Immunogenomic identification and characterization of granulocytic myeloid derived suppressor cells in multiple myeloma.

Granulocytic myeloid-derived suppressor cells (G-MDSCs) promote tumor growth and immunosuppression in multiple myeloma (MM). However, their phenotype is not well-established for accurate monitoring and clinical translation. Here, we aimed at providing the phenotypic profile of G-MDSCs based on their prognostic significance in MM, immunosuppressive potential, and molecular program. The pre-established phenotype of G-MDSCs was evaluated in bone marrow samples from controls and MM patients using multidimensional flow cytometry and, surprisingly, we found that CD11b+CD14-CD15+CD33+HLADR- cells overlapped with common eosinophils and neutrophils, which were not expanded in MM patients. Thus, we relied on automated clustering to unbiasedly identify all granulocytic subsets in the tumor microenvironment: basophils, eosinophils, immature, intermediate and mature neutrophils. In a series of 267 newly-diagnosed MM patients (GEM2012MENOS65 trial), only the frequency of mature neutrophils at diagnosis was significantly associated with patients' outcome, and a high mature-neutrophils/T-cell ratio resulted in inferior progression-free survival (P

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