A single-cell pan-cancer analysis to show the variability of tumor-infiltrating myeloid cells in immune checkpoint blockade.

Myeloid cells are vital components of the immune system and have pivotal functions in orchestrating immune responses. Understanding their functions within the tumor microenvironment and their interactions with tumor-infiltrating lymphocytes presents formidable challenges across diverse cancer types, particularly with regards to cancer immunotherapies. Here, we explore tumor-infiltrating myeloid cells (TIMs) by conducting a pan-cancer analysis using single-cell transcriptomics across eight distinct cancer types, encompassing a total of 192 tumor samples from 129 patients. By examining gene expression patterns and transcriptional activities of TIMs in different cancer types, we discern notable alterations in abundance of TIMs and kinetic behaviors prior to and following immunotherapy. We also identify specific cell-cell interaction targets in immunotherapy; unique and shared regulatory profiles critical for treatment response; and TIMs associated with survival outcomes. Overall, our study illuminates the heterogeneity of TIMs and improves our understanding of tissue-specific and cancer-specific myeloid subsets within the context of tumor immunotherapies.

Single-cell transcriptomics analysis of bullous pemphigoid unveils immune-stromal crosstalk in type 2 inflammatory disease.

Bullous pemphigoid (BP) is a type 2 inflammation- and immunity-driven skin disease, yet a comprehensive understanding of the immune landscape, particularly immune-stromal crosstalk in BP, remains elusive. Herein, using single-cell RNA sequencing (scRNA-seq) and in vitro functional analyzes, we pinpoint Th2 cells, dendritic cells (DCs), and fibroblasts as crucial cell populations. The IL13-IL13RA1 ligand-receptor pair is identified as the most significant mediator of immune-stromal crosstalk in BP. Notably, fibroblasts and DCs expressing IL13RA1 respond to IL13-secreting Th2 cells, thereby amplifying Th2 cell-mediated cascade responses, which occurs through the specific upregulation of PLA2G2A in fibroblasts and CCL17 in myeloid cells, creating a positive feedback loop integral to immune-stromal crosstalk. Furthermore, PLA2G2A and CCL17 contribute to an increased titer of pathogenic anti-BP180-NC16A autoantibodies in BP patients. Our work provides a comprehensive insight into BP pathogenesis and shows a mechanism governing immune-stromal interactions, providing potential avenues for future therapeutic research.

Tumor cell-directed STING agonist antibody-drug conjugates induce type III interferons and anti-tumor innate immune responses.

Activating interferon responses with STING agonists (STINGa) is a current cancer immunotherapy strategy, and therapeutic modalities that enable tumor-targeted delivery via systemic administration could be beneficial. Here we demonstrate that tumor cell-directed STING agonist antibody-drug-conjugates (STINGa ADCs) activate STING in tumor cells and myeloid cells and induce anti-tumor innate immune responses in in vitro, in vivo (in female mice), and ex vivo tumor models. We show that the tumor cell-directed STINGa ADCs are internalized into myeloid cells by Fcγ-receptor-I in a tumor antigen-dependent manner. Systemic administration of STINGa ADCs in mice leads to STING activation in tumors, with increased anti-tumor activity and reduced serum cytokine elevations compared to a free STING agonist. Furthermore, STINGa ADCs induce type III interferons, which contribute to the anti-tumor activity by upregulating type I interferon and other key chemokines/cytokines. These findings reveal an important role for type III interferons in the anti-tumor activity elicited by STING agonism and provide rationale for the clinical development of tumor cell-directed STINGa ADCs.

TSG-6+ cancer-associated fibroblasts modulate myeloid cell responses and impair anti-tumor response to immune checkpoint therapy in pancreatic cancer.

