A temporal perspective for tumor-associated macrophage identities and functions

Polarized Macrophages Show Diverse Pro-Angiogenic Characteristics Under Normo- and Hyperglycemic Conditions

Angiogenesis plays a crucial role in solid tumor growth. Ischemia and inflammation induce various angiogenic mediators, and patient metabolic conditions importantly influence this process. Macrophages closely interact with the vascular system and regulate angiogenesis through pro/anti-angiogenic factors. Traditionally, pro-angiogenic activity has been attributed to M2-like macrophages. We question this, as recent evidence suggests that also M1-like macrophages can be pro-angiogenic. Therefore, the aim is to identify the pro/anti-angiogenic gene expression profiles of human polarized macrophages unbiasedly. We also examine the effect of hyperglycemia on angiogenic gene expression, reflecting its role in diabetes and other metabolic conditions. Bioinformatic analysis was performed on the angiogenesis-related gene expression profiles of CD14+ monocyte-derived M1(IFN-γ)- and M2(IL-4)-polarized macrophages. The top differentially expressed genes were selected for validation. Macrophages were generated in vitro and polarized to M1(IFN-γ) and M2(IL-4/IL-6) cells under standard/hyperglycemic conditions. After immunophenotypic confirmation, selected gene expression was quantified using qPCR. IL-4 and IL-6 induce distinct M2-like phenotypes with mixed pro/anti-angiogenic gene expression. Remarkably, IFN-γ stimulation also increases several pro-angiogenic genes. Hyperglycemia affects the angiogenic expression profile in both M1- and M2-like macrophages, although distinctive identities remain intact. The pro-angiogenic phenotype is not limited to M2-polarized macrophages. Both M1- and M2-like macrophages express complex pro/anti-angiogenic gene profiles, which are only mildly influenced by hyperglycemia.

Tumor-associated macrophages remodel the suppressive tumor immune microenvironment and targeted therapy for immunotherapy

Despite the significant advances in the development of immune checkpoint inhibitors (ICI), primary and acquired ICI resistance remains the primary impediment to effective cancer immunotherapy. Residing in the tumor microenvironment (TME), tumor-associated macrophages (TAMs) play a pivotal role in tumor progression by regulating diverse signaling pathways. Notably, accumulating evidence has confirmed that TAMs interplay with various cellular components within the TME directly or indirectly to maintain the dynamic balance of the M1/M2 ratio and shape an immunosuppressive TME, consequently conferring immune evasion and immunotherapy tolerance. Detailed investigation of the communication network around TAMs could provide potential molecular targets and optimize ICI therapies. In this review, we systematically summarize the latest advances in understanding the origin and functional plasticity of TAMs, with a focus on the key signaling pathways driving macrophage polarization and the diverse stimuli that regulate this dynamic process. Moreover, we elaborate on the intricate interplay between TAMs and other cellular constituents within the TME, that is driving tumor initiation, progression and immune evasion, exploring novel targets for cancer immunotherapy. We further discuss current challenges and future research directions, emphasizing the need to decode TAM-TME interactions and translate preclinical findings into clinical breakthroughs. In conclusion, while TAM-targeted therapies hold significant promise for enhancing immunotherapy outcomes, addressing key challenges-such as TAM heterogeneity, context-dependent plasticity, and therapeutic resistance-remains critical to achieving optimal clinical efficacy.

MicroRNA-induced reprogramming of tumor-associated macrophages for modulation of tumor immune microenvironment

Tumor-associated macrophages (TAMs) are abundant in the tumor microenvironment and typically exhibit pro-tumoral phenotypes. TAMs overexpress the signal regulatory protein alpha (SIRPα) receptor on their surface, which interacts with CD47 on tumor cells to inhibit their phagocytic activity. In this study, we developed lipid nanoparticles modified with an anti-SIRPα antibody (aSIRPα) for the targeted delivery of microRNA-155 (miR155@aSIRPα-LNP) to TAMs, aiming to enhance their anti-tumoral phenotypes within the tumor microenvironment. The aSIRPα modification not only facilitated nanoparticle uptake by TAMs rather than B16F10 cells, but also blocked the anti-phagocytosis signal by disrupting the interaction between SIRPα and CD47 on cancer cells. This dual functionality enhanced the expression of anti-tumoral phenotype markers in TAMs and activated macrophage-mediated phagocytosis of tumor cells. In a melanoma model, intratumoral administration of miR155@aSIRPα-LNP to B16F10 tumor-bearing mice reprogrammed TAMs toward anti-tumoral phenotypes. The anti-tumoral cytokines released by these TAMs remodeled the immunosuppressive tumor microenvironment, increasing cytotoxic T cell infiltration and reducing the regulatory T cell population, inhibiting tumor progression. This approach indicates the potential of miRNA-based therapies to overcome the limitations of current immunotherapies in treating cold solid tumors. Overall, the results suggest that delivering miR155 to TAMs by targeting SIRPα is a promising strategy for modulating the immunosuppressive tumor microenvironment in cancer immunotherapy.

