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

Abstract

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 50-400nm 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 2M 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 ∼3-fold. IgG recovery was 80%. Remaining heteroaggregates were removed with 1M 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 94mg/mL, compared with 95mg/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 <100ppm, DNA to <10ppb, 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.

Keywords: Aggregates; Capacity; Chromatin; IgG; Leaching; Multimodal.