Determination of procoagulant activity in human normal immunoglobulin preparations for therapeutic use by FXIa chromogenic assay: Evaluation of test kit sensitivity, reference standard performance and product formulation effects on the FXIa assay.

In 2010, the reporting of thrombotic adverse events for one subcutaneous and certain intravenous immunoglobulins (IGs) raised some concerns. In Europe, regulatory bodies rapidly revised compendial specifications for therapeutic IGs to ensure they do not exhibit thrombogenic (procoagulant) activity (PCA). At the global level, a working group (GWG) was launched with the aim of assessing PCA measurement methods and limits, considering results obtained by human IG manufacturers during in-process controls. The GWG created three dedicated subgroups to investigate the FXIa chromogenic assay, the non-activated partial thromboplastin time (NAPTT) test and the thrombin generation assay (TGA). The European Directorate for the Quality of Medicines & HealthCare (EDQM) was responsible for co-ordinating the subgroup in charge of evaluating the FXIa chromogenic assay in a study that assessed the sensitivity and robustness of two commercial chromogenic FXIa test kits. The impact of IG product formulation on FXIa recovery and the suitability of PCA-containing IG products as potential reference standards/controls were also assessed. IG materials representative of marketed products were provided to four laboratories for a study that was carried out in two steps: 1) two chromogenic FXIa test kit manufacturers assessed the performance and determined optimal test conditions by their respective methods, 2) two OMCLs studied both kits using an optimised study design. Regarding sensitivity, the study results identified suitable dose-response intervals and limits with both chromogenic FXIa test kits. This allowed the establishment of dilution ranges for optimal detection of FXIa/PCA in 5 % and 10 % IG products in the range of 1-6 mIU/mL. However, careful optimisation of the sample dilutions was required (notably to avoid potential matrix effects) and the choice of the mode of data acquisition (kinetic or end-point method) contributed to sensitivity in routine use. Importantly, the composition of IG products was of minor concern for FXIa determination with both test kits. Potential reference materials evaluated in the study behaved as expected and could be useful should a separate reference standard to the FXIa WHO IS be deemed necessary in future.

Collaborative study for the establishment of Ph. Eur. Human albumin (molecular size) Biological Reference Preparation batches 1, 2 and 3.

To comply with European Pharmacopoeia (Ph. Eur.) monograph Human albumin solution (0255), albumin solutions have to be tested for molecular-size distribution by size-exclusion chromatography (SEC). However, differences in interpretation of the test results continue to be observed among albumin manufacturers in Europe. A collaborative study was run by the European Directorate for the Quality of Medicines & HealthCare (EDQM), under the aegis of the Biological Standardisation Programme (BSP), to support the revision of Ph. Eur. monograph 0255 and to establish a Biological Reference Preparation (BRP) for use in the molecular-size distribution test. In 2019, Ph. Eur. Expert Group 6B proposed to include an analytical improvement of the SEC procedure in the monograph, which was then submitted for public enquiry. This publication describes the evaluation of three candidate BRPs to serve as a tool for both the system suitability test (SST) and albumin monomer and dimer peak identification according to the proposed revised methodology. Three Official Medicines Control Laboratories (OMCLs) involved in the official batch release of human albumin solution took part in the study. Based on the study results, the candidate BRPs were found suitable for purpose and were adopted by the Ph. Eur. Commission as Ph. Eur. Human albumin (molecular size) BRP batches 1, 2 and 3 concomitantly with the revised monograph Human albumin solution (0255) in November 2020.

Collaborative study for the validation of cell line assays for in-process toxicity and antigenicity testing of Clostridium septicum vaccine antigens - Part 2: Optimisation of cell line assays.

During the production of clostridial vaccines large numbers of mice are used for various in-process control tests. Replacement in vitro assays had been developed for the testing of the toxins and toxoids of several clostridial species, but none of these assays had been assessed in an international collaborative study. Under the common aegis of the European Partnership for Alternative Approaches to Animal Testing (EPAA) and of the European Directorate for the Quality of Medicines & HealthCare (EDQM), a project on clostridial vaccines for veterinary use was started as part of the EDQM-co-ordinated Biological Standardisation Programme (BSP). Within the framework of this project (coded BSP130) a collaborative study was organised to evaluate Vero cell-based alternative methods to the current mouse tests used to measure: i) the toxicity of Clostridium septicum toxin, ii) the absence of toxicity of C. septicum toxoid and iii) the antigenicity of C. septicum toxoid. The principal aims of the study were to determine the repeatability and reproducibility of the in vitro assays and to demonstrate concordance of the in vitro and current in vivo tests. The study results demonstrated good concordance, but the information gathered through the study (later on called Part 1) and the participants' workshop prompted the extension of the project in order to further optimise the in vitro protocols and improve their repeatability and reproducibility, which were comparable to but not better than those of the in vivo assays in Part 1. The 3 in vitro assays to be optimised in the extension of the BSP130 project were : i) the in vitro toxin neutralisation equivalence plus (TNE+), as a replacement for the in vivo minimum lethal dose (MLD) test for quantification of the toxicity of toxin; ii) the in vitro MLD, as a replacement for the in vivo MLD test for detection of residual toxicity associated with toxoid; iii) the in vitro total combining power (TCP), as a replacement for the in vivo TCP test for quantification of the antigenicity of toxoid. At this point, the Analytical Method Transfer Laboratory of Ceva-Phylaxia (Hungary), supported by the project management team, developed suitable SOPs for the 3 in vitro assays. These optimised methods were further assessed in BSP130 through a second international collaborative study (Part 2) aimed at defining repeatability and reproducibility in different laboratories and determining the levels of improvement compared with the original in vivo tests and the initial in vitro assays used in Part 1 of the project. Fourteen laboratories, comprising 4 public sector and 10 manufacturers' medicines control laboratories, from 11 countries participated in the collaborative Part 2 study, each testing 6 different C. septicum toxins and 6 C. septicum toxoids. Improved repeatability and reproducibility were observed for the optimised assays. The results of this study confirm the suitability of these assays for in-process control of C. septicum vaccines, with better repeatability and reproducibility than their in vivo equivalents. It is expected that, with appropriate minor changes and the use of relevant reagents, these optimised in vitro assays could be used not only for the assessment of C. septicum toxins and toxoids but for all cytotoxin-based clostridial antigens. The development and implementation of such in vitro assays would offer a great opportunity to significantly reduce animal usage, shorten the duration of QC test procedures and increase the precision of toxicity and antigenicity assays in clostridial veterinary vaccine in-process control. This would also provide more accurate and reproducible dosing of antigens in the final vaccine products, help to promote compendial acceptance and to proffer a basis for improved international harmonisation across this area of product testing.