Macrophages and fibroblasts as regulators of the immune response in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the few cancers that has yet to benefit from immunotherapies. This is primarily a result of its characteristic 'cold' tumor microenvironment composed of cancer-associated fibroblasts (CAFs), a dense network of extracellular matrix and several immune cell types, the most abundant of which are the tumor-associated macrophages (TAMs). Advances in single-cell and spatial technologies have elucidated the vast functional heterogeneity of CAFs and TAMs, their symbiotic relationship and their cooperative role in the tumor microenvironment. In this Review, we provide an overview of the heterogeneity of CAFs and TAMs, how they establish an immunosuppressive microenvironment and their collaboration in the remodeling of the extracellular matrix. Finally, we examine why the impact of immunotherapy in PDAC has been limited and how a detailed molecular and spatial understanding of the combined role of CAFs and TAMs is paramount to the design of effective therapies.

Targeting VSIG4+ tissue-resident macrophages enhances T cell cytotoxicity and immunotherapy efficacy in cancer

Tissue-resident macrophage (TRM) is crucial for organ development and homeostasis. However, the role of TRM-derived tumor-associated macrophage (TAM) subpopulations in cancer remains unclear. Using single-cell RNA sequencing and lineage tracing, we reported a TRM-derived TAM subpopulation, characterized by VSIG4 overexpression in testicular cancer. Macroscopically, such subpopulation was also found in tumors such as hepatocellular carcinoma, lung cancer, and glioblastoma. It was associated with poor prognosis and the suppression of CD8+ T-cell-dependent immunity via VSIG4. Notably, VSIG4 promoted immunosuppressive effects through direct or indirect modes, including interacting with receptors on CD8+ T cells or inducing transcription of IL-11 in TAMs. More importantly, MEF2C was identified as a key transcription factor that maintained VSIG4 expression and determined the biological behaviors of VSIG4+ TAMs. In preclinical models, targeting VSIG4+ TAMs via VSIG4 or MEF2C demonstrated a favorable effect of enhancing the efficacy of immune checkpoint inhibitors.

Malignant mesothelioma-associated inflammatory microenvironment promotes tumor progression via GPNMB

BACKGROUND

Tumor-Associated Macrophages (TAMs) are the main immune component of the tumor stroma with heterogeneous functional activities, predominantly suppressing the immune response and promoting tumor progression, also via secretion of different factors. Among these, GPNMB (Glycoprotein non-metastatic B) is usually associated with disease progression in several tumor types. Malignant pleural mesothelioma (MPM) a severe neoplasia with poor prognosis, is characterized by an abundancy of TAMs, testifying the presence of a long-lasting inflammation which is pathogenetic of the disease. However, the role of GPNMB in MPM is unclear.

METHODS

Clinical samples from patients with MPM were used to measure RNA and protein levels of GPNMB. The functional role of GPNMB in vivo was studied in an orthotopic mouse model of mesothelioma using the murine cell lines AB1 and AB22. Experiments included in vivo tumor growth in wild type and in GPNMB-deficient mice and blocking of GPNMB-induced signaling with anti-CD44 antibodies.

RESULTS

We show that in human and murine MPM tissues the protein GPNMB is mainly produced by infiltrating TAMs. Gpnmb RNA levels in MPM patients from TCGA are significantly associated with lower survival. Using an orthotopic mouse model of mesothelioma we observed that in GPNMB-defective mice (DBA2/J mice) unable to produce the protein, tumors formed by AB1 and AB22 mesothelioma cells grow significantly less than in GPNMB-proficient mice (DBA2/J-Gpnmb+ mice), indicating that host GPNMB is involved in tumor progression. Likewise, the ectopic expression of GPNMB in AB1 and AB22 cells causes an acceleration of tumor growth in vivo, significantly different compared to mock-transduced cells. Treatment of tumor-bearing mice with blocking anti-CD44 (a major receptor for GPNMB) results in a significant reduction of tumor growth.

