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.

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.

2022 White Paper on Recent Issues in Bioanalysis: FDA Draft Guidance on Immunogenicity Information in Prescription Drug Labeling, LNP & Viral Vectors Therapeutics/Vaccines Immunogenicity, Prolongation Effect, ADA Affinity, Risk-based Approaches, NGS, qPCR, ddPCR Assays (Part 3 - Recommendations on Gene Therapy, Cell Therapy, Vaccines Immunogenicity & Technologies; Immunogenicity & Risk Assessment of Biotherapeutics and Novel Modalities; NAb Assays Integrated Approach)

The 2022 16th Workshop on Recent Issues in Bioanalysis (WRIB) took place in Atlanta, GA, USA on September 26-30, 2022. 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 16th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy, cell therapy and vaccines. Moreover, in-depth workshops on ICH M10 BMV final guideline (focused on this guideline training, interpretation, adoption and transition); mass spectrometry innovation (focused on novel technologies, novel modalities, and novel challenges); and flow cytometry bioanalysis (rising of the 3rd most common/important technology in bioanalytical labs) were the special features of the 16th 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 2022 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 2022 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 1 (Mass Spectrometry and ICH M10) and Part 2 (LBA, Biomarkers/CDx and Cytometry) are published in volume 15 of Bioanalysis, issues 16 and 15 (2023), respectively.

Evaluation of Cellular Immune Response to Adeno-Associated Virus-Based Gene Therapy

The number of approved or investigational late phase viral vector gene therapies (GTx) has been rapidly growing. The adeno-associated virus vector (AAV) technology continues to be the most used GTx platform of choice. The presence of pre-existing anti-AAV immunity has been firmly established and is broadly viewed as a potential deterrent for successful AAV transduction with a possibility of negative impact on clinical efficacy and a connection to adverse events. Recommendations for the evaluation of humoral, including neutralizing and total antibody based, anti-AAV immune response have been presented elsewhere. This manuscript aims to cover considerations related to the assessment of anti-AAV cellular immune response, including review of correlations between humoral and cellular responses, potential value of cellular immunogenicity assessment, and commonly used analytical methodologies and parameters critical for monitoring assay performance. This manuscript was authored by a group of scientists involved in GTx development who represent several pharma and contract research organizations. It is our intent to provide recommendations and guidance to the industry sponsors, academic laboratories, and regulatory agencies working on AAV-based GTx viral vector modalities with the goal of achieving a more consistent approach to anti-AAV cellular immune response assessment.

Determination of Anti-drug Antibody Affinity in Clinical Study Samples Provides a Tool for Evaluation of Immune Response Maturation

Characterization of clinical anti-drug antibody (ADA) responses to biotherapeutics can be important to understanding the consequences of immunogenicity. ADA are expected to be polyclonal, with composition and affinities that evolve over time. Measuring ADA binding affinity can be complicated by the polyclonal nature of response, residual drug in sample, and low ADA levels. We developed a novel workflow to determine the apparent ADA affinity (K_D) against a monoclonal antibody biotherapeutic, PF-06480605. An affinity capture elution pre-treatment step was used to isolate ADA and remove residual drug interference from samples. Solution-phase equilibrium incubation was performed using drug and sample ADA as variable and fixed binding interactants, respectively. Unbound ADA concentration was measured using a Singulex Erenna ligand-binding assay (LBA) method. Apparent ADA K_D values were calculated using a custom R Shiny algorithm. K_D values determined for ADA positive samples showed good correlation with other immunogenicity parameters, including titers and neutralizing antibody (NAb) activity with a general increase in affinity over time, indicative of a maturing immune response. Time of onset of high affinity responses (K_D < 100 pM) varied between patients, ranging from 16 to 24 weeks. Antibody responses appeared monophasic at earlier time points, trending towards a biphasic response with a variable transition time and general increase in proportion of high affinity ADA over time. Herein, we provide a novel, sensitive bioanalytical method to determine the K_D of ADA in clinical samples. The observed decrease in ADA K_D is consistent with evidence of a maturing immune response.

When to Extend Monitoring of Anti-drug Antibodies for High-risk Biotherapeutics in Clinical Trials: an Opinion from the European Immunogenicity Platform

The determination of a tailored anti-drug antibody (ADA) testing strategy is based on the immunogenicity risk assessment to allow a correlation of ADAs with changes to pharmacokinetics, efficacy, and safety. The clinical impact of ADA formation refines the immunogenicity risk assessment and defines appropriate risk mitigation strategies. Health agencies request for high-risk biotherapeutics to extend ADA monitoring for patients that developed an ADA response to the drug until ADAs return to baseline levels. However, there is no common understanding in which cases an extension of ADA follow-up sampling beyond the end of study (EOS) defined in the clinical study protocol is required. Here, the Immunogenicity Strategy Working Group of the European Immunogenicity Platform (EIP) provides recommendations on requirements for an extension of ADA follow-up sampling in clinical studies where there is a high risk of serious consequences from ADAs. The importance of ADA evaluation during a treatment-free period is recognized but the decision whether to extend ADA monitoring at a predefined EOS should be based on evaluation of ADA data in the context of corresponding clinical signals. If the clinical data set shows that safety consequences are minor, mitigated, or resolved, further ADA monitoring may not be required despite potentially detectable ADAs above baseline. Extended ADA monitoring should be centered on individual patient benefit.

