Assessment of immunogenicity of romiplostim in clinical studies with ITP subjects

Immunogenicity of erenumab: A pooled analysis of six placebo-controlled trials with long-term extensions

BACKGROUND

Immunogenicity of erenumab, a human anti-calcitonin gene-related peptide receptor monoclonal antibody developed for migraine prevention, has been evaluated throughout clinical development.

METHODS

Integrated post hoc analysis assessing immunogenicity of erenumab across six clinical trials in patients with episodic and chronic migraine (N = 2985). Anti-erenumab antibody incidence and potential impact on pharmacokinetics, efficacy, and safety were evaluated in short-term (double-blind treatment phase 12-24 weeks) and long-term (double-blind treatment phase plus extensions of up to 5 years) analyses.

RESULTS

Anti-erenumab binding antibody incidence was low with few patients developing neutralizing antibodies. Antibody responses were mostly transient with low magnitude. Binding antibodies developed as early as 2-4 weeks after the first dose; the majority developed within the first 6 months and very few after the first year. Serum concentrations of erenumab in antibody-positive patients were generally lower than, but within the range of, antibody-negative patients. There was no impact of anti-erenumab antibodies on erenumab efficacy or safety with no differences between antibody-positive and antibody-negative patients in change in monthly migraine days or adverse event rates.

CONCLUSIONS

This pooled analysis showed that immunogenicity had no meaningful clinical impact on efficacy or safety of erenumab in patients with migraine.Clinical Trial Registration: ClinicalTrials.gov, NCT01952574; ClinicalTrials.gov, NCT02456740; Clinicaltrials.gov NCT02483585; Clinicaltrials.gov, NCT02174861; Clinicaltrials.gov, NCT02630459; Clinicaltrials.gov, NCT03812224.

Assessment of romiplostim immunogenicity in pediatric patients in clinical trials and in a global postmarketing registry

Development of first-generation thrombopoietins (TPOs) was halted due to antibodies that neutralized endogenous TPO, causing protracted thrombocytopenia in some patients. The second-generation TPO receptor agonist romiplostim, having no homology to TPO, was developed to circumvent potential immunogenicity. We examined the development of binding and neutralizing antibodies to romiplostim and TPO among pediatric patients with primary immune thrombocytopenia (ITP) in 5 clinical trials and a global postmarketing registry. In the trials, 25 of 280 (8.9%) patients developed anti-romiplostim binding antibodies. The first positive result was detected 67 weeks (median) after romiplostim treatment was initiated. The median romiplostim dose was 8 µg/kg, and the median platelet count was 87 × 109/L. Most patients who developed anti-romiplostim binding antibodies (18 of 25 [72%]) had ≥90% of platelet assessments showing a response. Anti-romiplostim neutralizing antibodies developed in 8 of 280 (2.9%) patients. The development of anti-romiplostim neutralizing antibodies was unrelated to the romiplostim dose, and most patients who developed the antibodies (7 of 8 [88%]) had platelet response. Nine of 279 (3.2%) patients developed anti-TPO binding antibodies, and 1 (0.4%) developed transient anti-TPO neutralizing antibodies. In 8 patients who developed anti-romiplostim neutralizing antibodies, no TPO cross-reactivity was observed. In the postmarketing registry, 3 of 19 (15.8%) patients developed anti-romiplostim binding antibodies; 1 (5.3%) patient developed anti-romiplostim neutralizing antibodies. These results suggest that immunogenicity to romiplostim occurs infrequently in pediatric patients with ITP and is generally not associated with loss of platelet response or other negative clinical sequelae.

