Induction of differentiation of MK progenitors by CALR-del52. (A) Stability study of rhCALR-del52 colony-forming unit MK culture medium. Six samples maintained at 37°C for various lengths of time were measured in duplicate by ELISA and analyzed using a 1-phase decay model (Prism6) to determine the averaged half-life and R². Error bars represent SDs. CD34⁺CD41⁺ progenitors from 4 to 6 patients with mutated CALR (B), 3 patients with JAK2 V617F (B), and 3 normal controls (C) were sorted and cloned at 1 cell per well in 96-well plates in serum-free medium containing SCF and treated with a single, large dose of CALR-del52. Percentages of MK colonies were calculated compared with the Tpo condition. Results are shown as mean ± SEM. ∗∗∗∗P < .0001, ∗∗∗P < .001. One-way analysis of variance, Holm-Sidak multiple comparisons test. (D) Effect of daily treatment of CALR-del52 (0.1, 1, or 5 μg/mL) on MK colony formation. CD34⁺CD41⁺ progenitors from 4 patients with mutated CALR were tested and the percentages of MK colonies were calculated compared with the Tpo condition. Results are shown as mean ± SEM. ∗∗P < .01. One-way analysis of variance, Holm-Sidak multiple comparisons test.