Resistance to immune checkpoint therapy (ICT) presents a growing clinical challenge. The tumor microenvironment (TME) and its components, namely tumor-associated macrophages (TAMs) and cancer-associated fibroblasts (CAFs), play a pivotal role in ICT resistance; however, the underlying mechanisms remain under investigation. In this study, we identify expression of TNF-Stimulated Factor 6 (TSG-6) in ICT-resistant pancreatic tumors, compared to ICT-sensitive melanoma tumors, both in mouse and human. TSG-6 is expressed by CAFs within the TME, where suppressive macrophages expressing Arg1, Mafb, and Mrc1, along with TSG-6 ligand Cd44, predominate. Furthermore, TSG-6 expressing CAFs co-localize with the CD44 expressing macrophages in the TME. TSG-6 inhibition in combination with ICT improves therapy response and survival in pancreatic tumor-bearing mice by reducing macrophages expressing immunosuppressive phenotypes and increasing CD8 T cells. Overall, our findings propose TSG-6 as a therapeutic target to enhance ICT response in non-responsive tumors.

Immediate myeloid depot for SARS-CoV-2 in the human lung.

In the pathogenesis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, epithelial populations in the distal lung expressing Angiotensin-converting enzyme 2 (ACE2) are infrequent, and therefore, the model of viral expansion and immune cell engagement remains incompletely understood. Using human lungs to investigate early host-viral pathogenesis, we found that SARS-CoV-2 had a rapid and specific tropism for myeloid populations. Human alveolar macrophages (AMs) reliably expressed ACE2 allowing both spike-ACE2-dependent viral entry and infection. In contrast to Influenza A virus, SARS-CoV-2 infection of AMs was productive, amplifying viral titers. While AMs generated new viruses, the interferon responses to SARS-CoV-2 were muted, hiding the viral dissemination from specific antiviral immune responses. The reliable and veiled viral depot in myeloid cells in the very early phases of SARS-CoV-2 infection of human lungs enables viral expansion in the distal lung and potentially licenses subsequent immune pathologies.

Myeloid cell differentiation-related gene signature for predicting clinical outcome, immune microenvironment, and treatment response in lung adenocarcinoma.

Considering the key role of myeloid cell differentiation-related genes in the tumor microenvironment (TME), we aimed to build a prognostic risk model using these genes for Lung adenocarcinoma (LUAD). The mRNA gene expression profiles of LUAD patients from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases were downloaded as the training and validation sets. Then, "edgeR" R package was applied to screen out the differentially expressed genes (DEGs) and univariate cox regression, backward stepwise selection analyses were performed to construct a prognostic model for LUAD. ESTIMATE, TIMER, XCELL, CIBERSORT abs, QUANTISEQ, MCPCOUNTER, EPIC, and CIBERSORT algorithms were conducted to access the association of risk levels with the stromal and immune cell infiltration levels in LUAD. Six genes (F2RL1, PRKDC, TNFSF11, INHA, PLA2G3 and TUBB1) were utilized to construct the prognostic model. The risk model showed excellent prognostic performance for LUAD in both TCGA and GEO datasets. Also, compared to the low-risk patients, the high-risk patients had higher expression of immune checkpoint molecules and showed a lower IC50 value to the chemotherapy agents. Our findings provided a myeloid cell differentiation-related gene signature that could effectively predict prognosis and guide treatment strategies for LUAD patients.

The Expression of Non B Cell-Derived Immunoglobulins.

Although V(D)J recombination and immunoglobulin (Ig) production are traditionally recognised to occur only in B lymphocytes and plasma cells, the expression of Igs in non-lymphoid cells, which we call non B cell-derived Igs (non B Igs), has been documented by growing studies. It has been demonstrated that non B-Igs can be widely expressed in most cell types, including, but not limited to, epithelial cells, cardiomyocytes, hematopoietic stem/progenitor cells, myeloid cells, and cells from immune-privileged sites, such as neurons and spermatogenic cells. In particular, malignant tumour cells express high level of IgG. Moreover, different from B-Igs that mainly localised on the B cell membrane and in the serum and perform immune defence function mainly, non B-Igs have been found to distribute more widely and play critical roles in immune defence, maintaining cell proliferation and survival, and promoting progression. The findings of non B-Igs may provide a wealthier breakthrough point for more therapeutic strategies for a wide range of immune-related diseases.

