Recommendations for the validation of immunoassays used for detection of host antibodies against biotechnology products

MB09, a denosumab biosimilar candidate: Biosimilarity demonstration in a phase I study in healthy subjects

This was a Phase I, randomized, double-blinded, three-arm, single-dose, parallel study aimed to demonstrate pharmacokinetic (PK) similarity between MB09 (a denosumab biosimilar candidate) and reference denosumab (XGEVA® from European Union [EU-reference] and United States [US-reference]) in a healthy male population. The primary PK endpoints included: Area under the serum concentration versus time curve from time 0 to the last quantifiable concentration timepoint (AUC0-last); and maximum observed serum concentration (Cmax). Secondary endpoints included: AUC from time 0 extrapolated to infinity (AUC0-∞), time to reach maximum observed concentration, clearance, terminal phase half-life, pharmacodynamic, safety, and immunogenicity assessments. A total of 255 subjects were randomized (1:1:1) to receive a subcutaneous 35 mg dose of MB09 or reference denosumab. Cmax was reached after denosumab administration, followed by a decline in the concentration with similar terminal phase half-live across treatment arms. Systemic exposure of MB09 (AUC0-last and Cmax) was equivalent to the reference denosumab, as the 90% confidence intervals around the geometric least square mean ratios laid within the predefined acceptance limits (80.00%, 125.00%) across all comparisons. Pharmacodynamic parameters, based on the percent of change from baseline in serum C-terminal telopeptide of Type 1 collagen levels, were similar across the three arms. The treatments were considered safe and generally well tolerated, with 92 treatment-emergent adverse events reported (most Grade 2 and 3) and similarly distributed. Immunogenicity was low and similarly distributed. These results provide strong evidence that supports the biosimilarity between MB09 and denosumab reference products.

Re-thinking the current paradigm for clinical immunogenicity assessment: an update from the discussion in the European Bioanalysis Forum

Immunogenicity regulatory guidance and industry recommendations have evolved over the last two decades since unexpected immune reactions were first reported with erythropoietin. Since then, the guidelines and practices for immunogenicity have stemmed from a reaction to a high-risk molecule causing significant clinical impact. Similar thinking is often applied to all biotherapeutic drugs, even when a well-defined risk assessment suggests otherwise. In recent years, the current testing paradigm for immunogenicity has been challenged with more informative approaches being proposed. In a Focus Workshop held by the European Bioanalysis Forum in September 2023, the current immunogenicity testing paradigm was challenged based on the experience and learning of 20+ years of immunogenicity strategies. The workshop recommendations proposed a new paradigm, challenging the value of multiple tiers depending on the immunogenicity risk assessment based on context of use and moving toward treating immunogenicity as a pharmacodynamic biomarker for the drug. Such rethinking ultimately results in the appropriate and efficient focusing of resources on immunogenicity testing strategies that benefit patients most, moving to a new paradigm where implementation of appropriate and truly informative immunogenicity testing strategies, depending on the context-of-use, become the norm .

The European Bioanalysis Forum recommendation on establishing appropriate drug tolerance levels in antidrug antibody assays

The European Bioanalysis Forum, in collaboration with several key industry stakeholders, has recently led discussions that address international immunogenicity guidance documents, specifically the three tier approach for immunogenicity testing strategies, after more than 20 years of experience with biotherapeutics. As part of this, the strategy and methods used to assess drug tolerance across all immunogenicity assays are challenged, emphasizing that bioanalytical scientists need to consider the context-of-use of each assay. Here, recommendations for drug tolerance assessments, driven by strong scientific rationale and subject to reevaluation as needed, are provided. This includes carefully considering the drug and positive control concentrations considered to be appropriate and which tiers are most relevant for performing drug tolerance assessments.

Evaluating the Performance of Two Automated Anti-drug Antibodies Assays for Infliximab and Adalimumab Without Acid Dissociation

Monitoring anti-drug antibodies (ADAs) to infliximab and adalimumab is critical to treatment management in various autoimmune disorders. The growing need for proactive therapeutic monitoring further requires the detection of ADAs in the presence of measurable concentrations of infliximab or adalimumab. To provide robust analytical assays for clinical application, we evaluated two automated immunoassays developed using ImmunoCAP™ technology and based on the bridging format to measure serum ADAs to infliximab and adalimumab respectively. Without an acid-dissociation step, these research prototype assays can detect a positive control monoclonal ADA towards infliximab and adalimumab, ranging from < 25 ng/ml to 10,000 ng/mL. Both assays exhibit imprecision less than 20% at different ADA titer levels and can distinguish ADAs towards different drug targets. In method comparison using authentic patient samples, the quantitative results of the ADA assays are not directly comparable to two existing clinical immunoassays for ADAs (correlation coefficient rs = 0.673 for infliximab ADAs; rs = 0.510 for adalimumab ADAs), presumably due to the lack of commutable ADA standards and the polyclonal nature of ADAs. Nevertheless, there is qualitative agreement between the methods when evaluating putative positive and negative patient samples (overall agreement 0.83 for infliximab ADAs; 0.76 for adalimumab ADAs). Biotin and high levels of rheumatoid factors may interfere with the performance of the automated assays due to competitive binding with the biotinylated drug and non-specific formation of bridging complexes. The two ImmunoCAP assays can provide new analytical methods for proactive therapeutic monitoring of adalimumab and infliximab.

Critical reagent considerations for immunogenicity assay development for bispecific biotherapeutic candidates

Aim: To demonstrate the importance of critical reagent characterization for immunogenicity assay development for multi-specific drugs using two case studies. Methods: Bridging anti-drug antibody (ADA) assay with acid-dissociated samples were used for both cases. Results: In the first case study, the unexpected interference in an ADA assay from clinical samples was identified; a model was created to replicate the issue, and an anti-target antibody was identified to mitigate the target interference. In the second case study, an issue due to non-specific binding of a domain-specific confirmatory reagent was identified, and various mitigation techniques were evaluated. Conclusion: A thorough characterization of the critical reagents helped identify the issues with these ADA case studies and provided strategies for resolving them.

Mitigating target interference challenges in bridging immunogenicity assay to detect anti-tocilizumab antibodies

Aim: An assay to detect anti-tocilizumab antibodies in the presence of high levels of circulating target and drug is needed for immunogenicity assessment in comparative clinical studies.Methods: An assay was developed and validated using a combination of blocking agents and dilutions to overcome target interference challenges.Results: No false-positive signal was detected in serum samples spiked with 350-500 ng/ml of IL-6 receptor. As low as 50 ng/ml of positive control antibodies could be detected in the presence of either 500 ng/ml of IL-6 or 250 μg/ml of the drug product. Assay also demonstrated high sensitivity, selectivity and precision.Conclusion: A robust, easy to perform immunogenicity assay was developed and validated for detecting anti-tocilizumab antibodies.

Neutralizing Antibody Sample Testing and Report Harmonization

Immunogenicity testing and characterization is an important part of understanding the immune response to administration of a protein therapeutic. Neutralizing antibody (NAb) assays are used to characterize a positive anti-drug antibody (ADA) response. Harmonization of reporting of NAb assay performance and results enables efficient communication and expedient review by industry and health authorities. Herein, a cross-industry group of NAb assay experts have harmonized NAb assay reporting recommendations and provided a bioanalytical report (BAR) submission editable template developed to facilitate agency filings. This document addresses key bioanalytical reporting gaps and provides a report structure for documenting clinical NAb assay performance and results. This publication focuses on the content and presentation of the NAb sample analysis report including essential elements such as the method, critical reagents and equipment, data analysis, study samples, and results. The interpretation of immunogenicity data, including the evaluation of the impact of NAb on safety, exposure, and efficacy, is out of scope of this publication.