CONCLUSIONS

Overall, these results indicate that the protein GPNMB, a product and marker gene of TAMs, is a driver of mesothelioma progression and may constitute a promising therapeutic target.

Neoadjuvant immune checkpoint therapy: Enabling insights into fundamental human immunology and clinical benefit

While immune checkpoint therapy (ICT) has revolutionized cancer treatment, most patients with advanced disease fail to achieve durable benefit. To address this challenge, it is essential to integrate mechanistic research with clinical studies to: (1) understand response mechanisms, (2) identify patient-specific resistance pathways, (3) develop biomarkers for patient selection, and (4) design novel therapies to overcome resistance. We propose that incorporating "direct-in-patient" studies into clinical trials is crucial for bridging the gap between fundamental science and clinical oncology. In this review, we first highlight recent clinical success of ICT in the neoadjuvant setting, where treatment is given in earlier disease stages to improve outcomes. We then explore how neoadjuvant clinical trials could be utilized to drive mechanistic laboratory-based investigations. Finally, we discuss novel scientific concepts that will potentially aid in overcoming resistance to ICT, which will require future clinical trials to understand their impact on human immune responses.

Exposomal determinants of non-genetic plasticity in tumor initiation

The classical view of cancer as a genetically driven disease has been challenged by recent findings of oncogenic mutations in phenotypically healthy tissues, refocusing attention on non-genetic mechanisms of tumor initiation. In this context, gene-environment interactions take the stage, with recent studies showing how they unleash and redirect cellular and tissue plasticity towards protumorigenic states in response to the exposome, the ensemble of environmental factors impinging on tissue homeostasis. We conceptualize tumor-initiating plasticity as a phenotype-transforming force acting at three levels: cell-intrinsic, focusing on mutant epithelial cells' responses to environmental variation; reprogramming of non-neoplastic cells of the host, leading to protumor micro- and macroenvironments; and microbiome ecosystem dynamics. This perspective highlights cell, tissue, and organismal plasticity mechanisms underlying tumor initiation that are shaped by the exposome, and how their functional investigation may provide new opportunities to prevent, detect, and intercept cancer-promoting plasticity.

Inflammation and cancer: molecular mechanisms and clinical consequences

Inflammation, a hallmark of cancer, has been associated with tumor progression, transition into malignant phenotype and efficacy of anticancer treatments in cancer. It affects all stages of cancer, from the initiation of carcinogenesis to metastasis. Chronic inflammation induces immunosup-pression, providing an environment conducive to carcinogenesis, whereas acute inflammation induces an antitumor immune response, leading to tumor suppression. Solid tumors have an inflammatory tumor microenvironment (TME) containing cancer cells, immune cells, stromal cells, and soluble molecules, which plays a key role in tumor progression and therapy response. Both cancer cells and stromal cells in the TME are highly plastic and constantly change their phenotypic and functional properties. Cancer-associated inflammation, the majority of which consists of innate immune cells, plays an important role in cancer cell plasticity, cancer progression and the development of anticancer drug resistance. Today, with the combined used of advanced technologies, such as single-cell RNA sequencing and spatial molecular imaging analysis, the pathways linking chronic inflammation to cancer have been largely elucidated. In this review article, we highlighted the molecular and cellular mechanisms involved in cancer-associated inflammation and its effects on cancer progression and treatment response. We also comprehensively review the mechanisms linking chronic inflammation to cancer in the setting of GI cancers.

CD47 blockade reverses resistance to HDAC inhibitor by liberating anti-tumor capacity of macrophages

BACKGROUND

Targeting oncogenic histone modification by histone deacetylase inhibitors (HDACis) demonstrates promising prospects in clinical cancer treatment, whereas a notable proportion of patients cannot benefit from HDACi therapy. This study aims to explore how HDACi influences the tumor microenvironment, in order to identify potential targets for reversing the resistance to HDACi therapies.

METHODS

Macrophage infiltration was compared between HDACi-responding and HDACi-nonresponding cancer patients. The impact of HDACis on the phagocytic capacity of macrophages was investigated through macrophage-tumor cell co-culture system. CD47 expression in tumor cell lines and patient-derived organoids was evaluated by quantitative polymerase chain reaction (QPCR) and flow cytometry. Mechanistic studies were conducted through co-immunoprecipitation (co-IP) and chromatin immunoprecipitation (ChIP). The synergistic effect of HDACis and CD47 neutralizing antibody was assessed in subcutaneous murine tumor models. Bioinformatics approaches were adopted to analyze how macrophage infiltration determines the prognostic significance of CD47 expression in cancer patients.

