Characterization of FcγRIIIA effector cells used in in vitro ADCC bioassay: Comparison of primary NK cells with engineered NK-92 and Jurkat T cells

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.

Development, methodological evaluation and application of a cell-based TRF assay for analysis of ADCC activity

Interaction of an antibody with its FcγR plays an important role in effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC). Nowadays altered ADCC activity of an antibody can be achieved by utilizing an effective glyco-engineering strategy, which often involves changes of sugar moieties in Fc part of the antibody, thereby affecting its receptor binding with effector cells. We aimed to construct a cell-based time-resolved fluorescence (TRF) assay for the evaluation of ADCC activity triggered by the antibody drug Trastuzumab (anti-HER2) and T-DM1. The assay was initiated by incubating 2,2':6',2 "-Terpyridine-6,6"-dicarboxylic acid (TDA)-labeled target SK-BR3 cells with the testing antibodies and engineered NK-92 effector cells. After incubation, the target cells were lysed to detect TDA released into the supernatant. Together with added Eu, the TDA in the supernatant formed a stable chelate of EuTDA with high-intensity fluorescence. The ADCC activity was then determined by measuring the fluorescence of EuTDA. Consequently, the method demonstrated good accuracy, precision, linearity, and specificity over methodological assessment and compared well with the Luciferase release assay in terms of the agreement of the achieved results. Using the developed assay, we evaluated the ADCC activity of two glyco-engineered anti-HER-2 antibody-drug conjugates (ADCs) and the results showed that antibody Fc glycosylation modifications influenced antibody ADCC activity to varying degrees. In conclusion, the present assay is able to accurately assess the ADCC activity induced by Trastuzumab (anti-HER2) and T-DM1, and a similar methodology can be applied to other therapeutic antibodies during drug development to help screen for antibodies with desirable ADCC activity.

Detection of Antibody-Dependent Cell-Mediated Cytotoxicity-Supporting Antibodies by NK-92-CD16A Cell Externalization of CD107a: Recognition of Antibody Afucosylation and Assay Optimization

Antibody-dependent cell-mediated cytotoxicity (ADCC) by natural killer (NK) lymphocytes eliminates cells infected with viruses. Anti-viral ADCC requires three components: (1) antibody; (2) effector lymphocytes with the Fc-IgG receptor CD16A; and (3) viral proteins in infected cell membranes. Fc-afucosylated antibodies bind with greater affinity to CD16A than fucosylated antibodies; individuals' variation in afucosylation contributes to differences in ADCC. Current assays for afucosylated antibodies involve expensive methods. We report an improved bioassay for antibodies that supports ADCC, which encompasses afucosylation. This assay utilizes the externalization of CD107a by NK-92-CD16A cells after antibody recognition. We used anti-CD20 monoclonal antibodies, GA101 WT or glycoengineered (GE), 10% or ~50% afucosylated, and CD20-positive Raji target cells. CD107a increased detection 7-fold compared to flow cytometry to detect Raji-bound antibodies. WT and GE antibody effective concentrations (EC50s) for CD107a externalization differed by 20-fold, with afucosylated GA101-GE more detectable. The EC50s for CD107a externalization vs. 51Cr cell death were similar for NK-92-CD16A and blood NK cells. Notably, the % CD107a-positive cells were negatively correlated with dead Raji cells and were nearly undetectable at high NK:Raji ratios required for cytotoxicity. This bioassay is very sensitive and adaptable to assess anti-viral antibodies but unsuitable as a surrogate assay to monitor cell death after ADCC.

Uses and Challenges of Antiviral Polyclonal and Monoclonal Antibody Therapies

Viral diseases represent a major public health concerns and ever-present risks for developing into future pandemics. Antiviral antibody therapeutics, either alone or in combination with other therapies, emerged as valuable preventative and treatment options, including during global emergencies. Here we will discuss polyclonal and monoclonal antiviral antibody therapies, focusing on the unique biochemical and physiological properties that make them well-suited as therapeutic agents. We will describe the methods of antibody characterization and potency assessment throughout development, highlighting similarities and differences between polyclonal and monoclonal products as appropriate. In addition, we will consider the benefits and challenges of antiviral antibodies when used in combination with other antibodies or other types of antiviral therapeutics. Lastly, we will discuss novel approaches to the characterization and development of antiviral antibodies and identify areas that would benefit from additional research.