Tolerability and Safety of Large-Volume Hyaluronidase-Facilitated Subcutaneous Immunoglobulin 10% Administered with or without Dose Ramp-Up: A Phase 1 Study in Healthy Participants

PURPOSE

Facilitated subcutaneous immunoglobulin (fSCIG; immune globulin infusion 10% [human] with recombinant human hyaluronidase [rHuPH20]) permits high-volume subcutaneous immunoglobulin (SCIG) infusion, shorter infusion times and reduced dosing frequency relative to conventional SCIG. It is initiated by gradually increasing infusion volumes over time (dose ramp-up) to achieve target dose level (TDL). Whether ramp-up strategies have tolerability or safety advantages over direct initiation at full TDL has not been evaluated clinically.

METHODS

This phase 1 open-label study assessed tolerability and safety of fSCIG 10% with accelerated or no ramp-up compared with conventional ramp-up in healthy adults (NCT04578535). Participants were assigned to one of the three ramp-up arms to achieve TDLs of 0.4 or 1.0 g/kg/infusion. The primary endpoint was the proportion of infusions completed without interruption or infusion rate reduction owing to treatment-emergent adverse events (TEAEs). Safety was assessed as a secondary endpoint.

RESULTS

Of 51 participants enrolled, 50 (98.0%) tolerated all fSCIG 10% infusions initiated (n = 174). Infusion rate was reduced in one participant owing to headache in the 0.4 g/kg/infusion conventional ramp-up arm. Study discontinuations were higher in the no ramp-up arm (70%) versus the conventional (0%) and accelerated (22%) arms at the 1.0 g/kg/infusion TDL. Safety outcomes did not substantially differ between treatment arms.

CONCLUSION

The favorable tolerability and safety profiles of fSCIG 10% in healthy participants support initiating treatment with fSCIG 10% with accelerated ramp-up at TDLs up to 1.0 g/kg. Data support no ramp-up at TDLs close to 0.4 g/kg but additional data are needed for higher doses.

Comprehensive domain-specific analysis and immunoglobulin G profiling of anti-factor VIII antibodies using a bead-based multiplex immunoassay

BACKGROUND

Antibodies against factor (F)VIII are a major complication in the treatment of patients with severe hemophilia A. The Nijmegen-Bethesda assay (NBA) is the gold standard for detection of neutralizing antibodies (inhibitors), whereas both inhibitors and nonneutralizing antibodies can be detected by immunoassays such as enzyme-linked immunosorbent assay (ELISA) and multiplex bead-based assays.

OBJECTIVES

Evaluation of an in-house Luminex bead-based assay (LumiTope) compared with a commercially available ELISA and NBA.

METHODS

The LumiTope method comprised full-length and B-domain-deleted FVIII as well as 9 purified FVIII single or multidomains. The respective proteins were coupled to magnetic beads to detect domain-specific immunoglobulin (IgG; IgG1-4) anti-FVIII antibodies in a large cohort of patients with hemophilia A with and without inhibitors.

RESULTS

Overall, LumiTope assay had a high sensitivity (94.9%) and specificity (91.2%), particularly in patients with low-titer inhibitors compared with ELISA (sensitivity of 72.2% vs 27.7%). IgG4 was the most abundant IgG subclass in NBA-positive patients. NBA-positive and -negative patients showed different domain profiles. Patients with genetic variants in the heavy chain predominantly exhibited antibodies specific to this chain, while those with a light-chain variant showed a more diverse distribution of antibody specificities. Patients with an intron 22 inversion resembled those with a light-chain defect, with a majority of antibodies targeting the light chain.

CONCLUSION

LumiTope assay provides a sensitive and specific method for not only detection but also domain specification of anti-FVIII-antibodies. Implementation of bead-based assays could improve antibody detection, profiling, and comparability of results and complement NBA.

Characterization of anti-drug antibody responses to the T-cell engaging bispecific antibody cibisatamab to understand the impact on exposure

An appropriately designed pharmacokinetic (PK) assay that is sensitive for anti-drug antibody (ADA) impact on relevant exposure is an alternative strategy to understand the neutralizing potential of ADAs. However, guidance on how to develop such PK assays and how to confirm the functional ADA impact on exposure is missing. Here, the PK assay of a T-cell-engaging bispecific antibody, cibisatamab, was developed based on its mechanism of action (MoA). Using critical monoclonal anti-idiotypic (anti-ID) antibody positive controls as ADA surrogates, the impact on exposure was evaluated pre-clinically. In a phase I clinical trial (NCT02324257), initial data suggest that the combination of ADA and PK assays for correlation of the ADA response with cibisatamab exposure. To understand the neutralizing potential of patient-derived ADAs on drug activity, advanced ADA characterization has been performed. Structural binding analysis of ADAs to antibody domains of the drug and its impact on targeting were assessed. For this purpose, relevant patient ADA binding features were identified and compared with the specific monoclonal anti-ID antibody-positive controls. Comparable results of target binding inhibition and similar impacts on exposure suggest that the observed reduction of Cmax and Ctrough levels in patients is caused by the neutralizing potential of ADAs and allows a correlation between ADA response and loss of exposure. Therefore, the described study provides important functional aspects for the development of an appropriately designed PK assay for bispecific antibodies as an alternative option towards understanding the neutralizing ADA impact on exposure.

Implementation of a Three-Way Comparability Assessment for a Bioanalytical Anti-Drug Antibody Method

Immunogenicity evaluation is a critical part of drug development. Regulatory guidelines from multiple health agencies provide recommendations for the development and validation of anti-drug antibody (ADA) assays to assess immunogenicity in clinical trials. These recommendations primarily describe an ADA method run in one bioanalytical laboratory supporting a biotherapeutic molecule; however, there are increasing instances that may necessitate the support of the ADA method being run in more than one laboratory. A program can rapidly expand into multiple clinical studies within one or multiple countries, where the most appropriate way to support the program is by having multiple laboratories perform ADA sample analysis. In addition, there may be certain country-specific challenges that may make it infeasible to transport samples outside of the country for analysis. China for example has a lengthy sample exportation process that has potential to negatively impact study timelines. If multiple laboratories analyze samples using the same ADA method, comparable method performance should be established. Here, we describe a three-way assessment of ADA assay comparability between two US-based bioanalytical laboratories and one based in China.

Eliminating drug target interference with specific antibody or its F(ab')2 fragment in the bridging immunogenicity assay

Background: DB-1003 is a humanized anti-IgE monoclonal antibody with higher affinity than omalizumab. In the affinity capture elution (ACE)-based bridging electrochemiluminescent immunoassay (ECLIA) for antibodies to DB-1003, monkey serum IgE caused false-positive results. Materials & methods: The target-specific antibody or its F(ab')2 fragment was used to mitigate drug target interference in an ACE-based bridging ECLIA for the detection of anti-DB-1003 antibodies. Results: The sensitivity of the developed assay was at least 100 ng/ml. When the anti-drug antibody concentration was 250 ng/ml, the assay tolerated at least 20.0 μg/ml of the monkey IgE. Conclusion: Incorporating the target-specific antibody or its F(ab')2 fragment can overcome the interference from monkey serum IgE in ACE-based bridging ECLIA for anti-DB-1003 antibody detection.

