Impact of product-related factors on immunogenicity of biotherapeutics

Influence of aggregation and route of injection on the biodistribution of mouse serum albumin

Protein aggregates are a major risk factor for immunogenicity. Until now most studies on aggregate-driven immunogenicity have focused on linking physicochemical features of the aggregates to the formation of anti-drug antibodies. Lacking is however, basic knowledge on the effect of aggregation on the biodistribution and clearance of therapeutic proteins in vivo. The aim of current study was to get insight into the effect of aggregation on biodistribution in mice using different routes of administration. Fluorescently labeled stressed and unstressed mouse serum albumin was injected via different routes in mice and detected via in vivo fluorescence imaging up to 48 hrs post-injection. We found that biodistribution of stressed MSA significantly differed from its unstressed counterpart. Subcutaneous and intramuscular administration resulted in accumulation of protein at the site of injection, from which clearance of stressed MSA was considerably slower than clearance of unstressed MSA. Upon intravenous and intraperitoneal injection of stressed MSA, fluorescent “hotspots” were observed in the spleens, livers and lungs. Further and more detailed examination of biodistribution after intraperitoneal injection showed higher fluorescence in most of tested organs suggesting more efficient diffusion and/or lymphatic uptake from peritoneum of unstressed MSA than the stressed formulation.

Recombinant murine growth hormone particles are more immunogenic with intravenous than subcutaneous administration

Evaluation and mitigation of the risk of immunogenicity to protein aggregates and particles in therapeutic protein products remains a primary concern for drug developers and regulatory agencies. To investigate how the presence of protein particles and the route of administration influence the immunogenicity of a model therapeutic protein, we measured the immune response in mice to injections of formulations of recombinant murine growth hormone (rmGH) that contained controlled levels of protein particles. Mice were injected twice over 6 weeks with rmGH formulations via the subcutaneous, intraperitoneal, or intravenous (i.v.) routes. In addition to soluble, monomeric rmGH, the samples prepared contained either nanoparticles of rmGH or both nano- and microparticles of rmGH.The appearance of anti-rmGH IgG1, IgG2a, IgG2b, IgG2c, and IgG3 titers following the second injection of both preparations implies that multiple mechanisms contributed to the immune response. No dependence of the immune response on particle size and distribution was observed. The immune response measured after the second injection was most pronounced when i.v. administration was used. Despite producing high anti-rmGH titers mice appeared to retain the ability to properly regulate and use endogenous growth hormone.

Identification and characterization of host cell protein product-associated impurities in monoclonal antibody bioprocessing

Downstream processing of monoclonal antibodies (mAbs) has evolved to allow the specific process for a new product to be developed largely by empirical specialization of a platform process that enables removal of impurities of different kinds. A more complete characterization of impurities and the product itself would provide insights into the rational design of efficient downstream processes. This work identifies and characterizes host cell protein (HCP) product-associated impurities, that is, HCP species carried through the downstream processes via direct interactions with the mAb. Interactions between HCPs and mAbs are characterized using cross-interaction chromatography under solution conditions typical of those used in downstream processing. The interacting species are then identified by two-dimensional gel electrophoresis and mass spectrometry. This methodology has been applied to identify product-associated impurities in one particular purification step, namely protein A affinity chromatography, for four therapeutic mAbs as well as the Fab and Fc domains of one of these mAbs. The results show both the differences in HCP-mAb interactions among different mAbs, and the relative importance of product association compared to co-elution in protein A affinity chromatography.

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.

Immunogenicity of therapeutic proteins: influence of aggregation

The elicitation of anti-drug antibodies (ADA) against biotherapeutics can have detrimental effects on drug safety, efficacy, and pharmacokinetics. The immunogenicity of biotherapeutics is, therefore, an important issue. There is evidence that protein aggregation can result in enhanced immunogenicity; however, the precise immunological and biochemical mechanisms responsible are poorly defined. In the context of biotherapeutic drug development and safety assessment, understanding the mechanisms underlying aggregate immunogenicity is of considerable interest. This review provides an overview of the phenomenon of protein aggregation, the production of unwanted aggregates during bioprocessing, and how the immune response to aggregated protein differs from that provoked by non-aggregated protein. Of particular interest is the nature of the interaction of aggregates with the immune system and how subsequent ADA responses are induced. Pathways considered here include 'classical' activation of the immune system involving antigen presenting cells and, alternatively, the breakdown of B-cell tolerance. Additionally, methods available to screen for aggregation and immunogenicity will be described. With an increased understanding of aggregation-enhanced immune responses, it may be possible to develop improved manufacturing and screening processes to avoid, or at least reduce, the problems associated with ADA.