Evaluation of the Humoral Response to Adeno-Associated Virus-Based Gene Therapy Modalities Using Total Antibody Assays

The number of viral vector-based gene therapies (GTx) continues to grow with two products (Zolgensma® and Luxturna®) approved in the USA as of March 2021. To date, the most commonly used vectors are adeno-associated virus-based (AAV). The pre-existing humoral immunity against AAV (anti-AAV antibodies) has been well described and is expected as a consequence of prior AAV exposure. Anti-AAV antibodies may present an immune barrier to successful AAV transduction and hence negatively impact clinical efficacy and may also result in adverse events (AEs) due to the formation of large immune complexes. Patients may be screened for the presence of anti-AAV antibodies, including neutralizing (NAb) and total binding antibodies (TAb) prior to treatment with the GTx. Recommendations for the development and validation of anti-AAV NAb detection methods have been presented elsewhere. This manuscript covers considerations related to anti-AAV TAb-detecting protocols, including the advantages of the use of TAb methods, selection of assay controls and reagents, and parameters critical to monitoring assay performance. This manuscript was authored by a group of scientists involved in GTx development representing eleven organizations. It is our intent to provide recommendations and guidance to industry sponsors, academic laboratories, and regulatory agencies working on AAV-based GTx viral vector modalities with the goal of achieving a more consistent approach to anti-AAV TAb assessment.

Application of blood microsampling in cynomolgus monkey and demonstration of equivalent monoclonal antibody PK parameters compared to conventional sampling

PURPOSE

The purpose of this study was to evaluate the suitability of whole blood microsampling procedures in non-human primate (NHP) to support toxicokinetic assessments of biotherapeutics in non-human primates.

METHOD

A one-month single dose intravenous pharmacokinetic (PK) study was performed in male cynomolgus monkeys with a human IgG1 control monoclonal antibody (mAb) as a surrogate monoclonal antibody biotherapeutic. In this study, both serum samples (conventional sample collection) and microsampling samples were collected. Microsampling samples were collected from two sites on cynomolgus monkey, with each site using two different devices for the whole blood collection. The drug concentrations from all sample types were determined using a quantitative ligand binding assay (LBA). The PK parameters obtained from microsampling samples and serum samples were examined using a standard PK analysis method. The comparability of key PK parameters from both sample types were analyzed statistically.

RESULTS

Similar profiles of drug concentrations versus timepoints from all sampling procedures were observed. The correlations of PK concentration data obtained from serum and microsampling samples were ≥ 0.97 using Brand Alman Plot analysis. The key PK parameters obtained from microsampling samples were comparable to those obtained from serum samples (the % differences of mean PK parameters obtained from both sample types were within ±25%).

CONCLUSION

This study confirmed that PK parameters obtained from samples using microsampling were comparable to that of serum samples in cynomolgus monkeys. Therefore, the microsampling procedure described can be used as a substitute for conventional sampling procedure to support PK/TK studies of biotherapeutics in non-clinical product developments.

AAPS Perspective on the EURL Recommendation on the use of Non-Animal-Derived Antibodies

In May 2020, the EU Reference Laboratory for alternatives to animal testing (EURL ECVAM) published a recommendation report entitled "Recommendation on nonanimal-derived antibodies". In this report, the EURL ECVAM specifically states: "Therefore, taking into consideration the ESAC Opinion on the scientific validity of replacements for animal-derived antibodies, EURL ECVAM recommends that animals should no longer be used for the development and production of antibodies for research, regulatory, diagnostic and therapeutic applications. The provisions of Directive 2010/63/EU should be respected, and EU countries should no longer authorise the development and production of antibodies through animal immunisation, where robust, legitimate scientific justification is lacking." (1). Here, we are providing the American Association of Pharmaceutical Scientists (AAPS) opinion on the EURL ECVAM recommendation report. In brief, there has been a clear and strong progress in reduction of animal use in the drug discovery and development process, including significant reduction of animal use in production of antibody reagents. Yet, it is proposed that more data need to be generated, shared and discussed within the scientific community before a decision to implement the change to non-animal derived antibodies is made.

Current Considerations for Immunoglobulin Isotype Characterization of Antibody Response against Biotherapeutics

The ability of biotherapeutics to induce immune response in patients has been broadly accepted. Humoral immune response to biotherapeutics is expected to be polyclonal in nature with a high degree of diversity, including treatment-induced anti-drug antibodies (ADA) immunoglobulin isotype composition. Therapeutics with strong potential to induce immunity may produce a T cell-dependent response resulting in a gradual transition from initial IgM based to mature, IgG-based ADAs. Immunoglobulin class switch and transition to high affinity IgG1 and IgG4 antibodies were linked to a reduced drug efficacy, accelerated clearance, development of drug neutralizing antibodies, and modulation of hypersensitivity reaction rates. Examples presented herein demonstrate that understanding of isotype composition of ADA response can be highly important to predict future of disease progression. Isotype characterization of ADA response can be viewed highly useful, particularly for high immunogenicity risk biotherapeutics although may be less relevant or used as a research tool only for medium and low immunogenicity risk level therapeutics. Isotype-specific characteristics, methods of detection, and several case studies are presented herein.