2023 White Paper on Recent Issues in Bioanalysis: ISR for ADA Assays, the Rise of dPCR vs qPCR, International Reference Standards for Vaccine Assays, Anti-AAV TAb Post-Dose Assessment, NanoString Validation, ELISpot as Gold Standard (Part 3 - Recommendations on Gene Therapy, Cell Therapy, Vaccines Immunogenicity & Technologies; Biotherapeutics Immunogenicity & Risk Assessment; ADA/NAb Assay/Reporting Harmonization)

The 17th Workshop on Recent Issues in Bioanalysis (17th WRIB) took place in Orlando, FL, USA on June 19-23, 2023. Over 1000 professionals representing pharma/biotech companies, CROs, and multiple regulatory agencies convened to actively discuss the most current topics of interest in bioanalysis. The 17th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week to allow an exhaustive and thorough coverage of all major issues in bioanalysis of biomarkers, immunogenicity, gene therapy, cell therapy and vaccines. Moreover, in-depth workshops on "EU IVDR 2017/746 Implementation and impact for the Global Biomarker Community: How to Comply with these NEW Regulations" and on "US FDA/OSIS Remote Regulatory Assessments (RRAs)" were the special features of the 17th edition. As in previous years, WRIB continued to gather a wide diversity of international, industry opinion leaders and regulatory authority experts working on both small and large molecules as well as gene, cell therapies and vaccines to facilitate sharing and discussions focused on improving quality, increasing regulatory compliance, and achieving scientific excellence on bioanalytical issues. This 2023 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2023 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations on Gene Therapy, Cell therapy, Vaccines and Biotherapeutics Immunogenicity. Part 1A (Mass Spectrometry Assays and Regulated Bioanalysis/BMV), P1B (Regulatory Inputs) and Part 2 (Biomarkers, IVD/CDx, LBA and Cell-Based Assays) are published in volume 16 of Bioanalysis, issues 8 and 9 (2024), respectively.

Development and Validation of a Cell-Based Binding Neutralizing Antibody Assay for an Antibody-Drug Conjugate

The utilization of antibody-drug conjugates (ADCs) has gained considerable attention in the field of targeted cancer therapy due to their ability to synergistically combine the specificity of monoclonal antibodies (mAbs) and the potency of small molecular drugs. However, the immunogenic nature of the antibody component within ADCs warrants the need for robust immunogenicity testing, including a neutralizing antibody (NAb) assay. Since the mechanism of action (MOA) of the ADC is to first bind to the target cells and then release the payload intracellularly to kill the cells, the most relevant NAb assay format would be a cell-based killing assay. However, in this paper, we present a case where a cell-based killing assay could not be developed after multiple cell lines and NAb-positive controls (PC) had been tested. Surprisingly, contrary to our expectations, all NAb PCs tested exhibited an increased killing effect on the target cells, instead of the expected protective response. This unexpected phenomenon most likely is due to the non-specific internalization of drug/NAb complexes via FcγRs, as an excessive amount of human IgG1 and mouse IgG2a, but not mouse IgG1, greatly inhibited drug or drug/NAb complexes induced cell death. To overcome this obstacle, we implemented a novel cell-based binding assay utilizing the Meso Scale Discovery (MSD) platform. We also propose that an in vitro cell killing NAb assay is limited to at best monitoring the target binding and internalization induced cell death, but not by-stander killing induced by prematurely released or dead-cell released payload, hence cannot really mimic the in vivo MOA of ADC.

Novel assay format for total anti-adeno-associated virus antibody detection with low capsid consumption and built-in specificity control

Aim: To develop an assay format for detection of total anti-adeno-associated virus 2 (AAV2) antibodies with low capsid material consumption. Methods: An immune complex (IC) assay format was developed. The format is based on the formation of ICs in solution and their subsequent detection using an anti-AAV2 antibody for capture and an antibody against the study species IgG for detection. Results: The feasibility of the IC assay for detection of preexisting and treatment-emergent anti-AAV2 antibodies was demonstrated in cynomolgus monkey and human serum samples, including samples from a preclinical study with AAV2-based therapies. Conclusion: The presented IC assay is an easy-to-perform total anti-AAV2 antibody assay that requires a small amount of unlabeled capsid material and provides an intrinsic specificity control.

Preexisting antibody assays for gene therapy: Considerations on patient selection cutoffs and companion diagnostic requirements

Recombinant adeno-associated virus (AAV) vectors are the leading delivery vehicle used for in vivo gene therapies. Anti-AAV antibodies (AAV Abs) can interact with the viral capsid component of an AAV-based gene therapy (GT). Therefore, patients with preexisting AAV Abs (seropositive patients) are often excluded from GT trials to prevent treatment of patients who are unlikely to benefit1 or may have a higher risk for adverse events outweighing treatment benefits. On the contrary, unnecessary exclusion of patients with high unmet medical need should be avoided. Instead, a risk-benefit assessment that weighs the potential risks due to seropositivity vs. severity of disease and available treatment options, should drive the decision if patient selection is required. Assays for patient selection must be validated according to their intended use following national regulations/standards for diagnostic assays in appropriate laboratories. In this review, we summarize the current process of patient selection, including assay cutoff criteria and related assay validation approaches. We further provide considerations on regulatory requirements for the development of in vitro diagnostic tests supporting market authorization of a corresponding GT.

Strategy and validation of a nonclinical generic plug-and-play antidrug antibody method for human monoclonal antibody biotherapeutics

The measurement of antidrug antibodies (ADA) in nonclinical studies provides limited value because the formation and incidence of nonclinical ADA does not translate to clinical experience. The formation and presence of ADA in nonclinical species can, however, correlate to reduced drug exposure and safety observations including vasculitis and immune complex disease. Generic ADA methods for humanized monoclonal antibody biotherapeutics mitigate the need to develop bespoke ADA methods during nonclinical drug development. A drug-tolerant, sensitive, generic ADA immunoassay has been developed and validated for measuring ADA in cynomolgus monkey serum samples, allowing for immediate qualification of future monoclonal antibody biotherapeutics. This approach allows us to differentiate complexed and free ADA in a rapidly deployable manner when needed.

Stability of anti-drug antibodies in human serum samples

Stability of anti-drug antibodies (ADAs) is important as ADA-analysis should be reliable over time at different storage conditions. Stability of anti-insulin antibodies in serum samples was assessed after short-term storage at different temperatures and after long-term storage at -20 °C. Correlation between measurements was tested and acceptance criteria for incurred sample reanalysis were applied. ADAs were stable after 72 h at 22 °C, after 2 weeks at 4 °C, and after 6.3 years at -20 °C. The study confirms that ADAs in serum are stable for several years at -20 °C and suggests that investigation of short- and long-term stability of ADAs is not needed if samples are handled at standard laboratory-conditions.

Successful Development of Nonclinical Anti-Drug Antibody Assays to Support Zinpentraxin Alfa Reproductive Toxicology Studies

Immunogenicity assessment is an essential part of biotherapeutic drug development. While the immune response in animals is not always representative of the human immune response, immunogenicity data obtained in animal models is still informative for the evaluation of drug exposure and safety. The most common assay format used for the detection of anti-drug antibodies (ADAs) in preclinical and clinical studies is the bridging format. The advantage of this method is that it can detect all antibody isotypes generated against the therapeutic. However, the method development can be time-consuming and labor-intensive, due to the need for labeling of the drug which is used both as capture and detection. Various generic ADA assays have been successfully implemented to overcome these disadvantages and to enable faster assay development timelines to support nonclinical toxicology studies. Here, we describe the challenges in the development of an assay to detect antibodies to zinpentraxin alfa, a recombinant human pentraxin-2, in rabbit and rat toxicology studies. Our initial efforts to develop a bridging assay failed, prompting us to develop a method adapted from generic assay formats to detect anti-zinpentraxin alfa antibodies in the serum of different species with minimal optimization. However, while the general assay format remained similar, assay reagents were adapted between the different species, resulting in the development of two distinct assays for the detection of ADAs in rat and rabbit. Here, we share the final development/validation data and the immunogenicity study results. Our work highlights the need for the evaluation of alternate assay formats when evaluating novel drug modalities.

