Advancing the knowledge of human neutrophils displaying polymorphonucler myeloid-derived suppressor cell (PMN-MDSC) functions

Immunosuppressive CD66b+ low-density neutrophils (LDNs), also known as PMN-myeloid derived suppressor cells (PMN-MDSCs), are consistently found in cancer patients. However, the lack of specific markers, as well as the heterogeneity of PMN-MDSCs have limited our progress in defining their full functional and molecular features. In this field, our groups have demonstrated that neutrophil populations displaying PMN-MDSC-like features appear in great abundance in both LDNs and normal-density neutrophils (NDNs) of healthy subjects receiving G-CSF for stem cell mobilization (called as GDs)(Blood 2017;129(10):1343). We also uncovered that the mature - but not immature - fraction of PMN-MDSC populations present in GDs (i.e., GD-mLDNs and GD-mNDNs) and cancer patients (i.e., mPMN-MDSCs) represent the cells exerting most potent immunosuppressive functions (Blood 2017;129(10):1343). More recently, by computational comparison of RNA-seq transcriptomes of GD-mLDNs and GD-mNDNs with those of mPMN-MDSCs from head and neck and nonsmall cell lung cancer patients, we identified a specific gene signature common to all these immunosuppressive neutrophil populations (manuscript in preparation). These data once again support the notion that GD-mLDNs and GD-mNDNs represent reliable cellular models to define either the molecular features, or the specific markers, of mPMN-MDSCs. In another, more recent study (Nature Immunology, 2022 in press), we have discovered and partially characterized novel CD34+ and CD34dim/- neutrophil-committed progenitors (NCPs) which currently represent the earliest human neutrophil precursors that, to date, can be identified and sorted by flow cytometry. We therefore assume (and hence we intend to verify) that NCPs play a crucial role in physiological and pathological neutropoiesis, in the latter case also associated to cancer, for instance in generating immunosuppressive neutrophils. Based on these premises, we propose to perform a systematic characterization of the molecular and metabolic properties of GD-mNDNs/mLDNs, as well as to define their ontogenesis. As already explained, GD-mNDNs/mLDNs represent very reliable cellular models for characterizing in detail the phenotypic, functional and molecular features/signatures of mPMNMDSCs. The advantage to use GD-mNDNs/mLDNs as mPMN-MDSC model is that, contrary to cancer patients, the availability of GD-mNDNs/mLDNs guarantees sufficient numbers to work with. Hence, this project plans 2 major tasks to be accomplished in two years (and to be concomitantly carried out), namely: an extensive molecular and metabolic characterization of GD-mNDNs/mLDNs (TASK 1) and the attempt to develop in vitro models to generate mPMN-MDSCs (TASK 2).