Antigenic liposomes displaying CD22 ligands induce antigen-specific B cell apoptosis

Antibodies confer humoral immunity but can also be harmful when they target an autoantigen, alloantigen, allergen, or biotherapeutic. New strategies are needed for antigen-specific suppression of undesired antibody responses, particularly to T cell-dependent protein antigens, because they elicit T cell help. Here we show that liposomal nanoparticles, displaying both antigen and glycan ligands of the inhibitory coreceptor CD22, induce a tolerogenic program that selectively causes apoptosis in mouse and human B cells. These SIGLEC-engaging tolerance-inducing antigenic liposomes (STALs, where SIGLEC is defined as sialic acid-binding Ig-like lectin) induced robust antigen-specific tolerance to protein antigens in mice, preventing subsequent immune response to challenge with the same antigen. Since development of inhibitory antibodies to FVIII is a serious problem in treatment of hemophilia A patients, we investigated the potential of this approach for inducing tolerance to FVIII in a hemophilia mouse model. STALs prevented formation of inhibitory FVIII antibodies, allowing for effective administration of FVIII to hemophilia mice to prevent bleeding. These findings suggest that STALs could be used to eliminate or prevent harmful B cell-mediated immune responses.

Assessment and significance of protein-protein interactions during development of protein biopharmaceuticals

Early development of protein biotherapeutics using recombinant DNA technology involved progress in the areas of cloning, screening, expression and recovery/purification. As the biotechnology industry matured, resulting in marketed products, a greater emphasis was placed on development of formulations and delivery systems requiring a better understanding of the chemical and physical properties of newly developed protein drugs. Biophysical techniques such as analytical ultracentrifugation, dynamic and static light scattering, and circular dichroism were used to study protein-protein interactions during various stages of development of protein therapeutics. These studies included investigation of protein self-association in many of the early development projects including analysis of highly glycosylated proteins expressed in mammalian CHO cell cultures. Assessment of protein-protein interactions during development of an IgG1 monoclonal antibody that binds to IgE were important in understanding the pharmacokinetics and dosing for this important biotherapeutic used to treat severe allergic IgE-mediated asthma. These studies were extended to the investigation of monoclonal antibody-antigen interactions in human serum using the fluorescent detection system of the analytical ultracentrifuge. Analysis by sedimentation velocity analytical ultracentrifugation was also used to investigate competitive binding to monoclonal antibody targets. Recent development of high concentration protein formulations for subcutaneous administration of therapeutics posed challenges, which resulted in the use of dynamic and static light scattering, and preparative analytical ultracentrifugation to understand the self-association and rheological properties of concentrated monoclonal antibody solutions.

Challenges and approaches for the development of safer immunomodulatory biologics

Immunomodulatory biologics are a class of biotechnology-derived therapeutic products that are designed to engage immune-relevant targets and are indicated in the treatment and management of a range of diseases, including immune-mediated inflammatory diseases and malignancies.

Despite their high specificity and therapeutic advantages, immmunomodulatory biologics have been associated with adverse reactions such as serious infections, malignancies and cytokine release syndrome, which arise owing to the on-target or exaggerated pharmacological effects of these drugs. Immunogenicity resulting in the generation of antidrug antibodies is another unwanted effect that leads to loss of efficacy and — rarely — hypersensitivity reactions.

For some adverse reactions, mitigating and preventive strategies are in place, such as stratifying patients on the basis of responsiveness to therapy and the risk of developing adverse reactions. These strategies depend on the availability of robust biomarkers for therapeutic efficacy and the risk of adverse reactions: for example, seropositivity for John Cunningham virus is a risk factor for progressive multifocal leukoencephalopathy. The development of effective biomarkers will greatly aid these strategies.

The development and design of safer immunomodulatory biologics is reliant on a detailed understanding of the nature of the disease, target biology, the interaction of the target with the immunomodulatory biologic and the inherent properties of the biologic that elicit unwanted effects.

The availability of in vitro and in vivo models that can be used to predict adverse reactions associated with immunomodulatory biologics is central to the development of safer immunomodulatory biologics. Some progress has been made in developing in vitro and in silico tests for predicting cytokine release syndrome and immunogenicity, but there is still a lack of models for effectively predicting infections and malignancies.

Two pathways can be followed in designing and developing safer immunomodulatory biologics. The first pathway involves generating a biologic that engages an alternative target or mechanism to produce the desired pharmacodynamic effect without the associated adverse reaction, and is followed when the adverse reaction cannot be dissociated from the target biology. The second pathway involves redesigning the biologic to 'engineer out' components within the biologic structure that trigger adverse effects or to alter the nature of the target–biologic interactions.

Owing to their specificity, immunomodulatory biologics generally have better safety profiles than small-molecule drugs. However, adverse effects such as an increased risk of infections or cytokine release syndrome are of concern. Here, Park and colleagues discuss the current strategies used to predict and mitigate these adverse effects and consider how they can be used to inform the development of safer immunomodulatory biologics.

