CD66b-CD64dimCD115- cells in the human bone marrow represent neutrophil-committed progenitors

The Integrated Pulmonary Immune Response to Pneumonia

Pneumonia is an acute respiratory infection of the lower respiratory tract. The effectiveness of the host immune response determines the severity of infection, or whether pneumonia occurs at all. The lungs house both innate and adaptive immune systems, which integrate their activities to provide host defense that eliminates microbes and prevents lower respiratory infection from becoming severe. Professional immune cells in the lung, like macrophages and lymphocytes, work with lung constituents, like epithelial cells and fibroblasts, to optimize antimicrobial defense. The dynamics of the immune response during infection and the immune components contributing to defense are influenced by prior experiences with respiratory pathogens, remodeling lung immunity in ways that improve responses against subsequent infections. This review covers how innate and adaptive immune activities coordinate inside the lung to provide integrated and effective immune resistance against respiratory pathogens.

Exploring Neutrophil Heterogeneity and Plasticity in Health and Disease

Neutrophils, the most abundant polymorphonuclear leukocytes, are critical first responders to infection, and have historically been underappreciated in terms of their functional complexity within the immune response. Once viewed primarily as short-lived, innate immune cells with limited functional plasticity, recent research has illuminated their considerable heterogeneity and diverse functional roles, which extend beyond their involvement in steady-state immunity. This review seeks to provide an updated analysis of neutrophil development, maturation, heterogeneity, and plasticity, with a focus on how these characteristics influence immune modulation in both healthy and diseased tissues. Beginning with the origin of neutrophils, we explore their maturation into effector cells and their evolving roles in immune defense under homeostatic and disease-associated conditions. We then delve into their heterogeneity, discussing recent breakthroughs in neutrophil research that challenge the traditional view of neutrophils as a uniform population. We address the significant advances that have been made in identifying distinct neutrophil subsets, the emerging complexities of their plasticity, and the challenges that remain in fully understanding their functional diversity. Finally, we highlight future directions and opportunities for continued exploration in this rapidly advancing field, shedding light on how these insights could open new avenues for therapeutic interventions.

Uncovering two neutrophil-committed progenitors that immediately precede promyelocytes during human neutropoiesis

Technological advances have greatly improved our knowledge of myelopoiesis, for example, with the discovery of granulocyte‒monocyte‒dendritic cell (DC) progenitors (GMDPs), monocyte‒DC progenitors (MDPs), common DC progenitors (CDPs) and common monocyte progenitors (cMoPs) on the basis of flow cytometry approaches. Concomitantly, some progress has been made in characterizing the very early phases of human neutropoiesis with the description of novel CD66b+ progenitors, including eNePs, PMs w/o eNePs, ProNeus, and PreNeus. More recently, we identified four SSCloLin-CD66b-CD45dimCD34+/CD34dim/-CD64dimCD115- cells as the earliest precursors specifically committed to the neutrophil lineage present in human bone marrow (BM), which we called neutrophil-committed progenitors (NCPs, from NCP1s to NCP4s). In this study, we report the isolation and characterization of two new SSChiCD66b-CD64dimCD115-NCPs that, by phenotypic, transcriptomic, maturation and immunohistochemistry properties, as well as by flow cytometric side-scattered light (SSC), stand after NCP4s but precede promyelocytes during the neutropoiesis cascade. Similar to SSCloCD45RA+NCP2s/NCP3s and SSCloCD45RA-NCP1s/NCP4s, these cells exhibit phenotypic differences in CD45RA expression levels and, therefore, were named SSChiCD45RA+NCP5s and SSChiCD45RA-NCP6s. Moreover, NCP5s were more immature than NCP6s, as determined by cell differentiation and proliferative potential, as well as by transcriptomic and phenotypical features. Finally, by examining whether NCPs and all other CD66b+ neutrophil precursors are altered in representative hematological malignancies, we found that, in patients with chronic-phase chronic myeloid leukemia (CP-CML), but not with systemic mastocytosis (SM), there is an increased frequency of BM NCP4s, NCP6s, and all downstream CD45RA-negative neutrophil progenitors, suggesting their expansion in CML pathogenesis. Taken together, our data advance our knowledge of human neutropoiesis.

The success of the tumor immunotherapy: neutrophils from bench to beside

The present immune therapy was focused on the immune checkpoint blockade or Chimeric Antigen Receptor T-Cell Immunotherapy (CART) transfer, but how to activate the innate immune system to antitumor still lags out. Neutrophils are the most abundant circulating leukocytes in human, and heterogeneous neutrophils have been increasingly recognized as important players in tumor progression. They play double "edge-sward" by either supporting or suppressing the tumor growth, including driving angiogenesis, extracellular matrix remodeling to promote tumor growth, participating in antitumor adaptive immunity, or killing tumor cells directly to inhibit the tumor growth. The complex role of neutrophils in various tumors depends on the tumor microenvironment (TME) they are located, and emerging evidence has suggested that neutrophils may determine the success of tumor immunotherapy in the context of the immune checkpoint blockade, innate immune training, or drug-loaded extracellular microvesicles therapy, which makes them become an exciting target for tumor immunotherapy, but still with challenges. Here, we summarize the latest insights on how to activate neutrophils in antitumor immunity and discuss the advances of neutrophil-targeted immunotherapy strategies.

The impact of aging on neutrophil functions and the contribution to periodontitis

The increasing aging population and aging-associated diseases have become a global issue for decades. People over 65 show an increased prevalence and greater severity of periodontitis, which poses threats to overall health. Studies have demonstrated a significant association between aging and the dysfunction of neutrophils, critical cells in the early stages of periodontitis, and their crosstalk with macrophages and T and B lymphocytes to establish the periodontal lesion. Neutrophils differentiate and mature in the bone marrow before entering the circulation; during an infection, they are recruited to infected tissues guided by the signal from chemokines and cytokines to eliminate invading pathogens. Neutrophils are crucial in maintaining a balanced response between host and microbes to prevent periodontal diseases in periodontal tissues. The impacts of aging on neutrophils' chemotaxis, anti-microbial function, cell activation, and lifespan result in impaired neutrophil functions and excessive neutrophil activation, which could influence periodontitis course. We summarize the roles of neutrophils in periodontal diseases and the aging-related impacts on neutrophil functional responses. We also explore the underlying mechanisms that can contribute to periodontitis manifestation in aging. This review could help us better understand the pathogenesis of periodontitis, which could offer novel therapeutic targets for periodontitis.

