by growth inhibition, apoptosis induction, complement activation (CDC) or antibody-dependent cellular cytotoxicity (ADCC) by NK cells, antibody-dependent cellular phagocytosis (ADCP) by monocytes/macrophages, or trogoptosis by granulocytes. To enhance these effector mechanisms of IgG, protein and glyco-engineering has been successfully applied. As an alternative to IgG, antibodies of the IgA isotype have been shown to be very effective in tumor eradication. Using the IgA-specific receptor FcαRI expressed on myeloid cells, IgA antibodies show superior tumor-killing compared to IgG when granulocytes are employed. However, reasons why IgA has not been introduced in the clinic yet can be found in the intrinsic properties of IgA posing several technical limitations: (1) IgA is challenging to produce and purify, (2) IgA shows a very heterogeneous glycosylation profile, and (3) IgA has a relatively short serum half-life. Next to the technical challenges, pre-clinical evaluation of IgA efficacy in vivo is not straightforward as mice do not naturally express the FcαR. Here, we provide a concise overview of the latest insights in these engineering strategies overcoming technical limitations of IgA as a therapeutic antibody: developability, heterogeneity, and short half-life. In addition, alternative approaches using IgA/IgG hybrid and FcαR-engagers and the impact of engineering on the clinical application of IgA will be discussed.

Pharmacokinetics and pharmacodynamics of therapeutic antibodies in tumors and tumor-draining lymph nodes

The signaling axis from the primary tumor to the tumor-draining lymph node (TDLN) has emerged as a crucial mediator for the efficacy of immunotherapies in neoadjuvant settings, challenging the primary use of immunotherapy in adjuvant settings. TDLNs are regarded as highly opportunistic sites for cancer cell dissemination and promote further spread via several primary tumor-dependent mechanisms. Lesion-level mixed responses to antibody immunotherapy have been traced to local immune signatures present in the TDLN and the organ-specific primary tumors that they drain. However, the pharmacokinetics (PK) and biodistribution gradients of antibodies in primary tumors and TDLNs have not been systemically evaluated. These concentration gradients are critical in ensuring adequate antibody pharmacodynamic (PD) T-cell activation and/or anti-tumor response. The current work reviews the knowledge for developing physiologically-based PK and pharmacodynamic (PBPK/PD) models to quantify antibody biodistribution gradients in anatomically distinct primary tumors and TDLNs as a means to characterize the clinically observed heterogeneous responses to antibody therapies. Several clinical and pathophysiological considerations in modeling the primary tumor-TDLN axis, as well as a summary of both preclinical and clinical PK/PD lymphatic antibody disposition studies, will be provided.

Development of a Pharmacokinetic Model Describing Neonatal Fc Receptor-Mediated Recycling of HL2351, a Novel Hybrid Fc-Fused Interleukin-1 Receptor Antagonist, to Optimize Dosage Regimen

HL2351 (hIL‐1Ra‐hyFc) is a novel recombinant protein formed by the fusion of two human interleukin‐1 receptor antagonist components into one antibody‐derived fragment crystallizable portion. Although HL2351 has a pharmacological mechanism of action similar to that of anakinra as a commercialized biopharmaceutical drug, HL2351 has been desired to reduce the dose frequency and improve therapeutic efficacy due to its long circulation half‐life. In this study, we aimed to develop a population pharmacokinetic (PK) model for HL2351 using a neonatal Fc receptor (FcRn)–mediated recycling model based on a quasi‐steady‐state approximation of target‐mediated drug disposition (TMDD) for the description of interactions between the drug and FcRn. FcRn recycling was expected in the case of HL2351 because of PK related to the antibody portion. A TMDD model was also applied to describe interactions of IL1R with HL2351 or anakinra. PK data were collected from a phase I study conducted in six groups (1, 2, 4, 8, 12 mg/kg HL2351 and 100 mg anakinra single subcutaneous administration; n = 8 per group). In consequence, the PK of anakinra and HL2351 following administration of multiple doses at different dosages were simulated. Optimized doses were considered based on average concentrations of IL1R bound to anakinra and HL2351. HL2351 at doses of 326 mg or 4.267, 4.982, 5.288, 5.458, or 5.748 mg/kg once weekly or HL2351 at 1726 mg or 21.92, 26.86, 29.10, 30.36, or 32.53 mg/kg once biweekly would have similar therapeutic effects with anakinra at a dose of 100 mg or 1, 2, 3, 4, or 8 mg/kg administered once daily, respectively.

Benefits and Risks of IgG Transplacental Transfer

Maternal passage of immunoglobulin G (IgG) is an important passive mechanism for protecting the infant while the neonatal immune system is still immature and ineffective. IgG is the only antibody class capable of crossing the histological layers of the placenta by attaching to the neonatal Fc receptor expressed at the level of syncytiotrophoblasts, and it offers protection against neonatal infectious pathogens. In pregnant women with autoimmune or alloimmune disorders, or in those requiring certain types of biological therapy, transplacental passage of abnormal antibodies may cause fetal or neonatal harm. In this review, we will discuss the physiological mechanisms and benefits of transplacental transfer of maternal antibodies as well as pathological maternal situations where this system is hijacked, potentially leading to adverse neonatal outcomes.

Ranibizumab Population Pharmacokinetics and Free VEGF Pharmacodynamics in Preterm Infants With Retinopathy of Prematurity in the RAINBOW Trial

Purpose

To develop a population pharmacokinetic (PK) model for intravitreal ranibizumab in infants with retinopathy of prematurity (ROP) and assess plasma free vascular endothelial growth factor (VEGF) pharmacodynamics (PD).

Methods

The RAnibizumab compared with laser therapy for the treatment of INfants BOrn prematurely With retinopathy of prematurity (RAINBOW) trial enrolled 225 infants to receive a bilateral intravitreal injection of ranibizumab 0.1 mg, ranibizumab 0.2 mg, or laser in a 1:1:1 ratio and included sparse sampling of blood for population PK and PD analysis. An adult PK model using infant body weight as a fixed allometric covariate was re-estimated using the ranibizumab concentrations in the preterm population. Different variability, assumptions, and covariate relationships were explored. Model-based individual predicted concentrations of ranibizumab were plotted against observed free VEGF concentrations.

