Ensuring the consistency of rDNA-derived biologicals: the contribution of gene sequencing

The past few years have seen an interesting debate on the extent to which DNA-sequencing of expression systems is appropriate as a basis for assessing the quality and consistency of rDNA-derived products. While there is a need to improve and validate the ability of end-product testing procedures to detect low levels of variant proteins, there are several reasons why it may not be justified to require extensive DNA sequence analysis of large numbers of individual clones of producer cells. These include difficulties in interpreting the resultant data due to artefacts introduced by PCR and the fact that other events, such as translational errors and chemical and enzymic alterations during production and downstream processing, also lead to potential heterogeneity of pharmaceutical proteins. The evaluation of these products can only be made at the protein level. Some DNA sequencing will be required during product development, but in practice the quality and consistency of rDNA-derived products are best determined by a range of in-process and end-product testing procedures, including the use of biological assays and standardization.