Neutrophils in cancer: from biology to therapy

The view of neutrophils has shifted from simple phagocytic cells, whose main function is to kill pathogens, to very complex cells that are also involved in immune regulation and tissue repair. These cells are essential for maintaining and regaining tissue homeostasis. Neutrophils can be viewed as double-edged swords in a range of situations. The potent killing machinery necessary for immune responses to pathogens can easily lead to collateral damage to host tissues when inappropriately controlled. Furthermore, some subtypes of neutrophils are potent pathogen killers, whereas others are immunosuppressive or can aid in tissue healing. Finally, in tumor immunology, many examples of both protumorigenic and antitumorigenic properties of neutrophils have been described. This has important consequences for cancer therapy, as targeting neutrophils can lead to either suppressed or stimulated antitumor responses. This review will discuss the current knowledge regarding the pro- and antitumorigenic roles of neutrophils, leading to the concept of a confused state of neutrophil-driven pro-/antitumor responses.

Neutrophil diversity and function in health and disease

Neutrophils, the most abundant type of granulocyte, are widely recognized as one of the pivotal contributors to the acute inflammatory response. Initially, neutrophils were considered the mobile infantry of the innate immune system, tasked with the immediate response to invading pathogens. However, recent studies have demonstrated that neutrophils are versatile cells, capable of regulating various biological processes and impacting both human health and disease. Cytokines and other active mediators regulate the functional activity of neutrophils by activating multiple receptors on these cells, thereby initiating downstream signal transduction pathways. Dysfunctions in neutrophils and disruptions in neutrophil homeostasis have been implicated in the pathogenesis of numerous diseases, including cancer and inflammatory disorders, often due to aberrant intracellular signaling. This review provides a comprehensive synthesis of neutrophil biological functions, integrating recent advancements in this field. Moreover, it examines the biological roles of receptors on neutrophils and downstream signaling pathways involved in the regulation of neutrophil activity. The pathophysiology of neutrophils in numerous human diseases and emerging therapeutic approaches targeting them are also elaborated. This review also addresses the current limitations within the field of neutrophil research, highlighting critical gaps in knowledge that warrant further investigation. In summary, this review seeks to establish a comprehensive and multidimensional model of neutrophil regulation, providing new perspectives for potential clinical applications and further research.

Regulation of neutrophil associated RNASET2 expression in rheumatoid arthritis

Neutrophils (PMNs) are key players of innate immune responses through the release of cytoplasmic granule content and the formation of neutrophil extracellular traps (NETs). RNASET2 is an acidic ribonuclease, recently proposed as an alarmin signal associated with inflammatory responses. Here we show that, along the neutrophil maturation cascade, RNASET2 is expressed in segmented and mature PMNs. In human PMNs, RNASET2 colocalized with primary and tertiary granules and was found to be associated with NETs following PMA or Nigericin stimulation. Similarly, activation of PMNs by soluble immune complexes, a hallmark of several autoimmune diseases, also induced RNASET2-associated NETs. Genome-wide association studies recently identified RNASET2 among a cluster of genes associated with increased susceptibility to develop autoimmune diseases, including rheumatoid arthritis (RA). RNASET2 was found expressed by PMNs and macrophages infiltrating inflamed joints in a murine model of RA (K/BxN Serum-Transfer-Induced Arthritis, STIA), by immunostaining. Similar results were found in synovial biopsies of RA patients with active disease. In addition, we demonstrate that RNASET2 circulating levels correlated with the onset and the severity of disease in two mouse models of inflammatory arthritis, STIA and CIA (Collagen-Induced Arthritis) and in serum of RA patients. These results show that PMNs are an important source of RNASET2 and that its circulating levels are associated with RA development suggesting a role for RNASET2 in the pathogenesis of immune-mediated diseases.

scRNA-seq profiling of human granulocytes reveals expansion of developmentally flexible neutrophil precursors with mixed neutrophil and eosinophil properties in asthma

Neutrophils and eosinophils share common hematopoietic precursors and usually diverge into distinct lineages with unique markers before being released from their hematopoietic site, which is the bone marrow (BM). However, previous studies identified an immature Ly6g(+) Il-5Rα(+) neutrophil population in mouse BM, expressing both neutrophil and eosinophil markers suggesting hematopoietic flexibility. Moreover, others have reported neutrophil populations expressing eosinophil-specific cell surface markers in tissues and altered disease states, confusing the field regarding eosinophil origins, function, and classification. Despite these reports, it is still unclear whether hematopoietic flexibility exists in human granulocytes. To answer this, we utilized single-cell RNA sequencing and cellular indexing of transcriptomes and epitopes by sequencing to profile human BM and circulating neutrophils and eosinophils at different stages of differentiation and determine whether neutrophil plasticity plays role in asthmatic inflammation. We show that immature metamyelocyte neutrophils in humans expand during severe asthmatic inflammation and express both neutrophil and eosinophil markers. We also show an increase in trilobed eosinophils with mixed neutrophil and eosinophil markers in allergic asthma and that interleukin-5 promotes differentiation of immature blood neutrophils into trilobed eosinophilic phenotypes, suggesting a mechanism of emergency granulopoiesis to promote myeloid inflammatory or remodeling response in patients with chronic asthma. By providing insights into unexpectedly flexible granulocyte biology and demonstrating emergency hematopoiesis in asthma, our results highlight the importance of granulocyte plasticity in eosinophil development and allergic diseases.

Neutrophil Diversity (Immature, Aged, and Low-Density Neutrophils) and Functional Plasticity: Possible Impacts of Iron Overload in β-Thalassemia

Neutrophil dysfunction is a form of immune suppression in patients with β-thalassemia (Beta-thal), although data on this are limited. In this study, blood from patients and healthy volunteers was analyzed. Flow cytometry analysis demonstrated an increase in immature neutrophils (CD16- CD62L+) and aged (senescent) neutrophils (CD16+ CD62L-) in Beta-thal patients compared to healthy volunteers. The Beta-thal neutrophils demonstrated less prominent chemotaxis and phagocytosis than healthy neutrophils at the baseline. With phorbol myristate acetate (PMA) or lipopolysaccharide (LPS) stimulations, some of the indicators, including the flow cytometry markers (CD11b, CD62L, CD66b, CD63, apoptosis, and reactive oxygen species) and neutrophil extracellular traps (NETs; detected by anti-citrullinated histone 3 immunofluorescence), were lower than the control. Additionally, low-density neutrophils (LDNs), which are found in the peripheral blood mononuclear cell (PBMC) fraction, were observed in Beta-thal patients but not in the control group. The expression of CD11b, CD66b, CD63, arginase I, and ROS in LDNs was higher than the regular normal-density neutrophils (NDNs). The proliferation rate of CD3+ T cells isolated from the PBMC fraction of healthy volunteers was higher than that of the cells from patients with Beta-thal. The incubation of red blood cell (RBC) lysate plus ferric ions with healthy NDNs transformed the NDNs into the aged neutrophils (decreased CD62L) and LDNs. In conclusion, iron overload induces neutrophil diversity along with some dysfunctions.