Results

Elimination of ranibizumab had a median half-life of 5.6 days from the eye and 0.3 days from serum, resulting in an apparent serum half-life of 5.6 days. Time to reach maximum concentration was rapid (median: 1.3 days). Maximum concentration (median 24.3 ng/mL with ranibizumab 0.2 mg) was higher than that reported in adults. No differences in plasma free VEGF concentrations were apparent between the groups or over time. Plotted individual predicted concentrations of ranibizumab against observed free VEGF concentrations showed no relationship.

Conclusions

In preterm infants with ROP, elimination of ranibizumab from the eye was the rate-limiting step and was faster compared with adults. No reduction in plasma free VEGF was observed. The five-year clinical safety follow-up from RAINBOW is ongoing.

Translational Relevance

Our population PK and VEGF PD findings suggest a favorable ocular efficacy: systemic safety profile for ranibizumab in preterm infants.

Transport and fate of aflibercept in VEGF-A165-challenged retinal endothelial cells

Retinal vessels are at least in part involved in clearing of Fc terminus-containing proteins from the vitreous. In vitro, the Fc fusion protein aflibercept is transported through a monolayer of unchallenged immortalized bovine retinal endothelial cells (iBREC), mediated by the neonatal Fc receptor (FcRn), but part of the Fc fusion protein is also degraded. Aflibercept's target VEGF-A not only enhances the permeability of REC by destabilization of tight junctions (TJs) thereby allowing for paracellular flow, it may also lower the intracellular stability of the Fc fusion protein by changing its binding properties to the FcRn. Therefore, we investigated the transport and fate of aflibercept in VEGF-A₁₆₅-challenged iBREC. All cell culture media were supplemented with 5% fetal bovine serum (FBS) as its absence results in accumulation of aflibercept in iBREC due to deregulated expression of transport proteins. Early after exposure of a confluent iBREC monolayer cultivated on gold electrodes to 5% FBS, the cell index (CI) - assessed as a measure of barrier function, cell viability and cell adhesion - transiently declined but recovered again within a few hours to high values. These values remained stable for several days associated with a strong expression of the TJ-protein claudin-1, indicative of a functional barrier formed by the iBREC monolayer. Transient changes of the plasma membrane localizations of claudin-5 and vascular endothelial cadherin - both important for regulation of paracellular flow - accompanied the transient reduction of the CI not prevented by VEGF-binding proteins. Treatment of iBREC with 50 ng/ml VEGF-A₁₆₅ for one day resulted in a strong and persistent decline of the CI associated with a low expression level of the TJ-protein claudin-1; reversion to normal values was complete one day after aflibercept's addition at a final concentration of 250 μg/ml. Expressions of other proteins involved in regulation of paracellular flow or transcellular transport were not significantly changed. More aflibercept passed through the monolayer of iBREC cultivated on permeable membrane inserts pretreated with VEGF-A for one day, but this was not affected by a FcRn-inhibiting antibody. Subcellular localization of aflibercept was hardly changed in VEGF-A-exposed iBREC 3 h after its addition to the cells; inhibition of (non)-lysosomal or proteasomal proteases then only weakly affected the amount of internalized aflibercept. iBREC also internalized VEGF-A which was barely detectable as early as 2 h after addition of aflibercept. In contrast, blocking the tyrosine kinase activity of VEGF receptor(s) did not prevent VEGF-A's uptake. Inhibition of cellular proteases strongly increased the amount of internalized VEGF-A in the absence and presence of the Fc fusion protein. We therefore conclude that a FcRn-mediated transport plays a minor role in aflibercept's passage through a leaky barrier of REC. Even early after addition of aflibercept to VEGF-A-exposed iBREC, the levels of free intracellular VEGF-A are low, as aflibercept likely prevents binding of VEGF-A to its receptor. Interestingly, the growth factor's detrimental effects still persist for nearly one day.

IgG-mediated suppression of antibody responses: Hiding or snatching epitopes?

Antibodies forming a complex with antigen in vivo can dramatically change the antibody response to this antigen. In some situations, the response will be a 100-fold stronger than in animals immunized with antigen alone, and in other situations, the response will be completely suppressed. IgG is known to suppress the antibody response, for example to erythrocytes, and this is used clinically in Rhesus prophylaxis. The mechanism behind IgG-mediated immune suppression is still not understood. Here, we will review studies performed in experimental animal models and discuss the various hypotheses put forward to explain the profound suppressive effect of IgG. We conclude that an exclusive role for negative regulation of B cells through FcγRIIB, increased clearance of erythrocytes from the circulation or complement-mediated lysis is unlikely. Epitope masking, where IgG hides the epitope from B cells, or trogocytosis, where IgG removes the epitope from the erythrocyte, is compatible with many observations. These two mechanisms are not mutually exclusive. Moreover, it cannot be ruled out that clearance, in combination with other mechanisms, plays a role.

IgG Suppresses Antibody Responses to Sheep Red Blood Cells in Double Knock-Out Mice Lacking Complement Factor C3 and Activating Fcγ-Receptors

Antigen-specific IgG antibodies, passively administered together with erythrocytes, prevent antibody responses against the erythrocytes. The mechanism behind the suppressive ability of IgG has been the subject of intensive studies, yet there is no consensus as to how it works. An important question is whether the Fc-region of IgG is required. Several laboratories have shown that IgG suppresses equally well in wildtype mice and mice lacking the inhibitory FcγIIB, activating FcγRs (FcγRI, III, and IV), or complement factor C3. These observations consistently suggest that IgG-mediated suppression does not rely on Fc-mediated antibody functions. However, it was recently shown that anti-KEL sera failed to suppress antibody responses to KEL-expressing transgenic mouse erythrocytes in double knock-out mice lacking both activating FcγRs and C3. Yet, in the same study, antibody-mediated suppression worked well in each single knock-out strain. This unexpected observation suggested Fc-dependence of IgG-mediated suppression and prompted us to investigate the issue in the classical experimental model using sheep red blood cells (SRBC) as antigen. SRBC alone or IgG anti-SRBC together with SRBC was administered to wildtype and double knock-out mice lacking C3 and activating FcγRs. IgG efficiently suppressed the IgM and IgG anti-SRBC responses in both mouse strains, thus supporting previous observations that suppression in this model is Fc-independent.

