Mechanisms regulating transitory suppressive activity of neutrophils in newborns: PMNs-MDSCs in newborns

Insights of immune cell heterogeneity, tumor-initiated subtype transformation, drug resistance, treatment and detecting technologies in glioma microenvironment

BACKGROUND

With the gradual understanding of glioma development and the immune microenvironment, many immune cells have been discovered. Despite the growing comprehension of immune cell functions and the clinical application of immunotherapy, the precise roles and characteristics of immune cell subtypes, how glioma induces subtype transformation of immune cells and its impact on glioma progression have yet to be understood.

AIM OF THE REVIEW

In this review, we comprehensively center on the four major immune cells within the glioma microenvironment, particularly neutrophils, macrophages, lymphocytes, myeloid-derived suppressor cells (MDSCs), and other significant immune cells. We discuss (1) immune cell subtype markers, (2) glioma-induced immune cell subtype transformation, (3) the mechanisms of each subtype influencing chemotherapy resistance, (4) therapies targeting immune cells, and (5) immune cell-associated single-cell sequencing. Eventually, we identified the characteristics of immune cell subtypes in glioma, comprehensively summarized the exact mechanism of glioma-induced immune cell subtype transformation, and concluded the progress of single-cell sequencing in exploring immune cell subtypes in glioma.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In conclusion, we have analyzed the mechanism of chemotherapy resistance detailly, and have discovered prospective immunotherapy targets, excavating the potential of novel immunotherapies approach that synergistically combines radiotherapy, chemotherapy, and surgery, thereby paving the way for improved immunotherapeutic strategies against glioma and enhanced patient outcomes.

Single-cell transcriptomic analysis reveals heterogeneous features of myeloid-derived suppressor cells in newborns

The transitory emergence of myeloid-derived suppressor cells (MDSCs) in infants is important for the homeostasis of the immune system in early life. The composition and functional heterogeneity of MDSCs in newborns remain elusive, hampering the understanding of the importance of MDSCs in neonates. In this study, we unraveled the maturation trajectory of polymorphonuclear (PMN)-MDSCs from the peripheral blood of human newborns by performing single-cell RNA sequencing. Results indicated that neonatal PMN-MDSCs differentiated from self-renewal progenitors, antimicrobial PMN-MDSCs, and immunosuppressive PMN-MDSCs to late PMN-MDSCs with reduced antimicrobial capacity. We also established a simple framework to distinguish these distinct stages by CD177 and CXCR2. Importantly, preterm newborns displayed a reduced abundance of classical PMN-MDSCs but increased late PMN-MDSCs, consistent with their higher susceptibility to infections and inflammation. Furthermore, newborn PMN-MDSCs were distinct from those from cancer patients, which displayed minimum expression of genes about antimicrobial capacity. This study indicates that the heterogeneity of PMN-MDSCs is associated with the maturity of human newborns.

PMN-MDSC in newborns: Regulation of the regulators

PMN-MDSC are pathologically activated neutrophils that acquire T cell (and NK cell) suppressive activity and thus function as negative regulators of effector lymphocytes in many disease conditions.^[1] For many years, these PMN-MDSC have mainly been seen as contributors to disease progression and severity, best exemplified in the context of cancer. However, more recently, PMN-MDSC have also been described in newborn mice and humans.^[2] This finding raised the question on the potential functional roles of these regulatory myeloid cells in neonate immunobiology. During the first days (mice) or weeks (human) of life, an initial seeding of microbiota in the gut takes place. The appearance of these microbiota triggers immune responses that could potentially lead to harmful inflammation and immunopathology. In this early phase of life, PMN-MDSC could be beneficial by limiting overshooting immune responses. Indeed, a recent paper by He et al.^[3] describes the transient presence of PMN-MDSC during the first month of life. Such PMN-MDSC have been shown to suppress T cells in a contact-depended manner, but the mechanism behind the transitory nature of this phenomenon has not yet been elucidated. In this issue of the Journal of Leukocyte Biology Perego et al. describe molecular mechanisms that regulate this transient increase and subsequent decrease of PMN-MDSC in newborn mice.^[4].