Current methods for detecting antibodies against erythropoietin and other recombinant proteins

Acquired Pure Red Cell Aplasia and Recombinant Erythropoietin

Recombinant erythropoietin (rEPO)-associated immunologically driven acquired pure red cell aplasia (PRCA) is an underreported, potentially worsening clinical syndrome in the setting of treatment of anemia of chronic kidney disease. Most cases reported in world literature are related to different formulations of erythropoiesis-stimulating agents with an implication in diagnosis and management. This brief review highlights the clinical guidelines of rEPO usage in nephrology practice, the pathophysiologic mechanism of PRCA, clinical features, diagnosis, and suggested management protocols.

Immunogenicity of biologic treatments for psoriasis: therapeutic consequences and the potential value of concomitant methotrexate

The five biologic agents approved for the treatment of psoriasis-etanercept, infliximab, adalimumab, ustekinumab, and secukinumab-have been transformative in the clinical management of severe forms of the disease. However, a significant number of patients fail to respond to these agents or experience a loss of efficacy over time, which may be attributable to the development of antidrug antibodies (ADAs). Increasing evidence, primarily in the context of rheumatoid arthritis or other chronic inflammatory diseases, suggests that concomitant administration of methotrexate may prevent or diminish the development of ADAs, thereby improving response rates. However, methotrexate is infrequently coadministered with biologic agents in patients with psoriasis, and the potential benefits of this strategy in the context of psoriasis are largely unexplored. In this review, we discuss clinical studies regarding the development and consequences of antibodies targeting biologic agents used in the treatment of psoriasis and present key findings describing the potential role of methotrexate as an inhibitor of immunogenicity. We also discuss clinical considerations pertaining to the use of methotrexate as a tool to reduce immunogenicity, and encourage further investigation into potential techniques to optimize this treatment approach in patients with psoriasis.

Clinical Manifestations of an Anti-Drug Antibody Response: Autoimmune Reactions

Antibodies can be generated against a therapeutic protein upon administration to human subjects. When the therapeutic protein closely mimics one of the subject's endogenous proteins, those antibodies might bind to the endogenous protein in addition to the therapeutic protein. This scenario results when tolerance to the endogenous protein is broken. The consequences of breaking tolerance include an autoimmune response where antibodies are generated against the endogenous protein. These autoantibodies could have significant clinical relevance depending on several factors, including the redundancy of action of the endogenous protein as well as the concentration, binding affinity, and neutralizing potential of the antibodies. The consequences of a therapeutic-protein-induced autoimmune reaction can be challenging to manage as the stimulus for further perpetuation of the immune response can shift from the therapeutic protein to the endogenous protein. The potential for inducing an autoimmune response is one of the reasons that the immune response to a therapeutic protein should be monitored if it persists through the end of the study.

Measurement of anti-erythropoiesis-stimulating agent IgG4 antibody as an indicator of antibody-mediated pure red cell aplasia

Patients treated with erythropoietin-based erythropoiesis-stimulating agents (ESAs) can develop a rare but life-threatening condition called antibody-mediated pure red cell aplasia (amPRCA). The antibody characteristics in a nephrology patient with amPRCA include high antibody concentrations with neutralizing activity and a mixed IgG subclass including anti-ESA IgG4 antibodies. In contrast, anti-ESA IgG4 antibody is generally not detected in baseline samples and antibody-positive non-PRCA patients. Therefore, we validated a highly sensitive immunoassay on the ImmunoCAP 100 instrument to quantitate anti-ESA IgG4 antibodies using a human recombinant anti-epoetin alfa (EPO) IgG4 antibody as a calibrator. The biotinylated ESA was applied to a streptavidin ImmunoCAP, and bound anti-ESA IgG4 antibodies were detected using a β-galactosidase-conjugated mouse anti-human IgG4 antibody. The validated assay was used to detect anti-ESA IgG4 in amPRCA and non-PRCA patients. The immunoassay detected 15 ng/ml of human anti-EPO IgG4 antibody in the presence of a 200 M excess of human anti-ESA IgG1, IgG2, or IgM antibody and tolerated 2 μg/ml of soluble erythropoietin. All patient samples with confirmed amPRCA had measurable anti-ESA IgG4 antibodies. In addition, 94% (17/18) of non-PRCA patient samples were antibody negative or had below 15 ng/ml of anti-ESA IgG4 antibodies. This novel immunoassay can measure low-nanogram quantities of human anti-ESA IgG4 antibodies in the presence of other anti-ESA antibodies. An increased concentration of anti-ESA IgG4 antibody is associated with the development of amPRCA. We propose that the measurement of anti-ESA specific IgG4 antibodies may facilitate early detection of amPRCA in patients receiving all ESAs structurally related to human erythropoietin.

