Host cell protein

Host cell proteins (HCPs) are residual proteins from genetically modified host cells used to manufacture biologics or peptides. These proteins are unrelated to the intended drug and remain in the final product after purification. During production, host cells such as bacteria, yeast, or mammalian cells produce thousands of their own proteins alongside the target substance.

Host cell protein testing ensures product purity and safety

Laboratories measure host cell proteins to verify that the purification process effectively removed unwanted cellular proteins from the product. This measurement is critical for purity and safety, as residual HCPs can pose a clinical risk by triggering an immune response or causing drug degradation, which affects shelf life.

The standard test is an ELISA assay, which reports a total HCP value in nanograms per milligram (ng/mg or ppm). Because ELISA can have blind spots, laboratories may also use complementary mass spectrometry (LC-MS/MS) to identify specific individual proteins and ensure a thorough assessment.

• A numerical HCP value
• The assay method used
• The specified host cell line
• The relevant benchmark when provided, such as less than 100 ng/mg for certain biologicals

Host cell proteins are distinct from other manufacturing impurities

Host cell proteins are foreign proteins from the manufacturing cell and are distinct from other common impurities found in biologics. They differ from residual host cell DNA, endotoxins, and product-related impurities because HCPs are specifically foreign proteins originating from the manufacturing cell.

Sources

1. INTRODUCTION Biotechnology products, in many cases recombinant proteins, are derived from a complex expression/production system involving a genetically modified host cell (bacteria, yeast or mammalian cell). Among impurities to be eliminated during the downstream purification process, two components which are of major interest for safety and tolerance reasons are residual host cell DNA and residual host cell proteins (HCP). Since submission of the first marketing applications for recombinant proteins, depending mainly on the type of production cell system, the European regulatory authorities have adopted different approaches to deal with these impurities. In summary, for HCP, whatever the product and production system, residual HCP have to be tested for on a routine basis, whereas residual DNA is tested for on a routine basis only for products derived from continuous mammalian cells. It is necessary to guarantee that such impurities are reduced to an acceptable level in the medicinal product to be administered to the patient. For that, two approaches can be envisaged : • a “validation approach”: 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 to an acceptable level. Based on the reduction factors it may be possible to predict and guarantee the residual level of impurity in the final product. • a “routine approach”: to develop analytical tools that allow monitoring, as closely as possible, of the level of those impurities at various steps of the process and set fixed limits to be met, so that the impurities are well monitored in the final product. A combination of these two approaches is also possible, i.e. routine testing at an earlier step of the purification process and demonstrated reduction by validation in order to ensure a limit at the final product level, if tested. In the context of the world-wide use of recombinant proteins, it is necessary to harmonise the evaluation criteria between the three regions of USA, EC and Japan, so that manufacturers can develop their products on the same lines whatever the intended regions for submission and marketing. RESIDUAL HOST CELL DNA Regarding residual DNA, it is already accepted for bacteria- and yeast- derived products that there is no need for routine testing provided that acceptable levels in the final product are achieved and, adequate validation data are submitted in the dossier. As far as DNA from continuous mammalian cell lines (CCLs) is concerned, this impurity was considered, in the past, as a risk factor because of concerns that residual host DNA may be tumorigenic. Further information, however, now suggests that CCL DNA poses much less of a risk than previously thought and accordingly should be considered as a general impurity (WHO Expert Committee on Biological Standardisation: Highlights of the 46th meeting, October 1996, in WHO Weekly Epidemiological Record, 1997, 72, 141-145). Validation studies (e.g. spiking experiments using an adequate size distribution of DNA) should be performed in an attempt to identify the major steps capable of reducing the DNA burden and to document the capacity of those steps in reducing residual cellular DNA content in the final
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