In vitro screening methods of novel immune checkpoint inhibitors related to T cell infiltration and anti-PD-1 resistance

Immune checkpoint blockade-based cancer immunotherapy is an effective tool for cancer treatment. PD-1/PD-L1 blockade, however, is limited by a low response rate and adaptive resistance. A growing body of studies has shown that the high stromal content dense with extracellular matrix plays a significant role in immune checkpoint blockade resistance as well as T cell exclusion. In addition to physically obstructing immune cell infiltration, the extracellular matrix (ECM) may also interact with T cell receptors to indirectly impair their effector function and lead to anti-PD-1 resistance. Anti-PD-1 resistance may thus be overcome by rupturing the physical barrier related negative immune regulation, which may improve T cell infiltration and the efficacy of cancer immunotherapy. Here, we offer two straightforward methods based on flow cytometry and confocal microscopy to evaluate the effectiveness of an inhibitor targeting the novel "stromal checkpoint" DDR1/collagen, which aims to facilitate T cell migration and infiltration of tumor spheres by overcoming collagen barriers. With minor variations, the same method can be easily modified to test the inhibitors that target other immune checkpoints, and the extracellular matrix-associated drug targets that mediate anti-PD-1 resistance.

Development and validation of a novel criterion of histologic healing in ulcerative colitis defined by inflammatory cell enumeration in lamina propria mucosa: A multicenter retrospective cohort in China

BACKGROUND

Histological healing is closely associated with improved long-term clinical outcomes and lowered relapses in patients with ulcerative colitis (UC). Here, we developed a novel diagnostic criterion for assessing histological healing in UC patients.

METHODS

We conducted a retrospective cohort study in UC patients, whose treatment was iteratively optimized to achieve mucosal healing at Shanghai Tenth People's Hospital of Tongji University from January 2017 to May 2022. We identified an inflammatory cell enumeration index (ICEI) for assessing histological healing based on the proportions of eosinophils, CD177 + neutrophils, and CD40L + T cells in the colonic lamina propria under high power field (HPF), and the outcomes (risks of symptomatic relapses) of achieving histological remission vs . persistent histological inflammation using Kaplan-Meier curves. Intrareader reliability and inter-reader reliability were evaluated by each reader. The relationships to the changes in the Nancy index and the Geboes score were also assessed for responsiveness. The ICEI was further validated in a new cohort of UC patients from other nine university hospitals.

RESULTS

We developed an ICEI for clinical diagnosis of histological healing, i.e., Y = 1.701X 1 + 0.758X 2 + 1.347X 3 - 7.745 (X 1 , X 2 , and X 3 represent the proportions of CD177 + neutrophils, eosinophils, and CD40L + T cells, respectively, in the colonic lamina propria under HPF). The receiver operating characteristics curve (ROC) analysis revealed that Y <-0.391 was the cutoff value for the diagnosis of histological healing and that an area under the curve (AUC) was 0.942 (95% confidence interval [CI]: 0.905-0.979) with a sensitivity of 92.5% and a specificity of 83.6% ( P  <0.001). The intraclass correlation coefficient (ICC) for the intrareader reliability was 0.855 (95% CI: 0.781-0.909), and ICEI had good inter-reader reliability of 0.832 (95% CI: 0.748-0.894). During an 18-month follow-up, patients with histological healing had a substantially better outcome compared with those with unachieved histological healing ( P  <0.001) using ICEI. During a 12-month follow-up from other nine hospitals, patients with histological healing also had a lower risk of relapse than patients with unachieved histological healing.

CONCLUSIONS

ICEI can be used to predict histological healing and identify patients with a risk of relapse 12 months and 18 months after clinical therapy. Therefore, ICEI provides a promising, simplified approach to monitor histological healing and to predict the prognosis of UC.

REGISTRATION

Chinese Clinical Trial Registry, No. ChiCTR2300077792.

Single-cell sequencing reveals distinct immune cell features in cutaneous lesions of pemphigus vulgaris and bullous pemphigoid

Bullous pemphigoid (BP) and pemphigus vulgaris (PV) are two common subtypes of autoimmune bullous disease (AIBD). The key role of circulating autoreactive immune cells contributing to skin damage of AIBD has been widely recognized. Nevertheless, the immune characteristics in cutaneous lesions remain unclear. Here, we performed single-cell RNA sequencing (scRNA-seq) and single-cell VDJ sequencing (scRNA-seq) to generate transcriptional profiles for cells and T/B cell clonetype in skin lesions of BP and PV. We found that the proportions of NK&T, macrophages/ dendritic cells, B cells, and mast cells increased in BP and PV lesions. Then, BP and PV cells constituted over 75% of all myeloid cell subtypes, CD4+ T cell subtypes and CD8+ T cell subtypes. Strikingly, CD8+ Trm was identified to be expanded in PV, and located in the intermediate state of the pseudotime trajectory from CD8+ Tm to CD8+ Tem. Interestingly, CD8+ Tem and CD4+ Treg highly expressed exhaustion-related genes, especially in BP lesions. Moreover, the enhanced cell communication between stromal cells and immune cells like B cells and macrophages/ dendritic cells was also identified in BP and PV lesions. Finally, clone expansion was observed in T cells of BP and PV compared with HC, while CD8+ Trm represented the highest ratio of hyperexpanded TCR clones among all T cell subtypes. Our study generally depicts a large and comprehensive single-cell landscape of cutaneous lesions and highlights immune cell features in BP and PV. This offers potential research targets for further investigation.

P75NTR+CD64+ neutrophils promote sepsis-induced acute lung injury

Patients suffering from sepsis-induced acute lung injury (ALI) exhibit a high mortality rate, and their prognosis is closely associated with infiltration of neutrophils into the lungs. In this study, we found a significant elevation of CD64+ neutrophils, which highly expressed p75 neurotrophin receptor (p75NTR) in peripheral blood of mice and patients with sepsis-induced ALI. p75NTR+CD64+ neutrophils were also abundantly expressed in the lung of ALI mice induced by lipopolysaccharide. Conditional knock-out of the myeloid lineage's p75NTR gene improved the survival rates, attenuated lung tissue inflammation, reduced neutrophil infiltration and enhanced the phagocytic functions of CD64+ neutrophils. In vitro, p75NTR+CD64+ neutrophils exhibited an upregulation and compromised phagocytic activity in blood samples of ALI patients. Blocking p75NTR activity by soluble p75NTR extracellular domain peptide (p75ECD-Fc) boosted CD64+ neutrophils phagocytic activity and reduced inflammatory cytokine production via regulation of the NF-κB activity. The findings strongly indicate that p75NTR+CD64+ neutrophils are a novel pathogenic neutrophil subpopulation promoting sepsis-induced ALI.

