The following article describes the development of a purification platform for monoclonal antibodies (MAbs) at Pfizer's Global
Biologics division, including how the individual unit operations have been affected by increasing cell culture titers and
subsequent changes in the impurity profile, as well as viral clearance issues. The platform was developed to maximize the
efficiency of the purification process and product purity while minimizing the development time for early-phase therapeutic
antibodies. The success of this platform in its various stages has been demonstrated for several MAbs representing different
IgG classes produced in different cell lines.
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.
Figure 1. Flow scheme of the various monoclonal antibody platform purification processes developed at Pfizer
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.
Figure 2. Timeline outlining the phases of the development process for the various Pfizer monoclonal antibody purification