In vitro expansion of erythroid progenitors from polycythemia vera patients leads to decrease in JAK2V617F allele

ObjectivesA G>T transversion in a tyrosine kinase JAK2 (V617F) was reported in over 80% of patients with polycythemia vera (PV). Current evidence suggests that JAK2V617F somatic mutation is involved in the pathogenesis of PV, as it confers erythropoietin-independent proliferation to erythroid progenitor cells. However, several unanswered questions regarding the essential role of JAK2V617F arose as 1) it is not a dominant mutation, 2) it is not PV-specific as it is found in several myeloproliferative disorders, and 3) some (∼20%) PV patients lack the JAK2V617F mutation. We investigated the relative frequency of JAK2V617F in in vitro–expanded PV progenitors.MethodsIn vitro expansion of erythroid progenitors from mononuclear cells was optimized. Frequency of JAK2V617F allele was measured by using allele-specific real-time polymerase chain reaction. Clonality was performed using established procedure.ResultsIn vitro expansion of PV erythroid progenitors and differentiated dendritic cells resulted in a decrease of the frequency of JAK2V617F allele compared with granulocytes or CD235+ erythroid progenitors. Clonality analysis demonstrated that although granulocytes of these PV patients were clonal, expanded erythroid cells were polyclonal. However, in vitro–expanded PV erythroid progenitors still had approximately a twofold increased proliferative capacity in comparison with erythroid progenitors from healthy individuals. Erythropoietin favors the cells without JAK2V617F allele. Dendritic cells in one out of three patients remained clonal.ConclusionJAK2V617F mutation does not provide a proliferative/survival advantage to the PV clone during in vitro expansion. These data suggest that the JAK2V617F mutation plays an important role in the biology of PV, yet it may not be the PV-initiating event.