During a small-scale cell culture process producing a monoclonal antibody, a larger than expected difference was observed in the charge variants profile of the harvested cell culture fluid (HCCF) between the 2 L and larger scales (e.g., 400 L and 12 kL). Small-scale studies performed at the 2 L scale consistently showed an increase in acidic species when compared with the material made at larger scale. Since the 2 L bioreactors were made of clear transparent glass while the larger scale reactors are made of stainless steel, the effect of ambient laboratory light on cell culture process in 2 L bioreactors as well as handling the HCCF was carefully evaluated. Photoreactions in the 2 L glass bioreactors including light mediated increase in acidic variants in HCCF and formulation buffers were identified and carefully analyzed. While the acidic variants comprised of a mixture of sialylated, reduced disulfide, crosslinked (nonreducible), glycated, and deamidated forms, an increase in the nonreducible forms, deamidation and Met oxidation was predominantly observed under light stress. The monoclonal antibody produced in glass bioreactors that were protected from light behaved similar to the one produced in the larger scale. Our data clearly indicate that care should be taken when glass bioreactors are used in cell culture studies during monoclonal antibody production.
Keywords: CHO cells; acidic variants; glass bioreactors; mammalian cell culture; monoclonal antibodies; photosensitivity; protein oxidation; reactive oxygen species.
© 2014 American Institute of Chemical Engineers.