Changes in the amino acid sequence of the recombinant human factor VIIa analog, vatreptacog alfa, are associated with clinical immunogenicity

IQ Survey Results on Current Industry Practices-Part 1: Immunogenicity Risk Assessment

An immunogenicity risk assessment (IRA) is a relatively new expectation of health authorities that is increasingly incorporated into the drug development process across the pharmaceutical/biotech industry. The guiding principle for an IRA includes a comprehensive evaluation of product- and patient-related factors that may influence the immunogenic potential of a biotherapeutic drug and a potential action plan. The Immunogenicity Working Group from the IQ Consortium (Clinical Pharmacology Leadership Group) has conducted a survey to understand the current practices for conducting IRAs and relevant aspects of bioanalysis. Survey results were provided by 19 IQ member companies participating in the Clinical Pharmacology Leadership Group (CPLG) and the Translational and ADME Sciences Leadership Group (TALG). Nearly all the respondents reported experience with monoclonal antibodies (mAb), with 10 other drug modalities including bioengineered protein therapeutics such as fusion and multi-domain proteins, peptides, oligonucleotides as well as gene and cell therapies. The survey results demonstrate that most companies have a defined IRA process, and there was a common understanding that the IRA may need to be revised as more information becomes available or the drug development strategy changes. Some differences found across the respondents are related to the time frame for implementation of IRA document, the types of preclinical data and computational methods used to assess risk, and how the IRA informs clinical plans and documentation practices. These results highlight that while there have been widespread insights gained with performing IRA for mAbs, more experience is needed to perform IRAs for the novel modalities.

Immunogenicity risk assessment and mitigation for engineered antibody and protein therapeutics

Remarkable progress has been made in recent decades in engineering antibodies and other protein therapeutics, including enhancements to existing functions as well as the advent of novel molecules that confer biological activities previously unknown in nature. These protein therapeutics have brought major benefits to patients across multiple areas of medicine. One major ongoing challenge is that protein therapeutics can elicit unwanted immune responses (immunogenicity) in treated patients, including the generation of anti-drug antibodies. In rare and unpredictable cases, anti-drug antibodies can seriously compromise therapeutic safety and/or efficacy. Systematic deconvolution of this immunogenicity problem is confounded by the complexity of its many contributing factors and the inherent limitations of available experimental and computational methods. Nevertheless, continued progress with the assessment and mitigation of immunogenicity risk at the preclinical stage has the potential to reduce the incidence and severity of clinical immunogenicity events. This Review focuses on identifying key unsolved anti-drug antibody-related challenges and offers some pragmatic approaches towards addressing them. Examples are drawn mainly from antibodies, given that the majority of available clinical data are from this class of protein therapeutics. Plausible and seemingly tractable solutions are in sight for some immunogenicity problems, whereas other challenges will likely require completely new approaches.

Site-directed mutagenesis of tissue factor pathway inhibitor-binding exosite D60A on factor VII results in a new factor VII variant with lower coagulant activity

Background

Recombinant factor (F)VIIa (rFVIIa) has been approved by the US Food and Drug Administration for the treatment of hemophilia A and B with inhibitors and congenital FVII deficiency. Moreover, the investigational uses of rFVIIa are becoming of interest since it can be used to treat various clinical bleeding conditions. However, there is evidence showing that rFVIIa is a potent procoagulant agent that potentially leads to an increased risk of thrombotic complications.

Objectives

To design a new rFVII with lower coagulant activity that could potentially be used as an alternative hemostatic agent aiming to minimize the risk of thrombogenicity.

Methods

D60A was introduced into the F7 sequence by polymerase chain reaction-based mutagenesis. Wild type (WT) and D60A were generated in human embryonic kidney 293T cells by stable transfection. FVII coagulant activities were determined by amidolytic cleavage of the FVIIa-specific substrate, 2-step FXa generation, thrombin generation (TG), and clot-based assays.

Results

WT and D60A demonstrated similar FVIIa amidolytic activity. However, D60A showed approximately 50% activity on FX activation and significantly longer lag time in the TG assay than that shown by WT. The clotting time produced by D60A spiked in FVII-deficient plasma was significantly prolonged than that of WT. Additionally, the ex vivo plasma half-lives of WT and D60A were comparable.

Conclusion

D60A demonstrated lower coagulant activities, most likely due to the weakening of FX binding, leading to impaired FX activation and delayed TG and fibrin formation. Considering that a plasma FVII level of 15% to 25% is adequate for normal hemostasis, D60A is a molecule of interest for future development of an rFVII with a lesser extent of thrombogenicity.

The MHC Associated Peptide Proteomics assay is a useful tool for the non-clinical assessment of immunogenicity

The propensity of therapeutic proteins to elicit an immune response, poses a significant challenge in clinical development and safety of the patients. Assessment of immunogenicity is crucial to predict potential adverse events and design safer biologics. In this study, we employed MHC Associated Peptide Proteomics (MAPPS) to comprehensively evaluate the immunogenic potential of re-engineered variants of immunogenic FVIIa analog (Vatreptacog Alfa). Our finding revealed the correlation between the protein sequence affinity for MHCII and the number of peptides identified in a MAPPS assay and this further correlates with the reduced T-cell responses. Moreover, MAPPS enable the identification of "relevant" T cell epitopes and may contribute to the development of biologics with lower immunogenic potential.

Preclinical risk assessment strategy to mitigate the T-cell dependent immunogenicity of protein biotherapeutics: State of the art, challenges and future perspectives

Protein therapeutics hold a prominent role and have brought significant diversity in efficacious medicinal products. Not just monoclonal antibodies and different antibody formats (pegylated antigen-binding fragments, bispecifics, antibody-drug conjugates, single chain variable fragments, nanobodies, dia-, tria- and tetrabodies), but also purified blood products, growth factors, recombinant cytokines, enzyme replacement factors, fusion proteins are all good instances of therapeutic proteins that have been developed in the past decades and approved for their value in oncology, immune-oncology, and autoimmune diseases discovery programs. Although there was an ingrained belief that fully humanized proteins were expected to have limited immunogenicity, adverse effects associated with immune responses to biological therapies raised some concern in biotech companies. Consequently, drug developers are designing strategies to assess potential immune responses to protein therapeutics during both the preclinical and clinical phases of development. Despite the many factors that can contribute to protein immunogenicity, T cell- (thymus-) dependent (Td) immunogenicity seems to play a crucial role in the development of anti-drug antibodies (ADAs) to biologics. A broad range of methodologies to predict and rationally assess Td immune responses to protein drugs has been developed. This review aims to briefly summarize the preclinical immunogenicity risk assessment strategy to mitigate the risk of potential immunogenic candidates coming towards clinical phases, discussing the advantages and limitations of these technologies, and suggesting a rational approach for assessing and mitigating Td immunogenicity.

