Mesothelial cell CSF1 sustains peritoneal macrophage proliferation.

Macrophages play a central role during infection, inflammation and tissue homeostasis maintenance. Macrophages have been identified in all organs and their core transcriptomic signature and functions differ from one tissue to another. Interestingly, macrophages have also been identified in the peritoneal cavity and these cells have been extensively used as a model for phagocytosis, efferocytosis and polarization. Peritoneal macrophages are involved in B-cell IgA production, control of inflammation and wound healing following thermal-induced liver surface injury. These cells presumably require and interact with the omentum, where milky spot stromal cells have been proposed to secrete CSF1 (colony stimulating factor 1). Peritoneal macrophages depend on CSF1 for their generation and survival, but the identity of CSF1 producing cells inside the large peritoneal cavity remains unknown. Here we investigated peritoneal macrophage localization and their interaction with mesothelial cells, the major cell type predicted to secrete CSF1. Our data revealed that mesothelial cells produce membrane bound and secreted CSF1 that both sustain peritoneal macrophage growth.

INA03, a potent transferrin-competitive antibody-drug conjugate against CD71, for a safer acute leukemia treatment.

Innovative strategies to enhance efficacy and overcome drug resistance in hematologic cancers such as antibody-drug conjugates (ADCs) have shifted the paradigm of conventional care by delivering promising outcomes in cancer therapies with a significant reduction in the risk of relapse. The transferrin receptor 1, CD71, known to be overexpressed in malignant cells, is considered a potent anti-tumoral target. Therefore, we have developed an anti-CD71 ADC, INA03, a humanized antibody conjugated to the monomethyl auristatin E (MMAE) through a 3-arylpropiolonitrile-valine-citruline linker. In this study, we investigated both potency and safety of INA03, in competition with transferrin (Tf), the CD71's natural ligand, as a novel strategy to specifically target highly proliferative cells. The high expression of CD71 was confirmed on different leukemic cell lines, allowing INA03 to bind efficiently. Subsequently, INA03 rapidly internalizes into lysosomal compartments, where its cytotoxic drug is released following cathepsin-B cleavage. Downregulating CD71 expression using shRNA highlighted that INA03-induced cell death was dependent on CD71 density at the cell surface. INA03 intravenous treatment in acute leukemia mouse models significantly reduced tumor burden, increased mice survival and showed no residual disease compared to conventional chemotherapies. Since INA03 competes with the human Tf, a double knock-in (hCD71/hTf) competent mouse model was generated to mimic human pharmacokinetics and pharmacodynamics. INA03 administration in hCD71/hTf mice did not reveal, even at high doses, any improper toxicities. Hence, these data demonstrate promising pre-clinical efficacy and safety of INA03 and support its development as a novel acute leukemia treatment.

Unravelling the sex-specific diversity and functions of adrenal gland macrophages.

Despite the ubiquitous function of macrophages across the body, the diversity, origin, and function of adrenal gland macrophages remain largely unknown. We define the heterogeneity of adrenal gland immune cells using single-cell RNA sequencing and use genetic models to explore the developmental mechanisms yielding macrophage diversity. We define populations of monocyte-derived and embryonically seeded adrenal gland macrophages and identify a female-specific subset with low major histocompatibility complex (MHC) class II expression. In adulthood, monocyte recruitment dominates adrenal gland macrophage maintenance in female mice. Adrenal gland macrophage sub-tissular distribution follows a sex-dimorphic pattern, with MHC class IIlow macrophages located at the cortico-medullary junction. Macrophage sex dimorphism depends on the presence of the cortical X-zone. Adrenal gland macrophage depletion results in altered tissue homeostasis, modulated lipid metabolism, and decreased local aldosterone production during stress exposure. Overall, these data reveal the heterogeneity of adrenal gland macrophages and point toward sex-restricted distribution and functions of these cells.

Brown adipose tissue monocytes support tissue expansion.