Development of a Highly Specific Anti-drug Antibody Assay in Support of a Nanoparticle-based Therapeutic

PEGylated biotherapeutics can elicit anti-PEG (polyethylene glycol) immune responses in patients treated with this category of drugs. While anti-PEG antibody assays for this class of biotherapeutics have become a common element of the clinical immunogenicity testing strategy, the overall antibody incidence induced by the nanoparticle (NP) delivery system (such as ACCURINS®) has not been fully studied to date. To support the immunogenicity assessment of one of Pfizer's NP-based therapeutics, consisting of gedatolisib (GEDA) encapsulated in ACCURINS® (GEDA-NP), we developed an anti-GEDA-NP antibody (ADA) assay on the MSD platform for the detection of GEDA-NP induced ADA in human serum. The focus of our strategy was on developing a clinically relevant ADA assay and systematically addressing assay interference through rigorous assay optimization. Our efforts led to a fit-for-purpose assay for the detection of anti-GEDA-NP ADA in serum samples obtained from breast cancer patients. Results from method qualification indicated robust assay performance, as highlighted by inter and intra-assay precision within 25% CV for all controls, and reproducible response profiles across multiple runs during the assessment of assay cut points with breast cancer samples. The assay sensitivity was between 4.3 ng/mL and 123 ng/mL for surrogate positive controls of IgG and IgM isotypes, respectively. Additionally, assay interference from nonspecific matrix proteins and circulating drug was addressed, which ensured accurate assessment of ADA incidence that can be attributed to GEDA-NP.

Development of a Cell-Based Assay for the Detection of Neutralizing Antibodies to PF-06730512 Using Homogenous Time-Resolved Fluorescence

The administration of biotherapeutics has the potential to induce potent immune responses. Among these responses, the production of anti-drug antibodies (ADA), including a subset of ADA referred to as neutralizing antibodies (NAb), is of heightened concern. Aside from their capacity to alter the pharmacological profile of a given biotherapeutic, NAb can also pose significant safety risks, especially in instances where an endogenous counterpart to the drug exists. As such, the inclusion of an assay to detect NAb in clinical samples is critical to the effectiveness of a tiered approach to immunogenicity assessment. PF-06730512 is a biotherapeutic protein being developed for the treatment of primary Focal Segmental Glomerulosclerosis (FSGS). To support the immunogenicity assessment of PF-06730512, a cell-based assay was developed for the detection of NAb in FSGS serum samples. Herein, we describe the development of the assay with a focus on the challenges faced, including drug and blood collection tube interferences in NAb detection. The outcome of our efforts was a robust assay capable of detecting 1 μg/mL of a NAb positive control in the presence of clinically relevant drug concentrations up to 30 μg/mL.

Correction to: Recommendations for the Development of Cell-Based Anti-Viral Vector Neutralizing Antibody Assays

The first author's name was published incorrectly as "Gorovits Boris". The correct name is "Boris Gorovits".

Criteria to Reevaluate Anti-drug Antibody Assay Cut Point Suitability in the Target Population

After tier 1 and 2 cut points for anti-drug antibody (ADA) assays are derived during pre-study assay validation in a population, there is a need to verify the continued appropriateness of the previously derived cut points during sample analysis in the same or different populations, per FDA guidance (US HHS, FDA, CDER, CBER, 2019). Proper sample size-dependent criteria with statistical underpinning were derived and presented in this technical note to aid in assessing the appropriateness of tier 1 and tier 2 cut points, respectively.

Addressing soluble target interference in the development of a functional assay for the detection of neutralizing antibodies against a BCMA-CD3 bispecific antibody

Proper evaluation of immunogenicity during clinical development of biotherapeutics is a major challenge to bioanalytical scientists, in part due to matrix interference in anti-drug antibody (ADA) and neutralizing antibody (NAB) assays. If not addressed, matrix interference could confound the immunogenicity assessment of a given biotherapeutic in clinical development. To support clinical development of a B cell maturation antigen (BCMA)-CD3 bispecific antibody, a cell-based NAB assay was developed as part of a tiered approach to evaluating the immunogenicity of the drug. The assay endpoint (T cell activation) was chosen based on its strong association with the mechanism of action of the drug. The BCMA-CD3 bispecific antibody activates T cells through simultaneous binding of CD3 on T cells and BCMA on target cells. In this system, T cell activation was assessed through the measurement of luciferase activity in an engineered Jurkat cell line. In the presence of NAB, the degree of T cell activation measured by the amount of luciferase activity can be reduced. During method development, soluble BCMA (sBCMA) interference in the NAB assay was apparent. The binding of sBCMA to the anti-BCMA domain of the bispecific drug led to reduced T cell activation, which caused false positive results in NAB testing. To mitigate this interference, several strategies to eliminate sBCMA were investigated. Among the procedures tested, a bead-based approach proved most effective in depleting sBCMA, while maintaining robust assay performance and achieving fit-for-purpose sensitivity. Using this sample pretreatment procedure, the NAB assay tolerated sBCMA up to 2 μg/mL, or approximately four times the estimated median sBCMA concentration in serum samples from patients with active multiple myeloma.

Anti-drug Antibody Assay Validation: Improved Reporting of the Assay Selectivity via Simpler Positive Control Recovery Data Analysis

Anti-drug antibody (ADA) assay selectivity is evaluated during assay validation to assess the potential for individual matrices to interfere with detection of ADA. While current EMA and FDA guideline documents suggest comparative analysis with and without matrix, they do not provide specific recommendations on the acceptance criteria such as an acceptable percent positive control (PC) recovery range or positive rate. Industry has adopted an approach where recovery of PC spiked sample is expected to fall within ± 20% (80 to 120%) vs. that for the PC material spiked in negative control matrix or assay buffer. Here, it is proposed that ADA assay selectivity evaluated using a qualitative assessment of PC recovery vs. a PK-like quantitative method may be more appropriate. The PC recovery test should focus on the reliability of the method to detect the low PC level in individual samples and avoid false-negative ADA reporting. Therefore, it is proposed that assessment of high PC level as well as the assessment of quantitative percent recovery (within ± 20%) should not be included in the test. The recovery test may be viewed as acceptable should a pre-selected number of individual samples (for example at least 8 or 9 out of 10) prepared at the low PC concentration of the assay score as ADA positive.

