Hematoxylin inhibited the colony-forming capacity of CALR patient–derived CD34⁺ cells. (A) The colony formation assay of healthy individuals and JAK2V617F and CALR patients after hematoxylin treatment. CD34⁺ cells from 7 healthy controls, 7 JAK2 patients, and 10 CALR patients were isolated and plated for 10 to 14 days with DMSO or 40 μM of hematoxylin treatment before colony counting. Two-way analysis of variance followed by Sidak’s multiple comparisons test was used for P value calculation. Absolute colony count (left). Colony number of hematoxylin-treated plates normalized to the DMSO control plates from the same individual (middle). Reduced colony number of hematoxylin-treated plates normalized to the DMSO control plates from the same individual (bottom). (B) Western blot detecting mutant CALR protein extracted from CD34⁺ cells from 2 CALR del52/WT patients and 1 CALR ins5/WT patient with or without hematoxylin treatment. CD34⁺ cells were treated with DMSO or 40 μM of hematoxylin in StemSpan SFEM II with CD34⁺ expansion supplement for 16 hours before collection and protein extraction. ****P < .0001.