Immunomodulatory biologics, which render their therapeutic effects by modulating or harnessing immune responses, have proven their therapeutic utility in several complex conditions including cancer and autoimmune diseases. However, unwanted adverse reactions — including serious infections, malignancy, cytokine release syndrome, anaphylaxis and hypersensitivity as well as immunogenicity — pose a challenge to the development of new (and safer) immunomodulatory biologics. In this article, we assess the safety issues associated with immunomodulatory biologics and discuss the current approaches for predicting and mitigating adverse reactions associated with their use. We also outline how these approaches can inform the development of safer immunomodulatory biologics.

Effect of treatment regimen on the immunogenicity of human interferon Beta in immune tolerant mice

PURPOSE

Interferon beta is commonly used as therapeutic in the first line of therapy for multiple sclerosis. However, depending on the product, it induces an antibody response in up to 60% of patients. This study evaluated the impact of therapy related factors like dose, route of administration and administration frequency on the immunogenicity of one of the originator interferon beta drugs (Betaferon®) in an immune tolerant transgenic mouse model.

METHODS

Immune tolerant transgenic mice received injections with Betaferon® via different routes, doses and injection frequencies. Anti-drug antibody (ADA) production was measured by ELISA to assess immunogenicity.

RESULTS

A single injection of Betaferon® was found to be sufficient for the induction of ADAs. The antibody titer was enhanced with increasing dose and treatment frequency. Among the tested administration routes, the intravenous route was the most immunogenic one, which is in contradiction with one of the dogma in immunogenicity research according to which subcutaneous administration is the most immunogenic route. Intramuscular, intraperitoneal and subcutaneous injections resulted in comparable immunogenicity.

CONCLUSION

This study shows that treatment related factors affect significantly immunogenicity of Betaseron® and therefore substantiate the need for further studies on these factors in patients.

Clinical testing for neutralizing antibodies to interferon-β in multiple sclerosis

Biopharmaceuticals are drugs which are based on naturally occurring proteins (antibodies, receptors, cytokines, enzymes, toxins), nucleic acids (DNA, RNA) or attenuated microorganisms. Immunogenicity of these agents has been commonly described and refers to a specific antidrug antibody response. Such immunogenicity represents a major factor impairing the efficacy of biopharmaceuticals due to biopharmaceutical neutralization. Indeed, clinical experience has shown that induction of antidrug antibodies is associated with a loss of response to biopharmaceuticals and also with hypersensitivity reactions. The first disease-specific agent licensed to treat multiple sclerosis (MS) was interferon-β (IFNβ). In its various preparations, it remains the most commonly used first-line agent. The occurrence of antidrug antibodies has been extensively researched in MS, particularly in relation to IFNβ. However, much controversy remains regarding the significance of these antibodies and incorporation of testing into clinical practice. Between 2% and 45% of people treated with IFNβ will develop neutralizing antibodies, and this is dependent on the specific drug and dosing regimen. The aim of this review is to discuss the use of IFNβ in MS, the biological and clinical relevance of anti-IFNβ antibodies (binding and neutralizing antibodies), the incorporation of testing in clinical practice and ongoing research in the field.

Epoetin biosimilars in Europe: five years on

Biosimilars have been developed for several biologic therapeutic agents, including erythropoiesis-stimulating agents (ESAs). However, biosimilars cannot be assumed to be completely identical to the reference product, nor can two different biosimilars of the same reference product be considered equivalent. Accordingly, standards for approving biosimilars are distinct from those for generic versions of conventional pharmaceuticals.By late 2007, two biosimilar epoetins (HX575 and SB309) had been approved by the European Medicines Agency (EMA), following a series of pharmacokinetic and pharmacodynamic equivalence studies, as well as phase 3 clinical comparability evaluations. Additionally, the results of a limited number of postauthorization interventional or observational studies and quality comparisons were published subsequently on both products.The reported differences in glycosylation profiles between these epoetin biosimilars and their reference product, as well as the lack of long-term safety and efficacy evaluation, could indicate a need to develop a more comprehensive analysis of the available data, and to evaluate the post-authorization real-life data, in order to gain a better understanding of any potential implications of molecular structural or formulation differences on longterm safety and effectiveness.Switching between an original reference ESA and a biosimilar (and possibly also switching between biosimilar versions of the same product) should be regarded as a change in clinical management. Clinicians need to be fully involved in such decisions. Prescribing by brand name will prevent unintentional substitution by pharmacists and allow for effective pharmacovigilance, in accordance with recent EU directives. In this review, the authors have analyzed most of the published information on the two epoetin biosimilars, HX575 and SB309, to highlight the points that healthcare providers may need to consider when assessing an epoetin biosimilar.

