Validation of the BIACORE 3000 platform for detection of antibodies against erythropoietic agents in human serum samples

Toward Exosome-Based Neuronal Diagnostic Devices

Targeting exosome for liquid biopsy has gained significant attention for its diagnostic and therapeutic potential. For detecting neuronal disease diagnosis such as Alzheimer's disease (AD), the main technique for identifying AD still relies on positron-emission tomography (PET) imaging to detect the presence of amyloid-β (Aβ). While the detection of Aβ in cerebrospinal fluid has also been suggested as a marker for AD, the lack of quantitative measurements has compromised existing assays. In cerebrospinal fluid, in addition to Aβ, T-Tau, and P-Tau, alpha-synuclein has been considered a biomarker of neurodegeneration. This review suggests that and explains how the exosome can be used as a neuronal diagnostic component. To this end, we summarize current progress in exosome preparation/isolation and quantification techniques and comment on the outlooks for neuronal exosome-based diagnostic techniques.

Why you should be using more SPR biosensor technology

There are three ways of looking at surface plasmon resonance biosensor technology: bewilderment (I can not believe this sort of technology actually exists), love (without this technology I would cry), or hate (this technology does not work). Whether you love them or hate them, or just have never heard of them, it is time to take a fresh look at how SPR biosensors can help you get from point A to point B in your drug discovery efforts.:

Immunogenicity issues in drug development

Immunogenicity is an important factor that manufacturers must consider as they develop new protein therapeutics. It is important to understand the immunogenicity of new proteins both at the preclinical phase and in the clinical phase of development. This paper provides an overview of the issues that manufacturers should consider including some of the potential reasons that some proteins induce an immune response, a discussion regarding current methodology used to understand immunogenicity, and some examples of marketed protein therapeutics with immunogenicity issues. Given the increasing scrutiny from regulatory agencies around the way immunogenicity is assessed by manufacturers, the strategy of detecting and characterizing antibodies that are formed against protein therapeutics is becoming an important topic. Screening assays are typically performed first on all serum samples collected in the course of a trial to detect the presence of antibodies that can bind to the protein therapeutic. There are several platforms in use: radioimmune precipitation assays (RIP), enzyme linked immunosorbent assays (ELISA), electrochemiluminescent assays (ECL), and biosensor-based assays. Each has its advantages and disadvantages, and needs to be evaluated to identify the optimal platform for a specific therapeutic protein. Once antibodies are identified, a confirmatory assay is performed to verify and characterize the antibodies. A biological assay should be used next to test if these antibodies are capable of neutralizing the biological effect of the drug. Any sample that is positive for neutralizing antibodies, indicates that the antibody is probably having an impact on the patient's ability to derive full benefit from the therapeutic protein, and may be critical for patient safety.

An open-label extension study evaluating the safety and efficacy of romiplostim for up to 3.5 years in thrombocytopenic Japanese patients with immune thrombocytopenic purpura (ITP)

Long-term use of the thrombopoietin mimetic romiplostim was examined in Japanese patients with chronic immune thrombocytopenic purpura (ITP) in this open-label extension. The starting dose of romiplostim was the previous trial dose or 3 μg/kg/week, which was titrated up to 10 μg/kg/week to maintain platelet counts between 50 and 200 × 10(9)/L. As of April 2010, 44 patients had enrolled; 71 % women, median age 55.5 years, with five patients discontinuing romiplostim due to patient request (2), administrative decision (2), or not achieving study-defined platelet response (1). Median treatment duration was 100 weeks; median average weekly dose was 3.8 μg/kg. Twenty-eight patients (64 %) self-injected romiplostim. The most frequent adverse events were nasopharyngitis and headache. Nine patients (20 %) had a total of 14 serious adverse events (0.31/100 patient-weeks); of these, only oral hemorrhage was considered treatment related. Fifty hemorrhagic adverse events were reported in 20 patients (46 %) (1.12/100 patient-weeks). Ninety-six percent of patients had a platelet response (doubling of baseline platelet count and platelet count ≥ 50 × 10(9)/L). Of the 25 patients receiving concurrent ITP therapy at baseline, all reduced or discontinued the therapy. Eight patients (18 %) received rescue medications. Administration of up to 3.5 years of romiplostim increased platelet counts and was well tolerated in Japanese patients with chronic ITP.

