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Effects of Long‐Term Passaging of BTI‐Tn5B1–4 Insect Cells on Growth and Recombinant Protein Production

The BTI‐Tn‐5B1–4 insect cell line from Trichopulsi ni has enabled better secretion and higher productivity of recombinant proteins in the baculovirus expression system. An early passage stock of this cell line is compared here to the commercially available “High Five” cell line stock. The early passage Tn5B1–4 cells grew to over 11 × 106 cells/mL and expressed 2.5‐fold more recombinant secreted alkaline phosphatase (SEAP) than the High Five cells. While the specific productivity on a cell number basis was only slightly higher, the early passage Tn5B1–4 cells maintained this productivity at higher cell densities, increasing their volumetric productivity to 50 μg/mL under elevated oxygen conditions. We propose that the difference in these two stocks of cells is the length of time they have been cultured, 130 total passages for the early passage versus 360 passages for the High Five cells. This conclusion is supported by the facts that the early passage Tn5B1–4 cells are smaller in diameter by 4 μm, smaller in cellular protein content (206 versus 270 μg of protein/106 cells), have an increased propensity to clump in suspension culture, and are less susceptible to dispersion of these clumps by dextran sulfate compared to the High Five cells.