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Tissue-resident macrophages are essential for maintaining organismal homeostasis, but the precise mechanisms that macrophages use to perform this function are not fully understood. In this issue of Immunity , He et al. demonstrate that renal macrophages surveil and sample urine particles, ensuring optimal collecting duct flow and preventing kidney stone development. [ABSTRACT FROM AUTHOR]

Summary The contribution of thymic antigen-presenting-cell (APC) subsets in selecting a self-tolerant T cell population remains unclear. We show that bone marrow (BM) APCs and medullary thymic epithelial cells (mTECs) played nonoverlapping roles in shaping the T cell receptor (TCR) repertoire by deletion and regulatory T (Treg) cell selection of distinct TCRs. Aire, which induces tissue-specific antigen expression in mTECs, affected the TCR repertoire in a manner distinct from mTEC presentation. Approximately half of Aire-dependent deletion or Treg cell selection utilized a pathway dependent on antigen presentation by BM APCs. Batf3 -dependent CD8α + dendritic cells (DCs) were the crucial BM APCs for Treg cell selection via this pathway, showing enhanced ability to present antigens from stromal cells. These results demonstrate the division of function between thymic APCs in shaping the self-tolerant TCR repertoire and reveal an unappreciated cooperation between mTECs and CD8α + DCs for presentation of Aire-induced self-antigens to developing thymocytes. [ABSTRACT FROM AUTHOR]

Summary The development of T cell tolerance in the thymus requires the presentation of host proteins by multiple antigen-presenting cell (APC) types. However, the importance of transferring host antigens from transcription factor AIRE-dependent medullary thymic epithelial cells (mTECs) to bone marrow (BM) APCs is unknown. We report that antigen was primarily transferred from mTECs to CD8α + dendritic cells (DCs) and showed that CD36, a scavenger receptor selectively expressed on CD8α + DCs, mediated the transfer of cell-surface, but not cytoplasmic, antigens. The absence of CD8α + DCs or CD36 altered thymic T cell selection, as evidenced by TCR repertoire analysis and the loss of allo-tolerance in murine allogeneic BM transplantation (allo-BMT) studies. Decreases in these DCs and CD36 expression in peripheral blood of human allo-BMT patients correlated with graft-versus-host disease. Our findings suggest that CD36 facilitates transfer of mTEC-derived cell-surface antigen on CD8α + DCs to promote tolerance to host antigens during homeostasis and allo-BMT. [ABSTRACT FROM AUTHOR]

Summary New work in Caenorhabditis elegans shows that during embryogenesis endodermal cells interact with and regulate primordial germ cells by actively excising and digesting germ cell lobes. Endodermal cells utilize proteins linked to endocytosis to perform this unique ‘cannibalistic’ process. [ABSTRACT FROM AUTHOR]

The tumor microenvironment (TME) is critical for tumor progression. However, the establishment and function of the TME remain obscure because of its complex cellular composition. Using a mouse genetic system called mosaic analysis with double markers (MADMs), we delineated TME evolution at single-cell resolution in sonic hedgehog (SHH)-activated medulloblastomas that originate from unipotent granule neuron progenitors in the brain. First, we found that astrocytes within the TME (TuAstrocytes) were trans -differentiated from tumor granule neuron precursors (GNPs), which normally never differentiate into astrocytes. Second, we identified that TME-derived IGF1 promotes tumor progression. Third, we uncovered that insulin-like growth factor 1 (IGF1) is produced by tumor-associated microglia in response to interleukin-4 (IL-4) stimulation. Finally, we found that IL-4 is secreted by TuAstrocytes. Collectively, our studies reveal an evolutionary process that produces a multi-lateral network within the TME of medulloblastoma: a fraction of tumor cells trans -differentiate into TuAstrocytes, which, in turn, produce IL-4 that stimulates microglia to produce IGF1 to promote tumor progression. • A small number of medulloblastoma cells trans -differentiated into TME astrocytes • Astrocytes in human SHH-subtype medulloblastoma share lineage with tumor cells • Tumor-derived astrocytes secret IL-4 to polarize microglia for IGF1 production • IGF1 from tumor associated microglia is critical for tumor progression Tumors shape a microenvironmental network by acting as a source of tumor-associated astrocytes that provide paracrine stimulation to microglia to secret IGF1, which is critical for tumor progression in SHH-activated mouse medulloblastoma models. [ABSTRACT FROM AUTHOR]