Strategy to confirm the presence of anti-erythropoietin neutralizing antibodies in human serum

Functional cell-based assays are the preferred method to test for the presence of anti-rHuEPO neutralizing antibodies (NAbs). However, due to the unpredictable nature of test serum matrix effects on cell-based assays, confirmatory assays are essential for verifying NAb positive results observed during the course of sample testing. The cell-based assay used for the detection of NAbs described by Wei et al. [1] used 32D-EPOR cells, a murine myeloid cell line transfected with the human EPO receptor (EPOR). The 32D-EPOR cell line responded to either rHuEPO or murine interleukin 3 (mIL-3) with proliferation. NAbs were expected to only inhibit rHuEPO-induced cell proliferation and not mIL-3 induced proliferation. Due to reliance on proliferation, the results from this cell-based assay can be confounded by the presence of non-antibody inhibitory serum factors. This paper describes a strategy for confirming that the inhibition of rHuEPO-induced proliferation in a cell-based assay is only attributable to NAbs. The strategy of antibody depletion uses a resin mixture composed of Protein G Sepharose and Protein L Sepharose (Protein G/L resin) to significantly reduce the concentration of immunoglobulins of IgG, IgM and IgA isotypes from human serum prior to testing in the cell-based assay. If the reduction in immunoglobulins in a serum sample corresponds to a reduction in inhibition of EPO-induced proliferation, it would infer that EPO neutralizing activity is antibody-mediated and not due to non-antibody inhibitory serum factors.

Impact of matrix-associated soluble factors on the specificity of the immunogenicity assessment

BACKGROUND

Specificity and sensitivity are essential in assays for immunogenicity assessment of biotherapeutics. Nonspecific interactions from excess therapeutic or anti-therapeutic antibody, soluble ligands (e.g., target receptor), or serum proteins associated with autoimmune conditions (e.g., rheumatoid factor) in samples can impact the detection of a true anti-therapeutic response.

RESULTS

Electrochemiluminescence-based bridging assay formats could eliminate the interference due to rheumatoid factor with no pretreatment with Melon Gel™ or aggregated IgG. The interference due to soluble factors was not platform specific for the four therapeutics evaluated in this study.

CONCLUSION

Melon Gel pretreatment and avidin high-bind (Meso Scale Discovery) plates can effectively reduce interference due to rheumatoid factor in ELISA- and electrochemiluminescence-based assays, respectively. Excess levels of therapeutic and anti-therapeutic antibodies in bridging assays can impact assay specificity.

Challenges in developing bioanalytical assays for characterization of antibody–drug conjugates

With more than 34 targets being investigated and nearly 20 clinical trials at various phases of development, antibody–drug conjugates (ADCs) hold a lot of promise for improving oncological malignancy therapy. This therapeutic strategy designed to specifically or preferentially deliver a cytotoxic agent to tumor cells through conjugation to a monoclonal antibody is not new. Although this approach is relatively simple conceptually, the history of ADCs clearly attests to the high degree of complexity in their development. Each component of an ADC is important to achieve efficacy with minimal toxicity, and the ability to monitor this multicomponent therapeutic entity is deemed to be critical for their successful optimization. In this article we review the different bioanalytical strategies that have been implemented to characterize various ADCs and discuss the challenges and issues associated with these approaches.

Anti-erythropoietin antibodies followed by endogenous erythropoietin production in a dialysis patient

We present a case of a young girl with end-stage renal disease secondary to anti-glomerular basement membrane disease who was receiving maintenance peritoneal dialysis and developed pure red cell aplasia secondary to anti-erythropoietin (EPO) antibodies. This occurred 13 months after the initiation of EPO alfa therapy for anemia. Initially, the patient required intermittent red blood cell transfusions. After immunosuppressive therapy had been initiated with corticosteroids and cyclosporine, the EPO antibody levels decreased precipitously, associated with an increased level of endogenous EPO production. For the following 6 months, the patient maintained adequate (>10 g/dL) hemoglobin levels and did not require red cell transfusions.

