Advances in Non-Protein A Purification Processes for Human Monoclonal Antibodies - In three non-affinity purification processes based on cation exchange capture with high binding capacity, applying a


Advances in Non-Protein A Purification Processes for Human Monoclonal Antibodies
In three non-affinity purification processes based on cation exchange capture with high binding capacity, applying a host cell protein exclusion strategy enabled robust scale up and better economics.

BioPharm International Supplements

Process 2: Ion exchange process scheme with selective contaminant precipitation

Figure 1
Protein precipitation is often applied in the food, blood-product, and enzyme manufacturing industries9 and is accomplished by the addition of salts or organic solvents, or by pH titration. Antibody manufacturers are becoming more interested in these practices because they are suitable for processing bulk products at high throughput. Precipitation technologies have the potential to reduce or eliminate the bottlenecks that will inevitably be encountered when processing antibodies at the ton scale.10,11 They may also lead to the development of cost-effective downstream processes that require fewer unit operations for purification.

Figure 2
In the current case study, a small molecule (additive 1) was added to the clarified CHO cell culture supernatant and the pH was adjusted to precipitate most of the HCPs. The resulting precipitate was removed by depth filtration, leaving behind residual HCP in the feed. Scaling up the precipitation step is subject to variations in process parameters such as mixing speed, time, temperature, and pH, the results of which are better controlled when CEX conditions are optimized for differential binding, washing, and elution of the antibody. Transition from the precipitation step to CEX chromatography by applying the HCP exclusion strategy enables the effective integration of two-step non-affinity process schemes. Using this protocol, HCP levels can fall below 10 ng/mg after the first column (Figures 1 and 2). This degree of purity cannot be achieved in a single step when using Process 1, with diafiltration as the primary recovery step. Product quality even exceeds that achieved with Protein A as the capture step. Precipitation, combined with low pH conditioning, can prepare the feed stream for CEX chromatography with a binding capacity of up to 100 mg/mL resin, minimizing the number of process cycles while simultaneously providing virus inactivation. The material from capture is then processed by AEX membrane chromatography to remove negatively charged contaminants and adventitious viruses. Because the purity of antibodies eluting from the first column is so high, tens of grams of protein can be loaded per mL of membrane, making the AEX step faster and more economical for the application of disposable unit operations (Table 1).

Process 3. Ion exchange process scheme with selective antibody precipitation

Figure 3
Antibodies can be precipitated by the addition of salt or polyethylene glycol, and the precipitate can be separated from the bulk feed by centrifugation or filtration. In the current study, the antibody was precipitated with additive 2 and the precipitate was dissolved in a resuspension buffer with a pH and conductivity suitable for direct loading onto a CEX column. Based on the known behavior of HCPs on CEX resin, we were able to design a clearance strategy that reduced the level of HCP to 40 ng/mg of antibody. When further processed by AEX membrane chromatography, HCP levels fell below the detection limit, making a two-step non-affinity process feasible (Figure 3). Mixing, incubation time, and the temperature during precipitation must be controlled to reduce variation in the load material and to achieve consistent recovery and quality. Resuspension of the antibody precipitate requires approximately 30% of the original clarified bulk volume, therefore significantly reducing the processing time for multiple CEX cycles. The protein load on the AEX membrane is determined to ensure the robustness of the process at large scale. Dilution of the protein from the CEX column is sufficient for loading on the AEX membrane chromatography, which can be operated at very high flow rates.

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