Clinical overview and practical considerations for optimizing romiplostim therapy in patients with immune thrombocytopenia

The fundamental treatment goal for patients with immune thrombocytopenia (ITP) is reduced or ameliorated bleeding. Although various treatment options exist for the management of ITP, recent advances have led to the approval of three thrombopoietin receptor agonists (TPO-RAs; romiplostim, eltrombopag, and avatrombopag) in the United States and European Union. Current treatment guidelines for ITP indicate that medical therapy is preferred over surgical therapy and support the use of TPO-RAs as early as 3 months after disease onset. More recent data are available on the use of romiplostim in patients who have had ITP for <1 year, and romiplostim is now indicated for the treatment of adults who have not responded adequately to initial treatment, as well as children aged ≥1 year who have had ITP for ≥6 months. Here we review the role of romiplostim in the management of ITP, with a focus on efficacy and safety data, emerging data on early use (beginning within 3 months of disease onset) and treatment-free remission, and practical considerations for optimal management of ITP.

Deimmunization of protein therapeutics - Recent advances in experimental and computational epitope prediction and deletion

Biotherapeutics, and antimicrobial proteins in particular, are of increasing interest for human medicine. An important challenge in the development of such therapeutics is their potential immunogenicity, which can induce production of anti-drug-antibodies, resulting in altered pharmacokinetics, reduced efficacy, and potentially severe anaphylactic or hypersensitivity reactions. For this reason, the development and application of effective deimmunization methods for protein drugs is of utmost importance. Deimmunization may be achieved by unspecific shielding approaches, which include PEGylation, fusion to polypeptides (e.g., XTEN or PAS), reductive methylation, glycosylation, and polysialylation. Alternatively, the identification of epitopes for T cells or B cells and their subsequent deletion through site-directed mutagenesis represent promising deimmunization strategies and can be accomplished through either experimental or computational approaches. This review highlights the most recent advances and current challenges in the deimmunization of protein therapeutics, with a special focus on computational epitope prediction and deletion tools.

Failure Mode and Effects Analysis (FMEA) for Immunogenicity of Therapeutic Proteins

Biotherapeutic drugs made by cell-based systems are revolutionizing the practice of medicine. The next generation of biotherapeutics include recombinant proteins, monoclonal antibodies, viral vector expressed proteins, and cell therapies. Immunogenicity associated adverse events is one of the major risks for these biologics. Accurate and precise measurement of the immunogenicity of biologics is a critical component during all phases of drug development. We have utilized the principles of Failure Mode and Effects Analysis (FMEA) in performing assessment of risk of immunogenicity. The multi-dimensional approach involves: i) listing all the potential risks by likelihood of occurrence and severity as part of quality target product profile. ii) ascribing the causes by identifying the risks at each stage of development. iii) predicting the effects. iv) determining the risk mitigation strategy. v) implementing a monitoring process. vi) developing templates for data collection. vii) timely reporting and. viii) life cycle management. FMEA is a continuous process that works throughout the lifecycle of the product or the process and keeps on getting updated with new insights and knowledge.

A method combining blue native polyacrylamide gel electrophoresis with liquid chromatography tandem-mass spectrometry to detect circulating immune complexes between therapeutic monoclonal antibodies and anti-drug antibodies in animals

Therapeutic monoclonal antibodies can potentially induce unwanted immune responses, resulting in the production of anti-drug antibodies (ADAs). The binding of ADAs to drugs and subsequent formation of immune complexes (ICs) can trigger various responses, dependent on the size, concentration, and subclass of ADAs. To better understand the impact of ADAs on pharmacokinetics, pharmacodynamics, and toxicological profiles, a bioanalytical method was developed for the detection of ICs between human monoclonal immunoglobulin G (IgG) and ADAs in biological samples. Regarding the experimental procedure, in brief, the human antibody-specific ICs and unbound human antibody in biological samples are separated through blue native polyacrylamide gel electrophoresis (BN-PAGE). The target fractions are then cut from the gel, followed by in-gel trypsin digestion and subsequent liquid chromatography tandem-mass spectrometry (LC-MS/MS) to monitor the human IgG-specific peptide. This method was able to detect various types of human antibodies with a lower limit of detection of 10 μg/mL in monkey serum. The assay performance for the detection of ICs was demonstrated using spiked samples, and pre-incubated ICs in monkey serum were clearly detected. Taken together, these findings indicate that our method enables a semi-quantitative analysis for estimating the ratio of human antibody included ICs in comparison to the total antibody. This method was successfully applied to an in vivo study using mice, and the data helped explain the unexpectedly rapid clearance of a humanized antibody due to the formation of large ICs. The combination of the separation of ICs by BN-PAGE and the detection of the human IgG-specific peptide by LC-MS/MS is a useful general bioanalytical approach for the detection of ICs in animals.