Induction and Impact of Anti-Drug Responses Elicited by a Human Recombinant Coagulation Factor FXaI16L in Preclinical Species

This paper presents a systemic investigation of ADA development and ADA impact of a human coagulation factor in nonclinical species during drug development and provides insights into potential implications in human if a similar ADA occurs. FXa^I16L-induced ADA response was characterized in monkey, mouse, rat, and dog in different studies, and ADA effects on pharmacokinetic and/or pharmacodynamics of FXa^I16L were further examined in ADA-negative and ADA-positive animals. After repeated administrations, FXa^I16L elicited a dose and exposure day-dependent ADA response which ranged from no response to a transient or persistent response. Increase in exposure day and increase in dose generally enhanced ADA incidence except for a decrease in ADA incidence was observed in monkeys after repeated high-dose administrations. The observable ADA impact on pharmacokinetics was only found in some ADA+ animals and included decrease in clearance and increase in systemic exposure but no increase in half-life. In addition, no or limited effect on pharmacodynamics by ADA was observed. The earliest ADA response was observed after three exposure days, marked elevation of drug exposure was observed in some animals at log titer > 2.0, and the highest antibody titer excited was about 4 (Log10) in all species. A correlation between ADA induction and accumulative exposure after various repeat treatments in different species was found for FXa^I16L. In addition, potential immunogenicity risk and mitigation of ADA in clinics are discussed.

Neutralizing Antibody Assay Development with High Drug and Target Tolerance to Support Clinical Development of an Anti-TFPI Therapeutic Monoclonal Antibody

Immunogenicity is a major challenge for protein therapeutics which can potentially reduce drug efficacy and safety and is often being monitored by anti-drug antibody (ADA) and neutralizing antibody (NAb) assays. Circulating targets and residual drugs in matrices can have significant impacts on accuracy of results from ADA and NAb assays, and sufficient drug and target tolerance for these assays are necessary. Here, we report the development of a competitive ligand binding (CLB) NAb assay for an anti-TFPI (tissue factor pathway inhibitor) monoclonal antibody (PF-06741086) with high drug and target tolerance to support ongoing clinical studies. A double acid affinity capture elution approach was used to mitigate drug interference, and a robust target removal strategy was employed to enhance target tolerance. The validated NAb assay has sensitivity of 313 ng/mL, drug tolerance of 50 μg/mL, and target tolerance of 1200 ng/mL. A step-by-step tutorial of assay development is described in this manuscript along with the rationale for using a high drug/target tolerant NAb assay. The NAb assay cut point factor obtained was 0.78. Other assay performance characteristics, e.g., precision and selectivity, are also discussed. This validated method demonstrated a superior drug and target tolerance to warrant specific and precise characterization of the NAb responses in support of ongoing clinical studies.

Approaches to Resolve False Reporting in Neutralizing Antibody Assays Caused by Reagent Leaching from Affinity Capture Elution Solid Phase

Insufficient drug tolerance presents a major challenge in the development of neutralizing antibody (NAb) assays for biotherapeutics. Sample pre-treatment using solid-phase extraction with acid dissociation (SPEAD) is widely reported to improve drug tolerance. In this paper, a case study is presented in which SPEAD was used in conjunction with a competitive ligand binding NAb assay format. A significant degree of biotin-drug conjugate leaching was observed resulting in the reporting of both false positive and false negative results in NAb assay. Mitigation steps have been evaluated to address drug/biotin-drug conjugate leaching. These steps included assessment of the streptavidin-coated plate in conjunction with biotin-drug conjugates at various biotin molar challenge ratios (MCR). In addition, an alternative method based on covalent capture of the drug on an aldehyde-activated plate was assessed. Both approaches were compared for the degree of drug/biotin-drug conjugate leaching during the second elution step of the SPEAD procedure. Moreover, the impact of various conditions on the assay performance was assessed, including elution pH, sample incubation time, and biotin MCR. For the covalent drug capture method, capture conditions were evaluated. Optimized conditions in both streptavidin capture and covalent capture methods enabled a significant reduction of drug/biotin-drug conjugate leaching. A streptavidin high binding capacity approach using biotin-drug conjugate with a MCR of 50:1 was chosen as the optimal method yielding a NAb assay with a fit for purpose sensitivity (153 ng/mL) and a drug tolerance of up to 50 μg/mL with 500 ng/mL PC.

