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Precipitation can be used for the initial purification of monoclonal antibodies (mAbs), with the soluble host cell proteins removed in the permeate by tangential flow microfiltration. The objective of this study was to examine the use of a feed-and-bleed configuration to increase the effective conversion (ratio of permeate to feed flow rates) in the hollow fiber module to enable more effective washing of the precipitate. Experiments were performed using human serum Immunoglobulin G (IgG) precipitates formed with 10 mM zinc chloride and 7 wt% polyethylene glycol. The critical flux was evaluated as a function of the shear rate and IgG concentration, with the resulting correlation used to predict conditions that can achieve 90% conversion in a single pass with minimal fouling. Experimental data for both the start-up and steady-state performance are in good agreement with model calculations. These results were used to analyze the performance of an enhanced continuous precipitation–microfiltration process using the feed-and-bleed configuration for the initial capture / purification of a mAb product. 

There is renewed interest in the possibility of using precipitation for initial capture of high-value therapeutic proteins as part of an integrated continuous downstream process. Precipitation is greatly facilitated by the high product titers now achieved in most cell culture processes, in sharp contrast to chromatographic processes whose performance is reduced at high titers. The current study used a combination of reversible cross-linking (zinc chloride, ZnCl2) and volume exclusion (polyethylene glycol) agents to precipitate a monoclonal antibody product directly from harvested cell culture fluid using a continuous tubular precipitation reactor. The precipitates were then dewatered and continuously washed using tangential flow filtration, with a countercurrent-staged configuration used to reduce the amount of wash buffer required and increase host cell protein removal. Long-term operation was achieved by operating the membrane modules below the critical filtrate flux to avoid fouling. Experimental results demonstrate the feasibility of this fully continuous integrated precipitation process at bench scale, with design calculations used to explore the key factors affecting the performance of this system for initial antibody capture.