Assessment of romiplostim immunogenicity in adult patients in clinical trials and in a global postmarketing registry

Antibodies to first‐generation recombinant thrombopoietin (TPO) neutralized endogenous TPO and caused thrombocytopenia in some healthy subjects and chemotherapy patients. The second‐generation TPO receptor agonist romiplostim, having no sequence homology to TPO, was developed to avoid immunogenicity. This analysis examined development of binding and neutralising antibodies to romiplostim or TPO among adults with immune thrombocytopenia (ITP) in 13 clinical trials and a global postmarketing registry. 60/961 (6·2%) patients from clinical trials developed anti‐romiplostim‐binding antibodies post‐baseline. The first positive binding antibody was detected 14 weeks (median) after starting romiplostim, at median romiplostim dose of 2 µg/kg and median platelet count of 29.5 × 10⁹/l; most subjects had ≥98·5% of platelet assessments showing response. Neutralising antibodies to romiplostim developed in 0·4% of patients, but were unrelated to romiplostim dose and did not affect platelet count. Thirty‐three patients (3·4%) developed anti‐TPO‐binding antibodies; none developed anti‐TPO‐neutralising antibodies. In the global postmarketing registry, 9/184 (4·9%) patients with spontaneously submitted samples had binding antibodies. One patient with loss of response had anti‐romiplostim‐neutralising antibodies (negative at follow‐up). Collectively, anti‐romiplostim‐binding antibodies developed infrequently. In the few patients who developed neutralising antibodies to romiplostim, there was no cross‐reactivity with TPO and no associated loss of platelet response.

Quartz crystal microbalance as an assay to detect anti-drug antibodies for the immunogenicity assessment of therapeutic biologics

Because of their biological origins, therapeutic biologics can trigger an unwanted deleterious immune response with some patients. The immunogenicity of therapeutic biologics can affect drug efficacy and patient safety by the production of circulating anti-drug antibodies (ADA). In this study, quartz crystal microbalance (QCM) was developed as an assay to detect ADA. Etanercept (Enbrel®) was covalently grafted to dextran-modified QCM surfaces. Rabbits were immunized with etanercept to generate ADA. Results showed the QCM assay could detect purified ADA from rabbits at concentrations as low as 50 ng/mL, within the sensitivity range of ELISA. The QCM assay could also assess the ADA isotype. It was shown that the ADA were composed of the IgG isotype, but not IgM, as expected. Furthermore, it was shown that QCM surfaces that had been used to detect ADA could be regenerated in glycine-HCl solution and reused. The QCM assay was also demonstrated to detect ADA in crude serum samples. Serum was collected from the rabbits and analyzed before and after etanercept immunization. ADA were clearly detected in serum from rabbits after immunization, but not in serum before immunization. Serum from patients administered with etanercept for rheumatoid arthritis (RA) treatment was also analyzed and compared to serum from healthy donors. Sera from 10 RA patients were analyzed. Results showed one of the RA patient serum samples may have ADA present. In conclusion, QCM appears to be a viable assay to detect ADA for the immunogenicity assessment of therapeutic biologics.

Beyond immune thrombocytopenia: the evolving role of thrombopoietin receptor agonists

Since its discovery, the thrombopoietin (TPO) pathway has been an important pharmaceutical target for the treatment of thrombocytopenia. The first generation of TPO mimetics included peptide agents sharing homology with endogenous TPO, but these introduced a risk of antibody formation to endogenous TPO and were not successful. However, second-generation TPO mimetics or TPO receptor agonists (RAs) are currently being used to treat thrombocytopenia associated with a number of conditions, such as immune thrombocytopenia (ITP), severe aplastic anaemia (SAA), and hepatitis C virus-associated chronic liver disease. Accumulating efficacy and safety data suggest that the role of TPO-RAs in the treatment of thrombocytopenia may evolve in the near future with broader use of these agents in ITP and SAA, as well as approval in other indications, potentially including myelodysplastic syndromes, chemotherapy-associated thrombocytopenia, and post-transplant thrombocytopenia. This review provides an overview of clinical data on the efficacy and safety of TPO-RAs, emphasising recent findings that may expand their clinical utility.