Monocytes are part of the mononuclear phagocytic system. Monocytes play a central role during inflammatory conditions and a better understanding of their dynamics might open therapeutic opportunities. In the present study, we focused on the characterization and impact of monocytes on brown adipose tissue (BAT) functions during tissue remodeling. Single-cell RNA sequencing analysis of BAT immune cells uncovered a large diversity in monocyte and macrophage populations. Fate-mapping experiments demonstrated that the BAT macrophage pool requires constant replenishment from monocytes. Using a genetic model of BAT expansion, we found that brown fat monocyte numbers were selectively increased in this scenario. This observation was confirmed using a CCR2-binding radiotracer and positron emission tomography. Importantly, in line with their tissue recruitment, blood monocyte counts were decreased while bone marrow hematopoiesis was not affected. Monocyte depletion prevented brown adipose tissue expansion and altered its architecture. Podoplanin engagement is strictly required for BAT expansion. Together, these data redefine the diversity of immune cells in the BAT and emphasize the role of monocyte recruitment for tissue remodeling.

Non-canonical glutamine transamination sustains efferocytosis by coupling redox buffering to oxidative phosphorylation.

Macrophages rely on tightly integrated metabolic rewiring to clear dying neighboring cells by efferocytosis during homeostasis and disease. Here we reveal that glutaminase-1-mediated glutaminolysis is critical to promote apoptotic cell clearance by macrophages during homeostasis in mice. In addition, impaired macrophage glutaminolysis exacerbates atherosclerosis, a condition during which, efficient apoptotic cell debris clearance is critical to limit disease progression. Glutaminase-1 expression strongly correlates with atherosclerotic plaque necrosis in patients with cardiovascular diseases. High-throughput transcriptional and metabolic profiling reveals that macrophage efferocytic capacity relies on a non-canonical transaminase pathway, independent from the traditional requirement of glutamate dehydrogenase to fuel ɑ-ketoglutarate-dependent immunometabolism. This pathway is necessary to meet the unique requirements of efferocytosis for cellular detoxification and high-energy cytoskeletal rearrangements. Thus, we uncover a role for non-canonical glutamine metabolism for efficient clearance of dying cells and maintenance of tissue homeostasis during health and disease in mouse and humans.

ABCA1 Exerts Tumor-Suppressor Function in Myeloproliferative Neoplasms.

Defective cholesterol efflux pathways in mice promote the expansion of hematopoietic stem and progenitor cells and a bias toward the myeloid lineage, as observed in chronic myelomonocytic leukemia (CMML). Here, we identify 5 somatic missense mutations in ABCA1 in 26 patients with CMML. These mutations confer a proliferative advantage to monocytic leukemia cell lines in vitro. In vivo inactivation of ABCA1 or expression of ABCA1 mutants in hematopoietic cells in the setting of Tet2 loss demonstrates a myelosuppressive function of ABCA1. Mechanistically, ABCA1 mutations impair the tumor-suppressor functions of WT ABCA1 in myeloproliferative neoplasms by increasing the IL-3Rß signaling via MAPK and JAK2 and subsequent metabolic reprogramming. Overexpression of a human apolipoprotein A-1 transgene dampens myeloproliferation. These findings identify somatic mutations in ABCA1 that subvert its anti-proliferative and cholesterol efflux functions and permit the progression of myeloid neoplasms. Therapeutic increases in HDL bypass these defects and restore normal hematopoiesis.

Biology and function of adipose tissue macrophages, dendritic cells and B cells.

The increasing incidence of obesity and its socio-economical impact is a global health issue due to its associated co-morbidities, namely diabetes and cardiovascular disease [1-5]. Obesity is characterized by an increase in adipose tissue, which promotes the recruitment of immune cells resulting in low-grade inflammation and dysfunctional metabolism. Macrophages are the most abundant immune cells in the adipose tissue of mice and humans. The adipose tissue also contains other myeloid cells (dendritic cells (DC) and neutrophils) and to a lesser extent lymphocyte populations, including T cells, B cells, Natural Killer (NK) and Natural Killer T (NKT) cells. While the majority of studies have linked adipose tissue macrophages (ATM) to the development of low-grade inflammation and co-morbidities associated with obesity, emerging evidence suggests for a role of other immune cells within the adipose tissue that may act in part by supporting macrophage homeostasis. In this review, we summarize the current knowledge of the functions ATMs, DCs and B cells possess during steady-state and obesity.