Immunogenicity of Therapeutic Biological Modalities - Lessons from Hemophilia A Therapies

The introduction and development of biologics such as therapeutic proteins, gene-, and cell-based therapy have revolutionized the scope of treatment for many diseases. However, a significant portion of the patients develop unwanted immune reactions against these novel biological modalities, referred to as immunogenicity, and no longer benefit from the treatments. In the current review, using Hemophilia A (HA) therapy as an example, we will discuss the immunogenicity issue of multiple biological modalities. Currently, the number of therapeutic modalities that are approved or recently explored to treat HA, a hereditary bleeding disorder, is increasing rapidly. These include, but are not limited to, recombinant factor VIII proteins, PEGylated FVIII, FVIII Fc fusion protein, bispecific monoclonal antibodies, gene replacement therapy, gene editing therapy, and cell-based therapy. They offer the patients a broader range of more advanced and effective treatment options, yet immunogenicity remains the most critical complication in the management of this disorder. Recent advances in strategies to manage and mitigate immunogenicity will also be reviewed.

Detection of innate immune response modulating impurities (IIRMI) in therapeutic peptides and proteins: Impact of excipients

Unintended immunogenicity can affect the safety and efficacy of therapeutic proteins and peptides, so accurate assessments of immunogenicity risk can aid in the selection, development, and regulation of biologics. Product- and process- related impurities can act as adjuvants that activate the local or systemic innate immune response increasing the likelihood of product immunogenicity. Thus, assessing whether products have innate immune response modulating impurities (IIRMI) is a key component of immunogenicity risk assessments. Identifying trace levels of individual IIRMI can be difficult and testing individually for all potential impurities is not feasible. Therefore, to mitigate the risk, cell-based assays that use human blood cells or monocyte-macrophage reporter cell lines are being developed to detect minute quantities of impurities capable of eliciting innate immune activation. As these are cell-based assays, there is concern that excipients could blunt the cell responses, masking the presence of immunogenic IIRMI. Here, we explore the impact of frequently used excipients (non-ionic detergents, sugars, amino acids, bulking agents) on the sensitivity of reporter cell lines (THP-1- and RAW-Blue cells) and fresh human blood cells to detect purified TLR agonists as model IIRMI. We show that while excipients do not modulate the innate immune response elicited by TLR agonists in vivo, they can impact on the sensitivity of cell-based IIRMI assays. Reduced sensitivity to detect LPS, FSL-1, and other model IIRMI was also evident when testing 3 different recombinant drug products, product A (a representative mAb), B (a representative growth factor), C (a representative peptide), and their corresponding formulations. These results indicate that product formulations need to be considered when developing and validating cell-based assays for assessing clinically relevant levels of IIRMI in therapeutic proteins. Optimization of reporter cells, culture conditions and drug product concentration appear to be critical to minimize the impact of excipients and attain sensitive and reproducible assays.

Development of a Liquid Chromatography and High-Resolution and -Accuracy Mass Spectrometry Method to Evaluate New Biotherapeutic Entity Processing in Human Liver Lysosomes

Biotherapeutic immunogenicity remains a great challenge for researchers because multiple factors trigger immune responses. Predicting and assessing the potential human immune response against biological drugs could represent an impressive breakthrough toward generating potentially safer and more efficacious therapeutic proteins. This article describes an in vitro assay that can contribute to evaluating the potential immunogenicity of biotherapeutics by focusing on lysosomal proteolysis. We selected human liver lysosomes (hLLs) from four different donors as a surrogate in vitro model instead of APC lysosomes because they are a ready-to-use lysosomal source. To assess the biological comparability of this surrogate to APC lysosomal extract, we compared the proteome content of hLLs with literature data of lysosomal fractions extracted from murine bone marrow and human blood-derived dendritic cells. Then we tested infliximab (IFX; Remicade) under different proteolytic conditions using liquid chromatography and high-resolution and -accuracy mass spectrometry to better define the degradation kinetics inside the lysosomes. hLLs revealed similar enzymatic content compared with human and murine dendritic cell lysosomes. Degradation assays demonstrated that our liquid chromatography and high-resolution and -accuracy mass spectrometry method could identify both the intact protein and the peptides resulting from proteolysis with high specificity and resolution. The rapid and easy assay described in this article can be extremely useful for evaluating the immunogenic risk associated with therapeutic proteins. In addition, this method can complement information from MHC class II-associated peptide proteomics assays and other in vitro and in silico techniques.

Aggregates Associated with Instability of Antibodies during Aerosolization Induce Adverse Immunological Effects

Background: Immunogenicity refers to the inherent ability of a molecule to stimulate an immune response. Aggregates are one of the major risk factors for the undesired immunogenicity of therapeutic antibodies (Ab) and may ultimately result in immune-mediated adverse effects. For Ab delivered by inhalation, it is necessary to consider the interaction between aggregates resulting from the instability of the Ab during aerosolization and the lung mucosa. The aim of this study was to determine the impact of aggregates produced during aerosolization of therapeutic Ab on the immune system. Methods: Human and murine immunoglobulin G (IgG) were aerosolized using a clinically-relevant nebulizer and their immunogenic potency was assessed, both in vitro using a standard human monocyte-derived dendritic cell (MoDC) reporter assay and in vivo in immune cells in the airway compartment, lung parenchyma and spleen of healthy C57BL/6 mice after pulmonary administration. Results: IgG aggregates, produced during nebulization, induced a dose-dependent activation of MoDC characterized by the enhanced production of cytokines and expression of co-stimulatory markers. Interestingly, in vivo administration of high amounts of nebulization-mediated IgG aggregates resulted in a profound and sustained local and systemic depletion of immune cells, which was attributable to cell death. This cytotoxic effect was observed when nebulized IgG was administered locally in the airways as compared to a systemic administration but was mitigated by improving IgG stability during nebulization, through the addition of polysorbates to the formulation. Conclusion: Although inhalation delivery represents an attractive alternative route for delivering Ab to treat respiratory infections, our findings indicate that it is critical to prevent IgG aggregation during the nebulization process to avoid pro-inflammatory and cytotoxic effects. The optimization of Ab formulation can mitigate adverse effects induced by nebulization.

Tolerogenic nanoparticles mitigate the formation of anti-drug antibodies against pegylated uricase in patients with hyperuricemia

Biologic drugs have transformed the standard of care for many diseases. However, many biologics induce the formation of anti-drug antibodies (ADAs), which can compromise their safety and efficacy. Preclinical studies demonstrate that biodegradable nanoparticles-encapsulating rapamycin (ImmTOR), but not free rapamycin, mitigate the immunogenicity of co-administered biologic drugs. Here we report the outcomes from two clinical trials for ImmTOR. In the first ascending dose, open-label study (NCT02464605), pegadricase, an immunogenic, pegylated uricase enzyme derived from Candida utilis, is assessed for safety and tolerability (primary endpoint) as well as activity and immunogenicity (secondary endpoint); in the second single ascending dose Phase 1b trial (NCT02648269) composed of both a double-blind and open-label parts, we evaluate the safety of ImmTOR (primary endpoint) and its ability to prevent the formation of anti-drug antibodies against pegadricase and enhance its pharmacodynamic activity (secondary endpoint) in patients with hyperuricemia. The combination of ImmTOR and pegadricase is well tolerated. ImmTOR inhibits the development of uricase-specific ADAs in a dose-dependent manner, thus enabling sustained enzyme activity and reduction in serum uric acid levels. ImmTOR may thus represent a feasible approach for preventing the formation of ADAs to a broad range of immunogenic biologic therapies.

