Recombinant human IgG molecules lacking Fcgamma receptor I binding and monocyte triggering activities

Living in LALA land? Forty years of attenuating Fc effector functions

The Fc region of antibodies is vital for most of their physiological functions, many of which are engaged through binding to a range of Fc receptors. However, these same interactions are not always helpful or wanted when therapeutic antibodies are directed against self-antigens, and can sometimes cause catastrophic adverse reactions. Over the past 40 years, there have been intensive efforts to "silence" unwanted binding to Fc-gamma receptors, resulting in at least 45 different variants which have entered clinical trials. One of the best known is "LALA" (L234A/L235A). However, neither this, nor most of the other variants in clinical use are completely silenced, and in addition, the biophysical properties of many of them are compromised. I review the development of different variants to see what we can learn from their biological properties and use in the clinic. With the rise of powerful new uses of antibody therapy such as bispecific T-cell engagers, antibody-drug conjugates, and checkpoint inhibitors, it is increasingly important to optimize the Fc region as well as the antibody binding site in order to achieve the best combination of safety and efficacy.

Impact of structural modifications of IgG antibodies on effector functions

Immunoglobulin G (IgG) antibodies are a critical component of the adaptive immune system, binding to and neutralizing pathogens and other foreign substances. Recent advances in molecular antibody biology and structural protein engineering enabled the modification of IgG antibodies to enhance their therapeutic potential. This review summarizes recent progress in both natural and engineered structural modifications of IgG antibodies, including allotypic variation, glycosylation, Fc engineering, and Fc gamma receptor binding optimization. We discuss the functional consequences of these modifications to highlight their potential for therapeutical applications.

Profiling the Biophysical Developability Properties of Common IgG1 Fc Effector Silencing Variants

Therapeutic antibodies represent the most significant modality in biologics, with around 150 approved drugs on the market. In addition to specific target binding mediated by the variable fragments (Fvs) of the heavy and light chains, antibodies possess effector functions through binding of the constant region (Fc) to Fcγ receptors (FcγR), which allow immune cells to attack and kill target cells using a variety of mechanisms. However, for some applications, including T-cell-engaging bispecifics, this effector function is typically undesired. Mutations within the lower hinge and the second constant domain (CH2) of IgG1 that comprise the FcγR binding interface reduce or eliminate effector function ("Fc silencing") while retaining binding to the neonatal Fc receptor (FcRn), important for normal antibody pharmacokinetics (PKs). Comprehensive profiling of biophysical developability properties would benefit the choice of constant region variants for development. Here, we produce a large panel of representative mutations previously described in the literature and in many cases in clinical or approved molecules, generate select combinations thereof, and characterize their binding and biophysical properties. We find that some commonly used CH2 mutations, including D265A and P331S, are effective in reducing binding to FcγR but significantly reduce stability, promoting aggregation, particularly under acidic conditions commonly employed in manufacturing. We highlight mutation sets that are particularly effective for eliminating Fc effector function with the retention of WT-like stability, including L234A, L235A, and S267K (LALA-S267K), L234A, L235E, and S267K (LALE-S267K), L234A, L235A, and P329A (LALA-P329A), and L234A, L235E, and P329G (LALE-P329G).

Latozinemab, a novel progranulin-elevating therapy for frontotemporal dementia

BACKGROUND

Heterozygous loss-of-function mutations in the progranulin (PGRN) gene (GRN) cause a reduction in PGRN and lead to the development of frontotemporal dementia (FTD-GRN). PGRN is a secreted lysosomal chaperone, immune regulator, and neuronal survival factor that is shuttled to the lysosome through multiple receptors, including sortilin. Here, we report the characterization of latozinemab, a human monoclonal antibody that decreases the levels of sortilin, which is expressed on myeloid and neuronal cells and shuttles PGRN to the lysosome for degradation, and blocks its interaction with PGRN.

METHODS

In vitro characterization studies were first performed to assess the mechanism of action of latozinemab. After the in vitro studies, a series of in vivo studies were performed to assess the efficacy of a mouse-cross reactive anti-sortilin antibody and the pharmacokinetics, pharmacodynamics, and safety of latozinemab in nonhuman primates and humans.

RESULTS

In a mouse model of FTD-GRN, the rodent cross-reactive anti-sortilin antibody, S15JG, decreased total sortilin levels in white blood cell (WBC) lysates, restored PGRN to normal levels in plasma, and rescued a behavioral deficit. In cynomolgus monkeys, latozinemab decreased sortilin levels in WBCs and concomitantly increased plasma and cerebrospinal fluid (CSF) PGRN by 2- to threefold. Finally, in a first-in-human phase 1 clinical trial, a single infusion of latozinemab caused a reduction in WBC sortilin, tripled plasma PGRN and doubled CSF PGRN in healthy volunteers, and restored PGRN to physiological levels in asymptomatic GRN mutation carriers.

CONCLUSIONS

These findings support the development of latozinemab for the treatment of FTD-GRN and other neurodegenerative diseases where elevation of PGRN may be beneficial. Trial registration ClinicalTrials.gov, NCT03636204. Registered on 17 August 2018, https://clinicaltrials.gov/ct2/show/NCT03636204 .

A multicenter, open-label, phase 3 study to evaluate the safety of fremanezumab for migraine, subcutaneously self-administered with an auto-injection device at institutional sites and at home

BACKGROUND

Fremanezumab is a humanized monoclonal antibody against calcitonin gene-related peptide for subcutaneous use to suppress migraine attacks. A phase 3 study was conducted to investigate the safety of autoinjector (AI)-assisted self-injection of fremanezumab 225 mg.

RESEARCH DESIGN AND METHODS

The multicenter, open-label study involving 71 patients with migraine was conducted between June 2020 and November 2020 at ten institutions in Japan. The study consisted of a 4-week (28-day) screening period and an 8-week (57-day) treatment period. According to the investigator's instructions, all patients successfully performed self-injection for 4 weeks at the institutional site and at home and maintained eDiaries of their headaches. The primary endpoint was safety of the drug based on treatment-emergent adverse events (TEAEs).

RESULTS

Treatment-emergent adverse events were more frequent after at-home injection than after at-site injection, but they were mainly injection site reactions and mostly mild. The safety profile was comparable, raising no concerns compared with what has been reported in previous studies. Both migraine days and headache days were decreased considerably.

CONCLUSIONS

Overall, AI-assisted, at-home self-injection of fremanezumab was found to be generally safe and well-tolerated. This injection strategy is considered clinically meaningful in view of improved utility of and adherence to the drug.

Fc-based Duokines: dual-acting costimulatory molecules comprising TNFSF ligands in the single-chain format fused to a heterodimerizing Fc (scDk-Fc)

Targeting costimulatory receptors of the tumor necrosis factor superfamily (TNFSF) to activate T-cells and promote anti-tumor T-cell function have emerged as a promising strategy in cancer immunotherapy. Previous studies have shown that combining two different members of the TNFSF resulted in dual-acting costimulatory molecules with the ability to activate two different receptors either on the same cell or on different cell types. To achieve prolonged plasma half-life and extended drug disposition, we have developed novel dual-acting molecules by fusing single-chain ligands of the TNFSF to heterodimerizing Fc chains (scDuokine-Fc, scDk-Fc). Incorporating costimulatory ligands of the TNF superfamily into a scDk-Fc molecule resulted in enhanced T-cell proliferation translating in an increased anti-tumor activity in combination with a primary T-cell-activating bispecific antibody. Our data show that the scDk-Fc molecules are potent immune-stimulatory molecules that are able to enhance T-cell mediated anti-tumor responses.

