ITGA2B and myelofibrosis: In single-cell clonogenic assays supportive of myeloid and erythroid (but not megakaryocytic) colony formation (methocult), CD41+ and CD41– fractions of HSCs and MPPs gave rise to expected colony frequencies with myelofibrosis CD41- HSC/MPP showing a bias toward myeloid versus erythroid colonies (Figure S1B).