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Macrophages reside in essentially all tissues of the body and play key roles in innate and adaptive immune responses. Distinct populations of tissue macrophages also acquire context-specific functions that are important for normal tissue homeostasis. To investigate mechanisms responsible for tissue-specific functions, we analyzed the transcriptomes and enhancer landscapes of brain microglia and resident macrophages of the peritoneal cavity. In addition, we exploited natural genetic variation as a genome-wide "mutagenesis" strategy to identify DNA recognition motifs for transcription factors that promote common or subset-specific binding of the macrophage lineage-determining factor PU.1. We find that distinct tissue environments drive divergent programs of gene expression by differentially activating a common enhancer repertoire and by inducing the expression of divergent secondary transcription factors that collaborate with PU.1 to establish tissue-specific enhancers. These findings provide insights into molecular mechanisms by which tissue environment influences macrophage phenotypes that are likely to be broadly applicable to other cell types.

To determine the origin of adult tissue-resident macrophages, a mouse lineage tracing study has revealed that these cells derive from erythro-myeloid progenitors in the yolk sac that are distinct from fetal and adult haematopoietic stem cells. The origin of adult myeloid cells The developmental origin of tissue-resident macrophage progenitors and their contribution to macrophages in fetal and adult organs relative to bone marrow macrophages are still unclear. Using lineage tracing, Elisa Gomez Perdiguero et al. identify a population of yolk-sac-derived progenitors -- distinct from fetal and adult haematopoetic stem cells -- that gives rise to erythrocytes, macrophages, granulocytes and monocytes in the young mouse fetus, and to the vast majority of adult tissue-resident macrophages. Most haematopoietic cells renew from adult haematopoietic stem cells (HSCs).sup.1,2,3, however, macrophages in adult tissues can self-maintain independently of HSCs.sup.4,5,6,7. Progenitors with macrophage potential in vitro have been described in the yolk sac before emergence of HSCs.sup.8,9,10,11,12,13, and fetal macrophages.sup.13,14,15 can develop independently of Myb.sup.4, a transcription factor required for HSC.sup.16, and can persist in adult tissues.sup.4,17,18. Nevertheless, the origin of adult macrophages and the qualitative and quantitative contributions of HSC and putative non-HSC-derived progenitors are still unclear.sup.19. Here we show in mice that the vast majority of adult tissue-resident macrophages in liver (Kupffer cells), brain (microglia), epidermis (Langerhans cells) and lung (alveolar macrophages) originate from a Tie2.sup.+ (also known as Tek) cellular pathway generating Csf1r.sup.+ erythro-myeloid progenitors (EMPs) distinct from HSCs. EMPs develop in the yolk sac at embryonic day (E) 8.5, migrate and colonize the nascent fetal liver before E10.5, and give rise to fetal erythrocytes, macrophages, granulocytes and monocytes until at least E16.5. Subsequently, HSC-derived cells replace erythrocytes, granulocytes and monocytes. Kupffer cells, microglia and Langerhans cells are only marginally replaced in one-year-old mice, whereas alveolar macrophages may be progressively replaced in ageing mice. Our fate-mapping experiments identify, in the fetal liver, a sequence of yolk sac EMP-derived and HSC-derived haematopoiesis, and identify yolk sac EMPs as a common origin for tissue macrophages., Author(s): Elisa Gomez Perdiguero [sup.1] , Kay Klapproth [sup.2] , Christian Schulz [sup.1] , Katrin Busch [sup.2] , Emanuele Azzoni [sup.3] , Lucile Crozet [sup.1] , Hannah Garner [sup.1] , [...]

Most haematopoietic cells renew from adult haematopoietic stem cells (HSCs) (1-3), however, macrophages in adult tissues can self-maintain independently of HSCs (4-7). Progenitors with macrophage potential in vitro have been described in the yolk sac before emergence of HSCs (8-13), and fetal macrophages (13-15) can develop independently of Myb (4), a transcription factor required for HSC (16), and can persist in adult tissues (4,17,18). Nevertheless, the origin of adult macrophages and the qualitative and quantitative contributions of HSC and putative non-HSC-derived progenitors are still unclear (19). Here we show in mice that the vast majority of adult tissue-resident macrophages in liver (Kupffer cells), brain (microglia), epidermis (Langerhans cells) and lung (alveolar macrophages) originate from a [Tie2.sup.+] (also known as Tek) cellular pathway generating [Csf1r.sup.+] erythro-myeloid progenitors (EMPs) distinct from HSCs. EMPs develop in the yolk sac at embryonic day (E) 8.5, migrate and colonize the nascent fetal liver before E10.5, and give rise to fetal erythrocytes, macrophages, granulocytes and monocytes until at least E16.5. Subsequently, HSC-derived cells replace erythrocytes, granulocytes and monocytes. Kupffer cells, microglia and Langerhans cells are only marginally replaced in one-year-old mice, whereas alveolar macrophages may be progressively replaced in ageing mice. Our fate-mapping experiments identify, in the fetal liver, a sequence of yolk sac EMP-derived and HSC-derived haematopoiesis, and identify yolk sac EMPs as a common origin for tissue macrophages., Csf1r-expressing cells in the mouse embryo give rise to tissue-resident macrophages in adult tissues (4). To identify in the developing embryo the site of origin of Csf1r-expressing cells, we performed [...]