Secondary failure: immune responses to approved protein therapeutics

Recombinant therapeutic proteins are a broad class of biological products used to replace dysfunctional human proteins in individuals with genetic defects (e.g., factor VIII for hemophilia) or, in the case of monoclonal antibodies, bind to disease targets involved in cancers, autoimmune disorders, or other conditions. Unfortunately, immunogenicity (immune response to the drug) remains a key impediment, potentially affecting the safety and efficacy of these therapeutics. Immunogenicity risk is routinely evaluated during the licensure of therapeutic proteins. However, despite eliciting anti-drug immune responses in at least some patients, most protein drugs are nevertheless licensed as they address unmet medical needs. The pre-licensure immunogenicity assessments of therapeutic proteins are the subject of numerous reviews and white papers. However, observation and clinical management of the immunogenicity of approved therapeutic proteins face additional challenges. We survey the immunogenicity of approved therapeutic proteins, discuss the clinical management of immunogenicity, and identify the challenges to establishing clinically relevant immunogenicity assays for use in routine clinical practice.

Development of a novel fully functional coagulation factor VIII with reduced immunogenicity utilizing an in silico prediction and deimmunization approach

BACKGROUND

Up to 30% of hemophilia A patients develop inhibitory antibodies against the infused factor VIII (FVIII). The development of a deimmunized FVIII is an unmet high medical need. Although improved recombinant FVIII (rFVIII) products evolved within the last years, the immunogenicity has not been solved. A deimmunized FVIII could reduce the probability of inhibitor development, providing safer therapy.

OBJECTIVE

To develop a deimmunized FVIII molecule by modifying major histocompatibility complex (MHC) class II presentation, leading to a functional but less immunogenic molecule.

METHODS

We performed (1) in silico prediction of potentially immunogenic T cell epitopes and their modification by amino acid substitutions in the FVIII sequence, (2) evaluation of functional and structural similarity of the modified rFVIII to unmodified FVIII and registered products, and (3) confirmation of the reduced immunogenicity by in vitro testing.

RESULTS

A partially deimmunized fully functional FVIII molecule incorporating 19 amino acid substitutions was generated. The substitutions led to a reduction of the immunogenicity score, indicating a reduced immunogenicity based on in silico calculations. This was confirmed in an in vitro dendritic cell (DC)--T cell assay. Using this assay, cells from healthy donors proved the significantly reduced immunogenicity of the modified FVIII variant by revealing less proliferation of T helper cells to this variant than to the unmodified FVIII.

CONCLUSION

In silico predictions resulted in a partially deimmunized FVIII. This FVIII is fully functional and was demonstrated to be less immunogenic in in vitro testing. This approach may result in a reduction of the inhibitor risk for patients with hemophilia A.

Subcutaneous engineered factor VIIa marzeptacog alfa (activated) in hemophilia with inhibitors: Phase 2 trial of pharmacokinetics, pharmacodynamics, efficacy, and safety

BACKGROUND

Marzeptacog alfa (activated) (MarzAA), a novel recombinant activated human factor VII (FVIIa) variant, was developed to provide increased procoagulant activity, subcutaneous (SC) administration, and longer duration of action in people with hemophilia.

OBJECTIVES

To investigate if daily SC administration of MarzAA in subjects with inhibitors can provide effective prophylaxis.

METHODS

This multicenter, open-label phase 2 trial (NCT03407651) enrolled men with severe congenital hemophilia with an inhibitor. All subjects had a baseline annualized bleeding rate (ABR) of ≥12 events/year. Subjects received a single 18 μg/kg intravenous dose of MarzAA to measure 24-hour pharmacokinetics (PK) and pharmacodynamics (PD), single 30 μg/kg SC dose to measure 48-hour PK/PD, then daily SC 30 μg/kg MarzAA for 50 days. If spontaneous bleeding occurred, the dose was sequentially escalated to 60, 90, or 120 μg/kg, with 50 days at the final effective dose without spontaneous bleeding to proceed to a 30-day follow-up. The primary end point was reduction in ABR. Secondary end points were safety, tolerability, and antidrug antibody (ADA) formation.

RESULTS

In the 11 subjects, the mean ABR significantly reduced from 19.8 to 1.6, and the mean proportion of days with bleeding significantly reduced from 12.3% to 0.8%. Of a total of 517 SC doses, six injection site reactions in two subjects were reported. No ADAs were detected. One fatal unrelated serious adverse event occurred: intracerebral hemorrhage due to untreated hypertension.

CONCLUSIONS

The data demonstrated that MarzAA was highly efficacious for prophylactic treatment in patients with inhibitors by significantly decreasing bleed frequency and duration of bleeding episodes.

Engineering enhanced CAR T-cells for improved cancer therapy

Chimeric antigen receptor (CAR) T-cell therapies have evolved from a research tool to a paradigm-shifting therapy with impressive responses in B cell malignancies. This review summarizes the current state of the CAR T-cell field, focusing on CD19- and B cell maturation antigen-directed CAR T-cells, the most developed of the CAR T-cell therapies. We discuss the many challenges to CAR-T therapeutic success and innovations in CAR design and T-cell engineering aimed at extending this therapeutic platform beyond hematologic malignancies.

In vitro characterization of CT-001-a short-acting factor VIIa with enhanced prohemostatic activity

BACKGROUND

Traumatic injury and the associated acute bleeding are leading causes of death in people aged 1 to 44 years. Acute bleeding in pathological and surgical settings also represents a significant burden to the society. Yet there are no approved hemostatic drugs currently available. While clinically proven as an effective pro-coagulant, activated factor VII (FVIIa) use in acute bleeding has been hampered by unwanted thromboembolic events. Enhancing the ability of FVIIa to quickly stop a bleed and clear rapidly from circulation may yield an ideal molecule suitable for use in patients with acute bleeding.

OBJECTIVES

To address this need and the current liability of FVIIa, we produced a novel FVIIa molecule (CT-001) with enhanced potency and shortened plasma residence time by cell line engineering and FVIIa protein engineering for superior efficacy for acute bleeding and safety.

METHODS

To address safety, CT-001, a FVIIa protein with 4 desialylated N-glycans was generated to promote active recognition and clearance via the asialoglycoprotein receptor. To enhance potency, the gamma-carboxylated domain was modified with P10Q and K32E, which enhanced membrane binding.