Apoptotic cell (AC) clearance (efferocytosis) is performed by phagocytes, such as macrophages, that inhabit harsh physiological environments. Here, we find that macrophages display enhanced efferocytosis under prolonged (chronic) physiological hypoxia, characterized by increased internalization and accelerated degradation of ACs. Transcriptional and translational analyses revealed that chronic physiological hypoxia induces two distinct but complimentary states. The first, "primed" state, consists of concomitant transcription and translation of metabolic programs in AC-naive macrophages that persist during efferocytosis. The second, "poised" state, consists of transcription, but not translation, of phagocyte function programs in AC-naive macrophages that are translated during efferocytosis. Mechanistically, macrophages efficiently flux glucose into a noncanonical pentose phosphate pathway (PPP) loop to enhance NADPH production. PPP-derived NADPH directly supports enhanced efferocytosis under physiological hypoxia by ensuring phagolysosomal maturation and redox homeostasis. Thus, macrophages residing under physiological hypoxia adopt states that support cell fitness and ensure performance of essential homeostatic functions rapidly and safely., Competing Interests: Declaration of interests K.R.K. serves on the scientific advisory board of NVision Imaging Technologies. J.S.A.P. and K.R.K. holds patents related to imaging and modulation of cellular metabolism., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Clearance of apoptotic cells, or "efferocytosis," is essential for diverse processes including embryonic development, tissue turnover, organ regeneration, and immune cell development. The human body is estimated to remove approximately 1% of its body mass via apoptotic cell clearance daily. This poses several intriguing cell metabolism problems. For instance, phagocytes such as macrophages must induce or suppress metabolic pathways to find, engulf, and digest apoptotic cells. Then, phagocytes must manage the potentially burdensome biomass of the engulfed apoptotic cell. Finally, phagocytes reside in complex tissue architectures that vary in nutrient availability, the types of dying cells or debris that require clearance, and the neighboring cells they interact with. Here, we review advances in our understanding of these three key areas of phagocyte metabolism. We end by proposing a model of efferocytosis that integrates recent findings and establishes a new paradigm for testing how efferocytosis prevents chronic inflammatory disease and autoimmunity., Competing Interests: Declaration of interests The authors declare no competing financial interests., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Immune checkpoint blockade (ICB) has been a remarkable clinical advance for cancer; however, the majority of patients do not respond to ICB therapy. We show that metastatic disease in the pleural and peritoneal cavities is associated with poor clinical outcomes after ICB therapy. Cavity-resident macrophages express high levels of Tim-4, a receptor for phosphatidylserine (PS), and this is associated with reduced numbers of CD8 + T cells with tumor-reactive features in pleural effusions and peritoneal ascites from patients with cancer. We mechanistically demonstrate that viable and cytotoxic anti-tumor CD8 + T cells upregulate PS and this renders them susceptible to sequestration away from tumor targets and proliferation suppression by Tim-4 + macrophages. Tim-4 blockade abrogates this sequestration and proliferation suppression and enhances anti-tumor efficacy in models of anti-PD-1 therapy and adoptive T cell therapy in mice. Thus, Tim-4 + cavity-resident macrophages limit the efficacy of immunotherapies in these microenvironments., Competing Interests: Declaration of interests JDW is a consultant for Adaptive Biotech, Amgen, Apricity, Ascentage Pharma, Arsenal IO, Astellas, AstraZeneca, Bayer, Beigene, Boehringer Ingelheim, Bristol Myers Squibb, Celgene, Chugai, Daiichi Sankyo, Dragonfly, Eli Lilly, Elucida, F Star, Georgiamune, Idera, Imvaq, Kyowa Hakko Kirin, Linneaus, Maverick Therapeutics, Merck, Neon Therapeutics, Polynoma, Psioxus, Recepta, Takara Bio, Trieza, Truvax, Trishula, Sellas, Serametrix, Surface Oncology, Syndax, Syntalogic, and Werewolf Therapeutics. JDW has received grant/research support from Bristol Myers Squibb; Sephora. JDW has equity in Tizona Pharmaceuticals, Adaptive Biotechnologies, Imvaq, Beigene, Linneaus, Apricity, Arsenal IO, and Georgiamune. JDW is a co-inventor on patent applications related to heteroclitic cancer vaccines and recombinant poxviruses for cancer immunotherapy. JDW and TM are co-inventors on patent applications related to CD40 and in situ vaccination (PCT/US2016/045970). TM is a consultant for Immunos Therapeutics and Pfizer. TM is a cofounder of and equity holder in IMVAQ Therapeutics. TM receives research funding from Bristol-Myers Squibb, Surface Oncology, Kyn Therapeutics, Infinity Pharmaceuticals, Peregrine Pharmaceuticals, Adaptive Biotechnologies, Leap Therapeutics, and Aprea Therapeutics. TM is an inventor on patent applications related to work on oncolytic viral therapy, alpha virus–based vaccine, neoantigen modeling, CD40, GITR, OX40, PD-1, and CTLA-4. C.M.R. has consulted regarding oncology drug development with AbbVie, Amgen, Ascentage, AstraZeneca, BMS, Celgene, Daiichi Sankyo, Genentech/Roche, Ipsen, Loxo and PharmaMar and is on the scientific advisory boards of Elucida, Bridge and Harpoon. Unrelated to this work, D.Z. reports clinical research support to his institution from Astra Zeneca, Plexxikon, and Genentech; and personal/consultancy fees from Merck, Synlogic Therapeutics, GSK, Genentech, Xencor, Memgen, Immunos, CrownBio, and Agenus. D.Z. is an inventor on patents related to the use of Newcastle Disease Virus that has been licensed to Merck. MDH received research grant from BMS; personal fees from Achilles, Arcus, AstraZeneca, Blueprint, BMS, Genentech/Roche, Genzyme, Immunai, Instil Bio, Janssen, Merck, Mirati, Natera, Nektar, Pact Pharma, Regeneron, Shattuck Labs, Syndax, as well as equity options from Arcus, Factorial, Immunai, and Shattuck Labs. A patent filed by MSKCC related to the use of tumor mutational burden to predict response to immunotherapy (PCT/US2015/062208) is pending and licensed by PGDx. DTL serves on advisory boards for Merck, Bristol Myers Squibb, and Janssen and has received research funding from Merck, Bristol Myers Squibb, Aduro Biotech, Curegenix, Medivir, and Nouscom. She has received speaking honoraria from Merck and is an inventor of licensed intellectual property related to technology for mismatch repair deficiency for diagnosis and therapy (WO2016077553A1) from Johns Hopkins University. SS is a shareholder of Canexia Health Inc., (Copyright © 2021. Published by Elsevier Inc.)

