Classical BCR-ABL-negative myeloproliferative neoplasms (MPN) are acquired clonal disorders of hematopoietic stem cells (HSC) leading to the hyperplasia of one or several myeloid lineages. They are caused by recurrent mutations in 3 three main genes: JAK2, mainly JAK2V617F, calreticulin (CALR) and thrombopoietin receptor (MPL). Most therapies have limited effect on the malignant clone, except the interferon alpha (IFN) that has demonstrated some efficacy in inducing a molecular remission in patients. However, it is a long-lasting treatment and its mechanism of action is still largely unknown.
Our goal is not only to improve this treatment but also to use it for early therapeutic intervention.
Therefore, we aimed at understanding the kinetics of MPN development and the mechanisms involved. Particularly, we investigated when the mutations occur and how they impact HSC to induce the clonal dominance. We found main differences between JAK2V617F andCALRmut that can lead to different early treatment strategies.
In parallel, to understand the mechanism of action of IFN therapy, we studied how the it affects the different MPN hematopoietic cell compartments by following a longitudinal observational cohort of 48 JAK2V617F and CALRmut patients treated with IFN for more than 5 years. At 4-month intervals, we performed the clonal architecture in early and late hematopoietic progenitors and in mature cells. We also used a mathematical model to infer the behavior of IFN-targeted mutated HSC from those of mutated progenitors and mature cells. Our results predict that IFN slowly exhausts the mutated HSC by inducing their differentiation into progenitors and mature cells. In addition, we show that this effect was increased with high IFN doses and in patients with homozygous JAK2V617F HSC. In contrast, CALRmut HSC remain poor responders.
Finally, we searched to increase the IFN efficacy, focusing on PML, an IFN downstream effector whose targeting by arsenic (AS) was implicated in acute promyelocytic leukemia eradication. In a JAK2V617F mouse model, the combination of IFN and AS improved hematological and molecular responses at the level of early progenitors leading to disease-initiating cell eradication. The effects of this combination required PML and were associated with features of senescence.
Collectively, these studies identify HSC exhaustion as a mechanism of IFN disease eradication, may help clinicians for IFN therapy and show that a combination with AS will improve its clinical efficacy. Moreover, these types of treatments might be used earlier during life at the onset of mutation clonal amplification before MPN symptoms develop.