Development of a robust reporter-based ADCC assay with frozen, thaw-and-use cells to measure Fc effector function of therapeutic antibodies

Preclinical Characterization of Efficacy and Pharmacodynamic Properties of Finotonlimab, a Humanized Anti-PD-1 Monoclonal Antibody

Background/Objectives: Finotonlimab (SCTI10A) is a humanized anti-PD-1 antibody tested in Phase III trials for several solid tumor types. Methods: This study characterized the in vitro and in vivo efficacy, Fc-mediated effector function, and non-clinical PK/PD properties of finotonlimab. Results: The results demonstrated that finotonlimab is effective in stimulating human T cell function in vitro and exhibits marked antitumor efficacy in vivo using both PD-1-humanized and PBMC-reconstructed mouse models. Additionally, finotonlimab exhibited minimal impact on the activation of effector cells via Fc receptor-dependent pathways, potentially facilitating PD-1+ T cell killing. In cynomolgus monkeys, finotonlimab exhibited a nonlinear pharmacokinetic (PK) profile in a dose-dependent manner, and a receptor occupancy rate of approximately 90% was observed at 168 h following a single administration of 1 mg/kg. Finotonlimab's PK profile (especially Cmax) was better than that of marketed antibodies. Following a 13-week successive administration of finotonlimab, a pharmacodynamic analysis revealed that a sustained mean receptor occupancy of PD-1 molecules on circulating T cells remained at or above 93% for up to 8 weeks, even at a dose of 3 mg/kg, and that there were higher antibody accumulations in different dose groups. Conclusions: Taken together, the preclinical findings are promising and provide the groundwork for evaluating the efficacy and pharmacodynamic characteristics of finotonlimab in clinical trials.

Development of bioassay platforms for biopharmaceuticals using Jurkat-CAR cells by AICD

The assessment of bioactivity for therapeutic antibody release assay poses challenges, particularly when targeting immune checkpoints. An in vitro bioassay platform was developed using the chimeric antigen receptor on Jurkat cells (Jurkat-CAR) to analyze antibodies targeting immune checkpoints, such as CD47/SIRPα, VEGF/VEGFR1, PD-1/PD-L1, and CD70/CD27. For CD47/SIRPα, the platform involved a Jurkat-CAR cell line expressing the chimeric SIRPα receptor (CarSIRPα). CarSIRPα was created by sequentially fusing the SIRPα extracellular region with the CD8α hinge region, the transmembrane (TM) and intracellular (IC) domains of CD28, and the intracellular signaling domain of CD3ζ. The resulting Jurkat-CarSIRPα cells can undergo "activation-induced cell death (AICD)" upon incubation with purified or cellular CD47, as evidenced by the upregulation of CD69, IL-2, and IFN-γ. Similar results also appeared in Jurkat CarVEGFR1, Jurkat CarPD1 and Jurkat CARCD27 cells. These cells are perfectly utilized for the bioactivity analysis of therapeutic antibody. Our study indicates that the established in vitro assay platform based on Jurkat-CAR has been confirmed repeatedly and has shown robust reproducibility; thus, this platform can be used for screening or for release assays of given antibody drugs targeting immune checkpoints.

Systematic Preparation of a 66-IgG Library with Symmetric and Asymmetric Homogeneous Glycans and Their Functional Evaluation

Immunoglobulin G (IgG) antibodies possess a conserved N-glycosylation site in the Fc domain. In FcγRIIIa affinity column chromatography, unglycosylated, hemiglycosylated, and fully glycosylated IgG retention times differ considerably. Using retention-time differences, 66 different trastuzumab antibodies with symmetric and asymmetric homogeneous glycans were prepared systematically, substantially expanding the scope of IgGs with homogeneous glycans. Using the prepared trastuzumab with homogeneous glycans, thermal stability and antibody-dependent cellular cytotoxicity were investigated. In some glycan series, a directly proportional relationship was observed between the thermal unfolding temperature (Tm) and the calorimetric unfolding heat (ΔHcal). Antibody function could be deduced from the combination of a pair of glycans in an intact form. Controlling glycan structure through the combination of a pair of glycans permits the precise tuning of stability and effector functions of IgG. Overall, our technology can be used to investigate the effects of glycans on antibody functions.

Define Critical Parameters of Trastuzumab-Mediated ADCC Assays via Assay Optimization Processes, Focusing on the Impact of Cryopreserved Effector Cells on Assay Performance

The mechanisms of mAb-induced ADCC have been well established. However, the ADCC bioassays used to quantify mAb-induced ADCC require continued development/refinement to properly assess and compare the potency of newly developed therapeutic mAbs and biosimilars to meet regulatory requirements. We used trastuzumab and a lactate dehydrogenase (LDH)-based ADCC bioassay as a model to define critical parameters of the ADCC bioassay, describing how several bioassay parameters, including preparation of effector cells, E/T ratio, target cell selection, bioassay media components, and treatment time can influence the data quality of the ADCC activity. We confirm that a 4 to 24 h recovery cultivation is required to restore peripheral blood mononuclear cells (PBMCs) and natural killer (NK) cell activity toward ADCC when using cryopreserved PBMCs. Furthermore, we delineated the cellular mechanisms underlying the restored ADCC activity following the recovery cultivation. We observed that CD69, an early marker of NK cell activation, was upregulated and a new subset CD56dim/CD16dim population was dramatically increased in the recovered NK cells, which led to an increase in expression and secretion of perforin, granzyme B, and cytokine production. This study provides comprehensive technical insights into ADCC bioassay optimization to inform trastuzumab biosimilar development. The knowledge gained from this study can also be leveraged to guide bioassay development for therapeutic mAbs with ADCC as the primary mechanism of action.

An industry perspective approach and control strategy for implementation of ready-to-use cells in bioassays: survey outcome and recommendations

The BioPhorum Development Group is an industry collaboration enabling the sharing of common practices for the development of biopharmaceuticals. Bioassays are an important part of an analytical control system. Utilization of ready-to-use cells can increase operational flexibility and improve efficiency by providing frozen cell banks uniform stock while removing challenges associated with maintaining cultured cells. The BioPhorum Development Group-Bioassay workstream conducted an intercompany benchmarking survey and group discussions around the use of ready-to-use cells for bioassays. The results of the collaboration provide alignment on nomenclature, production, qualification and implementation of ready-to-use cells to support the assay life cycle.

Antibody dependent cellular cytotoxicity-inducing anti-EGFR antibodies as effective therapeutic option for cutaneous melanoma resistant to BRAF inhibitors

Introduction

About 50% of cutaneous melanoma (CM) patients present activating BRAF mutations that can be effectively targeted by BRAF inhibitors (BRAFi). However, 20% of CM patients exhibit intrinsic drug resistance to BRAFi, while most of the others develop adaptive resistance over time. The mechanisms involved in BRAFi resistance are disparate and globally seem to rewire the cellular signaling profile by up-regulating different receptor tyrosine kinases (RTKs), such as the epidermal growth factor receptor (EGFR). RTKs inhibitors have not clearly demonstrated anti-tumor activity in BRAFi resistant models. To overcome this issue, we wondered whether the shared up-regulated RTK phenotype associated with BRAFi resistance could be exploited by using immune weapons as the antibody-dependent cell cytotoxicity (ADCC)-mediated effect of anti-RTKs antibodies, and kill tumor cells independently from the mechanistic roots.

Methods and results

By using an in vitro model of BRAFi resistance, we detected increased membrane expression of EGFR, both at mRNA and protein level in 4 out of 9 BRAFi-resistant (VR) CM cultures as compared to their parental sensitive cells. Increased EGFR phosphorylation and AKT activation were observed in the VR CM cultures. EGFR signaling appeared dispensable for maintaining resistance, since small molecule-, antibody- and CRISPR-targeting of EGFR did not restore sensitivity of VR cells to BRAFi. Importantly, immune-targeting of EGFR by the anti-EGFR antibody cetuximab efficiently and specifically killed EGFR-expressing VR CM cells, both in vitro and in humanized mouse models in vivo, triggering ADCC by healthy donors' and patients' peripheral blood cells.

Conclusion

Our data demonstrate the efficacy of immune targeting of RTKs expressed by CM relapsing on BRAFi, providing the proof-of-concept supporting the assessment of anti-RTK antibodies in combination therapies in this setting. This strategy might be expected to concomitantly trigger the crosstalk of adaptive immune response leading to a complementing T cell immune rejection of tumors.