Dynamic light scattering as a powerful tool for gold nanoparticle bioconjugation and biomolecular binding studies

Dynamic light scattering (DLS) is an analytical tool used routinely for measuring the hydrodynamic size of nanoparticles and colloids in a liquid environment. Gold nanoparticles (GNPs) are extraordinary light scatterers at or near their surface plasmon resonance wavelength. In this study, we demonstrate that DLS can be used as a very convenient and powerful tool for gold nanoparticle bioconjugation and biomolecular binding studies. The conjugation process between protein A and gold nanoparticles under different experimental conditions and the quality as well as the stability of the prepared conjugates were monitored and characterized systematically by DLS. Furthermore, the specific interactions between protein A-conjugated gold nanoparticles and a target protein, human IgG, can be detected and monitored in situ by measuring the average particle size change of the assay solution. For the first time, we demonstrate that DLS is able to directly and quantitatively measure the binding stoichiometry between a protein-conjugated GNP probe and a target analyte protein in solution.

Challenges in developing antidrug antibody screening assays

Robert Dodge is the Laboratory Director for Immunochemistry and Cell Biology at Taylor Technology, a Pharmanet company in Princeton, NJ, USA. Taylor Technology is a contract research laboratory specializing in assay development and sample testing in a good laboratory practice environment. Robert oversees a staff of scientists responsible for the development of assays for use in protein drug quantitation, antidrug antibody screening and biomarker detection.

Protein drugs may elicit an immune response in the form of production of antidrug antibodies (ADAs) by a subject. This ADA response may have serious safety implications for subjects or, at a minimum, may affect drug efficacy. Bioanalytical testing for antidrug antibodies has therefore become a required part of safety testing for subjects receiving protein drugs. Regulatory guidance and scientific white papers recommend a tiered approach for bioanalytical ADA testing. The first assay in the tiered testing scheme is a screening assay, which tests all subjects in the study for the presence of ADAs. The screening assay is quasiquantitative, typically lacks a specific positive control and must be designed to detect numerous isotypes and subclasses of antibodies. These characteristics of an ADA screening assay differ from a those of a standard immunoassay designed to quantitate a specific protein in matrix and thus present unique challenges. This article reviews the unique challenges encountered during the development of an ADA assay.

Assessing specificity for immunogenicity assays

Developing sensitive and specific bioanalytical assays for measuring the immunogenicity of biological therapeutics has become an integral component of the drug-development process. The strategy for measuring these immune responses involves performing sensitive screening assays that are capable of detecting low levels of both low- and high-affinity antibodies. However, having sensitive assays inherently results in a certain rate of false-positivity. Hence, developing steps to determine specificity in these assays is important to confirm the presence of antidrug antibodies. The specificity assays are defined by the ability of an assay to score a positive result if the serum sample contains an antibody that can bind and/or neutralize the therapeutic protein. Here, we discuss the methodologies for determining specificity in the bioanalytical assays used for measuring antidrug antibodies. These methods will provide investigators and regulators with guidelines to develop and review assays to measure antidrug antibodies, which can specifically interfere with the actions of the drug and/or influence the safety profile of the therapeutic proteins.

The development and validation of a sensitive, dual-flow cell, SPR-based biosensor immunoassay for the detection, semi-quantitation, and characterization of antibodies to darbepoetin alfa and epoetin alfa in human serum

A surface plasmon resonance (SPR)-based biosensor immunoassay was developed and validated using the Biacore 3000 instrument to detect, semi-quantitate, and characterize serum antibodies against darbepoetin alfa (Aranesp) and epoetin alfa (EPOGEN). In this sensitive, dual-flow cell assay, epoetin alfa and darbepoetin alfa are covalently immobilized onto consecutive flow cells of a carboxymethyl dextran-coated sensor chip. Diluted human serum samples are injected sequentially over both surfaces. The binding of serum antibodies to the immobilized proteins are detected and recorded in real time based on the principles of SPR. Furthermore, antibody binding is confirmed with a secondary anti-human immunoglobulin antibody. Positive samples are further characterized to determine the relative concentration of the antibodies using an affinity-purified, rabbit anti-epoetin alfa antibody as a reference control. The assay can detect 80ng/ml and 100ng/ml of antibody to epoetin alfa and darbepoetin alfa, respectively. The dynamic range of the assay is from 0.078microg/ml to 10microg/ml using a rabbit antibody with demonstrated accuracy and intra- and inter-assay precision. Approximately 80 serum samples can be analyzed on each sensor chip while maintaining a stable baseline and consistent immunological reactivity. The analysis of serum samples from subjects administered with epoetin alfa or darbepoetin alfa provided evidence that the assay can detect varying concentrations of antibodies of different off rates, isotypes, and IgG subclasses.

