Phenotypic diversity of T cells in human primary and metastatic brain tumors revealed by multiomic interrogation

Regulatory T cell depletion promotes myeloid cell activation and glioblastoma response to anti-PD1 and tumor-targeting antibodies

Glioblastoma is invariably lethal and responds poorly to immune checkpoint blockade. Here, we examined the impact of regulatory T (Treg) cell depletion on glioblastoma progression and immunotherapy responsiveness. In human glioblastoma, elevated Treg cell signatures correlated with poorer survival outcomes, with these cells expressing high levels of CD25. In Nf1-/-Pten-/-EGFRvIII+ glioblastoma-bearing mice, a single dose of non-interleukin-2 (IL-2) blocking (NIB) anti-CD25 (anti-CD25NIB) antibody depleted Treg cells and promoted CD8+ T cell clonal expansion and partial tumor control, further enhanced by programmed cell death-1 (PD1)-blockade. Treg cell depletion induced interferon-γ (IFN-γ)-dependent tumor microenvironment remodeling, increasing Fcγ receptor (FcγR) expression on intratumoral myeloid cells and enhancing phagocytosis. Combination of anti-CD25NIB with anti-EGFRvIII tumor-targeting antibodies resulted in complete tumor control. Anti-human CD25NIB treatment of glioblastoma patient-derived tumor fragments effectively depleted Treg cells and activated CD8+ T cells. These findings underscore the therapeutic relevance of Treg targeting in glioblastoma and unveil potent combination strategies for anti-CD25NIB based on innate cell activation.

Immunotherapy in lung cancer brain metastases

Brain metastases (BM) occur frequently in lung cancer, particularly in non-small cell lung cancer (NSCLC) patients and remain a significant cause of morbidity and mortality. Standard therapies have limited efficacy due to poor crossing of the blood-brain barrier and the distinct features between BM and the primary tumor. This review explores the immune landscape of brain metastatic disease, emerging immunotherapeutic strategies, and promising biomarkers in NSCLC patients.

Single-cell atlas of endothelial and mural cells across primary and metastatic brain tumors

Central nervous system (CNS) malignancies include primary tumors, such as gliomas, and brain metastases (BrMs) originating from diverse extracranial cancers. The blood-brain barrier (BBB) is a key structural component of both primary and metastatic brain cancers. Here, we comprehensively analyzed the two major BBB cell types, endothelial and mural cells, across non-tumor brain tissue, isocitrate dehydrogenase (IDH) mutant (IDH mut) low-grade gliomas, IDH wild-type (IDH WT) high-grade glioblastomas (GBMs), and BrMs from various primary tumors. Bulk and single-cell RNA sequencing, integrated with spatial analyses, revealed that GBMs, but not low-grade gliomas, exhibit significant alterations in the tumor vasculature, including the emergence of diverse pathological vascular cell subtypes. However, these alterations are less pronounced in GBMs than in BrMs. Notably, the BrM vasculature shows higher permeability and more extensive interactions with distinct immune cell populations. This vascular atlas presents a resource toward understanding of tumor-specific vascular features in the brain, providing a foundation for developing vascular- and immune-targeting therapies.

The local microenvironment suppresses the synergy between irradiation and anti-PD1 therapy in breast-to-brain metastasis

The brain environment is uniquely specialized to protect its neuronal tissue from excessive inflammation by tightly regulating adaptive immunity. However, in the context of brain cancer progression, this regulation can lead to a conflict between T cell activation and suppression. Here, we show that, while CD8+ T cells can infiltrate breast cancer-brain metastases, their anti-tumor cytotoxicity is locally suppressed in the brain. Conversely, CD8+ T cells exhibited tumoricidal activity in extracranial mammary lesions originating from the same cancer cells. Consequently, combined high-dose irradiation and anti-programmed cell death protein 1 (PD1) therapy was effective in extracranial tumors but not intracranial lesions. Transcriptional analyses and functional studies identified neutrophils and Trem2-expressing macrophages as key sources for local T cell suppression within the brain, providing rational targets for future therapeutic strategies.