Systems pharmacology and enhanced pharmacodynamic models for understanding antibody-based drug action and toxicity

Pharmacokinetic (PK) and pharmacodynamic (PD) models seek to describe the temporal pattern of drug exposures and their associated pharmacological effects produced at micro- and macro-scales of organization. Antibody-based drugs have been developed for a large variety of diseases, with effects exhibited through a comprehensive range of mechanisms of action. Mechanism-based PK/PD and systems pharmacology models can play a major role in elucidating and integrating complex antibody pharmacological properties, such as nonlinear disposition and dynamical intracellular signaling pathways triggered by ligation to their cognate targets. Such complexities can be addressed through the use of robust computational modeling techniques that have proven powerful tools for pragmatic characterization of experimental data and for theoretical exploration of antibody efficacy and adverse effects. The primary objectives of such multi-scale mathematical models are to generate and test competing hypotheses and to predict clinical outcomes. In this review, relevant systems pharmacology and enhanced PD (ePD) models that are used as predictive tools for antibody-based drug action are reported. Their common conceptual features are highlighted, along with approaches used for modeling preclinical and clinically available data. Key examples illustrate how systems pharmacology and ePD models codify the interplay among complex biology, drug concentrations, and pharmacological effects. New hybrid modeling concepts that bridge cutting-edge systems pharmacology models with established PK/ePD models will be needed to anticipate antibody effects on disease in subpopulations and individual patients.

Role of romiplostim in splenectomized and nonsplenectomized patients with immune thrombocytopenia

Romiplostim is a thrombopoietin receptor agonist (TPO-RA) used for the treatment of adult primary immune thrombocytopenia (ITP). ITP is an autoimmune condition characterized by low platelet counts due to increased destruction and reduced platelet production. First-line interventions include corticosteroids, anti-D, and intravenous immunoglobulins, while second-line therapies comprise splenectomy, rituximab, cyclosporine A, and TPO-RAs. The recognition that compromised platelet production is a critical part of the pathogenesis of ITP prompted the development of therapeutic strategies based on the stimulation of the TPO receptor. TPO-RAs enhance megakaryocyte proliferation, increase platelet production, and lead to a reduction in bleeding episodes in ITP patients. This review will summarize current data on the TPO-RA romiplostim, with a particular focus on its relation to splenectomy.

T-cell dependent immunogenicity of protein therapeutics: Preclinical assessment and mitigation

Protein therapeutics hold a prominent and rapidly expanding place among medicinal products. Purified blood products, recombinant cytokines, growth factors, enzyme replacement factors, monoclonal antibodies, fusion proteins, and chimeric fusion proteins are all examples of therapeutic proteins that have been developed in the past few decades and approved for use in the treatment of human disease. Despite early belief that the fully human nature of these proteins would represent a significant advantage, adverse effects associated with immune responses to some biologic therapies have become a topic of some concern. As a result, drug developers are devising strategies to assess immune responses to protein therapeutics during both the preclinical and the clinical phases of development. While there are many factors that contribute to protein immunogenicity, T cell- (thymus-) dependent (Td) responses appear to play a critical role in the development of antibody responses to biologic therapeutics. A range of methodologies to predict and measure Td immune responses to protein drugs has been developed. This review will focus on the Td contribution to immunogenicity, summarizing current approaches for the prediction and measurement of T cell-dependent immune responses to protein biologics, discussing the advantages and limitations of these technologies, and suggesting a practical approach for assessing and mitigating Td immunogenicity.