Affinity-based biosensors as promising tools for gene doping detection

Innovative bioanalytical approaches can be foreseen as interesting means for solving relevant emerging problems in anti-doping control. Sport authorities fear that the newer form of doping, so-called gene doping, based on a misuse of gene therapy, will be undetectable and thus much less preventable. The World Anti-Doping Agency has already asked scientists to assist in finding ways to prevent and detect this newest kind of doping. In this Opinion article we discuss the main aspects of gene doping, from the putative target analytes to suitable sampling strategies. Moreover, we discuss the potential application of affinity sensing in this field, which so far has been successfully applied to a variety of analytical problems, from clinical diagnostics to food and environmental analysis.

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.

Determination of pharmacokinetic values of calicheamicin-antibody conjugates in mice by plasmon resonance analysis of small (5 microl) blood samples

PURPOSE

The present study aims to establish a method that provides fast, precise and reproducible pharmacokinetic (PK) parameters of antibody-calicheamicin conjugates. The method should discriminate between PK of the antibody moiety and PK of the conjugated calicheamicin (CM).

METHODS

The conjugates gemtuzumab ozogamicin (CMA-676, Mylotarg) or inotuzumab ozogamicin (CMC-544) were injected in the tail vein of nude mice. At regular time intervals, 5 mul whole blood samples were taken from the tail artery. Concentrations of conjugated CMA-676 or CMC-544 as well as concentrations of their respective antibody moiety were determined by sandwich plasmon resonance. This detection system measures changes in the plasma resonance angle caused by the interaction of macromolecules on biosensor chips. We determined as a first measure the binding of CMA-676 or CMC-544 to their respective antigens, CD33 or CD22. As a second measure we determined the amount of CM on the antigen-bound conjugates. This was done by determination of changes in plasma resonance angle after binding of an anti-CM antibody.

RESULTS

Sandwich plasmon resonance allowed detection of both conjugates in blood of mice in a range of 100-1,000 ng/ml protein. Due to the precision of the sampling and detection methods, PK values of each conjugate were determined in individual mice. Calicheamicin bound to antibody was eliminated faster than the antibody alone. The presence of a CD22-expressing tumour in mice reduced the plasma levels of the CD22-targeting conjugate but not of the CD33-targeting one.

CONCLUSIONS

Using small blood samples from a mouse, the sandwich plasmon resonance method provided PK-values of CM-conjugates and information about the stability of the linkage in vivo. Comparison between the PK-values of CM-conjugates in tumour-bearing and tumour-free mice suggested that retention of the conjugate in tumour tissue due to antigen targeting could be deduced from the plasma levels.

Feasibility of a multiplex flow cytometric bead immunoassay for detection of anti-epoetin alfa antibodies

Immunogenicity profiles of recombinant therapeutic proteins are important to understand because antibodies raised against these molecules may have important clinical sequelae. The purpose of the present study was to demonstrate that a flow cytometric bead array could be used to detect clinically relevant antibodies with specificity to such therapeutics. We chose to evaluate well-characterized specimens from persons treated with epoetin alfa that developed antibody-mediated pure red blood cell aplasia as a means to demonstrate the utility of this platform. Our data show that this assay is capable of detecting anti-epoetin alfa antibodies with a relative antibody concentration of 50 ng/ml, where 25 of 25 sera spiked with antibodies at this concentration scored positive. Moreover, the assay was designed to include positive and negative control beads for each specimen that is processed to ensure the specificity of the signal when detected. Measurement of interassay precision supports quantitative estimates of relative antibody concentrations in the range of 313 to 5,000 ng/ml, where the percent coefficient of variation did not exceed 20%. With respect to clinical specimens, antibodies with specificity for epoetin alfa could be easily detected in a set of specimens from persons with pure red blood cell aplasia that had prior exposure to the EPREX brand of recombinant epoetin alfa. Further development and validation of this approach may facilitate successful widespread application of the method for detection of anti-epoetin alfa antibodies, as well as antibodies directed against other recombinant therapeutic proteins.

Clinical validation of fiberoptic immunobiosensor for point-of-care analysis of plasma nerve growth factor

BACKGROUND

Upregulation of plasma nerve growth factor (NGF) is indicative of cardiac nerve sprouting that is underlying the mechanisms for cardiac arrhythmias. A conventional assay method (e.g., enzyme-linked immunosorbent assay [ELISA]) is usually time consuming and technically complicated for NGF analysis for potential arrhythmia prognosis.

