Removal of prion infectivity by affinity ligand chromatography during OctaplasLG® manufacturing – results from animal bioassay studies

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OctaplasLG(®) is a 2nd-generation virus inactivated pooled plasma for infusion. Prions are removed by the principle of chromatography, utilizing an affinity ligand gel (LG) developed for binding of prion proteins and their infectivity. The goal of this study was to verify, using the gold standard animal bioassay system, whether or not prion infectivity can be removed by the LG affinity step under conditions used in the routine manufacturing process. Aliquots of pooled plasma were spiked with a microsomal/cytosolic (MIC) fraction of brain-derived hamster-adapted scrapie 263K and subjected to the OctaplasLG(®) manufacturing process. Validated Western blot tests and animal bioassays studies were performed to determine the logarithmic reduction factors (RF) and the prion infectivity binding capacity. Bioassay studies demonstrated different logarithmic RFs (i.e. 1·73 and 0·76 log(10)) at two different plasma-to-resin ratios, the latter one representing the actual manufacturing ratio of 100:1, which can be explained by the differences in the study design. However, both bioassay studies showed a reproducible and high prion infectivity binding capacity of ≥5·64 log(10) ID(50)/ml gel. Bioassay studies confirmed the capacity of the LG to bind brain-derived MIC prion proteins spiked into plasma. Even through infectivity was still detected following passage over the LG, this can be attributed to the high loads used in the study design, and the binding capacity of the LG still ensures a significant safety margin--binding the prion agents at the levels of prion infectivity that might be present in plasma and beyond.