Loss of Dnmt3a increases self-renewal and resistance to pegIFNα in JAK2-V617F-positive myeloproliferative neoplasms

Pegylated interferon alfa (pegIFN- alpha ) can induce molecular remissions in patients with JAK2 -V617F-positive myeloproliferative neoplasms (MPNs) by targeting long-term hematopoietic stem cells (LT-HSCs). Additional somatic mutations in genes regulating LT-HSC self-renewal, such as DNMT3A , have been reported to have poorer responses to pegIFN alpha . We investigated whether DNMT3A loss leads to alterations in JAK2 -V617F LTHSC functions conferring resistance to pegIFN alpha treatment in a mouse model of MPN and in hematopoietic progenitors from patients with MPN. Long -term treatment with pegIFN alpha normalized blood parameters and reduced splenomegaly and JAK2 -V617F chimerism in single -mutant JAK2 -V617F ( VF ) mice. However, pegIFN alpha in VF ; Dnmt3a Delta / Delta ( VF;Dm Delta / Delta ) mice worsened splenomegaly and failed to reduce JAK2 -V617F chimerism. Furthermore, LT-HSCs from VF;Dm Delta / Delta mice compared with VF were less prone to accumulate DNA damage and exit dormancy upon pegIFN alpha treatment. RNA sequencing showed that IFN alpha induced stronger upregulation of in fl ammatory pathways in LT-HSCs from VF;Dm Delta / Delta than from VF mice, indicating that the resistance of VF;Dm Delta / Delta LT-HSC was not due tofailure in IFN alpha signaling. Transplantations of bone marrow from pegIFN alpha - treated VF;Dm Delta / Delta mice gave rise to more aggressive disease in secondary and tertiary recipients. Liquid cultures of hematopoietic progenitors from patients with MPN with JAK2 -V617F and DNMT3A mutation showed increased percentages of JAK2 -V617F-positive colonies upon IFN alpha exposure, whereas in patients with JAK2 -V617F alone, the percentages of JAK2 -V617F-positive colonies decreased or remained unchanged. PegIFN- alpha combined with 5-azacytidine only partially overcame resistance in VF;Dm Delta / Delta mice. However, this combination strongly decreased the JAK2 -mutant allele burden in mice carrying VF mutation only, showing potential to in fl ict substantial damage preferentially to the JAK2 -mutant clone.