Recent advances in mammalian cell culture technology have resulted in significant increases in upstream productivity, with antibody titers of >5 g/L becoming increasingly common. Such increases could change the characteristics of the cell culture broth, leading to higher levels of product-related heterogeneous proteins (aggregates, degradation products, processing variants) and cell-derived impurities such as host cell protein (HCP) and cellular DNA. In response, platform purification processes for MAbs, i.e., those designed to move a product through Phase 1 clinical trials with minimum development, have become more streamlined in their design and execution. Such platforms must accommodate the majority of antibodies and yet be flexible enough to cover most contingencies and cell culture or antibody-related processing issues. They must also save time and thus accelerate the progress of antibodies toward the clinic.Early Platform Description
The MAb purification platform used by Pfizer for early-phase clinical supplies has evolved over the last five years to accommodate increases in titer and associated issues, as well as unique challenges directly related to our own cell lines and upstream processes. This purification platform has been developed to accommodate antibodies derived from both NS0 and Chinese hamster ovary (CHO) cell lines. The original process, shown in Figure 1, followed a traditional antibody purification scheme.1–4 It consisted of three major chromatography steps with two additional unit operations designed to remove or inactivate viruses. After harvest, the cells were removed from the cell culture broth by depth filtration. In some cases, the broth was concentrated before the first chromatography step because of facility fit issues. Protein A chromatography was used in the initial capture step, where the antibody in cell culture broth was loaded at neutral pH, washed with various solutions, and eluted at a lower pH value. The eluate was then held at this low pH to inactivate viruses, and then adjusted to increase the pH before the cation exchange chromatography step.
After cation exchange, diafiltration was performed to prepare the product for anion exchange chromatography in flow through mode, in which impurities such as DNA and some HCPs were captured on the resin (and later removed by regeneration and cleaning steps). After anion exchange, the flow-through fraction containing the antibody was passed through a nanofiltration unit to remove potential viruses and then formulated in buffer in a final concentration and diafiltration step.
The relative purification development timeline for this original process is shown in Figure 2. Initially, several range-finding experiments were carried out to determine the optimal parameters for each unit operation and to maximize the yield and purity for that particular antibody. We used these results to determine the purification scheme, which was performed in its entirety at the bench scale before a larger demonstration run. After the demonstration run, this process was transferred to the pilot plant for manufacturing clinical supplies.