RESULTS

Together, these changes significantly enhanced potency and clearance while retaining the ability to interact with the key hemostatic checkpoint proteins antithrombin and tissue factor pathway inhibitor.

CONCLUSIONS

These results demonstrate that a FVIIa molecule engineered to combine supra-physiological activity and shorter duration of action has the potential to overcome the current limitations of recombinant FVIIa to be a safe and effective approach to the treatment of acute bleeding.

Molecular coevolution of coagulation factor VIII and von Willebrand factor

Ancestral sequence reconstruction provides a unique platform for investigating the molecular evolution of single gene products and recently has shown success in engineering advanced biological therapeutics. To date, the coevolution of proteins within complexes and protein-protein interactions is mostly investigated in silico via proteomics and/or within single-celled systems. Herein, ancestral sequence reconstruction is used to investigate the molecular evolution of 2 proteins linked not only by stabilizing association in circulation but also by their independent roles within the primary and secondary hemostatic systems of mammals. Using sequence analysis and biochemical characterization of recombinant ancestral von Willebrand factor (VWF) and coagulation factor VIII (FVIII), we investigated the evolution of the essential macromolecular FVIII/VWF complex. Our data support the hypothesis that these coagulation proteins coevolved throughout mammalian diversification, maintaining strong binding affinities while modulating independent and distinct hemostatic activities in diverse lineages.

Progress in the Development of Anti-tissue Factor Pathway Inhibitors for Haemophilia Management

The unprecedented progress in addressing unmet needs in haemophilia care to date includes developing several novel therapies that rebalance haemostasis by restoring thrombin generation in patients with haemophilia A or B with and without inhibitors. These novel therapies are FVIII mimetics, antithrombin interference RNA therapy and several monoclonal antibodies directed against the tissue factor pathway inhibitor (anti-TFPI). In this review, we provide an update on the progress made in developing anti-TFPI therapie. Phase 1 data from the three anti-TFPI studies showed acceptable safety profiles, and currently, available phase 2 data are encouraging. While these data support these molecules' further development progression, there is uncertainty on several aspects of their evolution. Two of the three anti-TFPIs have shown drug-related thrombosis, with one study consequently terminated. None of the thrombotic events is predictable with current monitoring tools, and none correlate with known coagulation parameters. All three anti-TFPIs undergo target mediated drug disposition, which impacts the formulation of dosing regimen fo these therapies. They would require more frequent dosing than some of the extended half-life clotting factor products and antithrombin RNAi therapy. There is no assay to measure the TFPI as the physiological levels are very low, which makes monitoring the impact of the anti-TFPI a challenge. The anti-TFPIs have several advantages, including their bioavailability when administered subcutaneously, their stable pharmacokinetics and their ability to prevent bleeds in haemophilia A or B patients with and without inhibitors. Whether these advantages can be realized will depend on the outcome of the currently ongoing studies.

Metreleptin worked in a diabetic woman with a history of hematopoietic stem cell transplantation (HSCT) during infancy: further support for the concept of 'HSCT-associated lipodystrophy'

A 17-year-old woman with a history of childhood leukemia and hematopoietic stem cell transplantation (HSCT), preceded by total body irradiation, developed diabetes, dyslipidemia, fatty liver, and marked insulin resistance. Based on Dunnigan phenotype, HSCT-associated lipodystrophy was suspected. Because of rapid deterioration of diabetes control, metreleptin was introduced at 23 years of age upon receipt of her caregiver's documented consent. This trial was initially planned as a prospective 18 month-long study, with regular assessments of the patient's physical activity, food intake, and body composition analysis. However, because an abrupt and transient attenuation of the metreleptin effect occurred 16 months after the treatment initiation, the entire course of 28 months is reported here. Over the period, her HbA1c decreased from 10.9% to 6.7% despite no significant increase of physical activity and with a stable food intake. Decreased levels of triglyceride and non-HDL cholesterol were found. Her liver function improved, indicating the amelioration of fatty liver. In addition, a 25% reduction in the subcutaneous fat area at umbilical level was found, accompanied by a decrease in fat percentage of both total-body and trunk. The formation of neutralizing antibodies to metreleptin may be responsible for the transient loss of efficacy, considering a sudden elevation in her serum leptin level. In conclusion, metreleptin is useful for the management of HSCT-associated lipodystrophy, supporting the concept that adipose tissue dysfunction is responsible for diverse post-HSCT metabolic aberrations.

BSTP Review of 12 Case Studies Discussing the Challenges, Pathology, Immunogenicity, and Mechanisms of Inhaled Biologics

The inhalation route is a relatively novel drug delivery route for biotherapeutics and, as a result, there is a paucity of published data and experience within the toxicology/pathology community. In recent years, findings arising in toxicology studies with inhaled biologics have provoked concern and regulatory challenges due, in part, to the lack of understanding of the expected pathology, mechanisms, and adversity induced by this mode of delivery. In this manuscript, the authors describe 12 case studies, comprising 18 toxicology studies, using a range of inhaled biotherapeutics (monoclonal antibodies, fragment antigen-binding antibodies, domain antibodies, therapeutic proteins/peptides, and an oligonucleotide) in rodents, nonhuman primates (NHPs), and the rabbit in subacute (1 week) to chronic (26 weeks) toxicology studies. Analysis of the data revealed that many of these molecules were associated with a characteristic pattern of toxicity with high levels of immunogenicity. Microscopic changes in the airways consisted of a predominantly lymphoid perivascular/peribronchiolar (PV/PB) mononuclear inflammatory cell (MIC) infiltrate, whereas changes in the terminal airways/alveoli were characterized by simple ("uncomplicated") increases in macrophages or inflammatory cell infiltrates ranging from mixed inflammatory cell infiltration to inflammation. The PV/PB MIC changes were considered most likely secondary to immunogenicity, whereas simple increases in alveolar macrophages were most likely secondary to clearance mechanisms. Alveolar inflammatory cell infiltrates and inflammation were likely induced by immune modulation or stimulation through pharmacologic effects on target biology or type III hypersensitivity (immune complex disease). Finally, a group of experts provide introductory thoughts regarding the adversity of inhaled biotherapeutics and the basis for reasonable differences of opinion that might arise between toxicologists, pathologists, and regulators.

Improved prediction of HLA antigen presentation hotspots: Applications for immunogenicity risk assessment of therapeutic proteins

Immunogenicity risk assessment is a critical element in protein drug development. Currently, the risk assessment is most often performed using MHC-associated peptide proteomics (MAPPs) and/or T-cell activation assays. However, this is a highly costly procedure that encompasses limited sensitivity imposed by sample sizes, the MHC repertoire of the tested donor cohort and the experimental procedures applied. Recent work has suggested that these techniques could be complemented by accurate, high-throughput and cost-effective prediction of in silico models. However, this work covered a very limited set of therapeutic proteins and eluted ligand (EL) data. Here, we resolved these limitations by showcasing, in a broader setting, the versatility of in silico models for assessment of protein drug immunogenicity. A method for prediction of MHC class II antigen presentation was developed on the hereto largest available mass spectrometry (MS) HLA-DR EL data set. Using independent test sets, the performance of the method for prediction of HLA-DR antigen presentation hotspots was benchmarked. In particular, the method was showcased on a set of protein sequences including four therapeutic proteins and demonstrated to accurately predict the experimental MS hotspot regions at a significantly lower false-positive rate compared with other methods. This gain in performance was particularly pronounced when compared to the NetMHCIIpan-3.2 method trained on binding affinity data. These results suggest that in silico methods trained on MS HLA EL data can effectively and accurately be used to complement MAPPs assays for the risk assessment of protein drugs.