Targeting drug delivery in the vascular system: Focus on endothelium

The bloodstream is the main transporting pathway for drug delivery systems (DDS) from the site of administration to the intended site of action. In many cases, components of the vascular system represent therapeutic targets. Endothelial cells, which line the luminal surface of the vasculature, play a tripartite role of the key target, barrier, or victim of nanomedicines in the bloodstream. Circulating DDS may accumulate in the vascular areas of interest and in off-target areas via mechanisms bypassing specific molecular recognition, but using ligands of specific vascular determinant molecules enables a degree of precision, efficacy, and specificity of delivery unattainable by non-affinity DDS. Three decades of research efforts have focused on specific vascular targeting, which have yielded a multitude of DDS, many of which are currently undergoing a translational phase of development for biomedical applications, including interventions in the cardiovascular, pulmonary, and central nervous systems, regulation of endothelial functions, host defense, and permeation of vascular barriers. We discuss the design of endothelial-targeted nanocarriers, factors underlying their interactions with cells and tissues, and describe examples of their investigational use in models of acute vascular inflammation with an eye on translational challenges.

Target-mediated exposure enhancement: a previously unexplored limit of TMDD

Target-mediated drug disposition (TMDD) is often observed for targeted therapeutics, and manifests as decreases in clearance and volume of distribution with increasing dose as a result of saturable, high affinity target binding. In the present work, we demonstrate that classically defined TMDD is just one of the characteristic features of the system. In fact, for molecules with rapid non-specific elimination relative to target-mediated elimination, binding to target may actually lead to improved exposure at sub-saturating doses. This feature, which we refer to as target-mediated exposure enhancement (TMEE), produces the opposite trend to classical TMDD, i.e., with increasing dose levels, clearance and volume of distribution will also increase. The general model of TMDD was able to well-characterize the pharmacokinetics of two molecules that display TMEE, ALX-0081 and linagliptin. Additional fittings using the commonly reported TMDD model approximations revealed that both the quasi-equilibrium and quasi-steady-state approximations were able to well-describe TMEE; however, the Michaelis-Menten approximation was unable to describe this behavior. With the development of next-generation therapeutics with high affinity for target and rapid non-specific elimination, such as antibody fragments and peptides, this previously unexplored limit of TMDD is anticipated to become increasingly relevant for describing pharmacokinetics of investigational therapeutics.

Relevance of the Materno-Fetal Interface for the Induction of Antigen-Specific Immune Tolerance

In humans, maternal IgGs are transferred to the fetus from the second trimester of pregnancy onwards. The transplacental delivery of maternal IgG is mediated by its binding to the neonatal Fc receptor (FcRn) after endocytosis by the syncytiotrophoblast. IgGs present in the maternal milk are also transferred to the newborn through the digestive epithelium upon binding to the FcRn. Importantly, the binding of IgGs to the FcRn is also responsible for the recycling of circulating IgGs that confers them with a long half-life. Maternally delivered IgG provides passive immunity to the newborn, for instance by conferring protective anti-flu or anti-pertussis toxin IgGs. It may, however, lead to the development of autoimmune manifestations when pathological autoantibodies from the mother cross the placenta and reach the circulation of the fetus. In recent years, strategies that exploit the transplacental delivery of antigen/IgG complexes or of Fc-fused proteins have been validated in mouse models of human diseases to impose antigen-specific tolerance, particularly in the case of Fc-fused factor VIII (FVIII) domains in hemophilia A mice or pre-pro-insulin (PPI) in the case of preclinical models of type 1 diabetes (T1D). The present review summarizes the mechanisms underlying the FcRn-mediated transcytosis of IgGs, the physiopathological relevance of this phenomenon, and the repercussion for drug delivery and shaping of the immune system during its ontogeny.

An intact C-terminal end of albumin is required for its long half-life in humans

Albumin has an average plasma half-life of three weeks and is thus an attractive carrier to improve the pharmacokinetics of fused therapeutics. The half-life is regulated by FcRn, a cellular receptor that protects against intracellular degradation. To tailor-design the therapeutic use of albumin, it is crucial to understand how structural alterations in albumin affect FcRn binding and transport properties. In the blood, the last C-terminal residue (L585) of albumin may be enzymatically cleaved. Here we demonstrate that removal of the L585 residue causes structural stabilization in regions of the principal FcRn binding domain and reduces receptor binding. In line with this, a short half-life of only 3.5 days was measured for cleaved albumin lacking L585 in a patient with acute pancreatitis. Thus, we reveal the structural requirement of an intact C-terminal end of albumin for a long plasma half-life, which has implications for design of albumin-based therapeutics.

Nilsen et al. show that structural alterations in the last C-terminal α-helix of albumin strongly reduce its binding to the neonatal Fc receptor, decreasing the half-life of albumin in humans. This study suggests the structural requirement of the C-terminal of albumin for its long plasma half-life, providing insights into the design of albumin used to carry drugs.

The impact of pregnancy on biologic therapies for the treatment of inflammatory bowel disease

Active inflammatory bowel disease during conception and pregnancy has been associated with adverse materno-fetal outcomes. Patients are often unduly concerned about the adverse effects of biologic medications on the growing fetus, however, continuing therapy is advised, with potential risks of therapy outweighed by the risks of active maternal disease. A number of physiological changes associated with pregnancy can alter the absorption, distribution and elimination of these therapies, which may impact on their safety and efficacy. We review the current evidence regarding the effects of pregnancy on the pharmacokinetics of biologic therapies, as well as drug concentration measurements during pregnancy and at time of delivery. A greater understanding of the impact of pregnancy on the pharmacokinetics of biologic therapies and the emerging utilisation of drug concentration monitoring during pregnancy may lead to improved materno-fetal outcomes in patients with inflammatory bowel disease.