The clinical successes of immune checkpoint blockade (ICB) in advanced cancer patients have recently spurred the clinical implementation of ICB in the neoadjuvant and perioperative setting. However, how neoadjuvant ICB therapy affects the systemic immune landscape and metastatic spread remains to be established. Tumors promote both local and systemic expansion of regulatory T cells (Tregs), which are key orchestrators of tumor-induced immunosuppression, contributing to immune evasion, tumor progression and metastasis. Tregs express inhibitory immune checkpoint molecules and thus may be unintended targets for ICB therapy counteracting its efficacy. Using ICB-refractory models of spontaneous primary and metastatic breast cancer that recapitulate the poor ICB response of breast cancer patients, we observed that combined anti-PD-1 and anti-CTLA-4 therapy inadvertently promotes proliferation and activation of Tregs in the tumor, tumor-draining lymph node and circulation. Also in breast cancer patients, Treg levels were elevated upon ICB. Depletion of Tregs during neoadjuvant ICB in tumor-bearing mice not only reshaped the intratumoral immune landscape into a state favorable for ICB response but also induced profound and persistent alterations in systemic immunity, characterized by elevated CD8+ T cells and NK cells and durable T cell activation that was maintained after treatment cessation. While depletion of Tregs in combination with neoadjuvant ICB did not inhibit primary tumor growth, it prolonged metastasis-related survival driven predominantly by CD8+ T cells. This study demonstrates that neoadjuvant ICB therapy of breast cancer can be empowered by simultaneous targeting of Tregs, extending metastasis-related survival, independent of a primary tumor response. [ABSTRACT FROM AUTHOR]

Background: Effective dissemination of research to health and social care practitioners enhances clinical practice and evidence-based care. Social media use has potential to facilitate dissemination to busy practitioners., Objective: This is a protocol for a systematic review that will quantitatively synthesize evidence of the effectiveness of social media, compared with no social media, for dissemination of research evidence to health and social care practitioners. Social media platforms, formats, and sharing mechanisms used for effective dissemination of research evidence will also be identified and compared., Methods: Electronic database searches (MEDLINE, PsycINFO, CINAHL, ERIC, LISTA, and OpenGrey) will be conducted from January 1, 2010, to January 10, 2023, for studies published in English. Randomized, nonrandomized, pre-post study designs or case studies evaluating the effect of social media on dissemination of research evidence to postregistration health and social care practitioners will be included. Studies that do not involve social media or dissemination or those that evaluate dissemination of nonresearch information (eg, multisource educational materials) to students or members of the public only, or without quantitative data on outcomes of interest, will be excluded. Screening will be carried out by 2 independent reviewers. Data extraction and quality assessment, using either the Cochrane tool for assessing risk of bias or the Newcastle-Ottawa Scale, will be completed by 2 independent reviewers. Outcomes of interest will be reported in 4 domains (reach, engagement, dissemination, and impact). Data synthesis will include quantitative comparisons using narrative text, tables, and figures. A meta-analysis of standardized pooled effects will be undertaken, and subgroup analyses will be applied, if appropriate., Results: Searches and screening will be completed by the end of May 2023. Data extraction and analyses will be completed by the end of July 2023, after which findings will be synthesized and reported by the end of October 2023., Conclusions: This systematic review will summarize the evidence for the effectiveness of social media for the dissemination of research evidence to health and social care practitioners. The limitations of the evidence may include multiple outcomes or methodological heterogeneity that limit meta-analyses, potential risk of bias in included studies, and potential publication bias. The limitations of the study design may include potential insensitivity of the electronic database search strategy. The findings from this review will inform the dissemination practice of health and care research., Trial Registration: PROSPERO CRD42022378793; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=378793., International Registered Report Identifier (irrid): DERR1-10.2196/45684., (©Sarah F Roberts-Lewis, Helen A Baxter, Gill Mein, Sophia Quirke-McFarlane, Fiona J Leggat, Hannah M Garner, Martha Powell, Sarah White, Lindsay Bearne. Originally published in JMIR Research Protocols (https://www.researchprotocols.org), 12.05.2023.)