Functional characterization of AF-04, an afucosylated anti-MARV GP antibody

Marburg virus (MARV), one member of the Filoviridae family, cause sporadic outbreaks of hemorrhagic fever with high mortality rates. No countermeasures are currently available for the prevention or treatment of MARV infection. Monoclonal antibodies (mAbs) are promising candidates to display high neutralizing activity against MARV infection in vitro and in vivo. Recently, growing evidence has shown that immune effector function including antibody-dependent cell-mediated cytotoxicity (ADCC) is also required for in vivo efficacy of a panel of antibodies. Glyco-engineered methods are widely utilized to augment ADCC function of mAbs. In this study, we generated a fucose-knockout MARV GP-specific mAb named AF-04 and showed that afucosylation dramatically increased its binding affinity to polymorphic FcγRIIIa (F176/V176) compared with the parental AF-03. Accordingly, AF-04-mediated NK cell activation and NFAT expression downstream of FcγRIIIa in effector cells were also augmented. In conclusion, this work demonstrates that AF-04 represents a novel avenue for the treatment of MARV-caused disease.

Host glycosylation of immunoglobulins impairs the immune response to acute Lyme disease

BACKGROUND

Lyme disease is caused by the bacteria Borreliella burgdorferi sensu lato (Bb) transmitted to humans from the bite of an infected Ixodes tick. Current diagnostics for Lyme disease are insensitive at the early disease stage and they cannot differentiate between active infections and people with a recent history of antibiotic-treated Lyme disease.

METHODS

Machine learning technology was utilized to improve the prediction of acute Lyme disease and identify sialic acid and galactose sugar structures (N-glycans) on immunoglobulins associated specifically at time points during acute Lyme disease time. A plate-based approach was developed to analyze sialylated N-glycans associated with anti-Bb immunoglobulins. This multiplexed approach quantitates the abundance of Bb-specific IgG and the associated sialic acid, yielding an accuracy of 90% in a powered study.

FINDINGS

It was demonstrated that immunoglobulin sialic acid levels increase during acute Lyme disease and following antibiotic therapy and a 3-month convalescence, the sialic acid level returned to that found in healthy control subjects (p < 0.001). Furthermore, the abundance of sialic acid on Bb-specific IgG during acute Lyme disease impaired the host's ability to combat Lyme disease via lymphocytic receptor FcγRIIIa signaling. After enzymatically removing the sialic acid present on Bb-specific antibodies, the induction of cytotoxicity from acute Lyme disease patient antigen-specific IgG was significantly improved.

INTERPRETATION

Taken together, Bb-specific immunoglobulins contain increased sialylation which impairs the host immune response during acute Lyme disease. Furthermore, this Bb-specific immunoglobulin sialyation found in acute Lyme disease begins to resolve following antibiotic therapy and convalescence.

FUNDING

Funding for this study was provided by the Coulter-Drexel Translational Research Partnership Program as well as from a Faculty Development Award from the Drexel University College of Medicine Institute for Molecular Medicine and Infectious Disease and the Department of Microbiology and Immunology.

An Antibody-Dependent Cellular Cytotoxicity Assay for Detecting Ocrelizumab Neutralizing Antibody

Ocrelizumab (OCREVUS®) is a humanized anti-CD20 monoclonal antibody approved for the treatment of adult patients with relapsing multiple sclerosis (RMS) and primary progressive multiple sclerosis (PPMS). Here, we discuss the strategic and technical considerations needed to develop a robust antibody-dependent cellular cytotoxicity (ADCC)-based neutralizing antibody (NAb) assay to detect anti-ocrelizumab NAb in patients enrolled in the ocrelizumab registered clinical trials. The NAb detection assay consisted of a two-tier assay that included a screening assay and a confirmation assay. In the screening assay, patient samples were analyzed in the presence of ocrelizumab. Samples that tested positive in the screening assay were subsequently analyzed in the confirmatory assay where another anti-CD20 mAb, obinutuzumab, was replaced by ocrelizumab, to verify NAb specificity. Both assays utilized MEC-2 cells, a chronic B cell leukemia cell line, pre-labeled with calcein AM as the target cells, and natural killer (NK) cells engineered to stably express Fc gamma receptor IIIa_ F158 as effector cells. Both cell lines were prepared to be thaw-and-use cells. The NAb assay measures fluorescence from the calcein AM released into the assay media upon the lysis of target cells by ADCC in the presence of ocrelizumab or obinutuzumab. Our validated NAb assay showed a relative sensitivity of 743 ng/mL and can detect 1500 ng/mL of a surrogate positive control antibody in the presence of 1500 ng/mL ocrelizumab. This ADCC assay is the first reported NAb assay that directly measures target cell lysis by using thaw-and-use target and effector cells simultaneously.

Optimizing effector functions of monoclonal antibodies via tailored N-glycan engineering using a dual landing pad CHO targeted integration platform

Monoclonal antibodies (mAbs) eliminate cancer cells via various effector mechanisms including antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), which are influenced by the N-glycan structures on the Fc region of mAbs. Manipulating these glycan structures on mAbs allows for optimization of therapeutic benefits associated with effector functions. Traditional approaches such as gene deletion or overexpression often lead to only all-or-nothing changes in gene expression and fail to modulate the expression of multiple genes at defined ratios and levels. In this work, we have developed a CHO cell engineering platform enabling modulation of multiple gene expression to tailor the N-glycan profiles of mAbs for enhanced effector functions. Our platform involves a CHO targeted integration platform with two independent landing pads, allowing expression of multiple genes at two pre-determined genomic sites. By combining with internal ribosome entry site (IRES)-based polycistronic vectors, we simultaneously modulated the expression of α-mannosidase II (MANII) and chimeric β-1,4-N-acetylglucosaminyl-transferase III (cGNTIII) genes in CHO cells. This strategy enabled the production of mAbs carrying N-glycans with various levels of bisecting and non-fucosylated structures. Importantly, these engineered mAbs exhibited different degrees of effector cell activation and CDC, facilitating the identification of mAbs with optimal effector functions. This platform was demonstrated as a powerful tool for producing antibody therapeutics with tailored effector functions via precise engineering of N-glycan profiles. It holds promise for advancing the field of metabolic engineering in mammalian cells.

Development and application of potency assays based on genetically modified cells for biological products

Potency assays are key to the development, registration, and quality control of biological products. Although previously preferred for clinical relevance, in vivo bioassays have greatly diminished with the advent of dependent cell lines as well as due to ethical concerns. However, for some products, the development of in vitro cell-based assay is challenging, or existing method has limitations such as tedious procedure or low sensitivity. The generation of genetically modified (GM) cell line with improved response to the analyte provides a scientific and promising solution. Potency assays based on GM cell lines are currently used for the quality control of biological products including cytokines, hormones, therapeutic antibodies, vaccines and gene therapy products. In this review, we have discussed the general principles of designing and developing GM cells-based potency assays, including identification of cellular signaling pathways and detectable biological effects, generation of responsive cell lines and constitution of test systems, based on the current research progress. In addition, the applications of some novel technologies and the common concerns regarding GM cells have also been discussed. The research presented in this review provides insights for the development and application of novel GM cells-based potency assays for biological products.

A non-neutralizing glycoprotein B monoclonal antibody protects against herpes simplex virus disease in mice

There is an unmet need for monoclonal antibodies (mAbs) for prevention or as adjunctive treatment of herpes simplex virus (HSV) disease. Most vaccine and mAb efforts focus on neutralizing antibodies, but for HSV this strategy has proven ineffective. Preclinical studies with a candidate HSV vaccine strain, ΔgD-2, demonstrated that non-neutralizing antibodies that activate Fcγ receptors (FcγRs) to mediate antibody-dependent cellular cytotoxicity (ADCC) provide active and passive protection against HSV-1 and HSV-2. We hypothesized that this vaccine provides a tool to identify and characterize protective mAbs. We isolated HSV-specific mAbs from germinal center and memory B cells and bone marrow plasmacytes of ΔgD-2-vaccinated mice and evaluated these mAbs for binding, neutralizing, and FcγR-activating activity and for protective efficacy in mice. The most potent protective mAb, BMPC-23, was not neutralizing but activated murine FcγRIV, a biomarker of ADCC. The cryo-electron microscopic structure of the Fab-glycoprotein B (gB) assembly identified domain IV of gB as the epitope. A single dose of BMPC-23 administered 24 hours before or after viral challenge provided significant protection when configured as mouse IgG2c and protected mice expressing human FcγRIII when engineered as a human IgG1. These results highlight the importance of FcR-activating antibodies in protecting against HSV.