IVT-mRNA reprogramming of myeloid cells for cancer immunotherapy.

In the past decade, in vitro transcribed messenger RNAs (IVT-mRNAs) have emerged as promising therapeutic molecules. The clinical success of COVID-19 mRNA vaccines developed by Pfizer-BioNTech and Moderna, have demonstrated that IVT-mRNAs can be safely and successfully used in a clinical setting, and efforts are underway to develop IVT-mRNAs for therapeutic applications. Current applications of mRNA-based therapy have been focused on (1) mRNA vaccines for infectious diseases and cancer treatment; (2) protein replacement therapy; (3) gene editing therapy; and (4) cell-reprogramming therapies. Due to the recent clinical progress of cell-based immunotherapies, the last direction-the use of IVT-mRNAs as a therapeutic approach to program immune cells for the treatment of cancer has received extensive attention from the cancer immunotherapy field. Myeloid cells are important components of our immune system, and they play critical roles in mediating disease progression and regulating immunity against diseases. In this chapter, we discussed the progress of using IVT-mRNAs as a therapeutic approach to program myeloid cells against cancer and other immune-related diseases. Towards this direction, we first reviewed the pharmacology of IVT-mRNAs and the biology of myeloid cells as well as myeloid cell-targeting therapeutics. We then presented a few cases of current IVT-mRNA-based approaches to target and reprogram myeloid cells for disease treatment and discussed the advantages and limitations of these approaches. Finally, we presented our considerations in designing mRNA-based approaches to target myeloid cells for disease treatment.

Mapping myeloid cell function: Spatial diversity in tumor and neuronal microenvironment.

In this issue of Cancer Cell, Zhong et al. explore the dual role of TREM2 in glioblastoma-associated myeloid cells, demonstrating its function in promoting inflammation at the tumor-neural interface and suppression within the tumor core, influenced by the local microenvironment. These findings open up promising prospects for advancements in neuro-oncological immunotherapy.

Crosstalk between efferocytic myeloid cells and T-cells and its relevance to atherosclerosis.

The interplay between myeloid cells and T-lymphocytes is critical to the regulation of host defense and inflammation resolution. Dysregulation of this interaction can contribute to the development of chronic inflammatory diseases. Important among these diseases is atherosclerosis, which refers to focal lesions in the arterial intima driven by elevated apolipoprotein B-containing lipoproteins, notably low-density lipoprotein (LDL), and characterized by the formation of a plaque composed of inflammatory immune cells, a collection of dead cells and lipids called the necrotic core, and a fibrous cap. As the disease progresses, the necrotic core expands, and the fibrous cap becomes thin, which increases the risk of plaque rupture or erosion. Plaque rupture leads to a rapid thrombotic response that can give rise to heart attack, stroke, or sudden death. With marked lowering of circulating LDL, however, plaques become more stable and cardiac risk is lowered-a process known as atherosclerosis regression. A critical aspect of both atherosclerosis progression and regression is the crosstalk between innate (myeloid cells) and adaptive (T-lymphocytes) immune cells. Myeloid cells are specialized at clearing apoptotic cells by a process called efferocytosis, which is necessary for inflammation resolution. In advanced disease, efferocytosis is impaired, leading to secondary necrosis of apoptotic cells, inflammation, and, most importantly, defective tissue resolution. In regression, efferocytosis is reawakened aiding in inflammation resolution and plaque stabilization. Here, we will explore how efferocytosing myeloid cells could affect T-cell function and vice versa through antigen presentation, secreted factors, and cell-cell contacts and how this cellular crosstalk may contribute to the progression or regression of atherosclerosis.

Characterising plasmacytoid and myeloid AXL+ SIGLEC-6+ dendritic cell functions and their interactions with HIV.