A chimeric thermostable M2e and H3 stalk-based universal influenza A virus vaccine

We developed a new chimeric M2e and H3 hemagglutinin (HA) stalk protein vaccine (M2e-H3 stalk) by genetic engineering of modified H3 stalk domain conjugated with conserved M2e epitopes to overcome the drawbacks of low efficacy by monomeric domain-based universal vaccines. M2e-H3 stalk protein expressed and purified from Escherichia coli was thermostable, displaying native-like antigenic epitopes recognized by antisera of different HA subtype proteins and influenza A virus infections. Adjuvanted M2e-H3 stalk vaccination induced M2e and stalk-specific IgG antibodies recognizing viral antigens on virus particles and on the infected cell surface, CD4⁺ and CD8⁺ T-cell responses, and antibody-dependent cytotoxic cell surrogate activity in mice. M2e-H3 stalk was found to confer protection against heterologous and heterosubtypic cross-group subtype viruses (H1N1, H5N1, H9N2, H3N2, H7N9) at similar levels in adult and aged mice. These results provide evidence that M2e-H3 stalk chimeric proteins can be developed as a universal influenza A virus vaccine candidate for young and aged populations.

Thermostable H1 hemagglutinin stem with M2e epitopes provides broad cross-protection against group1 and 2 influenza A viruses

Hemagglutinin (HA) stem-based vaccines have limitations in providing broad and effective protection against cross-group influenza viruses, despite being a promising universal vaccine target. To overcome the limited cross-protection and low efficacy by HA stem vaccination, we genetically engineered a chimeric conjugate of thermostable H1 HA stem and highly conserved M2e repeat (M2e-H1stem), which was expressed at high yields in Escherichia coli. M2e-H1stem protein presented native-like epitopes reactive to antisera of live virus infection. M2e-H1stem protein vaccination of mice induced strong M2e- and HA stem-specific immune responses, conferring broadly effective cross-protection against both antigenically distinct group 1 (H1N1, H5N1, and H9N2 subtypes) and group 2 (H3N2 and H7N9 subtypes) seasonal and pandemic potential influenza viruses. M2e-H1stem vaccination generated CD4⁺ and CD8⁺ T cell responses and antibody-dependent cytotoxic cellular and humoral immunity, which contributed to enhancing cross-protection. Furthermore, comparable broad cross-group protection was observed in older aged mice after M2e-H1stem vaccination. This study provides evidence warranting further development of chimeric M2e-stem proteins as a promising universal influenza vaccine candidate in adult and aged populations.

Introduction of a Capillary Gel Electrophoresis-Based Workflow for Biotherapeutics Characterization: Size, Charge, and N-Glycosylation Variant Analysis of Bamlanivimab, an Anti-SARS-CoV-2 Product

