Enabling accurate measurement of activated factor XI (FXIa) in therapeutic immunoglobulin products

Background and objectives

In 2010, an intravenous immunoglobulin (IVIG) product was removed from the market due to an association with serious thromboembolic events. Investigations revealed that factor XIa (FXIa) was present as a process‐related impurity. This study investigated the ability of two commercial FXIa assays to measure FXIa in immunoglobulin preparations and conducted a survey of FXIa activity in marketed immunoglobulin products.

Materials and methods

Factor XIa assays were modified to include spiking of samples with FXIa before testing. An immunoglobulin product and its excipient were used to assess the ability of the assays to recover the spiked FXIa levels.

Results

The Biophen FXIa assay required a high pre‐dilution of the sample to obtain statistically valid results and complete FXIa recovery. The ROX FXIa assay was more sensitive, giving statistically valid results at a lower sample pre‐dilution and FXIa spike level. This modified ROX FXIa assay was used to assay 17 lots of immunoglobulin products for FXIa. Two product lots had measurable FXIa levels without the need for spiking. A further 3 lots produced detectable but not statistically valid FXIa results when left unspiked. Spiking produced statistically valid assays and recoveries above 100%, demonstrating inherent FXIa.

Conclusion

This study shows marketed immunoglobulin products can contain detectable levels of FXIa. Spiking brings the FXIa levels into the quantifiable range of the assay, allowing measurement of inherent FXIa. Accurate measurement is important to inform on ‘safe’ levels of FXIa in these products and allow future safety guidelines to be set.

Absence of in vitro Procoagulant Activity in Immunoglobulin Preparations due to Activated Coagulation Factors

BACKGROUND

Immunoglobulin (IG) products, including intravenous (IVIG) or subcutaneous (SCIG) immunoglobulins are considered safe and effective for medical therapy; however, a sudden and unexpected increase in thromboembolic events (TE) after administration of certain batches of IVIG products has been attributed to the presence of activated coagulation factors, mainly factor XIa. Our aims were to examine the presence of enduring procoagulant activity during the manufacturing process of IGs, with special focus on monitoring factor XIa, and to evaluate the presence of in vitro procoagulant activity attributed to coagulation factors in different lots of IVIG and SCIG.

METHODS

Samples of different steps of IG purification, 19 lots of IVIG and 9 of SCIG were analyzed and compared with 1 commercial preparation of IVIG and 2 of SCIG, respectively. Factors II, VII, IX, XI and XIa and non-activated partial thromboplastin time (NAPTT) were assayed.

RESULTS

The levels of factors II, VII, IX, X and XI were non-quantifiable once fraction II had been re-dissolved and in all analyzed lots of IVIG and SCIG. The level of factor XIa at that point was under the detection limits of the assay, and NAPTT yielded values greater than the control during the purification process. In SCIG, we detected higher concentrations of factor XIa in the commercial products, which reached values up to 5 times higher than the average amounts found in the 9 batches produced by UNC-Hemoderivados. Factor XIa in commercial IVIG reached levels slightly higher than those of the 19 batches produced by UNC-Hemoderivados.

CONCLUSION

IVIG and SCIG manufactured by UNC-Hemoderivados showed a lack of thrombogenic potential, as demonstrated not only by the laboratory data obtained in this study but also by the absence of any reports of TE registered by the post marketing pharmacovigilance department.

Quantifying the thrombogenic potential of human plasma-derived immunoglobulin products

Polyvalent immunoglobulin G (IgG) products obtained by fractionation of human plasma are used to treat a broad range of conditions, including immunodeficiency syndromes and autoimmune, inflammatory, and infectious diseases. Recent incidences of increased thromboembolic events (TEEs) associated with intravenous (IV) IgG (IVIG) led to recalls of some products and increased regulatory oversight of manufacturing processes in order to ensure that products are essentially free of procoagulant/thrombogenic plasma protein contaminants. Laboratory investigations have now identified activated factor XI (FXIa) as the likely causative agent of IVIG-related TEEs. Quantification of the thrombogenic potential is becoming a requirement made to fractionators (a) to validate the capacity of IVIG and subcutaneous IgG manufacturing processes to remove procoagulant contaminants and (b) to establish the safety of the final products. However, in the absence of a recommended test by the main regulatory authorities, several analytical approaches have been evaluated by fractionators, regulators, and university groups. This review focuses on the scientific rationale, merits, and applications of several analytical methods of quantifying the thrombogenic potential of IgG products and intermediates to meet the latest regulatory requirements.