Controversies associated with the identification of the true origins of human neutrophils

Discussion on the lineage commitment of early human neutrophil progenitors.

Small-molecule α-lipoic acid targets ELK1 to balance human neutrophil and erythrocyte differentiation

BACKGROUND

Erythroid and myeloid differentiation disorders are commonly occurred in leukemia. Given that the relationship between erythroid and myeloid lineages is still unclear. To find the co-regulators in erythroid and myeloid differentiation might help to find new target for therapy of myeloid leukemia. In hematopoiesis, ALA (alpha lipoic acid) is reported to inhibit neutrophil lineage determination by targeting transcription factor ELK1 in granulocyte-monocyte progenitors via splicing factor SF3B1. However, further exploration is needed to determine whether ELK1 is a common regulatory factor for erythroid and myeloid differentiation.

METHODS

In vitro culture of isolated CD34+, CMPs (common myeloid progenitors) and CD34+ CD371- HSPCs (hematopoietic stem progenitor cells) were performed to assay the differentiation potential of monocytes, neutrophils, and erythrocytes. Overexpression lentivirus of long isoform (L-ELK1) or the short isoform (S-ELK1) of ELK1 transduced CD34+ HSPCs were transplanted into NSG mice to assay the human lymphocyte and myeloid differentiation differences 3 months after transplantation. Knocking down of SRSF11, which was high expressed in CD371+GMPs (granulocyte-monocyte progenitors), upregulated by ALA and binding to ELK1-RNA splicing site, was performed to analyze the function in erythroid differentiation derived from CD34+ CD123mid CD38+ CD371- HPCs (hematopoietic progenitor cells). RNA sequencing of L-ELK1 and S-ELK1 overexpressed CD34+ CD123mid CD38+ CD371- HPCs were performed to assay the signals changed by ELK1.

RESULTS

Here, we presented new evidence that ALA promoted erythroid differentiation by targeting the transcription factor ELK1 in CD34+ CD371- hematopoietic stem progenitor cells (HSPCs). Overexpression of either the long isoform (L-ELK1) or the short isoform (S-ELK1) of ELK1 inhibited erythroid-cell differentiation, but knockdown of ELK1 did not affect erythroid-cell differentiation. RNAseq analysis of CD34+ CD123mid CD38+ CD371- HPCs showed that L-ELK1 upregulated the expression of genes related to neutrophil activity, phosphorylation, and hypoxia signals, while S-ELK1 mainly regulated hypoxia-related signals. However, most of the genes that were upregulated by L-ELK1 were only moderately upregulated by S-ELK1, which might be due to a lack of serum response factor interaction and regulation domains in S-ELK1 compared to L-ELK1. In summary, the differentiation of neutrophils and erythrocytes might need to rely on the dose of L-ELK1 and S-ELK1 to achieve precise regulation via RNA splicing signals at early lineage commitment.

CONCLUSIONS

ALA and ELK1 are found to regulate both human granulopoiesis and erythropoiesis via RNA spliceosome, and ALA-ELK1 signal might be the target of human leukemia therapy.

An immunophenotype-coupled transcriptomic atlas of human hematopoietic progenitors

Analysis of the human hematopoietic progenitor compartment is being transformed by single-cell multimodal approaches. Cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) enables coupled surface protein and transcriptome profiling, thereby revealing genomic programs underlying progenitor states. To perform CITE-seq systematically on primary human bone marrow cells, we used titrations with 266 CITE-seq antibodies (antibody-derived tags) and machine learning to optimize a panel of 132 antibodies. Multimodal analysis resolved >80 stem, progenitor, immune, stromal and transitional cells defined by distinctive surface markers and transcriptomes. This dataset enables flow cytometry solutions for in silico-predicted cell states and identifies dozens of cell surface markers consistently detected across donors spanning race and sex. Finally, aligning annotations from this atlas, we nominate normal marrow equivalents for acute myeloid leukemia stem cell populations that differ in clinical response. This atlas serves as an advanced digital resource for hematopoietic progenitor analyses in human health and disease.

Human CD34+/dim neutrophil-committed progenitors do not differentiate into neutrophil-like CXCR1+CD14+CD16- monocytes in vitro

The advent of recent cutting-edge technologies has allowed the discovery and characterization of novel progenitors of human neutrophils, including SSCloCD66b+CD15+CD11b-CD49dhiproNeu1s, SSChiCD66b+CD15+CD11b-CD49dintproNeus2s, CD66b+CD15+CD11b+CD49d+CD101-preNeus, and Lin-CD66b+CD117+CD71+eNePs. In this research field, we recently identified CD66b-CD38+CD64dimCD115-, CD34+, and CD34dim/- cells exclusively committed to the neutrophil lineage (which we renamed as CD34+ and CD34dim/- neutrophil-committed progenitors), representing the earliest neutrophil precursors identifiable and sorted by flow cytometry. Moreover, based on their differential CD34 and CD45RA expression, we could identify 4 populations of neutrophil-committed progenitors: CD34+CD45RA-/NCP1s, CD34+CD45RA+/NCP2s, CD34dim/-CD45RA+/NCP3s, and CD34dim/-CD45RA-/NCP4s. This said, a very recent study by Ikeda and coworkers (PMID: 36862552) reported that neutrophil precursors, termed either neutrophil progenitors or "early neutrophil-committed progenitors," would generate immunosuppressive neutrophil-like CXCR1+CD14+CD16- monocytes. Hence, presuming that neutrophil progenitors/"early neutrophil-committed progenitors" correspond to neutrophil-committed progenitors, the selective neutrophil commitment that we attributed to neutrophil-committed progenitors is contradicted by Ikeda and coworkers' article. In this study, by performing a more analytical reevaluation at the phenotypic and molecular levels of the cells generated by neutrophil-committed progenitors 2 and 4 (selected as representatives of neutrophil-committed progenitors), we categorically exclude that neutrophil-committed progenitors generate neutrophil-like CXCR1+CD14+CD16- monocytes. Rather, we provide substantial evidence indicating that the cells generated by neutrophil progenitors/"early neutrophil-committed progenitors" are neutrophilic cells at a different stage of maturation, displaying moderate levels of CD14, instead of neutrophil-like CXCR1+CD14+CD16- monocytes, as pointed by Ikeda and coworkers. Hence, the conclusion that neutrophil progenitors/"early neutrophil-committed progenitors" aberrantly differentiate into neutrophil-like monocytes derives, in our opinion, from data misinterpretation.

