Engineering Trichoplusia ni (High-Five™) Insect Cells to Express a Cytosolic Pyruvate Carboxylase Enzyme Improves the Viability of the Cells in Batch, Fed-Batch and Perfusion Cultures

Abstract

Cultures of Trichoplusia ni High-Five™ cells show accumulation of large amounts of lactate and ammonia, which may be deleterious to the cell growth and final product quality. In this work we have investigated the metabolism of these cells with respect to the utilization of glucose and glutamine and we have used a metabolic engineering approach to overcome this problem demonstrating the successful culture of these cells at high cell densities. The cells have been modified to express a cytosolic pyruvate carboxylase (PYC2), an enzyme which had been earlier identified as a key enzyme in the flux of glucose to the TCA cycle. The modified cells showed a more efficient utilization of glucose and glutamine and a marked decrease, in the amount of lactate (up to 70%) and ammonia (up to 60%) produced when compared to the non-modified host cells. This resulted in maintaining cells at a higher viability for a prolonged time, a major advantage in high cell density cultures especially when combined with stable insect cell lines. These changes in the metabolism were further evaluated in 3L-bioreactor studies, under controlled conditions. The implications of these changes to the operation conditions have been evaluated under batch, fed-batch and perfusion culture modes.