Thromboembolic events (TEE) associated to trace amounts of plasmatic activated coagulation factor XI (FXIa) in administrated immunoglobulin (Ig) have recently raised concerns and hence there is a need for highly sensitive profiling of residual plasma source proteins. This study aims to consider LC-ESI-QTOF data-dependent acquisition in combination with sample fractionation for this purpose. Sample fractionation proved mandatory to enable identification of plasma residuals. Two approaches were compared: Ig depletion with protein G - protein A affinity chromatography and low-abundant protein enrichment with a combinatorial peptide ligand library (ProteoMiner™, Bio-Rad). The latter allowed a higher number of identifications. Highly sensitive detection of prothrombotic FXIa was assessed with confident identification of a 1ng/mg spike. Moreover, different residuals compositions were profiled for various commercial Ig products. Using a quantitative label free analysis, a TEE-positive Ig batch was distinguished from other regular Ig products, with increased levels of FXIa but also other unique proteins. This could have prevented the recently observed TEE problems with Ig. The method is a convenient tool to better characterize Ig products after any plasma pool or manufacture process change, gaining insights in the product quality profile without any prior information required.
BIOLOGICAL SIGNIFICANCE: This study characterized residual plasma proteins in Ig products, using bottom-up LC-MS/MS with conventional data-dependent acquisition, preceded by sample fractionation. Without any prior information or target-specific development, >30 proteins were identified in a commercial Ig product. Quality control relevance was demonstrated with the identification of FXIa spiked at 1ng/mg in Ig, which is below the minimal thrombotic dose of 3ng/mg observed in an in vivo model. Relative label-free quantitation highlighted significant differences in normalized abundances of residual proteins between Ig products. A TEE-positive batch was distinguished by unique profile of residual proteins, including FXIa but also various blood stream-regulator proteins (fibrinogen, angiotensinogen, antithrombin-III, complement component C8, …). Those results emphasize that MS screening is a relevant first-line test to prevent any undesired concentration of plasma impurities after a plasma pool or manufacturing process change.
