Development of a monoclonal antibody sandwich ELISA for the determination of antigen content and quality in diphtheria vaccines

At present, quality control of diphtheria vaccines by both manufacturers and national control laboratories relies heavily on in vivo assays to confirm potency. As part of the VAC2VAC project we have developed a monoclonal antibody (mAb) enzyme-linked immunosorbent assay (ELISA) to measure the relative amount and quality of diphtheria toxoid (DTxd) in diphtheria-tetanus based vaccines and believe this test has the potential to play a key role in a control strategy no longer including an in vivo potency test. The mAb ELISA is highly specific, has good dilutional linearity, and is suitable for detecting DTxd in a range of different human vaccine products. We demonstrate the ability of the assay to discriminate between batches of different content and quality using vaccine batches that were prepared to contain differing amounts of DTxd or were altered by exposure to heat or oxidative stress. We also demonstrate successful transfer of the method to other laboratories and show that different diphtheria antigen materials may be able to serve as a reference antigen for local standardization of the method. The assay is ideally suited for incorporation into a consistency approach for routine diphtheria vaccine quality control testing and may be suitable to serve as the stability indicating test in replacement of the current in vivo potency test.

Collaborative study for the establishment of Ph. Eur. Biological Reference Preparation for Human tetanus immunoglobulin batch 2

This publication describes the outcome of a project to develop a replacement European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for Human tetanus immunoglobulin (TIg) as well as for the World Health Organization (WHO) International Standard (IS) for Tetanus Immunoglobulin, Human. Bulk TIg was kindly provided by a European manufacturer and was used to prepare the candidate standard. The candidate standard was freeze-dried and calibrated in an international collaborative study jointly co-ordinated by the Medicines & Healthcare products Regulatory Agency (MHRA) and the European Directorate for the Quality of Medicines & HealthCare (EDQM, Council of Europe). The results of this study show that there was good agreement between laboratories for the potency estimates obtained for the candidate standard relative to the current WHO IS/Ph. Eur. BRP. The study also demonstrated that the candidate standard is suitable for use in Ph. Eur. assays for potency testing of TIg products and there was good agreement in the potency estimates obtained using the different assay methods included in the study. Accelerated degradation studies performed at the MHRA over a period of 4 years suggest that the freeze-dried candidate standard will be very stable. The candidate standard was established as Ph. Eur. BRP for Human tetanus immunoglobulin, batch 2 with an assigned potency of 45 IU/ampoule. The same preparation was also adopted by the WHO Expert Committee on Biological Standardization (ECBS) to serve as the WHO 2nd IS for Tetanus Immunoglobulin, Human (13/240).

Variability of in vivo potency assays of whole-cell pertussis, inactivated polio, and meningococcal B vaccines

For the batch release of vaccines, potency release assays are required. Non-animal in vitro tests have numerous advantages and are preferred; however, several vaccines are still released using in vivo assays. Their major drawback is the inherent variability with its practical implications. We quantified the variability of in vivo potency release assays for whole-cell pertussis, inactivated polio and meningococcal B (MenB) vaccines which showed large CV (Coefficient of Variation) ranging from 34% to 125%. As inherent variability might potentially be attributed to the highly variable immune system between individual animals, we evaluated the antibody titres to four MenB antigens in 344 individual outbred mice. These varied strongly, with more than 100-fold differences in antibody titres in responsive mice. Furthermore, within individual mice there was generally no correlation between the strengths of the responses to the four antigens. A mouse with a very low or no response to one antigen in many cases exhibited a strong response to another antigen. The large differences between individual animals is likely a considerable contributor to the inherent variability of in vivo potency assays. Our data again support the notion that it is preferred to move away from in vivo potency assays for monitoring batch to batch consistency as part of vaccine batch release testing.

Reproducibility and Harmonization in Research using Biological Standards: The Example of Platelet Agonist Collagen-Related Peptide

Metrology - the science of measure - is a subject few biological scientists are taught about in their training to their detriment; the application of simple standardization processes to everyday working practices provides confidence in data and reproducibility over distance and time. This method demonstrates how to standardize a core laboratory experiment used widely in hemostasis research and clinical practice, specifically, measuring responses to the platelet collagen receptor (glycoprotein [GP]VI) agonist collagen-related peptide, cross-linked (CRP-XL) by light transmission aggregometry (LTA). Using this approach will ensure intra-lab reproducibility and inter-lab harmonization, regardless of agonist stock or supplier. Importantly, this method is applicable to other platelet agonists and, indeed, many other biological molecules and bioassays. The process outlined below involves making a 6-8 point dilution series of the 'standard' and the 'test' (the material you are checking) and running them side by side in a chosen assay (in this case, LTA). CRP-XL is used at mass/volume concentrations, but not every material gives the same biological activity at a given concentration, so a dilution series is made to compare the standard and test material and determine what concentration is needed to give equivalent activity. The dilution series must span 0-100% aggregation. Data is plotted using non-linear regression, and the EC50 value of each sample (standard and test) is determined. To assign activity, divide the EC50 value of the standard by that of the test to determine how much more or less potent it is and adjust the concentration accordingly. This approach will ensure that the same biological 'activity' is added to the assay time and time again.

Assessing the stability-indicating properties of alternative potency assays for inactivated influenza vaccine

Determination of the potency of a vaccine is critical to ensuring that an appropriate dose is delivered, lot-to-lot consistency is maintained, and that the formulation is stable over the life of the vaccine. The potency of inactivated influenza vaccines is determined routinely by the Single Radial Immunodiffusion (SRID) assay. A number of alternative potency assays have been proposed and have been under evaluation in recent years. The aim of this study was to compare a surface plasmon resonance-based assay and two different enzyme linked immunoassays against the current potency assay, SRID, and against mouse immunogenicity when haemagglutinin antigen of the A(H1N1)pdm09 component of an inactivated influenza vaccine is stressed by elevated temperature, low pH and freezing. This analysis demonstrated that the alternative assays had good correspondence with SRID for samples from most stress conditions and that the immunogenicity in mice corresponded with potency in SRID for all stress samples. Subject to further analysis, the assays have been shown to have the potential to possibly replace, and at least complement, SRID.

Collaborative study for the calibration of a replacement International Standard for Diphtheria Antitoxin Equine

The International Standard for Diphtheria Antitoxin Equine is essential for the standardisation of assays used to determine the potency of therapeutic diphtheria antitoxin products produced from equine serum. This paper describes the production and characterization of the 2nd International Standard for Diphtheria Antitoxin Equine and its calibration in International Units. Calibration was performed by toxin neutralization test in vivo and in vitro (Vero cell assay), and potency was expressed relative to the 1st International Standard to ensure continuity of the International Unit. The candidate standard (NIBSC product code 18/180) was assigned a unitage of 57 IU/ampoule based on results from 14 laboratories in 9 different countries and was established by the World Health Organisation Expert Committee on Biological Standardization in 2021.

