Figure 1

Levels of pegfilgrastim detected in physiological salt buffers and human sera. (a,b) Pegfilgrastim (200 ng/mL) was spiked into formulation buffer or various physiological salt buffers as shown, and protein levels were measured using a commercial G-CSF ELISA (#1) (a) at baseline (T = 0) or (b) following 15 h incubation at 37 °C (T = 15 h). Error bars represent the standard deviations generated from three independent sample preparations and measurements. The symbol, *, indicates statistically significant differences between the levels in each solution compared to the level in the formulation buffer (**p < 0.0001, *p < 0.05, Student’s T-test). (c) Pegfilgrastim (400 ng/mL) was spiked into 10 individual sera obtained from healthy human volunteers (Donors S1-S10). Pegfilgrastim levels in each sample were measured using commercial ELISA #1 in a time-course experiment and are shown as red dots. Bars represent the means derived from levels detected in 10 individual sera collected at the time points shown. Red dots surrounded by grey squares or circles highlight results from sera from Donors S08 and S10, respectively, whose stability patterns differed greatly and were studied further in experiments shown in Fig. 6b,c.