Measurement of neutralising antibodies to type I interferons by gene expression assays specific for type 1 interferon-inducible 6-16 mRNA

Applications of cell-based bioassays measuring the induced expression of endogenous genes

Cell-based bioassays are used to determine the biological activity of complex biotherapeutic products, to assign potency and to assure the quality and consistency of the manufacturing process. Clinically, these assays are used to assess bioactivity in patient samples, particularly for the detection of antidrug neutralizing antibodies. Owing to their versatility, cellular assays that measure endogenous gene expression by quantitative reverse transcription PCR offer a rapid and automatable alternative to assays measuring functional, late-stage responses. Notably, detection of immediate early gene expression represents a direct response of the cell to receptor ligation by the biotherapeutic. We review current developments in the use of this approach and demonstrate its application to the detection of receptor-binding autoantibodies using, as a case study, the detection of autoantibodies to the thyroid-stimulating hormone receptor.

Reduction of cell viability induced by IFN-alpha generates impaired data on antiviral assay using Hep-2C cells

Type I interferons (IFNs) exert an array of important biological functions on the innate immune response and has become a useful tool in the treatment of various diseases. An increasing demand in the usage of recombinant IFNs, mainly due to the treatment of chronic hepatitis C infection, augmented the need of quality control for this biopharmaceutical. A traditional bioassay for IFN potency assessment is the cytopathic effect reduction antiviral assay where a given cell line is preserved by IFN from a lytic virus activity using the cell viability as a frequent measure of end point. However, type I IFNs induce other biological effects such as cell-cycle arrest and apoptosis that can influence directly on viability of many cell lines. Here, we standardized a cytopathic effect reduction antiviral assay using Hep-2C cell/mengovirus combination and studied a possible impact of cell viability variations caused by IFN-alpha 2b on responses generated on the antiviral assay. Using the four-parameter logistic model, we observed less correlation and less linearity on antiviral assay when responses from IFN-alpha 2b 1000 IU/ml were considered in the analysis. Cell viability tests with MTT revealed a clear cell growth inhibition of Hep-2C cells under stimulation with IFN-alpha 2b. Flow cytometric cell-cycle analysis and apoptosis assessment showed an increase of S+G2 phase and higher levels of apoptotic cells after treatment with IFN-alpha 2b 1000 IU/ml under our standardized antiviral assay procedure. Considering our studied dose range, we also observed strong STAT1 activation on Hep-2C cells after stimulation with the higher doses of IFN-alpha 2b. Our findings showed that the reduction of cell viability driven by IFN-alpha can cause a negative impact on antiviral assays. We assume that the cell death induction and the cell growth inhibition effect of IFNs should also be considered while employing antiviral assay protocols in a quality control routine and emphasizes the importance of new approaches for IFN potency determination.

Use of a standardized MxA protein measurement-based assay for validation of assays for the assessment of neutralizing antibodies against interferon-β

Effective monitoring of the development of neutralizing antibodies (NAbs) against IFN-β in multiple sclerosis (MS) patients on IFN-β therapy is important for clinical decision making and disease management. To date, antiviral assays have been the favored approach for NAb determination, but variations in assay conditions between laboratories and the increasing use of novel assays have contributed to the reporting of inconsistent antibody data between laboratories and between products. This study, undertaken at the request of the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA), is a joint effort by manufacturers of IFN-β products (approved in Europe) towards harmonization of a NAb assay that facilitates generation of comparable NAb data, which, in conjunction with clinical outcomes, should prove useful for clinicians treating MS patients with IFN-β products. This article describes the standardized cellular myxovirus resistance protein A (MxA) protein measurement-based assay for detection of IFN-β NAbs and its use for the validation of assays used for the quantitative determination of such antibodies. Although titers varied between laboratories and the products used, utilization of IFN-β1a rather than IFN-β1b as the challenge antigen produced more consistent results in the NAb assay. Adoption of the standardized assay improves comparability between laboratories circumventing problems that arise when different, nonstandardized assays are employed for immunogenicity assessment. Based on the data, the EMA recommended for standardization purposes, the use of IFN-β1a in NAb assays, independent of the therapeutic product used for therapy and validation of new NAb procedures against the standardized assay described.