Assay discrepancies using human coagulation factor VIII chromogenic kits: Results from a plasma-derived factor VIII collaborative study (BSP112)

Chromogenic assay discrepancies were reported at General European Official Medicines Control Laboratories Network (GEON) meetings by laboratories testing FVIII-products. The objectives of the present investigation were to carry out a controlled collaborative study to examine these reports and to delineate the reasons for these discrepancies by assessing affected and unaffected FVIII products. The laboratories followed a strict study protocol, which included assessing their own individual observed factor X (FX) activation times, i.e. the time to reach 50% of maximal FX activation (T_1/2), for each chromogenic kit. This measurement was used, in parallel with the kit manufacturers' prescribed FX activation times, to assess the performance of the chromogenic potency assays on FVIII test products. This study confirmed a significant discrepancy between Coatest® and Coamatic® kits and between Siemens and Coamatic® kits when the kit manufacturers' prescribed T_1/2 incubation times were followed. Coamatic® kits tended to produce higher potencies than the Coatest® or Siemens kits. Furthermore, FX activation assays revealed marked differences between individual laboratories for all three chromogenic kits in the observed T_1/2 incubation times, which also did not correspond to the prescribed T_1/2 incubation times. The resulting differences in potency between kits, in some cases, were significantly reduced when using the actual observed T_1/2 incubation times instead of the prescribed T_1/2 incubation times. The study showed that FVIII potency discrepancies can occur between chromogenic kits. To compensate for this, laboratories should ideally perform FX activation curves for each new chromogenic kit in order to determine the correct observed T_1/2 incubation times, which can then be used to determine FVIII potencies in therapeutic concentrates.

Collaborative study for the establishment of Ph. Eur. Biological Reference Preparation for Human tetanus immunoglobulin batch 2

This publication describes the outcome of a project to develop a replacement European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for Human tetanus immunoglobulin (TIg) as well as for the World Health Organization (WHO) International Standard (IS) for Tetanus Immunoglobulin, Human. Bulk TIg was kindly provided by a European manufacturer and was used to prepare the candidate standard. The candidate standard was freeze-dried and calibrated in an international collaborative study jointly co-ordinated by the Medicines & Healthcare products Regulatory Agency (MHRA) and the European Directorate for the Quality of Medicines & HealthCare (EDQM, Council of Europe). The results of this study show that there was good agreement between laboratories for the potency estimates obtained for the candidate standard relative to the current WHO IS/Ph. Eur. BRP. The study also demonstrated that the candidate standard is suitable for use in Ph. Eur. assays for potency testing of TIg products and there was good agreement in the potency estimates obtained using the different assay methods included in the study. Accelerated degradation studies performed at the MHRA over a period of 4 years suggest that the freeze-dried candidate standard will be very stable. The candidate standard was established as Ph. Eur. BRP for Human tetanus immunoglobulin, batch 2 with an assigned potency of 45 IU/ampoule. The same preparation was also adopted by the WHO Expert Committee on Biological Standardization (ECBS) to serve as the WHO 2nd IS for Tetanus Immunoglobulin, Human (13/240).

Assessing the Variability of Cell-Associated HIV DNA Quantification through a Multicenter Collaborative Study

Reliable and accurate quantification of cell-associated HIV DNA (CA HIV DNA) is critical for early infant diagnosis, clinical management of patients under therapy, and to inform new therapeutics efficacy. The present study assessed the variability of CA HIV DNA quantification obtained from various assays and the value of using reference materials to help harmonize the measurements. Using a common set of reagents, our multicenter collaborative study highlights significant variability of CA HIV DNA quantification and lower limit of quantification across assays. The quantification of CA HIV DNA from a panel of infected PBMCs can be harmonized through cross-subtype normalization but assay calibration with the commonly used 8E5 cell line failed to reduce quantification variability between assays, demonstrating the requirement to thoroughly evaluate reference material candidates to help improve the comparability of CA HIV DNA diagnostic assay performance. IMPORTANCE Despite a global effort, HIV remains a major public health burden with an estimated 1.5 million new infections occurring in 2020. HIV DNA is an important viral marker, and its monitoring plays a critical role in the fight against HIV: supporting diagnosis in infants and underpinning clinical management of patients under therapy. Our study demonstrates that HIV DNA measurement of the same samples can vary significantly from one laboratory to another, due to heterogeneity in the assay, protocol, and reagents used. We show that when carefully selected, reference materials can reduce measurement variability and harmonize HIV DNA quantification across laboratories, which will help contribute to improved diagnosis and clinical management of patients living with HIV.

An international collaborative study to assign value for Total Factor XIII-B Subunit Antigen to the WHO 1st International Standard for Factor XIII Plasma, (02/206): Communication from the ISTH SSC Subcommittee on Factor XIII and Fibrinogen

BACKGROUND

Factor XIII (FXIII)-B subunit measurements are required for the diagnosis and characterization of the type of FXIII deficiency. Furthermore, therapy for FXIII-A deficiency with recombinant FXIII (rFXIII-A) relies on available FXIII-B.

OBJECTIVE

To carry out a collaborative study to calibrate and assign value to the current WHO 1st International Standard (IS) FXIII Plasma for Total FXIII-B subunit, relative to locally collected normal plasma pools.

METHODS

Laboratories were instructed to use a validated method (specific ELISA antibodies provided) for assessment of Total FXIII-B subunit antigen potency. All laboratories used this method with one laboratory using an additional in-house method. Nine data sets were received from seven laboratories (37 assays in total), which provided a total of 35 valid estimates for this new assignment. Total FXIII-B subunit estimates were calculated relative to locally collected normal plasma pools, using an arbitrary value of 1.00 unit of Total FXIII-B subunit per ml, for each pool.

RESULTS

Combination of results produced an overall mean of 0.98 units/mL with an inter-laboratory variability (geometric coefficients of variation - GCV%) of 18.3% [95% confidence interval: 0.86-1.11]. Real-time and bench stability studies indicated good stability and preservation of the FXIII-B subunit analyte in the WHO 1st IS FXIII Plasma (02/206).

CONCLUSION

Following agreement by study participants, ISTH/SSC Experts, WHO-ISTH Liaison Group and the SSC Board, the WHO/ECBS established the current WHO 1st IS Factor XIII plasma (NIBSC code 02/206) by additionally assigning it with a Total FXIII-B subunit antigen value of 0.98 IU/ampoule, in October 2019.

International collaborative study to evaluate and calibrate two recombinant L chain Ferritin preparations for use as a WHO International Standard

OBJECTIVES

To evaluate and calibrate two candidate preparations for the 4th International Standard for Ferritin (Human, Recombinant) (codes: 19/118 and 19/162) against the 3rd International Standard for Ferritin (Human, Recombinant) (code: 94/572), and three serum commutability samples in an international collaborative study involving 12 laboratories in nine countries.

METHODS

Eleven of the 12 participating laboratories performed Ferritin quantitation using automated assay platforms and one laboratory used a manual ELISA kit.

RESULTS

There was better overall agreement between all laboratories and between assay methods for the potency of preparation 19/118 than for preparation 19/162. The overall geometric mean potency (from all methods) of the candidate 4th International Standard, 19/118, was 10.5 µg/ampoule, with inter-laboratory variability, expressed as % geometric coefficient of variation (GCV), of 4.7%. Accelerated stability studies have predicted both 19/118 and 19/162 to be very stable for long term storage at -20 °C.

CONCLUSIONS

The candidate 4th International Standard for Ferritin (Human, Recombinant) (19/118) has been shown to be immunologically similar to the 3rd International Standard for Ferritin (Human, Recombinant) (94/572). It was recommended to and accepted by the WHO Expert Committee on Biological Standardization that 19/118 be established as the 4th International Standard for Ferritin (Human, Recombinant) with an assigned potency of 10.5 µg/ampoule and expanded uncertainty limits 10.2-10.8 µg/ampoule (95% confidence; k=2.23).