Development of an Antibody Delivery Method for Cancer Treatment by Combining Ultrasound with Therapeutic Antibody-Modified Nanobubbles Using Fc-Binding Polypeptide

A key challenge in treating solid tumors is that the tumor microenvironment often inhibits the penetration of therapeutic antibodies into the tumor, leading to reduced therapeutic efficiency. It has been reported that the combination of ultrasound-responsive micro/nanobubble and therapeutic ultrasound (TUS) enhances the tissue permeability and increases the efficiency of delivery of macromolecular drugs to target tissues. In this study, to facilitate efficient therapeutic antibody delivery to tumors using this combination system, we developed therapeutic antibody-modified nanobubble (NBs) using an Fc-binding polypeptide that can quickly load antibodies to nanocarriers; since the polypeptide was derived from Protein G. TUS exposure to this Herceptin^®-modified NBs (Her-NBs) was followed by evaluation of the antibody's own ADCC activity, resulting the retained activity. Moreover, the utility of combining therapeutic antibody-modified NBs and TUS exposure as an antibody delivery system for cancer therapy was assessed in vivo. The Her-NBs + TUS group had a higher inhibitory effect than the Herceptin and Her-NBs groups. Overall, these results suggest that the combination of therapeutic antibody-modified NBs and TUS exposure can enable efficient antibody drug delivery to tumors, while retaining the original antibody activity. Hence, this system has the potential to maximize the therapeutic effects in antibody therapy for solid cancers.

Cell-based reporter assays for measurements of antibody-mediated cellular cytotoxicity and phagocytosis against SARS-CoV-2 spike protein

The COVID-19 pandemic caused by SARS-CoV-2 infections has led to excess deaths worldwide. Neutralizing antibodies (nAbs) against viral spike protein acquired from natural infections or vaccinations contribute to protection against new- and re-infections. Besides neutralization, antibody-mediated cellular cytotoxicity (ADCC) and phagocytosis (ADCP) are also important for viral clearance. However, due to the lack of convenient methods, the ADCC and ADCP responses elicited by viral infections or vaccinations remain to be explored. Here, we developed cell-based assays using target cells stably expressing SARS-CoV-2 spikes and Jurkat-NFAT-CD16a/CD32a effector cells for ADCC/ADCP measurements of monoclonal antibodies and human convalescent COVID-19 plasmas (HCPs). In control samples (n = 190), the specificity was 99.5% (95%CI: 98.4–100%) and 97.4% (95%CI: 95.1–99.6%) for the ADCC and ADCP assays, respectively. Among 87 COVID-19 HCPs, 83 (sensitivity: 95.4%, 95%CI: 91.0–99.8%) and 81 (sensitivity: 93.1%, 95%CI: 87.8–98.4%) showed detectable ADCC (titer range: 7.4–1721.6) and ADCP activities (titer range: 4–523.2). Notably, both ADCC and ADCP antibody titers positively correlated with the nAb titers in HCPs. In summary, we developed new tools for quantitative ADCC and ADCP analysis against SARS-CoV-2, which may facilitate further evaluations of Fc-mediated effector functions in preventing and treating against SARS-CoV-2.

Ganoderma immunomodulatory proteins: mushrooming functional FIPs

Fungal immunomodulatory protein (FIP) is a novel functional protein family with specific immunomodulatory activity identified from several macro-fungi. A variety of biological activities of FIPs have been reported, such as anti-allergy, anti-tumor, mitogenic activity, and immunomodulation. Among all known FIPs, the firstly discovered FIP was isolated from Ganoderma lucidum, and most FIP members were from Ganoderma genus. Compared with other FIPs, Ganoderma FIPs possess some advantageous bioactivities, like stronger anti-tumor activity. Therein, gene sequences, protein structural features, biofunctions, and recombinant expression of Ganoderma FIPs were summarized and addressed, focusing on elucidating their anti-tumor activity and molecular mechanisms. Combined with current advances, development potential and application of Ganoderma FIPs were also prospected. KEY POINTS: • More than a dozen of reported FIPs are identified from Ganoderma species. • Ganoderma immunomodulatory proteins have superior anti-tumor activity with promising prospects and application. • Current review comprehensively addresses characterization, biofunctions, and anti-tumor mechanisms of Ganoderma FIPs.

Detection and functional resolution of soluble immune complexes by an FcγR reporter cell panel

Fc-gamma receptor (FcγR) activation by soluble IgG immune complexes (sICs) represents a major mechanism of inflammation in certain autoimmune diseases such as systemic lupus erythematosus (SLE). A robust and scalable test system allowing for the detection and quantification of sIC bioactivity is missing. We developed a comprehensive reporter cell panel detecting activation of FcγRs. The reporter cell lines were integrated into an assay that enables the quantification of sIC reactivity via ELISA or a faster detection using flow cytometry. This identified FcγRIIA(H) and FcγRIIIA as the most sIC-sensitive FcγRs in our test system. Reaching a detection limit in the very low nanomolar range, the assay proved also to be sensitive to sIC stoichiometry and size reproducing for the first time a complete Heidelberger-Kendall curve in terms of immune receptor activation. Analyzing sera from SLE patients and mouse models of lupus and arthritis proved that sIC-dependent FcγR activation has predictive capabilities regarding severity of SLE disease. The assay provides a sensitive and scalable tool to evaluate the size, amount, and bioactivity of sICs in all settings.

Assessment of Functional Characterization and Comparability of Biotherapeutics: a Review

The development of monoclonal antibody (mAb) biosimilars is a complex process. The key to their successful development and commercialization is an in-depth understanding of the key product attributes that impact safety and efficacy and the strategies to control them. Functional assessment of mAb is a crucial part of the comparability of biopharmaceutical drugs. The development of a relevant and robust functional assay requires an interdisciplinary approach and sufficient flexibility to balance regulatory concerns as well as dynamics and variability during the manufacturing process. Although many advanced tools are available to study and compare the potency and bioactivity of the protein, most of these techniques suffer from major shortcomings that limit their routine use. These include the complexity of the task, establishment of the relevance of the chosen method with the mechanism of action (MOA) of the biosimilar, cost and extended time of analysis, and often the ambiguity in interpretation of the resulting data. To overcome or to address these challenges, the use of multiple orthogonal state-of-the-art techniques is a necessary prerequisite.

Determining ADCC Activity of Antibody-Based Therapeutic Molecules using Two Bioluminescent Reporter-Based Bioassays

Antibody Fc effector function is one of the main mechanisms of action (MoA) for therapeutic monoclonal antibodies. Measurement of antibody-dependent cellular cytotoxicity (ADCC) is critical for understanding the Fc effector function during monoclonal antibody development. This article covers two cell-based ADCC bioassays which can quantitatively measure the antibody potency in ADCC. Basic Protocol 1 describes the ADCC reporter bioassay using engineered ADCC effector cells which measures the FcγRIIIa-mediated luciferase reporter activation upon the binding of antibody-coated target cells. Basic Protocol 2 describes the PBMC ADCC bioassay using primary peripheral blood mononuclear cells (PBMC) as effector cells and engineered HiBiT target cells in an assay that measures the release of HiBiT from target cells upon antibody-mediated target lysis. Optimization of several key assay parameters including cell handling, effector:target (E:T) ratios, assay plate, and plate reader requirement, and how these parameters impact assay performance are discussed. © 2021 Promega Corporation. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: ADCC reporter bioassay using engineered ADCC bioassay effector cells Basic Protocol 2: PBMC ADCC bioassay using primary PBMC and engineered HiBiT target cells.

Treating Cells as Reagents to Design Reproducible Assays

The reproducibility of high-throughput cell-based assays is dependent on having a consistent source of cells for each experiment. Developing an understanding of the nature of cells growing in vitro and factors that influence their responsiveness to test compounds will contribute to the development of reproducible cell-based assays. Using good cell culture practices and establishing standard operating procedures (SOPs) for handling cultures can eliminate several potential contributors to variability in the responsiveness and performance of cells. The SOPs for handling each cell type must have clear and detailed instructions that can be understood and followed among different laboratories. The SOPs should include documenting the source of cells and authenticating their identity, both of which have become required to achieve peer acceptance of experimental data. Variability caused by biological issues such as phenotypic drift can be reduced by using standardized subculture procedures or using cryopreserved cells to set up experiments. Variability caused by inconsistent dispensing of cells per well and edge effects can be identified by measuring how many cells are present and whether they are alive or dead. Multiplex methods for real-time measurement of viable or dead cell number in each sample can be used for normalizing data and determining if proliferation or cytotoxicity has occurred during the experiment. Following good cell culture practices will go a long way toward executing reproducible cell-based assays. Resources will be included describing good cell culture practices, cell line authentication, and multiplex determination of cell number as an internal control.