Mitigation of T-cell dependent immunogenicity by reengineering factor VIIa analogue

Vatreptacog alfa (VA), a recombinant activated human factor VII (rFVIIa) variant with 3 amino acid substitutions, was developed to provide increased procoagulant activity in hemophilia patients with inhibitors to factor VIII or factor IX. In phase 3 clinical trials, changes introduced during the bioengineering of VA resulted in the development of undesired anti-drug antibodies in some patients, leading to the termination of a potentially promising therapeutic protein product. Here, we use preclinical biomarkers associated with clinical immunogenicity to validate our deimmunization strategy applied to this bioengineered rFVIIa analog. The reengineered rFVIIa analog variants retained increased intrinsic thrombin generation activity but did not elicit T-cell responses in peripheral blood mononuclear cells isolated from 50 HLA typed subjects representing the human population. Our algorithm, rational immunogenicity determination, offers a broadly applicable deimmunizing strategy for bioengineered proteins.

A mutated factor X activatable by thrombin corrects bleedings in vivo in a rabbit model of antibody-induced hemophilia A

Rendering coagulation factor X sensitive to thrombin was proposed as a strategy that can bypass the need for factor VIII. In this paper, this non-replacement strategy was evaluated in vitro and in vivo in its ability to correct factor VIII but also factor IX, X and XI deficiencies. A novel modified factor X, named Actiten, was generated and produced in the HEK293F cell line. The molecule possesses the required post-translational modifications, partially keeps its ability to be activated by RVV-X, factor VIIa/tissue factor, factor VIIIa/factor IXa and acquires the ability to be activated by thrombin. The potency of the molecule was evaluated in respective deficient plasmas or hemophilia A plasmas, for some with inhibitors. Actiten corrects dose dependently all the assayed deficient plasmas. It is able to normalize the thrombin generation at 20 μg/mL showing however an increased lagtime. It was then assayed in a rabbit antibody-induced model of hemophilia A where, in contrast to recombinant factor X wild-type, it normalized the bleeding time and the loss of hemoglobin. No sign of thrombogenicity was observed and the generation of activated factor X was controlled by the anticoagulation pathway in all performed coagulation assays. This data indicates that Actiten may be considered as a possible non replacement factor to treat hemophilia's with the advantage of being a zymogen correcting bleedings only when needed.

T-Cell Dependent Immunogenicity of Protein Therapeutics Pre-clinical Assessment and Mitigation-Updated Consensus and Review 2020

Immune responses to protein and peptide drugs can alter or reduce their efficacy and may be associated with adverse effects. While anti-drug antibodies (ADA) are a standard clinical measure of protein therapeutic immunogenicity, T cell epitopes in the primary sequences of these drugs are the key drivers or modulators of ADA response, depending on the type of T cell response that is stimulated (e.g., T helper or Regulatory T cells, respectively). In a previous publication on T cell-dependent immunogenicity of biotherapeutics, we addressed mitigation efforts such as identifying and reducing the presence of T cell epitopes or T cell response to protein therapeutics prior to further development of the protein therapeutic for clinical use. Over the past 5 years, greater insight into the role of regulatory T cell epitopes and the conservation of T cell epitopes with self (beyond germline) has improved the preclinical assessment of immunogenic potential. In addition, impurities contained in therapeutic drug formulations such as host cell proteins have also attracted attention and become the focus of novel risk assessment methods. Target effects have come into focus, given the emergence of protein and peptide drugs that target immune receptors in immuno-oncology applications. Lastly, new modalities are entering the clinic, leading to the need to revise certain aspects of the preclinical immunogenicity assessment pathway. In addition to drugs that have multiple antibody-derived domains or non-antibody scaffolds, therapeutic drugs may now be introduced via viral vectors, cell-based constructs, or nucleic acid based therapeutics that may, in addition to delivering drug, also prime the immune system, driving immune response to the delivery vehicle as well as the encoded therapeutic, adding to the complexity of assessing immunogenicity risk. While it is challenging to keep pace with emerging methods for the preclinical assessment of protein therapeutics and new biologic therapeutic modalities, this collective compendium provides a guide to current best practices and new concepts in the field.

Immunogenicity of Protein Therapeutics: A Lymph Node Perspective

The continuous development of molecular biology and protein engineering technologies enables the expansion of the breadth and complexity of protein therapeutics for in vivo administration. However, the immunogenicity and associated in vivo development of antibodies against therapeutics are a major restriction factor for their usage. The B cell follicular and particularly germinal center areas in secondary lymphoid organs are the anatomical sites where the development of antibody responses against pathogens and immunogens takes place. A growing body of data has revealed the importance of the orchestrated function of highly differentiated adaptive immunity cells, including follicular helper CD4 T cells and germinal center B cells, for the optimal generation of these antibody responses. Understanding the cellular and molecular mechanisms mediating the antibody responses against therapeutics could lead to novel strategies to reduce their immunogenicity and increase their efficacy.

Requirements to participate in haemophilia clinical trials

INTRODUCTION

Clinical trials in haemophilia product development are expanding rapidly however, the number of sites and expertise in the clinical trial conduct is limited. Guidance on the requirement for conducting clinical trials is required AIM: The aim of this paper is to outline generic requirements to participate in clinical trials in haemophilia MATERIALS: This paper describes three elements which are the requirements for success conduct of haemophilia clinical trials. These are the study product, study participant, and the global regulatory and ethics framework RESULTS AND CONCLUSION: In haemophilia clinical trials, requirements for participate in studies are many and include considerations of study product, study participant and ethical and regulatory framework. When these elements are in place, it is possible to conduct haemophilia clinical trials anywhere in the world.

Enhanced potency of recombinant factor VIIa with increased affinity to activated platelets

BACKGROUND

Recombinant factor VIIa (rFVIIa) enhances thrombin generation in a platelet-dependent manner; however, rFVIIa binds activated platelets with relatively low affinity. Triggering receptor expressed on myeloid cells (TREM)-like transcript (TLT)-1 is expressed exclusively on activated platelets.

OBJECTIVE

To enhance the potency of rFVIIa via binding TLT-1.