The First WHO International Standard for Harmonizing the Biological Activity of Bevacizumab

Several Bevacizumab products are approved for clinical use, with many others in late-stage clinical development worldwide. To aid the harmonization of potency assessment across different Bevacizumab products, the first World Health Organization (WHO) International Standard (IS) for Bevacizumab has been developed. Two preparations of a Bevacizumab candidate and comparator were assessed for their ability to neutralize and bind vascular endothelial growth factor (VEGF) using different bioassays and binding assays in an international collaborative study. Relative potency estimates were similar across different assays for the comparator or the duplicate-coded candidate sample. Variability in relative potency estimates was reduced when the candidate standard was used for calculation compared with various in-house reference standards, enabling harmonization in bioactivity evaluations. The results demonstrated that the candidate standard is suitable to serve as an IS for Bevacizumab, with assigned unitages for VEGF neutralization and VEGF binding activity. This standard coded 18/210 was established by the WHO Expert Committee on Biological Standardization, which is intended to support the calibration of secondary standards for product development and lifecycle management. The availability of IS 18/210 will help facilitate the global harmonization of potency evaluation to ensure patient access to Bevacizumab products with consistent safety, quality and efficacy.

Quantitation of thrombin-activatable fibrinolysis inhibitor in human plasma by isotope dilution mass spectrometry

Measurement of Thrombin-activatable fibrinolysis inhibitor (TAFI) in human plasma is dependent on reproducible assays. To date, standards for measuring TAFI are frequently calibrated relative to pooled normal human plasma and arbitrarily assigned a potency of 100% TAFI, despite variation in TAFI concentrations between plasma pools. Alternatively, TAFI calibrators can be assigned a value in SI units but the approach used for value assignment is not consistent and furthermore, if purified TAFI is used to determine TAFI concentration in plasma, may be adversely affected by matrix effects. A TAFI plasma standard in mass units with traceability to the SI unit of mass is desirable. We report here the establishment of a quantitative mass spectrometry method for TAFI in plasma. Traceability is obtained by reference to calibrators that consist of blank plasma spiked with a defined amount of purified TAFI, value assigned by amino acid analysis. The calibrators are run alongside the samples, using the same preparation steps and conditions; an acetonitrile assisted tryptic digestion and multi-dimensional liquid chromatography (LC) separation followed by SRM-MS analysis. We measured the TAFI quantitatively in human plasma with reproducibility, reliability and precision, and demonstrated the applicability of this approach for value assigning a common reference standard.

The First WHO International Standard for Adalimumab: Dual Role in Bioactivity and Therapeutic Drug Monitoring

The expanded availability of adalimumab products continues to widen patient access and reduce costs with substantial benefit to healthcare systems. However, the long-term success of these medicines is highly dependent on maintaining consistency in quality, safety and efficacy while minimizing any risk of divergence during life-cycle management. In recognition of this need and demand from global manufacturers, the World Health Organization (WHO) Expert Committee on Biological standardization established the WHO 1^st International standard (IS) for Adalimumab (coded 17/236) in October 2019 with a defined unitage ascribed to each of the individual bioactivities evaluated in the study namely, TNF-α binding, TNF-α neutralization, complement dependent cytotoxicity and antibody-dependent cellular cytotoxicity. For development of the IS, two candidate standards were manufactured as per WHO recommendations. Analysis of extensive datasets generated by testing of a common set of samples including the candidate standards by multiple stakeholders including regulatory agencies using their own qualified assays in a large international collaborative study showed comparable biological activity for the tested candidates for the different activities. Use of a common standard significantly decreased the variability of bioassays and improved agreement in potency estimates. Data from this study clearly supports the utility of the IS as an important tool for assuring analytical assay performance, for bioassay calibration and validation, for identifying and controlling changes in bioactivity during life-cycle management and for global harmonization of adalimumab products. In addition, in a separate multi-center study which included involvement of hospital and clinical diagnostic laboratories, the suitability of the adalimumab IS for therapeutic drug monitoring assays was examined by analysis of data from testing of a common blind coded panel of adalimumab spiked serum samples representative of the clinical scenario along with the IS and in-house standards in diverse immunoassays/platforms. Both commercially available and in-house assays that are routinely used for assessing adalimumab trough levels were included. Excellent agreement in estimates for adalimumab content in the spiked samples was observed regardless of the standard or the method with inter-laboratory variability also similar regardless of the standard employed. This data, for the first time, provides support for the extended applicability of the IS in assays in use for therapeutic drug monitoring based on the mass content of the IS. The adalimumab IS, in fulfilling clinical demand, can help toward standardizing and harmonizing clinical monitoring assays for informed clinical decisions and/or personalized treatment strategies for better patient outcomes. Collectively, a significant role for the adalimumab IS in assuring the quality, safety and efficacy of adalimumab products globally is envisaged.

The Use of Next-Generation Sequencing for the Quality Control of Live-Attenuated Polio Vaccines

BACKGROUND

Next-generation sequencing (NGS) analysis was compared to the current MAPREC (mutational analysis by polymerase chain reaction and restriction enzyme cleavage) assay for quality control of live-attenuated oral polio vaccine (OPV).

METHODS

MAPREC measures reversion of the main OPV attenuating mutations such as uracil (U) to cytosine (C) at nucleotide 472 in the 5' noncoding region of type 3 OPV. Eleven type 3 OPV samples were analyzed by 8 laboratories using their in-house NGS method.

RESULTS

Intraassay, intralaboratory, and interlaboratory variability of NGS 472-C estimates across samples and laboratories were very low, leading to excellent agreement between laboratories. A high degree of correlation between %472-C results by MAPREC and NGS was observed in all laboratories (Pearson correlation coefficient r = 0.996). NGS estimates of sequences at nucleotide 2493 with known polymorphism among type 3 OPV lots also produced low assay variability and excellent between-laboratory agreement.

CONCLUSIONS

The high consistency of NGS data demonstrates that NGS analysis can be used as high-resolution test alternative to MAPREC, producing whole-genome profiles to evaluate OPV production consistency, possibly eliminating the need for tests in animals. This would be very beneficial for the quality assessment of next-generation polio vaccines and, eventually, for other live-attenuated viral vaccines.

An international collaborative study to establish the WHO 3rd International Standard for Thrombin: Communication from the ISTH SSC subcommittee on factor XIII and fibrinogen

The calibration of thrombin products relies on the World Health Organization (WHO) 2nd International Standard (IS) for Thrombin (01/580) which defines the international unit (IU) for thrombin potency. With stocks of the 2nd IS (01/580) running low, an international collaborative study was organized to calibrate a replacement. Twenty laboratories from 13 countries took part in the study and measured the potency of two candidate replacement standards (coded 01/578 and 19/188) relative to the 2nd IS. In total, 111 valid assays were returned, which were a combination of plasma/fibrinogen clotting assays and chromogenic assays. Variation between and within laboratories was low, with inter- and intra-laboratory geometric coefficient of variation (GCV) generally <5% for all assay methods and substrates. For 01/578, potency estimates by clotting assays (101.1 IU/ampoule) were significantly lower than estimates by chromogenic assays (111.5 IU/ampoule). Mean potency estimates for 19/188 were 90.4 IU/ampoule by clotting assay and 88.1 IU/ampoule by chromogenic assay, which was not a statistically significant difference. The close ratio between clotting and chromogenic assay potency estimates for 19/188 suggests it has a higher α-thrombin content than 01/578 and is equivalent to the current IS (01/580). Accelerated degradation studies predicted excellent long-term stability profiles for preparations 01/580, 01/578, and 19/188. Based on the results of this study, the WHO Expert Committee on Biological Standardization established 19/188 as the 3rd IS for Thrombin with a potency of 90 IU/ampoule in August 2020.