OBJECTIVE

This study is to develop a rapid and and reliable assay method for point-of-care (POC) testing of plasma NGF.

METHODS

We recently developed a fiberoptic immunobiosensor for point-of-care testing of human plasma NGF. Physiological concentrations of NGF (1 to 200 ng/ml) could be quantified in both buffer and human blood plasma samples (100 microl) within 5 min. The intra-assay coefficient of variation was 5%, and the interassay coefficient of variation was 8%. The clinical utility of the NGF biosensor was evaluated using clinical blood samples from atrial fibrillation patients (n = 21). Peripheral venous blood was sampled before and immediately after radiofrequency ablation and again at postoperative day 1.

RESULTS

The NGF level did not change significantly between before (15.73 +/- 16.67 ng/ml) and immediately after radiofrequency ablation (13.58 +/- 11.45 ng/ml, P = NS); however, there was a significant elevation to 28.41 +/- 19.52 ng/ml in postoperative day 1 (P <.01). In a follow-up study (11 +/- 1 months), the increased magnitude in patients with atrial fibrillation recurrence (4.1-fold +/- 1.96-fold) was significantly higher than those without (1.72-fold +/- 0.53-fold; P <.001). The results were highly comparable to those of the ELISA analysis.

CONCLUSION

Because of the comparable data accuracy and much faster assay time as compared with ELISA, the fiberoptic biosensor is promising as a clinical POC assay method for plasma NGF analysis at patient bedsides for potential cardiac disease diagnosis and prognosis.

Clinical validation of the "in silico" prediction of immunogenicity of a human recombinant therapeutic protein

Antibodies elicited by protein therapeutics can cause serious side effects in humans. We studied immunogenicity of a recombinant fusion protein (FPX) consisting of two identical, biologically active, peptides attached to human Fc fragment. EpiMatrix, an in silico epitope-mapping tool, predicted promiscuous T-cell epitope(s) within the 14-amino-acid carboxy-terminal region of the peptide portion of FPX. On administration of FPX in 76 healthy human subjects, 37% developed antibodies after a single injection. A memory T-cell response against the above carboxy-terminus of the peptide was observed in antibody-positive but not in antibody-negative subjects. Promiscuity of the predicted T-cell epitope(s) was confirmed by representation of all common HLA alleles in antibody-positive subjects. As predicted by EpiMatrix, HLA haplotype DRB1*0701/1501 was associated with the highest T-cell and antibody response. In conclusion, in silico prediction can be successfully used to identify Class II restricted T-cell epitopes within therapeutic proteins and predict immunogenicity thereof in humans.

Quantitative Measurement of Cardiac Markers in Undiluted Serum

Two mycocardial infarction biomarkers, myoglobin (MG) and cardiac troponin I (cTnI), were quantified at biological levels and in undiluted serum without sample pretreatment using surface plasmon resonance (SPR) sensors. To achieve detection of biomarkers in undiluted serum (72 mg/mL total protein concentration), minimization of the nonspecific signal from the serum protein was achieved by immobilizing the antibody for the biomarkers on an N-hydroxysuccinimide activated 16-mercaptohexadecanoic acid self-assembled monolayer. This monolayer reduces the nonspecific signal from serum proteins in such a manner that short exposure of the sensor to serum prior to analysis prevents any further nonspecific adsorption during analysis. Thus, sensing of MG and cTnI was achieved on the basis of the difference between signals from the active sensor and a reference sensor that captured background interference. This resulted in direct measurement of these biomarkers in undiluted serum. Detection limits for both markers were below 1 ng/mL, which is below the threshold needed to detect myocardial infarction. Detecting biomarkers in the low ng/mL range without signal amplification in such a complex matrix as serum corresponds to a selectivity of 108. The root-mean-square-error (RMSE) of calibration was below 2 ng/mL.

