Japanese–English glossary
Host cell protein (HCP)
宿主細胞タンパク質（HCP）shukushu saibō tanpakushitsu (HCP)
Proteins from the production host, such as CHO cells or E. coli, that remain in the product as process-related impurities. They are measured mainly by ELISA, often supported by mass spectrometry to identify individual proteins, and removed by downstream purification. Some host cell proteins, such as certain lipases and proteases, can degrade polysorbate or the product itself even at trace levels, which affects stability. Japanese specifications usually express HCP in nanograms per milligram of product.