VWF and polycythemia: Interestingly, VWF, a marker of platelet-biased stem cells (Sanjuan-Pla et al., 2013), was specifically upregulated in JAK2V617F mutant cells from patients IF0602 and OX4739, whose disease was characterized by abnormal megakaryocytic differentiation and MF, but it was not upregulated in JAK2V617F mutant cells from patient IF0111, who had a polycythemia phenotype (Figure 3I).