Immunoassay methods used in clinical studies for the detection of anti-drug antibodies to adalimumab and infliximab

We examined the assay formats used to detect anti-drug antibodies (ADA) in clinical studies of the anti-tumour necrosis factor (TNF) monoclonal antibodies adalimumab and infliximab in chronic inflammatory disease and their potential impact on pharmacokinetic and clinical outcomes. Using findings of a recent systematic literature review of the immunogenicity of 11 biological/biosimilar agents, we conducted an ancillary qualitative review of a subset of randomized controlled trials and observational studies of the monoclonal antibodies against anti-TNF factor adalimumab and infliximab. Among studies of adalimumab and infliximab, the immunoassay method used to detect antibodies was reported in 91 of 111 (82%) and 154 of 206 (75%) adalimumab and infliximab studies, respectively. In most adalimumab and infliximab studies, an enzyme-linked immunosorbent assay or radioimmunoassay was used [85 of 91 (93%) and 134 of 154 (87%), respectively]. ADA incidence varied widely among assays and inflammatory diseases (adalimumab, 0-87%; infliximab, 0-79%). Pharmacokinetic and clinical outcomes were only reported for ADA-positive patients in 38 of 91 (42%) and 61 of 154 (40%) adalimumab and infliximab studies, respectively. Regardless of assay format or biological used, ADA formation was associated with lower serum concentrations, reduced efficacy and elevated rates of infusion-related reactions. Consistent with previous recommendations to improve interpretation of immunogenicity data for biologicals, greater consistency in reporting of assay methods and clinical consequences of ADA formation may prove useful. Additional standardization in immunogenicity testing and reporting, application of modern, robust assays that satisfy current regulatory expectations and implementation of international standards for marketed products may help to improve our understanding of the impact of immunogenicity to biologics.

A Simple Approach to Determine a Curve Fitting Model with a Correct Weighting Function for Calibration Curves in Quantitative Ligand Binding Assays

In ligand binding assays (LBA), the concentration to response data is a nonlinear relationship driven by the law of mass action. Four parameter logistic (4PL) and five parameter logistic (5PL) curve fitting models are two widely accepted and validated models for LBA calibration curve data. Selection of the appropriate regression model and weighting function are key components of LBA development. Assessment of selected model and weighting function should be performed during assay development and confirmed later during validation. There has been limited published work on practical approaches to determining an appropriate weighting function and selection of a regression model for ligand binding assays. Herein, a structured scheme is presented to determine both. By applying commonly available software, assay performance data were analyzed to determine weighting functions and associated choice of a curve fitting model in three presented case studies. As a result, assay ranges of quantification were improved by reducing lower limit of quantification (from 1.00 to 0.317 ng/mL in one case study and from 2.06 to 1.37 ng/mL in another) or extending both low and upper limits of quantification(e.g., 1.04 to 48.3 ng/mL improved to 0.602 to 145 ng/mL). In addition, assay calibration curve performance demonstrated improved assay accuracy (%RE) and precision (%CV). Recommendations on decision flow when determining appropriate weighting function and curve fit model are presented.

Calibration Curves in Quantitative Ligand Binding Assays: Recommendations and Best Practices for Preparation, Design, and Editing of Calibration Curves

The accuracy of reported sample results is contingent upon the quality of the assay calibration curve, and as such, calibration curves are critical components of ligand binding and other quantitative methods. Regulatory guidance and lead publications have defined many of the requirements for calibration curves which encompass design, acceptance criteria, and selection of a regression model. However, other important aspects such as preparation and editing guidelines have not been addressed by health authorities. The goal of this publication is to answer many of the commonly asked questions and to present a consensus and the shared views of members of the ligand binding assay (LBA) community on topics related to calibration curves with focus on providing recommendations for the preparation and editing of calibration curves.

Preclinical Pharmacokinetics, Pharmacodynamics, Tissue Distribution, and Interspecies Scaling of Recombinant Human Coagulation Factor XaI16L

FXa^I16L is a recombinant human FXa variant which is currently being evaluated in the clinic for treating intracerebral hemorrhage. The aim of our studies is to investigate overall pharmacokinetics, pharmacodynamics, and distribution of FXa^I16L in preclinical species, and to understand its potential implication in human. Pharmacokinetics of FXa^I16L was examined using active site probes and the results showed that FXa^I16L displayed fast clearance, low volume of distribution, and a very short plasma resident time in mice, rats, and monkeys. When pharmacodynamics was examined in monkeys, concentration effects of FXa^I16L on shortening of active partial prothrombin time and formation of thrombin-antithrombin complex were observed. Furthermore, biodistribution study was conducted in mice using radiolabeled FXa^I16L, and showed that ¹²⁵I-FXa^I16L has high plasma protein binding and significant liver and kidney distribution. Human pharmacokinetic prediction for first-in-human dosing was evaluated using allometric scaling, liver blood flow, and a fixed coefficient method, and single species allometric scaling using monkey data was most predictive for human pharmacokinetics of FXa^I16L.

Pre-existing Antibody: Biotherapeutic Modality-Based Review

Pre-existing antibodies to biotherapeutic drugs have been detected in drug-naïve subjects for a variety of biotherapeutic modalities. Pre-existing antibodies are immunoglobulins that are either specific or cross-reacting with a protein or glycan epitopes on a biotherapeutic compound. Although the exact cause for pre-existing antibodies is often unknown, environmental exposures to non-human proteins, glycans, and structurally similar products are frequently proposed as factors. Clinical consequences of the pre-existing antibodies vary from an adverse effect on patient safety to no impact at all and remain highly dependent on the biotherapeutic drug modality and therapeutic indication. As such, pre-existing antibodies are viewed as an immunogenicity risk factor requiring a careful evaluation. Herein, the relationships between biotherapeutic modalities to the nature, prevalence, and clinical consequences of pre-existing antibodies are reviewed. Initial evidence for pre-existing antibody is often identified during anti-drug antibody (ADA) assay development. Other interfering factors known to cause false ADA positive signal, including circulating multimeric drug target, rheumatoid factors, and heterophilic antibodies, are discussed.