We tested the hypothesis that voluntary wheel running would complement microdystrophin gene therapy to improve muscle function in young mdx mice, a model of Duchenne muscular dystrophy. mdx mice injected with a single dose of AAV9-CK8-microdystrophin or vehicle at age 7 weeks were assigned to three groups: mdxRGT (run, gene therapy), mdxGT (no run, gene therapy), or mdx (no run, no gene therapy). Wild-type (WT) mice were assigned to WTR (run) and WT (no run) groups. WTR and mdxRGT performed voluntary wheel running for 21 weeks; remaining groups were cage active. Robust expression of microdystrophin occurred in heart and limb muscles of treated mice. mdxRGT versus mdxGT mice showed increased microdystrophin in quadriceps but decreased levels in diaphragm. mdx final treadmill fatigue time was depressed compared to all groups, improved in mdxGT, and highest in mdxRGT. Both weekly running distance (km) and final treadmill fatigue time for mdxRGT and WTR were similar. Remarkably, mdxRGT diaphragm power was only rescued to 60% of WT, suggesting a negative impact of running. However, potential changes in fiber type distribution in mdxRGT diaphragms could indicate an adaptation to trade power for endurance. Post-treatment in vivo maximal plantar flexor torque relative to baseline values was greater for mdxGT and mdxRGT versus all other groups. Mitochondrial respiration rates from red quadriceps fibers were significantly improved in mdxGT animals, but the greatest bioenergetic benefit was observed in the mdxRGT group. Additional assessments revealed partial to full functional restoration in mdxGT and mdxRGT muscles relative to WT. These data demonstrate that voluntary wheel running combined with microdystrophin gene therapy in young mdx mice improved whole-body performance, affected muscle function differentially, mitigated energetic deficits, but also revealed some detrimental effects of exercise. With microdystrophin gene therapy currently in clinical trials, these data may help us understand the potential impact of exercise in treated patients., Competing Interests: Research funding for R.W.G. was provided by Solid Biosciences, Inc.; R.W.G. is a consultant for Lion Therapeutics, Inc., Cytokinetics, Inc., Prothelia Inc., and Anagenesis Biotechnologies, Inc. Research funding for M.W.L. was provided by Solid Biosciences, Audentes Therapeutics, Taysha Therapeutics, and Prothelia. M.W.L. was a board member for Solid Biosciences and Audentes Therapeutics during the period when studies were performed. M.W.L. is a consultant for Audentes Therapeutics, AGADA Biosciences, Encoded Therapeutics, Kate Therapeutics, Lacerta Therapeutics, Affinia Therapeutics, Modis Therapeutics, Dynacure, and Biomarin. Research funding and D.L.M. was provided by Audentes Therapeutics and Cytokinetics. D.L.M. is a consultant for Audentes Therapeutics, Kate Therapeutics, and Affinia Therapeutics. Research funding for K.E.C. was provided by Solid Biosciences, Inc.; no other remuneration was received. J.P.G. and C.A.M. are employees of Solid Biosciences, Inc. All other authors declare no competing interests., (© 2021 The Author(s).)

