TREM2 mediates MHCII-associated CD4+ T-cell response against gliomas

TREM2 promotes the formation of a tumor-supportive microenvironment in hepatocellular carcinoma

BACKGROUND

Triggering receptor expressed on myeloid cells 2 (TREM2), a surface receptor predominantly expressed on myeloid cells, is a major hub gene in pathology-induced immune signaling. However, its function in hepatocellular carcinoma (HCC) remains controversial. This study aimed to evaluate the role of TREM2 in the tumor microenvironment in the context of HCC progression.

METHODS

HCC was experimentally induced in wild-type (WT) and Trem2-deficient (Trem2-/-) mice, and clinical sample analysis and in vitro studies on macrophages were conducted. HCC cells were treated with conditioned medium from WT or Trem2-/- macrophages, and their malignant phenotypes and underlying mechanisms were analyzed.

RESULTS

TREM2 deficiency reduced liver tumor burden in orthotopic and subcutaneous HCC models by altering CD8+ T cell infiltration. Trem2-deficient macrophages presented increased chemokine secretion. TGF-β1 was found to be positively correlated with TREM2 expression in HCC, and TGF-β blockade reversed TREM2 induction. On the other hand, TREM2+ macrophages were found to be associated with glycolysis and PKM2 expression in HCC cells; this association may be related to the secretion of IL-1β, which enhances the malignant phenotypes of HCC cells.

CONCLUSIONS

These results reveal that TREM2+ macrophages play a driving role in HCC progression by suppressing CD8+ T cell infiltration and promoting tumor cell glycolysis, providing a new therapeutic target for HCC.

Targeting tumor-associated macrophages: Novel insights into immunotherapy of skin cancer

BACKGROUND

The incidence of skin cancer is currently increasing, and conventional treatment options inadequately address the demands of disease management. Fortunately, the recent rapid advancement of immunotherapy, particularly immune checkpoint inhibitors (ICIs), has ushered in a new era for numerous cancer patients. However, the efficacy of immunotherapy remains suboptimal due to the impact of the tumor microenvironment (TME). Tumor-associated macrophages (TAMs), a major component of the TME, play crucial roles in tumor invasion, metastasis, angiogenesis, and immune evasion, significantly impacting tumor development. Consequently, TAMs have gained considerable attention in recent years, and their roles have been extensively studied in various tumors. However, the specific roles of TAMs and their regulatory mechanisms in skin cancer remain unclear.

AIM OF REVIEW

This paper aims to elucidate the origin and classification of TAMs, investigate the interactions between TAMs and various immune cells, comprehensively understand the precise mechanisms by which TAMs contribute to the pathogenesis of different types of skin cancer, and finally discuss current strategies for targeting TAMs in the treatment of skin cancer.

KEY SCIENTIFIC CONCEPTS OF OVERVIEW

With a specific emphasis on the interrelationship between TAMs and skin cancer, this paper posits that therapeutic modalities centered on TAMs hold promise in augmenting and harmonizing with prevailing clinical interventions for skin cancer, thereby charting a novel trajectory for advancing the landscape of immunotherapeutic approaches for skin cancer.

Unveiling the Inflammatory Landscape of Recurrent Glioblastoma through Histological-Based Assessments

The glioblastoma (GBM) tumor microenvironment consists of a heterogeneous mixture of neoplastic and non-neoplastic cells, including immune cells. Tumor recurrence following standard-of-care therapy results in a rich landscape of inflammatory cells throughout the glioma-infiltrated cortex. Immune cells consisting of glioma-associated macrophages and microglia (GAMMs) overwhelmingly constitute the bulk of the recurrent glioblastoma (rGBM) microenvironment, in comparison to the highly cellular and proliferative tumor microenvironment characteristic of primary GBM. These immune cells dynamically interact within the tumor microenvironment and can contribute to disease progression and therapy resistance while also providing novel targets for emerging immunotherapies. Within these varying contexts, histological-based assessments of immune cells in rGBM, including immunohistochemistry (IHC) and immunofluorescence (IF), offer a critical way to visualize and examine the inflammatory landscape. Here, we exhaustively review the available body of literature on the inflammatory landscape in rGBM as identified through histological-based assessments. We highlight the heterogeneity of immune cells throughout the glioma-infiltrated cortex with a focus on microglia and macrophages, drawing insights from canonical and novel immune-cell histological markers to estimate cell phenotypes and function. Lastly, we discuss opportunities for immunomodulatory treatments aiming to harness the inflammatory landscape in rGBM.