Saccharide dosage content of meningococcal polysaccharide conjugate vaccines determined using WHO International Standards for serogroup A, C, W, Y and X polysaccharides

Potency of meningococcal polysaccharide-protein conjugate vaccines relies on the polysaccharide content to prevent meningitis. NIBSC, as the official national control laboratory in UK, analysed ten different mono- and multi-meningococcal conjugate vaccines, using established International Standards for meningococcal serogroups A, C, W, Y and X, by resorcinol or HPAEC-PAD assay. Most saccharide contents were within ±20% of their claimed content for licensure with taking different O-acetylation levels into consideration, with only MenC content in two vaccines below (by 60% and 54%) the labelled value, however, previous study showed different dosage was not necessarily correlated to the immunogenicity of those vaccines. This study demonstrated the use of International Standards to quantify saccharide content in polysaccharide-based vaccines with different percentage of O-acetylation. These International Standards are suitable to serve as either quantitative standard or calibrator of in-house standards, with supplied stability data.

Calibration of the WHO 5th IS for Blood Coagulation Factor IX, Concentrate and Ph. Eur. Human Coagulation Factor IX Concentrate Biological Reference Preparation Batch 3 and investigation of the suitability of an IS as potency standard for purified full-length recombinant FIX

A joint World Health Organization (WHO) - European Directorate for the Quality of Medicines & HealthCare (EDQM) study was run to calibrate the WHO 5th International Standard (IS) for Blood Coagulation Factor IX (FIX), Concentrate, and European Pharmacopoeia (Ph. Eur.) Human Coagulation Factor IX concentrate Biological Reference Preparation (BRP) Batch 3. The suitability of the 4th IS as a potency standard for purified full-length recombinant FIX (rFIX) was also investigated. Forty-nine laboratories contributed data for the calibration of 2 plasma-derived FIX candidates, relative to the 4th IS, from clotting and chromogenic assays. The intra-laboratory variability was reasonably low; the inter-laboratory variation was lower for sample B (14/148) than for sample C (14/162). Although there were no discrepancies between clotting and chromogenic assays, a significantly lower potency was obtained for sample C with clotting assays when buffer rather than FIX-deficient plasma was used as pre-diluent. A significant assay discrepancy was observed with estimates for the 4th IS for Blood Coagulation Factors FII, VII, IX, X, Plasma against the 4th IS, resulting in a clotting to chromogenic activity ratio of 1.11. The study also investigated the comparability of the plasma-derived concentrate standard with the rFIX products and considered the establishment of an IS for rFIX. The 3 rFIX products currently licensed were represented in this study. Data from 49 laboratories for 2 rFIX candidates were received, with additional results for another full-length rFIX test sample returned by 6 laboratories. The intra-laboratory variability when the rFIX samples were assayed against the 4th IS was acceptably low. Although the full-length rFIX could be assayed against the plasma-derived 4th IS and provided statistically valid results, there were large discrepancies among the clotting assays using different APTT reagents. The inter-laboratory variability of the chromogenic assays was similarly high. There were also significant clotting and chromogenic assay discrepancies. The data from the present study indicate that a recombinant standard for rFIX products will minimise assay discrepancies and improve inter-laboratory agreement. However, they also underline that the value assignment of the 1st rFIX IS needs careful consideration. The Expert Committee on Biological Standardization (ECBS) of WHO was therefore not requested to consider the establishment of an IS for rFIX. In order to ensure continued harmonised standards, sample B (14/148) was established as the WHO 5th IS for Blood Coagulation Factor IX, Concentrate, and as Ph. Eur. Human Coagulation Factor IX, concentrate BRP Batch 3 with the functional activity of 10.5 IU/ampoule.

Development of the first reference antibody panel for qualification and validation of cytokine release assay platforms - Report of an international collaborative study

Immunomodulatory therapeutics such as monoclonal antibodies (mAb) carry an inherent risk of undesired immune reactions. One such risk is cytokine release syndrome (CRS), a rapid systemic inflammatory response characterized by the secretion of pro-inflammatory cytokines from immune cells. It is crucial for patient safety to correctly identify potential risk of CRS prior to first-in-human dose administration. For this purpose, a variety of in vitro cytokine release assays (CRA) are routinely used as part of the preclinical safety assessment of novel therapeutic mAbs. One of the challenges for the development and comparison of CRA performance is the lack of availability of standard positive and negative control mAbs for use in assay qualification. To address this issue, the National Institute for Biological Standards and Control (NIBSC) developed a reference panel of lyophilised mAbs known to induce CRS in the clinic: human anti-CD52, mouse anti-CD3 and human superagonistic (SA) anti-CD28 mAb manufactured according to the respective published sequences of Campath-1H® (alemtuzumab, IgG1) , Orthoclone OKT-3® (muromonab, IgG2a) and TGN1412 (theralizumab, IgG4), as well as three isotype matched negative controls (human IgG1, mouse IgG2a and human IgG4, respectively). The relative capacity of these control mAbs to stimulate the release of IFN-γ, IL-2, TNF-α and IL-6 in vitro was evaluated in eleven laboratories in an international collaborative study mediated through the HESI Immuno-safety Technical Committee Cytokine Release Assay Working Group. Participants tested the NIBSC mAbs in a variety of CRA platforms established at each institution. This paper presents the results from the centralised cytokine quantification on all the plasma/supernatants corresponding to the stimulation of immune cells in the different CRA platforms by a single concentration of each mAb. Each positive control mAb induced significant cytokine release in most of the tested CRA platforms. There was a high inter-laboratory variability in the levels of cytokines produced, but similar patterns of response were observed across laboratories that replicated the cytokine release patterns previously published for the respective clinical therapeutic mAbs. Therefore, the positive and negative mAbs are suitable as a reference panel for the qualification and validation of CRAs, comparison of different CRA platforms (e.g. solid vs aqueous phase), and intra- and inter-laboratory comparison of CRA performance. Thus, the use of this panel of positive and negative control mAbs will increase the confidence in the robustness of a CRA platform to identify a potential CRS risk for novel immunomodulatory therapeutic candidates.

Development and Assessment of a Pooled Serum as Candidate Standard to Measure Influenza A Virus Group 1 Hemagglutinin Stalk-Reactive Antibodies

The stalk domain of the hemagglutinin has been identified as a target for induction of protective antibody responses due to its high degree of conservation among numerous influenza subtypes and strains. However, current assays to measure stalk-based immunity are not standardized. Hence, harmonization of assay readouts would help to compare experiments conducted in different laboratories and increase confidence in results. Here, serum samples from healthy individuals (n = 110) were screened using a chimeric cH6/1 hemagglutinin enzyme-linked immunosorbent assay (ELISA) that measures stalk-reactive antibodies. We identified samples with moderate to high IgG anti-stalk antibody levels. Likewise, screening of the samples using the mini-hemagglutinin (HA) headless construct #4900 and analysis of the correlation between the two assays confirmed the presence and specificity of anti-stalk antibodies. Additionally, samples were characterized by a cH6/1N5 virus-based neutralization assay, an antibody-dependent cell-mediated cytotoxicity (ADCC) assay, and competition ELISAs, using the stalk-reactive monoclonal antibodies KB2 (mouse) and CR9114 (human). A “pooled serum” (PS) consisting of a mixture of selected serum samples was generated. The PS exhibited high levels of stalk-reactive antibodies, had a cH6/1N5-based neutralization titer of 320, and contained high levels of stalk-specific antibodies with ADCC activity. The PS, along with blinded samples of varying anti-stalk antibody titers, was distributed to multiple collaborators worldwide in a pilot collaborative study. The samples were subjected to different assays available in the different laboratories, to measure either binding or functional properties of the stalk-reactive antibodies contained in the serum. Results from binding and neutralization assays were analyzed to determine whether use of the PS as a standard could lead to better agreement between laboratories. The work presented here points the way towards the development of a serum standard for antibodies to the HA stalk domain of phylogenetic group 1.