Therapeutic antibodies targeting ovarian cancer (OvCa)-enriched receptors have largely been disappointing due to limited tumor-specific antibody-dependent cellular cytotoxicity. Here we report a symbiotic approach that is highly selective and superior compared with investigational clinical antibodies. This bispecific-anchored cytotoxicity activator antibody is rationally designed to instigate "cis" and "trans" cytotoxicity by combining specificities against folate receptor alpha-1 (FOLR1) and death receptor 5 (DR5). Whereas the in vivo agonist DR5 signaling requires FcγRIIB interaction, the FOLR1 anchor functions as a primary clustering point to retain and maintain a high level of tumor-specific apoptosis. The presented proof of concept study strategically makes use of a tumor cell-enriched anchor receptor for agonist death receptor targeting to potentially generate a clinically viable strategy for OvCa., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Pulsed electric fields with microsecond pulse width (μsPEFs) are used clinically; namely, irreversible electroporation/Nanoknife is used for soft tissue tumor ablation. The μsPEF pulse parameters used in irreversible electroporation (0.5-1 kV/cm, 80-100 pulses, ∼100 μs each, 1 Hz frequency) may cause an internal field to develop within the cell because of the disruption of the outer cell membrane and subsequent penetration of the electric field. An internal field may disrupt voltage-sensitive mitochondria, although the research literature has been relatively unclear regarding whether such disruptions occur with μsPEFs. This investigation reports the influence of clinically used μsPEF parameters on mitochondrial respiration in live cells. Using a high-throughput Agilent Seahorse machine, it was observed that μsPEF exposure comprising 80 pulses with amplitudes of 600 or 700 V/cm did not alter mitochondrial respiration in 4T1 cells measured after overnight postexposure recovery. To record alterations in mitochondrial function immediately after μsPEF exposure, high-resolution respirometry was used to measure the electron transport chain state via responses to glutamate-malate and ADP and mitochondrial membrane potential via response to carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. In addition to measuring immediate mitochondrial responses to μsPEF exposure, measurements were also made on cells permeabilized using digitonin and those with compromised cytoskeleton due to actin depolymerization via treatment with the drug latrunculin B. The former treatment was used as a control to tease out the effects of plasma membrane permeabilization, whereas the latter was used to investigate indirect effects on the mitochondria that may occur if μsPEFs impact the cytoskeleton on which the mitochondria are anchored. Based on the results, it was concluded that within the pulse parameters tested, μsPEFs alone do not hinder mitochondrial physiology but can be used to impact the mitochondria upon compromising the actin. Mitochondrial susceptibility to μsPEF after actin depolymerization provides, to our knowledge, a novel avenue for cancer therapeutics., (Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.)