| Tanja Beilke, Oliver Halbig and Andreas Richter at NewLab BioQuality AG examine the development and validation of generic host cell protein assays
Host cell proteins (HCP) are potential impurities which might be co-purified with the drug substance and could be a potential cause of adverse immune responses or allergic reactions (1). To date there is only limited clinical evidence that shows an allergic reaction was clearly attributable to residual host cell protein. However, there is growing concern about the potential induction of anti-drug antibodies (2,3,4).
The risk of contaminants and impurities in biopharmaceuticals is anticipated by a set of measurements, including the rigorous control of the material entering a production process. According to the European Agency for the Evaluation of Medicinal Products (EMEA) the concept of controlling impurities can either be a ‘routine approach’ or a ‘validation approach’ (5). A routine approach would be to develop analytical tools that allow monitoring the level of those impurities as closely as possible at various steps of the process and setting fixed limits to be met, so that the impurities of the final product are well monitored in the final product.
A validation approach means to validate the production process to establish that, at given steps of the purification scheme, those impurities are removed in a consistent and reproducible manner. Based on the reduction factors, it may be possible to predict and guarantee the residual level of impurity in the final product. The EMEA suggests that HCPs should be analysed either on a routine or validation basis depending on the individual product and process. In either case, powerful analytical methods are needed to accurately determine the concentration of the impurities in the different process steps.
DEVELOPMENT OF A RESIDUAL HCP ASSAY
An HCP assay is usually an immunological-based assay using an antiserum produced against proteins obtained from a mock fermentation process (6,7,8). The development of such an assay is usually time consuming due to the necessary immunisation of animals.
The first step is the generation and isolation of the appropriate antigen to be used for immunisation. This requires the fermentation of the native cell line without the gene sequence of the target protein. This is commonly referred to as a mock fermentation run. As illustrated in Figure 1, it is important to choose the correct step in the purification scheme for the production of the antigen. By using the protein following the first purification step, a very wide spectrum of HCPs would be detectable, but this is not representative of the potential HCP in the final product. By using a protein derived from the final purification step as the antigen, the HCP may be more representative of the final product but may also be too specific and not demonstrate sufficient HCP removal. |
