Chromatin-mediated depression of fractionation performance on electronegative multimodal chromatography media, its prevention, and ramifications for purification of immunoglobulin G

Chromatin heteroaggregates comprising nucleosomal arrays, DNA, histone and non-histone host cell proteins contributed 28% of the host contaminant mass in an IgG cell culture harvest. A subset comprising soluble particles of 50-400 nm was retained through its histone component by an electronegative multimodal chromatography adsorbent. Accumulated heteroaggregates hindered pore access and depressed IgG capacity by 69% compared with capacity determined with purified IgG. Heteroaggregate retention persisted in 2 M NaCl but some associations within them were dissociated. This manifested during IgG elution as contaminant leaching from the retained heteroaggregate mass, which contributed more than 95% of the contaminants in the IgG. Retained heteroaggregates also interfered with pore egress of eluted IgG, increasing peak width similar to 3-fold. IgG recovery was 80%. Remaining heteroaggregates were removed with 1 M NaOH. Advance reduction of heteroaggregates with a hybrid fatty acid-solid phase clarification method reduced DNA more than 3 logs, histones beneath the level of detectability, and non-histone proteins by 90% while conserving 90% of the IgG. Non-lipid-enveloped virus was reduced by 5 logs and lipid-enveloped virus by 9 logs. IgG capacity on the multimodal adsorbent was 94 mg/mL, compared with 95 mg/mL when loaded with protein A-purified IgG. Non-histone host protein reduction increased to 98%. IgG eluted in a sharp concentrated peak and step recovery was >95%. Residual fatty acids did not bind the adsorbent and were mostly eliminated during sample loading. A single polishing step with an electropositive multimodal adsorbent reduced non-histone host proteins to <100 ppm, DNA to <10 ppb, and aggregates to <0.05%. IgG recovery across the entire process was >80%. These results qualify electronegative multimodal adsorbents as an IgG capture option, but more importantly reveal chromatin heteroaggregate content as a keystone process variable at all stages of purification process development. (C) 2014 Elsevier B.V. All rights reserved.