Establishment of a WHO Reference Reagent for anti-Mullerian hormone

BACKGROUND

There is a need for a reference material to support the development and ensure the quality of immunoassays for human AMH. A batch of ampoules, coded 16/190, containing lyophilised recombinant AMH was evaluated in a WHO Collaborative Study. The aims of the study were to determine the AMH content in terms of the calibration of each immunoassay method, to predict long-term stability and to assess the suitability of the preparation to calibrate AMH immunoassays.

METHODS

Study participants were asked to report the AMH content of specific dilutions of coded ampoules of 16/190 and a comparator preparation containing approximately half the AMH content. In each assay, participants also reported the AMH content of 22 patient samples to assess commutability. A robust all-laboratory geometric mean of the content estimates was determined using the laboratory geometric mean estimates. Commutability was assessed using a difference in bias approach. Stability was predicted by the measurement of thermally accelerated degradation samples.

RESULTS

Seven laboratories performed twenty-one immunoassay method-platform combinations, sixteen of which provided data which met the validity criteria, giving a consensus geometric mean estimate of AMH content of 511 ng/ampoule (95% CI, 426-612, n = 16, GCV 42%) and a robust geometric mean of 489 ng/ampoule. By contrast, the GCV% for the all-laboratory geometric mean of the relative content estimates for the comparator sample to 16/190 was 12%. Commutability was assessed using 20 of the 22 representative patient samples. Of the valid assays, 16/190 was within the limits of acceptable commutability for 6 methods, partially commutable for a further 3 methods and non-commutable when measured by 7 methods. The preparation was predicted to be highly stable when stored at - 20 °C.

CONCLUSION

The majority of methods met the validity criteria. Content estimates showed a high between-method variability, yet assays exhibited a similar proportionality of response as demonstrated using the comparator sample. 16/190 was commutable in some but not all methods. On the basis of these results, it was agreed by the WHO Expert Committee on Biological Standardization to establish 16/190 as a WHO Reference Reagent for AMH with a content defined by consensus immunoassay of 489 ng/ampoule.

An international collaborative study to establish the WHO 4th International Standard for Streptokinase: Communication from the SSC of the ISTH

Streptokinase is used worldwide as a cost-effective treatment for acute myocardial infarction. Manufacturers use the World Health Organization (WHO) International Standard (IS) for Streptokinase to potency label their products, ensuring consistent, safe, and effective dosing. Stocks of the third IS for streptokinase (coded 00/464) are running low, and an international collaborative study was organized to calibrate a replacement. A total of 15 laboratories from nine countries took part, using chromogenic and/or fibrin clot lysis methods to determine the potency of two candidate preparations, coded 16/356 (sample B) and 16/358 (sample C), relative to the third IS (00/464). A third sample (88/824, sample A), which was used in the collaborative studies to establish the second and third IS, was also included. There was good agreement in potency estimates from different assay methods and low variability both within and between laboratories. Long-term stability modeling indicated the candidates are very stable. Comparison of potency estimates for 88/824 (sample A) with potencies calculated in previous studies revealed a variability of only 1.9% over the course of three collaborative studies spanning 30 years and more than 50 years of streptokinase standardization. This indicates excellent continuity of the International Unit (IU) and assay methods. Following agreement by study participants and Scientific and Standardization Committee experts of the International Society on Thrombosis and Haemostasis, the WHO Expert Committee on Biological Standardization established 16/358 (sample C) as the fourth IS for Streptokinase with a potency of 1013 IU per ampoule in October 2019.

Collaborative study for the establishment of Etanercept Biological Reference Preparation Batch 1

Three preparations of the human tumour necrosis factor (TNF) receptor II Fc fusion protein (TNFR II-Fc) Etanercept were formulated and lyophilised at the National Institute for Biological Standards & Control (NIBSC) prior to evaluation in a collaborative study for their suitability to serve as a World Health Organization (WHO) International Standard (IS)/European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for the potency assay of Etanercept. Seven laboratories tested the preparations using an in vitro cell-based bioassay (TNF-α neutralisation) prescribed by the Ph. Eur. monograph on Etanercept (2895). The results of this study indicated that the candidate preparation, coded 13/204, established as the first IS for Etanercept with an assigned potency for TNF neutralisation activity of 10 000 IU per ampoule was also suitable to serve as Ph. Eur. BRP batch 1. The results were compared to those obtained with different cell-based neutralisation assays that were used by further laboratories in the context of establishing the 1st WHO IS for Etanercept. Based on these analyses, preparation 13/204 was adopted by the Ph. Eur. Commission as Etanercept BRP batch 1 with an assigned potency of 10 000 IU per ampoule.

Collaborative study for the establishment of Infliximab Biological Reference Preparation Batch 1

Two preparations of the chimeric anti-Tumour Necrosis Factor (TNF) monoclonal antibody Infliximab were formulated and lyophilised at the National Institute for Biological Standards & Control (NIBSC) prior to evaluation in a collaborative study for their suitability to serve as a World Health Organization (WHO) International Standard (IS)/European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for the potency assay of Infliximab. Twenty-six laboratories tested the preparations using different in vitro cell-based bioassays (TNF-α neutralisation, antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity) and binding assays. Amongst them, 19 laboratories performed cell-based bioassays. The results of this study indicated that the candidate preparation coded 16/170 was suitable to serve as an International Standard for Infliximab based on the data obtained for biological activity. This candidate standard was established in 2017 as the first International Standard for Infliximab with an assigned potency for TNF neutralisation activity of 500 IU per ampoule. In the same study, the suitability of preparation 16/170 of Infliximab to serve as the European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) for the Infliximab potency assay as described in the Ph. Eur. monograph on Infliximab concentrated solution (2928) was also evaluated. The corresponding analysis, based on the measurement of the inhibitory action of anti-human TNF (Infliximab) on the cytotoxic activity of TNF-alpha, was performed using data from a subset of 9 laboratories using the TNF-alpha-sensitive fibrosarcoma cell line WEHI-164. The results obtained were compared to those obtained from different cell-based neutralisation assays that were used by other laboratories in the context of establishing the 1st World Health Organization (WHO) International Standard (IS) for Infliximab. Based on the analyses, preparation 16/170 was adopted by the Ph. Eur. Commission in June 2018 as Infliximab BRP batch 1 with an assigned potency of 500 IU per ampoule.

Comparison of Serologic Assays for Middle East Respiratory Syndrome Coronavirus

Middle East respiratory syndrome coronavirus (MERS-CoV) was detected in humans in 2012. Since then, sporadic outbreaks with primary transmission through dromedary camels to humans and outbreaks in healthcare settings have shown that MERS-CoV continues to pose a threat to human health. Several serologic assays for MERS-CoV have been developed globally. We describe a collaborative study to investigate the comparability of serologic assays for MERS-CoV and assess any benefit associated with the introduction of a standard reference reagent for MERS-CoV serology. Our study findings indicate that, when possible, laboratories should use a testing algorithm including >2 tests to ensure correct diagnosis of MERS-CoV. We also demonstrate that the use of a reference reagent greatly improves the agreement between assays, enabling more consistent and therefore more meaningful comparisons between results.