CD8 positive T-cells decrease neurogenesis and induce anxiety-like behaviour following hepatitis B vaccination

Mounting evidence indicates the involvement of peripheral immunity in the regulation of brain function, influencing aspects such as neuronal development, emotion, and cognitive abilities. Previous studies from our laboratory have revealed that neonatal hepatitis B vaccination can downregulate hippocampal neurogenesis, synaptic plasticity and spatial learning memory. In the current post-epidemic era characterized by universal vaccination, understanding the impact of acquired immunity on neuronal function and neuropsychiatric disorders, along with exploring potential underlying mechanisms, becomes imperative. We employed hepatitis B vaccine-induced CD3 positive T cells in immunodeficient mice to investigate the key mechanisms through which T cell subsets modulate hippocampal neurogenesis and anxiety-like behaviours. Our data revealed that mice receiving hepatitis B vaccine-induced T cells exhibited heightened anxiety and decreased hippocampal cell proliferation compared to those receiving phosphate-buffered saline-T cells or wild-type mice. Importantly, these changes were predominantly mediated by infiltrated CD8+ T cells into the brain, rather than CD4+ T cells. Transcriptome profiling of CD8+ T cells unveiled that C-X-C motif chemokine receptor 6 positive (CXCR6+) CD8+ T cells were recruited into the brain through microglial and astrocyte-derived C-X-C motif chemokine ligand 16 (CXCL16). This recruitment process impaired neurogenesis and induced anxiety-like behaviour via tumour necrosis factor-α-dependent mechanisms. Our findings highlight the role of glial cell derived CXCL16 in mediating the recruitment of CXCR6+CD8+ T cell subsets into the brain. This mechanism represents a potential avenue for modulating hippocampal neurogenesis and emotion-related behaviours after hepatitis B vaccination.

The peripheral CD4+ T cells predict efficacy in non-small cell lung cancer (NSCLC) patients with the anti-PD-1 treatment

Background

Programmed cell death protein 1 (PD-1) inhibitor therapy has become a routine treatment for advanced non-small cell lung cancer (NSCLC). However, only some NSCLC patients would benefit from anti-PD-1 therapy. We urgently need to identify biomarkers associated with clinical response to change treatment strategies promptly for patients who fail to benefit from anti-PD-1 treatment. This study was aimed to explore whether circulating CD4+ T cells and CD8+ T cells could be biomarkers for predicting anti-PD-1 efficacy.

Methods

In this study, 118 NSCLC patients who received anti-PD-1 therapy were enrolled. The percentages of circulating CD4+ T cells and CD8+ T cells before and after anti-PD-1 treatment were determined by flow cytometry. The programmed cell death ligand 1 (PD-L1) expression of tumor tissues was detected by immunocytochemistry. The anti-PD-1 treatment efficacy was assessed by immune response evaluation criteria in solid tumors (iRECIST).

Results

The percentage of CD4+ T cells and CD4+/CD8+ ratio in the peripheral blood (PB) was significantly elevated after anti-PD-1 treatment. In contrast, the percentage of CD8+ T cells in the PB was significantly decreased after anti-PD-1 treatment. Furthermore, we found that the percentages of CD4+ T cells and CD4+/CD8+ ratios considerably increased, and the percentages of CD8+ T cells significantly reduced in the effective group. On the contrary, the patients in the ineffective group showed no significant differences in the biomarkers. Multivariate logistic revealed that the percentage of CD4+ T cells at baseline was an independent predictor of anti-PD-1 treatment. The area under the curve (AUC) of the CD4+ T cells percentage was 0.7834 with a cut-off value of 28.53% (sensitivity =82.5%, specificity =66.23%).

Conclusions

The percentage of CD4+ T cells at baseline could predict anti-PD-1 efficacy in NSCLC patients.

Galectin-3 induces pathogenic immunosuppressive macrophages through interaction with TREM2 in lung cancer

BACKGROUND

High infiltration of tumor-associated macrophages (TAMs) is associated with tumor promotion and immunosuppression. The triggering receptor expressed on myeloid cells 2 (TREM2) is emerged as a key immunosuppressive regulator for TAMs, however, how TREM2-expressing TAMs are recruited and what ligands TREM2 interacts with to mediate immunosuppression is unknown.