Characterization of Fc-fusion protein aggregates derived from extracellular domain disulfide bond rearrangements

Aggregation of protein biotherapeutics has consequences for decreasing production and has been implicated in immunogenicity. The mechanisms of protein aggregation vary depending on the protein and the expression system utilized, making it difficult to elucidate the conditions that promote their formation. Nonnative aggregation of recombinant immunoglobulin G protein therapeutics from mammalian expression systems has been extensively studied. To better understand the mechanisms behind aggregation of glycosylated fusion proteins produced in Chinese hamster ovarian cells, we have examined the high-molecular-weight (HMW) species of activin receptor-like kinase 1 Fc fusion protein. Size-exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicate that two populations of aggregate exist: (1) nondisulfide-linked, higher-order aggregates and (2) disulfide-linked oligomers. The largest aggregated species have increased nonnative structure, whereas the smallest aggregated species maintain structure similar to monomer. The HMW species display decreased levels of O-linked glycosylation, higher occupancy of high-mannose N-linked oligosaccharide structures, and overall less sialylation as their size increases. Disulfide-linked aggregate species were found to associate through the extracellular domain. N-linked glycosylation on the extracellular domain (ECD) appears to discourage disulfide-linked aggregation. Elucidation of the specific mechanisms behind disulfide-linked aggregate formation may assist in designing processes that limit aggregate formation in cell culture, with implications for increased production.

Adsorption behavior of a human monoclonal antibody at hydrophilic and hydrophobic surfaces

One aspiration for the formulation of human monoclonal antibodies (mAb) is to reach high solution concentrations without compromising stability. Protein surface activity leading to instability is well known, but our understanding of mAb adsorption to the solid-liquid interface in relevant pH and surfactant conditions is incomplete. To investigate these conditions, we used total internal reflection fluorescence (TIRF) and neutron reflectometry (NR). The mAb tested ("mAb-1") showed highest surface loading to silica at pH 7.4 (~12 mg/m(2)), with lower surface loading at pH 5.5 (~5.5 mg/m(2), further from its pI of 8.99) and to hydrophobized silica (~2 mg/m(2)). The extent of desorption of mAb-1 from silica or hydrophobized silica was related to the relative affinity of polysorbate 20 or 80 for the same surface. mAb-1 adsorbed to silica on co-injection with polysorbate (above its critical micelle concentration) and also to silica pre-coated with polysorbate. A bilayer model was developed from NR data for mAb-1 at concentrations of 50-5000 mg/L, pH 5.5, and 50-2000 mg/L, pH 7.4. The inner mAb-1 layer was adsorbed to the SiO₂ surface at near saturation with an end-on" orientation, while the outer mAb-1 layer was sparse and molecules had a "side-on" orientation. A non-uniform triple layer was observed at 5000 mg/L, pH 7.4, suggesting mAb-1 adsorbed to the SiO₂ surface as oligomers at this concentration and pH. mAb-1 adsorbed as a sparse monolayer to hydrophobized silica, with a layer thickness increasing with bulk concentration - suggesting a near end-on orientation without observable relaxation-unfolding.

The utility of modeling and simulation approaches to evaluate immunogenicity effect on the therapeutic protein pharmacokinetics

While therapeutic proteins (TP), particularly recombinant human proteins and fully human monoclonal antibodies, are designed to have a low immunogenic potential in humans, a clinical immune response does sometimes occur and cannot be predicted from preclinical studies. Changes in TP pharmacokinetics may be perceived as an early indication of antibody formation and serve as a surrogate for later changes in efficacy and safety in individual subjects. Given the substantial increase in number of biological products, including biosimilars, there is an urgent need to quantitatively predict and quantify the immune response and any consequential changes in TP pharmacokinetics. The purpose of this communication is to review the utility of population-based modeling and simulation approaches developed to date for investigating the development of an immune response and assessing its impact on TP pharmacokinetics. Two examples of empirical modeling approaches for pharmacokinetic assessment are presented. The first example presents methods to analyze pharmacokinetic data in the presence of anti-drug antibody (ADA) and confirm the effect of immunogenicity on TP pharmacokinetics in early phases of drug development. The second example provides a framework to analyze pharmacokinetic data in the absence or with very low incidence of ADA and confirm with enough power the lack of an immunogenicity effect on TP pharmacokinetics in late phases of drug development. Finally, a theoretical mechanism-based modeling framework is presented to mathematically relate the complex interaction among TP, their targets, and ADA.

The Göttingen minipig® as an alternative non-rodent species for immunogenicity testing: a demonstrator study using the IL-1 receptor antagonist anakinra

