Figure 4
GFP 1–10mat was superior to non-maturated GFP 1–10 for distinguishing between recombinant EPO secretion from CHO cells. CHO cell lines expressing recombinant EPO, genetically tagged with GFP 11, were cultured in microtiter plates with either GFP 1–10mat or GFP 1–10 protein present in the medium from the start and expression was monitored over time. Secreted EPO-GFP 11 resulted in GFP 1–10 complementation and thereby a fluorescent signal. Three strains with different specific productivities were monitored: low producer (“efficiency too low to measure”); medium producer (0.2 pg/cell/day); and high producer (1.5 pg/cell/day). Cultures were run in triplicates and signal values analyzed with a two-tailed, unpaired t-test. To be qualified as differentiable at a certain time point, a p-value below 0.05 was required also for all following time points. (a) Using GFP 1–10, it was not possible to discriminate between the cell lines. (b) Using GFP 1–10mat, it was already from the first time-point possible to distinguish between the high and medium producers, and after 5 hours, it was likewise possible to distinguish the signal between the medium and low producing strains.