Factor VIII-Fc Activates Natural Killer Cells via Fc-Mediated Interactions With CD16

The most challenging complication associated with Factor VIII (FVIII) replacement therapy is the development of neutralizing anti-drug antibodies, or inhibitors, which occur in 23-35% of severe (FVIII level <1%) hemophilia A (HA) patients and are a serious hindrance to effective management of HA. Consequently, strategies that can either prevent anti-FVIII inhibitors from developing or "tolerize" individuals who develop such antibodies represent a clinically important unmet need. One intervention for patients with high-titer inhibitors is immune tolerance induction (ITI) therapy. Although ITI therapy is the only clinically proven strategy to eradicate anti-FVIII inhibitors, mechanisms of inhibitor reduction remain unknown. Factor VIII Fc-fusion (rFVIIIFc) is an enhanced half-life antihemophilic factor used in replacement therapy for HA. Fc-fusion is a successful protein bio-engineering platform technology. In addition to enhancement of plasma half-life via neonatal Fc receptor (FcRn) binding, other Fc-mediated interactions, including engagement with Fc gamma receptors (FcγR), may have immunological consequences. Several case reports and retrospective analyses suggest that rFVIIIFc offers superior outcomes with respect to ITI compared to other FVIII products. Previously we and others demonstrated rFVIIIFc interactions with activating FcγRIIIA/CD16. Here, we investigated if rFVIIIFc activates natural killer (NK) cells via CD16. We demonstrated rFVIIIFc signaling via CD16 independent of Von Willebrand Factor (VWF):FVIII complex formation. We established that rFVIIIFc potently activated NK cells in a CD16-dependent fashion resulting in IFNγ secretion and cytolytic perforin and granzyme B release. We also demonstrated an association between rFVIIIFc-mediated NK cell IFNγ secretion levels and the high-affinity (158V) CD16 genotype. Furthermore, we show that rFVIIIFc-activated CD16⁺ NK cells were able to lyse a B-cell clone (BO2C11) bearing an anti-FVIII B-cell receptor in an antibody-dependent cellular cytotoxicity (ADCC) assay. These in vitro findings provide an underlying molecular mechanism that may help explain clinical case reports and retrospective studies suggesting rFVIIIFc may be more effective in tolerizing HA patients with anti-FVIII inhibitors compared to FVIII not linked to Fc. Our in vitro findings suggest a potential use of Fc-fusion proteins acting via NK cells to target antigen-specific B-cells, in the management of unwanted immune responses directed against immunogenic self-antigens or therapeutic protein products.

Development of a Macrophage-Based ADCC Assay

Fc-dependent effector functions are an important determinant of the in vivo potency of therapeutic antibodies. Effector function is determined by the combination of FcRs bound by the antibody and the cell expressing the relevant FcRs, leading to antibody-dependent cellular cytotoxicity (ADCC). A number of ADCC assays have been developed; however, they suffer from limitations in terms of throughput, reproducibility, and in vivo relevance. Existing assays measure NK cell-mediated ADCC activity; however, studies suggest that macrophages mediate the effector function of many antibodies in vivo. Here, we report the development of a macrophage-based ADCC assay that relies on luciferase expression in target cells as a measure of live cell number. In the presence of primary mouse macrophages and specific antibodies, loss of luciferase signal serves as a surrogate for ADCC-dependent killing. We show that the assay functions for a variety of mouse and human isotypes with a model antigen/antibody complex in agreement with the known effector function of the isotypes. We also use this assay to measure the activity of a number of influenza-specific antibodies and show that the assay correlates well with the known in vivo effector functions of these antibodies.

Site-Selective Chemoenzymatic Modification on the Core Fucose of an Antibody Enhances Its Fcγ Receptor Affinity and ADCC Activity

Fc glycosylation profoundly impacts the effector functions of antibodies and often dictates an antibody's pro- or anti-inflammatory activities. It is well established that core fucosylation of the Fc domain N-glycans of an antibody significantly reduces its affinity for FcγRIIIa receptors and antibody-dependent cellular cytotoxicity (ADCC). Previous structural studies have suggested that the presence of a core fucose remarkably decreases the unique and favorable carbohydrate-carbohydrate interactions between the Fc and the receptor N-glycans, leading to reduced affinity. We report here that in contrast to natural core fucose, special site-specific modification on the core fucose could dramatically enhance the affinity of an antibody for FcγRIIIa. The site-selective modification was achieved through an enzymatic transfucosylation with a novel fucosidase mutant, which was shown to be able to use modified α-fucosyl fluoride as the donor substrate. We found that replacement of the core l-fucose with 6-azide- or 6-hydroxy-l-fucose (l-galactose) significantly enhanced the antibody's affinity for FcγRIIIa receptors and substantially increased the ADCC activity. To understand the mechanism of the modified fucose-mediated affinity enhancement, we performed molecular dynamics simulations. Our data revealed that the number of glycan contacts between the Fc and the Fc receptor was increased by the selective core-fucose modifications, showing the importance of unique carbohydrate-carbohydrate interactions in achieving high FcγRIIIa affinity and ADCC activity of antibodies. Thus, the direct site-selective modification turns the adverse effect of the core fucose into a favorable force to promote the carbohydrate-carbohydrate interactions.

Incorporation of a Novel CD16-Specific Single-Domain Antibody into Multispecific Natural Killer Cell Engagers With Potent ADCC

Multispecific antibodies that bridge immune effector and tumor cells have shown promising preclinical and clinical efficacies. Here, we isolated and characterized novel llama single-domain antibodies (sdAbs) against CD16. One sdAb, NRC-sdAb048, bound recombinant human and cynomolgus monkey CD16 ectodomains with equivalent affinity (K_D: 1 nM) but did not recognize murine CD16. Binding was similar for human CD16a expressed on NK cells and CD16b (NA2) expressed on neutrophils but dramatically weaker (K_D: ∼6 μM) for the CD16b (NA1) allotype. The sdAb stained primary human peripheral blood NK cells. Irrespective of fusion orientation and linker length, bispecific sdAb-sdAb and sdAb-scFv dimers (anti-CD16/EGFR, anti-CD16/HER2, and anti-CD16/CD19) retained full binding affinity for each target, coengaged both antigens simultaneously, elicited ADCC against target antigen-expressing tumor cells in a reporter bioassay, and triggered target-specific activation and degranulation of primary NK cells as measured via interferon-γ and CD107a expression. These molecules may have applications in cancer immunotherapy.

The First WHO International Standard for Adalimumab: Dual Role in Bioactivity and Therapeutic Drug Monitoring

The expanded availability of adalimumab products continues to widen patient access and reduce costs with substantial benefit to healthcare systems. However, the long-term success of these medicines is highly dependent on maintaining consistency in quality, safety and efficacy while minimizing any risk of divergence during life-cycle management. In recognition of this need and demand from global manufacturers, the World Health Organization (WHO) Expert Committee on Biological standardization established the WHO 1^st International standard (IS) for Adalimumab (coded 17/236) in October 2019 with a defined unitage ascribed to each of the individual bioactivities evaluated in the study namely, TNF-α binding, TNF-α neutralization, complement dependent cytotoxicity and antibody-dependent cellular cytotoxicity. For development of the IS, two candidate standards were manufactured as per WHO recommendations. Analysis of extensive datasets generated by testing of a common set of samples including the candidate standards by multiple stakeholders including regulatory agencies using their own qualified assays in a large international collaborative study showed comparable biological activity for the tested candidates for the different activities. Use of a common standard significantly decreased the variability of bioassays and improved agreement in potency estimates. Data from this study clearly supports the utility of the IS as an important tool for assuring analytical assay performance, for bioassay calibration and validation, for identifying and controlling changes in bioactivity during life-cycle management and for global harmonization of adalimumab products. In addition, in a separate multi-center study which included involvement of hospital and clinical diagnostic laboratories, the suitability of the adalimumab IS for therapeutic drug monitoring assays was examined by analysis of data from testing of a common blind coded panel of adalimumab spiked serum samples representative of the clinical scenario along with the IS and in-house standards in diverse immunoassays/platforms. Both commercially available and in-house assays that are routinely used for assessing adalimumab trough levels were included. Excellent agreement in estimates for adalimumab content in the spiked samples was observed regardless of the standard or the method with inter-laboratory variability also similar regardless of the standard employed. This data, for the first time, provides support for the extended applicability of the IS in assays in use for therapeutic drug monitoring based on the mass content of the IS. The adalimumab IS, in fulfilling clinical demand, can help toward standardizing and harmonizing clinical monitoring assays for informed clinical decisions and/or personalized treatment strategies for better patient outcomes. Collectively, a significant role for the adalimumab IS in assuring the quality, safety and efficacy of adalimumab products globally is envisaged.