Coronavirus Disease 2019 (COVID-19) is a major public health problem worldwide with 5–10% hospitalization and 2–3% global mortality rates at the time of this publication. The disease is caused by a betacoronavirus called Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The receptor-binding domain (RBD) of the Spike protein expressed on the surface of the virus plays a key role in the viral entry into the host cell via the angiotensin-converting enzyme 2 receptor. Neutralizing monoclonal antibodies having the RBD as a target have the ability to inhibit angiotensin-converting enzyme 2 (ACE2) receptor binding, therefore, prevent SARS-CoV-2 infection, represent a promising pharmacological strategy. Bamlanivimab is the first anti-spike neutralizing monoclonal antibody, which got an emergency use authorization from the FDA for COVID-19 treatment. Albeit, bamlanivimab is primarily a neutralizing mAb, some of its effector function related activity was also emphasized. The effector function of antibody therapeutics is greatly affected by their N-linked carbohydrates at the conserved Fc region, possibly influenced by the manufacturing process. Various capillary gel electrophoresis methods are widely accepted in the biopharmaceutical industry for the characterization of therapeutic antibodies. In this paper we introduce a capillary gel electrophoresis based workflow for 1) size heterogeneity analysis to determine the presence/absence of the non-glycosylated heavy chain (NGHC) fragment (SDS-CGE); 2) capillary gel isoelectric focusing for possible N-glycosylation mediated charge heterogeneity determination, e.g., for excess sialylation and finally, 3) capillary gel electrophoresis for N-glycosylation profiling and sequencing. Our results have shown the presence of negligible amount of non-glycosylated heavy chain (NGHC) while 25% acidic charge variants were detected. Comprehensive N-glycosylation characterization revealed the occurrence of approximately 8.2% core-afucosylated complex and 17% galactosylated N-linked oligosaccharides, suggesting the possible existence of antibody dependent cell mediated cytotoxicity (ADCC) effector function in addition to the generally considered neutralizing effect of this particular therapeutic antibody molecule.

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.

Enhanced cross protection by hetero prime-boost vaccination with recombinant influenza viruses containing chimeric hemagglutinin-M2e epitopes

Annual repeat influenza vaccination raises concerns about protective efficacy against mismatched viruses. We investigated the impact of heterologous prime-boost vaccination on inducing cross protection by designing recombinant influenza viruses with chimeric hemagglutinin (HA) carrying M2 extracellular domains (M2e-HA). Heterologous prime-boost vaccination of C57BL/6 mice with M2e-HA chimeric virus more effectively induced M2e and HA stalk specific IgG antibodies correlating with cross protection than homologous prime-boost vaccination. Induction of M2e and HA stalk specific IgG antibodies was compromised in 1-year old mice, indicating significant aging effects on priming subdominant M2e and HA stalk IgG antibody responses. This study demonstrates that a heterologous prime-boost strategy with recombinant influenza virus expressing extra M2e epitopes provides more effective cross protection than homologous vaccination.

Carbon ion (12C6+) irradiation induces the expression of Klrk1 in lung cancer and optimizes the tumor microenvironment based on the NKG2D/NKG2D-Ls pathway

With the identification of "negative immune regulation" defects in the immune system and the continuous improvement of immunotherapy, natural killer cells (NK) have received more attention, especially as tools in combined immunotherapy. Carbon ions (12C6+) have become the ideal radiation for combined immunotherapy due to their significant radiobiological advantages and synergistic effects. The purpose of this study was to explore the NK cell-mediated cytotoxicity pathway and related mechanisms in lung cancer induced by carbon ion irradiation. KLRK1, which specifically encodes the NKG2D receptor, was significantly correlated with the prognosis, clinical stage, functional status of NK cells, and the immune microenvironment of lung cancer, as shown by bioinformatics analysis. Based on RNA-seq data of Lewis lung cancer in C57BL/6 mice, carbon ion irradiation was found to significantly induce Klrk1 gene expression and activate the NKG2D/NKG2D-Ls pathway. The Treg inhibition pathway combined with carbon ion radiotherapy could significantly increase the infiltration and function of NK cells in the tumor microenvironment of lung cancer and prolong the survival time of C57BL/6 mice. In conclusion, carbon ions have significant radiobiological advantages, especially under conditions of combined immunotherapy. Carbon ions combined with Treg inhibitors can significantly improve the infiltration and functional status of NK cells.