RESULTS

High macrophage infiltration is a determinant of therapeutic non-response to HDACi, cancer patients who did not respond to HDACi exhibit massive infiltration of tumor-associated macrophages (TAMs). TAM depletion reversed the resistance to HDACi therapy. Mechanistically, HDACi impaired the phagocytic capacity of macrophages against tumor cells through epigenetically upregulating CD47 expression. Reciprocally, HDACi-upregulated CD47 polarized macrophages towards a pro-tumor M2 phenotype through SIRPα ligation. In tumor-bearing mice, HDACi monotherapy only marginally delayed tumor progression, while the concurrent neutralization of CD47 exhibited potent anti-tumor effect through re-educating TAMs towards a tumoricidal phenotype. In cancer patients, CD47 was found to determine the prognostic significance of TAMs.

CONCLUSIONS

Our study offers a rationale for targeting macrophage infiltration or blocking CD47 to sensitize HDACi therapies in cancer patients.

Advanced Nanoprobe Strategies for Imaging Macrophage Polarization in Cancer Immunology

Macrophages are ubiquitous within the human body and serve pivotal roles in immune surveillance, inflammation, and tissue homeostasis. Phenotypic plasticity is a hallmark of macrophages, allowing their polarization into distinct phenotypes M1 (pro-inflammatory, anti-tumor) and M2 (anti-inflammatory, pro-tumor) in response to local microenvironmental cues. In tumor tissues, the polarization of tumor-associated macrophages profoundly shapes the tumor microenvironment, influencing tumor progression, immune evasion, and metastasis. Therefore, the ability to image and monitor macrophage polarization is essential for comprehending tumor biology and optimizing therapeutic strategies. With the rapid advancement of nanomedicine, a diverse array of nanoprobes has been engineered to specifically target tumor-associated macrophages, offering new avenues for noninvasive in vivo imaging and real-time monitoring of macrophage dynamics within the tumor microenvironment. This perspective highlights recent advancements in macrophage-targeting nanoprobes for imaging macrophage polarization both in vitro and in vivo. It also addresses the current challenges in the field, such as enhancing probe sensitivity, specificity, and biocompatibility, while outlining the future directions for the development of next-generation nanoprobes aimed at precision oncology.

Tumor microbiome: roles in tumor initiation, progression, and therapy

Over the past few years, the tumor microbiome is increasingly recognized for its multifaceted involvement in cancer initiation, progression, and metastasis. With the application of 16S ribosomal ribonucleic acid (16S rRNA) sequencing, the intratumoral microbiome, also referred to as tumor-intrinsic or tumor-resident microbiome, has also been found to play a significant role in the tumor microenvironment (TME). Understanding their complex functions is critical for identifying new therapeutic avenues and improving treatment outcomes. This review first summarizes the origins and composition of these microbial communities, emphasizing their adapted diversity across a diverse range of tumor types and stages. Moreover, we outline the general mechanisms by which specific microbes induce tumor initiation, including the activation of carcinogenic pathways, deoxyribonucleic acid (DNA) damage, epigenetic modifications, and chronic inflammation. We further propose the tumor microbiome may evade immunity and promote angiogenesis to support tumor progression, while uncovering specific microbial influences on each step of the metastatic cascade, such as invasion, circulation, and seeding in secondary sites. Additionally, tumor microbiome is closely associated with drug resistance and influences therapeutic efficacy by modulating immune responses, drug metabolism, and apoptotic pathways. Furthermore, we explore innovative microbe-based therapeutic strategies, such as engineered bacteria, oncolytic virotherapy, and other modalities aimed at enhancing immunotherapeutic efficacy, paving the way for microbiome-centered cancer treatment frameworks.

Extrinsic and Cell-Intrinsic Stress in the Immune Tumor Micro-Environment

In continuously progressive tumor tissues, the causes of cellular stress are multiple: metabolic alterations, nutrient deprivation, chronic inflammation and hypoxia. To survive, tumor cells activate the stress response program, a highly conserved molecular reprogramming proposed to cope with challenges in a hostile environment. Not only cancer cells are affected, but stress responses in tumors also have a profound impact on their normal cellular counterparts: fibroblasts, endothelial cells and infiltrating immune cells. In recent years, there has been a growing interest in the interaction between cancer and immune cells, especially in difficult conditions of cellular stress. A growing literature indicates that knowledge of the molecular pathways activated in tumor and immune cells under stress conditions may offer new insights for possible therapeutic interventions. Counter-regulating the stress caused by the presence of a growing tumor can therefore be a weapon to limit disease progression. Here, we review the main pathways activated in cellular stress responses with a focus on immune cells present in the tumor microenvironment.