Engineering the interactions between a plant-produced HIV antibody and human Fc receptors

Plants can provide a cost-effective and scalable technology for production of therapeutic monoclonal antibodies, with the potential for precise engineering of glycosylation. Glycan structures in the antibody Fc region influence binding properties to Fc receptors, which opens opportunities for modulation of antibody effector functions. To test the impact of glycosylation in detail, on binding to human Fc receptors, different glycovariants of VRC01, a broadly neutralizing HIV monoclonal antibody, were generated in Nicotiana benthamiana and characterized. These include glycovariants lacking plant characteristic α1,3-fucose and β1,2-xylose residues and glycans extended with terminal β1,4-galactose. Surface plasmon resonance-based assays were established for kinetic/affinity evaluation of antibody-FcγR interactions, and revealed that antibodies with typical plant glycosylation have a limited capacity to engage FcγRI, FcγRIIa, FcγRIIb and FcγRIIIa; however, the binding characteristics can be restored and even improved with targeted glycoengineering. All plant-made glycovariants had a slightly reduced affinity to the neonatal Fc receptor (FcRn) compared with HEK cell-derived antibody. However, this was independent of plant glycosylation, but related to the oxidation status of two methionine residues in the Fc region. This points towards a need for process optimization to control oxidation levels and improve the quality of plant-produced antibodies.

Safety, tolerability and pharmacokinetics and pharmacodynamics of HL2351, a novel hybrid fc-fused interleukin-1 receptor antagonist, in healthy subjects: A first-in-human study

AIMS

We performed a first-in-human study with HL2351, a novel hybrid Fc-fused interleukin (IL)-1 receptor antagonist, to evaluate its tolerability, pharmacokinetics and pharmacodynamics (PD) after a single subcutaneous (SC) administration in healthy subjects.

METHODS

A randomized, double-blind, placebo- and active-controlled, dose-escalation study was conducted. Eligible subjects randomly received a single SC administration of HL2351 (1, 2, 4, 8 and 12 mg/kg) or placebo in a ratio of 8:2. Subjects in the active-controlled group received a single SC administration of anakinra at 100 mg. Serial blood samples were collected for pharmacokinetics and PD analyses. An ex-vivo activation test was performed to evaluate the PD using peripheral blood mononuclear cells treated with IL-1β. Anti-HL2351 antibodies were determined at baseline and 29 days postdose. Tolerability was assessed throughout the study.

RESULTS

HL2351 was eliminated more slowly than anakinra (terminal half-life: 27.21-45.28 vs 3.97 h). Serum concentrations of HL2351 were increased dose-proportionally. The mean apparent clearance of HL2351 were 0.6, 0.66, 0.75, 0.51, 0.65 L/h at 1, 2, 4, 8 and 12 mg/kg, respectively. The percent inhibition of IL-6 expression varied widely (range: 0-92.1%), showing no clear trend or discernible difference between HL2351, anakinra and placebo. HL2351 was well tolerated after a single SC administration.

CONCLUSION

HL2351 was well tolerated and showed linear pharmacokinetic characteristics after a single SC administration at doses up to 12 mg/kg in healthy subjects. HL2351 remained in the body 7-11 times longer than anakinra. HL2351 can be developed as a potential therapeutic alternative to anakinra.

Rapid desensitization of humanized mice with anti-human FcεRIα monoclonal antibodies

BACKGROUND

Anaphylaxis is classically mediated by allergen cross-linking of IgE bound to the α chain of FcεRI, the mast cell/basophil high affinity IgE receptor. Allergen cross-linking of the IgE/FcεRI complex activates these cells, inducing release of disease-causing mediators, cytokines, and enzymes. We previously demonstrated that IgE-mediated anaphylaxis could be safely prevented in wild-type BALB/c mice by rapid desensitization with anti-mouse FcεRIα mAb.

OBJECTIVE

This study sought to use humanized mice to extend these results to humans.

METHODS

We actively immunized huFcεRIα/F709 mice, which express human (hu) instead of mouse FcεRIα and a mutant IL-4 receptor that lacks inhibitory function. We passively immunized huFcεRIα mice, as well as human cord blood-reconstituted reNSGS mice, which are immune-deficient, produce mast cell-stimulating human cytokines, and develop numerous human mast cells. For desensitization, we used anti-huFcεRIα mAbs that bind FcεRIα regardless of its association with IgE (noncompeting mAbs), and/or mAbs that compete with IgE for huFcεRIα binding (competing mAbs). Anaphylaxis was induced by intravenous injection of antigen or anti-huIgE mAb.

RESULTS

Anti-huFcεRIα mAb rapid desensitization was safer and more effective than allergen rapid desensitization and suppressed anaphylaxis more rapidly than omalizumab or ligelizumab. Rapid desensitization of naïve, IgE-sensitized huFcεRIα mice and huFcεRIα/F709 mice that were egg-allergic with anti-FcεRIα mAbs safely removed >98% of IgE from peritoneal mast cells and completely suppressed IgE-mediated anaphylaxis. Rapid desensitization of reNSGS mice with anti-FcεRIα mAbs also safely removed ∼98% of mast cell IgE and prevented IgE-mediated anaphylaxis.

CONCLUSIONS

Rapid desensitization with anti-FcεRIα mAbs may be a safe, effective, and practical way to prevent IgE-mediated anaphylaxis.

Understanding Inter-Individual Variability in Monoclonal Antibody Disposition

Monoclonal antibodies (mAbs) are currently the largest and most dominant class of therapeutic proteins. Inter-individual variability has been observed for several mAbs; however, an understanding of the underlying mechanisms and factors contributing to inter-subject differences in mAb disposition is still lacking. In this review, we analyze the mechanisms of antibody disposition and the putative mechanistic determinants of inter-individual variability. Results from in vitro, preclinical, and clinical studies were reviewed evaluate the role of the neonatal Fc receptor and Fc gamma receptors (expression and polymorphism), target properties (expression, shedding, turnover, internalization, heterogeneity, polymorphism), and the influence of anti-drug antibodies. Particular attention is given to the influence of co-administered drugs and disease, and to the physiological relevance of covariates identified by population pharmacokinetic modeling, as determinants of variability in mAb pharmacokinetics.