Stepping forward in antibody-drug conjugate development

Antibody-drug conjugates (ADCs) are cancer therapeutic agents comprised of an antibody, a linker and a small-molecule payload. ADCs use the specificity of the antibody to target the toxic payload to tumor cells. After intravenous administration, ADCs enter circulation, distribute to tumor tissues and bind to the tumor surface antigen. The antigen then undergoes endocytosis to internalize the ADC into tumor cells, where it is transported to lysosomes to release the payload. The released toxic payloads can induce apoptosis through DNA damage or microtubule inhibition and can kill surrounding cancer cells through the bystander effect. The first ADC drug was approved by the United States Food and Drug Administration (FDA) in 2000, but the following decade saw no new approved ADC drugs. From 2011 to 2018, four ADC drugs were approved, while in 2019 and 2020 five more ADCs entered the market. This demonstrates an increasing trend for the clinical development of ADCs. This review summarizes the recent clinical research, with a specific focus on how the in vivo processing of ADCs influences their design. We aim to provide comprehensive information about current ADCs to facilitate future development.

Fc-engineered antibodies with immune effector functions completely abolished

Elimination of the binding of immunoglobulin Fc to Fc gamma receptors (FcγR) is highly desirable for the avoidance of unwanted inflammatory responses to therapeutic antibodies and fusion proteins. Many different approaches have been described in the literature but none of them completely eliminates binding to all of the Fcγ receptors. Here we describe a set of novel variants having specific amino acid substitutions in the Fc region at L234 and L235 combined with the substitution G236R. They show no detectable binding to Fcγ receptors or to C1q, are inactive in functional cell-based assays and do not elicit inflammatory cytokine responses. Meanwhile, binding to FcRn, manufacturability, stability and potential for immunogenicity are unaffected. These variants have the potential to improve the safety and efficacy of therapeutic antibodies and Fc fusion proteins.

Low-Level Endothelial TRAIL-Receptor Expression Obstructs the CNS-Delivery of Angiopep-2 Functionalised TRAIL-Receptor Agonists for the Treatment of Glioblastoma

Glioblastoma (GBM) is the most malignant and aggressive form of glioma and is associated with a poor survival rate. Latest generation Tumour Necrosis Factor Related Apoptosis-Inducing Ligand (TRAIL)-based therapeutics potently induce apoptosis in cancer cells, including GBM cells, by binding to death receptors. However, the blood-brain barrier (BBB) is a major obstacle for these biologics to enter the central nervous system (CNS). We therefore investigated if antibody-based fusion proteins that combine hexavalent TRAIL and angiopep-2 (ANG2) moieties can be developed, with ANG2 promoting receptor-mediated transcytosis (RMT) across the BBB. We demonstrate that these fusion proteins retain the potent apoptosis induction of hexavalent TRAIL-receptor agonists. Importantly, blood-brain barrier cells instead remained highly resistant to this fusion protein. Binding studies indicated that ANG2 is active in these constructs but that TRAIL-ANG2 fusion proteins bind preferentially to BBB endothelial cells via the TRAIL moiety. Consequently, transport studies indicated that TRAIL-ANG2 fusion proteins can, in principle, be shuttled across BBB endothelial cells, but that low TRAIL receptor expression on BBB endothelial cells interferes with efficient transport. Our work therefore demonstrates that TRAIL-ANG2 fusion proteins remain highly potent in inducing apoptosis, but that therapeutic avenues will require combinatorial strategies, such as TRAIL-R masking, to achieve effective CNS transport.

A SARS-CoV-2 neutralizing antibody selected from COVID-19 patients binds to the ACE2-RBD interface and is tolerant to most known RBD mutations

The novel betacoronavirus severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) causes a form of severe pneumonia disease called coronavirus disease 2019 (COVID-19). To develop human neutralizing anti-SARS-CoV-2 antibodies, antibody gene libraries from convalescent COVID-19 patients were constructed and recombinant antibody fragments (scFv) against the receptor-binding domain (RBD) of the spike protein were selected by phage display. The antibody STE90-C11 shows a subnanometer IC50 in a plaque-based live SARS-CoV-2 neutralization assay. The in vivo efficacy of the antibody is demonstrated in the Syrian hamster and in the human angiotensin-converting enzyme 2 (hACE2) mice model. The crystal structure of STE90-C11 Fab in complex with SARS-CoV-2-RBD is solved at 2.0 Å resolution showing that the antibody binds at the same region as ACE2 to RBD. The binding and inhibition of STE90-C11 is not blocked by many known emerging RBD mutations. STE90-C11-derived human IgG1 with FcγR-silenced Fc (COR-101) is undergoing Phase Ib/II clinical trials for the treatment of moderate to severe COVID-19.

The TNFR1 Antagonist Atrosimab Is Therapeutic in Mouse Models of Acute and Chronic Inflammation

Therapeutics that block tumor necrosis factor (TNF), and thus activation of TNF receptor 1 (TNFR1) and TNFR2, are clinically used to treat inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease and psoriasis. However, TNFR1 and TNFR2 work antithetically to balance immune responses involved in inflammatory diseases. In particular, TNFR1 promotes inflammation and tissue degeneration, whereas TNFR2 contributes to immune modulation and tissue regeneration. We, therefore, have developed the monovalent antagonistic anti-TNFR1 antibody derivative Atrosimab to selectively block TNFR1 signaling, while leaving TNFR2 signaling unaffected. Here, we describe that Atrosimab is highly stable at different storage temperatures and demonstrate its therapeutic efficacy in mouse models of acute and chronic inflammation, including experimental arthritis, non-alcoholic steatohepatitis (NASH) and experimental autoimmune encephalomyelitis (EAE). Our data support the hypothesis that it is sufficient to block TNFR1 signaling, while leaving immune modulatory and regenerative responses via TNFR2 intact, to induce therapeutic effects. Collectively, we demonstrate the therapeutic potential of the human TNFR1 antagonist Atrosimab for treatment of chronic inflammatory diseases.

Engineered Fc-glycosylation switch to eliminate antibody effector function

Antibodies mediate effector functions through Fcγ receptor (FcγR) interactions and complement activation, causing cytokine release, degranulation, phagocytosis, and cell death. They are often undesired for development of therapeutic antibodies where only antigen binding or neutralization would be ideal. Effector elimination has been successful with extensive mutagenesis, but these approaches can potentially lead to manufacturability and immunogenicity issues. By switching the native glycosylation site from position 297 to 298, we created alternative antibody glycosylation variants in the receptor interaction interface as a novel strategy to eliminate the effector functions. The engineered glycosylation site at Asn298 was confirmed by SDS-PAGE, mass spectrometry, and X-ray crystallography (PDB code 6X3I). The lead NNAS mutant (S298N/T299A/Y300S) shows no detectable binding to mouse or human FcγRs by surface plasmon resonance analyses. The effector functions of the mutant are completely eliminated when measured in antibody-dependent cell-meditated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays. In vivo, the NNAS mutant made on an antibody against a human lymphocyte antigen does not deplete T cells or B cells in transgenic mice, in contrast to wild-type antibody. Structural study confirms the successful glycosylation switch to the engineered Asn298 site. The engineered glycosylation would clash with approaching FcγRs based on reported Fc-FcγR co-crystal structures. In addition, the NNAS mutants of multiple antibodies retain binding to antigens and neonatal Fc receptor, exhibit comparable purification yields and thermal stability, and display normal circulation half-life in mice and non-human primate. Our work provides a novel approach for generating therapeutic antibodies devoid of any ADCC and CDC activities with potentially lower immunogenicity.

Scaling Approaches for Pediatric Dose Selection: The Fremanezumab (AJOVY®) Journey to Select a Phase 3 Dose Using Pharmacokinetic Data from a Phase 1 Study

Fremanezumab, a fully humanized IgG2Δa/kappa monoclonal antibody, selectively targets the calcitonin-gene-related peptide (CGRP) and prevents it from binding to the CGRP receptor. The safety, tolerability, pharmacokinetics (PK), and efficacy of fremanezumab for treating migraines administered as a once monthly 225 mg dose or a once quarterly 675 mg dose have been well characterized in adults. The fremanezumab exposure and body weight relationship supported the use of the approved 225 mg monthly adult dose for pediatric patients weighing ≥45 kg. In the pediatric Phase 3 program, a 120 mg dose for patients weighing <45 kg was determined using the results of an open-label study and a population PK modeling and simulation strategy. A thorough evaluation was conducted to further characterize the population PK of fremanezumab and assess the predictive performance of the adult population PK model when applied to the Phase 1 pediatric data, the predictive performance of alternative pediatric population PK models, and the predictive performance of the selected pediatric population PK model via a noncompartmental-based approach. This latter comparison to noncompartmental results provided additional evidence that the pediatric population PK model predicts the observed data well and supports the 120 mg monthly dose in patients weighing <45 kg.

