PROJECT SUMMARY
The myeloproliferative neoplasms (MPNs) which include Polycythemia Vera (PV), Essential
Thrombocythemia (ET) and Myelofibrosis (MF) are clonal hematopoietic stem cell disorders molecularly
characterized by aberrant activation of the JAK-STAT signaling pathway. The JAK-STAT pathway is most often
activated by mutations in JAK2, CALR, or MPL. Biologically, theses disease are characterized by proliferation
of mature myeloid and erythroid cells, and overproduction of inflammatory cytokines. Clinically, these diseases
result in increased risk of thrombotic and hemorrhagic events, progressive bone marrow fibrosis, a high degree
of symptom burden, and ultimately transformation to acute leukemia. Cytoreductive therapy, including
hydroxyurea (HU) and pegylated Interferon (pegINF) are commonly used agents used to control disease
manifestations in patients with ET and PV. Notably, pegINF has demonstrated the ability to procure clinical
response (including hematologic and pathologic response in patients with ET and PV). Further, peripheral
blood DNA sequencing studies of mature neutrophils and mononuclear cells have demonstrated that pegINF
can results in decreases of JAK2V617F allele burden, in some cases to levels below the limits of detection of
employed assays. However, the mechanisms by which INF exerts its effects in MPN, including its effects on
MPN hematopoietic stem and progenitor cells (HSPCs), remains to be resolved.
The observation that pegINF therapy can normalize peripheral blood counts, decrease mutant JAK2
allele burden in the peripheral blood, and alter cytokine expression in the serum of MPN patients suggests the
possibility that pegINF may work by depleting JAK2 mutant HSPCs, alter the fitness of JAK2 mutant HSCs, or
alter the transcriptional profile of HSPCs to reduce megakaryocyte/erythroid lineage bias. However, no
comprehensive analysis of the impact of pegINF therapy on mutant and wildtype HPSCs in MPN patients has
been reported. We hypothesize that pegINF therapy results in hematologic and molecular responses by
reducing the clonal output of JAK2mut HSPCs and attenuates inflammatory cytokine production by
reducing the number of mature and immature myeloid and erythroid cells derived from JAKmut HSPCs
as well as the cytokine production per cell.
Using primary patient samples for the recently reported phase II study of pegINF in ET and PV patients
(MPD-RC 111 study) and the Phase III trial of hydroxyurea versus INF in untreated PV and ET patients (MPD-
RC 112 study) we will undertake single-cell approaches to determine the impact of pegINF on the lineage
trajectory of JAK2 mutant HSPCs, the transcriptional output of HSPCs, and on cytokine production by these
populations. Our experiments will reveal insights into how pegINF alters hematopoiesis and inflammation in the
bone marrow of MPN patients, and identify predictors of disease response.