The use of recombinant human proteins for the treatment of several diseases has increased considerably during the last decades. A major safety and efficacy issue of biopharmaceuticals is their potential immunogenicity. To prevent immunogenicity, biotechnology-derived proteins are engineered to be as human-like as possible. Immunogenicity is mainly determined in non-human primates (NHP), as they are considered to be the best predictive animal species for human safety, based on their close relatedness to man. As minipigs are increasingly used in the safety evaluation of (bio)pharmaceuticals, the predictive value of the minipig in immunogenicity testing was evaluated in this study, using anakinra as a model compound. Animals were treated subcutaneously with either placebo, low- (0.5 mg/kg), or high-dose (5 mg/kg) anakinra daily on 29 consecutive days. After the first and last dose, the pharmacokinetic (PK) profile of anakinra was evaluated. Antibodies directed to anakinra were measured on several time points during the treatment period. Furthermore, hematology, clinical chemistry, body weight, clinical signs, and histopathology of several organs were evaluated. No signs of toxicity were observed upon treatment with anakinra. PK parameters were comparable with those found in human and NHP studies performed with anakinra. All animals developed anti-anakinra antibodies. The results obtained in minipigs were comparable to those observed in monkeys. For anakinra, the predictive value of the minipig for immunogenicity testing was found to be comparable to that seen in NHP. However, more studies evaluating additional biopharmaceutical products are needed to support the use of the minipig as an alternative model for (immuno)toxicity testing, including immunogenicity.

Comparative binding of disulfide-bridged PEG-Fabs

Protein PEGylation is the most clinically validated method to improve the efficacy of protein-based medicines. Antibody fragments such as Fabs display rapid clearance from blood circulation and therefore are good candidates for PEGylation. We have developed PEG-bis-sulfone reagents 1 that can selectively alkylate both sulfurs derived from a native disulfide. Using PEG-bis-sulfone reagents 1, conjugation of PEG specifically targets the disulfide distal to the binding region of the Fab (Scheme 2 ). PEG-bis-sulfone reagents 1 (10-40 kDa) were used to generate the corresponding PEG-mono-sulfones 2 that underwent essentially quantitative conjugation to give the PEG-Fab product 4. Four Fabs were PEGylated: Fab(beva), Fab'(beva), Fab(rani), and Fab(trast). Proteolytic digestion of bevacizumab with papain gave Fab(beva), while digestion of bevacizumab with IdeS gave F(ab')(2-beva), which after reaction with DTT and PEG-mono-sulfone 2 gave PEG(2)-Fab'(beva). Ranibizumab, which is a clinically used Fab, was directly PEGylated to give PEG-Fab(rani). Trastuzumab was proteolytically digested with papain, and its corresponding Fab was PEGylated to give PEG-Fab(trast). Purification of the PEGylated Fabs was accomplished by a single ion exchange chromatography step to give pure PEG-Fab products as determined by silver-stained SDS-PAGE. No loss of PEG was detected post conjugation. A comparative binding study by SPR using Biacore with low ligand immobilization density was conducted using (i) VEGF(165) for the bevacizumab and ranibizumab derived products or (ii) HER2 for the trastuzumab derived products. VEGF(165) is a dimeric ligand with two binding sites for bevacizumab. HER2 has one domain for the binding of trastuzumab. Binding studies with PEG-Fab(beva) indicated that the apparent affinity was 2-fold less compared to the unPEGylated Fab(beva). Binding properties of the PEG-Fab(beva) products appeared to be independent of PEG molecular weight. Site-specific conjugation of two PEG molecules gave PEG(2×20)-Fab'(beva), whose apparent binding affinity was similar to that observed for PEG-Fab(beva) derivatives. The k(d) values were similar to those of the unPEGylated Fab(beva); hence, once bound, PEG-Fab(beva) remained bound to the same degree as Fab(beva). Biacore analysis indicated that both Fab(rani) and PEG(20)-Fab(rani) did not dissociate from the immobilized VEGF at 25 °C, but ELISA using immobilized VEGF showed 2-fold less apparent binding affinity for PEG(20)-Fab(rani) compared to the unPEGylated Fab(rani). Additionally, the apparent binding affinities for trastuzumab and Fab(trast) were comparable by both Biacore and ELISA. Biacore results suggested that trastuzumab had a slower association rate compared to Fab(trast); however, both molecules displayed the same apparent binding affinity. This could have been due to enhanced rebinding effects of trastuzumab, as it is a bivalent molecule. Analogous to PEG-Fab(beva) products, PEG(20)-Fab(trast) displayed 2-fold lower binding compared to Fab(trast) when evaluated by ELISA. The variations in the apparent affinity for the PEGylated Fab variants were all related to the differences in the association rates (k(a)) rather than the dissociation rates (k(d)). We have shown that (i) Fabs are well-matched for site-specific PEGylation with our bis-alkylation PEG reagents, (ii) PEGylated Fabs display only a 2-fold reduction in apparent affinity without any change in the dissociation rate, and (iii) the apparent binding rates and affinities remain constant as the PEG molecular weight is varied.