Immunogenicity of Cemiplimab: Low Incidence of Antidrug Antibodies and Cut-Point Suitability Across Tumor Types

The immunogenicity of cemiplimab, a fully human immunoglobulin G4 monoclonal antibody directed against programmed cell death 1, was assessed in patients across multiple tumor types. The development of antidrug antibodies (ADAs) against cemiplimab was monitored using a validated bridging immunoassay. To identify ADA-positive samples in the assay, statistically determined cut points were established by analyzing baseline clinical study samples from a mixed population of different tumor types, and this validation cut point was used to assess immunogenicity in all subsequent studies. Regulatory guidance requires that ADA assay cut points be verified for appropriateness in different patient populations. Thus, for the cemiplimab ADA assay, we evaluated whether each new oncology population was comparable with the validation population used to set the cut point. Assay responses from 2393 individual serum samples from 8 different tumor types were compared with the validation population, using established statistical methods for cut-point determination and comparison, with no significant differences observed. Across tumor types, the immunogenicity of cemiplimab was low, with an overall treatment-emergent ADA incidence rate of 1.9% and 2.5% at intravenous dose regimens of 3 mg/kg every 2 weeks and 350 mg every 3 weeks, respectively. Moreover, no neutralizing antibodies to cemiplimab were detected in patients with ADA-positive samples, and there was no observed impact of cemiplimab ADAs on pharmacokinetics. Study-specific cut points may be required in some diseases, such as immune and inflammatory diseases; however, based on this analysis, in-study cut points are not required for each new oncology disease indication for cemiplimab.

Two-center validation of assays for the detection of binding and neutralizing anti-factor VIII antibodies

INTRODUCTION

Patients with hemophilia A treated with coagulation Factor VIII (FVIII) products are at risk for developing anti-FVIII antibodies. The ABIRISK Consortium aimed to provide knowledge on the formation and detection of anti-drug antibodies against biopharmaceutical products, including FVIII. Accordingly, standardized and validated assays for the detection of binding (total) and neutralizing antibodies are needed.

AIM

Two-center validation of an ELISA for the detection of total FVIII-binding IgG-antibodies and Nijmegen-Bethesda assays for the quantification of FVIII-neutralizing antibodies according to consensus validation guidelines.

METHODS

Validation of assays at both sites was done according to published recommendations and included preanalytics, the determination of key assay parameters, including cut-points, assay sensitivity, precision, and FVIII interference.

RESULTS

The validated assays reproducibly detected FVIII-binding and -neutralizing antibodies with comparable performance in both laboratories. Floating screening cut-points were established for both assays. Determined mass-based sensitivity of both assays (all values ≤66 ng/mL) complied with the minimum sensitivity for the detection of anti-drug antibodies as recommended by the FDA (<100 ng/mL). Intra- and inter-assay coefficients of variation did not exceed 25%. Assay validation further revealed that pre-analytical heat treatment led to potentially false-positive ELISA results, while up to 0.15 IU/mL, residual FVIII showed no significant impact. Overall, good agreement of results was found for patient samples analyzed at both study sites.

CONCLUSION

Comprehensive validation of different anti-FVIII-antibody assays in two laboratories gave novel insights into the impact of pre-analytical sample treatment as well as the comparability of test results generated by the use of methodically different assays.

Signal-to-noise ratio to assess magnitude, kinetics and impact on pharmacokinetics of the immune response to an adalimumab biosimilar

Background: The antidrug antibody (ADA) signal-to-noise (S/N) ratio was explored as a novel immunogenicity measure to evaluate the immune response of healthy subjects to a single dose of GP2017, an adalimumab biosimilar. Methodology/results: Bioanalytical methods used for the analysis of ADA S/N ratios and ADA titers were validated for sensitivity, precision and drug interference. ADA S/N ratios strongly correlated with ADA titers. Correlations between ADA area under the curve and ADAmax and pharmacokinetics (PK) were stronger for ADA S/N ratio than for ADA titers. Conclusion: ADA S/N ratio allowed for a more sensitive evaluation of the magnitude and kinetics of the immune response, was better correlated with adalimumab PK and was superior to ADA titers in assessing the impact of the immune response on PK.

A sensitive AAV transduction inhibition assay assists evaluation of critical factors for detection and concordance of pre-existing antibodies

Pre-existing antibodies to viral capsids may have a negative impact on the efficacy and safety of adeno-associated virus (AAV)-based gene therapies. Total antibody (TAb) and/or cell-based transduction inhibition (TI) assays have been used to exclude seropositive individuals in clinical studies. Published AAV seroprevalence and patient enrollment criteria regarding antibody status lack comparability between assay formats, hindering a direct cross-study comparison. To identify critical factors impacting TI assay detection of AAV neutralizing antibodies (NAbs), we created a reporter construct expressing NanoLuc® luciferase (Nluc) that enabled a more sensitive and robust detection of AAV6 NAbs than using firefly luciferase. Assessment of additional factors including multiplicity of infection, cell lines, viral production, and capsid purity revealed the reporter is the major determinant of assay sensitivity impacting NAb detection. The Nluc reporter was further used to assess seroprevalence to AAV5, 8, and 9. Last, we compared AAV6 Nluc TI with two TAb assay formats. A higher correlation of Nluc TI was observed with direct binding (90%) than with the more sensitive bridging TAb assay (65%), suggesting both assay sensitivity and TAb formats contribute to AAV seropositivity concordance. Our results support a need to standardize assay formats to ensure proper assessment of pre-existing AAV immunity.

Stability assessment of anti-bacterial antibodies in immunoglobulin G-depleted serum with validated immunoassays

Aim: To investigate the stability of the anti-pneumococcal (PCP) and anti-haemophilus type B (Hib) immunoglobulins (IgGs) in human IgG-depleted serum samples frozen at -20°C. Materials & methods: Modified commercially available immunoassays (ELISAs) were bioanalytically validated. These ELISAs were used to measure levels of the two anti-bacterial IgG in samples kept at -20°C for up to 15 months. Human IgG-depleted serum was spiked with GAMMAGARD Liquid to obtain those samples. Results: Both ELISAs passed the validation test. Anti-PCP IgG and anti-Hib IgG were shown to be stable for at least 15 months at -20°C. Conclusion: These data confirm the stability of anti-bacterial IgG in human IgG-depleted serum and support the common practice of testing frozen samples.

Modeling immunogenecity data to establish screening bioassays cut point

The response of immunogenecity anti-drug antibody (ADA) generally includes biological and analytical variability. The nature of biological and analytical variations may lead to a variety of symmetric and asymmetric ADA data. As a result, current statistical methods may yield unreliable results because these methods assume special types of symmetric or asymmetric ADA data. In this paper, we survey and compare parametric models that are useful for analyzing a variety of asymmetric data that have rarely been used to calculate assay cut points. These models include symmetric distributions as limiting case; therefore, they are useful in the analysis of a variety of symmetric data. We also investigate two nonparametric approaches that have received little attention in screening cut point calculations. A simulation study was conducted to compare the performance of the methods. We evaluate the methods using four published different types of data, and make recommendations concerning the use of the methods.

Cases of less-than-expected FVIII activity in previously treated patients during post-marketing surveillance of N8-GP

INTRODUCTION

Turoctocog alfa pegol (N8-GP) is a glycoPEGylated, extended half-life (EHL), human recombinant factor VIII (FVIII) approved for the treatment and prevention of bleeding episodes in patients with haemophilia A. Since its launch in August 2019, > 800 patients have been treated worldwide.

AIM

To present data from identified post-marketing cases of less-than-expected FVIII activity in previously treated patients (PTPs) without inhibitors after switching to N8-GP.

