Although infectious complications represent a relevant cause of morbidity and mortality in patients with myelofibrosis (MF), little is known about their incidence, outcome and risk factors. We retrospectively evaluated a cohort of 507 MF patients, diagnosed between 1980 and 2014 in five Italian hematology centers, to define the epidemiology of infections and describe the impact of ruxolitinib (RUX) treatment. Overall, 112 patients (22%) experienced 160 infectious events (grade 3-4, 45%) for an incidence rate of 3.9% per patientyear. Infections were mainly bacterial (78%) and involving the respiratory tract (52% of cases). Also, viral (11%) and fungal infections (2%) were recorded. Overall, infections were fatal in 9% of the cases. Among baseline features, high/intermediate-2 IPSS category (HR 1.8, 95%CI:1.2-2.7; P 5 0.02) and spleen length 10 cm below left costal margin (HR 1.6, 95%CI:1.1-2.5; P 5 0.04) were associated with higher infectious risk in multivariate analysis. Overall, the rate of infections was higher in the cohort of 128 RUX-treated patients (44% vs. 20%, P < 0.001). In conclusion, IPSS-category and splenomegaly, emerged as the main risk factors for infections in MF. RUX-treated patients experienced significantly more infection episodes; however, future prospective studies are needed to isolate the confounding contribution of other risk factors such as disease stage.

We investigated the influence of molecular status on disease characteristics and clinical outcome in young patients (⩽ 40 years) with World Health Organization (WHO)-defined essential thrombocythemia (ET) or early/prefibrotic primary myelofibrosis (early-PMF). Overall, 217 patients with ET (number 197) and early-PMF (number 20) were included in the analysis. Median follow-up time was 10.2 years. The cumulative incidence of thrombosis, hemorrhages and disease evolution into myelofibrosis/acute leukemia were 16.6%, 8.6% and 3% at 15 years, respectively. No differences were detectable between ET and early-PMF patients, although the latter cohort showed a trend for worse combined-event free survival (EFS). Mutation frequency were 61% for JAK2V617F, 25% for CALR and 1% for MPLW515K, and were comparable across WHO diagnosis; however, JAK2V617F allele burden was higher in the early-PMF group. Compared with JAK2V617F-positive patients, CALR-mutated patients displayed higher platelet count and lower hemoglobin level. CALR mutations significantly correlated with lower thrombotic risk (9.1% versus 21.7%, P = 0.04), longer survival (100% versus 96%, P = 0.05) and better combined-EFS (86% versus 71%, P = 0.02). However, non-type 1/type 2 CALR mutations ('minor' mutations) and abnormal karyotype were found to correlate with increased risk of disease evolution. At last contact, six patients had died; in five cases, the causes of death were related to the hematological disease and occurred at a median age of 64 years (range: 53-68 years). Twenty-eight patients (13%) were unmutated for JAK2, CALR and MPL: no event was registered in these 'triple-negative' patients.

Myelofibrosis (MF) is a clonal neoplasia associated with chronic inflammation due to aberrant cytokine production. Mutations in Janus Kinase-2 (JAK2), calreticulin (CALR) and myeloproliferative leukemia protein (MPL) genes have been recently associated to MF and they all activate the JAK/STAT signaling pathway. Since this pathway is essential in shaping the immune response, we investigated the role of circulating immune subsets and cytokines in 38 patients (20 carrying JAK2,13 exon-9 CALR mutation and 5 triple negative). In comparison to healthy donors, patients presented a reduced amount of circulating dendritic cells (DCs) associated with a defective ability of monocytes in differentiating into DCs. In addition, we found a reduction in circulating T-helper (Th)1 and Th17 and hypo-functional innate lymphoid cells (ILC). Results analyzed according to the mutational status showed that patients carrying JAK2 mutation had a reduction in Th17, myeloid-DCs and effector Tregs as well as increased ILC1 and cytokine producing Tregs. The CALR mutated patients revealed high ILC3 levels, reduced Th1 and their monocytes had a reduced capacity to mature into fully committed DCs. Their Tregs were also less effective in inhibiting the proliferation of autologous effector T-cells due to an increased proliferative status induced by CALR mutation. Triple negative patients presented a reduced amount of total circulating CD3, effectors Tregs and Th1 with increased ILC1. Overall, we have demonstrated that in MF different mutations lead to phenotypic and functional alterations in different immune subsets that may have a potential role in disease progression and susceptibility to infections.

Along with molecular abnormalities (mutations in JAK2, Calreticulin (CALR) and MPL genes), chronic inflammation is the major hallmark of Myelofibrosis (MF). Here, we investigated the in vitro effects of crucial factors of the inflammatory microenvironment (Interleukin (IL)-1β, Tumor Necrosis Factor (TNF)-α, Tissue Inhibitor of Metalloproteinases (TIMP)-1 and ATP) on the functional behaviour of MF-derived circulating CD34+ cells.We found that, regardless mutation status, IL-1β or TNF-α increases the survival of MF-derived CD34+ cells. In addition, along with stimulation of cell cycle progression to the S-phase, IL-1β or TNF-α ± TIMP-1 significantly stimulate(s) the in vitro clonogenic ability of CD34+ cells from JAK2V617 mutated patients. Whereas in the JAK2V617F mutated group, the addition of IL-1β or TNF-α + TIMP-1 decreased the erythroid compartment of the CALR mutated patients. Megakaryocyte progenitors were stimulated by IL-1β (JAK2V617F mutated patients only) and inhibited by TNF-α. IL-1β + TNF-α + C-X-C motif chemokine 12 (CXCL12) ± TIMP-1 highly stimulates the in vitro migration of MF-derived CD34+ cells. Interestingly, after migration toward IL-1β + TNF-α + CXCL12 ± TIMP-1, CD34+ cells from JAK2V617F mutated patients show increased clonogenic ability.Here we demonstrate that the interplay of these inflammatory factors promotes and selects the circulating MF-derived CD34+ cells with higher proliferative activity, clonogenic potential and migration ability. Targeting these micro-environmental interactions may be a clinically relevant approach.