A robust reporter assay for the determination of the bioactivity of IL-4R-targeted therapeutic antibodies

Type 2 inflammatory cytokines, including IL-4, IL-5 and IL-13, contribute considerably to the pathogenesis of asthma. Anti-IL-4R monoclonal antibody (mAb) has been approved for the therapeutic treatment of asthma, and many mAbs with the same target are in the different stages of R&D and clinical trials. Bioactivity determination is required to ensure the quality control of mAbs. However, current ELISA and SPR assays or cell-based anti-proliferation assays for IL-4R mAbs are either not mechanism-of-action (MOA) representative or tedious and time consuming. Therefore, we developed a reporter gene assay (RGA) based on the HEK-293 cell line that stably expressed signal transducer and activator of transcription 6 (STAT6) and the luciferase reporter controlled by STAT6 binding elements. Anti-4R mAb could bind to IL-4R, and block the interaction between IL-4 and IL-4R, resulting in the reduction of IL-4 induced STAT6 controlled luciferase expression. After careful optimization of the experiment parameters, the RGA method demonstrated optimal dose-response curve between anti-IL-4R mAb concentration and luciferase expression level. Validation according ICH-Q2 proved the excellent assay performance characteristics of the established RGA, including specificity, accuracy, precision, linearity and range. The established transgenic cell line was stable for the bioactivity determination of anti-IL-4R mAb up to 46 generations, and the RGA was also suitable for the bioactivity determination of anti-IL-4 mAbs, and potentially of anti-IL-13 mAbs. The established RGA could be adopted to determine the bioactivity during the development, characterization, lot release, stability, and comparability studies of anti-IL-4R mAbs.

Mutations in the Hemagglutinin Stalk Domain Do Not Permit Escape from a Protective, Stalk-Based Vaccine-Induced Immune Response in the Mouse Model

Current seasonal influenza virus vaccines target regions of the hemagglutinin (HA) head domain that undergo constant antigenic change, forcing the painstaking annual reformulation of vaccines. The development of broadly protective or universal influenza virus vaccines that induce cross-reactive, protective immune responses could circumvent the need to reformulate current seasonal vaccines. Many of these vaccine candidates target the HA stalk domain, which displays epitopes conserved within and across influenza virus subtypes, including those with pandemic potential. While HA head-mediated antigenic drift is well understood, the potential for antigenic drift in the stalk domain is understudied. Using a panel of HA stalk-specific monoclonal antibodies (MAbs), we applied selection pressure to the stalk domain of A/Netherlands/602/2009 (pdmH1N1) to determine fitness and phenotypes of escape mutant viruses (EMVs). We found that HA stalk MAbs with lower cross-reactivity caused single HA stalk escape mutations, whereas MAbs with broader cross-reactivity forced multiple mutations in the HA. Each escape mutant virus greatly decreased mAb neutralizing activity, but escape mutations did not always ablate MAb binding or Fc-Fc receptor-based effector functions. Escape mutant viruses were not attenuated in vitro but showed attenuation in an in vivo mouse model. Importantly, mice vaccinated with a chimeric HA universal vaccine candidate were protected from lethal challenge with EMVs despite these challenge viruses containing escape mutations in the stalk domain. Our study indicates that while the HA stalk domain can mutate under strong MAb selection pressure, mutant viruses may have attenuated phenotypes and do not evade a polyclonal, stalk-based vaccine-induced response.

Characterization of Novel Cross-Reactive Influenza B Virus Hemagglutinin Head Specific Antibodies That Lack Hemagglutination Inhibition Activity

Humoral immune responses to influenza virus vaccines in elderly individuals are poorly adapted toward new antigenically drifted influenza virus strains. Instead, older individuals respond in an original antigenic sin fashion and produce much more cross-reactive but less potent antibodies. Here, we investigated four influenza B virus hemagglutinin (HA) head specific, hemagglutination inhibition-inactive monoclonal antibodies (MAbs) from elderly individuals. We found that they were broadly reactive within the B/Victoria/2/1987-like lineage, and two were highly cross-reactive with B/Yamagata/16/1988-like lineage viruses. The MAbs were found to be neutralizing, to utilize Fc effector functions, and to be protective against lethal viral challenge in a mouse model. In order to identify residues on the influenza B virus hemagglutinin interacting with the MAbs, we generated escape mutant viruses. Interestingly, escape from these MAbs led to numerous HA mutations within the head domain, including in the defined antigenic sites. We observed that each individual escape mutant virus was able to avoid neutralization by its respective MAb along with other MAbs in the panel, although in many cases binding activity was maintained. Point mutant viruses indicated that K90 is critical for the neutralization of two MAbs, while escape from the other two MAbs required a combination of mutations in the hemagglutinin. Three of four escape mutant viruses had increased lethality in the DBA2/J mouse model. Our work indicates that these cross-reactive antibodies have the potential to cause antigenic drift in the viral population by driving mutations that increase virus fitness. However, binding activity and cross-neutralization were maintained by a majority of antibodies in the panel, suggesting that this drift may not lead to escape from antibody-mediated protection.IMPORTANCE Understanding the immune response that older individuals mount to influenza virus vaccination and infection is critical in order to design better vaccines for this age group. Here, we show that older individuals make broadly neutralizing antibodies that have no hemagglutination-inhibiting activity and are less potent than strain-specific antibodies. These antibodies could drive viral escape from neutralization but did not result in escape from binding. Given their different mechanisms of action, they might retain protective activity even against escape variants.

Toward a Better Understanding of Bioassays for the Development of Biopharmaceuticals by Exploring the Structure-Antibody-Dependent Cellular Cytotoxicity Relationship in Human Primary Cells

Pharmaceutical manufacturing relies on rigorous methods of quality control of drugs and in particular of the physico-chemical and functional characterizations of monoclonal antibodies. To that end, robust bioassays are very often limited to reporter gene assays and the use of immortalized cell lines that are supposed to mimic immune cells such as natural killer (NK) cells to the detriment of primary materials, which are appreciated for their biological validity but are also difficult to exploit due to the great diversity between individuals. Here, we characterized the phenotype of the peripheral blood circulating cytotoxic cells of 30 healthy donors, in particular the repertoire of cytotoxic markers, using flow cytometry. In parallel, we characterized the antibody-dependent cellular cytotoxicity (ADCC) effector functions of these primary cells by measuring their cytolytic activity against a cancer cell-line expressing HER2 in the presence of trastuzumab and with regards to FCGR3A genotype. We could not establish a correlation or grouping of individuals using the data generated from whole peripheral blood mononuclear cells, however the isolation of the CD56-positive population, which is composed not only of NK cells but also of natural killer T (NKT) and γδ-T cells, as well as subsets of activated cytotoxic T cells, monocytes and dendritic cells, made it possible to standardize the parameters of the ADCC and enhance the overall functional avidity without however eliminating the inter-individual diversity. Finally, the use of primary CD56+ cells in ADCC experiments comparing glycoengineered variants of trastuzumab was conclusive to test the limits of this type of ex vivo system. Although the effector functions of CD56+ cells reflected to some extent the in vitro receptor binding properties and cytolytic activity data using NK92 cells, as previously published, reaching a functional avidity plateau could limit their use in a quality control framework.

Development of an antibody-dependent cellular cytotoxicity reporter assay for measuring anti-Middle East Respiratory Syndrome antibody bioactivity

Middle East Respiratory Syndrome coronavirus (MERS-CoV) is a highly virulent pathogen that causes Middle East Respiratory Syndrome (MERS). Anti-MERS-CoV antibodies play an integral role in the prevention and treatment against MERS-CoV infections. Bioactivity is a key quality attribute of therapeutic antibodies, and high accuracy and precision are required. The major methods for evaluating the antiviral effect of antiviral antibodies include neutralization assays using live viruses or pseudoviruses are highly variable. Recent studies have demonstrated that the antibody-dependent cellular cytotoxicity (ADCC) activity of antiviral antibodies is more consistent with the virus clearance effect in vivo than neutralization activity. However, no reports evaluating the ADCC activity of anti-MERS antibodies have been published to date. Here, we describe the development of a robust and reliable cell-based reporter gene assay for the determination of ADCC activity of anti-MERS antibodies using 293T/MERS cells stably expressing the spike protein of MERS-CoV (MERS-S) as target cells and the engineered Jurkat/NFAT-luc/FcγRIIIa stably expressing FcγRIIIA and NFAT reporter gene as effector cells. According to the ICH-Q2 analytical method guidelines, we carefully optimized the experimental conditions and assessed the performance of our assay. In addition, we found that the ADCC activity of afucosylated anti-MERS antibodies is higher than their fucosylated counterparts. The establishment of this ADCC determination system provides a novel method for evaluating the bioactivity of anti-MERS antibodies and improving ADCC activity through modification of N-glycosylation of the Fc segment.