Workshop report: Crystal City V--quantitative bioanalytical method validation and implementation: the 2013 revised FDA guidance

In September 2013, the FDA released a draft revision of the Bioanalytical Method Validation (BMV) Guidance, which included a number of changes to the expectations for bioanalysis, most notably the inclusion of biomarker assays and data. To provide a forum for an open, inclusive discussion of the revised draft BMV Guidance, the AAPS and FDA once again collaborated to convene a two-and-a-half day workshop during early December 2013 in Baltimore, MD, USA. The resulting format embodied extensive open discussion and each thematic session included only brief, concise descriptions by Agency and industry representatives prior to opening the floor discussion. The Workshop was built around four thematic sessions (Common Topics, Chromatographic, Ligand-Binding Assays, and Biomarkers) and a final session with international regulators, concluding with a review of the outcomes and recommendations from the thematic sessions. This Workshop report summarizes the outcomes and includes topics of agreement, those where the FDA will consider the Industry's perspective, and those where the workshop provided a first open dialogue. This article will be available to the bioanalytical community at http://www.aaps.org/BMV13 .

A white paper--consensus and recommendations of a global harmonization team on assessing the impact of immunogenicity on pharmacokinetic measurements

The Global Bioanalysis Consortium (GBC) set up an international team to explore the impact of immunogenicity on pharmacokinetic (PK) assessments. The intent of this paper is to define the field and propose best practices when developing PK assays for biotherapeutics. We focus on the impact of anti-drug antibodies (ADA) on the performance of PK assay leading to the impact on the reported drug concentration and exposure. The manuscript describes strategies to assess whether the observed change in the drug concentration is due to the ADA impact on drug clearance rates or is a consequence of ADA interference in the bioanalytical method applied to measure drug concentration. This paper provides the bioanalytical scientist guidance for developing ADA-tolerant PK methods. It is essential that the data generated in the PK, ADA, pharmacodynamic and efficacy/toxicity evaluations are viewed together. Therefore, the extent for the investigation of the PK sensitivity to the presence of ADA should be driven by the project needs and risk based.

Large molecule specific assay operation: recommendation for best practices and harmonization from the global bioanalysis consortium harmonization team

The L2 Global Harmonization Team on large molecule specific assay operation for protein bioanalysis in support of pharmacokinetics focused on the following topics: setting up a balanced validation design, specificity testing, selectivity testing, dilutional linearity, hook effect, parallelism, and testing of robustness and ruggedness. The team additionally considered the impact of lipemia, hemolysis, and the presence of endogenous analyte on selectivity assessments as well as the occurrence of hook effect in study samples when no hook effect had been observed during pre-study validation.

Considerations for the nonclinical safety evaluation of antibody drug conjugates for oncology

Antibody drug conjugates (ADCs) include monoclonal antibodies that are linked to cytotoxic small molecules. A number of these agents are currently being developed as anti-cancer agents designed to improve the therapeutic index of the cytotoxin (i.e., cytotoxic small molecule or cytotoxic agent) by specifically delivering it to tumor cells. This paper presents primary considerations for the nonclinical safety evaluation of ADCs and includes strategies for the evaluation of the entire ADC or the various individual components (i.e., antibody, linker or the cytotoxin). Considerations are presented on how to design a nonclinical safety assessment program to identify the on- and off-target toxicities to enable first-in-human (FIH) studies. Specific discussions are also included that provide details as to the need and how to conduct the studies for evaluating ADCs in genetic toxicology, tissue cross-reactivity, safety pharmacology, carcinogenicity, developmental and reproductive toxicology, biotransformation, toxicokinetic monitoring, bioanalytical assays, immunogenicity testing, test article stability and the selection of the FIH dose. Given the complexity of these molecules and our evolving understanding of their properties, there is no single all-encompassing nonclinical strategy. Instead, each ADC should be evaluated on a case-by-case scientifically-based approach that is consistent with ICH and animal research guidelines.

Pre-existing biotherapeutic-reactive antibodies: survey results within the American Association of Pharmaceutical Scientists

The immunogenicity profile of a biotherapeutic is determined by a multitude of product and patient-related risk factors that can influence the observed incidence and clinical consequences of immunogenicity. Pre-existing antibodies, i.e., biotherapeutic-reactive antibodies present in samples from treatment-naïve subjects, have been commonly observed during immunogenicity assessments; however their relevance in terms of the safety and efficacy of a biotherapeutic is poorly understood. An American Association of Pharmaceutical Scientists-sponsored survey was conducted to gather information about the prevalence, nature, and consequences of pre-existing antibodies in clinical and nonclinical studies. The survey results indicate that pre-existing antibodies against a variety of biotherapeutics (e.g., mAbs, fusion proteins) are frequently encountered, especially in the context of autoimmune diseases, but that the methods and approaches used to detect, characterize, and report these antibodies vary. In most cases, pre-existing antibodies did not appear to have clinical consequences; however, a few of the respondents reported having observed an effect on pharmacokinetic, pharmacodynamic, safety, and/or efficacy parameters. The findings from this survey are an important first step in evaluating the potential risks associated with the presence of pre-existing antibodies and highlight the importance of standardizing the approaches for detection and characterization of these antibodies. Cross-industry sharing of case studies and relevant data collection will help better inform biotherapeutic risk/benefit profiles and provide deeper understanding of the biological consequences of pre-existing antibodies.

