Microcarrier Culture of Lepidopteran Cell Lines: Implications for Growth and Recombinant Protein Production

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Abstract
Several microcarrier systems were screened with Sf‐9 and High‐Five cell lines as to their ability to support cell growth and recombinant (β‐galactosidase) protein production. Growth of both cell lines on compact microcarriers, such as Cytodex‐1 and glass beads, was minimal, as cells detached easily from the microcarrier surface and grew as single cells in the medium. Cell growth was also problematic on Cytopore‐1 and ‐2 porous microcarriers. Cells remained attached for several days inside the microcarrier pores, but no cell division and proliferation were observed. On the contrary, insect cells grew well in the interior of Fibra‐Cel disks mainly as aggregates at points of fiber intersection, reaching final (plateau) densities of about 4 × 106 (Sf‐9) and 2.7 × 106 (High‐Five) cells mL‐1 (8 × 106 and 5.5 × 106 cells per cm2 of projected disk area, respectively). Their growth was described well by the logistic equation, which takes into account possible inhibition effects. β‐Galactosidase (β‐gal) production of Sf‐9 cells on Fibra‐Cel disks (infected at 3.3 × 106 cells mL‐1) was prolonged (192 h), and specific protein production was similar to that of high‐density free cell infection. Cultispher‐S microcarriers were found to be a very efficient system for the growth of High‐Five cells, whereas no growth of Sf‐9 cells took place for the same system. Concentrations of about 9 × 106 cells mL‐1 were reached within 120 h, with cell growth in both microcarriers and aggregates, appearance of cellular bridges between microcarriers and aggregates, and eventual formation of macroaggregates incorporating several microcarriers. Specific protein productions after β‐gal baculovirus infection at increasing cell concentrations were almost constant, thus leading to elevated volumetric protein production: final β‐gal titers of 946, 1728, and 1484 U mL‐1 were obtained for infection densities of 3.4, 7.2, and 8.9 × 106 cells mL‐1, respectively.