AXL+ Siglec-6+ dendritic cells (ASDC) are novel myeloid DCs which can be subdivided into CD11c+ and CD123+ expressing subsets. We showed for the first time that these two ASDC subsets are present in inflamed human anogenital tissues where HIV transmission occurs. Their presence in inflamed tissues was supported by single cell RNA analysis of public databases of such tissues including psoriasis diseased skin and colorectal cancer. Almost all previous studies have examined ASDCs as a combined population. Our data revealed that the two ASDC subsets differ markedly in their functions when compared with each other and to pDCs. Relative to their cell functions, both subsets of blood ASDCs but not pDCs expressed co-stimulatory and maturation markers which were more prevalent on CD11c+ ASDCs, thus inducing more T cell proliferation and activation than their CD123+ counterparts. There was also a significant polarisation of naïve T cells by both ASDC subsets toward Th2, Th9, Th22, Th17 and Treg but less toward a Th1 phenotype. Furthermore, we investigated the expression of chemokine receptors that facilitate ASDCs and pDCs migration from blood to inflamed tissues, their HIV binding receptors, and their interactions with HIV and CD4 T cells. For HIV infection, within 2 hours of HIV exposure, CD11c+ ASDCs showed a trend in more viral transfer to T cells than CD123+ ASDCs and pDCs for first phase transfer. However, for second phase transfer, CD123+ ASDCs showed a trend in transferring more HIV than CD11c+ ASDCs and there was no viral transfer from pDCs. As anogenital inflammation is a prerequisite for HIV transmission, strategies to inhibit ASDC recruitment into inflamed tissues and their ability to transmit HIV to CD4 T cells should be considered.

Plasma membrane abundance dictates phagocytic capacity and functional cross-talk in myeloid cells.

Professional phagocytes like neutrophils and macrophages tightly control what they consume, how much they consume, and when they move after cargo uptake. We show that plasma membrane abundance is a key arbiter of these cellular behaviors. Neutrophils and macrophages lacking the G protein subunit Gß4 exhibited profound plasma membrane expansion, accompanied by marked reduction in plasma membrane tension. These biophysical changes promoted the phagocytosis of bacteria, fungus, apoptotic corpses, and cancer cells. We also found that Gß4-deficient neutrophils are defective in the normal inhibition of migration following cargo uptake. Sphingolipid synthesis played a central role in these phenotypes by driving plasma membrane accumulation in cells lacking Gß4. In Gß4 knockout mice, neutrophils not only exhibited enhanced phagocytosis of inhaled fungal conidia in the lung but also increased trafficking of engulfed pathogens to other organs. Together, these results reveal an unexpected, biophysical control mechanism central to myeloid functional decision-making.

Expression of modified FcγRI enables myeloid cells to elicit robust tumor-specific cytotoxicity.

Despite the central role of T cells in tumor immunity, attempts to harness their cytotoxic capacity as a therapy have met limited efficacy, partially as a result of the suppressive microenvironment which limits their migration and activation. In contrast, myeloid cells massively infiltrate tumors and are well adapted to survive these harsh conditions. While they are equipped with cell-killing abilities, they often adopt an immunosuppressive phenotype upon migration to tumors. Therefore, the questions of how to modify their activation programming against cancer, and what signaling cascades should be activated in myeloid cells to elicit their cytotoxicity have remained unclear. Here, we found that activation of IgM-induced signaling in murine myeloid cells results in secretion of lytic granules and massive tumor cell death. These findings open venues for designing novel immunotherapy by equipping monocytes with chimeric receptors that target tumor antigens and consequently, signal through IgM receptor. Nonetheless, we found that myeloid cells do not express the antibody-derived portion used to recognize the tumor antigen due to the induction of an ER stress response. To overcome this limitation, we designed chimeric receptors that are based on the high-affinity FcγRI for IgG. Incubation of macrophages expressing these receptors along with tumor-binding IgG induced massive tumor cell killing and secretion of reactive oxygen species and Granzyme B. Overall, this work highlights the challenges involved in genetically reprogramming the signaling in myeloid cells and provides a framework for endowing myeloid cells with antigen-specific cytotoxicity.

