The fact that pharmaceutical products must be free of impurities has long been undisputed. Particulate impurities have hit the headlines several times in recent years.
But with the increasing number of biopharmaceutical products, including those based on recombinant proteins, the importance of protein-based impurities has also increased. As a rule, host organisms ranging from yeast to E.coli and CHO (Chinese Hamster Ovary) cell lines serve as producers of the recombinant proteins.
From these host cells, own proteins can appear as impurities of the active substance or the drug. These are grouped together as HCPs.
Host cell proteins (HCPs) are an inevitable impurity of biopharmaceuticals, regardless of whether they are produced by recombinant fermentation or extracted from natural sources. Even after multiple sophisticated purification steps, HCPs remain or copurify with product. Host Cell Proteins represent a heterogeneous variety of different proteins that need to be quantified in the drug substance and in intermediates from the downstream purification process. The risk for adverse effects, such as immunogenic reaction, does not necessarily correlate with the amount of certain host cell proteins, and even small traces of certain HCPs can be highly immunogenic.
The heterogeneity of the HCPs requires a thorough control regime and sophisticated assays for detection and quantitation in various samples matrices. Historically, immunoassays using polyclonal antibodies have been used for process development, validation, and release testing. However, with the advance in Mass Spectrometry, new orthogonal tools for identification and quantitation became available which help to gain a deep understanding of the HCP composition at various stages of the purification process and in the drug substance.