The role of macrophage migratory behavior in development, homeostasis and tumor invasion

Tumor-associated macrophages (TAMs) recapitulate the developmental and homeostatic behaviors of tissue resident macrophages (TRMs) to promote tumor growth, invasion and metastasis. TRMs arise in the embryo and colonize developing tissues, initially to guide tissue morphogenesis and then to form complex networks in adult tissues to constantly search for threats to homeostasis. The macrophage growth factor, colony-stimulating factor-1 (CSF-1), which is essential for TRM survival and differentiation, is also responsible for the development of the unique motility machinery of mature macrophages that underpins their ramified morphologies, migratory capacity and ability to degrade matrix. Two CSF-1-activated kinases, hematopoietic cell kinase and the p110δ catalytic isoform of phosphatidylinositol 3-kinase, regulate this machinery and selective inhibitors of these proteins completely block macrophage invasion. Considering tumors co-opt the invasive capacity of TAMs to promote their own invasion, these proteins are attractive targets for drug development to inhibit tumor progression to invasion and metastasis.

Macrophage diversity in cancer dissemination and metastasis

Invasion and metastasis are hallmarks of cancer. In addition to the well-recognized hematogenous and lymphatic pathways of metastasis, cancer cell dissemination can occur via the transcoelomic and perineural routes, which are typical of ovarian and pancreatic cancer, respectively. Macrophages are a universal major component of the tumor microenvironment and, in established tumors, promote growth and dissemination to secondary sites. Here, we review the role of tumor-associated macrophages (TAMs) in cancer cell dissemination and metastasis, emphasizing the diversity of myeloid cells in different tissue contexts (lungs, liver, brain, bone, peritoneal cavity, nerves). The generally used models of lung metastasis fail to capture the diversity of pathways and tissue microenvironments. A better understanding of TAM diversity in different tissue contexts may pave the way for tailored diagnostic and therapeutic approaches.

Developing Cell-Membrane-Associated Liposomes for Liver Diseases

Over the past decade, a marked escalation in the prevalence of hepatic pathologies has been observed, adversely impacting the quality of life for many. The predominant therapeutic strategy for liver diseases has been pharmacological intervention; however, its efficacy is often constrained. Currently, liposomes are tiny structures that can deliver drugs directly to targeted areas, enhancing their effectiveness. Specifically, cell membrane-associated liposomes have gained significant attention. Despite this, there is still much to learn about the binding mechanism of this type of liposome. Thus, this review comprehensively summarizes relevant information on cell membrane-associated liposomes, including their clinical applications and future development directions. First, we will briefly introduce the composition and types of cell membrane-associated liposomes. We will provide an overview of their structure and discuss the various types of liposomes associated with cell membranes. Second, we will thoroughly discuss various strategies of drug delivery using these liposomes. Lastly, we will discuss the application and clinical challenges associated with using cell membrane-associated liposomes in treating liver diseases. We will explore their potential benefits while also addressing the obstacles that need to be overcome. Furthermore, we will provide prospects for future development in this field. In summary, this review underscores the promise of cell membrane-associated liposomes in enhancing liver disease treatment and highlights the need for further research to optimize their utilization. In summary, this review underscores the promise of cell membrane-associated liposomes in enhancing liver disease treatment and highlights the need for further research to optimize their utilization.

Metformin impacts the differentiation of mouse bone marrow cells into macrophages affecting tumour immunity

Background

Epidemiological studies suggest that metformin reduces the risk of developing several types of cancer, including gliomas, and improves the overall survival in cancer patients. Nevertheless, while the effect of metformin on cancer cells has been extensively studied, its impact on other components of the tumour microenvironment, such as macrophages, is less understood.

Results

Metformin-treated mouse bone marrow cells differentiate into spindle-shaped macrophages exhibiting increased phagocytic activity and tumour cell cytotoxicity coupled with modulated expression of co-stimulatory molecules displaying reduced sensitivity to inflammatory cues compared with untreated cells. Transcriptional analyses of metformin-treated mouse bone marrow-derived macrophages show decreased expression levels of pro-tumour genes, including Tgfbi and Il1β, related to enhanced mTOR/HIF1α signalling and metabolic rewiring towards glycolysis.

