Achieving reproducible product titers is crucial for developing this protein expression technology for applications ranging from high-throughput screening to commercial-scale production of therapeutic proteins. For large-scale production, predictable and high-level productivity is needed to minimize capital investment as well as develop downstream processing and purification.
Plant tissue culture-based transient expression provides an ideal platform for controlling variability once the required environmental conditions are identified. Physical and physiological sources of batch-to-batch variation in high-level transient protein expression will be discussed in detail. Some of the important parameters that have been identified and studied as potential contributors to this variation include the organic and inorganic nutrient status of the culture, culture maintenance schedule, gas exchange in shake-flasks, incubator temperature control, and the timing of the nutrient-controlled 'synchronization by starvation' relative to the co-culture of the plant tissues with A. tumefaciens.