Hematopoietic stem cell transplantation for myelofibrosis: where are we now?

LepR+ cells dispute hegemony with Gli1+ cells in bone marrow fibrosis

Bone marrow fibrosis is a reactive process, and a central pathological feature of primary myelofibrosis. Revealing the origin of fibroblastic cells in the bone marrow is crucial, as these cells are considered an ideal, and essential target for anti-fibrotic therapy. In 2 recent studies, Decker et al. (2017) and Schneider et al. (2017), by using state-of-the-art techniques including in vivo lineage-tracing, provide evidence that leptin receptor (LepR)-expressing and Gli1-expressing cells are responsible for fibrotic tissue deposition in the bone marrow. However, what is the relationship between these 2 bone marrow cell populations, and what are their relative contributions to bone marrow fibrosis remain unclear. From a drug development perspective, these works bring new cellular targets for bone marrow fibrosis.

Acute respiratory distress syndrome in a patient with primary myelofibrosis after ruxolitinib treatment discontinuation

Ruxolitinib is a Janus kinase (JAK) inhibitor used for the treatment of myelofibrosis with demonstrated efficacy for the alleviation of disease-related symptoms and splenomegaly. Anemia and thrombocytopenia are the main secondary effects. However, there are case reports of rare but serious adverse events following drug withdrawal. We present a case of a 76-year-old man diagnosed with primary myelofibrosis who presented with constitutional symptoms and symptomatic splenomegaly. Ruxolitinib was started (15 mg twice daily) and his disease-related symptoms disappeared. Six weeks later, he developed grade 4 thrombocytopenia and grade 3 anemia. Ruxolitinib was stopped and corticosteroid treatment (prednisone 1 mg/kg/day) was started to avoid a cytokine-rebound reaction. The patient then developed fever, chills, a biological inflammatory syndrome, and an acute respiratory disease syndrome. Full workup excluded an infection and we concluded that ruxolitinib withdrawal syndrome was the likely cause. Continued treatment with corticosteroids, as well as oxygen supply and continuous positive airway pressure, allowed an alleviation of his symptoms. This case report describes acute respiratory distress syndrome as another potential complication of ruxolitinib withdrawal syndrome.

Rescue of a primary myelofibrosis model by retinoid-antagonist therapy

Molecular targeting of the two receptor interaction domains of the epigenetic repressor silencing mediator of retinoid and thyroid hormone receptors (SMRT(mRID)) produced a transplantable skeletal syndrome that reduced radial bone growth, increased numbers of bone-resorbing periosteal osteoclasts, and increased bone fracture risk. Furthermore, SMRT(mRID) mice develop spontaneous primary myelofibrosis, a chronic, usually idiopathic disorder characterized by progressive bone marrow fibrosis. Frequently linked to polycythemia vera and chronic myeloid leukemia, myelofibrosis displays high patient morbidity and mortality, and current treatment is mostly palliative. To decipher the etiology of this disease, we identified the thrombopoietin (Tpo) gene as a target of the SMRT-retinoic acid receptor signaling pathway in bone marrow stromal cells. Chronic induction of Tpo in SMRT(mRID) mice results in up-regulation of TGF-β and PDGF in megakaryocytes, uncontrolled proliferation of bone marrow reticular cells, and fibrosis of the marrow compartment. Of therapeutic relevance, we show that this syndrome can be rescued by retinoid antagonists, demonstrating that the physical interface between SMRT and retinoic acid receptor can be a potential therapeutic target to block primary myelofibrosis disease progression.