Significance

Our study provides novel insights into the immunomodulatory properties of metformin in macrophages and its potential application in preventing tumour onset and in cancer immunotherapy.

Dissecting prostate Cancer: Single-Cell insight into Macrophage Diversity, molecular Prognosticators, and the role of Peptidylprolyl Isomerase F

BACKGROUND

Prostate cancer remains a prominent challenge in oncology, with advanced stages showing poor prognosis. The tumor microenvironment (TME), and particularly tumor-associated macrophages (TAMs), plays a crucial role in disease progression. This study explores the single-cell transcriptomics of prostate cancer, determines macrophage heterogeneity, identifies prognostic gene markers, and assesses the role of PPIF in TAMs.

METHODS

Single-cell RNA sequencing data from the GEO database (GSE176031) and transcriptome data from the TCGA were processed to characterize cell populations and identify prognostic genes in prostate cancer. Macrophage subpopulations were examined through clustering, followed by gene set scoring based on migration, activation, and proliferation. PPIF expression in macrophages was investigated using multiplex immunofluorescence staining on matched prostate cancer and adjacent non-tumoral tissues.

RESULTS

The single-cell analysis identified 9,178 cells, categorized into 10 principal cell types, with macrophages constituting a significant part of the immune microenvironment. Four macrophage subgroups demonstrated distinct functional pathways: phagocytic, immune-regulatory, and proliferative. A total of 39 genes correlated with prostate cancer prognosis were identified, of which 10 carried the most significant prognostic information. Peptidylprolyl Isomerase F (PPIF) expression was significantly higher in TAMs from tumor tissue than normal tissue, indicating its potential regulatory role in the immune microenvironment.

CONCLUSION

The intricate cellular architecture of the prostate cancer TME has been elucidated, with a focus on macrophage heterogeneity and functional specialization. Prognostic genes, including PPIF, were associated with survival outcomes, providing potential therapeutic targets. PPIF's prominent expression in TAMs may serve as a lever in cancer progression, warranting further investigation as a biomarker and a molecule of interest for therapeutic targeting within the prostate cancer milieu.

Mononuclear Phagocytes, Cellular Immunity, and Nobel Prizes: A Historic Perspective

The mononuclear phagocyte system includes monocytes, macrophages, some dendritic cells, and multinuclear giant cells. These cell populations display marked heterogeneity depending on their differentiation from embryonic and bone marrow hematopoietic progenitors, tissue location, and activation. They contribute to tissue homeostasis by interacting with local and systemic immune and non-immune cells through trophic, clearance, and cytocidal functions. During evolution, they contributed to the innate host defense before effector mechanisms of specific adaptive immunity emerged. Mouse macrophages appear at mid-gestation and are distributed throughout the embryo to facilitate organogenesis and clear cells undergoing programmed cell death. Yolk sac, AGM, and fetal liver-derived tissue-resident macrophages persist throughout postnatal and adult life, supplemented by bone marrow-derived blood monocytes, as required after injury and infection. Nobel awards to Elie Metchnikoff and Paul Ehrlich in 1908 drew attention to cellular phagocytic and humoral immunity, respectively. In 2011, prizes were awarded to Jules Hoffmann and Bruce Beutler for contributions to innate immunity and to Ralph Steinman for the discovery of dendritic cells and their role in antigen presentation to T lymphocytes. We trace milestones in the history of mononuclear phagocyte research from the perspective of Nobel awards bearing directly and indirectly on their role in cellular immunity.

Timing and location dictate monocyte fate and their transition to tumor-associated macrophages

Tumor-associated macrophages (TAMs) are a heterogeneous population of cells whose phenotypes and functions are shaped by factors that are incompletely understood. Herein, we asked when and where TAMs arise from blood monocytes and how they evolve during tumor development. We initiated pancreatic ductal adenocarcinoma (PDAC) in inducible monocyte fate-mapping mice and combined single-cell transcriptomics and high-dimensional flow cytometry to profile the monocyte-to-TAM transition. We revealed that monocytes differentiate first into a transient intermediate population of TAMs that generates two longer-lived lineages of terminally differentiated TAMs with distinct gene expression profiles, phenotypes, and intratumoral localization. Transcriptome datasets and tumor samples from patients with PDAC evidenced parallel TAM populations in humans and their prognostic associations. These insights will support the design of new therapeutic strategies targeting TAMs in PDAC.