Harmonization of Zika neutralization assays by using the WHO International Standard for anti-Zika virus antibody

During outbreaks of emerging viruses, such as the Zika outbreak in 2015-2016, speed and accuracy in detection of infection are critical factors to control the spread of the disease; often serological and diagnostic methods for emerging viruses are not well developed and validated. Thus, vaccines and treatments are difficult to evaluate due to the lack of comparable methods. In this study, we show how the 1st WHO International Standard for anti-Zika antibody was able to harmonize the neutralization titres of a panel of serological Zika-positive samples from laboratories worldwide. Expression of the titres in International Unit per millilitre reduced the inter-laboratory variance, allowing for greater comparability between laboratories. We advocate the use of the International Standard for anti-Zika virus antibodies for the calibration of neutralization assays to create a common language, which will permit a clear evaluation of the results of different clinical trials and expedite the vaccine/treatment development.

A WHO Reference Reagent for lupus (anti-dsDNA) antibodies: international collaborative study to evaluate a candidate preparation

Introduction

Antibodies against double-stranded DNA (anti-dsDNA) are a specific biomarker for systemic lupus erythematosus (SLE). The first WHO International Standard (IS) for anti-dsDNA (established in 1985), which was used to assign units to diagnostic tests, was exhausted over a decade ago.

Methods

Plasma from a patient with SLE was first evaluated in 42 European laboratories. The plasma was thereafter used by the National Institute for Biological Standards and Control to prepare a candidate WHO reference preparation for lupus (anti-dsDNA) antibodies. That preparation, coded 15/174, was subjected to an international collaborative study, including 36 laboratories from 17 countries.

Results

The plasma mainly contained anti-dsDNA, other anti-chromatin antibodies and anti-Ku. The international collaborative study showed that the field would benefit from 15/174 as a common reference reagent improving differences in performance between different assays. However, no statistically meaningful overall potency or assay parallelism and commutability could be shown.

Conclusion

15/174 cannot be considered equivalent to the first IS for anti-dsDNA (Wo/80) and was established as a WHO Reference Reagent for lupus (oligo-specific) anti-dsDNA antibodies with a nominal value of 100 units/ampoule. This preparation is intended to be used to align test methods quantifying levels of anti-dsDNA antibodies.

Evaluation of a capture antigen ELISA for the characterisation of tetanus vaccines for veterinary use

We previously developed an ELISA assay for detection of tetanus toxoid antigen in tetanus vaccines for human use. Tetanus vaccines for veterinary use are qualitatively different to those used in humans, often containing a larger number and variety of non-tetanus antigens in the multi-valent products, and adjuvants that are not found in human vaccines. We assessed performance of the capture ELISA with a range of veterinary tetanus vaccines as a first step towards development of an immunoassay as a potential in vivo potency substitute. Nine tetanus vaccines were tested and all produced a good dose response in the ELISA. The shape of the dose response curve for the whole vaccine compared to a matched non-adjuvanted tetanus toxoid antigen was more comparable for vaccines containing a non-aluminium adjuvant than products containing aluminium adjuvants. Elution of the antigen from aluminium adjuvant did not improve the comparability of the dose response curve but did increase the total amount of tetanus antigen available for detection. The ELISA was highly specific for tetanus with no signal obtained for a large number of non-tetanus antigens. These results suggest that a capture ELISA assay can be applied to a control strategy for veterinary tetanus vaccines.

The third international standard for anti-D immunoglobulin: international collaborative study to evaluate candidate preparations

BACKGROUND AND OBJECTIVES

The purpose of the study was to evaluate a lyophilized anti-D immunoglobulin preparation to serve as a replacement WHO International Standard for the calibration of potency assays of anti-D immunoglobulin products. Such products are used to prevent haemolytic disease of the foetus and newborn due to maternal alloanti-D.

MATERIALS AND METHODS

The candidate 3rd International Standard for anti-D immunoglobulin (16/332) was evaluated and calibrated against the 2nd International Standard for anti-D immunoglobulin (01/572), along with a coded duplicate, a second candidate preparation (16/278) and a comparability sample (16/272) in an international collaborative study. Twenty of 21 laboratories in 15 countries performed one or more of the three European Pharmacopoeia reference methods.

RESULTS

The overall geometric mean potency (from all methods) of the candidate 3rd International Standard, 16/332, was 296·6 IU/ampoule, with inter-laboratory variability, expressed as % GCV, of 4·7%. SE-HPLC of the immunoglobulin preparations demonstrated combined monomeric and dimeric IgG peak areas of >95% for all samples. Accelerated stability studies have shown both 16/332 and 16/278 to be very stable for long-term storage at -20°C.

CONCLUSIONS

Preparation 16/332 was established by the World Health Organisation Expert Committee on Biological Standardization as the 3rd International Standard for anti-D immunoglobulin with an assigned potency of 297 IU/ampoule.

Comparison of Volumetric and Bead-Based Counting of CD34 Cells by Single-Platform Flow Cytometry

Background

Over 2,000 people a year in the United Kingdom need a bone marrow or blood stem cell transplant. It is important to accurately quantify the hematopoietic stem cells to predict whether the transplant will be successful in replenishing the immune system. However, they are present at low frequency, which complicates accurate quantification. The current gold standard method is single‐platform flow cytometry using internal reference counting beads to determine the concentration of CD34 cells. However, volumetric flow cytometers have the ability to measure the acquisition volume, which removes the need for reference beads for calculation of cell concentrations.

Method

In this study, we compared both methods for calculating CD34 cell concentrations in volumetric cytometers, using either the volume reading or the number of reference beads for calculation. In addition, the uncertainty of measurement for each method was estimated.

Results

The results show that both methods have similar uncertainties of measurement. Regression analysis showed low to no statistical difference in CD34 cell concentrations obtained with each method.

Conclusions

Overall, this study suggests that the volumetric method is a valid approach but that the adoption of this technology may be hindered without some form of external calibration of volume readings to increase confidence in the measurement. © 2019 The Authors. Cytometry Part B: Clinical Cytometry published by Wiley Periodicals, Inc. on behalf of International Clinical Cytometry Society.

Evaluation of two WHO First International Standards for Vi polysaccharide from Citrobacter freundii and Salmonella enterica subspecies enterica serovar Typhi

Numerous Vi capsular polysaccharide (Vi PS) conjugate vaccines to protect young children and infants from Typhoid are either licensed or under development. These vaccines are evaluated by laboratory methods to ensure their potency and that quality requirement are met. International Standard (IS) preparations of Vi PS are needed to calibrate and harmonise these assays. Twenty laboratories from 12 countries participated in a collaborative study to evaluate two candidate ISs: Citrobacter freundii Vi PS (NIBSC code 12/244) and Salmonella enterica serovar Typhi Vi PS (16/126). On the basis of returned results and stability profiles, these standards were established by the WHO Expert Committee on Biological Standardization in Oct 2017 as the First WHO IS for C. freundii Vi PS with a content of 1.94 ± 0.12 mg Vi PS per ampoule (expanded uncertainty with coverage factor of k = 2.11 corresponding to a 95% level of confidence) and the First WHO IS for S. Typhi Vi PS with a content of 2.03 ± 0.10 mg Vi PS per ampoule (expanded uncertainty with coverage factor of k = 2.11), as determined by quantitative NMR. The study also showed the ISs are suitable for physicochemical and immuno assays used for the quantitation of the Vi PS component in Vi PS and conjugate vaccines.