Strategies and assays for the assessment of unwanted immunogenicity

The assessment of unwanted immunogenicity associated with biological products continues to be a major issue for the biotechnology industry. Monitoring of unwanted immunogenicity during the development of the product from pre-clinical stage through clinical trials is now a regulatory expectation with extended post-marketing commitments required for at least some of these products. Prospective planning of immunogenicity studies incorporating appropriately devised strategies is critical if valid conclusions concerning the immunogenicity profile of a product are to be derived. An important consideration of such studies is the selection of optimized, rigorously validated and standardized methodologies for detection and characterization of antibodies with emphasis on desired assay design, assay controls, and performance criteria. Binding assays with different formats and detection systems, radioimmuno-precipitation assays or surface plasmon resonance procedures are often used as the basis for a screening assay. For assessing the neutralizing capacity of the antibodies, however, a neutralization assay is an absolute requirement. Therefore, a panel of methods is usually necessary for a detailed understanding of the type(s) of antibodies induced against a therapeutic product. This manuscript considers briefly the benefits and limitations of the different techniques available for antibody detection and characterization. A strategy that can be adopted for the assessment of unwanted immunogenicity of therapeutic products is also suggested.

Development and characterization of a human antibody reference panel against erythropoietin suitable for the standardization of ESA immunogenicity testing

Recombinant human erythropoietin (EPO) has been used therapeutically for more than two decades in the treatment of anemia. Although EPO is generally well tolerated, in rare cases, patients have developed anti-EPO antibodies that can negatively impact safety and efficacy. Therefore, the detection of antibodies against EPO is a regulatory requirement during clinical development and post-approval. Although it is a rare phenomenon, antibody-mediated pure red cell aplasia (PRCA) is a serious complication than can result from antibodies that develop and neutralize EPO as well as endogenous erythropoietin. Currently, there are no universally accepted analytical methods to detect the full repertoire of binding and neutralizing anti-EPO antibodies. A number of different methods that differ in terms of antibodies detected and assay sensitivities are used by different manufacturers. There is also a lack of antibody reference reagents, and therefore no consistent basis for detecting and measuring anti-EPO antibodies. Reference reagents, with established ranges, are essential to monitor the safety and efficacy of all erythropoiesis-stimulating agents (ESAs) structurally related to human erythropoietin. This is the first report of the development and characterization of a panel of fully human antibodies against EPO suitable as reference reagents. The characteristics of antibodies within the panel were selected based on the prevalence of non-neutralizing IgG and IgM antibodies in non-PRCA patients and neutralizing IgG antibodies, including IgG1 and IgG4, in antibody-mediated PRCA subjects. The reference panel includes antibodies of high- and low-affinity with binding specificity to neutralizing and non-neutralizing erythropoietin epitopes. The subclass of human antibodies in this reference panel includes an IgG1, IgG2, and IgG4, as well as an IgM isotype. This antibody panel could help select appropriate immunogenicity assays, guide validation, and monitor assay performance. Further, this human anti-ESA antibody panel may help set the limits of each assay platform in terms of the full repertoire of the anti-ESA antibodies, and may facilitate standardization of ESA immunogenicity reporting across assay platforms.