Development and optimization of neutralizing antibody assays to monitor clinical immunogenicity

The development of an unwanted immune response to a protein therapeutic is a constant concern and necessitates careful monitoring of this class of drugs during clinical development. Neutralizing antibodies can have a significant impact on bioavailability, efficacy and safety of a protein therapeutic. Consequently, immunogenicity testing is required prior to obtaining regulatory approval and in some cases even after a product is marketed. Given the importance of this testing, it is critical that sensitive and robust assays are developed for detection of clinically relevant neutralizing antibodies. This review will describe considerations and current best practices for developing assays to detect neutralizing antibodies to protein therapeutics.

Detection of neutralizing antibodies to erythropoietin by inhibition of rHuEPO-stimulated EGR1 gene expression in the UT-7/EPO cell line

Recombinant erythropoietin (rHuEPO) is used extensively to treat anaemia associated with chronic kidney disease. However, the development of neutralizing antibodies (NAbs) to rHuEPO can result in the development of antibody-mediated pure red cell aplasia (PRCA). The detection of NAb in patient sera by in vitro bioassay relies on the inhibition of a cellular response to rHuEPO. Current bioassays for rHuEPO measure proliferation in responsive cell lines such as the erythroleukaemic cell lines, UT-7 and UT-7/EPO, the latter sensitized to EPO. Using these cell lines, we show the dose-responsive induction of both PIM1 and EGR1 gene expression in UT-7 cells and of EGR1 in UT-7/EPO cells. The expression of EGR1 in UT-7/EPO cells in response to rHuEPO was comparable to the proliferative response measured by (3)H-thymidine incorporation and could be inhibited by serum from a patient with NAb-mediated PRCA in a dilution-dependent manner. Bioassays based on the induction of endogenous gene expression are comparable to current bioassays but are considerably quicker given that incubation time is decreased from 2-3 days to 50 min. Measurement of EGR1 gene expression in response to rHuEPO in UT-7/EPO cells offers a rapid, non-radioactive and automatable alternative to current assays for the detection of rHuEPO NAbs.

Improved analytical methods for the detection and quantification of neutralizing antibodies to biopharmaceuticals

Biopharmaceuticals are used extensively for the treatment of a number of chronic debilitating and fatal diseases such as cancer and inflammatory or autoimmune diseases. Although biopharmaceuticals are in general well tolerated, the development of anti-drug antibodies can impair their safety and efficacy. Assessment of immunogenicity is essential for a more effective and rational use of biopharmaceuticals, and is dependent upon the establishment of efficient standardized assays that allow direct comparison of immunogenicity data with clinical outcome. Although regulatory authorities recommend the use of cell-based assays that reflect the mechanism of action of the drug for the detection of neutralizing anti-drug antibodies, conventional cell-based assays are difficult to standardize and often give variable results. A number of strategies have been adopted to improve the performance of cell-based assays, including quantification of drug-induced proteins using either real-time RT-PCR or branched DNA to detect mRNA, or ELISAs to detect protein, bridging assays using immobilized cells and the use of reporter gene assays. The relative merits and limitations of each of these methods is reviewed herein.

Potency determination of recombinant IFN-alpha based on phosphorylated STAT1 using flow cytometry

The interferon (IFN) family of cytokines is recognized as a key component of the innate immune response and the first line of defense against viral infection. The usage of the IFN-alpha as a biopharmaceutical has been mainly applied in the treatment of chronic hepatitis C. In the literature it is possible to find a great variety of methods to determine the potency of these cytokines, and many efforts have been made in order to develop practical bioassays to study the biological activity of IFNs. In this technical note, we present a different approach to determine the potency of a recombinant IFN-alpha preparation based on the activation of the signal transducers and activators of transcription 1 (STAT1) using flow cytometry technique. Under the conditions of this study, this new approach proved to be useful and promising to assess the potency of these biopharmaceuticals and may also be used as an important tool in the quality control of such biological products.