Theoretical considerations and practical approaches to address the effect of anti-drug antibody (ADA) on quantification of biotherapeutics in circulation

Continuous improvement in bioanalytical method development is desired in order to ensure the quality of the data and to better support pharmacokinetic (PK) and safety studies of biotherapeutics. One area that has been getting increasing attention recently is in the assessment of "free" and "total" analyte and the impact of the assay format on those assessments. To compliment these considerations, the authors provide a critical review of available literature and prospectively explore methods to mitigate the potential impact of anti-drug antibody on PK assay measurement. This challenge is of particular interest and importance since biotherapeutic drugs often elicit an immune response, and thus may have a direct impact on quantification of the drug for its PK and safety evaluations.

Proposed mechanism of off-target toxicity for antibody-drug conjugates driven by mannose receptor uptake

Antibody-drug conjugates (ADCs) are developed with the goal of increasing compound therapeutic index by specific and targeted delivery of a toxic payload to the site of action while considerably reducing damage to normal tissues. Yet, off-target hepatic toxicities have been reported for several ADC. Locations of these off-target toxicities coincide with the reported locations of cell surface mannose receptor (MR). The relative proportion of agalactosylated glycans on the Fc domain (G0F vs. G1F and G2F components) in monoclonal antibody (mAb)-based biotherapeutics is closer to some disease state IgG rather than to a normal serum-derived immunoglobulin. The lack of the terminal galactose on a G0F glycan creates an opportunity for the mAb to interact with soluble and cell surface MRs. MR is a known multi-domain lectin that specifically binds and internalizes glycoproteins and immune complexes with relatively high G0F content and has been found on the surface of various cell types, including immune cells of myeloid lineage, endothelial cells, and hepatic and splenic sinusoids. In this review paper it is proposed that the mechanism of the off-target toxicities for ADC biotherapeutics is at least in part driven by the carbohydrates, specifically agalactosylated glycans, such as G0F, their interactions with MR and resulting glycan-derived cellular uptake of ADCs. Several case studies are reviewed presenting corroborating information.

Prevalence and isotypic complexity of the anti-Chinese hamster ovary host cell protein antibodies in normal human serum

Host cell-derived protein impurities may be present at low levels in biopharmaceutical products. Antibodies to host cell proteins are present in individuals with no known exposure to these products. In this study, antibodies to drug process-specific Chinese hamster ovary host cell-derived proteins (CHO-HCP) were measured in unexposed individuals using a validated enzyme-linked immunosorbent assay. Samples that tested positive for anti-CHO-HCP reactivity were further characterized to determine the isotypes and IgG subclasses expressed in each positive individual. The specificity of the detected anti-CHO-HCP antibody isotypes was confirmed by the competitive inhibition assay and the uncoated plate specificity testing. These antibody characterization experiments revealed that the prevalent anti-CHO-HCP antibody subclasses were predominantly IgG1 (present in 66.6% of individuals) and IgG2 (60%), with 33.3% positive for IgG3 while IgG4 was detected in low abundance. Forty percent (40%) of the individuals with IgG type reactivity were also identified as IgM-positive. Anti-CHO-HCP-specific IgE was not detected in the assays used in this study. Some individuals exhibited single isotype anti-CHO-HCP reactivity; others contained a combination of multiple antibody isotypes. Data presented in this study demonstrate the isotypic complexity and the high prevalence of anti-CHO-HCP antibodies in human serum with no known exposure to CHO cell-derived therapeutic biologics.

Antidrug antibody assay validation: industry survey results

Immunogenicity of biopharmaceutical products has attracted considerable attention from the industrial, academia, and regulatory organizations. Many methods exist to detect and characterize level of antidrug antibody response in patients. Still, additional work is required to harmonize various approaches used throughout the industry. This review presents results of a survey sponsored by the American Association of Pharmaceutical Scientists that was designed to collect relevant information and to understand various methods used throughout the bioanalytical field for the detection and evaluation of antidrug antibody responses.

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

Most biological drug products elicit some level of anti-drug antibody (ADA) response. This antibody response can, in some cases, lead to potentially serious side effects and/or loss of efficacy. In humans, ADA often causes no detectable clinical effects, but in the instances of some therapeutic proteins these antibodies have been shown to cause a variety of clinical consequences ranging from relatively mild to serious adverse events. In nonclinical (preclinical) studies, ADA can affect drug exposure, complicating the interpretation of the toxicity, pharmacokinetic (PK) and pharmacodynamic (PD) data. Therefore, the immunogenicity of therapeutic proteins is a concern for clinicians, manufacturers and regulatory agencies. In order to assess the immunogenic potential of biological drug molecules, and be able to correlate laboratory results with clinical events, it is important to develop reliable laboratory test methods that provide valid assessments of antibody responses in both nonclinical and clinical studies. For this, method validation is considered important, and is a necessary bioanalytical component of drug marketing authorization applications. Existing regulatory guidance documents dealing with the validation of methods address immunoassays in a limited manner, and in particular lack information on the validation of immunogenicity methods. Hence this article provides scientific recommendations for the validation of ADA immunoassays. Unique validation performance characteristics are addressed in addition to those provided in existing regulatory documents pertaining to bioanalyses. The authors recommend experimental and statistical approaches for the validation of immunoassay performance characteristics; these recommendations should be considered as examples of best practice and are intended to foster a more unified approach to antibody testing across the biopharmaceutical industry.

