Host Cell Proteins - FDA seeks Comments on Immunogenicity Assessment

Additional substantive information
I. Background
The FDA uses the term ‘peptide’ in this notice to refer to alpha-amino acid polymers consisting of 40 or fewer amino acids. Peptides can be isolated from natural sources or produced synthetically or by recombinant expression in a host cell. Peptides isolated from recombinant sources (i.e., genetically modified) prokaryotic or eukaryotic host cells by cell culture/fermentation processes are referred to as recombinant peptides (rPeptides). The FDA describes at this point:
HCPs are process-derived impurities from the host cell that copurify with the recombinant peptide of interest and may be present in the final drug product. HCPs are characterised and routinely well controlled during the manufacture of the peptide product. The types and amounts of HCPs in a product depend on many parameters, including differences in the substrate of the expression cells, culture conditions, purification procedure and between different facilities. Therefore, for a proposed rPeptide follow-on product, differences in HCP profiles between the follow-on product and the listed drug product are to be expected, and these differences may impact the safety and/or efficacy of the follow-on product by increasing the immunogenicity risk of that product. Advances in technology may support the use of IVISIA methods to assess comparative immunogenicity risk. Comments submitted by 23 September will be considered. This cannot be guaranteed for comments submitted later.

II. Request for comments
Interested parties are invited to submit detailed information (including supporting data) and comments on appropriate methods for the detection, identification and quantification of HCPs and the minimum residual levels of HCPs that can be achieved in commercial batches of rPeptide products. To assess the potential impact of HCP differences, the FDA is particularly interested in answers to the following questions:

1. What is the lowest and routinely achievable total HCP content in your well-controlled rPeptide manufacturing processes, and how is it calculated/determined?
2. What are the challenges in reducing HCP levels?
3. What analytical methods are currently used to detect, identify and quantify HCPs in a rPeptide product? Do you perform comparative assessments of HCPs during production development, e.g. ELISA (enzyme-linked immunosorbent assay) versus LC/MS/MS (liquid chromatography tandem mass spectrometry)? How sensitive are these methods for the detection of HCPs and what are their quantification limits? Do you use a combination of orthogonal analytical methods (e.g. ELISA + LC/MS/MS) for HCP control during process development and manufacturing?
4. What is the generally achievable percentage coverage of the HCP spectrum for your HCP quantification test? What considerations (e.g., percentage coverage of HCPs, other coverage characteristics, etc.) are important when selecting methods for evaluating HCPs?
5. Are there qualitative or quantitative characteristics of HCPs that are associated with a higher likelihood of adverse clinical outcomes?
6. What tools (in silico, in vitro or in vivo studies) do you currently use or plan to use to compare the potential immunogenicity risk of two products with different HCP profiles? What is your approach to risk assessment of HCPs based on such data?

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