Immunogenicity to biologics: mechanisms, prediction and reduction

Currently, there is a significant rise in the development and clinical use of a unique class of pharmaceuticals termed as Biopharmaceuticals or Biologics, in the management of a range of disease conditions with, remarkable therapeutic benefits. However, there is an equally growing concern regarding development of adverse effects like immunogenicity in the form of anti-drug antibodies (ADA) production and hypersensitivity. Immunogenicity to biologics represents a significant hurdle in the continuing therapy of patients in a number of disease settings. Efforts focussed on the identification of factors that contribute towards the onset of immunogenic response to biologics have led to reductions in the incidence of immunogenicity. An in-depth understanding of the cellular and molecular mechanism underpinning immunogenic responses will likely improve the safety profile of biologics. This review addresses the mechanistic basis of ADA generation to biologics, with emphasis on the role of antigen processing and presentation in this process. The article also addresses the potential contribution of complement system in augmenting or modulating this response. Identifying specific factors that influences processing and presentation of biologic-derived antigens in different genotype and disease background may offer additional options for intervention in the immunogenic process and consequently, the management of immunogenicity to biologics.

Comparative evaluation of the potency and antigenicity of two distinct BoNT/A-derived formulations

IncobotulinumtoxinA (Xeomin®) and onabotulinumtoxinA (BOTOX®) are unique botulinum neurotoxin type A (BoNT/A)-derived drugs. IncobotulinumtoxinA utilizes the naked 150 kDa holotoxin portion of BoNT/A, whereas onabotulinumtoxinA uses the complete native 900 kDa complex as drug substance. On the basis of purportedly similar pharmacological characteristics, these formulations were evaluated for potency by LD₅₀ and mouse Digit Abduction Score (DAS) bioassays. DAS was also used to assess antigenicity. Full-range DAS dose-response profiles were achieved with four lots of each product, with similar observations between lots for a given product. Between products, however, the mean DAS potency of incobotulinumtoxinA (ED₅₀ range 7.0-10.2 U/kg) was significantly lower than that of onabotulinumtoxinA (ED₅₀ range 4.4-6.4 U/kg), consistent with lower measured potencies in the LD₅₀ assay for incobotulinumtoxinA (potency range 62-82 U). In assessments of DAS duration of effect at similar unit doses, the observed lower potency of incobotulinumtoxinA translated into decreased peak efficacy and dose effect over time (i.e. shorter duration). In contrast, at equi-efficacious doses yielding near-maximal DAS responses, both toxin formulations were uniformly inhibited in a statistically significant manner when preincubated with rabbit-derived, onabotulinumtoxinA-neutralizing antibodies, supporting the position that inhibition of 150 kDa holotoxin serves as the common basis for neutralization and, therefore, incobotulinumtoxinA would not be expected to be effective in onabotulinumtoxinA-immunoresistant subjects (and vice versa). Further, with lower lot-to-lot relative potency, incobotulinumtoxinA is not dose-equivalent or interchangeable with onabotulinumtoxinA, suggesting that various aspects of drug product formulation may influence observed pharmacology.

Biosimilars and biobetters as tools for understanding and mitigating the immunogenicity of biotherapeutics

In this article, we review key steps for the development of biosimilars and biobetters and related bioanalytical challenges, with a focus on how they are associated with immunogenicity. We analyze the factors that can impact antidrug antibody (ADA) responses and their correlations with preclinical and clinical outcomes to provide relevant insights and to answer questions, including what types of aggregate are immunogenic. We also address strategies for developing less-immunogenic biotherapeutics. Using interferon-β (IFN-β) as a case study, we explore the correlation between aggregation and immunogenicity. We dissect and integrate with clinical data the IFN-β preclinical immunogenicity and aggregation predictions and discuss the feasibility of developing an IFN-β with lower aggregation and/or immunogenicity.

Analytical tools for characterizing biopharmaceuticals and the implications for biosimilars

Biologics such as monoclonal antibodies are much more complex than small-molecule drugs, which raises challenging questions for the development and regulatory evaluation of follow-on versions of such biopharmaceutical products (also known as biosimilars) and their clinical use once patent protection for the pioneering biologic has expired. With the recent introduction of regulatory pathways for follow-on versions of complex biologics, the role of analytical technologies in comparing biosimilars with the corresponding reference product is attracting substantial interest in establishing the development requirements for biosimilars. Here, we discuss the current state of the art in analytical technologies to assess three characteristics of protein biopharmaceuticals that regulatory authorities have identified as being important in development strategies for biosimilars: post-translational modifications, three-dimensional structures and protein aggregation.

