Therapy free remissions, in which the malignant clone remains suppressed or even undetectable without pharmacological intervention is very rare in MPN patients, sometimes becoming possible after treatment with interferon-alpha, albeit only in a proportion of patients. Nonetheless, the JAK2V617F mutation, found in the majority of patients, can also be detected in healthy individuals and by estimations, only one in 40 individuals carrying a JAK2V617F mutation will develop a clinically overt MPN in their lifetime.

Moreover, while it has been elegantly demonstrated that presence of the JAK2V617F mutation in a single murine hematopoietic stem cell (HSC) can be sufficient to induce an MPN phenotype, in other murine models, HSCs carrying the JAK2V617F mutation did not show a proliferative advantage. One possible explanation for these observations, and a model that we propose in this project, is that two factors are required for an MPN clone to expand to an extent that clinically apparent disease is established: the neoplastic MPN HSC and an aberrant, supportive bone marrow microenvironment.

In this project, we present a novel murine model, which is uniquely suited to investigate both the consequences of intrinsic defects in HSCs as well as the interaction between altered HSCs and a diseased, inflammatory BM niche. We propose that a two-pronged approach, targeting both, the neoplastic clone and the bone marrow niche, will be required to alter disease biology, such that the malignant clone can be reduced or eliminated.

Whether reducing the clonal burden indeed translates to clinical benefit in MPN patients has been a subject of controversy in the field, however, very recently, a measurable clinical benefit from reduction of the JAK2V617F allele burden was demonstrated for the first time in PV patients. Therefore, reversal of the clonal expansion and reduction or elimination of the malignant clone must constitute our goal in the treatment of MPN patients. We propose that combination therapies, which target both the altered niche and the malignant clone, will lead to larger reductions in clonal burden than JAK-inhibitor monotherapy.

We have shown that the transcription factor NFE2 is overexpressed in the vast majority of patients with MPN. In addition, a fraction of MPN patients carry mutations in NFE2 that are either activating or dominant negative in their effect and therefore change the level of NFE2 transcription factor activity. In several mouse models, we have demonstrated that altering NFE2 activity causes an MPN phenotype with spontaneous transformation to acute leukemia and our data demonstrate that changing the level of NFE2 activity in HSCs is sufficient both, to induce an MPN phenotype, and to promote the acquisition of additional mutations, causing leukemic transformation. Our preliminary data demonstrate that proliferation, self-renewal, lineage restriction and differentiation capacity of NFE2 deficient HSCs is regulated by an interplay between cell intrinsic and cell extrinsic factors. Thus, in this project:

We will delineate the cell intrinsic effects of NFE2 deletion on HSC physiology.

We will analyze the mechanisms determining the effect of NFE2 depletion in different niche contexts.

We will investigate the induced changes in detail and integrate data obtained to propose mechanistic models.