Resin Lifespan Studies
Resin lifespan studies may be more appropriately carried out concurrently, provided the analytical methods are demonstrated
to be sufficiently sensitive and appropriate.10 Virus clearance by aged resins has been a topic of discussion for several years. Surrogate measurements that replace the
need to evaluate virus clearance after repeated use have been proposed for some types of chromatographic steps (i.e., affinity
and flow-through mode anion exchange chromatography used in MAb production).11,12
Conformance Batches and Beyond
Once the process is characterized and scale up verified, 3–5 consecutive batches are run at center point to demonstrate manufacturing
consistency. The validation effort does not stop here, however. The level of process understanding increases with manufacturing
experience (Figure 3).
Better process understanding may lead to changes to improve process control, increase productivity or reduce costs. Often,
implementing such changes is delayed due to concerns about validating changes and submitting regulatory filings. The concept
of design space, defined by process development, DoE, empirical studies, and experience, and approval of that space may now
enable changes to be made within that space without incurring regulatory delays (see ICH Q8).
Validation Strategy and Activities for A Cation Exchange Step
Although there is no one protocol for process validation for a chromatography step, a strategy and activity plan for validating
a cation exchange step in a purification process for a MAb summarizes the key elements (Figure 4 and Table 2).
To validate this step, it is necessary to know why it was designed into the process. Most monoclonal antibodies bind to cation
exchangers. This step is used to capture the MAb and remove process impurities such as host cell proteins (HCP), DNA, leached
Protein A, other process impurities from cell culture and clarification steps, and product-related impurities. This cation
exchange step is also used to enhance overall virus clearance.
Based on the intended use of this cation exchange step, assays are developed and validated. A decision will be made whether
to use clearance studies, routine in-process assays, or API testing for removal of HCP, DNA, and Protein A. The choice is
dictated by assay sensitivity, the practicality of performing the assay, and relevance of the assay for in-process control.
Table 2. Validation of a cation exchange step in the production of a monoclonal antibody
Antibody titer and purity by high performance liquid chromatography (HPLC) are commonly used methods for assessing product
quality. Impurities, such as aggregates and other product modifications, may also be detected by the HPLC assay. Other modes
of HPLC may be used to detect glycoforms, and isoelectric focusing (IEF) might also be a useful assay.
Viral clearance studies will be performed in a scaled down model, validated to represent manufacturing scale. Adherence to
the ICH guideline for virus validation will be confirmed, which means prospective cation exchanger lifespan studies must be
performed.13 In the future, it is possible that the surrogate determinations (i.e., removal of a specific impurity, height equivalent
to a theoretical plate (HETP), and backpressure) might be acceptable for assessing column performance for a cation exchanger.