No Evidence for JAK2V617F Mutation in Monoclonal B Cells in 2 Patients with Polycythaemia Vera and Concurrent Monoclonal B Cell Disorder

Occurrence of Philadelphia chromosome-negative myeloproliferative neoplasms (Ph – MPN) and lymphoproliferative disorders, like B cell chronic lymphocytic leukaemia (B-CLL), in the same patient is rare. JAK2 V617F mutation was recently introduced as a powerful diagnostic tool for Ph – MPN. JAK2 V617F mutation is not present in B-CLL. In 4 previously reported patients with JAK2 V617F -positive Ph – MPN and B-CLL there was no definitive proof of JAK2 V617F mutation in B-CLL cells, although this was suggested in 1 patient. We present 2 patients with JAK2 V617F -positive polycythaemia vera who subsequently developed a monoclonal B cell disorder. The granulocytes were separated from the mononuclear cells by centrifugation on density gradient. Using an ARIA-SORP sorter, the CD20+/CD5+ B cells were separated from the CD20+/CD5– B cells, T cells, NK cells and monocytes. On each of the fractions JAK2 V617F mutation was analysed by allele-specific competitive blocker-PCR. In both patients JAK2 V617F mutation was present in granulocytes confirming the clinical diagnosis of polycythaemia vera. We did not detect the JAK2 V617F mutation in the CD20+/CD5+ B cells but detected it in CD20+/CD5– B cells, T and NK cells, indicating a lymphoid subdifferentiation of the JAK2 V617F MPN clonality. JAK2 V617F MPN and monoclonal B cell disorder can coexist but there is no evidence that the proliferative behaviour of these B cells is mediated through the JAK2 V617F mutation.