High-resolution characterization of antibody fragment/antigen interactions using Biacore T100

A Biacore T100 optical biosensor was used to characterize the binding kinetics of a panel of antigen binding fragments (Fabs) directed against the PcrV protein from Pseudomonas aeruginosa. PcrV protein forms part of the type III secretion system complex of this opportunistic pathogen. We demonstrate that the biosensor response data for each Fab collected from three different surface densities of the antigen could be fit globally to a simple 1:1 interaction model. Importantly, we found that the Fabs with the slowest dissociation rate provided the best protection in cell cytotoxicity studies. To further characterize the Fab interactions, binding data were automatically acquired at different temperatures and under different buffer conditions. The comprehensive characterization of these Fabs shows how Biacore T100 can be used to complement protein therapeutic discovery programs from basic research to the selection of therapeutic candidates.

Qualification and application of a surface plasmon resonance-based assay for monitoring potential HAHA responses induced after passive administration of a humanized anti Lewis-Y antibody

A sensitive, surface plasmon resonance (SPR)-based assay monitoring potential human-anti-human antibody (HAHA) reactions against the monoclonal antibody (mAb) IGN311 is presented. The latter is a fully humanized Lewis-Y carbohydrate specific mAb that is currently tested in a passive immune therapy approach in a clinical phase I trial. For the SPR experiments a BIACORE 3000 analyzer was used. The ligand IGN311 was covalently coupled to the carboxy-methylated dextran matrix of a CM5 research grade chip (BIACORE). In the course of a fully nested experimental design, a four parameter logistic equation was identified as appropriate calibration model ranging from 0.3 microg/mL (lower limit of quantitation, LLOQ) to 200 microg/mL (upper limit of quantitation, ULOQ) using an anti-idiotypic mAb ('HAHA mimic') as calibrator. The bias ranged from -2.4% to 5.5% and the intermediate precision expressed as 95% CI revealed values from 5.6% to 8.3%. Specificity was evaluated using six human serum matrices from healthy donors spiked with calibrator at the limit of quantitation (LOQ) with >80% of values being recovered with less than 25% relative error. The qualified assay was applied to monitor potentially induced HAHA reactivity in 11 patients from a clinical phase I trial with passively administered IGN311. Of the 11 patients, one high HAHA responder and several low responders were identified. Protein-G depletion experiments with human serum samples revealed that the observed response is predominantly caused by IgG binding to the ligand. The characteristics of these HAHA responses were all of the so-called 'Type I' which is defined by a peak response around day 15 that decreases from this point steadily suggesting that some kind of tolerance is established. Therefore, this type of HAHA response is regarded as non critical for the patient's safety.

An in vivo model to assess factors that may stimulate the generation of an immune reaction to erythropoietin

The incidence of pure red cell aplasia (PRCA) in patients with chronic kidney disease associated with the subcutaneous (s.c.) administration of epoetin alfa (EPREX) began to increase in 1998. As part of an intensive investigation into the reasons for this increase, in vivo models were developed to assess the ability of potential causative factors to stimulate an immune response to recombinant human erythropoietin (rHuEPO). It was difficult to generate anti-EPO antibodies in mice. In animals injected with rHuEPO alone, anti-EPO antibodies were either absent or present at very low levels. The addition of an adjuvant to the immunization protocol was able to increase both the frequency of occurrence and titer of the immune response and resulted in the generation of anti-EPO antibodies that, in most cases, recognized both human and mouse EPO. Some mice exhibited a reduction in hematocrit, suggesting neutralization of endogenous EPO by anti-EPO antibodies. To evaluate the primary lead identified in the technical investigation, leachates from the uncoated syringe stoppers of EPREX syringes, a surrogate antigen (chicken egg albumin, OVA) was used to avoid possible interferences that could arise from the use of an endogenous protein like EPO. These leachates yielded a positive, concentration-dependent antibody response in the OVA animal model, demonstrating their adjuvant properties and providing support for the hypothesis generated through the technical investigation that leachates were capable of enhancing the immune response to rHuEPO.

Directional surface plasmon-coupled emission: application for an immunoassay in whole blood