Freeze thaw and lyophilization induced alteration in mAb therapeutics: Trastuzumab as a case study

Long-term stability of therapeutic monoclonal antibody (mAb) products is necessary for their successful commercialization. Freeze-thaw (F/T) operations are often performed for a mAb product during processing, storage and distribution. Lyophilization (Lyo) is another unit operation that is commonly used for drug product manufacturing of mAbs. This paper aims to explore the impact of these operations on structure and function of a mAb therapeutic, as well as of biosimilars. Trastuzumab innovator and its five biosimilars were analysed for aggregation, charge heterogeneity, secondary structure, binding kinetics, and potency after each freeze-thaw and lyophilization cycle. It is observed that both F/T and Lyo induce protein aggregation, which in turn causes perturbations in the biological potency of the mAb therapeutic. The average value of the percentage of aggregation increased from 0.6 % (week 1) to 5.3 % (week 10) in F/T study and from 0.8 % (week 1) to 10.1 % (week 10) in Lyo study. The acidic pool increased from 26.5 % (week 1) to 44.4 % (week 10) and the basic variants from 13.9 % (week 1) to 24.0 % (week 10) in F/T study. Similarly, acidic pool increased from 27.1 % (week 1) to 42.0 % (week 10) and basic variants from 14.8 % (week 1) to 24.4 % (week 10) in Lyo study. The average percentage of beta-sheet increased from 58.4 % (week 1) to 60.9 % (week 10) in F/T study and from 59.7 % (week 1) to 72.6 % (week 10) in Lyo study. Lower binding affinity was found in week 7 as compared to week 1 in Lyo study whereas no change in binding affinity was observed in the F/T study. The average potency value gradually decreased from 0.97IU/ ml (week 1) to 0.75IU/ ml (week 10) in F/T study and from 1.0IU/ ml (week 1) to 0.66IU/ ml (week 10) in Lyo study. Results indicate that lyophilization has a bigger impact on binding affinity than freeze thaw and as expected, the impact was comparable across the innovator and biosimilar products.

Small molecule inhibitors against PD-1/PD-L1 immune checkpoints and current methodologies for their development: a review

Programmed death-1/programmed death ligand-1 (PD-1/PD-L1) based immunotherapy is a revolutionary cancer therapy with great clinical success. The majority of clinically used PD-1/PD-L1 inhibitors are monoclonal antibodies but their applications are limited due to their poor oral bioavailability and immune-related adverse effects (irAEs). In contrast, several small molecule inhibitors against PD-1/PD-L1 immune checkpoints show promising blockage effects on PD-1/PD-L1 interactions without irAEs. However, proper analytical methods and bioassays are required to effectively screen small molecule derived PD-1/PD-L1 inhibitors. Herein, we summarize the biophysical and biochemical assays currently employed for the measurements of binding capacities, molecular interactions, and blocking effects of small molecule inhibitors on PD-1/PD-L1. In addition, the discovery of natural products based PD-1/PD-L1 antagonists utilizing these screening assays are reviewed. Potential pitfalls for obtaining false leading compounds as PD-1/PD-L1 inhibitors by using certain binding bioassays are also discussed in this review.

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.

The development and kinetics of functional antibody-dependent cell-mediated cytotoxicity (ADCC) to SARS-CoV-2 spike protein

Since the COVID-19 pandemic, functional non-neutralizing antibody responses to SARS-CoV-2, including antibody-dependent cell-mediated cytotoxicity (ADCC), are poorly understood. We developed an ADCC assay utilizing a stably transfected, dual-reporter target cell line with inducible expression of a SARS-CoV-2 spike protein on the cell surface. Using this assay, we analyzed 61 convalescent serum samples from adults with PCR-confirmed COVID-19 and 15 samples from healthy uninfected controls. We found that 56 of 61 convalescent serum samples induced ADCC killing of SARS-CoV-2 S target cells, whereas none of the 15 healthy controls had detectable ADCC. We then found a modest decline in ADCC titer over a median 3-month follow-up in 21 patients who had serial samples available for analysis. We confirmed that the antibody-dependent target cell lysis was mediated primarily via the NK FcγRIIIa receptor (CD16). This ADCC assay had high sensitivity and specificity for detecting serologic immune responses to SARS-CoV-2.

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.