Development of a biosensor-based immunogenicity assay capable of blocking soluble drug target interference

As with other protein therapeutics, trebananib (AMG 386), an investigational peptide Fc-fusion protein ("peptibody") that inhibits angiogenesis by neutralizing the interaction of angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) with the Tie2 receptor, has the potential to trigger an immune response in cancer patients treated with the therapeutic. An electrochemiluminescence bridging anti-drug antibody (ADA) assay that was utilized to support early-phase clinical trials in the development of trebananib was found to lack adequate sensitivity and drug tolerance in later-phase clinical studies when higher doses of trebananib were administered. Therefore, we developed a surface plasmon resonance (SPR) immunoassay method utilizing a secondary confirmatory detector antibody (goat anti-human IgG F[ab']2) known to cross-react with human IgG and IgM to better assess the potential impact of immunogenicity on the pharmacokinetics, pharmacodynamics, and toxicity of trebananib. The SPR method was more sensitive than the electrochemiluminescence bridging assay because of signal amplification from the confirmatory binding of the detector antibody; drug tolerance was improved since antibody binding avidity does not affect detection on this platform. Despite the inability of the confirmatory detector antibody to bind angiopoietins in protein-free buffer, false-positive ADA results were generated from patient serum samples containing Ang1 and Ang2 through an apparently specific binding between the angiopoietins and the confirmatory detector antibody, likely mediated by the interaction of the angiopoietins with serum immunoglobulins. Addition to the sample diluent of a human antibody that specifically binds to Ang1 and Ang2 with high affinity resulted in a complete block of angiopoietin interference without affecting ADA detection. This biosensor-based assay provides a reliable method for assessing immunogenicity in phase 3 clinical trials.

Increased sensitivity of SPR assays in plasma through efficient parallel assay optimization

The sensitivity of biosensor assays in complex media such as plasma or serum is often limited by non-specific binding. The degree of binding often varies between individuals and therefore a large number of different plasma samples have to be used during assay development. Some surface plasmon resonance (SPR) biosensors allow for parallel screening of several running buffer compositions, with a number of different immobilization levels for each buffer. These technical possibilities combined with statistical design of experiments (DoE) enable efficient parallel optimization of multiple assay conditions. In this paper we outline how to increase the sensitivity in SPR-based assays by minimizing background binding and variability from negative control plasma while retaining high signals from positive samples. To mimic immunogenicity studies of biotherapeutics we have used a model assay with anti-rituximab as an anti-drug antibody to be detected in plasma by binding to immobilized rituximab. Immobilization level and sodium chloride concentration were found to be the most important factors to optimize. There were also a number of significant interaction effects and strong non-linearites between the buffer composition/immobilization level and the assay performance, which necessitated DoE based optimization strategies. The applicability of the optimized conditions was verified with several assays (anti-erythropoietin, omalizumab, anti-IgE and anti-myoglobin) in spiked plasma samples resulting in detection levels in the range of 80-170 ng ml(-1). The buffer conditions presented in this paper can be used for other immunogenicity assays on biosensor platforms or as a good starting point for further assay development for new immunogenicity assays.