Comparative transcriptomics coupled to developmental grading via transgenic zebrafish reporter strains identifies conserved features in neutrophil maturation

Neutrophils are evolutionarily conserved innate immune cells playing pivotal roles in host defense. Zebrafish models have contributed substantially to our understanding of neutrophil functions but similarities to human neutrophil maturation have not been systematically characterized, which limits their applicability to studying human disease. Here we show, by generating and analysing transgenic zebrafish strains representing distinct neutrophil differentiation stages, a high-resolution transcriptional profile of neutrophil maturation. We link gene expression at each stage to characteristic transcription factors, including C/ebp-β, which is important for late neutrophil maturation. Cross-species comparison of zebrafish, mouse, and human samples confirms high molecular similarity of immature stages and discriminates zebrafish-specific from pan-species gene signatures. Applying the pan-species neutrophil maturation signature to RNA-sequencing data from human neuroblastoma patients reveals association between metastatic tumor cell infiltration in the bone marrow and an overall increase in mature neutrophils. Our detailed neutrophil maturation atlas thus provides a valuable resource for studying neutrophil function at different stages across species in health and disease.

Surface CD52, CD84, and PTGER2 mark mature PMN-MDSCs from cancer patients and G-CSF-treated donors

Precise molecular characterization of circulating polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) is hampered by their mixed composition of mature and immature cells and lack of specific markers. Here, we focus on mature CD66b+CD10+CD16+CD11b+ PMN-MDSCs (mPMN-MDSCs) from either cancer patients or healthy donors receiving G-CSF for stem cell mobilization (GDs). By RNA sequencing (RNA-seq) experiments, we report the identification of a distinct gene signature shared by the different mPMN-MDSC populations under investigation, also validated in mPMN-MDSCs from GDs and tumor-associated neutrophils (TANs) by single-cell RNA-seq (scRNA-seq) experiments. Analysis of such a gene signature uncovers a specific transcriptional program associated with mPMN-MDSC differentiation and allows us to identify that, in patients with either solid or hematologic tumors and in GDs, CD52, CD84, and prostaglandin E receptor 2 (PTGER2) represent potential mPMN-MDSC-associated markers. Altogether, our findings indicate that mature PMN-MDSCs distinctively undergo specific reprogramming during differentiation and lay the groundwork for selective immunomonitoring, and eventually targeting, of mature PMN-MDSCs.

Immune cell networking in solid tumors: focus on macrophages and neutrophils

The tumor microenvironment is composed of tumor cells, stromal cells and leukocytes, including innate and adaptive immune cells, and represents an ecological niche that regulates tumor development and progression. In general, inflammatory cells are considered to contribute to tumor progression through various mechanisms, including the formation of an immunosuppressive microenvironment. Macrophages and neutrophils are important components of the tumor microenvironment and can act as a double-edged sword, promoting or inhibiting the development of the tumor. Targeting of the immune system is emerging as an important therapeutic strategy for cancer patients. However, the efficacy of the various immunotherapies available is still limited. Given the crucial importance of the crosstalk between macrophages and neutrophils and other immune cells in the formation of the anti-tumor immune response, targeting these interactions may represent a promising therapeutic approach against cancer. Here we will review the current knowledge of the role played by macrophages and neutrophils in cancer, focusing on their interaction with other immune cells.

Clinical and transcriptomic characteristics of a novel SMARCD2 mutation that disrupts neutrophil maturation and function

We report a novel case of SMARCD2 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily D, member 2) mutation successfully treated with hematopoietic stem cell transplantation. The female patient presented delayed cord separation, chronic diarrhea, skin abscesses, skeletal dysmorphisms, and neutropenia with specific granule deficiency. Analysis of the transcriptomic profile of peripheral blood sorted mature and immature SMARCD2 neutrophils showed defective maturation process that associated with altered expression of genes related to specific, azurophilic, and gelatinase granules, such as LTF, CRISP3, PTX3, and CHI3L1. These abnormalities account for the prevalence of immature neutrophils in the peripheral blood, impaired function, and deregulated inflammatory responses.

The slan antigen identifies the prototypical non-classical CD16+-monocytes in human blood

Introduction

Peripheral monocytes in humans are conventionally divided into classical (CL, CD14++CD16-), intermediate (INT, CD14++CD16+) and non-classical (NC, CD14dim/-CD16++) cells, based on their expression levels of CD14 and CD16. A major fraction of the NC-monocytes has been shown to express the 6-sulfo LacNAc (slan) antigen, but whether these slan+/NC-monocytes represent the prototypical non-classical monocytes or whether they are simply a sub-fraction with identical features as the remainder of NC monocytes is still unclear.

Methods

We analyzed transcriptome (by bulk and single cell RNA-seq), proteome, cell surface markers and production of discrete cytokines by peripheral slan+/NC- and slan-/NC-monocytes, in comparison to total NC-, CL- and INT- monocytes.

Results

By bulk RNA-seq and proteomic analysis, we found that slan+/NC-monocytes express higher levels of genes and proteins specific of NC-monocytes than slan-/NC-monocytes do. Unsupervised clustering of scRNA-seq data generated one cluster of NC- and one of INT-monocytes, where all slan+/NC-monocytes were allocated to the NC-monocyte cluster, while slan-/NC-monocytes were found, in part (13.4%), within the INT-monocyte cluster. In addition, total NC- and slan-/NC-monocytes, but not slan+/NC-monocytes, were found by both bulk RNA-seq and scRNA-seq to contain a small percentage of natural killer cells.

Conclusion

In addition to comparatively characterize total NC-, slan-/NC- and slan+/NC-monocyte transcriptomes and proteomes, our data prove that slan+/NC-, but not slan-/NC-, monocytes are more representative of prototypical NC-monocytes.

Canonical and atypical chemokine receptors in the neutrophil life cycle

Chemokines are mainly studied for their local function in the control of leukocyte extravasation in homeostatic and inflammatory conditions. However, they have additional roles at the systemic level including the regulation of the hematopoietic process and leukocyte differentiation. Due to the redundancy and pleiotropicity of the chemokine system, chemokines have often multiple and complex roles in neutrophil differentiation ranging from retention and control of proliferation of progenitors to the mobilization of mature cells from the bone marrow (BM) to the bloodstream and their further differentiation in tissues. Atypical chemokine receptors (ACKRs) are regulators of the chemokine system by controlling chemokine bioavailability and chemokine receptor function. Even though ACKRs bind a wide range of chemokines, they appear to have a selective role in the process of neutrophil production and differentiation. The aim of this review is to give an overview of the current evidence regarding the role of chemokines and chemokine receptors in the life of neutrophils with a focus on the regulation exerted by ACKRs.