A Multi-Targeting, Nucleoside-Modified mRNA Influenza Virus Vaccine Provides Broad Protection in Mice

Influenza viruses are respiratory pathogens of public health concern worldwide with up to 650,000 deaths occurring each year. Seasonal influenza virus vaccines are employed to prevent disease, but with limited effectiveness. Development of a universal influenza virus vaccine with the potential to elicit long-lasting, broadly cross-reactive immune responses is necessary for reducing influenza virus prevalence. In this study, we have utilized lipid nanoparticle-encapsulated, nucleoside-modified mRNA vaccines to intradermally deliver a combination of conserved influenza virus antigens (hemagglutinin stalk, neuraminidase, matrix-2 ion channel, and nucleoprotein) and induce strong immune responses with substantial breadth and potency in a murine model. The immunity conferred by nucleoside-modified mRNA-lipid nanoparticle vaccines provided protection from challenge with pandemic H1N1 virus at 500 times the median lethal dose after administration of a single immunization, and the combination vaccine protected from morbidity at a dose of 50 ng per antigen. The broad protective potential of a single dose of combination vaccine was confirmed by challenge with a panel of group 1 influenza A viruses. These findings support the advancement of nucleoside-modified mRNA-lipid nanoparticle vaccines expressing multiple conserved antigens as universal influenza virus vaccine candidates.

A Chimeric Japanese Encephalitis Vaccine Protects against Lethal Yellow Fever Virus Infection without Inducing Neutralizing Antibodies

Efficient and safe vaccines against yellow fever (e.g., YFV-17D) that provide long-lasting protection by rapidly inducing neutralizing antibody responses exist. However, the vaccine supply cannot cope with an increasing demand posed by urban outbreaks in recent years. Here we report that JE-CVax/Imojev, a YFV-17D-based chimeric Japanese encephalitis vaccine, also efficiently protects against YFV infection in mice. In case of shortage of the YFV vaccine during yellow fever outbreaks, (off-label) use of JE-CVax/Imojev may be considered. Moreover, wider use of JE-CVax/Imojev in Asia may lower the risk of the much-feared YFV spillover to the continent. More generally, chimeric vaccines that combine surface antigens and replication machineries of two distinct flaviviruses may be considered dual vaccines for the latter pathogen without induction of surface-specific antibodies. Following this rationale, novel flavivirus vaccines that do not hold a risk for antibody-dependent enhancement (ADE) of infection (inherent to current dengue vaccines and dengue vaccine candidates) could be designed.

Recent outbreaks of yellow fever virus (YFV) in West Africa and Brazil resulted in rapid depletion of global vaccine emergency stockpiles and raised concerns about being unprepared against future YFV epidemics. Here we report that a live attenuated virus similar to the Japanese encephalitis virus (JEV) vaccine JE-CVax/Imojev that consists of YFV-17D vaccine from which the structural (prM/E) genes have been replaced with those of the JEV SA14-14-2 vaccine strain confers full protection in mice against lethal YFV challenge. In contrast to the YFV-17D-mediated protection against YFV, this protection is not mediated by neutralizing antibodies but correlates with YFV-specific nonneutralizing antibodies and T cell responses against cell-associated YFV NS1 and other YFV nonstructural (NS) proteins. Our findings reveal the potential of YFV NS proteins to mediate protection and demonstrate that chimeric flavivirus vaccines, such as Imojev, could confer protection against two flaviviruses. This dual protection may have implications for the possible off-label use of JE-CVax in case of emergency and vaccine shortage during YFV outbreaks. In addition, populations in Asia that have been vaccinated with Imojev may already be protected against YFV should outbreaks ever occur on that continent, as several countries/regions in the Asia-Pacific are vulnerable to international spread of the YFV.

Influenza A Virus Antibodies with Antibody-Dependent Cellular Cytotoxicity Function

Influenza causes millions of cases of hospitalizations annually and remains a public health concern on a global scale. Vaccines are developed and have proven to be the most effective countermeasures against influenza infection. Their efficacy has been largely evaluated by hemagglutinin inhibition (HI) titers exhibited by vaccine-induced neutralizing antibodies, which correlate fairly well with vaccine-conferred protection. Contrarily, non-neutralizing antibodies and their therapeutic potential are less well defined, yet, recent advances in anti-influenza antibody research indicate that non-neutralizing Fc-effector activities, especially antibody-dependent cellular cytotoxicity (ADCC), also serve as a critical mechanism in antibody-mediated anti-influenza host response. Monoclonal antibodies (mAbs) with Fc-effector activities have the potential for prophylactic and therapeutic treatment of influenza infection. Inducing mAbs mediated Fc-effector functions could be a complementary or alternative approach to the existing neutralizing antibody-based prevention and therapy. This review mainly discusses recent advances in Fc-effector functions, especially ADCC and their potential role in influenza countermeasures. Considering the complexity of anti-influenza approaches, future vaccines may need a cocktail of immunogens in order to elicit antibodies with broad-spectrum protection via multiple protective mechanisms.

A LAG-3-Specific Agonist Antibody for the Treatment of T Cell-Induced Autoimmune Diseases

T cells chronically stimulated with the same peptide tend to express exhaustion markers such as PD-1 or LAG-3. Deficiencies in the PD-1 and LAG-3 pathways have been linked to the development of autoimmune diseases. IMP761 is a LAG-3-specific humanized agonist Ab with immunosuppressive properties both in vitro and in vivo in an Ag-specific delayed-type hypersensitivity (DTH) model in the cynomolgus macaque (Macaca fascicularis). IMP761 inhibits TCR-mediated NFAT activation and Ag-induced human T cell proliferation and activation. In the DTH model, assessment of T cell infiltration and gene expression profile at the DTH biopsy site corresponds to immunosuppression of an Ag-induced T cell response. IMP761 is the first LAG-3-specific agonist product candidate, acting upstream on activated T cells, the root cause of self-Ag-specific T cell-induced autoimmune diseases.

Characterization of a single reporter-gene potency assay for T-cell-dependent bispecific molecules

T-cell-dependent bispecific antibodies (TDBs) are promising cancer immunotherapies that recruit patients' T cells to kill cancer cells. There are many TDBs in clinical trials, demonstrating their widely recognized therapeutic potential. However, their complex, multi-step mechanism of action (MoA), which includes bispecific antigen binding, T-cell activation, and target-cell killing, presents unique challenges for biological characterization and potency assay selection. Here, we describe the development of a single reporter-gene potency assay for a TDB (TDB1) that is MoA reflective and sensitive to binding of both antigens. Our reporter-gene assay measures T-cell activation using Jurkat cells engineered to express luciferase under the control of an NFkB response element. The potencies of select samples were measured both by this assay and by a flow-cytometry-based cell-killing assay using human lymphocytes as effector cells. Correlating the two sets of potency results clearly establishes our reporter-gene assay as MoA reflective. Furthermore, correlating potencies for the same panel of samples against binding data measured by binding assays for each individual arm demonstrates that the reporter-gene potency assay reflects dual-antigen binding and can detect changes in affinity for either arm. This work demonstrates that one reporter-gene assay can be used to measure the potency of TDB1 while capturing key aspects of its MoA, thus serving as a useful case study of selection and justification of reporter-gene potency assays for TDBs. Furthermore, our strategy of correlating reporter-gene potency, target-cell killing, and antigen binding for each individual arm serves as a useful example of a thorough, holistic approach to biological characterization for TDBs that can be applied to other bispecific molecules.

Knowns and Unknowns of Assaying Antibody-Dependent Cell-Mediated Cytotoxicity Against HIV-1

It is now well-accepted that Fc-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC), can contribute to vaccine-elicited protection as well as post-infection control of HIV viremia. This picture was derived using a wide array of ADCC assays, no two of which are strictly comparable, and none of which is qualified at the clinical laboratory level. An earlier comparative study of assay protocols showed that while data from different ADCC assay formats were often correlated, they remained distinct in terms of target cells and the epitopes and antigen(s) available for recognition by antibodies, the effector cells, and the readout of cytotoxicity. This initial study warrants expanded analyses of the relationships among all current assay formats to determine where they detect overlapping activities and where they do not. Here we summarize knowns and unknowns of assaying ADCC against HIV-1.

