Single in-line biomass probe detects CHO cell growth by capacitance and bacterial contamination by conductivity in...

Real time process data facilitates timely decisions, enables better process control, and can increase quality assurance. Biological drugs (mol. Wt. ≥ 40 kDa) are manufactured using mammalian cells such as Chinese hamster ovary (CHO) cells in bioreactors and have significant risks of contamination during processing. In such processes, in-line monitoring of biomass can provide real-time cell growth profiles and indications of bioreactor health.

An in-line conductivity/capacitance probe (Aber Instruments, Aberystwyth, UK) for monitoring CHO cell growth during fed batch cultures for producing an IgG1 monoclonal antibody was employed. Cell growth was measured in real-time using the capacitance probe (pF cm^-1 ) while being compared with off-line measurements using a metabolic analyzer (Nova Biomedical, Waltham, MA, USA). Conductivity measurements (mS cm^-1 ) detected variations in the solute concentrations in the bioreactor due to nutrient feed, bicarbonate buffer, and cellular metabolism by-products.

Abnormal increases in conductivity were found to consistently correspond to bacterial contamination, which was confirmed by orthogonal methods. The contaminated bioreactor runs exhibited sharp increases in conductivity rates hours before dissolved oxygen levels precipitously decreased due to bacterial growth. It is proposed that in-line measurement of conductivity could be employed for early detection of bacterial contaminations. The probe may be adopted in pharmaceutical aseptic aqueous liquid handling processes.