Suppression of c-Met-Overexpressing Tumors by a Novel c-Met/CD3 Bispecific Antibody

INTRODUCTION

Overexpression of c-Met, or hepatocyte growth factor (HGF) receptor, is commonly observed in tumor biopsies and often associated with poor patient survival, which makes HGF/c-Met pathway an attractive molecular target for cancer therapy. A number of antibody-based therapeutic strategies have been explored to block c-Met or HGF in cancers; however, clinical efficacy has been very limited, indicating that blockade of c-Met signal alone is not sufficient. Thus, an alternative approach is to develop an immunotherapy strategy for c-Met-overexpressing cancers. c-Met/CD3 bispecific antibody (BsAb) could bridge CD3-positive T lymphocytes and tumor cells to result in potent tumor cell killing.

MATERIALS AND METHODS

A bispecific antibody, BS001, which binds both c-Met and CD3, was generated using a novel BsAb platform. Western blotting and T cells-mediated killing assays were utilized to evaluate the BsAb's effects on cell proliferation, survival and signal transduction in tumor cells. Subcutaneous tumor mouse models were used to analyze the in vivo anti-tumor effects of the bispecific antibody and its combination therapy with PD-L1 antibody.

RESULTS

BS001 showed potent T-cell mediated tumor cells killing in vitro. Furthermore, BS001 inhibited phosphorylation of c-Met and downstream signal transduction in tumor cells. In A549 lung cancer xenograft model, BS001 inhibited tumor growth and increased the proportion of activated CD56+ tumor infiltrating lymphocytes. In vivo combination therapy of BS001 with Atezolizumab (an anti-programmed cell death protein1-ligand (PD-L1) antibody) showed more potent tumor inhibition than monotherapies. Similarly, in SKOV3 xenograft model, BS001 showed a significant efficacy in tumor growth inhibition and tumor recurrence was not observed in more than half of mice treated with a combination of BS001 and Pembrolizumab.

CONCLUSION

c-Met/CD3 bispecific antibody BS001 exhibited potent anti-tumor activities in vitro and in vivo, which was achieved through two distinguished mechanisms: through antibody-mediated tumor cell killing by T cells and through inhibition of c-Met signal transduction.

Exploiting antibody biology for the treatment of cancer

Over the last decade, antibodies have become an important component in the arsenal of cancer therapeutics. High-specificity, low off-target effects, desirable pharmacokinetics and high success rate are a few of the many attributes that make antibodies amenable for development as drugs. To design antibodies for successful clinical applications, however, it is critical to have an understanding of their structure, functions, mechanisms of action and pharmacokinetic/pharmacodynamic properties. This review highlights some of these key aspects, as well as certain limitations encountered, with monoclonal antibody therapy. Further, we discuss rational combination therapies for clinical applications, some of which could help overcome the limitations.

Activity of human serum antibodies in an influenza virus hemagglutinin stalk-based ADCC reporter assay correlates with activity in a CD107a degranulation assay

The stalk of the influenza virus hemagglutinin (HA) is an attractive target for antibody-based universal influenza virus vaccine development. While antibodies that target this part of the virus can be neutralizing, it has been shown in recent years that Fc receptor-mediated effector functions are of significant importance for the protective effect of anti-stalk antibodies. Several assays to measure Fc-Fc receptor interaction-based effector functions like antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis exist, but they suffer from limitations such as low throughput and high run-to-run variability. Reporter assays for antibody-dependent cellular cytotoxicity based on reporter cells that express luciferase upon engagement of human FcγRIIIa with the Fc of antigen-bound antibodies have been developed as well. These reporter assays can be used in a higher throughput setting with limited run-to-run assay variability but since they express only one Fc receptor, their biological relevance is unclear. Here we optimized an antibody-dependent cellular cytotoxicity reporter assay to measure the activity of antibodies to the conserved stalk domain of H1 hemagglutinin. The assay was then correlated to a CD107a-based degranulation assay, and a strong and significant correlation could be observed. This data suggests that the FcγRIIIa-based reporter assay is a good substitute for functional assays, especially in settings where larger sample numbers need to be analyzed.