We present a new approach for performing fluorescence immunoassay in whole blood using fluorescently labeled anti-rabbit immunoglobulin G (IgG) on a silver surface. This approach, which is based on surface plasmon-coupled emission (SPCE), provides increased sensitivity and substantial background reduction due to exclusive selection of the signal from the fluorophores located near a bioaffinity surface. This article describes the effect of an optically dense sample matrix, namely human whole blood and serum, on the intensity of the SPCE. An antigen (rabbit IgG) was adsorbed to a slide covered with a thin silver metal layer, and the SPCE signal from the fluorophore-labeled anti-rabbit antibody, binding to the immobilized antigen, was detected. The effect of the sample matrix (buffer, human serum, or human whole blood) on the end-point immunoassay SPCE signal was studied. It was demonstrated that the kinetics of binding could be monitored directly in whole blood or serum. The results showed that human serum and human whole blood attenuate the SPCE end-point signal and the immunoassay kinetic signal only approximately two- and threefold, respectively, as compared with buffer, resulting in signals that are easily detectable even in whole blood. The high optical absorption of the hemoglobin can be tolerated because only fluorophores within a couple of hundred nanometers from the metallic film contribute to SPCE. Excited fluorophores outside the 200-nm layer do not contribute to SPCE, and their free space emission is not transmitted through the opaque metallic film into the glass substrate. We believe that SPCE has the potential of becoming a powerful approach for performing immunoassays based on surface-bound analytes or antibodies for many biomarkers directly in dense samples such as whole blood with no need for washing steps.

A polypyrrole protein microarray for antibody–antigen interaction studies using a label-free detection process

Protein microarray is a promising technology that should combine rapidity and easy use with high throughput and versatility. This article describes a method in which an electrocopolymerization process is employed to graft biological molecules on to a chip so that surface plasmon resonance imaging may be used to detect molecular interactions. Copolymerization of pyrrole-modified protein and pyrrole is an efficient grafting process which immobilizes molecules at defined positions on a gold surface. Surface plasmon resonance imaging is an optical technique that allows real-time simultaneous detection of molecular interactions on a large number of spots without labeling. This method was successfully used to analyze antibody-antigen interactions. This illustrates its high specificity and good sensitivity and demonstrates its suitability for biological studies.

Recommendations on haematological criteria for the diagnosis of epoetin-induced pure red cell aplasia

Pure red cell aplasia (PRCA) is a rare condition characterised by an arrest in red blood cell production, which may be congenital or acquired. Recombinant human erythropoietin (epoetin) was introduced in 1989 for the treatment of anaemia of chronic kidney disease patients and has maintained an excellent therapeutic and safety record while treating hundreds of thousands of patients. A very rare, but serious adverse event associated with epoetin administration is a condition in which patients develop neutralising anti-erythropoietin antibodies and, consequently, PRCA. This condition is referred to as epoetin-induced PRCA (epo-PRCA). Since it is a rare condition, many haematologists and nephrologists around the world see the condition infrequently and may be uncertain about the diagnosis. For this reason, an ad hoc international working group of expert haematologists and nephrologists met together to derive new recommendations for the haematological diagnosis of epo-PRCA. These recommendations, which represent the consensus opinions of the working group, address haematological approaches to monitor and investigate suspected epo-PRCA and should help physicians differentiate between PRCA and other bone marrow diseases, as well as, between PRCA and epo-PRCA.

Survey of the year 2003 commercial optical biosensor literature

In the year 2003 there was a 17% increase in the number of publications citing work performed using optical biosensor technology compared with the previous year. We collated the 962 total papers for 2003, identified the geographical regions where the work was performed, highlighted the instrument types on which it was carried out, and segregated the papers by biological system. In this overview, we spotlight 13 papers that should be on everyone's 'must read' list for 2003 and provide examples of how to identify and interpret high-quality biosensor data. Although we still find that the literature is replete with poorly performed experiments, over-interpreted results and a general lack of understanding of data analysis, we are optimistic that these shortcomings will be addressed as biosensor technology continues to mature.

Development and validation of a cell-based bioassay for the detection of neutralizing antibodies against recombinant human erythropoietin in clinical studies

An in vitro cell-based bioassay capable of detecting neutralizing antibodies (NAb) to recombinant human erythropoietin (rHuEPO) in clinical samples was developed and validated. The bioassay uses the IL-3-dependent murine 32D cell line transfected with human EPO receptors (EPOR). This cell line responds to rHuEPO with proliferation measurable by [methyl-3H] thymidine incorporation into the cellular DNA. The reduction of rHuEPO-induced cell proliferation response indicates the possible presence of anti-rHuEPO NAb. In addition, a specificity assay using murine IL-3 (mIL-3) induced proliferation of the same cell line was developed and validated. The specificity assay allowed testing of samples that inhibited the biologic activity of rHuEPO to evaluate whether the inhibition was specific and not attributable to cytotoxicity of the serum sample. Both assays are conducted in a 5% human serum matrix in 96-well microtiter plates. The Guidelines of the International Conference on Harmonization (ICH) were followed for the validation of different assay parameters including analytical recovery, precision, sensitivity, specificity, selectivity, and robustness. The anti-rHuEPO NAb assay is capable of detecting concentrations of NAb equivalent to 500 ng/ml of the positive control antibody in undiluted human serum. The anti-rHuEPO NAb assay yielded consistent results with cells cultured for up to 30 days. The positive control antibody maintained its ability to inhibit the biologic activity of rHuEPO upon freezing and thawing. The presence of free rHuEPO in serum samples interfered with the detection of the antibody. The validated assay was sensitive, specific and robust and was successfully used to monitor NAb development in patients.