METHODS

Recombinant FVIIa was conjugated to a TLT-1 binding Fab. In vitro potency of this platelet-targeted rFVIIa (PT-rFVIIa) was evaluated using factor X activation assays and by measuring viscoelastic changes in whole blood. In vivo potency was evaluated using a tail vein transection model in F8-/- mice expressing human TLT-1.

RESULTS

PT-rFVIIa and rFVIIa had similar dissociation constant values for tissue factor binding and similar tissue factor-dependent factor X activation. However, PT-rFVIIa had increased catalytic efficiency on TLT-1-loaded vesicles and activated platelets. The in vitro potency in normal human blood with antibody-induced hemophilia A was dependent on assay conditions used; with maximally activated platelets, the half maximal effective concentration for clot time for PT-rFVIIa was 49-fold lower compared with rFVIIa. In the murine bleeding model, a 53-fold lower half maximal effective concentration was observed for blood loss for PT-rFVIIa, supporting the relevance of the assay conditions with maximally activated platelets. In vitro analysis of blood from subjects with hemophilia A confirmed the data obtained with normal blood.

CONCLUSIONS

Increasing the affinity of rFVIIa to activated platelets resulted in approximately 50-fold increased potency both in vitro and in the mouse model. The correlation of in vivo with in vitro data using maximally activated platelets supports that these assay conditions are relevant when evaluating platelet-targeted hemostatic concepts.

SampPick: Selection of a Cohort of Subjects Matching a Population HLA Distribution

Immune responses to therapeutic proteins and peptides can adversely affect their safety and efficacy; consequently, immunogenicity risk-assessments are part of the development, licensure and clinical use of these products. In most cases the development of anti-drug antibodies is mediated by T cells which requires antigen presentation by Major Histocompatibility Complex Class II (MHCII) molecules (also called Human Leucocyte Antigen, HLA in humans). Immune responses to many protein therapeutics are thus HLA-restricted and it is important that the distribution of HLA variants used in the immunogenicity assessments provides adequate coverage of the target population. Due to biases inherent to the collection of samples in a blood bank or donor pool, simple random sampling will not achieve a truly representative sample of the population of interest. To help select a donor cohort we introduce SampPick, an implementation of simulated annealing which optimizes cohort selection to closely match the frequency distribution of a target population or subpopulation. With inputs of a target background frequency distribution for a population and a set of available, HLA-typed donors, the algorithm will iteratively create a cohort of donors of a user selected size that will closely match the target population rather than a random sample. In addition to optimizing the HLA types of donor cohorts, the software presented can be used to optimize donor cohorts for any other biallelic or monoallelic trait.

The evolution of factor VIIa in the treatment of bleeding in haemophilia with inhibitors

The use of activated factor VII (FVIIa) for the treatment of bleeding events in haemophilia patients with inhibitors was first reported over 30 years ago. Since then clinical trials, registries, case series, real‐world experience and an understanding of its mechanism of action have transformed what was originally a scientific curiosity into one of the major treatments for inhibitor patients, with innovative therapeutic regimens, dose optimization and individualized care now widely practiced. Given current understanding and use, it might be easy to forget the years of clinical research that led up to this point; in this review, we lay out changes based on broad eras of rFVIIa use. These eras cover the original uncertainty associated with dosing, efficacy and safety; the transformation of care ushered in with its widespread use; and the optimization and individualization of patient care and the importance of specialized support provided by haemophilia treatment centres. Today with the introduction of novel prophylactic agents such as emicizumab, we once again find ourselves dealing with the uncertainties of how best to utilize rFVIIa and newer investigational variants such as marzeptacog alfa and eptacog beta; we hope that the experiences of the past three decades will serve as a guide for this new era of care.

TCPro: an In Silico Risk Assessment Tool for Biotherapeutic Protein Immunogenicity

Most immune responses to biotherapeutic proteins involve the development of anti-drug antibodies (ADAs). New drugs must undergo immunogenicity assessments to identify potential risks at early stages in the drug development process. This immune response is T cell-dependent. Ex vivo assays that monitor T cell proliferation often are used to assess immunogenicity risk. Such assays can be expensive and time-consuming to carry out. Furthermore, T cell proliferation requires presentation of the immunogenic epitope by major histocompatibility complex class II (MHCII) proteins on antigen-presenting cells. The MHC proteins are the most diverse in the human genome. Thus, obtaining cells from subjects that reflect the distribution of the different MHCII proteins in the human population can be challenging. The allelic frequencies of MHCII proteins differ among subpopulations, and understanding the potential immunogenicity risks would thus require generation of datasets for specific subpopulations involving complex subject recruitment. We developed TCPro, a computational tool that predicts the temporal dynamics of T cell counts in common ex vivo assays for drug immunogenicity. Using TCPro, we can test virtual pools of subjects based on MHCII frequencies and estimate immunogenicity risks for different populations. It also provides rapid and inexpensive initial screens for new biotherapeutics and can be used to determine the potential immunogenicity risk of new sequences introduced while bioengineering proteins. We validated TCPro using an experimental immunogenicity dataset, making predictions on the population-based immunogenicity risk of 15 protein-based biotherapeutics. Immunogenicity rankings generated using TCPro are consistent with the reported clinical experience with these therapeutics.

Crystal structure, epitope, and functional impact of an antibody against a superactive FVIIa provide insights into allosteric mechanism

BACKGROUND

Blood coagulation factor VIIa (FVIIa) plays its critical physiological role in the initiation of hemostasis. Even so, recombinant FVIIa is successfully used as a bypassing agent for factor VIII or IX in the treatment of bleeds in patients with severe hemophilia with inhibitors. To investigate the utility of more potent FVIIa variants with enhanced intrinsic activity, molecules such as V21D/E154V/M156Q-FVIIa (FVIIaDVQ) were designed.

METHODS

Surface plasmon resonance was used to characterize the binding of mAb4F5 to FVIIaDVQ and related variants. X-ray crystallography was used to determine the structure of the Fab fragment of mAb4F5 (Fab4F5). Molecular docking and small angle X-ray scattering led to a model of FVIIaDVQ:Fab4F5 complex.

RESULTS

The binding experiments, functional effects on FVIIaDVQ and structure of mAb4F5 (originally intended for quantification of FVIIaDVQ in samples containing FVII(a)) pinpointed the epitope (crucial role for residue Asp21) and shed light on the role of the N-terminus of the protease domain in FVIIa allostery. The potential antigen-combining sites are composed of 1 hydrophobic and 1 negatively charged pocket formed by 6 complementarity-determining region (CDR) loops. Structural analysis of Fab4F5 shows that the epitope interacts with the periphery of the hydrophobic pocket and provides insights into the molecular basis of mAb4F5 recognition and tight binding of FVIIaDVQ.

CONCLUSION

The binary complex explains and supports the selectivity and functional consequences of Fab4F5 association with FVIIaDVQ and illustrates the potentially unique antigenicity of this FVIIa variant. This will be useful in the design of less immunogenic variants.