Romiplostim: a review of its use in immune thrombocytopenia

Romiplostim (Nplate®) is an Fc-peptide fusion protein (peptibody) that acts as a thrombopoietin receptor agonist; it has no amino acid sequence homology with endogenous thrombopoietin. This article reviews the clinical efficacy and tolerability of subcutaneous romiplostim in adults with immune thrombocytopenia (ITP), as well as summarizing its pharmacological properties. The efficacy of 12 or 24 weeks' therapy with subcutaneous romiplostim was compared with that of placebo in patients with ITP in three randomized, double-blind, multicentre, phase III trials. In the two 24-week trials, the durable platelet response rate (primary endpoint) was significantly higher with romiplostim than with placebo in both splenectomized and nonsplenectomized patients. In addition, the majority of romiplostim recipients were able to discontinue or reduce their concurrent ITP therapy, and romiplostim improved health-related quality of life (HR-QOL). In the 12-week trial in splenectomized or nonsplenectomized Japanese patients with ITP, the median number of weeks with a platelet response (primary endpoint) was significantly higher with romiplostim than with placebo. Two extension studies (with median durations of romiplostim treatment of 78 and 100 weeks) demonstrated that long-term therapy with romiplostim maintained platelet counts in the target range in patients with ITP. In a randomized, open-label, multicentre, 52-week, phase IIIb trial, romiplostim was more effective than the medical standard of care in nonsplenectomized patients with ITP who had received at least one prior ITP treatment. Significantly fewer patients receiving romiplostim versus the medical standard of care experienced treatment failure or required splenectomy (co-primary endpoints), and clinically meaningful improvements from baseline in HR-QOL scores were seen with romiplostim. Subcutaneous romiplostim was generally well tolerated in patients with ITP; in short-term trials, the majority of adverse events were of mild to moderate severity and appeared to be related to the underlying thrombocytopenia. The incidence of bleeding events of at least grade 3 severity did not significantly differ between romiplostim and placebo recipients, and was significantly lower with romiplostim than with the medical standard of care. Romiplostim did not appear to be associated with an increased risk of haematological malignancies or an increased risk of thrombotic events. Although binding antibodies against romiplostim or thrombopoietin developed in some romiplostim recipients, with neutralizing antibodies to romiplostim detected in two romiplostim recipients, antibodies cross reacting to thrombopoietin have not been detected. Romiplostim was associated with modest increases in bone marrow reticulin in some patients with ITP; reductions in reticulin were usually seen when romiplostim was discontinued. In conclusion, subcutaneous romiplostim is a valuable agent for use in patients with refractory chronic ITP.

Immunogenicity to therapeutic proteins: impact on PK/PD and efficacy

The development of therapeutic proteins requires the understanding of the relationship between the dose, exposure, efficacy, and toxicity of these molecules. Several intrinsic and extrinsic factors contribute to the challenges for measuring therapeutic proteins in a precise and accurate manner. In addition, induction of an immune response to therapeutic protein results in additional complexities in the analysis of the pharmacokinetic profile, toxicity, safety, and efficacy of this class of molecules. Assessment of immunogenicity of therapeutic proteins is a required aspect of regulatory filings for a licensing application and for the safe and efficacious use of these compounds. A systematic strategy and well-defined criteria for measuring anti-drug antibodies (ADA) have been established, to a large extent, through coordinated efforts. These recommendations are based on risk assessment and include the determination of ADA content (concentration/titer), affinity, immunoglobulin isotype/subtype, and neutralization capacity. This manuscript reviews the requirements necessary for understanding the nature of an ADA response in order to discern the impact of immunogenicity on pharmacokinetics/pharmacodynamics and efficacy.

A randomized, double-blind study of romiplostim to determine its safety and efficacy in children with immune thrombocytopenia

Romiplostim, a thrombopoietin-mimetic peptibody, increases and maintains platelet counts in adults with immune thrombocytopenia (ITP). In this first study of a thrombopoietic agent in children, patients with ITP of ≥ 6 months' duration were stratified by age 1:2:2 (12 months-< 3 years; 3-< 12 years; 12-< 18 years). Children received subcutaneous injections of romiplostim (n = 17) or placebo (n = 5) weekly for 12 weeks, with dose adjustments to maintain platelet counts between 50 × 109/L and 250 × 109/L. A platelet count ≥ 50 × 109/L for 2 consecutive weeks was achieved by 15/17 (88%) patients in the romiplostim group and no patients in the placebo group (P = .0008). Platelet counts ≥ 50 × 109/L were maintained for a median of 7 (range, 0-11) weeks in romiplostim patients and 0 (0-0) weeks in placebo patients (P = .0019). The median weekly dose of romiplostim at 12 weeks was 5 μg/kg. Fourteen responders received romiplostim for 4 additional weeks for assessment of pharmacokinetics. No patients discontinued the study. There were no treatment-related, serious adverse events. The most commonly reported adverse events in children, as in adults, were headache and epistaxis. In this short-term study, romiplostim increased platelet counts in 88% of children with ITP and was well-tolerated and apparently safe.

The trial was registered with http://www.clinicaltrials.gov as NCT00515203.