Highlights d Flow cytometry, RNA-seq, and protein and image analyses reveal brain TME complexity d Glioma IDH mutation status and brain metastasis primary tumors shape the brain TME d Microglia and monocyte-derived macrophages exhibit multifaceted activation d TME immune cells show disease-and cell-type-specific expression patterns

In normal tissue repair, macrophages exhibit a pro-inflammatory phenotype (M1) at early stages and a pro-healing phenotype (M2) at later stages. We have previously shown that M1 macrophages initiate angiogenesis while M2 macrophages promote vessel maturation. Therefore, we reasoned that scaffolds that promote sequential M1 and M2 polarization of infiltrating macrophages should result in enhanced angiogenesis and healing. To this end, we first analyzed the in vitro kinetics of macrophage phenotype switch using flow cytometry, gene expression, and cytokine secretion analysis. Then, we designed scaffolds for bone regeneration based on modifications of decellularized bone for a short release of interferon-gamma (IFNg) to promote the M1 phenotype, followed by a more sustained release of interleukin-4 (IL4) to promote the M2 phenotype. To achieve this sequential release profile, IFNg was physically adsorbed onto the scaffolds, while IL4 was attached via biotin-streptavidin binding. Interestingly, despite the strong interactions between biotin and streptavidin, release studies showed that biotinylated IL4 was released over 6 days. These scaffolds promoted sequential M1 and M2 polarization of primary human macrophages as measured by gene expression of ten M1 and M2 markers and secretion of four cytokines, although the overlapping phases of IFNg and IL4 release tempered polarization to some extent. Murine subcutaneous implantation model showed increased vascularization in scaffolds releasing IFNg compared to controls. This study demonstrates that scaffolds for tissue engineering can be designed to harness the angiogenic behavior of host macrophages towards scaffold vascularization.

Colony-stimulating factor 1 (CSF1) is a key regulator of monocyte/macrophage differentiation that sustains the protumorigenic functions of tumor-associated macrophages (TAMs). We show that CSF1 is expressed in human melanoma, and patients with metastatic melanoma have increased CSF1 in blood compared to healthy subjects. In tumors, CSF1 expression correlated with the abundance of CD8 + T cells and CD163 + TAMs. Human melanoma cell lines consistently produced CSF1 after exposure to melanoma-specific CD8 + T cells or T cell-derived cytokines in vitro, reflecting a broadly conserved mechanism of CSF1 induction by activated CD8 + T cells. Mining of publicly available transcriptomic data sets suggested co-enrichment of CD8 + T cells with CSF1 or various TAM-specific markers in human melanoma, which was associated with nonresponsiveness to programmed cell death protein 1 (PD1) checkpoint blockade in a smaller patient cohort. Combination of anti-PD1 and anti-CSF1 receptor (CSF1R) antibodies induced the regression of BRAF V600E-driven, transplant mouse melanomas, a result that was dependent on the effective elimination of TAMs. Collectively, these data implicate CSF1 induction as a CD8 + T cell-dependent adaptive resistance mechanism and show that simultaneous CSF1R targeting may be beneficial in melanomas refractory to immune checkpoint blockade and, possibly, other T cell-based therapies.

No abstract

Alternatively activated “M2” macrophages are believed to function during late stages of wound healing, behaving in an anti-inflammatory manner to mediate the resolution of the pro-inflammatory response caused by “M1” macrophages. However, the differences between two main subtypes of M2 macrophages, namely interleukin-4 (IL-4)-stimulated “M2a” macrophages and IL-10-stimulated “M2c” macrophages, are not well understood. M2a macrophages are characterized by their ability to inhibit inflammation and contribute to the stabilization of angiogenesis. However, the role and temporal profile of M2c macrophages in wound healing are not known. Therefore, we performed next generation sequencing (RNA-seq) to identify biological functions and gene expression signatures of macrophages polarized in vitro with IL-10 to the M2c phenotype in comparison to M1 and M2a macrophages and an unactivated control (M0). We then explored the expression of these gene signatures in a publicly available data set of human wound healing. RNA-seq analysis showed that hundreds of genes were upregulated in M2c macrophages compared to the M0 control, with thousands of alternative splicing events. Following validation by Nanostring, 39 genes were found to be upregulated by M2c macrophages compared to the M0 control, and 17 genes were significantly upregulated relative to the M0, M1, and M2a phenotypes (using an adjusted p-value cutoff of 0.05 and fold change cutoff of 1.5). Many of the identified M2c-specific genes are associated with angiogenesis, matrix remodeling, and phagocytosis, including CD163, MMP8, TIMP1, VCAN, SERPINA1, MARCO, PLOD2, PCOCLE2 and F5. Analysis of the macrophage-conditioned media for secretion of matrix-remodeling proteins showed that M2c macrophages secreted higher levels of MMP7, MMP8, and TIMP1 compared to the other phenotypes. Interestingly, temporal gene expression analysis of a publicly available microarray data set of human wound healing showed that M2c-related genes were upregulated at early times after injury, similar to M1-related genes, while M2a-related genes appeared at later stages or were downregulated after injury. While further studies are required to confirm the timing and role of M2c macrophages in vivo, these results suggest that M2c macrophages may function at early stages of wound healing. Identification of markers of the M2c phenotype will allow more detailed investigations into the role of M2c macrophages in vivo.

Highlights d Macrophages produce abundant extracellular vesicles in tumors d Macrophage-derived extracellular vesicles (TAM-EVs) display unique proteomic profiles d TAM-EVs enhance thromboxane synthesis in cancer cells d TAM-EVs promote, rather than limit, T cell proliferation and activation

No abstract

Pericytes regulate the development of organ-specific characteristics of the brain vasculature such as the blood–brain barrier (BBB) and astrocytic end-feet. Whether pericytes are involved in the control of leukocyte trafficking in the adult central nervous system (CNS), a process tightly regulated by CNS vasculature, remains elusive. Using adult pericyte-deficient mice (Pdgfbret/ret), we show that pericytes limit leukocyte infiltration into the CNS during homeostasis and autoimmune neuroinflammation. The permissiveness of the vasculature toward leukocyte trafficking in Pdgfbret/ret mice inversely correlates with vessel pericyte coverage. Upon induction of experimental autoimmune encephalomyelitis (EAE), pericyte-deficient mice die of severe atypical EAE, which can be reversed with fingolimod, indicating that the mortality is due to the massive influx of immune cells into the brain. Additionally, administration of anti-VCAM-1 and anti–ICAM-1 antibodies reduces leukocyte infiltration and diminishes the severity of atypical EAE symptoms of Pdgfbret/ret mice, indicating that the proinflammatory endothelium due to absence of pericytes facilitates exaggerated neuroinflammation. Furthermore, we show that the presence of myelin peptide-specific peripheral T cells in Pdgfbret/ret;2D2tg mice leads to the development of spontaneous neurological symptoms paralleled by the massive influx of leukocytes into the brain. These findings indicate that intrinsic changes within brain vasculature can promote the development of a neuroinflammatory disorder.