The future of bypassing agents for hemophilia with inhibitors in the era of novel agents

Bypassing agents are presently the standard of care for the treatment of bleeding episodes in patients with hemophilia and high-titer inhibitors and are also used for bleed prevention. Only two bypassing agents are available to patients, and these products trace their lineage to the 1970s (activated prothrombin complex concentrates) and the 1980s (recombinant factor VIIa). Given the limited repertoire of available products, clinicians have relied on experience, empirical observation, registry data and individualized care to improve clinical outcomes on a case-by-case basis. Research over the past two decades has culminated in a greatly improved understanding of human coagulation; resulting from this, new products have been developed that offer treatment options and mechanisms of actions that differ from current bypassing agents. The most advanced in clinical development is emicizumab, a bispecific antibody that mimics the function of FVIIIa in the intrinsic Xase complex and is indicated for once-weekly or every-other-week prophylactic dosing in inhibitor patients. Other non-traditional products in clinical development include fitusiran and antibodies directed against tissue factor pathway inhibitor. As non-factor-based therapies become more widely utilized over time, the use of bypassing agents may be expected to decrease; however, bypassing agents will remain essential for the foreseeable future. As such, clinical development of bypassing agents continues, with some products (e.g. eptacog beta) under regulatory review. In this review we examine the optimal use of bypassing agents and their mechanism of action. We also discuss newer products and how these might theoretically be administered in conjunction with traditional bypassing agents.

Human platelets express endothelial protein C receptor, which can be utilized to enhance localization of factor VIIa activity

Essentials Factor VIIa binds activated platelets to promote hemostasis in hemophilia patients with inhibitors. The interactions and sites responsible for platelet-FVIIa binding are not fully understood. Endothelial cell protein C receptor (EPCR) is expressed on activated human platelets. EPCR binding enhances the efficacy of a FVIIa variant and could impact design of new therapeutics.

SUMMARY

Background High-dose factor VIIa (FVIIa) is routinely used as an effective bypassing agent to treat hemophilia patients with inhibitory antibodies that compromise factor replacement. However, the mechanism by which FVIIa binds activated platelets to promote hemostasis is not fully understood. FVIIa-DVQ is an analog of FVIIa with enhanced tissue factor (TF)-independent activity and hemostatic efficacy relative to FVIIa. Our previous studies have shown that FVIIa-DVQ exhibits greater platelet binding, thereby suggesting that features in addition to lipid composition contribute to platelet-FVIIa interactions. Objectives Endothelial cell protein C receptor (EPCR) also functions as a receptor for FVIIa on endothelial cells. We therefore hypothesized that an interaction with EPCR might play a role in platelet-FVIIa binding. Methods/results In the present study, we used flow cytometric analyses to show that platelet binding of both FVIIa and FVIIa-DVQ is partially inhibited in the presence of excess protein C or an anti-EPCR antibody. This decreased binding results in a corresponding decrease in the activity of both molecules in FXa and thrombin generation assays. Enhanced binding to EPCR was sufficient to account for the increased platelet binding of FVIIa-DVQ compared with wild-type FVIIa. As EPCR protein expression has not previously been shown in platelets, we confirmed the presence of EPCR in platelets using immunofluorescence, flow cytometry, immunoprecipitation, and mass spectrometry. Conclusions This work represents the first demonstration that human platelets express EPCR and suggests that modulation of EPCR binding could be utilized to enhance the hemostatic efficacy of rationally designed FVIIa analogs.

Anti-Drug Antibodies: Emerging Approaches to Predict, Reduce or Reverse Biotherapeutic Immunogenicity

The development of anti-drug antibodies (ADAs) following administration of biotherapeutics to patients is a vexing problem that is attracting increasing attention from pharmaceutical and biotechnology companies. This serious clinical problem is also spawning creative research into novel approaches to predict, avoid, and in some cases even reverse such deleterious immune responses. CD4⁺ T cells are essential players in the development of most ADAs, while memory B-cell and long-lived plasma cells amplify and maintain these responses. This review summarizes methods to predict and experimentally identify T-cell and B-cell epitopes in therapeutic proteins, with a particular focus on blood coagulation factor VIII (FVIII), whose immunogenicity is clinically significant and is the subject of intensive current research. Methods to phenotype ADA responses in humans are described, including T-cell stimulation assays, and both established and novel approaches to determine the titers, epitopes and isotypes of the ADAs themselves. Although rational protein engineering can reduce the immunogenicity of many biotherapeutics, complementary, novel approaches to induce specific tolerance, especially during initial exposures, are expected to play significant roles in future efforts to reduce or reverse these unwanted immune responses.

The effect of acylation with fatty acids and other modifications on HLA class II:peptide binding and T cell stimulation for three model peptides

Immunogenicity is a major concern in drug development as anti-drug antibodies in many cases affect both patient safety and drug efficacy. Another concern is often the limited half-life of drugs, which can be altered by different chemical modifications, like acylation with fatty acids. However, acylation with fatty acids has been shown in some cases to modulate T cell activation. Therefore, to understand the role of acylation with fatty acids on immunogenicity we tested three immunogenic non-acylated peptides and 14 of their acylated analogues for binding to 26 common HLA class II alleles, and their ability to activate T cells in an ex vivo T cell assay. Changes in binding affinity associated with acylation with fatty acids were typically modest, though a significant decrease was observed for influenza HA acylated with a stearic acid, and affinities for DQ alleles were consistently increased. Importantly, we showed that for all three immunogenic peptides acylation with fatty acids decreased their capacity to activate T cells, a trend particularly evident with longer fatty acids typically positioned within the peptide HLA class II binding core region, or when closer to the C-terminus. With these results we have demonstrated that acylation with fatty acids of immunogenic peptides can lower their stimulatory capacity, which could be important knowledge for drug design and immunogenicity mitigation.

Development of a strategy and computational application to select candidate protein analogues with reduced HLA binding and immunogenicity

Unwanted immune responses against protein therapeutics can reduce efficacy or lead to adverse reactions. T-cell responses are key in the development of such responses, and are directed against immunodominant regions within the protein sequence, often associated with binding to several allelic variants of HLA class II molecules (promiscuous binders). Herein, we report a novel computational strategy to predict 'de-immunized' peptides, based on previous studies of erythropoietin protein immunogenicity. This algorithm (or method) first predicts promiscuous binding regions within the target protein sequence and then identifies residue substitutions predicted to reduce HLA binding. Further, this method anticipates the effect of any given substitution on flanking peptides, thereby circumventing the creation of nascent HLA-binding regions. As a proof-of-principle, the algorithm was applied to Vatreptacog α, an engineered Factor VII molecule associated with unintended immunogenicity. The algorithm correctly predicted the two immunogenic peptides containing the engineered residues. As a further validation, we selected and evaluated the immunogenicity of seven substitutions predicted to simultaneously reduce HLA binding for both peptides, five control substitutions with no predicted reduction in HLA-binding capacity, and additional flanking region controls. In vitro immunogenicity was detected in 21·4% of the cultures of peptides predicted to have reduced HLA binding and 11·4% of the flanking regions, compared with 46% for the cultures of the peptides predicted to be immunogenic. This method has been implemented as an interactive application, freely available online at http://tools.iedb.org/deimmunization/.