Neutrophil diversity and plasticity: Implications for organ transplantation

Neutrophils, as the first defenders against external microbes and stimuli, are highly active and finely regulated innate immune cells. Emerging evidence has challenged the conventional dogma that neutrophils are a homogeneous population with a short lifespan that promotes tissue damage. Recent findings on neutrophil diversity and plasticity in homeostatic and disease states have centered on neutrophils in the circulation. In contrast, a comprehensive understanding of tissue-specialized neutrophils in health and disease is still lacking. This article will first discuss how multiomics advances have contributed to our understanding of neutrophil heterogeneity and diversification in resting and pathological settings. This discussion will be followed by a focus on the heterogeneity and role of neutrophils in solid organ transplantation and how neutrophils may contribute to transplant-related complications. The goal of this article is to provide an overview of the research on the involvement of neutrophils in transplantation, with the aim that this may draw attention to an underappreciated area of neutrophil research.

The double-edged role of neutrophil heterogeneity in inflammatory diseases and cancers

Neutrophils are important immune cells act as the body's first line of defense against infection and respond to diverse inflammatory cues. Many studies have demonstrated that neutrophils display plasticity in inflammatory diseases and cancers. Clarifying the role of neutrophil heterogeneity in inflammatory diseases and cancers will contribute to the development of novel treatment strategies. In this review, we have presented a review on the development of the understanding on neutrophil heterogeneity from the traditional perspective and a high-resolution viewpoint. A growing body of evidence has confirmed the double-edged role of neutrophils in inflammatory diseases and tumors. This may be due to a lack of precise understanding of the role of specific neutrophil subsets in the disease. Thus, elucidating specific neutrophil subsets involved in diseases would benefit the development of precision medicine. Thusly, we have summarized the relevance and actions of neutrophil heterogeneity in inflammatory diseases and cancers comprehensively. Meanwhile, we also discussed the potential intervention strategy for neutrophils. This review is intended to deepen our understanding of neutrophil heterogeneity in inflammatory diseases and cancers, while hold promise for precise treatment of neutrophil-related diseases.

Systemic alterations in neutrophils and their precursors in early-stage chronic obstructive pulmonary disease

Systemic inflammation is established as part of late-stage severe lung disease, but molecular, functional, and phenotypic changes in peripheral immune cells in early disease stages remain ill defined. Chronic obstructive pulmonary disease (COPD) is a major respiratory disease characterized by small-airway inflammation, emphysema, and severe breathing difficulties. Using single-cell analyses we demonstrate that blood neutrophils are already increased in early-stage COPD, and changes in molecular and functional neutrophil states correlate with lung function decline. Assessing neutrophils and their bone marrow precursors in a murine cigarette smoke exposure model identified similar molecular changes in blood neutrophils and precursor populations that also occur in the blood and lung. Our study shows that systemic molecular alterations in neutrophils and their precursors are part of early-stage COPD, a finding to be further explored for potential therapeutic targets and biomarkers for early diagnosis and patient stratification.

Neutrophil diversity in inflammation and cancer

Neutrophils are the most abundant circulating leukocytes in humans and the first immune cells recruited at the site of inflammation. Classically perceived as short-lived effector cells with limited plasticity and diversity, neutrophils are now recognized as highly heterogenous immune cells, which can adapt to various environmental cues. In addition to playing a central role in the host defence, neutrophils are involved in pathological contexts such as inflammatory diseases and cancer. The prevalence of neutrophils in these conditions is usually associated with detrimental inflammatory responses and poor clinical outcomes. However, a beneficial role for neutrophils is emerging in several pathological contexts, including in cancer. Here we will review the current knowledge of neutrophil biology and heterogeneity in steady state and during inflammation, with a focus on the opposing roles of neutrophils in different pathological contexts.

Origin and Heterogeneity of Tissue Myeloid Cells: A Focus on GMP-Derived Monocytes and Neutrophils

Myeloid cells are a significant proportion of leukocytes within tissues, comprising granulocytes, monocytes, dendritic cells, and macrophages. With the identification of various myeloid cells that perform separate but complementary functions during homeostasis and disease, our understanding of tissue myeloid cells has evolved significantly. Exciting findings from transcriptomics profiling and fate-mapping mouse models have facilitated the identification of their developmental origins, maturation, and tissue-specific specializations. This review highlights the current understanding of tissue myeloid cells and the contributing factors of functional heterogeneity to better comprehend the complex and dynamic immune interactions within the healthy or inflamed tissue. Specifically, we discuss the new understanding of the contributions of granulocyte-monocyte progenitor-derived phagocytes to tissue myeloid cell heterogeneity as well as the impact of niche-specific factors on monocyte and neutrophil phenotype and function. Lastly, we explore the developing paradigm of myeloid cell heterogeneity during inflammation and disease.

Single-cell dissection of human hematopoietic reconstitution after allogeneic hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation is an effective regenerative therapy for many malignant, inherited, or autoimmune diseases. However, our understanding of reconstituted hematopoiesis in transplant patients remains limited. Here, we uncover the reconstitution dynamics of human allogeneic hematopoietic stem and progenitor cells (HSPCs) at single-cell resolution after transplantation. Transplanted HSPCs underwent rapid and measurable changes during the first 30 days after transplantation, characterized by a strong proliferative response on the first day. Transcriptomic analysis of HSPCs enabled us to observe that immunoregulatory neutrophil progenitors expressing high levels of the S100A gene family were enriched in granulocyte colony-stimulating factor-mobilized peripheral blood stem cells. Transplant recipients who developed acute graft-versus-host disease (aGVHD) infused fewer S100A^high immunoregulatory neutrophil progenitors, immunophenotyped as Lin^-CD34⁺CD66b⁺CD177⁺, than those who did not develop aGVHD. Therefore, our study provides insights into the regenerative process of transplanted HSPCs in human patients and identifies a potential criterion for identifying patients at high risk for developing aGVHD early after transplant.