METHODS

The post-marketing safety database was searched using keywords such as 'coagulation FVIII level decreased'. Identified cases reported prior to 13 October 2021 were included in this report. Cases in which patients had FVIII inhibitors were excluded.

RESULTS

Here we report 14 cases of less-than-expected FVIII activity. Details varied greatly amongst the cases. At presentation, FVIII activity ranged from 1% (15 min post-dose) to 51% (2 days post-dose). Seven patients experienced bleeding episodes after switching to N8-GP with heterogeneity in bleeding presentations. Six out of seven patients who were tested for anti-PEG IgG and/or IgM antibodies were positive. In all known cases, FVIII activity returned to the expected range when switched to an alternative FVIII replacement product.

CONCLUSION

In conclusion, the 14 reported cases of less-than-expected FVIII activity, without presence of detectable FVIII inhibitors, presented with heterogenous characteristics, and wide variations in FVIII activity and anti-PEG antibody titre. FVIII activity returned to the expected range after switching to alternative FVIII products. In line with WFH guidelines, monitoring of FVIII activity can ensure FVIII activity in the expected range. The safety surveillance of N8-GP continues.

Evaluation of multiple immunoassay formats for detection of anti-drug antibodies to zinpentraxin alfa

Zinpentraxin alfa (rhPTX-2; PRM-151) is currently being developed for the treatment of fibrotic diseases such as idiopathic pulmonary fibrosis and myelofibrosis. Notably, because it is administered chronically and has an endogenously expressed counterpart, clinical studies of zinpentraxin alpha must include immunogenicity assessments. Since the typical homogenous bridging ELISA assay does not adequately measure anti-drug antibodies (ADAs) against zinpentraxin alfa, additional assay formats have been developed to evaluate immunogenicity of this therapeutic. Here, we present the evaluation of four distinct assay formats that were used to measure zinpentraxin alpha ADA: step-wise bridging, direct binding, total ADA, and the semi-homogeneous formats, based on multiple parameters including assay sensitivity, precision, and drug tolerance. This paper presents the full details of method development for each of the aforementioned assay formats including evaluation of sample pre-treatment, determination of cut point, and assessment of assay performance by analyzing a subset of clinical samples. Overall, the semi-homogenous ADA assay format with no sample pre-treatment was selected for the measurement of zinpentraxin alpha immunogenicity as it provided the desired sensitivity, drug tolerance, and reproducibility. Our study emphasizes the importance of assay format evaluation during drug development and the necessity to select the most suitable assay format and sample pre-treatment method by which to evaluate therapeutic drug immunogenicity.

Development and validation of an automated assay for anti-drug-antibodies in rat serum

The potential immunogenicity of therapeutic human and humanized monoclonal antibodies (mAb) is a significant concern, and so preclinical testing of therapeutic mAbs routinely includes assessment of anti-drug antibody (ADA) induction. Here, we report the development of automated screening and confirmatory bridging ELISAs for the detection of rat antibodies against DH1042, an engineered human mAb for the SARS-CoV-2 receptor-binding domain. The assays were evaluated for specificity, sensitivity, selectivity, absence of a prozone effect, linearity, intra- and inter- assay precision, and robustness, and found to be suitable for purpose. The assays were then used to evaluate anti-DH1042 antibodies in the sera of rats dosed with lipid-nanoparticle (LNP)-encapsulated mRNA encoding DH1042. Rats received two doses of 0.1, 0.4 or 0.6 mg/kg/dose LNP-mRNA 8 days apart. Twenty-one days after the second dose, 50-100% of rats had developed confirmed anti-DH1042 ADA depending on dose level. No animals in the control group developed anti-DH1042 ADA. These assays reflect new applications for a non-specialized laboratory automation platform, and the methodologies and approaches reported here provide a template that can be adapted for the automated detection and confirmation of ADA in preclinical testing of other biologics.

Validation of Anti-Adeno Associated Virus Serotype rh10 (AAVrh.10) Total and Neutralizing Antibody Immunogenicity Assays

Immunogenicity assessment of Adeno-Associated Virus (AAV) vectors is a critical part of gene therapy drug development. Whether the assays are used for inclusion/exclusion criteria or to monitor the safety and efficacy of the gene therapy, they are critical bioanalytical assessments. While total anti-AAV assays are perceived as easier to develop and implement than neutralizing anti-AAV assays, the gene therapy field is still nascent, and it is not yet clear which of the assays should be implemented at what stage of drug development. Recently AAVrh.10 has gained interest for use in gene therapies targeting cardiac, neurological, and other diseases due to its enhanced transduction efficiency. There is limited information on anti-AAVrh.10 antibodies and their clinical impact; thus, the information presented herein documents the validation of both a total antibody assay (TAb) and a neutralizing antibody (NAb) assay for anti-AAVrh.10 antibodies. In this manuscript, the validation was performed in accordance with the 2019 FDA immunogenicity guidance with additional evaluations to comply with CLIA where applicable. The AAVrh.10 TAb and NAb assays were compared in terms of sensitivity, drug tolerance, and precision, along with a concordance analysis using the same individual serum samples. This comparison gave insight into the utility of each format as a screening assay for inclusion into clinical studies.

A Monovalent Fab Affinity-Capture and Elution Bridging Immunoassay Overcomes Rheumatoid Factor Interference while Accurately Detecting Antidrug Antibodies

BACKGROUND

Rheumatoid factor (RF) consists of autoantibodies that bind the fragment crystallizable (Fc) region of human immunoglobulin G (IgG) and present in sera of rheumatoid arthritis (RA) patients. Immunoassays to detect antidrug antibodies (ADA) in RA patient samples may experience interference due to RF binding and crosslinking Fc regions of the capture and detection antibody reagents. To overcome this interference, a novel Fab affinity-capture and elution (ACE)-bridging immunoassay (Fab ACE-Bridge) was developed with monovalent-recombinant Fab to avoid RF interference.

METHODS

ACE and ACE-Bridge assays were developed to detect ADA against a therapeutic monoclonal antibody using samples from healthy donors, psoriasis patients, and RA patients. The performance of these assays was compared to a novel Fab ACE-Bridge assay, in which monoclonal antibody was replaced with monovalent Fab.

RESULTS

High screening signals in the ACE and ACE-Bridge assays were detected in RA patient samples but not in samples from healthy donors or psoriasis patients. The high screening signals in RA samples did not inhibit to the expected extent in the confirmatory assay, a consistent feature of false-positive screening results. Further investigation revealed RF as the interferent affecting assay performance. Modification of the ACE-Bridge assay by using monovalent Fab eliminated RF interference while allowing for sensitive and drug-tolerant detection of authentic ADA.

CONCLUSIONS

RF interfered significantly in traditional ACE and ACE-Bridge assays. Implementation of a novel monovalent Fab ACE-Bridge assay overcame RF interference. The use of monovalent Fab is recommended for immunogenicity assays when assessing ADA in RA patient samples.

