Hematopoietic Clonal Dominance and Evolutionary Pattern Of JAK2V617F Allele Burden In Polycythemia Vera Patients

The JAK2V617F allele burden at progenitor levels increases over time in polycythemia vera (PV), with the dominance of the JAK2V617F-positive clone at the CD34+ compartment being an important modifier of the disease phenotype. The relationship between clonal dominance and the evolutionary pattern of JAK2V617F granulocytic load is presently unknown.

To analyze the relationship between clonal dominance of CD34+ cells with the evolution of the granulocytic JAK2V617F mutant load in PV patients.

A total of 37 patients with PV were included in the study. At time of the study, 30 patients corresponded to the chronic phase of the disease, whereas 7 patients had evolved to myelofibrosis (post-PV MF). Seventeen patients were in early chronic phase (less than 5 years from diagnosis) and 13 patients in late chronic phase (more than 5 years from diagnosis). Granulocytes were isolated from peripheral blood by density gradient, whereas CD34+ cells were purified by immunomagnetic positive selection. Stem cells (CD34+, CD38-) and progenitors (CD34+, CD38+) populations were further separated by fluorescence-activated cell sorting. JAK2V617F allele burden was measured by quantitative PCR in all three cell fractions. Clonal dominance was defined as an absolute difference ≤ 10% in JAK2V617F between granulocytes and CD34+ populations. Granulocytic JAK2V617F mutant load was measured every year with the evolutionary pattern of the JAK2V617F allele burden being stratified as follows: stable < 50%, stable ≥ 50%, progressive increase and unexplained decrease. The study was approved by the local Ethics Committee and informed consent was obtained according to the Declaration of Helsinki.

JAK2V617F allele burden in CD34+/CD38- cells was 8%, 24.9% and 71.4% in early chronic phase, late chronic phase and post-PV MF, respectively (p < 0.001). Similar results were observed in CD34+/CD38+ cells (JAK2V617F allele burden: 19.1%, 36.1% and 71.8% in early chronic phase, late chronic phase and post-PV MF, respectively, p < 0.001). No significant differences were observed among the three groups in granulocyte JAK2V617F allele burden. Six patients (16.2%) presented clonal dominance. According to disease status, clonal dominance was observed in 5 out of 7 (71.4%) patients with post-PV MF and in 1 out of 13 (7.7%) patients in late chronic phase, whereas no patient in early chronic phase showed clonal dominance.

JAK2V617F monitoring was performed in 29 patients. According to their granulocytic JAK2V617F evolutionary patterns, 9 patients remained with a stable JAK2V617F below 50%, 13 patients showed a stable JAK2V617F ≥ 50%, 6 patients experienced a progressive increase of the JAK2V617F mutant load and 1 case presented an unexplained decrease of JAK2V617F. Clonal dominance was observed in 5 out of 20 (25%) patients with a stable JAK2V617F >50% or a changing profile in comparison to 0 out of 9 patients with stable JAK2V617F < 50% (p=0.05).

Clonal dominance correlates with JAK2V617F allele burden evolutionary pattern.This may be a factor to be taken into account in the therapeutic strategy of PV patients and supports the need to monitor JAK2V617F burden during clinical follow-up.

this study was supported by grants from the Ministry of Education and Science of Spain and Instituto de Salud Carlos III FEDER (EC10-136, FIS PI10/018087, RD09/0076/00036 and RD12/0036/0010), 2009SGR929 and by grant from Asociación Española Contra el Cáncer Catalunya.

No relevant conflicts of interest to declare.