Transcriptomic characterization of mature PMN-MDSCs from cancer patients and G-CSF-treated donors

A precise phenotypic and molecular characterization of circulating human polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) is hampered by their mixed composition of mature and immature cells and lack of specific markers. Recently, we demonstrated that neutrophil populations displaying PMN-MDSC-like features appear in abundance in both CD66b+ low-density neutrophils (LDNs) and normaldensity neutrophils (NDNs) of healthy subjects receiving G-CSF for stem cell mobilization (GDs). Furthermore, we demonstrated that only the mature, and not the immature, fraction of PMN-MDSC populations present in LDNs and NDNs from GDs and in LDNs from cancer patients exert the most potent immunosuppressive functions. Herein, we focused on mature CD66b+CD10+CD16+CD11b+ PMN-MDSCs from either cancer patients (mPMN-MDSCs) or GDs (mNDNs/mLDNs) to define their specific transcriptomic features. By RNA-seq experiments, we report the identification of a distinct gene signature shared by the different mPMN-MDSC populations under investigation, which was validated also in tumor-associated neutrophils (TANs). Analysis of such gene signature uncovered a specific transcriptional program associated with mPMN-MDSC differentiation. Moreover, this study further demonstrated that mNDNs/mLDNs from GDs can function as reliable cellular models to study mPMN-MDSCs. Based on these premises, we further validated by scRNA-seq experiments on mNDNs/mLDNs from GDs, that these cells are highly heterogeneous and display a strong metabolic reprogramming as well as specific transcription factor (TF) regulatory networks. Altogether, our findings indicate that mPMN-MDSCs distinctively undergo specific reprogramming during differentiation and lay the groundwork for selective immunomonitoring, and eventually targeting, of mPMN-MDSCs.