The role of neutrophils in trained immunity

The principle of trained immunity represents innate immune memory due to sustained, mainly epigenetic, changes triggered by endogenous or exogenous stimuli in bone marrow (BM) progenitors (central trained immunity) and their innate immune cell progeny, thereby triggering elevated responsiveness against secondary stimuli. BM progenitors can respond to microbial and sterile signals, thereby possibly acquiring trained immunity-mediated long-lasting alterations that may shape the fate and function of their progeny, for example, neutrophils. Neutrophils, the most abundant innate immune cell population, are produced in the BM from committed progenitor cells in a process designated granulopoiesis. Neutrophils are the first responders against infectious or inflammatory challenges and have versatile functions in immunity. Together with other innate immune cells, neutrophils are effectors of peripheral trained immunity. However, given the short lifetime of neutrophils, their ability to acquire immunological memory may lie in the central training of their BM progenitors resulting in generation of reprogrammed, that is, "trained", neutrophils. Although trained immunity may have beneficial effects in infection or cancer, it may also mediate detrimental outcomes in chronic inflammation. Here, we review the emerging research area of trained immunity with a particular emphasis on the role of neutrophils and granulopoiesis.

The early neutrophil-committed progenitors aberrantly differentiate into immunoregulatory monocytes during emergency myelopoiesis

Inflammatory stimuli cause a state of emergency myelopoiesis leading to neutrophil-like monocyte expansion. However, their function, the committed precursors, or growth factors remain elusive. In this study we find that Ym1⁺Ly6C^hi monocytes, an immunoregulatory entity of neutrophil-like monocytes, arise from progenitors of neutrophil 1 (proNeu1). Granulocyte-colony stimulating factor (G-CSF) favors the production of neutrophil-like monocytes through previously unknown CD81⁺CX3CR1^lo monocyte precursors. GFI1 promotes the differentiation of proNeu2 from proNeu1 at the cost of producing neutrophil-like monocytes. The human counterpart of neutrophil-like monocytes that also expands in response to G-CSF is found in CD14⁺CD16^- monocyte fraction. The human neutrophil-like monocytes are discriminated from CD14⁺CD16^- classical monocytes by CXCR1 expression and the capacity to suppress T cell proliferation. Collectively, our findings suggest that the aberrant expansion of neutrophil-like monocytes under inflammatory conditions is a process conserved between mouse and human, which may be beneficial for the resolution of inflammation.

A single-cell map of peripheral alterations after FMT treatment in patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by loss of self-tolerance and persistent self-aggression, sustained chronic inflammation, production of autoantibodies and multi-system damage, and is largely incurable to date. The gut microbiota and its metabolites, now recognized as crucial environmental triggers of local/systemic immune reactions, have been implicated in the development and progression of SLE. Fecal microbiota transplantation (FMT) is restoration of disturbed microbiota by transplanting foreign gut microbiota from healthy individuals into the gastrointestinal tract of diseased individuals. Our previous clinical trial suggests that FMT is a potentially safe and effective treatment for SLE. In order to elucidate the potential effect of FMT on peripheral immune cells of patients with SLE, we collected PBMCs (n = 30) of 13 SLE patients who participated in the clinical trial before and after the FMT-treatment, and performed single-cell RNA sequencing. The results first revealed that peripheral T lymphocytes of SLE patients decreased and NK cells increased after the FMT treatment. Then, sub-clustering analysis discovered that total CD4⁺ T cells highly expressed genes of IL7R, CD28, and CD8⁺ T cells highly expressed genes of GZMH and NKG7 after FMT treatment. Moreover, FMT treatment reduced the expression of interferon-related genes (IRGs) in CD4⁺ T, CD8⁺ T, DP, NK, and B cells of SLE patients. More importantly, interferon-related pathways were more enriched in cells of the FMT non-responder group, and further the interferon genes expression of lymphocytes and myeloid cells was negatively correlated with the efficiency of FMT treatment. Collectively, our data identified various immunophenotypic and associated gene set changes following FMT treatment, illustrating the heterogeneity of response to FMT treatment in SLE.

CD14+-Monocytes Exposed to Apolipoprotein CIII Express Tissue Factor

Apolipoprotein CIII (ApoCIII) represents a key regulator of plasma lipid metabolism and a recognized risk factor for atherosclerosis and cardiovascular diseases. Beyond the regulation of lipoprotein trafficking, ApoCIII is also involved in endothelial dysfunction and monocyte recruitment related to atherothrombosis. With tissue factor (TF) being the primary initiator of the blood coagulation cascade, we hypothesized that ApoCIII-treated monocytes could express it. Hence, human CD14⁺-monocytes and autologous neutrophils were incubated with ApoCIII and sera from human subjects containing previously measured ApoCIII amounts. By RT-qPCR and ELISA, CD14⁺-monocytes, but not neutrophils, were found to show increased mRNA expression and production of TNFα, IL-1β and IL-6 as well as TF mRNA once exposed to ultra-purified ApoCIII. By flow cytometry, CD14⁺-monocytes were found to rapidly express TF on their cell surface membrane when incubated with either ApoCIII or sera with known concentrations of ApoCIII. Finally, preincubation with specific ApoCIII-neutralizing antibodies significantly reduced the ability of most sera with known concentrations of ApoCIII to upregulate TF protein, other than partially inhibiting cytokine release, in CD14⁺-monocytes. In sum, herein we demonstrate that ApoCIII activates CD14⁺-monocytes to express TF. The data identify a potential mechanism which links circulating apolipoproteins with inflammation and atherothrombosis-related processes underlying cardiovascular risk.

Improving the performance of single-cell RNA-seq data mining based on relative expression orderings

The advent of single-cell RNA-sequencing (scRNA-seq) provides an unprecedented opportunity to explore gene expression profiles at the single-cell level. However, gene expression values vary over time and under different conditions even within the same cell. There is an urgent need for more stable and reliable feature variables at the single-cell level to depict cell heterogeneity. Thus, we construct a new feature matrix called the delta rank matrix (DRM) from scRNA-seq data by integrating an a priori gene interaction network, which transforms the unreliable gene expression value into a stable gene interaction/edge value on a single-cell basis. This is the first time that a gene-level feature has been transformed into an interaction/edge-level for scRNA-seq data analysis based on relative expression orderings. Experiments on various scRNA-seq datasets have demonstrated that DRM performs better than the original gene expression matrix in cell clustering, cell identification and pseudo-trajectory reconstruction. More importantly, the DRM really achieves the fusion of gene expressions and gene interactions and provides a method of measuring gene interactions at the single-cell level. Thus, the DRM can be used to find changes in gene interactions among different cell types, which may open up a new way to analyze scRNA-seq data from an interaction perspective. In addition, DRM provides a new method to construct a cell-specific network for each single cell instead of a group of cells as in traditional network construction methods. DRM's exceptional performance is due to its extraction of rich gene-association information on biological systems and stable characterization of cells.