The first World Health Organization International Standard for infliximab products: A step towards maintaining harmonized biological activity

Due to the increase in the number of infliximab products, the need for global harmonization of the bioactivity of this monoclonal antibody was recognized by the World Health Organization (WHO). In response, the National Institute for Biological Standards and Control (NIBSC) developed the first international standard (IS) for infliximab, which targets tumour necrosis factor (TNF). Each ampoule is assigned values of 500 IU of TNF neutralizing activity and 500 IU of binding activity. Two preparations of infliximab were formulated and lyophilized at NIBSC prior to evaluation in a collaborative study for their suitability to serve as an IS for the in vitro biological activity of infliximab. The study involved participants using in vitro cell-based bioassays (TNF neutralization, antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity) and binding assays. The results of this study showed that the candidate preparation, coded 16/170, is suitable as an IS for infliximab bioactivity. This infliximab IS from NIBSC, is intended to support in vitro bioassay calibration and validation by defining international units of bioactivity. The proposed unitages, however, are not intended to revise product labelling or dosing requirements, as any decisions regarding this relies solely with the regulatory authorities. Furthermore, the infliximab IS is not intended for determining the specific activity of products, nor to serve any regulatory role in defining biosimilarity. We briefly discuss the future use of WHO international standards in supporting the global harmonisation of biosimilar infliximab products.

Establishment of the first International Standard for human anti-typhoid capsular Vi polysaccharide IgG

Vi capsular polysaccharide (Vi) conjugate vaccines, which can prevent typhoid in infants and young children, are being developed. Comparative immunogenicity studies are facilitated by an International Standard (IS) for human anti-Vi IgG. 16/138, a pool of sera from volunteers which received either Vi conjugate vaccine or plain Vi vaccine, was assessed as an IS alongside U.S. reference reagent Vi-IgGR1, 2011. Samples were tested in a commercial ELISA (n = 7), a standardised ELISA based on biotinylated Vi (n = 7) and in-house ELISAs (n = 7). Valid estimates were obtained for the potency of all samples in the commercial ELISA, and the commutability of 16/138 and Vi-IgGR1, 2011 was evident for the commercial ELISA and in-house ELISAs based on a coating of Vi and protein. The WHO Expert Committee on Biological Standardization established 16/138 as the first IS for anti-Vi IgG with 100 IU per ampoule and assigned 163 IU per vial of Vi-IgGR1, 2011.

Establishment of the first WHO International Standard for antiserum to Respiratory Syncytial Virus: Report of an international collaborative study

Respiratory Syncytial Virus (RSV), a leading cause of lower respiratory tract illness, has been a focus of vaccine development efforts in recent years. RSV neutralisation assays are particularly useful in the evaluation of immunogenicity of RSV vaccine candidates. Here we report a collaborative study that was conducted with the aim to establish the 1st International Standard for antiserum to RSV, to enable the standardisation of results across multiple assay formats. Two candidate standards were produced from serum samples donated by healthy adult individuals. 25 laboratories from 12 countries, including university laboratories, manufacturers/developers of RSV vaccines and public health laboratories, participated in the study. The study samples comprised the two candidate standards, NIBSC codes 16/284 and 16/322, naturally infected adult sera, age stratified naturally infected paediatric sera, sera from RSV vaccine clinical trials in maternal and elderly subjects, a monoclonal antibody to RSV (palivizumab), two cotton rat serum samples and samples from the BEI Resources panel of human antiserum and immune globulin to RSV. The collaborative study showed that between-laboratory variability in neutralisation titres was substantially reduced when values were expressed relative to those of either of the two candidate international standards. Stability of 16/284 and 16/322 maintained for 6 months at different temperatures showed no significant loss of activity (relative to that at -20 °C storage temperature) at temperatures of up to +20 °C. Based on these results, 16/284 was established as the 1st International Standard for antiserum to RSV, with an assigned unitage of 1000 International Units (IU) of anti-RSV neutralising antibodies per vial, by the WHO Expert Committee on Biological Standardisation, with 16/322 suitable as a possible replacement standard for 16/284.

Establishment of the 1st WHO International Standard for anti-EV71 serum (Human)

Enterovirus A71 (EV71) is the major causative agent of severe and fatal hand, foot and mouth disease. There is plenty of evidence that EV71 has circulated widely in the Western Pacific Region for the last twenty years. Vaccines against EV71 are already available or under development. A collaborative study to establish the 1st WHO International Standard for anti-EV71 serum (Human) was conducted to ensure that methods used to measure the serum neutralizing activity or antibody levels against EV71 are accurate, sensitive and reproducible. Two candidate samples as well as a third candidate reference containing low anti-EV71 antibody titre were produced from plasma samples donated by healthy individuals. All three serum samples exhibited good levels of neutralizing antibodies against a wide range of EV71 strains of various genotypes. The study showed that between laboratory variations in neutralization titres were significantly reduced when values were expressed relative to those of either of the two candidate sera. Sample 14/140 was established as the WHO 1st International Standard for anti-EV71 serum (human), 14/138 as its potential replacement and 13/238 as a WHO Reference Reagent, with assigned unitage of 1,000, 1090 and 300 International Units (IU) of anti-EV71 neutralizing antibodies per ampoule, respectively.

The effect of increasing the sulfation level of chondroitin sulfate on anticoagulant specific activity and activation of the kinin system

Oversulfated chondroitin sulfate (OSCS) was identified as a contaminant in certain heparin preparations as the cause of adverse reactions in patients. OSCS was found to possess both plasma anticoagulant activity and the ability to activate prekallikrein to kallikrein. Differentially sulfated chondroitin sulfates were prepared by synthetic modification of chondroitin sulfate and were compared to the activity of OSCS purified from contaminated heparin. Whilst chondroitin sulfate was found to have minimal anticoagulant activity, increasing sulfation levels produced an anticoagulant response which we directly show for the first time is mediated through heparin cofactor II. However, the tetra-sulfated preparations did not possess any higher anticoagulant activity than several tri-sulfated variants, and also had lower heparin cofactor II mediated activity. Activation of prekallikrein was concentration dependent for all samples, and broadly increased with the degree of sulfation, though the di-sulfated preparation was able to form more kallikrein than some of the tri-sulfated preparations. The ability of the samples to activate the kinin system, as measured by bradykinin, was observed to be through kallikrein generation. These results show that whilst an increase in sulfation of chondroitin sulfate did cause an increase in anticoagulant activity and activation of the kinin system, there may be subtler structural interactions other than sulfation at play given the different responses observed.

Establishment of the World Health Organization First International Standard for Factor XII, Plasma, Human

Until recently, the role of factor XII (FXII) in hemostasis was not considered to be important since patients with FXII deficiency do not present with bleeding. The activation of FXII by agents including mast cells and platelet polyphosphates suggests that it may have a role in thrombogenesis. The inhibition of FXII therefore presents an option for antithrombotic therapy, and antibodies and inhibitors are already in development. Assays for FXII will be required to support these technologies, and an international standard (IS) for FXII would be useful for the development of these methods and for the clinical monitoring of patients. The purpose of this study was to develop an IS for FXII, with values for functional activity (FXII:C) and antigen (FXII:Ag). Double-spun normal plasma was pooled, filled into siliconized glass ampoules, and freeze-dried to prepare the candidate material. Data from 20 laboratories using the one-stage clotting assay were used to assign the functional activity value in units (u). The antigen value was calculated using data from eight laboratories that carried out antigen assays. Each laboratory was requested to collect two local normal plasma pools. Units of activity and antigen were calculated relative to these pools, as is usual for new coagulation factor analytes. The amount of activity or antigen in 1 ml of normal plasma from each pool was taken to be 1 unit. A total of 566 donors were used across the pools for the FXII:C study and 216 donors for the FXII:Ag study. The overall geometric mean per ampoule for FXII:C was 0.86 u and for FXII:Ag was 0.80 u. The inter-laboratory variation was 10 and 11%, respectively (expressed as the geometric coefficient of variation). Based on these data, the candidate was deemed suitable for use as an IS for FXII. In 2017, the candidate was established by the World Health Organization (WHO) Expert Committee on Biological Standardization as the WHO first IS for blood coagulation FXII, Plasma (National Institute for Biological Standards and Control code 15/180). The values assigned were 0.86 international units (IU) of functional activity (FXII:C) per ampoule and 0.80 IU/ampoule of antigen (FXII:Ag).

