Production of Human Alkaline Phosphatase, a Secreted, Glycosylated Protein, from a Baculovirus Expression System and the Attachment‐Dependent Cell Line Trichoplusia ni BTI‐Tn 5B1‐4 Using a Split‐Flow, Air‐Lift Bioreactor

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Abstract
A split‐flow, air‐lift bioreactor for the cultivation of insect cells to produce recombinant protein is described. It can be used advantageously with attached cell systems. This bioreactor incorporates two sections: a rise and a downcomer. Trichoplusia ni BTI‐Tn 5B1‐4 cells are grown on a support material of glass beads or microcarriers placed in the downcomer. This cell line is more productive than other commonly used insect cell lines, but it has the disadvantage of being difficult to use at large volumes since it is not easily adaptable to suspension culture. Adequate oxygen demand is supplied by sparging without direct exposure of cells to air bubbles. Nutrients are supplied convectively to the attached cells on support material as the fluid flows through the downcomer. The split‐flow, air‐lift bioreactor appears to be suitable for insect cell culture and is potentially scalable. It can provide a high surface‐to‐volume ratio and can be operated in batch or continuous mode. A lab‐scale prototype bioreactor has been constructed and tested for the production of a secreted, glycosylated recombinant protein (human alkaline phosphatase) or seAP using an Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) vector. With a ratio of riser cross‐sectional area to downcomer cross‐sectional area of 1, an aspect ratio of 4.4, an air‐flow rate of 54 mL/min in the riser, and a bed of 2400 3‐min nonporous glass beads, 10.7 μg/mL of seAP was produced using an MOI (multiplicity of infection or the ratio of plaque‐forming units to cells) of 10. On a specific productivity basis, the split‐flow, air‐lift system and T‐flasks gave similar values (about 13 μg/106 cells).