Antibody Structure and Function: The Basis for Engineering Therapeutics

Antibodies and antibody-derived macromolecules have established themselves as the mainstay in protein-based therapeutic molecules (biologics). Our knowledge of the structure–function relationships of antibodies provides a platform for protein engineering that has been exploited to generate a wide range of biologics for a host of therapeutic indications. In this review, our basic understanding of the antibody structure is described along with how that knowledge has leveraged the engineering of antibody and antibody-related therapeutics having the appropriate antigen affinity, effector function, and biophysical properties. The platforms examined include the development of antibodies, antibody fragments, bispecific antibody, and antibody fusion products, whose efficacy and manufacturability can be improved via humanization, affinity modulation, and stability enhancement. We also review the design and selection of binding arms, and avidity modulation. Different strategies of preparing bispecific and multispecific molecules for an array of therapeutic applications are included.

A Review of PCSK9 Inhibitors and their Effects on Cardiovascular Diseases

BACKGROUND

Cardiovascular diseases remain the leading cause of morbidity and mortality in the world, with elevated Low-Density Lipoprotein-Cholesterol (LDL-C) levels as the major risk factor. Lower levels of LDL-C can effectively reduce the risk of cardiovascular diseases. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in regulating the degradation of hepatic LDL receptors that remove LDL-C from the circulation. PCSK9 inhibitors are a new class of agents that are becoming increasingly important in the treatment to reduce LDL-C levels. Two PCSK9 inhibitors, alirocumab and evolocumab, have been approved to treat hypercholesterolemia and are available in the United States and the European Union. Through the inhibition of PCSK9 and increased recycling of LDL receptors, serum LDL-C levels can be significantly reduced.

OBJECTIVE

This review will describe the chemistry, pharmacokinetics, and pharmacodynamics of PCSK9 inhibitors and their clinical effects.

Genetic Variation in the Magnitude and Longevity of the IgG Subclass Response to a Diphtheria-Tetanus-Acellular Pertussis (DTaP) Vaccine in Mice

The type of IgG subclasses induced by vaccination is an important determinant of vaccine efficacy because the IgG subclasses vary in their biological function. The goal of this study was to determine the influence of the genetic background on the production and duration of vaccine-induced IgG subclasses. IgG1, IgG2b, and IgG3 titers against diphtheria toxoid (DT), pertussis toxin (PT), filamentous hemagglutinin (FHA), and pertactin (Prn) were measured in mice from 28 different inbred and wild-derived strains vaccinated with an aluminum hydroxide-adjuvanted DTaP vaccine. The titers and duration of vaccine-specific IgG subclass responses were different among mouse strains, indicating that genetic factors contribute to this variation. Statistical associations were used to identify potential mechanisms that contribute to antibody production and longevity. This analysis showed that the mechanisms guiding the magnitude of antibody production were antigen-dependent for IgG1 but antigen-independent for IgG2b and IgG3. However, the mechanisms driving the longevity of antibody titers were antigen-independent for IgG1, IgG2b, and IgG3. The ratio of IgG1 and IgG3 titers identified Th1 and Th2-prone mouse strains. TLR4-deficient C3H/HeJ mice had an enhanced IgG1 response compared with C3H/HeOuJ mice with intact TLR4. This work demonstrates that the genetic background contributes significantly to the magnitude and longevity of vaccine-induced IgG1, IgG2b, and IgG3 titers in mice.

Pharmacokinetic and Pharmacodynamic Properties of Drug Delivery Systems

The use of drug delivery systems (DDS) is an attractive approach to facilitate uptake of therapeutic agents at the desired site of action, particularly when free drug has poor pharmacokinetics/biodistribution (PK/BD) or significant off-site toxicities. Successful translation of DDS into the clinic is dependent on a thorough understanding of the in vivo behavior of the carrier, which has, for the most part, been an elusive goal. This is, at least in part, due to significant differences in the mechanisms controlling pharmacokinetics for classic drugs and DDSs. In this review, we summarize the key physiologic mechanisms controlling the in vivo behavior of DDS, compare and contrast this with classic drugs, and describe engineering strategies designed to improve DDS PK/BD. In addition, we describe quantitative approaches that could be useful for describing PK/BD of DDS, as well as critical steps between tissue uptake and pharmacologic effect.

Neuronal BC RNA Transport Impairments Caused by Systemic Lupus Erythematosus Autoantibodies

The etiology of the autoimmune disorder systemic lupus erythematosus (SLE) remains poorly understood. In neuropsychiatric SLE (NPSLE), autoimmune responses against neural self-antigens find expression in neurological and cognitive alterations. SLE autoantibodies often target nucleic acids, including RNAs and specifically RNA domains with higher-order structural content. We report that autoantibodies directed against neuronal regulatory brain cytoplasmic (BC) RNAs were generated in a subset of SLE patients. By contrast, anti-BC RNA autoantibodies (anti-BC abs) were not detected in sera from patients with autoimmune diseases other than SLE (e.g., rheumatoid arthritis or multiple sclerosis) or in sera from healthy subjects with no evidence of disease. SLE anti-BC abs belong to the IgG class of immunoglobulins and target both primate BC200 RNA and rodent BC1 RNA. They are specifically directed at architectural motifs in BC RNA 5' stem-loop domains that serve as dendritic targeting elements (DTEs). SLE anti-BC abs effectively compete with RNA transport factor heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2) for DTE access and significantly diminish BC RNA delivery to synapto-dendritic sites of function. In vivo experiments with male BALB/c mice indicate that, upon lipopolysaccharide-induced opening of the blood-brain barrier, SLE anti-BC abs are taken up by CNS neurons where they significantly impede localization of endogenous BC1 RNA to synapto-dendritic domains. Lack of BC1 RNA causes phenotypic abnormalities including epileptogenic responses and cognitive dysfunction. The combined data indicate a role for anti-BC RNA autoimmunity in SLE and its neuropsychiatric manifestations.SIGNIFICANCE STATEMENT Although clinical manifestations of neuropsychiatric lupus are well recognized, the underlying molecular-cellular alterations have been difficult to determine. We report that sera of a subset of lupus patients contain autoantibodies directed at regulatory brain cytoplasmic (BC) RNAs. These antibodies, which we call anti-BC abs, target the BC RNA 5' domain noncanonical motif structures that specify dendritic delivery. Lupus anti-BC abs effectively compete with RNA transport factor heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2) for access to BC RNAs. As a result, hnRNP A2 is displaced, and BC RNAs are impaired in their ability to reach synapto-dendritic sites of function. The results reveal an unexpected link between BC RNA autoantibody recognition and dendritic RNA targeting. Cellular RNA dysregulation may thus be a contributing factor in the pathogenesis of neuropsychiatric lupus.