Pharmacokinetics of gemtuzumab ozogamicin as a single-agent treatment of pediatric patients with refractory or relapsed acute myeloid leukemia

Gemtuzumab ozogamicin is currently approved to treat CD33-positive acute myeloid leukemia (AML) in first relapse in patients older than age 60 years. The objective of this study was to characterize the pharmacokinetics of gemtuzumab ozogamicin in pediatric patients with relapsed or refractory AML. The study population comprised 29 subjects younger than age 18 with AML in first relapse. Dosages of 6, 7.5, and 9 mg/m(2) were administered during the study. Pharmacokinetic parameters were determined following each dose for hP67.6, total calicheamicin derivatives, and unconjugated calicheamicin derivatives. hP67.6 pharmacokinetic parameters had a consistent and statistically significant change between the first and second doses. Increases in AUC and decreases in both CL and V(ss) from the first dose to the second dose were consistent with those of the adult population. Changes between dose periods for total calicheamicin derivatives and unconjugated calicheamicin derivatives were consistent with those of hP67.6. Changes in pharmacokinetic parameters between dose periods are attributed to saturation of CD33 binding sites and diminished clearance resulting from a lower peripheral blast burden and antigen. Children receiving 9 mg/m(2) had the following hP67.6 pharmacokinetic parameters: C(max), 3.47+/-1.04 mg/L; AUC, 136 +/- 107 mg x h/L; CL, 0.12 +/- 0.15 L/h/m(2); V(ss), 6.5 +/- 5.5 L; and t(1/2), 64 +/- 44 h after their first dose. Mean pharmacokinetic values are similar to values reported in adults. Individual children demonstrated large intersubject variability, similar to adults. The pharmacokinetics of gemtuzumab ozogamicin in pediatric patients closely follow the profile and variability of adult patients.

Antibody-targeted chemotherapy with CMC-544: a CD22-targeted immunoconjugate of calicheamicin for the treatment of B-lymphoid malignancies

Antibody-targeted chemotherapy with gemtuzumab ozogamicin (CMA-676, a CD33-targeted immunoconjugate of N-acetyl-γ-calicheamicin dimethyl hydrazide [CalichDMH], a potent DNA-binding cytotoxic antitumor antibiotic) is a clinically validated therapeutic option for patients with acute myeloid leukemia (AML). Here, we describe the preclinical profile of another immunoconjugate of CalichDMH, CMC-544, targeted to CD22 expressed by B-lymphoid malignancies. CMC-544 comprises a humanized IgG4 anti-CD22 monoclonal antibody (mAb), G5/44, covalently linked to CalichDMH via an acid-labile 4-(4′-acetylphenoxy) butanoic acid (AcBut) linker. Both CMC-544 and unconjugated G5/44 bound human CD22 with subnanomolar affinity. CMC-544, but not unconjugated G5/44, exerted potent cytotoxicity against CD22+ B-cell lymphoma (BCL) cell lines (inhibitory concentration of 50%: 6-600 pM CalichDMH). CMC-544 caused a potent inhibition of growth of small but established BCL xenografts leading to cures (therapeutic index &gt; 10). CMC-544 prevented the establishment of BCL xenografts and also caused regression of large BCLs (&gt; 1.5 g tumor mass). In contrast, unconjugated CalichDMH, unconjugated G5/44, and an isotype-matched control conjugate, CMA-676, were ineffective against these BCL xenografts. Thus, CD22-targeted delivery of CalichDMH is a potent and effective preclinical therapeutic strategy for BCLs. The strong antitumor profile of CMC-544 supports its clinical evaluation as a treatment option for B-lymphoid malignancies.

High hydrostatic pressure induces the dissociation of cpn60 tetradecamers and reveals a plasticity of the monomers

Hydrostatic pressures up to 2 kbar have been used to form monomers from the 14-subunit oligomer of the chaperonin, Cpn60. The fluorescence of 1,1'-bi(4-anilino) naphthalene-5,5'-disulfonic acid (bisANS), followed at high pressure, demonstrated an increase in hydrophobic exposure on dissociation. Cpn60 dissociated with first order kinetics. The transition occurred between 1.3 and 2 kbar (P50 = 1.75 kbar), and it was facilitated by MgATP (P50 = 1.1 kbar). With MgATP, the fluorescence showed a rapid first order phase (t1/2 = 3.7 min) in addition to a phase that was similar to the single phase for Cpn60 alone (t1/2 = 11.4 min). The bisANS fluorescence decreased slowly after depressurization, and the relaxation was faster at 25 degrees C (t1/2 = 58 h) than at 4 degrees C (t1/2 = 86 h) and faster still if the sample at 4 degrees C contained MgATP when it was pressurized (t1/2 = 18 h). There was no significant effect if the MgATP was added after depressurization. Analytical ultracentrifugation, after depressurization, confirmed that metastable monomers were produced that slowly reassociated to form the oligomers (t1/2 = 150 h at 25 degrees C). Immediately after depressurization, the monomers (a) had all three sulfhydryl groups exposed for labeling with 6-iodoacetamidofluorescein, (b) showed a proteolytic susceptibility that was intermediate between native Cpn60 and Cpn60 in 2.5 M urea, and (c) were not able to capture a folding intermediate of the enzyme rhodanese. After incubation at atmospheric pressure, monomeric Cpn60 regained the ability to interact with rhodanese intermediates, and the sulfhydryl reactivity fell before significantly reassociating to 14-mers. The different rates of recovery of the native properties indicate that a complex series of conformational events occur following depressurization. Finally, the monomers resulting from pressure were different from those produced from Cpn60 by the action of 2.5 M urea. These results demonstrate that there is a fast, pressure-induced dissociation of the Cpn60 14-mer followed by a conformational drift of the dissociated monomers that can be influenced by the presence of MgATP.