Biosimilar recombinant human erythropoietins ("epoetins") and future erythropoiesis-stimulating treatments

INTRODUCTION

Recombinant human erythropoietin (rhEPO, epoetin) has prospered in the treatment of renal and chemotherapy-associated anemias. Since the patents of the original epoetins expired, biosimilars have been launched. Because these are not fully identical to the original products, non-clinical and clinical studies are necessary to show similarity with respect to quality, safety, and efficacy.

AREAS COVERED

The article summarizes experiences with EU-approved biosimilar epoetins. In particular, the issue of immunogenicity is considered. Neutralizing anti-EPO antibodies can cause pure red cell aplasia (PRCA). Further, a first view is offered on future erythropoiesis-stimulating therapies.

EXPERT OPINION

The term "biosimilar" should only be used for follow-on biopharmaceuticals approved under a defined regulatory pathway. The primary rationale for the therapy with biosimilars is cost saving. Two biosimilar epoetins are available in the EU that are used at the same dose(s) and dosing regimen(s) for indications of the reference product. Their advent has stimulated innovator companies to develop second-generation products with improved pharmacokinetic properties. EPO-mimicking peptides are a new therapeutic option. Other strategies focus on orally active chemical drugs that induce endogenous EPO production ("HIF stabilizers"). Epo gene transfer is also possible, but needs to be further explored with respect to efficacy and safety.

Biosimilar epoetins and other "follow-on" biologics: update on the European experiences

After the patents of biopharmaceuticals have expired, based on specific regulatory approval pathways copied products ("biosimilars" or "follow-on biologics") have been launched in the EU. This article summarizes experiences with hematopoietic medicines, namely the epoetins (two biosimilars traded under five different brand names) and the filgrastims (two biosimilars, six brand names). Physicians and pharmacists should be familiar with the legal and pharmacological specialities of biosimilars: The production process can differ from that of the original, clinical indications can be extrapolated, glycoproteins contain varying isoforms, the formulation may differ from the original, and biopharmaceuticals are potentially immunogenic. Only on proof of quality, efficacy and safety, biosimilars are a viable option because of their lower costs.

B-1 cells and naturally occurring antibodies: influencing the immunogenicity of recombinant human therapeutic proteins?

Recombinant human therapeutic proteins are increasingly being used to treat serious and life-threatening diseases like multiple sclerosis, diabetes mellitus, and cancer. An important side effect of these proteins is the development of antidrug antibodies, which can be neutralizing and thus interfere with the efficacy and safety of the drug. Some biophysical properties, for example, aggregation, also can initiate the immunogenic response to human therapeutics. Many other factors including patients' characteristics may influence this response. Besides induced antibodies, autoantibodies (i.e. naturally occurring antibodies [NAs]) against therapeutic relevant proteins in naïve patients are increasingly being identified. The role of autoreactive B cells and their escape from deletion, production of NAs and their pivotal function in the immune system, the dualistic role of B-1 cells in autoimmunity, and the influence of NAs on disease outcome and their possible impact on the efficacy of human therapeutics will be presented and discussed.

Epoetin-induced pure red cell aplasia: diagnosis and treatment

PURPOSE OF REVIEW

Antibody-mediated pure red cell aplasia is now recognized as a rare complication of erythropoiesis-stimulating agent therapy. The incidence of this adverse effect peaked in 2002, but new cases still appear sporadically. The aim of this review is to discuss the latest opinions regarding the detection and management of this condition.

RECENT FINDINGS

The diagnosis of classical erythropoiesis-stimulating agent induced pure red cell aplasia is made by a constellation of clinical features, including severe transfusion-dependent anaemia, reticulocytopenia, low or absent erythroblasts in the bone marrow, and the presence of circulating antierythropoietin antibodies. Recently, some cases have been reported in which the bone marrow findings show red cell hypoplasia rather than aplasia; this may represent earlier presentations of the same condition.

SUMMARY

Management of pure red cell aplasia as a complication of erythropoiesis-stimulating agent therapy consists of stopping the drug and implementing an immunosuppressive regimen to reduce or abolish erythropoietin antibody production. A recent animal study suggested that a possible alternative strategy may be to administer a novel peptide-based erythropoietin receptor agonist called Hematide that does not cross react with antierythropoietin antibodies, and will allow ongoing stimulation of erythropoiesis; this is the subject of a current clinical trial.

