Differentiation of megakaryocytes, as indicated by increased expression of CD41⁺, and effects of imetelstat on CFU-MEG growth and TA, as well as hTERT expression. (A) Dose-response analysis of CFU-MEG growth from PB MNCs from patients with ET compared with HIs at different clinically relevant concentrations of imetelstat. (B) Percentage of differentiated megakaryocytes from the total number of human CD34⁺ CB cells incubated with cytokines for megakaryocytic development and TA. An internal control in each reaction was used to normalize the telomerase product signal. (C-D) Megakaryocytic differentiation in the presence of developmental cytokines, with and without different concentrations of imetelstat. Each panel is the result of 1 experiment. “Standard control” indicates treatment with cell culture media alone. Because imetelstat is solubilized in dimethyl sulfoxide, an additional “Solvent control” treatment with dimethyl sulfoxide alone was included. (E) TA in the presence of different concentrations of imetelstat during the development of megakaryocytes from human CB, normalized to control without imetelstat. (F) Comparison of hTERT mRNA levels in ET patients vs HIs, normalized to ABL1. (G) Reduction in hTERT mRNA levels in ET patients treated with imetelstat.