Metabolic reprogramming of terminally exhausted CD8+ T cells by IL-10 enhances anti-tumor immunity

T cell exhaustion presents one of the major hurdles to cancer immunotherapy. Among exhausted CD8⁺ tumor-infiltrating lymphocytes (TILs), the terminally exhausted subset contributes directly to tumor cell killing owing to its cytotoxic effector function. However, this subset does not respond to immune checkpoint blockades and is difficult to be reinvigorated with restored proliferative capacity. Here, we show that a half-life–extended interleukin (IL)-10/Fc fusion protein directly and potently enhanced expansion and effector function of terminally exhausted CD8⁺ TILs by promoting oxidative phosphorylation (OXPHOS), a process independent of the progenitor exhausted T cells. IL-10/Fc was a safe and highly efficient metabolic intervention that synergized with adoptive T cell transfer immunotherapy, leading to eradication of established solid tumors and durable cures in a majority of treated mice. These findings show that metabolic reprogramming by upregulating mitochondrial pyruvate carrier-dependent OXPHOS can revitalize terminally exhausted T cells and enhance the response to cancer immunotherapy.

SARS-CoV-2 neutralizing human recombinant antibodies selected from pre-pandemic healthy donors binding at RBD-ACE2 interface

COVID-19 is a severe acute respiratory disease caused by SARS-CoV-2, a new recently emerged sarbecovirus. This virus uses the human ACE2 enzyme as receptor for cell entry, recognizing it with the receptor binding domain (RBD) of the S1 subunit of the viral spike protein. We present the use of phage display to select anti-SARS-CoV-2 spike antibodies from the human naïve antibody gene libraries HAL9/10 and subsequent identification of 309 unique fully human antibodies against S1. 17 antibodies are binding to the RBD, showing inhibition of spike binding to cells expressing ACE2 as scFv-Fc and neutralize active SARS-CoV-2 virus infection of VeroE6 cells. The antibody STE73-2E9 is showing neutralization of active SARS-CoV-2 as IgG and is binding to the ACE2-RBD interface. Thus, universal libraries from healthy human donors offer the advantage that antibodies can be generated quickly and independent from the availability of material from recovering patients in a pandemic situation.

Engineering therapeutic antibodies for patient safety: tackling the immunogenicity problem

Established monoclonal antibodies (mAbs) allow treatment of cancers, autoimmune diseases and other severe illnesses. Side effects either arise due to interaction with the target protein and its biology or result from of the patient's immune system reacting to the foreign protein. This immunogenic reaction against therapeutic antibodies is dependent on various factors. The presence of non-human sequences can trigger immune responses as well as chemical and post-translational modifications of the antibody. However, even fully human antibodies can induce immune response through T cell epitopes or aggregates. In this review, we briefly describe, how therapeutic antibodies can interact with the patient's immune system and summarize recent advancements in protein engineering and in silico methods to reduce immunogenicity of therapeutic monoclonal antibodies.

Immunogenicity of biologic therapies for migraine: a review of current evidence

Background

Monoclonal antibodies (mAbs) targeting the calcitonin gene-related peptide (CGRP) pathway have been shown to be effective in migraine prevention. Eptinezumab, erenumab, fremanezumab, and galcanezumb have shown efficacy in clinical trials along with favorable safety and tolerability profiles. Although erenumab is a human mAb and the others have been humanized to varying degrees, they all have the capacity to provoke immune reactions. The present review article aims to discuss the current relationship between mAbs targeting the CGRP pathway (CGRP mAbs) and immunogenicity and their potential clinical implications.

Findings

The incidence of patients developing anti-drug antibodies (ADAs), their titer, and clinical significance are highly variable and depend on a variety of different drug and patient factors. Neutralizing ADAs (NAbs) bind to and inhibit or reduce the pharmacologic activity of the biologic drug molecule, whereas non-neutralizing antibodies (Non-NAbs) bind to the biologic drug molecule without affecting pharmacologic activity in an in vitro test, although pharmacokinetics and drug clearance may be affected. A direct comparison of immunogenicity data across clinical trials with different biologics is not possible due to a lack of standardized assays. Several phase 2, phase 3, and long-term studies evaluating CGRP mAbs for migraine prevention have reported immunogenicity data (5 studies each for eptinezumab, erenumab, fremanezumab, and galcanezumab). Across these studies, prevalence of ADAs varied, ranging from < 1% to ~ 18%. Neutralizing ADAs were slightly less common, with a prevalence ranging from 0 to 12%. Adverse events related to ADA formation were rare.

Conclusions

As more CGRP mAb studies are conducted and more long-term follow-up data become available, evidence is increasing that immunogenicity rates of biologic therapies for migraine are low, and adverse events related to ADAs are rare. Taken together, these results add to the growing body of evidence for the safety and tolerability of this class of migraine medications.

A bivalent, bispecific Dab-Fc antibody molecule for dual targeting of HER2 and HER3

Dual targeting of surface receptors with bispecific antibodies is attracting increasing interest in cancer therapy. Here, we present a novel bivalent and bispecific antagonistic molecule (Dab-Fc) targeting human epidermal growth factors 2 and 3 (HER2 and HER3) derived from the Db-Ig platform, which was developed for the generation of multivalent and multispecific antibody molecules. Dab-Fc comprises the variable domains of the anti-HER2 antibody trastuzumab and the anti-HER3 antibody 3-43 assembled into a diabody-like structure stabilized by CH1 and CL domains and further fused to a human γ1 Fc region. The resulting Dab-Fc 2 × 3 molecule retained unhindered binding to both antigens and was able to bind both antigens sequentially. In cellular experiments, the Dab-Fc 2 × 3 molecule strongly bound to different tumor cell lines expressing HER2 and HER3 and was efficiently internalized. This was associated with potent inhibition of the proliferation and migration of these tumor cell lines. Furthermore, IgG-like pharmacokinetics and anti-tumoral activity were demonstrated in a xenograft tumor model of the gastric cancer cell-line NCI-N87. These results illustrate the suitability of our versatile Db-Ig platform technology for the generation of bivalent bispecific molecules, which has been successfully used here for the dual targeting of HER2 and HER3.

Targeted glycan degradation potentiates the anticancer immune response in vivo

Currently approved immune checkpoint inhibitor therapies targeting the PD-1 and CTLA-4 receptor pathways are powerful treatment options for certain cancers; however, most patients across cancer types still fail to respond. Consequently, there is interest in discovering and blocking alternative pathways that mediate immune suppression. One such mechanism is an upregulation of sialoglycans in malignancy, which has been recently shown to inhibit immune cell activation through multiple mechanisms and therefore represents a targetable glycoimmune checkpoint. Since these glycans are not canonically druggable, we designed an αHER2 antibody-sialidase conjugate that potently and selectively strips diverse sialoglycans from breast cancer cells. In syngeneic breast cancer models, desialylation enhanced immune cell infiltration and activation and prolonged the survival of mice, an effect that was dependent on expression of the Siglec-E checkpoint receptor found on tumor-infiltrating myeloid cells. Thus, antibody-sialidase conjugates represent a promising modality for glycoimmune checkpoint therapy.