Pharmacokinetic Similarity of ABP 654, an Ustekinumab Biosimilar Candidate: Results from a Randomized, Double-blind Study in Healthy Subjects

ABP 654 is a proposed biosimilar to ustekinumab reference product (RP) which works through antagonism of interleukin-12 and interleukin-23. Ustekinumab RP is used for the treatment of chronic inflammatory conditions, including some forms of plaque psoriasis, psoriatic arthritis, Crohn's disease, and ulcerative colitis. A randomized, double-blinded, single-dose, 3-arm, parallel-group study was conducted to assess the pharmacokinetic (PK) similarity of ABP 654 with ustekinumab RP sourced from the United States (US) and the European Union (EU); the PK similarity of ustekinumab US versus ustekinumab EU; and the comparative safety, tolerability, and immunogenicity of all 3 products. A total of 238 healthy subjects were randomized 1:1:1 and stratified by gender and ethnicity (Japanese versus non-Japanese) to receive a single 90 mg subcutaneous injection of ABP 654 or ustekinumab US or ustekinumab EU. PK similarity was established based on 90% confidence intervals (CIs) for the primary endpoints of area under the concentration-time curve from time 0 extrapolated to infinity (AUCinf ) and maximum observed serum concentration (Cmax ) being contained within the prespecified margin of 0.8-1.25. No clinically meaningful differences in immunogenicity were found among the 3 products. Adverse events were similar between treatment groups and consistent with the safety profile of ustekinumab RP. Results indicate that ABP 654, ustekinumab US and ustekinumab EU share similar PK and safety profiles.

Evolution of Antidrug Antibody Assays During the Development of Anti-Tissue Factor Pathway Inhibitor Monoclonal Antibody Marstacimab

Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of the extrinsic coagulation pathway. In patients with hemophilia A or B, inhibition of TFPI is an alternative therapeutic approach that augments the extrinsic coagulation pathway. Marstacimab is an investigational fully human monoclonal antibody that binds and neutralizes TFPI and is being evaluated as a prophylactic treatment to prevent or reduce the frequency of bleeding episodes in patients with severe hemophilia A or B, with or without inhibitors (antibodies against coagulation factors). However, the efficacy, safety, and pharmacokinetics of marstacimab may be affected by the induction of antidrug antibody (ADA) responses. Here, we describe the evolution and validation of three quasi-quantitative electrochemiluminescence-based methods to detect marstacimab ADAs, starting from their use in a first-in-human phase 1 study to their use in phase 2 and 3 clinical studies of patients with severe hemophilia. For all three methods, validation criteria evaluated the performance of the assays in screening and confirmatory cut points, precision, selectivity, drug tolerance, target interference, and stability. Additional criteria for validation were dilution linearity (Methods 1 and 2) and low positive control concentration, prozone effect, plate homogeneity, and robustness (Method 3). The three methods met validation criteria and are a potentially valuable tool in detecting the induction of marstacimab ADAs during treatment in patients with hemophilia.

Development of a Cell-based Neutralizing Antibody Assay for Zinpentraxin Alfa: Challenges and Mitigation Strategies

Therapeutic protein drugs can potentially induce immune responses in patients and result in the production of anti-drug antibodies (ADAs), including a subset of ADAs called neutralizing antibodies (NAbs) that might cause loss of efficacy by inhibiting clinical activities of the drug. Herein, we describe the unique challenges encountered during the development of a fit-for-purpose cell-based NAb assay for a new protein modality, zinpentraxin alfa, including our strategies for assay design to overcome various matrix interferences and improve assay drug tolerance. We demonstrated that a typical biotin-drug extraction with acid dissociation (BEAD) approach alone was not sufficient to eliminate matrix interferences in this assay. Instead, the combination of the BEAD and ZebaTM spin size exclusion plate (SEP) was required to achieve the desirable assay performance. We also demonstrated that appropriate acidic buffers were critical in sample pretreatment to improve assay drug tolerance, which not only dissociated the drug/NAb immune complex but also effectively and irreversibly denatured the free drug. The final assay performed well with confirmed assay robustness and suitability for the clinical applications.

Neutralizing Antibody Validation Testing and Reporting Harmonization

Evolving immunogenicity assay performance expectations and a lack of harmonized neutralizing antibody validation testing and reporting tools have resulted in significant time spent by health authorities and sponsors on resolving filing queries. A team of experts within the American Association of Pharmaceutical Scientists' Therapeutic Product Immunogenicity Community across industry and the Food and Drug Administration addressed challenges unique to cell-based and non-cell-based neutralizing antibody assays. Harmonization of validation expectations and data reporting will facilitate filings to health authorities and are described in this manuscript. This team provides validation testing and reporting strategies and tools for the following assessments: (1) format selection; (2) cut point; (3) assay acceptance criteria; (4) control precision; (5) sensitivity including positive control selection and performance tracking; (6) negative control selection; (7) selectivity/specificity including matrix interference, hemolysis, lipemia, bilirubin, concomitant medications, and structurally similar analytes; (8) drug tolerance; (9) target tolerance; (10) sample stability; and (11) assay robustness.

Aptamer-based sample purification for mass spectrometric quantification of trastuzumab in human serum

In this study, we developed a simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay to quantify trastuzumab in human serum using aptamers for sample purification. Trastuzumab was extracted from serum samples using the capture probe based on its aptamer CH1S-3, followed by reduction, alkylation, trypsin digestion, and quantification using LC-MS/MS. Additionally, a unique peptide, FTISADTSK, was employed as a surrogate peptide and quantified, and *FTISADTSK (¹³C₉¹⁵N-labeled phenylalanine) was used as an internal standard to minimize variability in detection among the samples. The detection range for this method was 0.5-250 μg/mL, with a high correlation coefficient (r² > 0.99). The intra- and inter-day precision (%CV, the coefficient of variation) of the quality control samples was less than 12.7%, and the accuracy (%bias) was below 8.64%. After optimization and verification, this assay was used to determine trastuzumab levels in clinical human serum samples. The results indicated that the trastuzumab concentrations had an approximate 4-fold difference among ten patients (range: 11.80-41.90 μg/mL). This study provides a novel approach for the accurate and quantitative monitoring of the mAb-trastuzumab.

Statistical Approaches for Establishing Appropriate Immunogenicity Assay Cut Points: Impact of Sample Distribution, Sample Size, and Outlier Removal

The statistical assessments needed to establish anti-drug antibody (ADA) assay cut points (CPs) can be challenging for bioanalytical scientists. Poorly established CPs that are too high could potentially miss treatment emergent ADA or, when set too low, result in detection of responses that may have no clinical relevance. We evaluated 16 validation CP datasets generated with ADA assays at Regeneron's bioanalytical laboratory and compared results obtained from different CP calculation tools. We systematically evaluated the impact of various factors on CP determination including biological and analytical variability, number of samples for capturing biological variability, outlier removal methods, and the use of parametric vs. non-parametric CP determination. In every study, biological factors were the major component of assay response variability, far outweighing the contribution from analytical variability. Non-parametric CP estimations resulted in screening positivity in drug-naïve samples closer to the targeted rate (5%) and were less impacted by skewness. Outlier removal using the boxplot method with an interquartile range (IQR) factor of 3.0 resulted in screening positivity close to the 5% targeted rate when applied to entire drug-naïve dataset. In silico analysis of CPs calculated using different sample sizes showed that using larger numbers of individuals resulted in CP estimates closer to the CP of the entire population, indicating a larger sample size (~ 150) for CP determination better represents the diversity of the study population. Finally, simpler CP calculations, such as the boxplot method performed in Excel, resulted in CPs similar to those determined using complex methods, such as random-effects ANOVA.