T-Cell Engagers Based Bioassay for Evaluation of PD-1/PD-L1 Inhibitors Activity

PD-1/PD-L1-based therapy has been named a revolution in cancer treatment. By the end of 2018, more than 100 anti-PD-1 and anti-PD-L1 antibodies were in various stages of development, and more than 2000 clinical trials with their use have been registered. Characterization of such antibodies requires a bioassay to determine their biological activity. In this study, we developed a cell-based bioassay for analyzing the activity of anti-PD-1 and anti-PD-L1 antibodies. We chose reporter system consisting of two cell lines and compared several approaches for activation of effector cell line based on superantigens, soluble anti-CD3 antibodies, transmembrane anti-CD3 antibodies, chimeric antigenic receptors (CARs) and bispecific T-cell engager antibodies. The bispecific T-cell engager antibodies offer several advantages over the other approaches. We characterized the bioassay and demonstrated its applicability for analyzing the activity of anti-PD-1 and anti-PD-L1 antibodies. The proposed bioassay can be useful in the development of new therapeutic agents and methods for their characterization.

Assessing Analytical and Functional Similarity of Proposed Amgen Biosimilar ABP 980 to Trastuzumab

Background

ABP 980 has been developed as a biosimilar to Herceptin^® (trastuzumab). Comprehensive analytical characterization incorporating orthogonal analytical techniques was used to compare ABP 980 to trastuzumab reference products sourced from the United States (US) and the European Union (EU).

Methods

Physicochemical property comparisons included the following: primary structure related to amino acid sequence and post-translational modifications, including glycans; higher-order structure; product-related substances and impurities, including size and charge variants; subvisible and submicron particles, and protein content. In addition, functional similarity was assessed for Fab-mediated, Fc-mediated, and combined Fab- and Fc-mediated activities.

Results

ABP 980 has the same amino acid sequence as and similar post-translational modification profiles to trastuzumab (US) and trastuzumab (EU). Importantly, ABP 980 was found to be highly similar to trastuzumab for all functional activities related to the mechanism(s) of action. Higher-order structure, product-related substances and impurities, particles and aggregates were also highly similar between ABP 980 and trastuzumab. Where minor differences were noted, they were evaluated and found unlikely to impact clinical performance. The totality of evidence, including the pharmacokinetic clinical similarity of ABP 980, further supports that ABP 980 is highly similar to trastuzumab.

Conclusion

Based on the comprehensive analytical similarity assessment, ABP 980 is analytically highly similar to the reference product, trastuzumab.

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.

Chimeric Antigen Receptor Expressing Natural Killer Cells for the Immunotherapy of Cancer

Adoptive cell therapy has emerged as a powerful treatment for advanced cancers resistant to conventional agents. Most notable are the remarkable responses seen in patients receiving autologous CD19-redirected chimeric antigen receptor (CAR) T cells for the treatment of B lymphoid malignancies; however, the generation of autologous products for each patient is logistically cumbersome and has restricted widespread clinical use. A banked allogeneic product has the potential to overcome these limitations, yet allogeneic T-cells (even if human leukocyte antigen-matched) carry a major risk of graft-versus-host disease (GVHD). Natural killer (NK) cells are bone marrow-derived innate lymphocytes that can eliminate tumors directly, with their activity governed by the integration of signals from activating and inhibitory receptors and from cytokines including IL-15, IL-12, and IL-18. NK cells do not cause GVHD or other alloimmune or autoimmune toxicities and thus, can provide a potential source of allogeneic “off-the-shelf” cellular therapy, mediating major anti-tumor effects without inducing potentially lethal alloreactivity such as GVHD. Given the multiple unique advantages of NK cells, researchers are now exploring the use of CAR-engineered NK cells for the treatment of various hematological and non-hematological malignancies. Herein, we review preclinical data on the development of CAR-NK cells, advantages, disadvantages, and current obstacles to their clinical use.