Immunogenicity assessment during the development of protein therapeutics

Objective

Here we provide a critical review of the state of the art with respect to non-clinical assessments of immunogenicity for therapeutic proteins.

Key findings

The number of studies on immunogenicity published annually has more than doubled in the last 5 years. The science and technology, which have reached a critical mass, provide multiple of non-clinical approaches (computational, in vitro, ex vivo and animal models) to first predict and then to modify or eliminate T-cell or B-cell epitopes via de-immunization strategies. We discuss how these may be used in the context of drug development in assigning the immunogenicity risk of new and marketed therapeutic proteins.

Summary

Protein therapeutics represents a large share of the pharma market and provide medical interventions for some of the most complex and intractable diseases. Immunogenicity (the development of antibodies to therapeutic proteins) is an important concern for both the safety and efficacy of protein therapeutics as immune responses may neutralize the activity of life-saving and highly effective protein therapeutics and induce hypersensitivity responses including anaphylaxis. The non-clinical computational tools and experimental technologies that offer a comprehensive and increasingly accurate estimation of immunogenic potential are surveyed here. This critical review also discusses technologies which are promising but are not as yet ready for routine use.

Canine models of inherited bleeding disorders in the development of coagulation assays, novel protein replacement and gene therapies

Animal models of inherited bleeding disorders are important for understanding disease pathophysiology and are required for preclinical assessment of safety prior to testing of novel therapeutics in human and veterinary medicine. Experiments in these animals represent important translational research aimed at developing safer and better treatments, such as plasma-derived and recombinant protein replacement therapies, gene therapies and immune tolerance protocols for antidrug inhibitory antibodies. Ideally, testing is done in animals with the analogous human disease to provide essential safety information, estimates of the correct starting dose and dose response (pharmacokinetics) and measures of efficacy (pharmacodynamics) that guide the design of human trials. For nearly seven decades, canine models of hemophilia, von Willebrand disease and other inherited bleeding disorders have not only informed our understanding of the natural history and pathophysiology of these disorders but also guided the development of novel therapeutics for use in humans and dogs. This has been especially important for the development of gene therapy, in which unique toxicities such as insertional mutagenesis, germ line gene transfer and viral toxicities must be assessed. There are several issues regarding comparative medicine in these species that have a bearing on these studies, including immune reactions to xenoproteins, varied metabolism or clearance of wild-type and modified proteins, and unique tissue tropism of viral vectors. This review focuses on the results of studies that have been performed in dogs with inherited bleeding disorders that closely mirror the human condition to develop safe and effective protein and gene-based therapies that benefit both species.

Half-life extended biotherapeutics

INTRODUCTION

Many of the biotherapeutics approved or under development suffer from a short half-life necessitating frequent applications in order to maintain a therapeutic concentration over an extended period of time. The implementation of half-life extension strategies allows the generation of long-lasting therapeutics with improved pharmacokinetic and pharmacodynamic properties.

AREAS COVERED

This review gives an overview of the different half-life extension strategies developed over the past years and their application to generate next-generation biotherapeutics. It focuses on srategies already used in approved drugs and drugs that are in clinical development. These strategies include those aimed at increasing the hydrodynamic radius of the biotherapeutic and strategies which further implement recycling by the neonatal Fc receptor (FcRn).

EXPERT OPINION

Half-life extension strategies have become an integral part of development for many biotherapeutics. A diverse set of these strategies is available for the fine-tuning of half-life and adaption to the intended treatment modality and disease. Currently, half-life extension is dominated by strategies utilizing albumin binding or fusion, fusion to an immunoglobulin Fc region and PEGylation. However, a variety of alternative strategies, such as fusion of flexible polypeptide chains as PEG mimetic substitute, have reached advanced stages and offer further alternatives for half-life extension.

Safety, Stability and Pharmacokinetic Properties of (super)Factor Va, a Novel Engineered Coagulation Factor V for Treatment of Severe Bleeding

PURPOSE

Activated (super)Factor V ((super)FVa) is a novel engineered FV with excellent prohemostatic efficacy. (Super)FVa has three APC cleavage site mutations and an interdomain disulfide bond. Stability, pharmacokinetics, and immunogenic and thrombogenic potential are reported here.

METHODS

Stability and circulating half-life were determined after incubation in buffer and human plasma, and after injection into FVIII-deficient mice. Immunogenicity potential was assessed by B- and T-cell specific epitope prediction and structural analysis using surface area and atomic depth computation. Thrombogenic potential was determined by quantification of lung fibrin deposition in wild-type mice after intravenous injection of (super)FVa (200 U/kg), recombinant human (rh) Tissue Factor (0.4-16 pmol/kg), rhFVIIa (3 mg/kg) or saline.

RESULTS

FVa retained full activity over 30 h in buffer, the functional half-life in human plasma was 4.9 h, and circulating half-life in FVIII-deficient mice was ~30 min. Predicted immunogenicity was not increased compared to human FV. While rh Tissue Factor, the positive control, resulted in pronounced lung fibrin depositions (mean 121 μg/mL), (super)FVa did not (6.7 μg/mL), and results were comparable to fibrin depositions with rhFVIIa (7.6 μg/mL) or saline (5.6 μg/mL).

CONCLUSION

FVa has an appropriate safety and stability profile for further preclinical development as a prohemostatic against severe bleeding.

Engineering less immunogenic and antigenic FVIII proteins

The development of neutralizing antibodies against blood coagulation factor VIII (FVIII), referred to clinically as "inhibitors", is the most challenging and deleterious adverse event to occur following intravenous infusions of FVIII to treat hemophilia A. Inhibitors occlude FVIII surfaces that must bind to activated phospholipid membranes, the serine proteinase factor IXa, and other components of the 'intrinsic tenase complex' in order to carry out its important role in accelerating blood coagulation. Inhibitors develop in up to one of every three patients, yet remarkably, a substantial majority of severe hemophilia A patients, who circulate no detectable FVIII antigen or activity, acquire immune tolerance to FVIII during initial infusions or else after intensive FVIII therapy to overcome their inhibitor. The design of less immunogenic FVIII proteins through identification and modification ("de-immunization") of immunodominant T-cell epitopes is an important goal. For patients who develop persistent inhibitors, modification of B-cell epitopes through substitution of surface-exposed amino acid side chains and/or attachment of bulky moieties to interfere with FVIII attachment to antibodies and memory B cells is a promising approach. Both experimental and computational methods are being employed to achieve these goals. Future therapies for hemophilia A, as well as other monogenic deficiency diseases, are likely to involve administration of less immunogenic proteins in conjunction with other novel immunotherapies to promote a regulatory cellular environment promoting durable immune tolerance.