Modulating antibody-dependent cellular cytotoxicity of epidermal growth factor receptor-specific heavy-chain antibodies through hinge engineering

Human IgG1 and IgG3 antibodies (Abs) can mediate Ab-dependent cellular cytotoxicity (ADCC), and engineering of the Ab Fc (point mutation; defucosylation) has been shown to affect ADCC by modulating affinity for FcRγIIIa. In the absence of a C_H 1 domain, many camelid heavy-chain Abs (HCAbs) naturally bear very long and flexible hinge regions connecting their V_H H and C_H 2 domains. To better understand the influence of hinge length and structure on HCAb ADCC, we produced a series of hinge-engineered epidermal growth factor receptor (EGFR)-specific chimeric camelid V_H H-human Fc Abs and characterized their affinities for recombinant EGFR and FcRγIIIa, their binding to EGFR-positive tumor cells, and their ability to elicit ADCC. In the case of one chimeric HCAb (EG2-hFc), we found that variants bearing longer hinges (IgG3 or camelid hinge regions) showed dramatically improved ADCC in comparison with a variant bearing the human IgG1 hinge, in similar fashion to a variant with reduced C_H 2 fucosylation. Conversely, an EG2-hFc variant bearing a truncated human IgG1 upper hinge region failed to elicit ADCC. However, there was no consistent association between hinge length and ADCC for four similarly engineered chimeric HCAbs directed against distinct EGFR epitopes. These findings demonstrate that the ADCC of some HCAbs can be modulated simply by varying the length of the Ab hinge. Although this effect appears to be heavily epitope-dependent, this strategy may be useful to consider during the design of V_H H-based therapeutic Abs for cancer.

Chimeric Antigen Receptor Library Screening Using a Novel NF-κB/NFAT Reporter Cell Platform

Chimeric antigen receptor (CAR)-T cell immunotherapy is under intense preclinical and clinical investigation, and it involves a rapidly increasing portfolio of novel target antigens and CAR designs. We established a platform that enables rapid and high-throughput CAR-screening campaigns with reporter cells derived from the T cell lymphoma line Jurkat. Reporter cells were equipped with nuclear factor κB (NF-κB) and nuclear factor of activated T cells (NFAT) reporter genes that generate a duplex output of enhanced CFP (ECFP) and EGFP, respectively. As a proof of concept, we modified reporter cells with CD19-specific and ROR1-specific CARs, and we detected high-level reporter signals that allowed distinguishing functional from non-functional CAR constructs. The reporter data were highly reproducible, and the time required for completing each testing campaign was substantially shorter with reporter cells (6 days) compared to primary CAR-T cells (21 days). We challenged the reporter platform to a large-scale screening campaign on a ROR1-CAR library, and we showed that reporter cells retrieved a functional CAR variant that was present with a frequency of only 6 in 1.05 × 106. The data illustrate the potential to implement this reporter platform into the preclinical development path of novel CAR-T cell products and to inform and accelerate the selection of lead CAR candidates for clinical translation.

Validation of an ADCC assay using human primary natural killer cells to evaluate biotherapeutic products bearing an Fc region

The development of biotherapeutics requires continuous improvement in analytical methodologies for the assessment of their quality attributes. A subset of biotherapeutics is designed to interact with specific antigens that are exposed on the membranes of target cells or circulating in a soluble form, and effector functions are achieved via recognition of their Fc region by effector cells that induce mechanisms such as antibody-dependent cell-mediated cytotoxicity (ADCC). Thus, ADCC induction is a critical quality attribute (CQA) that must be evaluated to ensure biotherapeutic efficacy. Induction of ADCC can be evaluated by employing effector cells from different sources, such as peripheral blood mononuclear cells (PBMC) and genetically modified cell lines (e.g., transfected NKs or Jurkat cells), and different approaches can be used for detection and results interpretation depending on the type of effector cells used. In this regard, validation of the assays is relevant to ensure the reliability of the results according to the intended purpose. Herein, we show the standardization and validation of ADCC assays to test the potency of three biotherapeutic proteins using primary NK cells obtained from fresh blood as effector cells and detecting cell death by flow cytometry. The advantage of using primary NKs instead of modified cells is that the response is closer to that occurring in vivo since cytotoxicity is evaluated in a direct manner. Our results indicate that in all cases, the assays exhibited a characteristic sigmoidal dose/response curve complying with accurate, precise and specific parameters. Thereby, the validated ADCC assay is an appropriate alternative to evaluate the biological activities of these type of biotherapeutics.

The first World Health Organization International Standard for infliximab products: A step towards maintaining harmonized biological activity

Due to the increase in the number of infliximab products, the need for global harmonization of the bioactivity of this monoclonal antibody was recognized by the World Health Organization (WHO). In response, the National Institute for Biological Standards and Control (NIBSC) developed the first international standard (IS) for infliximab, which targets tumour necrosis factor (TNF). Each ampoule is assigned values of 500 IU of TNF neutralizing activity and 500 IU of binding activity. Two preparations of infliximab were formulated and lyophilized at NIBSC prior to evaluation in a collaborative study for their suitability to serve as an IS for the in vitro biological activity of infliximab. The study involved participants using in vitro cell-based bioassays (TNF neutralization, antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity) and binding assays. The results of this study showed that the candidate preparation, coded 16/170, is suitable as an IS for infliximab bioactivity. This infliximab IS from NIBSC, is intended to support in vitro bioassay calibration and validation by defining international units of bioactivity. The proposed unitages, however, are not intended to revise product labelling or dosing requirements, as any decisions regarding this relies solely with the regulatory authorities. Furthermore, the infliximab IS is not intended for determining the specific activity of products, nor to serve any regulatory role in defining biosimilarity. We briefly discuss the future use of WHO international standards in supporting the global harmonisation of biosimilar infliximab products.

Enhancing antibody-dependent cell-mediated cytotoxicity: a strategy for improving antibody-based immunotherapy

The targeting of surface antigens expressed on tumor cells by monoclonal antibodies (mAbs) has revolutionized cancer therapeutics. One mechanism of action of antibody-based immunotherapy is the activation of immune effector cells to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). This review will summarize the process of ADCC, its important role in the efficacy of mAb therapy, how to measure it, and finally future strategies for antibody design that can take advantage of it to improve clinical performance.

Targeting Tissue Factor for Immunotherapy of Triple-Negative Breast Cancer Using a Second-Generation ICON

Triple-negative breast cancer (TNBC) is a leading cause of breast cancer death and is often associated with BRCA1 and BRCA2 mutation. Due to the lack of validated target molecules, no targeted therapy for TNBC is approved. Tissue factor (TF) is a common yet specific surface target receptor for cancer cells, tumor vascular endothelial cells, and cancer stem cells in several types of solid cancers, including breast cancer. Here, we report evidence supporting the idea that TF is a surface target in TNBC. We used in vitro cancer lines and in vivo tumor xenografts in mice, all with BRCA1 or BRCA2 mutations, derived from patients' tumors. We showed that TF is overexpressed on TNBC cells and tumor neovasculature in 50% to 85% of TNBC patients (n = 161) and in TNBC cell line-derived xenografts (CDX) and patient-derived xenografts (PDX) from mice, but was not detected in adjacent normal breast tissue. We then describe the development of a second-generation TF-targeting immunoconjugate (called L-ICON1, for lighter or light chain ICON) with improved efficacy and safety profiles compared with the original ICON. We showed that L-ICON1 kills TNBC cells in vitro via antibody-dependent cell-mediated cytotoxicity and can be used to treat human and murine TNBC CDX as well as PDX in vivo in orthotopic mouse models. Thus, TF could be a useful target for the development of immunotherapeutics for TNBC patients, with or without BRCA1 and BRCA2 mutations. Cancer Immunol Res; 6(6); 671-84. ©2018 AACR.

