Optimisation of Cell Growth and Recombinant Protein Production in Small-Scale Culture Vessels by Using Optical Sensors for On-line Measurement of Dissolved Oxygen

Abstract

Conventional polarographic oxygen sensors which are routinely used for process monitoring of animal cell cultures in bioreactors show only limited applicability for small-scale cultures (e.g. shake or spinner flasks). Their bulky size and the invasive measurement principle (that is incompatible with standard culture vessels lacking adequate sensor ports) prevent oxygen measurement in this scale. In contrast, optical measurement of oxygen allows the introduction of small sensor spots into these vessels which are connected non-invasively via fibre-optic cables through the light-transmissive walls of the vessels with a controlling unit. This technology, applied to several process optimisation experiments for recombinant protein expression with reusable small-scale culture vessels, was shown to provide almost identical results to a conventional polarographic electrode and the sensor spots showed a very good long-term stability allowing repeated use for more than 1 year. The technology proved to be valuable in process optimisation experiments for recombinant protein expression in spinner or shake flasks such as identifying suitable filling levels of these solely surface-aerated vessels. In addition, online measurement of oxygen concentrations provides a valuable tool to sensitively estimate metabolic cell activities via the cellular uptake of oxygen thus allowing a prediction of the performance of individual expression experiments. This is shown using both Sf21 and High Five™ insect cells in combination with the baculovirus expression vector system as well as transiently transfected HEK293 EBNA cells.