Comparison of Pre-existing Anti-AAV8 Total Antibody Screening and Confirmatory Assays with a Cell-Based Neutralizing Assay in Normal Human Serum

Pre-existing adeno-associated viruses (AAV) neutralizing antibodies (NAb) can prevent AAV vectors from transducing target tissues. The immune responses can include binding/total antibodies (TAb) and neutralizing antibodies (NAb). This study is aimed at comparing total antibody assay (TAb) and cell-based NAb assay against AAV8 to help inform the best assay format for patient exclusion criteria. We developed a chemiluminescence-based enzyme-linked immunosorbent assay to analyze AAV8 TAb in human serum. The specificity of AAV8 TAb was determined using a confirmatory assay. A COS-7-based assay was used to analyze anti-AAV8 NAbs. The TAb screening cut point factor was determined to be 2.65, and the confirmatory cut point (CCP) was 57.1%. The prevalence of AAV8 TAb in 84 normal subjects was 40%, of which 24% were NAb positive and 16% were NAb negative. All NAb-positive subjects were confirmed to be TAb-positive and also passed the CCP-positive criteria. All 16 NAb-negative subjects did not pass the CCP criterion for the positive specificity test. There was a high concordance between AAV8 TAb confirmatory assay and NAb assay. The confirmatory assay improved the specificity of the TAb screening test and confirmed neutralizing activity. We proposed a tiered assay approach, in which an anti-AAV8 screening assay should be followed by a confirmatory assay during pre-enrollment for patient exclusions for AAV8 gene therapy. This approach can be used in lieu of developing a NAb assay and can be also implemented as a companion diagnostic assay for post-marketing seroreactivity assessments due to ease of development and use.

The establishment of B cell-deficient Igh-J KO mouse model by gene editing and efficacy evaluation

Over the last few years, immunotherapy has made significant progress in treating various cancers with therapeutic antibodies. However, therapeutic antibodies have been validated for inducing an unintended immune response in human and animal models, which leads to the emergence of anti-drug antibodies (ADAs) and affects their effectiveness and safety. In preclinical research, ADAs production by B cells may accelerate antibody metabolism and result in missing potential candidate molecules. Thus, it is urgent to develop preclinical models that remove only B cells without affecting the function of T and NK cells. Rearrangement of immunoglobulin heavy chain J gene fragment (Igh-J) is the first link in B cell development, and immunotherapies are currently leaning toward combination treatments with PD-1/PD-L1 antibodies, here we created humanized PD-1, PD-L1 and Igh-J knockout (hPD-1/hPD-L1, Igh-J KO) mice and validated by using the reported high immunogenicity drug M7824 (a protein designed to simultaneously block PD-L1 and TGF-β pathways, poorly anti-tumor efficacy in immunocompetent mice). Phenotypic analysis revealed that human PD-1 and PD-L1 were detectable in hPD-1/hPD-L1, Igh-J KO mice, but not mouse IgM and IgD. Igh-J KO depleted B cells while increased the percentage of other immune cell types. Meanwhile, the humanization of PD-1/PD-L1 and Igh-J KO had neither effect on the overall development, differentiation, or distribution of T cell subtypes, nor on the activation of NK and T cells, indicating that mice can be used for T and NK-related immunotherapies. Furthermore, M7824 treatment of these B cell-deficient mice inhibited tumor growth significantly, with higher M7824 analog concentrations and lower ADA-positive rates. These findings demonstrate that Igh-J KO mice are an effective and stable preclinical model for testing drugs based on T and NK cells with high immunogenicity in vivo.

Donanemab Population Pharmacokinetics, Amyloid Plaque Reduction, and Safety in Participants with Alzheimer's Disease

Donanemab is an amyloid-targeting therapy that resulted in robust amyloid plaque reduction and slowed Alzheimer's disease (AD) progression compared with placebo in the phase II TRAILBLAZER-ALZ study (NCT03367403). The objectives of the current analyses are to characterize (i) the population pharmacokinetics of donanemab, (ii) the relationship between donanemab exposure and amyloid plaque reduction (response), and (iii) the relationship between donanemab exposure and amyloid-related imaging abnormalities with edema or effusions (ARIA-E). Model development included data from participants with mild cognitive impairment or mild to moderate dementia due to AD from the phase Ib study on donanemab (NCT02624778) and participants with early symptomatic AD from the TRAILBLAZER-ALZ study. The analysis showed donanemab has a terminal elimination half-life of 11.8 days. Body weight and antidrug antibody titer impact donanemab exposure but not the pharmacodynamic response. Maintaining a donanemab serum concentration above 4.43 μg/mL (95% confidence interval: 0.956, 10.4) is associated with amyloid plaque reduction. The time to achieve amyloid plaque clearance (amyloid plaque level < 24.1 Centiloids) varied depending on the baseline amyloid level, where higher baseline levels were associated with fewer participants achieving amyloid clearance. The majority of participants achieved amyloid clearance by 52 weeks on treatment. Apolipoprotein ε4 carriers, irrespective of donanemab serum exposure, were 4 times more likely than noncarriers to have an ARIA-E event by 24 weeks.

A method for detection of anti-drug antibodies to a biotherapeutic (CSL112) with endogenous counterpart (apolipoprotein A-I) using a novel sample pre-treatment electrochemiluminescence assay

BACKGROUND

There are numerous challenges encountered during clinical testing for an immunogenic response to a plasma-derived therapeutic. Distinguishing between antibodies that recognize endogenous versus therapeutic protein can be particularly difficult. This study focused on CSL112 (human plasma-derived apolipoprotein A-I; apoA-I), which is in clinical development for reducing the risk of recurrent major adverse cardiovascular events following acute myocardial infarction.

AIM

To develop and validate a high-throughput, highly sensitive and specific assay to detect antibodies to CSL112 that can be used for immunogenicity assessment in large clinical studies.

RESULTS

We developed a clinical anti-drug antibody (ADA) assay utilizing an immunoglobulin purification step that improved specificity and drug tolerance, demonstrating that measurement of pre-existing or treatment emergent ADAs was highly dependent on assay format. The Sample Pre-treatment Electrochemiluminescence (ECL; SPECL) assay incorporates a protein A extraction of serum samples before a bridging assay is performed on an ECL platform. The assay is qualitative, sensitive (lower limit of quantification <39 ng/mL) and has a drug tolerance of 0.5 mg/mL in line with U.S. Food and Drug Administration requirements for clinical immunogenicity assays for therapeutic proteins. Importantly, the SPECL assay demonstrated the absence of antibodies to both apoA-I and CSL112 both prior to drug exposure and after repeated dosing across multiple trials (n = 970 subjects).

CONCLUSION

The SPECL method has been validated and applied to support the CSL112 preclinical and clinical development program and has broader application to similar protein therapeutics. Attributes of the methodology include high drug tolerance, high sensitivity, selectivity, and precision. This format is amenable to automation providing the high throughput and reduced variability required to support large scale clinical studies that span extended time periods.

Clinical enrollment assay to detect preexisting neutralizing antibodies to AAV6 with demonstrated transgene expression in gene therapy trials

Recombinant adeno-associated virus (AAV) vectors are the leading platform for gene delivery for a variety of clinical applications. Patients with preexisting antibodies to AAV are currently excluded from most AAV gene therapy trials to avoid vector neutralization and ensure response to therapy. Anti-AAV neutralizing antibodies (NAbs) are typically assessed by in vitro cell-based transduction inhibition (TI) assays. However, clinical relevance of the determined enrollment cutoff and the inherent variability of a cell-based assay present challenges for use as an enrollment screening test. Here, we describe an enrollment cutoff that was clinically validated and strategies to overcome assay challenges to enable long-term stable performance. A validated anti-AAV6 cell-based TI assay was used to support clinical enrollment across multiple investigational gene therapies and to evaluate AAV6 seroprevalence in healthy and disease populations. The clinical enrollment cutoff was determined statistically using samples collected from healthy donors, applying a 0.1% false error rate with the inclusion of a minimum significant ratio (MSR) metric and in consideration of results from in vivo mouse passive transfer studies. Our strategy for long-term monitoring and control of assay performance employed plate quality control samples flanking the predefined cutoff. An approach using donor samples was implemented to bridge different lots of critical reagents without the need to redefine the cutoff.