Recommendations of the VAC2VAC workshop on the design of multi-centre validation studies

Within the Innovative Medicines Initiative 2 (IMI 2) project VAC2VAC (Vaccine batch to vaccine batch comparison by consistency testing), a workshop has been organised to discuss ways of improving the design of multi-centre validation studies and use the data generated for product-specific validation purposes. Moreover, aspects of validation within the consistency approach context were addressed. This report summarises the discussions and outlines the conclusions and recommendations agreed on by the workshop participants.

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In Europe, use of non-animal methods is encouraged and being informed is key.

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Manufacturers should engage in validation studies at an early stage.

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Participants in validation studies can use data for product-specific validation.

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More regulatory guidance on setting specifications and validity criteria needed.

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Communication of key players crucial for implementation/acceptance of methods.

A Performance Evaluation of Commercial Fibrinogen Reference Preparations and Assays for Clauss and PT-derived Fibrinogen

The wide availability of fibrinogen estimations based on the prothrombin time (PT-Fg) has caused concern about the variability and clinical utility of fibrinogen assays. In a multi-centre study, we investigated fibrinogen assays using various reagents and analysers. Clauss assays generally gave good agreement, although one reagent gave 15–30% higher values in DIC and thrombolysis. Two commercial reference preparations had much lower potencies than the manufacturers declared, and plasma turbidity influenced parallelism in some Clauss assays. PT-Fg assays gave higher values than Clauss and showed calibrant dependent effects, the degree of disparity correlating with calibrant and test sample turbidity. Analyser and thromboplastin dependent differences were noted. The relationship between Clauss and PT-Fg assays was sigmoid, and the plateau of maximal PT-Fg differed by about 2 g/l between reagents. ELISA and immunonephelometric assays correlated well, but with a high degree of scatter. Antigen levels were higher than Clauss, but slightly lower than PT-Fg assays, which appeared to be influenced by degraded fibrinogen. Clauss assays are generally reproducible between centres, analysers and reagents, but PT-Fg assays are not reliable in clinical settings.

Standardisation of Factor VIII and von Willebrand Factor in Plasma: Calibration of the 4th International Standard (97/586)

The 4th International Standard (IS) Factor VIII/von Willebrand Factor (FVIII/VWF) plasma was calibrated in 25 laboratories by assay against the 3rd IS plasma and fresh normal plasma pools. Five parameters were measured, FVIII:coagulant activity (FVIII:C), FVIII:Antigen (FVIII:Ag), VWF:Antigen (VWF:Ag), VWF:Ristocetin Cofactor (VWF:RCof), and a new parameter, VWF:collagen binding (VWF:CB). Mean potency estimates for the 4th IS, calculated relative to the 3rd IS, were significantly greater than the mean estimates calculated relative to the fresh normal pools by 15, 14 and 20% respectively for FVIII:C, VWF:Ag and VWF:RCof. These results indicate a drift in the International Unit away from the fresh plasma unit. Partial rectification of this drift was achieved by assigning the mean of the estimates calculated relative to the 3rd IS and the fresh plasma pools, i.e. FVIII:C 0.57 IU/ampoule, VWF:Ag 0.79 IU/ampoule and VWF:RCof 0.73 IU/ampoule. This represents a shift in the IU between the 3rd and 4th IS of 7.5% for FVIII:C, 7% for VWF:Ag and 10% for VWF:RCof. Mean estimates of FVIII:Ag relative to the 3rd IS and the fresh normal pools agreed to give an assigned value of 0.89 IU/ampoule. Excessive inter-laboratory variability and a low number of estimates (n = 6) precluded the assignment of a potency for VWF:CB. The 4th IS Factor VIII/VWF plasma (97/586) was established in October 1998.

International standards for monoclonal antibodies to support pre- and post-marketing product consistency: Evaluation of a candidate international standard for the bioactivities of rituximab

The intrinsic complexity and heterogeneity of therapeutic monoclonal antibodies is built into the biosimilarity paradigm where critical quality attributes are controlled in exhaustive comparability studies with the reference medicinal product. The long-term success of biosimilars will depend on reassuring healthcare professionals and patients of consistent product quality, safety and efficacy. With this aim, the World Health Organization has endorsed the need for public bioactivity standards for therapeutic monoclonal antibodies in support of current controls. We have developed a candidate international potency standard for rituximab that was evaluated in a multi-center collaborative study using participants' own qualified Fc-effector function and cell-based binding bioassays. Dose-response curve model parameters were shown to reflect similar behavior amongst rituximab preparations, albeit with some differences in potency. In the absence of a common reference standard, potency estimates were in poor agreement amongst laboratories, but the use of the candidate preparation significantly reduced this variability. Our results suggest that the candidate rituximab standard can support bioassay performance and improve data harmonization, which when implemented will promote consistency of rituximab products over their life-cycles. This data provides the first scientific evidence that a classical standardization exercise allowing traceability of bioassay data to an international standard is also applicable to rituximab. However, we submit that this new type of international standard needs to be used appropriately and its role not to be mistaken with that of the reference medicinal product.

The establishment of a WHO Reference Reagent for anti-malaria (Plasmodium falciparum) human serum

Background

At a World Health Organization (WHO) sponsored meeting it was concluded that there is an urgent need for a reference preparation that contains antibodies against malaria antigens in order to support serology studies and vaccine development. It was proposed that this reference would take the form of a lyophilized serum or plasma pool from a malaria-endemic area. In response, an immunoassay standard, comprising defibrinated human plasma has been prepared and evaluated in a collaborative study.

Results

A pool of human plasma from a malaria endemic region was collected from 140 single plasma donations selected for reactivity to Plasmodium falciparum apical membrane antigen-1 (AMA-1) and merozoite surface proteins (MSP-1₁₉, MSP-1₄₂, MSP-2 and MSP-3). This pool was defibrinated, filled and freeze dried into a single batch of ampoules to yield a stable source of naturally occurring antibodies to P. falciparum. The preparation was evaluated by an enzyme-linked immunosorbent assay (ELISA) in a collaborative study with sixteen participants from twelve different countries. This anti-malaria human serum preparation (NIBSC Code: 10/198) was adopted by the WHO Expert Committee on Biological Standardization (ECBS) in October 2014, as the first WHO reference reagent for anti-malaria (Plasmodium falciparum) human serum with an assigned arbitrary unitage of 100 units (U) per ampoule.

Conclusion

Analysis of the reference reagent in a collaborative study has demonstrated the benefit of this preparation for the reduction in inter- and intra-laboratory variability in ELISA. Whilst locally sourced pools are regularly use for harmonization both within and between a few laboratories, the presence of a WHO-endorsed reference reagent should enable optimal harmonization of malaria serological assays either by direct use of the reference reagent or calibration of local standards against this WHO reference. The intended uses of this reference reagent, a multivalent preparation, are (1) to allow cross-comparisons of results of vaccine trials performed in different centres/with different products; (2) to facilitate standardization and harmonization of immunological assays used in epidemiology research; and (3) to allow optimization and validation of immunological assays used in malaria vaccine development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1958-x) contains supplementary material, which is available to authorized users.