The Neonatal Fc Receptor (FcRn): A Misnomer?

Antibodies are essential components of an adaptive immune response. Immunoglobulin G (IgG) is the most common type of antibody found in circulation and extracellular fluids. Although IgG alone can directly protect the body from infection through the activities of its antigen binding region, the majority of IgG immune functions are mediated via proteins and receptors expressed by specialized cell subsets that bind to the fragment crystallizable (Fc) region of IgG. Fc gamma (γ) receptors (FcγR) belong to a broad family of proteins that presently include classical membrane-bound surface receptors as well as atypical intracellular receptors and cytoplasmic glycoproteins. Among the atypical FcγRs, the neonatal Fc receptor (FcRn) has increasingly gained notoriety given its intimate influence on IgG biology and its ability to also bind to albumin. FcRn functions as a recycling or transcytosis receptor that is responsible for maintaining IgG and albumin in the circulation, and bidirectionally transporting these two ligands across polarized cellular barriers. More recently, it has been appreciated that FcRn acts as an immune receptor by interacting with and facilitating antigen presentation of peptides derived from IgG immune complexes (IC). Here we review FcRn biology and focus on newer advances including how emerging FcRn-targeted therapies may affect the immune responses to IgG and IgG IC.

The neonatal Fc receptor: Key to homeostasic control of IgG and IgG-related biopharmaceuticals

IgG and albumin are the most abundant proteins in the circulation and have the longest half-lives. These properties are due to a unique receptor, the neonatal Fc receptor (FcRn). Although FcRn is named for its function of transferring IgG across the placenta from maternal to fetal circulation, FcRn functions throughout life to maintain IgG and albumin concentrations. FcRn protects IgG and albumin from intracellular degradation and recycles them back into the circulation. Clinical trials have confirmed that pathogenic antibodies can be depleted by blocking this homeostatic function of FcRn. Moreover, understanding the molecular interactions between IgG and FcRn has resulted in the design of therapeutic monoclonal antibodies with more efficacious pharmacokinetics. As a result of genetic engineering these monoclonals can be delivered at lower doses and at longer intervals. More recent findings have demonstrated that FcRn enhances phagocytosis by neutrophils, immune complex clearance by podocytes and antigen presentation by dendritic cells, macrophages, and B cells. This minireview highlights the relevance of FcRn to transplantation.

Pemphigus: Current and Future Therapeutic Strategies

Pemphigus encompasses a heterogeneous group of autoimmune blistering diseases, which affect both mucous membranes and the skin. The disease usually runs a chronic-relapsing course, with a potentially devastating impact on the patients' quality of life. Pemphigus pathogenesis is related to IgG autoantibodies targeting various adhesion molecules in the epidermis, including desmoglein (Dsg) 1 and 3, major components of desmosomes. The pathogenic relevance of such autoantibodies has been largely demonstrated experimentally. IgG autoantibody binding to Dsg results in loss of epidermal keratinocyte adhesion, a phenomenon referred to as acantholysis. This in turn causes intra-epidermal blistering and the clinical appearance of flaccid blisters and erosions at involved sites. Since the advent of glucocorticoids, the overall prognosis of pemphigus has largely improved. However, mortality persists elevated, since long-term use of high dose corticosteroids and adjuvant steroid-sparing immunosuppressants portend a high risk of serious adverse events, especially infections. Recently, rituximab, a chimeric anti CD20 monoclonal antibody which induces B-cell depletion, has been shown to improve patients' survival, as early rituximab use results in higher disease remission rates, long term clinical response and faster prednisone tapering compared to conventional immunosuppressive therapies, leading to its approval as a first line therapy in pemphigus. Other anti B-cell therapies targeting B-cell receptor or downstream molecules are currently tried in clinical studies. More intriguingly, a preliminary study in a preclinical mouse model of pemphigus has shown promise regarding future therapeutic application of Chimeric Autoantibody Receptor T-cells engineered using Dsg domains to selectively target autoreactive B-cells. Conversely, previous studies from our group have demonstrated that B-cell depletion in pemphigus resulted in secondary impairment of T-cell function; this may account for the observed long-term remission following B-cell recovery in rituximab treated patients. Likewise, our data support the critical role of Dsg-specific T-cell clones in orchestrating the inflammatory response and B-cell activation in pemphigus. Monitoring autoreactive T-cells in patients may indeed provide further information on the role of these cells, and would be the starting point for designating therapies aimed at restoring the lost immune tolerance against Dsg. The present review focuses on current advances, unmet challenges and future perspectives of pemphigus management.

Reduced FcRn-mediated transcytosis of IgG2 due to a missing Glycine in its lower hinge

Neonatal Fc-receptor (FcRn), the major histocompatibility complex (MHC) class I-like Fc-receptor, transports immunoglobuline G (IgG) across cell layers, extending IgG half-life in circulation and providing newborns with humoral immunity. IgG1 and IgG2 have similar half-lives, yet IgG2 displays lower foetal than maternal concentration at term, despite all known FcRn binding residues being preserved between IgG1 and IgG2. We investigated FcRn mediated transcytosis of V_H-matched IgG1 and IgG2 and mutated variants thereof lacking Fc-gamma receptor (FcγR) binding in human cells expressing FcRn. We observed that FcγR binding was not required for transport and that FcRn transported less IgG2 than IgG1. Transport of IgG1 with a shortened lower hinge (ΔGly236, absent in germline IgG2), was reduced to levels equivalent to IgG2. Conversely, transport of IgG2 + Gly236 was increased to IgG1 levels. Gly236 is not a contact residue between IgG and FcRn, suggesting that its absence leads to an altered conformation of IgG, possibly due to a less flexible Fab, positioned closer to the Fc portion. This may sterically hinder FcRn binding and transport. We conclude that the lack of Gly236 is sufficient to explain the reduced FcRn-mediated IgG2 transcytosis and accounts for the low maternal/fetal IgG2 ratio at term.