Validation and the Determination of Antibody Bioactivity Using MILKSHAKE and Sundae Protocols

To develop reproducible results, it is critical that all reagents used in an experiment be validated in an alternative or independent method. We present two such independent methods for determining the specificity of antibodies: (1) "MILKSHAKE," which can be used to validate the liability and specificity of antibodies directed against post-translationally-modified epitopes, and (2) "Sundae," which is a more complete alanine-like scanning method that can be used to better understand the binding and bioactivity of specific residues of a protein. We apply both of these methods to the interaction between an antibody and its antigen.

Fit-for-purpose validation of a drug-tolerant immunogenicity assay for a human mAb drug in animal safety studies

A modified biotin-drug extraction and acid dissociation (BEAD) immunogenicity assay was developed to detect anti-drug-antibodies (ADA) against the human anti-FXIIa monoclonal antibody (mAb) drug, Garadacimab (previously called CSL312). Multiple strategies were tested to optimize the signal-to-background (S/B) ratio, assay sensitivity and the drug tolerance. The modified BEAD assay was found to be highly drug tolerant (>500 μg/ml) with a sensitivity of 100 ng/ml, in line with current FDA regulatory guidelines. The assay was validated for use in a repeat-dose animal safety study and showed an acceptable intra-assay precision and robustness but a lower inter-assay precision. In-study sample analysis confirmed that the assay was fit-for-purpose (FFP) for the context-of-use (COU) in the nonclinical study and the results obtained were deemed meaningful.

An electrochemiluminescence assay for quantification of Denileukin Diftitox and its anti-drug antibodies in rat serum

Denileukin Diftitox (DD), comprising fragments of diphtheria toxin (DT) and interleukin-2 (IL2), was developed for the treatment of lymphoma and has been approved for marketing in Japan. Toxicological evaluation including pharmacokinetics and immunogenicity in preclinical animals is important for drug development and thus the assays of DD and anti-drug antibody (ADA) were developed by electrochemiluminescence (ECL) detection. For the DD assay, ruthenium-labeled anti-DT Ab and biotinylated anti-IL2 Ab were mixed with serum samples and the mixture was captured by streptavidin-coated wells for ECL detection. For the ADA assay, signals of immuno-complex of biotinylated DD, ruthenium-labeled DD, and ADA, bound to streptavidin plate were determined. DD was quantifiable from 10 ng/mL. Accuracy and precision of quality control samples were within ±20% and 20%, respectively, and stability of DD in rat serum was successfully assessed. Precision of positive control samples of ADA was within the acceptance criteria and cut point values for ADA detection in the screening and confirmatory assay were determined by statistical analysis. Drug-induced ADA was detected by screening assay followed by confirmatory assay. The developed method was successfully applied to assess pharmacokinetics and immunogenicity to support toxicity studies in rats.

Affinity Capture Elution (ACE) ELISA Method Development and Validation for Novel RPH-104 Drug Immunogenicity Evaluation

As the number of therapeutic protein products is growing rapidly, there is a strong need for the development of bioanalytical methods that are easy to perform, specific, sensitive, robust, and affordable. Methods for immunogenicity evaluation of therapeutic proteins take an important place in this field of bioanalytics. The aim of the study was to develop a method for immunogenicity testing of the novel RPH-104 drug using the Affinity Capture Elution (ACE) ELISA technique. RPH-104 is a promising Interleukin-1 (IL-1) inhibitor that is currently undergoing a series of clinical studies, including those on socially significant and orphan diseases. The developed method was validated for assay cut-point, sensitivity, selectivity, drug tolerance, hook effect, specificity, precision, and stability. Method sensitivity was established at 114.9 ng/mL, while low and high positive controls were equal to anti-RPH-104 antibody concentrations of 155 ng/mL and 2500 ng/mL, respectively. Method specificity was confirmed in the presence of the interfering compounds, namely IL-1α, IL-1β, and IL1-Ra. The developed and validated ELISA method was successfully applied to subject samples.

Anti-drug Antibody Sample Testing and Reporting Harmonization

A clear scientific and operational need exists for harmonized bioanalytical immunogenicity study reporting to facilitate communication of immunogenicity findings and expedient review by industry and health authorities. To address these key bioanalytical reporting gaps and provide a report structure for documenting immunogenicity results, this cross-industry group was formed to establish harmonized recommendations and a develop a submission template to facilitate agency filings. Provided here are recommendations for reporting clinical anti-drug antibody (ADA) assay results using ligand-binding assay technologies. This publication describes the essential bioanalytical report (BAR) elements such as the method, critical reagents and equipment, study samples, results, and data analysis, and provides a template for a suggested structure for the ADA BAR. This publication focuses on the content and presentation of the bioanalytical ADA sample analysis report. The interpretation of immunogenicity data, including the evaluation of the impact of ADA on safety, exposure, and efficacy, is out of scope of this publication.

A Randomized, Double-Blind, Parallel Controlled, Single-Dose Phase I Study Comparing the Pharmacokinetics, Safety, and Immunogenicity of the Infliximab Biosimilar CMAB008 and the Reference Product in Healthy Chinese Male Subjects

This study aimed to evaluate the pharmacokinetics (PK), safety, and immunogenicity of the infliximab biosimilar CMAB008 compared to the reference product (Remicade) in healthy Chinese male subjects to provide the basis for the similarity evaluation of the 2 drugs. In this phase I randomized, double-blind, parallel-controlled, single-dose study, a total of 90 subjects were randomized 1:1 to receive CMAB008 or infliximab reference product with single intravenous injections (5 mg/kg). Blood samples were collected at designed time points for PK and immunogenicity assessment. If the 90%CI of the geometric mean ratio of area under the plasma concentration-time curve from 0 to the time of the last observation, maximum observed plasma concentration, area under the plasma concentration-time curve from 0 to infinity was completely within the range of 80% to 125%, the PK bioequivalence was established. Other PK parameters including time to maximum plasma concentration_, half-life time, clearance, apparent volume of distribution, and last measurable concentration time point were also assessed. Adverse events (AEs) were recorded. Serum concentration-time profiles were similar across the 2 groups, and PK parameters were comparable in the 2 groups. The 90%CI of the geometric mean ratio of test to reference was within the predefined bioequivalence range of 80% to 125%. The AEs occurred similarly in 2 groups. One serious AE (rhabdomyolysis, grade 3) occurred in the test group. The total positive rates of antidrug antibody and neutralizing antibodies in the test group (85.7% and 5.6%, respectively) were numerically lower than infliximab reference product group (90.9% and 15%, respectively). The PK profile of the 2 groups is statistically equivalent. The preliminary safety and immunogenicity evaluation of the 2 drugs are comparable.

Pre-existing Reactivity to an IgG4 Fc-Epitope: Characterization and Mitigation of Interference in a Bridging Anti-drug Antibody Assay

Twenty percent of baseline patient samples exhibited a pre-existing response in a bridging anti-drug antibody (ADA) assay for a human IgG4 monoclonal antibody (mAb) therapeutic. In some cases, assay signals were more than 100-fold higher than background, potentially confounding detection of true treatment-emergent ADA responses. The pre-existing reactivity was mapped by competitive inhibition experiments using recombinant proteins or chimeric human mAbs with IgG4 heavy chain regions swapped for IgG1 sequences. These experiments demonstrated that the majority of the samples had reactivity to an epitope containing leucine 445 in the CH3 domain of human IgG4. The pre-existing reactivity in baseline patient samples was mitigated by replacing the ADA assay capture reagent with a version of the drug containing a wild type IgG1 proline substitution at residue 445 without impacting detection of drug-specific, treatment-emergent ADA. Finally, purification on Protein G or anti-human IgG (H + L) columns indicated the pre-existing response was likely due to immunoglobulins in patient samples.

Graphical abstract