JAK2^V617F induces a hyper-recombination phenotype in cells from PV and MF patients. (A,B) Cells were cultured for 5 days in medium containing SCF, IL-3, IL-6, FLT3-L, and TPO. Cells were immunostained with an anti-RAD51 antibody (A), and the percentage of cells with RAD51 foci was calculated (B). At least 60 cells were counted for each patient (PV, n = 5; MF, n = 6) and for mobilized donors (n = 6). Horizontal line represents the mean. (C,D) CD34⁺ cells were immunopurified either from the blood of either JAK2^V617F positive–patients or from the blood of G-CSF–mobilized donors and were cultured in medium containing SCF, IL-3, and EPO. (C) The number of cells was counted during 7 days. (D) At day 5, cells were infected with the retrovirus containing HR substrate (HR-EGFP/3′EGFP), and GFP⁺ cells were measured 5 days later by cytometric analysis. Error bars represent SE.