Particularly in the case of ex vivo-cultured PV patient-derived CD34+ progenitors, one should take into consideration that the hyper-recombination phenotype, observed by Plo et al. [77], was manifested in cells maintained for several days in medium containing DNA damage-promoting cytokines (such as IL-6 [80]) or other growth factors (SCF, IL-3, TPO) promoting ROS production in stimulated human hematopoietic cells [81]. This evidence concerns the gene CD34 and acquired polycythemia vera.