Fc-Engineering for Modulated Effector Functions-Improving Antibodies for Cancer Treatment

The majority of monoclonal antibody (mAb) therapeutics possess the ability to engage innate immune effectors through interactions mediated by their fragment crystallizable (Fc) domain. By delivering Fc-Fc gamma receptor (FcγR) and Fc-C1q interactions, mAb are able to link exquisite specificity to powerful cellular and complement-mediated effector functions. Fc interactions can also facilitate enhanced target clustering to evoke potent receptor signaling. These observations have driven decades-long research to delineate the properties within the Fc that elicit these various activities, identifying key amino acid residues and elucidating the important role of glycosylation. They have also fostered a growing interest in Fc-engineering whereby this knowledge is exploited to modulate Fc effector function to suit specific mechanisms of action and therapeutic purposes. In this review, we document the insight that has been generated through the study of the Fc domain; revealing the underpinning structure-function relationships and how the Fc has been engineered to produce an increasing number of antibodies that are appearing in the clinic with augmented abilities to treat cancer.

Glycine 236 in the Lower Hinge Region of Human IgG1 Differentiates FcγR from Complement Effector Function

Abs of the IgG isotype mediate effector functions like Ab-dependent cellular cytotoxicity and Ab-dependent cellular phagocytosis by Fc interactions with FcγRs and complement-dependent cytotoxicity upon IgG-Fc binding to C1q. In this study, we describe the crucial role of the highly conserved dual glycines at position 236-237 in the lower hinge region of human IgG, including the lack of one glycine as found in IgG2. We found several permutations in this region that either silence or largely abrogate FcγR binding and downstream FcγR effector functions, as demonstrated by surface plasmon resonance, Ab-dependent cellular phagocytosis, and Ab-dependent cellular cytotoxicity assays. Although the binding regions of FcγRs and C1q on the IgG-Fc largely overlap, IgG1 with a deletion of G236 only silences FcγR-mediated effector functions without affecting C1q-binding or activation. Several mutations resulted in only residual FcγRI binding with differing affinities that are either complement competent or silenced. Interestingly, we also found that IgG2, naturally only binding FcγRIIa, gains binding to FcγRI and FcγRIIIa after insertion of G236, highlighting the crucial importance of G236 in IgG for FcγR interaction. These mutants may become invaluable tools for FcγR-related research as well as for therapeutic purposes in which only complement-mediated functions are required without the involvement of FcγR.

No "Wearing-Off Effect" Seen in Quarterly or Monthly Dosing of Fremanezumab: Subanalysis of a Randomized Long-Term Study

OBJECTIVE

To evaluate whether quarterly or monthly administration of fremanezumab for migraine prevention exhibits a pattern of decreased efficacy toward the end of the dosing interval (wearing-off effect).

BACKGROUND

The main goals of migraine preventive treatment are to reduce the frequency, severity, and duration of migraine attacks, and migraine-associated disability. Wearing-off refers to the phenomenon whereby clinical symptoms return or worsen before the next dose of a drug is due and has been reported previously with migraine preventive medications.

DESIGN AND METHODS

This was a long-term, 12-month, multicenter, randomized, double-blind, parallel-group phase 3 study (NCT02638103) that included chronic (CM) and episodic migraine (EM) patients who rolled over from the 12-week phase 3 HALO CM (NCT02621931) and EM trials (NCT02629861), as well as an additional subset of 312 new patients. Patients with CM or EM received fremanezumab either monthly or quarterly. In this post hoc analysis, for selected months, the difference in the average number of migraine days between weeks 1-2 and weeks 3-4, between weeks 1-3 and week 4, and between weeks 1-2 and weeks 11-12 were calculated.

RESULTS

A total of 1890 patients (CM, 1110; EM, 780) were enrolled. At months 3, 6, 9, and 15, there were no substantial differences in mean weekly migraine days between weeks 1-2 and weeks 3-4 or between weeks 1-3 and week 4 with quarterly or monthly fremanezumab in the CM or EM subgroups. There were no substantial increases in mean weekly migraine days between weeks 1-2 and weeks 11-12 during the first quarter of treatment (months 1-3) or the second quarter of treatment (months 4-6) with quarterly or monthly fremanezumab in the CM or EM subgroups. Across both dosing subgroups in CM and EM patients, the mean weekly number of migraine days decreased substantially (30%-42%) during the first 2 weeks; decreases in weekly migraine days remained steady during the last 2 weeks of the first quarter, with a similar maintenance of response during the second quarter.

CONCLUSIONS

This analysis of data from a long-term, phase 3 study showed that patients receiving quarterly fremanezumab or monthly fremanezumab did not experience a wearing-off effect toward the end of the dosing interval.

Long-term safety, tolerability, and efficacy of fremanezumab in migraine: A randomized study

OBJECTIVE

To assess the long-term safety, tolerability, and efficacy of fremanezumab, a fully humanized monoclonal antibody approved for the preventive treatment of migraine.

METHODS

A 52-week, multicenter, randomized, double-blind, parallel-group study evaluated fremanezumab monthly or quarterly in adults with chronic migraine (CM) or episodic migraine (EM). Safety and tolerability were assessed by adverse event (AE) monitoring (performed by the investigators), systematic local injection-site assessments (immediately and 1 hour after injection), laboratory/vitals assessments, and immunogenicity testing. Prespecified exploratory evaluations included change from baseline in the monthly number of migraine days, headache days of at least moderate severity, and days with any acute headache medication use. Change from baseline in headache-related disability (6-item Headache Impact Test scores) was also measured.

RESULTS

Of 1,890 patients enrolled, 551 and 559 patients with CM received quarterly and monthly dosing; 394 and 386 patients with EM received quarterly or monthly, respectively. The most commonly reported AEs were injection-site reactions (induration 33%, pain 31%, and erythema 26%). Fremanezumab reduced monthly migraine days (CM quarterly -7.2 days, CM monthly -8.0 days, EM quarterly -5.2 days, EM monthly -5.1 days) and headache days of at least moderate severity (CM quarterly -6.4 days, CM monthly -6.8 days, EM quarterly -4.4, EM monthly -4.2 days) from baseline to 12 months. Reductions in any acute headache medication use and headache-related disability were also maintained over 12 months.

CONCLUSIONS

Fremanezumab quarterly and fremanezumab monthly were well tolerated and demonstrated sustained improvements in monthly migraine days, headache days, and headache-related disability for up to 12 months in patients with migraine.

CLINICALTRIALSGOV

NCT02638103.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that long-term fremanezumab treatment is safe, well tolerated, and effective at sustaining reductions in monthly migraine and headache days.

Fremanezumab: a disease-specific option for the preventive treatment of migraine, including difficult-to-treat migraine

Fremanezumab is a fully humanized monoclonal antibody (IgG2Δa) that targets calcitonin gene-related peptide (CGRP), a key neuropeptide involved in the pathophysiology of migraine. Fremanezumab is approved for quarterly and monthly subcutaneous dosing for the preventive treatment of migraine in adults. The phase 3 clinical development program for fremanezumab aimed to evaluate the efficacy of this preventive treatment across different patient populations, including those with difficult-to-treat migraine. Two pivotal 12-week, phase 3, placebo-controlled studies investigated quarterly and monthly dosing of fremanezumab in participants with chronic migraine (HALO CM) and episodic migraine (HALO EM). The efficacy of fremanezumab was further explored in individuals with difficult-to-treat chronic or episodic migraine in the 12-week FOCUS study, which enrolled participants who had previously experienced an inadequate response to 2-4 pharmacological classes of migraine preventive medications. The long-term efficacy of fremanezumab was assessed in a 12-month long-term study (HALO LTS), which enrolled participants completing the 12-week HALO studies and new participants. Across these studies, treatment with fremanezumab dosed quarterly or monthly provided significant reductions in the frequency of migraine days, headache days of at least moderate severity, and migraine- and headache-related disability compared with placebo. Sustained improvements were seen with long-term fremanezumab treatment. Subgroup analyses of participants with difficult-to-treat migraine (those with comorbid depression, overuse of acute headache medications, and concomitant use of other migraine preventive medications) demonstrated the effectiveness of quarterly or monthly fremanezumab in these populations. Ongoing studies are further exploring the potential benefits of fremanezumab in difficult-to-treat migraine and other headache and pain disorders.