Intra-bone marrow mesenchymal stem cell transplantation modulates myeloid bias tendency of hematopoietic stem and progenitor cells in severe MRL/lpr lupus mice.

The hematopoietic homeostasis in the bone marrow is inextricably intertwined with the immune milieu in peripheral circulation. Researches investigating the pathogenesis of systemic lupus erythematosus (SLE) have defined considerable secretion of inflammatory mediators and activation of pro-inflammatory cells. However, the impacts of "extrinsic" factors on hematopoietic stem and progenitor cells (HSPCs) remain unclear, and it is uncertain whether treatments can help coordinate the biased differentiation. In this study, we showed differences in the proportions of common myeloid progenitors (CMP) and myeloid output in the bone marrow of premorbid and morbid MRL/lpr mice using flow cytometry. RNA-seq analysis of lineage-affiliated transcriptional factors and dysregulated genes within lin- HSPCs revealed inflammation potentiation during disease progression. Further, intra-bone marrow mesenchymal stem cells transplantation (IBM-MSCT) partially coordinated myeloid generation and counteracted lupus-associated inflammation gene alterations, compared to intravenous injection. Additionally, co-culturing with umbilical cord mesenchymal stem cells (UC-MSCs) intervened in myeloid lineage tendency, as detected by RT-qPCR of myeloid-related genes. Our research demonstrated enhanced tendency toward myeloid differentiation and highlighted the feasibility of IBM-MSCT for lineage-biased HSPCs in MRL/lpr lupus model, providing novel insight into hematopoiesis and MSC-related treatments for SLE.

Protocol for real-time monitoring of CD8+ T and myeloid cell behavior in human high-grade serous ovarian cancer slices.

Studying cell behavior in live human tumors is crucial to understand and improve response to immunotherapies. Here, we present a protocol to slice human ovarian tumors ex vivo, maintain their viability for 24 h, and monitor the behavior of CD8+ T and myeloid cells in real time. Furthermore, we detail procedures to semi-automatically analyze cell movements and aggregate and process behavior data. This protocol can potentially be applied for multiple tumor types and mouse cancer models. For complete details on the use and execution of this protocol, please refer to Laforets et al.1.

The role of myeloid differentiation of hematopoietic stem cells in pregnancy immunological tolerance: a systematic review.

The present research aimed to conduct a comprehensive critical analysis of existing literature, focusing on the differentiation of myeloid cells from hematopoietic stem cells within the context of immunological tolerance during pregnancy. A comprehensive systematic review was conducted by searching databases including PubMed, Scopus Biomedicine, EBSCOhost, ScienceDirect, Embase, Cochrane Library, and Web of Science. The focus was on the role of myeloid differentiation from hematopoietic stem cells in modulating immune tolerance, particularly during pregnancy and in certain disease states where they act to suppress the immune response. The quality of the evidence gathered was assessed using the GRADE rating system. Our analysis maintains objectivity and independence from the outcomes presented. The current systematic review offers a synthesis of existing research on the transformation of hematopoietic stem cells into fibroblasts across different tissue types. A thorough search of databases such as PubMed, EBSCOhost, Embase, ScienceDirect, Cochrane Library, and Web of Science was performed in conjunction with a specialist in medical information to identify original research on the derivation of fibroblasts following hematopoietic stem cell transplantation. This search yielded a total of 159 studies, of which 10 met the criteria for inclusion in this review. Reflecting on the constraints of this preliminary review, further in-depth and scientific investigations are warranted to comprehensively assess the impact of varied treatments, with a recommendation for clinicians to proceed with increased circumspection. The myeloid differentiation pathway of hematopoietic stem cells is pivotal in modulating the immune environment during pregnancy, supporting the sustenance of a healthy gestational period. Future research in this domain is expected to advance our understanding of the immunological processes occurring at the maternal-fetal boundary.