Computer-assembled cross-species/cross-modalities two-pore physiologically based pharmacokinetic model for biologics in mice and rats

Two-pore physiologically-based pharmacokinetic (PBPK) models can be expected to describe the tissue distribution and elimination kinetics of soluble proteins, endogenous or dosed, as function of their size. In this work, we amalgamated our previous two-pore PBPK model for an inert domain antibody (dAb) in mice with the cross-species platform PBPK model for monoclonal antibodies described in literature into a unified two-pore platform that describes protein modalities of different sizes and includes neonatal Fc receptor (FcRn) mediated recycling. This unified PBPK model was parametrized for organ-specific lymph flow rates and the endosomal recycling rate constant using an extended tissue distribution time-course dataset that included an inert dAb, albumin and IgG in rats and mice. The model was evaluated by comparing the ab initio predictions for the tissue distribution and elimination properties of albumin-binding dAbs (AlbudAbs^TM) in mice and rats with the experimental observations. Due to the large number of molecular species and reactions involved in large-scale PBPK models, we have also developed and deployed a Matlab^TM script for automating the assembly of SimBiology^TM-based two-pore biologics PBPK models which drastically cuts the time and effort required for model building.

Parameter Identification for a Model of Neonatal Fc Receptor-Mediated Recycling of Endogenous Immunoglobulin G in Humans

Salvage of endogenous immunoglobulin G (IgG) by the neonatal Fc receptor (FcRn) is implicated in many clinical areas, including therapeutic monoclonal antibody kinetics, patient monitoring in IgG multiple myeloma, and antibody-mediated transplant rejection. There is a clear clinical need for a fully parameterized model of FcRn-mediated recycling of endogenous IgG to allow for predictive modeling, with the potential for optimizing therapeutic regimens for better patient outcomes. In this paper we study a mechanism-based model incorporating nonlinear FcRn-IgG binding kinetics. The aim of this study is to determine whether parameter values can be estimated using the limited in vivo human data, available in the literature, from studies of the kinetics of radiolabeled IgG in humans. We derive mathematical descriptions of the experimental observations-timecourse data and fractional catabolic rate (FCR) data-based on the underlying physiological model. Structural identifiability analyses are performed to determine which, if any, of the parameters are unique with respect to the observations. Structurally identifiable parameters are then estimated from the data. It is found that parameter values estimated from timecourse data are not robust, suggesting that the model complexity is not supported by the available data. Based upon the structural identifiability analyses, a new expression for the FCR is derived. This expression is fitted to the FCR data to estimate unknown parameter values. Using these parameter estimates, the plasma IgG response is simulated under clinical conditions. Finally a suggestion is made for a reduced-order model based upon the newly derived expression for the FCR. The reduced-order model is used to predict the plasma IgG response, which is compared with the original four-compartment model, showing good agreement. This paper shows how techniques for compartmental model analysis-structural identifiability analysis, linearization, and reparameterization-can be used to ensure robust parameter identification.

IgG and Fcγ Receptors in Intestinal Immunity and Inflammation

Fcγ receptors (FcγR) are cell surface glycoproteins that mediate cellular effector functions of immunoglobulin G (IgG) antibodies. Genetic variation in FcγR genes can influence susceptibility to a variety of antibody-mediated autoimmune and inflammatory disorders, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). More recently, however, genetic studies have implicated altered FcγR signaling in the pathogenesis of inflammatory bowel disease (IBD), a condition classically associated with dysregulated innate and T cell immunity. Specifically, a variant of the activating receptor, FcγRIIA, with low affinity for IgG, confers protection against the development of ulcerative colitis, a subset of IBD, leading to a re-evaluation of the role of IgG and FcγRs in gastrointestinal tract immunity, an organ system traditionally associated with IgA. In this review, we summarize our current understanding of IgG and FcγR function at this unique host-environment interface, from the pathogenesis of colitis and defense against enteropathogens, its contribution to maternal-fetal cross-talk and susceptibility to cancer. Finally, we discuss the therapeutic implications of this information, both in terms of how FcγR signaling pathways may be targeted for the treatment of IBD and how FcγR engagement may influence the efficacy of therapeutic monoclonal antibodies in IBD.

Mind the Gap: How Interspecies Variability in IgG and Its Receptors May Complicate Comparisons of Human and Non-human Primate Effector Function

The field of HIV research relies heavily on non-human primates, particularly the members of the macaque genus, as models for the evaluation of candidate vaccines and monoclonal antibodies. A growing body of research suggests that successful protection of humans will not solely rely on the neutralization activity of an antibody's antigen binding fragment. Rather, immunological effector functions prompted by the interaction of the immunoglobulin G constant region and its cognate Fc receptors help contribute to favorable outcomes. Inherent differences in the sequences, expression, and activities of human and non-human primate antibody receptors and immunoglobulins have the potential to produce disparate results in the observations made in studies conducted in differing species. Having a more complete understanding of these differences, however, should permit the more fluent translation of observations between model organisms and the clinic. Here we present a guide to such translations that encompasses not only what is presently known regarding the affinity of the receptor-ligand interactions but also the influence of expression patterns and allelic variation, with a focus on insights gained from use of this model in HIV vaccines and passive antibody therapy and treatment.

FcRn-Dependent Transcytosis of Monoclonal Antibody in Human Nasal Epithelial Cells In Vitro: A Prerequisite for a New Delivery Route for Therapy?

Monoclonal antibodies (mAbs) are promising therapies to treat airway chronic inflammatory disease (asthma or nasal polyps). To date, no study has specifically assessed, in vitro, the potential function of neonatal Fc receptor (FcRn) in IgG transcytosis through the human nasal airway epithelium. The objective of this study was to report the in vitro expression and function of FcRn in nasal human epithelium. FcRn expression was studied in an air–liquid interface (ALI) primary culture model of human nasal epithelial cells (HNEC) from polyps. FcRn expression was characterized by quantitative RT-PCR, western blot, and immunolabeling. The ability of HNECs to support mAb transcytosis via FcRn was assessed by transcytosis assay. This study demonstrates the expression of FcRn mRNA and protein in HNEC. We report a high expression of FcRn in the cytosol of ciliated, mucus, and basal cells by immunohistochemistry with a higher level of FcRn proteins in differentiated HNEC. We also proved in vitro transepithelial delivery of an IgG1 therapeutic mAb with a dose–response curve. This is the first time that FcRn expression and mAb transcytosis has been shown in a model of human nasal respiratory epithelium in vitro. This study is a prerequisite for FcRn-dependent nasal administration of mAbs.