The clinical successes of immune checkpoint blockade (ICB) in advanced cancer patients have recently spurred the clinical implementation of ICB in the neoadjuvant and perioperative setting. However, how neoadjuvant ICB therapy affects the systemic immune landscape and metastatic spread remains to be established. Tumors promote both local and systemic expansion of regulatory T cells (T regs ), which are key orchestrators of tumor-induced immunosuppression, contributing to immune evasion, tumor progression and metastasis. T regs express inhibitory immune checkpoint molecules and thus may be unintended targets for ICB therapy counteracting its efficacy. Using ICB-refractory models of spontaneous primary and metastatic breast cancer that recapitulate the poor ICB response of breast cancer patients, we observed that combined anti-PD-1 and anti-CTLA-4 therapy inadvertently promotes proliferation and activation of T regs in the tumor, tumor-draining lymph node and circulation. Also in breast cancer patients, T reg levels were elevated upon ICB. Depletion of T regs during neoadjuvant ICB in tumor-bearing mice not only reshaped the intratumoral immune landscape into a state favorable for ICB response but also induced profound and persistent alterations in systemic immunity, characterized by elevated CD8+ T cells and NK cells and durable T cell activation that was maintained after treatment cessation. While depletion of T regs in combination with neoadjuvant ICB did not inhibit primary tumor growth, it prolonged metastasis-related survival driven predominantly by CD8+ T cells. This study demonstrates that neoadjuvant ICB therapy of breast cancer can be empowered by simultaneous targeting of T regs, extending metastasis-related survival, independent of a primary tumor response., Competing Interests: K.E.d.V. reports research funding from Roche and is consultant for Macomics, outside the scope of this work. M.K. reports funding to the institute from BMS, Roche/Genentech, AZ and an advisory role for BMS, Roche, MSD and Daiichi Sankyo, outside the submitted work., (© 2023 The Author(s). Published with license by Taylor & Francis Group, LLC.)

Immune checkpoint blockade (ICB) has heralded a new era in cancer therapy. Research into the mechanisms underlying response to ICB has predominantly focused on T cells; however, effective immune responses require tightly regulated crosstalk between innate and adaptive immune cells. Here, we combine unbiased analysis of blood and tumors from metastatic breast cancer patients treated with ICB with mechanistic studies in mouse models of breast cancer. We observe an increase in systemic and intratumoral eosinophils in patients and mice responding to ICB treatment. Mechanistically, ICB increased IL-5 production by CD4 + T cells, stimulating elevated eosinophil production from the bone marrow, leading to systemic eosinophil expansion. Additional induction of IL-33 by ICB-cisplatin combination or recombinant IL-33 promotes intratumoral eosinophil infiltration and eosinophil-dependent CD8 + T cell activation to enhance ICB response. This work demonstrates the critical role of eosinophils in ICB response and provides proof-of-principle for eosinophil engagement to enhance ICB efficacy., Competing Interests: Declaration of interests O.S.B., H.G., L.S., L.V., O.I.I., E.v.D., N.B., C.K., M.D., K. Kersten, M.B., D.P., C.-S.H., K.V., E.A.M.R., D.K., L.H., K. Kos, I.S.A., P.K., R.B., and D.S.T. have no competing interests to declare. M.C. reports funding to the institute from BMS and Roche/Genentech and an advisory role for BMS, outside the submitted work. W.S.M.E.T. reports receiving grants from MSD during the conduct of the PEMBRO-RT trial. P.B. reports receiving grants and medication delivery from MSD during the conduct of the PEMBRO-RT trial as well as grants and consultancy fees from BMS outside the submitted work. E.E.V. is legally responsible for all contracts with pharmaceutical companies at the NKI and reports research funding from BMS, outside the submitted work. L.F.A.W. reports funding to the institute from Genmab BV. K.E.d.V. reports research funding from Roche/Genentech and is consultant for Macomics, outside the scope of this work. M.K. reports funding to the institute from BMS, Roche/Genentech, AZ, and an advisory role for BMS, Roche, MSD, and Daiichi Sankyo, outside the submitted work., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Inflammation triggers the differentiation of Ly6C hi monocytes into microbicidal macrophages or monocyte-derived dendritic cells (moDCs). Yet, it is unclear whether environmental inflammatory cues control the polarization of monocytes toward each of these fates or whether specialized monocyte progenitor subsets exist before inflammation. Here, we have shown that naive monocytes are phenotypically heterogeneous and contain an NR4A1- and Flt3L-independent, CCR2-dependent, Flt3 + CD11c - MHCII + PU.1 hi subset. This subset acted as a precursor for FcγRIII + PD-L2 + CD209a + , GM-CSF-dependent moDCs but was distal from the DC lineage, as shown by fate-mapping experiments using Zbtb46. By contrast, Flt3 - CD11c - MHCII - PU.1 lo monocytes differentiated into FcγRIII + PD-L2 - CD209a - iNOS + macrophages upon microbial stimulation. Importantly, Sfpi1 haploinsufficiency genetically distinguished the precursor activities of monocytes toward moDCs or microbicidal macrophages. Indeed, Sfpi1 +/- mice had reduced Flt3 + CD11c - MHCII + monocytes and GM-CSF-dependent FcγRIII + PD-L2 + CD209a + moDCs but generated iNOS + macrophages more efficiently. Therefore, intercellular disparities of PU.1 expression within naive monocytes segregate progenitor activity for inflammatory iNOS + macrophages or moDCs., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)