Targeting CD70 with cusatuzumab eliminates acute myeloid leukemia stem cells in patients treated with hypomethylating agents

Acute myeloid leukemia (AML) is driven by leukemia stem cells (LSCs) that resist conventional chemotherapy and are the major cause of relapse^1,2. Hypomethylating agents (HMAs) are the standard of care in the treatment of older or unfit patients with AML, but responses are modest and not durable^3-5. Here we demonstrate that LSCs upregulate the tumor necrosis factor family ligand CD70 in response to HMA treatment resulting in increased CD70/CD27 signaling. Blocking CD70/CD27 signaling and targeting CD70-expressing LSCs with cusatuzumab, a human αCD70 monoclonal antibody with enhanced antibody-dependent cellular cytotoxicity activity, eliminated LSCs in vitro and in xenotransplantation experiments. Based on these preclinical results, we performed a phase 1/2 trial in previously untreated older patients with AML with a single dose of cusatuzumab monotherapy followed by a combination therapy with the HMA azacitidine ( NCT03030612 ). We report results from the phase 1 dose escalation part of the clinical trial. Hematological responses in the 12 patients enrolled included 8 complete remission, 2 complete remission with incomplete blood count recovery and 2 partial remission with 4 patients achieving minimal residual disease negativity by flow cytometry at <10^-3. Median time to response was 3.3 months. Median progression-free survival was not reached yet at the time of the data cutoff. No dose-limiting toxicities were reported and the maximum tolerated dose of cusatuzumab was not reached. Importantly, cusatuzumab treatment substantially reduced LSCs and triggered gene signatures related to myeloid differentiation and apoptosis.

Selective Targeting of TNF Receptors as a Novel Therapeutic Approach

Tumor necrosis factor (TNF) is a central regulator of immunity. Due to its dominant pro-inflammatory effects, drugs that neutralize TNF were developed and are clinically used to treat inflammatory and autoimmune diseases, such as rheumatoid arthritis, inflammatory bowel disease and psoriasis. However, despite their clinical success the use of anti-TNF drugs is limited, in part due to unwanted, severe side effects and in some diseases its use even is contraindicative. With gaining knowledge about the signaling mechanisms of TNF and the differential role of the two TNF receptors (TNFR), alternative therapeutic concepts based on receptor selective intervention have led to the development of novel protein therapeutics targeting TNFR1 with antagonists and TNFR2 with agonists. These antibodies and bio-engineered ligands are currently in preclinical and early clinical stages of development. Preclinical data obtained in different disease models show that selective targeting of TNFRs has therapeutic potential and may be superior to global TNF blockade in several disease indications.

Anti-D monoclonal antibodies from 23 human and rodent cell lines display diverse IgG Fc-glycosylation profiles that determine their clinical efficacy

Anti-D immunoglobulin (Anti-D Ig) prophylaxis prevents haemolytic disease of the fetus and newborn. Monoclonal IgG anti-Ds (mAb-Ds) would enable unlimited supplies but have differed in efficacy in FcγRIIIa-mediated ADCC assays and clinical trials. Structural variations of the oligosaccharide chains of mAb-Ds are hypothesised to be responsible. Quantitative data on 12 Fc-glycosylation features of 23 mAb-Ds (12 clones, 5 produced from multiple cell lines) and one blood donor-derived anti-D Ig were obtained by HPLC and mass spectrometry using 3 methods. Glycosylation of mAb-Ds from human B-lymphoblastoid cell lines (B) was similar to anti-D Ig although fucosylation varied, affecting ADCC activity. In vivo, two B mAb-Ds with 77–81% fucosylation cleared red cells and prevented D-immunisation but less effectively than anti-D Ig. High fucosylation (>89%) of mouse-human heterohybridoma (HH) and Chinese hamster ovary (CHO) mAb-Ds blocked ADCC and clearance. Rat YB2/0 mAb-Ds with <50% fucosylation mediated more efficient ADCC and clearance than anti-D Ig. Galactosylation of B mAb-Ds was 57–83% but 15–58% for rodent mAb-Ds. HH mAb-Ds had non-human sugars. These data reveal high galactosylation like anti-D Ig (>60%) together with lower fucosylation (<60%) as safe features of mAb-Ds for mediating rapid red cell clearance at low doses, to enable effective, inexpensive prophylaxis.

Population pharmacokinetic modelling and simulation of fremanezumab in healthy subjects and patients with migraine

Aims

Fremanezumab is a fully humanized IgG₂Δa/κ monoclonal antibody specific for calcitonin gene‐related peptide developed and approved for the preventive treatment of migraine in adults. The population pharmacokinetics (PK) of fremanezumab were characterized in healthy subjects and patients with chronic migraine and episodic migraine, including the effects of intrinsic and extrinsic factors on PK variability.

Methods

Nonlinear mixed effects modelling was performed using NONMEM with data from 7 phase 1–3 clinical trials evaluating selected intravenous and subcutaneous dose regimens. The influence of covariates on fremanezumab PK was assessed and model evaluation was performed through visual predictive checks.

Results

A 2‐compartment model with first‐order absorption and elimination described the PK data well. Typical values for fremanezumab central clearance (0.0902 L/d) and central distribution volume (1.88 L) for a 71‐kg subject were consistent with previously reported values for IgG antibodies. Higher body weight was associated with increased central clearance and distribution volume. Effects of other covariates (age, albumin, renal function, sex, race, injection site, and acute, analgesic and preventive medication use for migraine) were not found to statistically significantly influence fremanezumab PK. There was no indication of reduced exposure in participants with positive anti‐drug antibody status or with mild to moderate hepatic impairment. Absolute bioavailability was estimated at 0.658.

Conclusions

A comprehensive population PK model was developed for fremanezumab following intravenous and subcutaneous administration in healthy subjects and patients with chronic migraine or episodic migraine, which will be used to further evaluate exposure–response relationships for efficacy and safety endpoints.

biAb Mediated Restoration of the Linkage between Dystroglycan and Laminin-211 as a Therapeutic Approach for α-Dystroglycanopathies

Patients with α-dystroglycanopathies, a subgroup of rare congenital muscular dystrophies, present with a spectrum of clinical manifestations that includes muscular dystrophy as well as CNS and ocular abnormalities. Although patients with α-dystroglycanopathies are genetically heterogeneous, they share a common defect of aberrant post-translational glycosylation modification of the dystroglycan alpha-subunit, which renders it defective in binding to several extracellular ligands such as laminin-211 in skeletal muscles, agrin in neuromuscular junctions, neurexin in the CNS, and pikachurin in the eye, leading to various symptoms. The genetic heterogeneity associated with the development of α-dystroglycanopathies poses significant challenges to developing a generalized treatment to address the spectrum of genetic defects. Here, we propose the development of a bispecific antibody (biAb) that functions as a surrogate molecular linker to reconnect laminin-211 and the dystroglycan beta-subunit to ameliorate sarcolemmal fragility, a primary pathology in patients with α-dystroglycan-related muscular dystrophies. We show that the treatment of LARGE^myd-3J mice, an α-dystroglycanopathy model, with the biAb improved muscle function and protected muscles from exercise-induced damage. These results demonstrate the viability of a biAb that binds to laminin-211 and dystroglycan simultaneously as a potential treatment for patients with α-dystroglycanopathy.

