PF658 THE NEUTROPHIL TO LYMPHOCYTE RATIO (NLR) IS A CHEAP SURROGATE OF EXPANSION OF MYELOID‐DERIVED SUPPRESSOR CELLS IN MYELOFIBROSIS BEFORE AND AFTER TREATMENT WITH RUXOLITINIB: A SINGLE‐CENTER EXPERIENCE

Abstract

Background:In myelofibrosis (MF), majority clinical benefits of ruxolitinib are presumably derived from reduction of inflammatory cytokines even if the exact mechanism remains unclear. Polymorphonuclear myeloid‐derived suppressor cells (PMN‐MDSC) are important regulators of immune responses in cancer, directly implicated in promotion of tumor progression. NLR, the ratio between absolute neutrophils count (ANC) and absolute lymphocyte count (ALC), mirrors the inflammatory status and the myeloid associated immune suppression, predictor of progression free survival (PFS) and overall survival (OS).Aims:To investigate the amount of circulating MDSC in MF patients undergoing treatment with ruxolitinib and any potential association with clinical variables at baseline and during treatment.Methods:From September 2016 through January 2019, we prospectively evaluated 40 healthy volunteers and 52 consecutive MF patients before and during treatment with ruxolitinib and measured NLR, MDSC by flow cytometry defined as monocytic‐like CD45+CD11b+ CD15−, CD14+ HLA‐DR− (mo‐MDSC) and granulocytic‐like CD45+CD11b+ CD15+, Lox1+ CD14− HLA‐DR− (PMN‐MDSC). Immune‐suppressive cytokines IL‐6, IL‐8, TGF‐beta and aminoacid‐degrading enzymes Arginase‐1 (Arg‐1) and indoleamine‐deoxygenase1 (IDO‐1) were evaluated in peripheral sera as functional markers of MDSC expansion.Spleen diameters were evaluated by physical examination before treatment and after 12 and 24 weeks of ruxolitinib continuous treatment according to drug label in a real‐life setting. NLR was calculated using data obtained from the complete blood count at diagnosis and correlated with driver mutations and clinical response outcome.Results:While there were not significant differences in mo‐MDSC percentages among MF and healthy subjects, PMN‐MDSC were increased (p < 0.001) and showed increased p‐STAT3 and p‐STAT5 (p < 0.001), markers of immune‐suppression in myeloid regulatory cells. Accordingly, immune‐suppressive cytokines IL‐6, IL‐8, TGF‐beta and aminoacid‐degrading enzymes Arg‐1 and IDO‐1 were significantly increased (p < 0.001).For 26 patients, matched samples before and after 12‐weeks treatment with ruxolitinib were available and showed a significant decrease of both PMN‐MDSC (p < 0.0001), associated to reduction of p‐STAT5 up to values measurable in healthy subjects (p = 0.003), but not p‐STAT3.PMN‐MDSC percentage was positively associated to NLR (r‐square 0.52, p = 0.003). NLR was increased upon progression of disease, and positively associated to fibrosis grading as detected by immune‐histochemistry. Patients with lower bone marrow fibrosis had lower median NLR (grade 0: 4.1, G1: 4.8, G2: 5.2, G3: 8.1, p < 0.001), while cases positive for JAK2V617F had increased NLR (p = 0.002). Receiving operator curve identified NLR = 6 as cut‐off to distinguish healthy and MF subjects with 97 % sensitivity and 89% specificity (AUC = 0.92, p < 0.001), and it was applied for further evaluations.Patients with NLR>6 before starting ruxolitinib treatment did not achieve spleen reduction higher than 50% in the first 12 weeks (p = 0.001). At 24 weeks, patients with lower NLR had more chances to reduce spleen size of 100% (p = 0.001). After a median follow‐up of 30.2 months, NLR at diagnosis was not predictor of neither TTP nor OS.Summary/Conclusion:In MF, PMN‐MDSC are increased and positively associated to NLR, mutational status and bone marrow fibrosis. NLR is an useful, simple and early predictor of response and spleen reduction in patients treated with ruxolitinib, despite it does not have any impact on TTP and OS.