NR0B2 re-educates myeloid immune cells to reduce regulatory T cell expansion and progression of breast and other solid tumors.

Although survival from breast cancer has dramatically increased, many will develop recurrent, metastatic disease. Unfortunately, survival for this stage of disease remains very low. Activating the immune system has incredible promise since it has the potential to be curative. However, immune checkpoint blockade (ICB) which works through T cells has been largely disappointing for metastatic breast cancer. One reason for this is a suppressive myeloid immune compartment that is unaffected by ICB. Cholesterol metabolism and proteins involved in cholesterol homeostasis play important regulatory roles in myeloid cells. Here, we demonstrate that NR0B2, a nuclear receptor involved in negative feedback of cholesterol metabolism, works in several myeloid cell types to impair subsequent expansion of regulatory T cells (Tregs); Tregs being a subset known to be highly immune suppressive and associated with poor therapeutic response. Within myeloid cells, NR0B2 serves to decrease many aspects of the inflammasome, ultimately resulting in decreased IL1ß; IL1ß driving Treg expansion. Importantly, mice lacking NR0B2 exhibit accelerated tumor growth. Thus, NR0B2 represents an important node in myeloid cells dictating ensuing Treg expansion and tumor growth, thereby representing a novel therapeutic target to re-educate these cells, having impact across different solid tumor types. Indeed, a paper co-published in this issue demonstrates the therapeutic utility of targeting NR0B2.

Development of NR0B2 as a therapeutic target for the re-education of tumor associated myeloid cells.

Immune checkpoint blockade (ICB) has had limited utility in several solid tumors such as breast cancer, a major cause of cancer-related mortality in women. Therefore, there is considerable interest in alternate strategies to promote an anti-cancer immune response. A paper co-published in this issue describes how NR0B2, a protein involved in cholesterol homeostasis, functions within myeloid immune cells to modulate the inflammasome and reduce the expansion of immune-suppressive regulatory T cells (Treg). Here, we develop NR0B2 as a potential therapeutic target. NR0B2 in tumors is associated with improved survival for several cancer types including breast. Importantly, NR0B2 expression is also prognostic of ICB success. Within breast tumors, NR0B2 expression is inversely associated with FOXP3, a marker of Tregs. While a described agonist (DSHN) had some efficacy, it required high doses and long treatment times. Therefore, we designed and screened several derivatives. A methyl ester derivative (DSHN-OMe) emerged as superior in terms of (1) cellular uptake, (2) ability to regulate expected expression of genes, (3) suppression of Treg expansion using in vitro co-culture systems, and (4) efficacy against the growth of primary and metastatic tumors. This work identifies NR0B2 as a target to re-educate myeloid immune cells and a novel ligand with significant anti-tumor efficacy in preclinical models.

Identification and functional analyses of CD4-1+ cells in grass carp (Ctenopharyngodon idella).

In mammals, CD4 is found to be expressed on T cells and innate immune cells, however, teleost cells bearing CD4 have not been well identified and characterized. In this study, we identified two different CD4-1+ cell subsets in grass carp (Ctenopharyngodon idella): CD4-1+ lymphocytes (Lym) and CD4-1+ myeloid cells (Mye), both of which had the highest proportions in the head kidney. The mRNA expression analysis showed that CD4-1, CD4-2, TCRß, CD3γ/δ, and LCK1 are highly expressed in CD4-1+ Lym and also expressed in CD4-1+ Mye. Furthermore, we found that CD4-1+ Lym have a Lym morphology and highly express T-cell cytokines, suggesting that they are CD4+ T cells equivalent to mammalian Th cells. On the other hand, CD4-1+ Mye were found to have a morphology of macrophage and highly express macrophage marker gene MCSFR, indicating that they are macrophages. In addition, functional analysis revealed that CD4-1+ Mye possess phagocytic ability and great antigen-processing ability. Taken together, our study sheds further light on the composition and function of CD4+ cells in teleost fish.