Relationship between potential aggregation-prone regions and HLA-DR-binding T-cell immune epitopes: implications for rational design of novel and follow-on therapeutic antibodies

Aggregation and unwanted immunogenicity are hurdles to avoid in successful commercial development of antibody-based therapeutics. In this article, the relationship between aggregation-prone regions (APRs), capable of forming cross-β motifs/amyloid fibrils, and major histocompatibility complex class II-restricted human leukocyte antigen (HLA)-DR-binding T-cell immune epitopes (TcIEs) is analyzed using amino acid sequences of 25 therapeutic antibodies, 55 TcIEs recognized by T-regulatory cells (tregitopes), 1000 randomly generated 15-residue-long peptides, 2257 human self-TcIEs (autoantigens), and 11 peptides in HLA-peptide cocrystal structures. Sequence analyses from these diverse sources consistently show a high level of correlation between APRs and TcIEs: approximately one-third of TcIEs contain APRs, but the majority of APRs occur within TcIE regions (TcIERs). Tregitopes also contain APRs. Most APR-containing TcIERs can bind multiple HLA-DR alleles, suggesting that aggregation-driven adverse immune responses could impact a broad segment of patient population. This article has identified common molecular sequence-structure loci that potentially contribute toward both manufacturability and safety profiles of the therapeutic antibodies, thereby laying a foundation for simultaneous optimization of these attributes in novel and follow-on candidates. Incidence of APRs within TcIERs is not special to biotherapeutics, self-TcIEs from human proteins, involved in various diseases, also contain predicted APRs and experimentally proven amyloid-fibril-forming peptide sequence portions.

Highly aggregated antibody therapeutics can enhance the in vitro innate and late-stage T-cell immune responses

Aggregation of biotherapeutics has the potential to induce an immunogenic response. Here, we show that aggregated therapeutic antibodies, previously generated and determined to contain a variety of attributes (Joubert, M. K., Luo, Q., Nashed-Samuel, Y., Wypych, J., and Narhi, L. O. (2011) J. Biol. Chem. 286, 25118–25133), can enhance the in vitro innate immune response of a population of naive human peripheral blood mononuclear cells. This response depended on the aggregate type, inherent immunogenicity of the monomer, and donor responsiveness, and required a high number of particles, well above that detected in marketed drug products, at least in this in vitro system. We propose a cytokine signature as a potential biomarker of the in vitro peripheral blood mononuclear cell response to aggregates. The cytokines include IL-1β, IL-6, IL-10, MCP-1, MIP-1α, MIP-1β, MMP-2, and TNF-α. IL-6 and IL-10 might have an immunosuppressive effect on the long term immune response. Aggregates made by stirring induced the highest response compared with aggregates made by other methods. Particle size in the 2–10 μm range and the retention of some folded structure were associated with an increased response. The mechanism of aggregate activation at the innate phase was found to occur through specific cell surface receptors (the toll-like receptors TLR-2 and TLR-4, FcγRs, and the complement system). The innate signal was shown to progress to an adaptive T-cell response characterized by T-cell proliferation and secretion of T-cell cytokines. Investigating the ability of aggregates to induce cytokine signatures as biomarkers of immune responses is essential for determining their risk of immunogenicity.

Immunogenicity of protein aggregates--concerns and realities

Protein aggregation is one of the key challenges in the development of protein biotherapeutics. It is a critical product quality issue as well as a potential safety concern due to the increased immunogenicity potential of these aggregates. The overwhelming safety concern has led to an increased development effort and regulatory scrutiny in recent years. The main purposes of this review are to examine the literature data on the relationship between protein aggregates and immunogenicity, to highlight the linkage and existing inconsistencies/uncertainties, and to propose directions for future investigations/development.

Selective domain stabilization as a strategy to reduce human serum albumin-human granulocyte colony stimulating factor aggregation rate

Therapeutic proteins must be generally formulated to reduce unwanted aggregation. Fusion proteins, which comprise domains assembled from separate proteins, may require unique formulation strategies in order to maximize their stability. A fusion protein of human serum albumin (HSA) and human granulocyte colony stimulating factor (GCSF; HSA-GCSF) was used as a model to test the hypothesis that formulations that increase the thermodynamic conformational stability of the least stable domain of a fusion protein will stabilize the entire fusion protein against aggregation. Conformational stability of HSA-GCSF was modulated by addition of octanoic acid, which was previously shown to increase the conformational stability of HSA, the least stable domain. Contrary to our hypothesis, increased conformational stability of the HSA domain did not result in increased resistance to aggregation of HSA-GCSF. These results for HSA-GCSF were also compared with similar studies conducted previously on a therapeutic protein formed by the fusion of HSA and human growth hormone (hGH; HSA-hGH).

Native-like aggregates of factor VIII are immunogenic in von Willebrand factor deficient and hemophilia a mice

The administration of recombinant factor VIII (FVIII) is the first-line therapy for hemophilia A (HA), but 25%-35% of patients develop an inhibitory antibody response. In general, the presence of aggregates contributes to unwanted immunogenic responses against therapeutic proteins. FVIII has been shown to form both native-like and nonnative aggregates. Previously, we showed that nonnative aggregates of FVIII are less immunogenic than the native protein. Here, we investigated the effect of native-like aggregates of FVIII on immunogenicity in HA and von Willebrand factor knockout (vWF(-/-)) mice. Mice immunized with native-like aggregates showed significantly higher inhibitory antibody titers than animals that received native FVIII. Following restimulation in vitro with native FVIII, the activation of CD4+ T-cells isolated from mice immunized with native-like aggregates is approximately fourfold higher than mice immunized with the native protein. Furthermore, this is associated with increases in the secretion of proinflammatory cytokines IL-6 and IL-17 in the native-like aggregate treatment group. The results indicate that the native-like aggregates of FVIII are more immunogenic than native FVIII for both the B-cell and the T-cell responses.