An antibody with Fab-constant domains exchanged for a pair of CH3 domains

We have designed a complete antibody-like construct where the C_H1 and C_κ domains are exchanged for a pair of the C_H3 domains and efficient pairing of the heavy and light variable domain is achieved using “Knobs-into-Holes” strategy. This construct, composed of only naturally occurring immunoglobulin sequences without artificial linkers, expressed at a high level in mammalian cells, however exhibited low solubility. Rational mutagenesis aimed at the amino acid residues located at the interface of the variable domains and the exchanged C_H3 domains was applied to improve the biophysical properties of the molecule. The domain-exchanged construct, including variable domains of the HER2/neu specific antibody trastuzumab, was able to bind to the surface of the strongly HER2/neu positive cell line SK-BR3 4-fold weaker than trastuzumab, but could nevertheless incite a more potent response in an antibody-dependent cell cytotoxicity (ADCC) reporter assay with FcγRIIIa-overexpressing T-cells. This could be explained with a stronger binding to the FcγRIIIa. Importantly, the novel construct could mediate a specific ADCC effect with natural killer cells similar to the parental antibody.

Targeting tissue factor as a novel therapeutic oncotarget for eradication of cancer stem cells isolated from tumor cell lines, tumor xenografts and patients of breast, lung and ovarian cancer

Targeting cancer stem cell (CSC) represents a promising therapeutic approach as it can potentially fight cancer at its root. The challenge is to identify a surface therapeutic oncotarget on CSC. Tissue factor (TF) is known as a common yet specific surface target for cancer cells and tumor neovasculature in several solid cancers. However, it is unknown if TF is expressed by CSCs. Here we demonstrate that TF is constitutively expressed on CD133 positive (CD133+) or CD24-CD44+ CSCs isolated from human cancer cell lines, tumor xenografts from mice and breast tumor tissues from patients. TF-targeted agents, i.e., a factor VII (fVII)-conjugated photosensitizer (fVII-PS for targeted photodynamic therapy) and fVII-IgG1Fc (Immunoconjugate or ICON for immunotherapy), can eradicate CSC via the induction of apoptosis and necrosis and via antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity, respectively. In conclusion, these results demonstrate that TF is a novel surface therapeutic oncotarget for CSC, in addition to cancer cell TF and tumor angiogenic vascular endothelial TF. Moreover, this research highlights that TF-targeting therapeutics can effectively eradicate CSCs, without drug resistance, isolated from breast, lung and ovarian cancer with potential to translate into other most commonly diagnosed solid cancer, in which TF is also highly expressed.

Detection of Experimental and Clinical Immune Complexes by Measuring SHIP-1 Recruitment to the Inhibitory FcγRIIB

Fc γ receptors (FcγR) are involved in multiple aspects of immune cell regulation, are central to the success of mAb therapeutics, and underpin the pathology of several autoimmune diseases. However, reliable assays capable of accurately measuring FcγR interactions with their physiological ligands, IgG immune complexes (IC), are limited. A method to study and detect IC interactions with FcγRs was therefore developed. This method, designed to model the signaling pathway of the inhibitory FcγRIIB (CD32B), used NanoLuc Binary Interaction Technology to measure recruitment of the Src homology 2 domain-containing inositol phosphatase 1 to the ITIM of this receptor. Such recruitment required prior cross-linking of an ITAM-containing activatory receptor, and evoked luciferase activity in discrete clusters at the cell surface, recapitulating the known biology of CD32B signaling. The assay detected varying forms of experimental IC, including heat-aggregated IgG, rituximab-anti-idiotype complexes, and anti-trinitrophenol-trinitrophenol complexes in a sensitive manner (≤1 μg/ml), and discriminated between complexes of varying size and isotype. Proof-of-concept for the detection of circulating ICs in autoimmune disease was provided, as responses to sera from patients with systemic lupus erythematosus and rheumatoid arthritis were detected in small pilot studies. Finally, the method was translated to a stable cell line system. In conclusion, a rapid and robust method for the detection of IC was developed, which has numerous potential applications including the monitoring of IC in autoimmune diseases and the study of underlying FcγR biology.

A Method to Assess Fc-mediated Effector Functions Induced by Influenza Hemagglutinin Specific Antibodies

Antibodies play a crucial role in coupling the innate and adaptive immune responses against viral pathogens through their antigen binding domains and Fc-regions. Here, we describe how to measure the activation of Fc effector functions by monoclonal antibodies targeting the influenza virus hemagglutinin with the use of a genetically engineered Jurkat cell line expressing an activating type 1 Fc-FcγR. Using this method, the contribution of specific Fc-FcγR interactions conferred by immunoglobulins can be determined using an in vitro assay.

FcγRII-binding Centyrins mediate agonism and antibody-dependent cellular phagocytosis when fused to an anti-OX40 antibody

Immunostimulatory antibodies against the tumor necrosis factor receptors (TNFR) are emerging as promising cancer immunotherapies. The agonism activity of such antibodies depends on crosslinking to Fc gamma RIIB receptor (FcγRIIB) to enable the antibody multimerization that drives TNFR activation. Previously, Fc engineering was used to enhance the binding of such antibodies to Fcγ receptors. Here, we report the identification of Centyrins as alternative scaffold proteins with binding affinities to homologous FcγRIIB and FcγRIIA, but not to other types of Fcγ receptors. One Centyrin, S29, was engineered at distinct positions of an anti-OX40 SF2 antibody to generate bispecific and tetravalent molecules named as mAbtyrins. Regardless of the position of S29 on the SF2 antibody, SF2-S29 mAbtyrins could bind FcγRIIB and FcγRIIA specifically while maintaining binding to OX40 receptors. In a NFκB reporter assay, attachment of S29 Centyrin molecules at the C-termini, but not the N-termini, resulted in SF2 antibodies with increased agonism owing to FcγRIIB crosslinking. The mAbtyrins also showed agonism in T-cell activation assays with immobilized FcγRIIB and FcγRIIA, but this activity was confined to mAbtyrins with S29 specifically at the C-termini of antibody heavy chains. Furthermore, regardless of the position of the molecule, S29 Centyrin could equip an otherwise Fc-silent antibody with antibody-dependent cellular phagocytosis activity without affecting the antibody's intrinsic antibody-dependent cell-meditated cytotoxicity and complement-dependent cytotoxicity. In summary, the appropriate adoption FcγRII-binding Centyrins as functional modules represents a novel strategy to engineer therapeutic antibodies with improved functionalities.

International standards for monoclonal antibodies to support pre- and post-marketing product consistency: Evaluation of a candidate international standard for the bioactivities of rituximab

The intrinsic complexity and heterogeneity of therapeutic monoclonal antibodies is built into the biosimilarity paradigm where critical quality attributes are controlled in exhaustive comparability studies with the reference medicinal product. The long-term success of biosimilars will depend on reassuring healthcare professionals and patients of consistent product quality, safety and efficacy. With this aim, the World Health Organization has endorsed the need for public bioactivity standards for therapeutic monoclonal antibodies in support of current controls. We have developed a candidate international potency standard for rituximab that was evaluated in a multi-center collaborative study using participants' own qualified Fc-effector function and cell-based binding bioassays. Dose-response curve model parameters were shown to reflect similar behavior amongst rituximab preparations, albeit with some differences in potency. In the absence of a common reference standard, potency estimates were in poor agreement amongst laboratories, but the use of the candidate preparation significantly reduced this variability. Our results suggest that the candidate rituximab standard can support bioassay performance and improve data harmonization, which when implemented will promote consistency of rituximab products over their life-cycles. This data provides the first scientific evidence that a classical standardization exercise allowing traceability of bioassay data to an international standard is also applicable to rituximab. However, we submit that this new type of international standard needs to be used appropriately and its role not to be mistaken with that of the reference medicinal product.

A Novel System for the Quantification of the ADCC Activity of Therapeutic Antibodies

Novel ADCC effector cells expressing the V-variant or F-variant of FcγRIIIa (CD16a) and firefly luciferase under the control of a chimeric promoter incorporating recognition sequences for the principal transcription factors involved in FcγRIIIa signal transduction, together with novel target cells overexpressing a constant high level of the specific antigen recognized by rituximab, trastuzumab, cetuximab, infliximab, adalimumab, or etanercept, confer improved sensitivity, specificity, and dynamic range in an ADCC assay relative to effector cells expressing a NFAT-regulated reporter gene and wild-type target cells. The effector cells also contain a normalization gene rendering ADCC assays independent of cell number or serum matrix effects. The novel effector and target cells in a frozen thaw-and-use format exhibit low vial-to-vial and lot-to-lot variation in their performance characteristics reflected by CVs of 10% or less. Homologous control target cells in which the specific target gene has been invalidated by genome editing providing an ideal control and a means of correcting for nonspecific effects were observed with certain samples of human serum. The novel effector cells and target cells expressing noncleavable membrane-bound TNFα have been used to quantify ADCC activity in serum from patients with Crohn's disease treated with infliximab and to relate ADCC activity to drug levels.