An improved method to quantify human NK cell-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) per IgG FcR-positive NK cell without purification of NK cells

Natural killer (NK) lymphocyte ADCC supports anti-viral protection and monoclonal antibody (mAb) anti-tumor therapies. To predict in vivo ADCC therapeutic responses of different individuals, measurement of both ADCC cellular lytic capacity and their NK cellular receptor recognition of antibodies on 'target' cells are needed, using clinically available amounts of blood. Twenty ml of blood provides sufficient peripheral blood mononuclear cells (PBMCs) for the new assay for lytic capacity described here and for an antibody EC₅₀ assay for Fc-receptor recognition. For the lytic capacity assay, we employed flow cytometry to quantify the CD16A IgG Fc-receptor positive NK effector cells from PBMCs to avoid loss of NKs during isolation. Targets were ⁵¹Cr-labeled Daudi B cells pretreated with excess obinutuzumab type 2 anti-CD20 mAb and washed; remaining free mAb was insufficient to convert B cells in the PBMCs into 'targets'. We calculated: the percentage Daudis killed at a 1:1 ratio of CD16A-positive NK cells to Daudis (CX1:1); lytic slopes; and ADCC₅₀ lytic units. Among 27 donors, we detected wide ranges in CX1:1 (16-73% targets killed) and in lytic slopes. Slope variations prevented application of lytic units. We recommend CX1:1 to compare individuals' ADCC capacity. CX1:1 was similar for purified NK cells vs. PBMCs and independent of CD16A V & F genotypes and antibody EC₅₀s. With high mAb bound onto targets and the high affinity of obinutuzumab Fc for CD16A, CX1:1 measurements discern ADCC lytic capacity rather than antibody recognition. This assay allows ADCC to be quantified without NK cell isolation and avoids distortion associated with lytic units.

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.

NK-92 cell, another ideal carrier for chimeric antigen receptor

The remarkable clinical outcomes of the treatment for B-cell malignancies through the application of CD19 chimeric antigen receptor T (CAR-T) cells have made adoptive immunotherapy with genetically modified immune effector cells a hotspot in the field of antitumor. However, numerous toxicities of CAR-T cells have been identified. Thus, some studies have resorted to another cytotoxic cell, NK-92 cell, to reach for better efficacy with minimal toxicity. Preclinical studies have confirmed the safety and feasibility of the genetically modified NK-92 cells with highly specific cytotoxicity in vitro and in vivo. Therefore, it is expected that NK-92 cell becomes another ideal carrier for CAR for its unique advantages over primary NK cells, parental NK-92 cells and autologous T cells.

Surrogate CD16-expressing effector cell lines for determining the bioactivity of therapeutic monoclonal antibodies

Traditional antibody dependent cellular cytotoxicity (ADCC) assays use donor derived natural killer (NK) or peripheral blood mononuclear cells, but donor genetic variability and the technically challenging nature of the assay means that alternative in vitro assay formats are required. We explored the utility of two reporter gene cell lines, the J2 and J9, as surrogate effector cells for ADCC assays. Both express the ADCC relevant Fcγ receptor CD16, crosslinking of which leads to firefly luciferase expression. For anti-CD20 rituximab and anti-HER2 trastuzumab (both IgG1 monoclonal antibodies, mAbs) a dose dependent firefly luciferase response was observed exclusively in the presence of their respective targets, representing the molecular interaction which potentiates ADCC activity. Importantly, both surrogate effector and NK cell based assays gave statistically similar values for rituximab ADCC activity. Increased engagement with target cell bound mAbs was determined to be cytotoxic for the J2 and J9 cell lines at the assay end point (at which luciferase expression is measured). However, use of the J9 cells containing the constitutively expressed renilla luciferase gene enabled data normalisation and corrected for fluctuations in both cell number and viability providing an advantage over currently available surrogate effector cell-lines. Abrogated ADCC activity with IgG4 mAbs, but enhanced activity with an IgG1 non-fucosylated mAb, was seen with the J9 cell line, as expected. Additionally, two rituximab products (biosimilars in development) with similar binding by flow cytometry, N-glycan profiles using HPLC and CD16 binding by surface plasmon resonance showed comparable ADCC activity to Mabthera. The ADCC activity of another anti-CD20 mAb, ofatumumab, reported only with primary cell based assays to date was also measured. This is the first report of a dual reporter gene based ADCC assay.