METHODS

Flow cytometry and single-cell RNA sequencing were used to analyze TREM2 expression. Mechanistically, mass spectrometry and immunoprecipitation were employed to identify proteins binding to TREM2. Phagocytosis and co-culture experiments were used to explore the in vitro functions of galectin3-TREM2 pair. Establishment of TREM2f/f-Lyz2-cre mice to validate the role of TREM2 signaling pathway in lung carcinogenesis. GB1107 were further supplemented to validate the therapeutic effect of Galectin3 based on TREM2 signaling regulation.

RESULTS

This study identified that abundant TREM2+ macrophages were recruited at the intra-tumor site through the CCL2-CCR2 chemotactic axis. Galectin-3 impaired TREM2-mediated phagocytosis and promoted the conversion of TREM2+ macrophages to immunosuppressive TAMs with attenuated antigen presentation and co-stimulatory functions both in vitro both in vivo, and galectin-3 is a potential ligand for TREM2. Genetic and pharmacological blockade of TREM2 and galectin-3 significantly inhibited lung cancer progression in subcutaneous and orthotopic cancer models by remodeling the tumor immune microenvironment.

CONCLUSION

Our findings revealed a previously unknown association between galectin-3 and TREM2 in TAMs of lung cancer, and suggested simultaneous inhibition of galectin3 and TREM2 as potent therapeutic approach for lung cancer therapy.

Knockdown of trem2 promotes proinflammatory microglia and inhibits glioma progression via the JAK2/STAT3 and NF-κB pathways

BACKGROUND

In the tumor immune microenvironment (TIME), triggering receptor expressed on myeloid cells 2 (trem2) is widely considered to be a crucial molecule on tumor-associated macrophages(TAMs). Multiple studies have shown that trem2 may function as an immune checkpoint in various malignant tumors, mediating tumor immune evasion. However, its specific molecular mechanisms, especially in glioma, remain elusive.

METHODS

Lentivirus was transfected to establish cells with stable knockdown of trem2. A Transwell system was used for segregated coculture of glioma cells and microglia. Western blotting, quantitative real-time polymerase chain reaction (qRT‒PCR), and immunofluorescence (IF) were used to measure the expression levels of target proteins. The proliferation, invasion, and migration of cells were detected by colony formation, cell counting kit-8 (CCK8), 5-ethynyl-2'-deoxyuridine (EdU) and transwell assays. The cell cycle, apoptosis rate and reactive oxygen species (ROS) level of cells were assessed using flow cytometry assays. The comet assay and tube formation assay were used to detect DNA damage in glioma cells and angiogenesis activity, respectively. Gl261 cell lines and C57BL/6 mice were used to construct the glioma orthotopic transplantation tumor model.

RESULTS

Trem2 was highly overexpressed in glioma TAMs. Knocking down trem2 in microglia suppressed the growth and angiogenesis activity of glioma cells in vivo and in vitro. Mechanistically, knockdown of trem2 in microglia promoted proinflammatory microglia and inhibited anti-inflammatory microglia by activating jak2/stat1 and inhibiting the NF-κB p50 signaling pathway. The proinflammatory microglia produced high concentrations of nitric oxide (NO) and high levels of the proinflammatory cytokines TNF-α, IL-6, and IL-1β, and caused further DNA damage and promoted the apoptosis rate of tumor cells.

CONCLUSIONS

Our findings revealed that trem2 in microglia plays a significant role in the TIME of gliomas. Knockdown of trem2 in microglia might help to improve the efficiency of inhibiting glioma growth and delaying tumor progression and provide new ideas for further treatment of glioma.

CCR2+ monocytes replenish border-associated macrophages in the diseased mouse brain

Border-associated macrophages (BAMs) are tissue-resident macrophages that reside at the border of the central nervous system (CNS). Since BAMs originate from yolk sac progenitors that do not persist after birth, the means by which this population of cells is maintained is not well understood. Using two-photon microscopy and multiple lineage-tracing strategies, we determine that CCR2+ monocytes are significant contributors to BAM populations following disruptions of CNS homeostasis in adult mice. After BAM depletion, while the residual BAMs possess partial self-repopulation capability, the CCR2+ monocytes are a critical source of the repopulated BAMs. In addition, we demonstrate the existence of CCR2+ monocyte-derived long-lived BAMs in a brain compression model and in a sepsis model after the initial disruption of homeostasis. Our study reveals that the short-lived CCR2+ monocytes transform into long-lived BAM-like cells at the CNS border and subsequently contribute to BAM populations.