Placental transfer of 125 iodinated humanized immunoglobulin G2Δa in the cynomolgus monkey

Antibody-like biopharmaceuticals cross the placenta by utilizing existing transport pathways (e.g., FcRn receptor). There are limited data evaluating this transfer during organogenesis in any species. Understanding placental transfer of antibody-like biopharmaceuticals can help to predict risk of developmental toxicity across species, including humans. To complement previously published placental transfer data in the rat with humanized IgGΔ2 (hIgG2), the timing and magnitude of transfer in the cynomolgus monkey and embryo/fetal biodistribution of maternally administered ¹²⁵ I-radiolabeled hIgG2 was quantified on gestation days (GD) 35, 40, 50, 70, and 140 using gamma counting and whole body autoradiography 24 hr following intravenous injection. Chorioallantoic placental tissues were collected at all time points for Western Blot analysis with anti-FcRn antibody. Maternally administered ¹²⁵ I-hIgG2 was found in embryo/fetal tissues at all time points, including organogenesis. Embryo/fetal plasma ¹²⁵ I-hIgG2 concentration increased during gestation, but only slightly up to GD 70 in embryo/fetal tissues, with hIgG2 tissue concentrations generally similar between GD70 and 140. The embryo/fetal:maternal ¹²⁵ I-hIgG2 plasma concentration ratio was approximately 2.3 fold higher on GD 140, in comparison to ratios on GD 40. Importantly, placental FcRn protein expression was confirmed at all timepoints. These data demonstrate placental transfer of hIgG2 in a nonhuman primate model, and at levels comparable to the rat model, raising the potential for adverse developmental outcomes by direct antibody binding to biological targets.

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.

Soluble Fc-Disabled Herpes Virus Entry Mediator Augments Activation and Cytotoxicity of NK Cells by Promoting Cross-Talk between NK Cells and Monocytes

CD160 is highly expressed by NK cells and is associated with cytolytic effector activity. Herpes virus entry mediator (HVEM) activates NK cells for cytokine production and cytolytic function via CD160. Fc-fusions are a well-established class of therapeutics, where the Fc domain provides additional biological and pharmacological properties to the fusion protein including enhanced serum t 1/2 and interaction with Fc receptor-expressing immune cells. We evaluated the specific function of HVEM in regulating CD160-mediated NK cell effector function by generating a fusion of the HVEM extracellular domain with human IgG1 Fc bearing CD16-binding mutations (Fc*) resulting in HVEM-(Fc*). HVEM-(Fc*) displayed reduced binding to the Fc receptor CD16 (i.e., Fc-disabled HVEM), which limited Fc receptor-induced responses. HVEM-(Fc*) functional activity was compared with HVEM-Fc containing the wild type human IgG1 Fc. HVEM-(Fc*) treatment of NK cells and PBMCs caused greater IFN-γ production, enhanced cytotoxicity, reduced NK fratricide, and no change in CD16 expression on human NK cells compared with HVEM-Fc. HVEM-(Fc*) treatment of monocytes or PBMCs enhanced the expression level of CD80, CD83, and CD40 expression on monocytes. HVEM-(Fc*)-enhanced NK cell activation and cytotoxicity were promoted via cross-talk between NK cells and monocytes that was driven by cell-cell contact. In this study, we have shown that soluble Fc-disabled HVEM-(Fc*) augments NK cell activation, IFN-γ production, and cytotoxicity of NK cells without inducing NK cell fratricide by promoting cross-talk between NK cells and monocytes without Fc receptor-induced effects. Soluble Fc-disabled HVEM-(Fc*) may be considered as a research and potentially therapeutic reagent for modulating immune responses via sole activation of HVEM receptors.

Improved monovalent TNF receptor 1-selective inhibitor with novel heterodimerizing Fc

The development of alternative therapeutic strategies to tumor necrosis factor (TNF)-blocking antibodies for the treatment of inflammatory diseases has generated increasing interest. In particular, selective inhibition of TNF receptor 1 (TNFR1) promises a more precise intervention, tackling only the pro-inflammatory responses mediated by TNF while leaving regenerative and pro-survival signals transduced by TNFR2 untouched. We recently generated a monovalent anti-TNFR1 antibody fragment (Fab 13.7) as an efficient inhibitor of TNFR1. To improve the pharmacokinetic properties of Fab 13.7, the variable domains of the heavy and light chains were fused to the N-termini of newly generated heterodimerizing Fc chains. This novel Fc heterodimerization technology, designated "Fc-one/kappa" (Fc1κ) is based on interspersed constant Ig domains substituting the CH3 domains of a γ1 Fc. The interspersed immunoglobulin (Ig) domains originate from the per se heterodimerizing constant CH1 and CLκ domains and contain sequence stretches of an IgG1 CH3 domain, destined to enable interaction with the neonatal Fc receptor, and thus promote extended serum half-life. The resulting monovalent Fv-Fc1κ fusion protein (Atrosimab) retained strong binding to TNFR1 as determined by enzyme-linked immunosorbent assay and quartz crystal microbalance, and potently inhibited TNF-induced activation of TNFR1. Atrosimab lacks agonistic activity for TNFR1 on its own and in the presence of anti-human IgG antibodies and displays clearly improved pharmacokinetic properties.

A robust heterodimeric Fc platform engineered for efficient development of bispecific antibodies of multiple formats

Bispecific monoclonal antibodies can bind two protein targets simultaneously and enable therapeutic modalities inaccessible by traditional mAbs. Bispecific formats containing a heterodimeric Fc region are of particular interest, as a heterodimeric Fc empowers both bispecificity and altered valencies while retaining the developability and druggability of a monoclonal antibody. We present a robust heterodimeric Fc platform, called the XmAb® bispecific platform, engineered for efficient development of bispecific antibodies and Fc fusions of multiple formats. First, we engineer a purification solution for proteins containing a heterodimeric Fc using engineered isoelectric point differences in the Fc region that enable straightforward purification of the heterodimeric species. Then, we combine this purification solution with a novel set of Fc substitutions capable of achieving heterodimer yields over 95% with little change in thermostability. Next, we illustrate the flexibility of our heterodimeric Fc with a case study in which a wide range of tumor-associated antigen × CD3 bispecifics are generated, differing in choice of tumor antigen, affinities for both tumor antigen and CD3, and tumor antigen valency. Finally, we present manufacturing data reinforcing the robustness of the heterodimeric Fc platform at scale.

Engineered hexavalent Fc proteins with enhanced Fc-gamma receptor avidity provide insights into immune-complex interactions

Autoantibody-mediated diseases are currently treated with intravenous immunoglobulin, which is thought to act in part via blockade of Fc gamma receptors, thereby inhibiting autoantibody effector functions and subsequent pathology. We aimed to develop recombinant molecules with enhanced Fc receptor avidity and thus increased potency over intravenous immunoglobulin. Here we describe the molecular engineering of human Fc hexamers and explore their therapeutic and safety profiles. We show Fc hexamers were more potent than IVIG in phagocytosis blockade and disease models. However, in human whole-blood safety assays incubation with IgG1 isotype Fc hexamers resulted in cytokine release, platelet and complement activation, whereas the IgG4 version did not. We used a statistically designed mutagenesis approach to identify the key Fc residues involved in these processes. Cytokine release was found to be dependent on neutrophil FcγRIIIb interactions with L234 and A327 in the Fc. Therefore, Fc hexamers provide unique insights into Fc receptor biology.

Tania Rowley et al. present multivalent Fc molecules with enhanced avidity for Fc gamma receptors in order to improve the treatment of autoantibody-mediated human diseases. They found several key amino acids involved in Fc receptor binding interactions.

IgG-single-chain TRAIL fusion proteins for tumour therapy

Single-chain formats of TNF-related apoptosis inducing ligand (scTRAIL) can serve as effector components of tumour-associated antigen-targeted as well as non-targeted fusion proteins, being characterized by high tumour cell-specific induction of apoptosis through death receptor activation. We studied the suitability of immunoglobulin G as a scaffold for oligovalent and bispecific TRAIL fusion proteins. Thus, we developed novel targeted hexa- and dodecavalent IgG-scTRAIL molecules by fusing scTRAIL to the C-terminus of either light (LC-scTRAIL) or heavy immunoglobulin chain (HC-scTRAIL), or to both ends (LC/HC-scTRAIL) of the anti-EGFR IgG antibody hu225. The binding specificity to EGFR and death receptors was retained in all IgG-scTRAIL formats and translated into high antigen-specific bioactivity on EGFR-positive Colo205, HCT116 and WM1366 tumour cell lines, with or without sensitization to apoptosis by bortezomib. In vivo, therapeutic potential was assessed for one of the targeted variants, HC-scTRAIL, compared to the non-targeted Fc-scTRAIL. Both molecules showed a significant reduction of tumour volume and synergism with a Smac mimetic in a Colo205 xenograft tumour model. The IgG-scTRAIL format allows directing a defined, highly bioactive form of TRAIL to a wide variety of tumour antigens, enabling customized solutions for a patient-specific targeted cancer therapy with a reduced risk of side effects.