Bioactivity determination of native and variant forms of therapeutic interferons

The traditional antiviral assays for the determination of interferon potency are reported to have considerable variability between and within assays. Although several reporter gene assays based on interferon-inducible promoter activities have been reported, data from comprehensive validation studies are lacking and few studies have been conducted to analyze the variant forms of interferons, which could have undesirable clinical implications. Here, a reporter gene assay employing a HEK293 cell line stably transfected with luciferase gene under the control of interferon-stimulated response element promoter was developed and validated. The assay was found to be more sensitive, with a larger detection range than the antiviral assay. Several cytokines tested did not interfere with the test, suggesting the assay possesses a certain degree of selectivity. Moreover, the robustness of the assay was demonstrated by minimal variations in the results generated by different analysts and cell passage number (up to 52 passages). Finally, the method was employed to analyze several interferon variants (interferon-α 2a) and we found that the aggregated form has completely lost its potency; while a modest loss of bioactivity in oxidized interferon was observed (approx. 23%), the deamidated form essentially retained its activity.

Unwanted immunogenicity: lessons learned and future challenges

All biological therapeutics have the potential to induce an immune response in recipients of these products. Elicitation of an immune response can result in variable clinical impact, ranging from benign to severe adverse effects, a diminution in clinical efficacy or, in some cases, hypersensitivity or allergic reactions. Consequently, assessment of unwanted immunogenicity is an important element of the data required for regulatory submission for product approval. However, issues relating to immunogenicity occur throughout the life-cycle of a biotherapeutic and need to be considered appropriately when introducing any product change(s). Evaluation of immunogenicity of a product requires a well-considered strategy and a panel of appropriately validated (or ‘fit-for-purpose’) assays for antibody detection and characterization in clinical samples. An overview of the bioanalytical methods that are currently being used for assessment of immunogenicity of biotherapeutics and the guidance available along with some of the challenges facing the industry are discussed in this review.

One-step assay for quantification of neutralizing antibodies to biopharmaceuticals

Assessment of immunogenicity is an important part of biopharmaceutical drug safety evaluation and a prerequisite for the development of less immunogenic and safer biopharmaceuticals since anti-drug antibodies can impair the activity and compromise the safety of biopharmaceuticals. Although regulatory authorities recommend cell-based assays for detection of neutralizing antibodies (NAbs), such assays are difficult to standardize, and ill adapted to high-throughput analysis. These limitations have been overcome by the development of a unique one-step cell-based assay that allows both drug activity and drug NAbs to be quantified rapidly and with a high degree of precision simply be adding reporter cells to a sample. The reporter cells have been engineered to express firefly luciferase (FL) under the control of a drug-responsive promoter, and to express the drug of interest, the production of which is normalized relative to the expression of Renilla luciferase (RL) transcribed from a common doxycycline-inducible promoter. Residual drug levels present in a sample are first quantified by determination of FL expression, autocrine drug synthesis is then induced, and NAb activity is quantified from the difference in the ratio of FL/RL expression in the presence or absence of the sample. Since assay results are normalized relative to the expression of an internal standard, results are independent of cell number or differences in cell viability thus affording a high degree of assay precision and reducing serum matrix effects to a minimum. This unique assay platform is ideally suited for high-throughput analysis, is applicable to most biopharmaceuticals, and will facilitate standardization and comparison of immunogenicity data. The performance of the one-step assay is illustrated for interferon alpha2 (IFNalpha2) used widely to treated chronic hepatitis C (HCV) infection and neoplastic disease.