Pure red cell aplasia induced by erythropoiesis-stimulating agents

Pure red cell aplasia in patients who are treated for anemia of chronic kidney disease with erythropoiesis-stimulating agents such as epoetin was first reported in 1998. Although the incidence of pure red cell aplasia peaked in 2002, it remains important for nephrologists to know how to investigate a suspected case of pure red cell aplasia and how to identify other causes of hyporesponsiveness to erythropoiesis-stimulating agents, which account for the vast majority of such cases. The authors reviewed the current status of information in the literature and drew on their personal experiences with patients regarding the diagnosis and management of epoetin-induced pure red cell aplasia. The mechanism for development of epoetin-induced pure red cell aplasia remains unconfirmed. It generally occurs after the production of neutralizing anti-erythropoietin antibodies. Elucidation of a suspected pure red cell aplasia case requires a systematic approach, beginning with simple measurements such as blood cell counts, because most cases of erythropoiesis-stimulating agent hyporesponsiveness are attributable to other causes. If these criteria indicate that the patient's response to erythropoiesis-stimulating agent therapy is very poor, then bone marrow examination and measurement of anti-erythropoietin antibodies is justified. If pure red cell aplasia is confirmed, then cessation of erythropoiesis-stimulating agent therapy and initiation of immunosuppressive therapy are recommended. Continued study of epoetin-induced pure red cell aplasia is needed to help nephrologists prevent or manage future cases and will have implications for the use of other protein-based therapeutic agents.

Biosimilars: how similar or dissimilar are they?

The imminent expiry of patents on biological medicinal products, such as epoetin alfa in 2006, has significant implications for nephrology in Australia. The purpose of this review is to examine the differences between biosimilars (similar biological medicinal products) and generic low molecular weight (chemical) drugs. The approach that regulatory agencies, including the European Medicines Agency (EMEA) and the Therapeutic Goods Administration (TGA), are taking towards biosimilars is also discussed. Biosimilars differ from generic chemical drugs in many important ways, including the size and complexity of the active substance, the nature of the starting materials (cell banks, tissues and other biological products), and the complexity of the manufacturing processes. Therefore, it has been acknowledged by the EMEA that established legal and regulatory principles of 'essential similarity' that are applied to standard chemical generics cannot be readily applied to biosimilars. One of the key areas of concern with the introduction of biosimilars into the field of nephrology will be guaranteeing the safety and efficacy of biosimilars. New manufacturers will need to ensure that their biopharmaceutical has a similar efficacy and safety profile to the innovator product through more extensive clinical trials than the limited testing done for generic versions of low molecular weight chemical medicines.

Detection of anti-EPO antibodies in human sera by a bridging ELISA is much more sensitive when coating biotinylated rhEPO to streptavidin rather than using direct coating of rhEPO

Sensitive and efficient methods for detecting anti-erythropoietin (anti-EPO) antibodies are needed for analysis and, above all, for large scale screening of human serum samples. ELISA is an attractive alternative to labor-intensive radioimmunoprecipitation assays but apparently conflicting reports question its sensitivity. We sought to resolve this issue by directly comparing different reported ELISA approaches to determine whether rhEPO-coating methods affect detection of anti-EPO antibodies. Investigators reporting low sensitivity had used ELISAs in which rhEPO was directly coated to microtiter plates while the high sensitivity ELISA used plate-bound streptavidin to bind biotinylated rhEPO. Using anti-EPO positive human sera, our results confirmed a large (100- to 300-fold) difference in sensitivity between the ELISAs and suggested that the inferiority of the low sensitivity ELISA was caused by the direct coating of rhEPO which may disrupt epitopes by masking recognition sites or introducing conformational changes. Thus, a bridging ELISA can be an appropriate and effective system for antibody analysis and screening of human sera with high sensitivity and specificity but only if performed with streptavidin binding of biotinylated antigen. This finding may also be more generally applicable to the detection of antibodies against other protein antigens.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.