Modulation of Dengue/Zika Virus Pathogenicity by Antibody-Dependent Enhancement and Strategies to Protect Against Enhancement in Zika Virus Infection

Antibody-dependent enhancement (ADE) is a phenomenon in which preexisting poorly neutralizing antibodies leads to enhanced infection. It is a serious concern with mosquito-borne flaviviruses such as Dengue virus (DENV) and Zika virus (ZIKV). In vitro experimental evidences have indicated the preventive, as well as a pathogenicity-enhancing role, of preexisting DENV antibodies in ZIKV infections. ADE has been confirmed in DENV but not ZIKV infections. Principally, the Fc region of the anti-DENV antibody binds with the fragment crystallizable gamma receptor (FcγR), and subsequent C1q interactions and immune effector functions are responsible for the ADE. In contrast to normal DENV infections, with ADE in DENV infections, inhibition of STAT1 phosphorylation and a reduction in IRF-1 gene expression, NOS2 levels, and RIG-1 and MDA-5 expression levels occurs. FcγRIIA is the most permissive FcγR for DENV-ADE, and under hypoxic conditions, hypoxia-inducible factor-1 alpha transcriptionally enhances expression levels of FcγRIIA, which further enhances ADE. To produce therapeutic antibodies with broad reactivity to different DENV serotypes, as well as to ZIKV, bispecific antibodies, Fc region mutants, modified Fc regions, and anti-idiotypic antibodies may be engineered. An in-depth understanding of the immunological and molecular mechanisms of DENV-ADE of ZIKV pathogenicity will be useful for the design of common and safe therapeutics and prophylactics against both viral pathogens. The present review discusses the role of DENV antibodies in modulating DENV/ZIKV pathogenicity/infection and strategies to counter ADE to protect against Zika infection.

Assessing the Heterogeneity of the Fc-Glycan of a Therapeutic Antibody Using an engineered FcγReceptor IIIa-Immobilized Column

The N-glycan moiety of IgG-Fc has a significant impact on multifaceted properties of antibodies such as in their effector function, structure, and stability. Numerous studies have been devoted to understanding its biological effect since the exact composition of the Fc N-glycan modulates the magnitude of effector functions such as the antibody-dependent cell mediated cytotoxicity (ADCC), and the complement-dependent cytotoxicity (CDC). To date, systematic analyses of the properties and influence of glycan variants have been of great interest. Understanding the principles on how N-glycosylation modulates those properties is important for the molecular design, manufacturing, process optimization, and quality control of therapeutic antibodies. In this study, we have separated a model therapeutic antibody into three fractions according to the composition of the N-glycan by using a novel FcγRIIIa chromatography column. Notably, Fc galactosylation was a major factor influencing the affinity of IgG-Fc to the FcγRIIIa immobilized on the column. Each antibody fraction was employed for structural, biological, and physicochemical analysis, illustrating the mechanism by which galactose modulates the affinity to FcγRIIIa. In addition, we discuss the benefits of the FcγRIIIa chromatography column to assess the heterogeneity of the N-glycan.

Human IgG lacking effector functions demonstrate lower FcRn-binding and reduced transplacental transport

We have previously generated human IgG1 antibodies that were engineered for reduced binding to the classical Fcγ receptors (FcγRI-III) and C1q, thereby eliminating their destructive effector functions (constant region G1Δnab). In their potential use as blocking agents, favorable binding to the neonatal Fc receptor (FcRn) is important to preserve the long half-life typical of IgG. An ability to cross the placenta, which is also mediated, at least in part, by FcRn is desirable in some indications, such as feto-maternal alloimmune disorders. Here, we show that G1Δnab mutants retain pH-dependent binding to human FcRn but that the amino acid alterations reduce the affinity of the IgG1:FcRn interaction by 2.0-fold and 1.6-fold for the two antibodies investigated. The transport of the modified G1Δnab mutants across monolayers of human cell lines expressing FcRn was approximately 75% of the wild-type, except that no difference was observed with human umbilical vein endothelial cells. G1Δnab mutation also reduced transport in an ex vivo placenta model. In conclusion, we demonstrate that, although the G1Δnab mutations are away from the FcRn-binding site, they have long-distance effects, modulating FcRn binding and transcellular transport. Our findings have implications for the design of therapeutic human IgG with tailored effector functions.

The making of bispecific antibodies

During the past two decades we have seen a phenomenal evolution of bispecific antibodies for therapeutic applications. The 'zoo' of bispecific antibodies is populated by many different species, comprising around 100 different formats, including small molecules composed solely of the antigen-binding sites of two antibodies, molecules with an IgG structure, and large complex molecules composed of different antigen-binding moieties often combined with dimerization modules. The application of sophisticated molecular design and genetic engineering has solved many of the technical problems associated with the formation of bispecific antibodies such as stability, solubility and other parameters that confer drug properties. These parameters may be summarized under the term 'developability'. In addition, different 'target product profiles', i.e., desired features of the bispecific antibody to be generated, mandates the need for access to a diverse panel of formats. These may vary in size, arrangement, valencies, flexibility and geometry of their binding modules, as well as in their distribution and pharmacokinetic properties. There is not 'one best format' for generating bispecific antibodies, and no single format is suitable for all, or even most of, the desired applications. Instead, the bispecific formats collectively serve as a valuable source of diversity that can be applied to the development of therapeutics for various indications. Here, a comprehensive overview of the different bispecific antibody formats is provided.

Anti-Bovine Programmed Death-1 Rat-Bovine Chimeric Antibody for Immunotherapy of Bovine Leukemia Virus Infection in Cattle

Blockade of immunoinhibitory molecules, such as programmed death-1 (PD-1)/PD-ligand 1 (PD-L1), is a promising strategy for reinvigorating exhausted T cells and preventing disease progression in a variety of chronic infections. Application of this therapeutic strategy to cattle requires bovinized chimeric antibody targeting immunoinhibitory molecules. In this study, anti-bovine PD-1 rat–bovine chimeric monoclonal antibody 5D2 (Boch5D2) was constructed with mammalian expression systems, and its biochemical function and antiviral effect were characterized in vitro and in vivo using cattle infected with bovine leukemia virus (BLV). Purified Boch5D2 was capable of detecting bovine PD-1 molecules expressed on cell membranes in flow cytometric analysis. In particular, Biacore analysis determined that the binding affinity of Boch5D2 to bovine PD-1 protein was similar to that of the original anti-bovine PD-1 rat monoclonal antibody 5D2. Boch5D2 was also capable of blocking PD-1/PD-L1 binding at the same level as 5D2. The immunomodulatory and therapeutic effects of Boch5D2 were evaluated by in vivo administration of the antibody to a BLV-infected calf. Inoculated Boch5D2 was sustained in the serum for a longer period. Boch5D2 inoculation resulted in activation of the proliferation of BLV-specific CD4⁺ T cells and decrease in the proviral load of BLV in the peripheral blood. This study demonstrates that Boch5D2 retains an equivalent biochemical function to that of the original antibody 5D2 and is a candidate therapeutic agent for regulating antiviral immune response in vivo. Clinical efficacy of PD-1/PD-L1 blockade awaits further experimentation with a large number of animals.