Use of biologics during pregnancy and risk of serious infections in the mother and baby: a Canadian population-based cohort study

OBJECTIVES

To investigate the association between exposure to biologics during pregnancy and serious infections in mothers and infants.

DESIGN

Retrospective cohort study.

SETTING

Population-based.

PARTICIPANTS

Women with one or more autoimmune diseases identified by International Classification of Diseases 9th/10th revision codes in healthcare administrative databases in British Columbia, Canada, who had pregnancies ending in a live or stillbirth between 1 January 2002 and 31 December 2012. Women were defined as exposed if they had at least one biologic prescription during pregnancy, and infants born to these women were considered exposed in utero. Disease-matched women with no biologics prescriptions during pregnancy, and their infants, comprised the unexposed groups.

PRIMARY OUTCOME MEASURES

Serious infections requiring hospitalisation.

RESULTS

Over the 10-year study period, there were 6218 women (8607 pregnancies) who had an autoimmune disease diagnosis, of which 90 women were exposed to biologics during pregnancy, with 100 babies born to these women. Among women exposed to biologics during pregnancy, occurrence of serious postpartum infections were low, ranging from 0% to 5%, depending on concomitant exposures to immunosuppressants. In multivariable models using logistic regression, the OR for the association of biologics exposure with serious maternal postpartum infections was 0.79 (95% CI 0.24 to 2.54). In infants exposed to biologics in utero, occurrence of serious infections during the first year of life ranged from 0% to 7%, depending on concomitant exposures to immunosuppressants in utero. Multivariable models showed no association between biologics exposure in utero and serious infant infections (OR 0.56, 95% CI 0.17 to 1.81).

CONCLUSIONS

These population-based data suggest that the use of biologics by women with autoimmune diseases during pregnancy is not associated with an increased risk of serious infections in mothers, during post partum or in infants during the first year of life.

Physiologically-based modeling of monoclonal antibody pharmacokinetics in drug discovery and development

Over the past few decades, monoclonal antibodies (mAbs) have become one of the most important and fastest growing classes of therapeutic molecules, with applications in a wide variety of disease areas. As such, understanding of the determinants of mAb pharmacokinetic (PK) processes (absorption, distribution, metabolism, and elimination) is crucial in developing safe and efficacious therapeutics. In the present review, we discuss the use of physiologically-based pharmacokinetic (PBPK) models as an approach to characterize the in vivo behavior of mAbs, in the context of the key PK processes that should be considered in these models. Additionally, we discuss current and potential future applications of PBPK in the drug discovery and development timeline for mAbs, spanning from identification of potential target molecules to prediction of potential drug-drug interactions. Finally, we conclude with a discussion of currently available PBPK models for mAbs that could be implemented in the drug development process.

IVIG-mediated effector functions in autoimmune and inflammatory diseases

Intravenous immunoglobulin (IVIG) is a pooled preparation of normal IgG obtained from several thousand healthy donors. It is widely used in the immunotherapy of a large number of autoimmune and inflammatory diseases. The mechanisms of action of IVIG are complex and, as discussed in this review, experimental and clinical data provide an indicator that the therapeutic benefit of IVIG therapy is due to several mutually non-exclusive mechanisms affecting soluble mediators as well as cellular components of the immune system. These mechanisms depend on Fc and/or F(ab')2 fragments. A better understanding of the effector functions of IVIG should help in identification of biomarkers of responses to IVIG in autoimmune patients.

Application of Physiologically Based Pharmacokinetic Modeling to Predict the Effects of FcRn Inhibitors in Mice, Rats, and Monkeys

There is a growing interest in developing inhibitors of the neonatal Fc-receptor, FcRn, for use in the treatment for humoral autoimmune conditions. We have developed a new physiologically based pharmacokinetic model that is capable of characterizing the pharmacokinetics and pharmacodynamics of anti-FcRn monoclonal antibodies (mAb) in mice, rats, and monkeys. The model includes incorporation of FcRn recycling of immune gamma globulin (IgG) in hematopoietic cells in addition to FcRn recycling of IgG in vascular endothelial cells and considers FcRn turnover and intracellular cycling. The model captured antibody disposition in wild-type and FcRn-knockout mice and rats, and also predicted the effects of intravenous immune globulin and anti-FcRn mAb on IgG disposition. Simulations predicted the change in IgG clearance in response to intravenous immune globulin with good accuracy in rats (mean prediction error of 7.15% ± 7.67%). In monkeys, prediction windows for simulated IgG concentration versus time data, as generated through Monte Carlo simulation, were able to capture the effects of anti-FcRn mAb on endogenous IgG. The model may have utility in guiding preclinical evaluations of anti-FcRn therapies in development, potentially assisting in the identification of optimal dosing strategies for this emerging class of immunosuppressive drugs.

Targeting therapeutics to endothelium: are we there yet?

Vascular endothelial cells represent an important therapeutic target in many pathologies, including inflammation, oxidative stress, and thrombosis; however, delivery of drugs to this site is often limited by the lack of specific affinity of therapeutics for these cells. Selective delivery of both small molecule drugs and therapeutic proteins to the endothelium has been achieved through the use of targeting ligands, such as monoclonal antibodies, directed against endothelial cell surface markers, particularly cell adhesion molecules (CAMs). Careful selection of target molecules and targeting agents allows for precise delivery to sites of inflammation, thereby maximizing therapeutic drug concentrations at the site of injury. A good understanding of the physiological and pathological determinants of drug and drug carrier pharmacokinetics and biodistribution may allow for a priori identification of optimal properties of drug carrier and targeting agent. Targeted delivery of therapeutics such as antioxidants and antithrombotic agents to the injured endothelium has shown efficacy in preclinical models, suggesting the potential for translation into clinical practice. As with all therapeutics, demonstration of both efficacy and safety are required for successful clinical implementation, which must be considered not only for the individual components (drug, targeting agent, etc.) but also for the sum of the parts (e.g., the drug delivery system), as unexpected toxicities may arise with complex delivery systems. While the use of endothelial targeting has not been translated into the clinic to date, the preclinical results summarized here suggest that there is hope for successful implementation of these agents in the years to come.