Development and evaluation of a new ELISA for the detection and quantification of antierythropoietin antibodies in human sera

Assays for the analysis of antierythropoietin antibodies (anti-EPO Abs) currently suffer from a high degree of nonspecificity or are cumbersome and time consuming to perform. They are therefore not well suited for the analysis of large numbers of human sera samples, a task that has become increasingly important due to an increase in the number of patients developing anti-EPO Abs. The objective of this study was to develop and validate a sensitive and specific ELISA for the determination of anti-EPO Abs that would suit these purposes. In this new double antigen bridging ELISA, anti-EPO Abs bind via one site to recombinant human erythropoietin (rhEPO)-biotin immobilized to streptavidin-coated microtiter plates (MTPs) and by a second site to rhEPO labelled with digoxigenin (DIG). The amount of bound antibody is determined using an anti-DIG antibody coupled to peroxidase. A rabbit polyclonal anti-EPO Ab purified by immunoadsorption is used as reference antibody preparation. The dynamic range of this ELISA was 1-75 ng/ml per assay calibrated with the reference antibody preparation. The assay was specific for anti-EPO Abs and did not react with other immunoglobulins (Ig) present in human serum. The lower limit of detection (LLD) of the assay was 0.5 ng/ml, and the lower limit of quantitation (LLQ) was 1.0 ng/ml. Anti-EPO Abs could be detected in the sera of pure red cell aplasia (PRCA) patients. In contrast to previous reports, no anti-EPO Abs could be detected in the sera of patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Sjogren's syndrome (SS), or in the sera of dialysis patients.

Darbepoetin alfa effectively treats anemia in patients with chronic kidney disease with de novo every-other-week administration

AIM

This multicenter, open-label study determined safety and efficacy of once-every-other-week administration of darbepoetin alfa for anemia of chronic kidney disease in erythropoietin-naive patients not on dialysis.

METHODS

Participants with hemoglobin levels <11.0 g/dl at baseline were administered darbepoetin alfa at an initial dosage of 0.75 microg/kg once every other week. The dose was titrated to achieve and maintain a hemoglobin response, defined as a hemoglobin range of between 11.0 and 13.0 g/dl for up to 24 weeks. The primary end point was the dose of darbepoetin alfa at initial hemoglobin response.

RESULTS

Six hundred and eight patients were enrolled, and 463 completed the study; 95% (95% confidence interval: 0.93, 0.97) of the patients who completed treatment achieved a hemoglobin response. The mean darbepoetin alfa dose at the time of response was 63.5 +/- (SD) 16.9 microg, and the mean time to hemoglobin response was 5.7 +/- (SD) 4.5 weeks. Oral iron therapy was administered to 60% and intravenous iron to 16% of the participants. Darbepoetin alfa was well tolerated, and adverse events were consistent with those expected in patients with chronic kidney disease.

CONCLUSION

Darbepoetin alfa administered once every other week is effective and safe for achieving and maintaining target hemoglobin levels in anemic patients with chronic kidney disease.

Drug-induced and antibody-mediated pure red cell aplasia: a review of literature and current knowledge

Anti-erythropoietin (EPO)-induced pure red cell aplasia (PRCA) is an uncommon, potentially life-threatening condition in which the bone marrow stops manufacturing red blood cells. In the past few years, reports of drug-induced, anti-EPO antibody-mediated PRCA have increased substantially, with most cases attributed to the use of one erythropoiesis-stimulating protein, Eprex. A literature review was undertaken to document the reports of drug-induced PRCA, with all drugs and drug regimens. The sudden increase in reports of antibody-mediated PRCA is discussed.