In vitro and in vivo antivirus activity of an anti-programmed death-ligand 1 (PD-L1) rat-bovine chimeric antibody against bovine leukemia virus infection

Programmed death-1 (PD-1), an immunoinhibitory receptor on T cells, is known to be involved in immune evasion through its binding to PD-ligand 1 (PD-L1) in many chronic diseases. We previously found that PD-L1 expression was upregulated in cattle infected with bovine leukemia virus (BLV) and that an antibody that blocked the PD-1/PD-L1 interaction reactivated T-cell function in vitro. Therefore, this study assessed its antivirus activities in vivo. First, we inoculated the anti-bovine PD-L1 rat monoclonal antibody 4G12 into a BLV-infected cow. However, this did not induce T-cell proliferation or reduction of BLV provirus loads during the test period, and only bound to circulating IgM⁺ B cells until one week post-inoculation. We hypothesized that this lack of in vivo effects was due to its lower stability in cattle and so established an anti-PD-L1 rat-bovine chimeric antibody (Boch4G12). Boch4G12 was able to bind specifically with bovine PD-L1, interrupt the PD-1/PD-L1 interaction, and activate the immune response in both healthy and BLV-infected cattle in vitro. Therefore, we experimentally infected a healthy calf with BLV and inoculated it intravenously with 1 mg/kg of Boch4G12 once it reached the aleukemic (AL) stage. Cultivation of peripheral blood mononuclear cells (PBMCs) isolated from the tested calf indicated that the proliferation of CD4⁺ T cells was increased by Boch4G12 inoculation, while BLV provirus loads were significantly reduced, clearly demonstrating that this treatment induced antivirus activities. Therefore, further studies using a large number of animals are required to support its efficacy for clinical application.

Development of cell-based assay for predictively evaluating the FcγR-mediated human immune cell activation by therapeutic monoclonal antibodies

Therapeutic monoclonal antibodies (mAbs) have important roles in treatments for various cancers and inflammatory diseases. Their highly target specificities provide controlled safety profiles. However, therapeutic mAbs commonly pose a risk of the induction of the release of cytokines, which may result in adverse events including infusion reaction and cytokine release syndrome. Several mechanisms are involved in the cytokine releases induced by therapeutic mAbs, and the activation of immune effector cells via Fcγ receptors (FcγRs) is one of the putative mechanisms for most IgG-subclass mAbs. The relationship between cytokine releases and mAbs' Fc functions is not fully understood. Here we developed a simple reporter cell-based assay for estimating the FcγR-mediated activation of human immune effector cells by mAbs. Our use of the cell-based assay to compare Fc-engineered mAbs with different FcγR-activation profiles revealed that the releases of inflammatory cytokines and chemokines from human peripheral blood mononuclear cells (hPBMCs) induced by the mAbs were elevated by treatment with Fc-engineered mAbs with higher FcγR-activation properties. Our results also suggested the involvement of monocytic effector cells in the activation of hPBMCs as sources of released cytokines and chemokines, which may lead to the immune cell-mediated adverse events. Our new reporter cell assay is a promising tool for evaluating and predicting the activation of human immune cells by novel Fc-engineered mAbs.

Rational Design of Dual Agonist-Antibody Fusions as Long-acting Therapeutic Hormones

Recent studies have suggested that modulation of two or more signaling pathways can achieve substantial weight loss and glycemic stability. We have developed an approach to the generation of bifunctional antibody agonists that activate leptin receptor and GLP-1 receptor. Leptin was fused into the complementarity determining region 3 loop of the light chain alone, or in combination with exendin-4 (EX4) fused at the N-terminus of the heavy chain of Herceptin. The antibody fusions exhibit similar or increased in vitro activities on their cognate receptors, but 50-100-fold longer circulating half-lives in rodents compared to the corresponding native peptides/proteins. The efficacy of the leptin/EX4 dual antibody fusion on weight loss, especially fat mass loss, was enhanced in ob/ob mice and DIO mice compared to the antibody fusion of either EX4 or leptin alone. This work demonstrates the versatility of this combinatorial fusion strategy for generating dual antibody agonists with long half-lives.

TTI-621 (SIRPαFc): A CD47-Blocking Innate Immune Checkpoint Inhibitor with Broad Antitumor Activity and Minimal Erythrocyte Binding

Purpose: The ubiquitously expressed transmembrane glycoprotein CD47 delivers an anti-phagocytic (do not eat) signal by binding signal-regulatory protein α (SIRPα) on macrophages. CD47 is overexpressed in cancer cells and its expression is associated with poor clinical outcomes. TTI-621 (SIRPαFc) is a fully human recombinant fusion protein that blocks the CD47-SIRPα axis by binding to human CD47 and enhancing phagocytosis of malignant cells. Blockade of this inhibitory axis using TTI-621 has emerged as a promising therapeutic strategy to promote tumor cell eradication.Experimental Design: The ability of TTI-621 to promote macrophage-mediated phagocytosis of human tumor cells was assessed using both confocal microscopy and flow cytometry. In vivo antitumor efficacy was evaluated in xenograft and syngeneic models and the role of the Fc region in antitumor activity was evaluated using SIRPαFc constructs with different Fc tails.Results: TTI-621 enhanced macrophage-mediated phagocytosis of both hematologic and solid tumor cells, while sparing normal cells. In vivo, TTI-621 effectively controlled the growth of aggressive AML and B lymphoma xenografts and was efficacious in a syngeneic B lymphoma model. The IgG1 Fc tail of TTI-621 plays a critical role in its antitumor activity, presumably by engaging activating Fcγ receptors on macrophages. Finally, TTI-621 exhibits minimal binding to human erythrocytes, thereby differentiating it from CD47 blocking antibodies.Conclusions: These data indicate that TTI-621 is active across a broad range of human tumors. These results further establish CD47 as a critical regulator of innate immune surveillance and form the basis for clinical development of TTI-621 in multiple oncology indications. Clin Cancer Res; 23(4); 1068-79. ©2016 AACR.

Checkpoint Inhibition of KIR2D with the Monoclonal Antibody IPH2101 Induces Contraction and Hyporesponsiveness of NK Cells in Patients with Myeloma

PURPOSE

Immune checkpoint inhibitors have recently revolutionized cancer immunotherapy. On the basis of data showing KIR-ligand mismatched natural killer (NK) cells reduce the risk of leukemia and multiple myeloma relapse following allogeneic hematopoietic stem cell transplantation, investigators have developed a checkpoint inhibition antibody that blocks KIR on NK cells. Although in vitro studies suggest the KIR2D-specific antibody IPH2101 induces KIR-ligand mismatched tumor killing by NK cells, our single-arm phase II clinical trial in patients with smoldering multiple myeloma was prematurely terminated due to lack of clinical efficacy. This study aimed at unveiling the underlying mechanisms behind the lack of clinical efficacy.

EXPERIMENTAL DESIGN

Treatment-naïve patients received an intravenous infusion of 1 mg/kg IPH2101 every other month for up to a year. Peripheral blood was collected at baseline and 24 hours after first infusion, followed by weekly samples for the first month and monthly samples thereafter. NK cell phenotype and function was analyzed using high-resolution flow cytometry.

RESULTS

Unexpectedly, infusion of IPH2101 resulted in rapid reduction in both NK cell responsiveness and KIR2D expression on the NK cell surface. In vitro assays revealed KIR2D molecules are removed from the surface of IPH2101-treated NK cells by trogocytosis, with reductions in NK cell function directly correlating with loss of free KIR2D surface molecules. Although IPH2101 marginally augmented the antimyeloma cytotoxicity of remaining KIR2D^dull patient NK cells, the overall response was diminished by significant contraction and reduced function of KIR2D-expressing NK cells.

CONCLUSIONS

These data raise concerns that the unexpected biological events reported in this study could compromise antibody-based strategies designed at augmenting NK cell tumor killing via checkpoint inhibition. Clin Cancer Res; 22(21); 5211-22. ©2016 AACRSee related commentary by Felices and Miller, p. 5161.