High yields of monomeric recombinant β‐interferon from macroporous microcarrier cultures under hypothermic conditions

Macroporous microcarriers such as Cytopore entrap mammalian cells in a mesh network allowing growth to high cell concentrations in a protected environment within a stirred culture. Chinese hamster ovary (CHO) cells producing recombinant human β‐interferon (IFN‐β) and grown in Cytopore microcarriers showed a 2.6‐ to 2.8‐fold increase in the volumetric product titer compared with cells grown in an equivalent suspension culture. In an attempt to maximize production of IFN‐β, microcarrier cultures were subjected to a low temperature regime. Low temperature culture conditions (32°C) have been shown previously to enhance cell specific productivity in suspension cultures although at reduced cell growth rates. These conditions can be optimized by a timely shift from physiological to hypothermic conditions during the culture run to maximize volumetric protein production. In the case of IFN‐β production the lower temperature has the added advantage of stabilizing the product and reducing intramolecular aggregation. Using a biphasic temperature‐shift regime from 37 to 32°C the volumetric production of IFN‐β was enhanced to 4.2‐fold compared with a single temperature suspension culture in a controlled bench‐top bioreactor. Furthermore, the degree of intramolecular aggregation of IFN‐β was reduced significantly (59%) compared with control cultures, largely due to the lower temperature but also partially due to the presence of microcarriers. These results indicate that the hypothermic conditions in a Cytopore culture had a combined and possibly synergistic effect of increasing volumetric production of the recombinant protein.