Drug development: longer-lived proteins

Protein therapeutics represent a powerful class of clinically approved drugs for the prevention and treatment of various diseases. Once administered, the biological fate of protein therapeutics is governed by the body's various complex biochemical and biophysical clearance mechanisms, several of which may decrease the drug's circulation time and efficiency. In this tutorial review, we introduce the concepts of physiological protein clearance from the body, and describe several chemical modification and protein engineering approaches used to improve the life span of administered protein therapeutics.

Site-specific PEGylation at histidine tags

The efficacy of protein-based medicines can be compromised by their rapid clearance from the blood circulatory system. Achieving optimal pharmacokinetics is a key requirement for the successful development of safe protein-based medicines. Protein PEGylation is a clinically proven strategy to increase the circulation half-life of protein-based medicines. One limitation of PEGylation is that there are few strategies that achieve site-specific conjugation of PEG to the protein. Here, we describe the covalent conjugation of PEG site-specifically to a polyhistidine tag (His-tag) on a protein. His-tag site-specific PEGylation was achieved with a domain antibody (dAb) that had a 6-histidine His-tag on the C-terminus (dAb-His(6)) and interferon α-2a (IFN) that had an 8-histidine His-tag on the N-terminus (His(8)-IFN). The site of PEGylation at the His-tag for both dAb-His(6)-PEG and PEG-His(8)-IFN was confirmed by digestion, chromatographic, and mass-spectral studies. A methionine was also inserted directly after the N-terminal His-tag in IFN to give His(8)Met-IFN. Cyanogen bromide digestion studies of PEG-His(8)Met-IFN were also consistent with PEGylation at the His-tag. By using increased stoichiometries of the PEGylation reagent, it was possible to conjugate two separate PEG molecules to the His-tag of both the dAb and IFN proteins. Stability studies followed by in vitro evaluation confirmed that these PEGylated proteins retained their biological activity. In vivo PK studies showed that all of the His-tag PEGylated samples displayed extended circulation half-lives. Together, our results indicate that site-specific, covalent PEG conjugation at a His-tag can be achieved and biological activity maintained with therapeutically relevant proteins.

Advancements in high throughput biophysical technologies: applications for characterization and screening during early formulation development of monoclonal antibodies

The formulation development of monoclonal antibodies is extremely challenging, due to the diversity and complexity contained within this class of molecules. The physical and chemical properties of a monoclonal antibody dictate the behavior of the protein drug during manufacturing, storage and clinical administration. In the past few years, the use of high throughput technologies has been widely adapted to delineate unique properties of individual immunoglobulin G's (IgG's) important for their development. Numerous screening techniques have been designed to reveal physical and chemical characteristics of a protein relevant to stability under production, formulation and delivery conditions. In addition, protein stability under accelerated stresses has been utilized to predict long-term storage behavior for monoclonal antibodies in the formulation. In this review, we summarize the recent advancements in the field of biophysical technology, with a specific focus on the techniques that can be directly applied to the formulation development of monoclonal antibodies. Several case studies are also presented here to provide examples of combining existing biophysical methods with high throughput screening technology in the formulation development of monoclonal antibody drugs.

Development of resistance to biologic therapies with reference to IFN-β

All biotherapeutics have the potential to generate anti-drug antibodies (ADAs) in patients. The main factors leading to an immune response are thought to be product, treatment and patient related. In this review, reasons for the formation of ADAs, and particularly neutralizing antibodies (NAbs), are considered, with a focus on IFN-β as a well-studied example. The time course for the production of NAbs, the measurement of NAbs, the defining of IFN-β responders and non-responders, the implications for disease progression in patients, and future methods for avoiding the production of ADAs and of tolerizing patients are considered.

Analysis of glycoforms on the glycosylation site and the glycans in monoclonal antibody biopharmaceuticals

Therapeutic monoclonal antibodies (mAbs), immunoglobulins, have been efficiently used in the treatment of many diseases, such as cancer, inflammatory and cardiovascular diseases, and organ transplantation. mAbs are glycoprotein molecules undergoing posttranslational modifications. Glycosylation is one of the posttranslational modifications. Different glycoforms that are important for maintaining the potency of mAb drugs show various biological activities. Therefore, the profile of the glycans and glycosylation sites should be determined to produce safe, good quality, consistent mAb drugs for human use. For this reason, simple, robust, accurate, and reproducible analytical methods need to be developed. In this article, chromatographic methods for the analysis of the glycoforms on the glycosylation site and the glycans in mAb biopharmaceuticals have been evaluated.