N1 versus N2 and PMN-MDSC: A critical appraisal of current concepts on tumor-associated neutrophils and new directions for human oncology

Research on tumor-associated neutrophils (TAN) currently surges because of the well-documented strong clinical relevance of tumor-infiltrating neutrophils. This relevance is illustrated by strong correlations between high frequencies of intratumoral neutrophils and poor outcome in the majority of human cancers. Recent high-dimensional analysis of murine neutrophils provides evidence for unexpected plasticity of neutrophils in murine models of cancer and other inflammatory non-malignant diseases. New analysis tools enable deeper insight into the process of neutrophil differentiation and maturation. These technological and scientific developments led to the description of an ever-increasing number of distinct transcriptional states and associated phenotypes in murine models of disease and more recently also in humans. At present, functional validation of these different transcriptional states and potential phenotypes in cancer is lacking. Current functional concepts on neutrophils in cancer rely mainly on the myeloid-derived suppressor cell (MDSC) concept and the dichotomous and simple N1-N2 paradigm. In this manuscript, we review the historic development of those concepts, critically evaluate these concepts against the background of our own work and provide suggestions for a refinement of current concepts in order to facilitate the transition of TAN research from experimental insight to clinical translation.

Current knowledge on the early stages of human neutropoiesis

Polymorphonuclear neutrophils are no longer considered as a homogeneous population of terminally differentiated and short-lived cells that belong to the innate immune system only. In fact, data from the past decades have uncovered that neutrophils exhibit large phenotypic heterogeneity and functional versatility that render them more plastic than previously thought. Hence, their precise role as effector cells in inflammation, in immune response and in other pathophysiological processes, including tumors, needs to be better evaluated. In such a complex scenario, common knowledge of the differentiation of neutrophils in bone marrow refers to lineage precursors, starting from the still poorly defined myeloblasts, and proceeding sequentially to promyelocytes, myelocytes, metamyelocytes, band cells, segmented neutrophils, and mature neutrophils, with each progenitor stage being more mature and better characterized. Thanks to the development and utilization of cutting-edge technologies, novel information about neutrophil precursors at stages earlier than the promyelocytes, hence closer to the hematopoietic stem cells, is emerging. Accordingly, this review discusses the main findings related to the very early precursors of human neutrophils and provides our perspectives on human neutropoiesis.

Cellular and transcriptional dynamics of human neutrophils at steady state and upon stress

Traditionally viewed as poorly plastic, neutrophils are now recognized as functionally diverse; however, the extent and determinants of neutrophil heterogeneity in humans remain unclear. We performed a comprehensive immunophenotypic and transcriptome analysis, at a bulk and single-cell level, of neutrophils from healthy donors and patients undergoing stress myelopoiesis upon exposure to growth factors, transplantation of hematopoietic stem cells (HSC-T), development of pancreatic cancer and viral infection. We uncover an extreme diversity of human neutrophils in vivo, reflecting the rates of cell mobilization, differentiation and exposure to environmental signals. Integrated control of developmental and inducible transcriptional programs linked flexible granulopoietic outputs with elicitation of stimulus-specific functional responses. In this context, we detected an acute interferon (IFN) response in the blood of patients receiving HSC-T that was mirrored by marked upregulation of IFN-stimulated genes in neutrophils but not in monocytes. Systematic characterization of human neutrophil plasticity may uncover clinically relevant biomarkers and support the development of diagnostic and therapeutic tools.

Refractory pemphigus vulgaris and high-intensity extracorporeal photopheresis: A case report

A 41-year-old man with oral pemphigus vulgaris (PV) presented to our clinic with a history of no response to numerous immunosuppressant agents and was referred for extracorporeal photopheresis (ECP) therapy. Although the patient underwent a high-intensity ECP regimen for five months, which included two different photopheresis systems, his oral dysesthesia continued to interfere with oral intake, leading to continued weight loss and other adverse events. The intervention was associated with changes in several immune cell subpopulations without modifying the anti-epidermal antibody titers, aligned with his poor clinical outcome. To the best of the authors' knowledge, this is the first report to examine immunophenotyping of a PV patient who was refractory to previous immunosuppression and recalcitrant to high-intensity ECP therapy.

Neutrophils: Musketeers against immunotherapy

Neutrophils, the most copious leukocytes in human blood, play a critical role in tumorigenesis, cancer progression, and immune suppression. Recently, neutrophils have attracted the attention of researchers, immunologists, and oncologists because of their potential role in orchestrating immune evasion in human diseases including cancer, which has led to a hot debate redefining the contribution of neutrophils in tumor progression and immunity. To make this debate fruitful, this review seeks to provide a recent update about the contribution of neutrophils in immune suppression and tumor progression. Here, we first described the molecular pathways through which neutrophils aid in cancer progression and orchestrate immune suppression/evasion. Later, we summarized the underlying molecular mechanisms of neutrophil-mediated therapy resistance and highlighted various approaches through which neutrophil antagonism may heighten the efficacy of the immune checkpoint blockade therapy. Finally, we have highlighted several unsolved questions and hope that answering these questions will provide a new avenue toward immunotherapy revolution.

Dissecting the process of human neutrophil lineage determination by using alpha-lipoic acid inducing neutrophil deficiency model

Granulocyte-monocyte progenitors (GMPs) differentiate into both neutrophils and monocytes. Recently, uni-potential neutrophil progenitors have been identified both in mice and humans using an array of surface markers. However, how human GMPs commit to neutrophil progenitors and the regulatory mechanisms of fate determination remain incompletely understood. In the present study, we established a human neutrophil deficiency model using the small molecule alpha-lipoic acid. Using this neutrophil deficiency model, we determined that the neutrophil progenitor commitment process from CD371⁺ CD115^– GMPs defined by CD34 and CD15 and discovered that critical signals generated by RNA splicing and rRNA biogenesis regulate the process of early commitment for human early neutrophil progenitors derived from CD371⁺ CD115^– GMPs. These processes were elucidated by single-cell RNA sequencing both in vitro and in vivo derived cells. Sequentially, we identified that the transcription factor ELK1 is essential for human neutrophil lineage commitment using the alpha-lipoic acid (ALA)-inducing neutrophil deficiency model. Finally, we also revealed differential roles for long-ELK1 and short-ELK1, balanced by SF3B1, in the commitment process of neutrophil progenitors. Taken together, we discovered a novel function of ALA in regulating neutrophil lineage specification and identified that the SF3B1-ELK axis regulates the commitment of human neutrophil progenitors from CD371⁺ CD115^– GMPs.

•

ALA completely blocks the differentiation of human neutrophils derived from CD34⁺ stem cells in ex-vivo culture.

•

CD34 and CD15 could be used to define the early differentiation stages of human neutrophil lineage determination.

•

SF3B1-ELK1 signal axis regulates human neutrophil lineage determination.