Mathematical Modeling Predicts Optimal Immune Checkpoint Inhibitor and Radiotherapy Combinations and Timing of Administration

Radiotherapy (RT) combined with immune checkpoint inhibitor (ICI) therapy has attracted substantial attention due to its potential to improve outcomes for patients with several types of cancer. However, the optimal administration timepoints and drug combinations remain unclear because the mechanisms underlying RT-induced changes in immune checkpoint molecule expression and interaction with their ligand(s) remain unclear. In this study, we demonstrated the dynamics of lymphocyte-mediated molecular interactions in tissue samples from patients with esophageal cancer throughout RT schedules. Single-cell RNA sequencing and spatial transcriptomic analyses were performed to investigate the dynamics of these interactions. The biological signal in lymphocytes transitioned from innate to adaptive immune reaction, with increases in ligand-receptor interactions, such as PD-1-PD-L1, CTLA4-CD80/86, and TIGIT-PVR interactions. A mathematical model was constructed to predict the efficacy of five types of ICIs when administered at four different timepoints. The model suggested that concurrent anti-PD-1/PD-L1 therapy or concurrent/adjuvant anti-CTLA4/TIGIT therapy would exert a maximal effect with RT. This study provides rationale for clinical trials of RT combined with defined ICI therapy, and these findings will support future studies to search for more effective targets and timing of therapy administration.

Mucin 5AC Promotes Breast Cancer Brain Metastasis through cMET/CD44v6

PURPOSE

Breast cancer brain metastasis remains a significant clinical problem. Mucins have been implicated in metastasis; however, whether they are also involved in breast cancer brain metastasis remains unknown. We queried databases of patients with brain metastasis and found mucin 5AC (MUC5AC) to be upregulated and therefore sought to define the role of MUC5AC in breast cancer brain metastasis.

EXPERIMENTAL DESIGN

In silico dataset analysis, RNA-sequence profiling of patient samples and cell lines, analysis of patient serum samples, and in vitro/in vivo knockdown experiments were performed to determine the function of MUC5AC in breast cancer brain metastasis. Coimmunoprecipitation was used to unravel the interactions that can be therapeutically targeted.

RESULTS

Global in silico transcriptomic analysis showed that MUC5AC is significantly higher in patients with breast cancer brain metastasis. Analysis of archived breast cancer brain metastasis tissue further revealed significantly higher expression of MUC5AC in all breast cancer subtypes, and high MUC5AC expression predicted poor survival in HER2+ breast cancer brain metastasis. We validated these observations in breast cancer brain metastatic cell lines and tissue samples. Interestingly, elevated levels of MUC5AC were detected in the sera of patients with breast cancer brain metastasis. MUC5AC silencing in breast cancer brain metastatic cells reduced their migration and adhesion in vitro and in brain metastasis in the intracardiac injection mouse model. We found high expression of cMET and CD44v6 in breast cancer brain metastasis, which increased MUC5AC expression via hepatocyte growth factor signaling. In addition, MUC5AC interacts with cMET and CD44v6, suggesting that MUC5AC promotes breast cancer brain metastasis via the cMET/CD44v6 axis. Inhibition of the MUC5AC/cMET/CD44v6 axis with the blood-brain barrier-permeable cMET inhibitor bozitinib (PLB1001) effectively inhibits breast cancer brain metastasis.

CONCLUSIONS

Our study establishes that the MUC5AC/cMET/CD44v6 axis is critical for breast cancer brain metastasis, and blocking this axis will be a novel therapeutic approach for breast cancer brain metastasis.

Density and entropy of immune cells within the tumor microenvironment of primary tumors and matched brain metastases

BACKGROUND

Tumor-infiltrating lymphocytes (TILs) and tumor-associated macrophages (TAMs) have increasingly been reported to impact the brain metastatic process of solid tumors. However, data on intra-individual differences between primary tumor and brain metastasis (BM), as well as their correlation with clinical outcome parameters, is scarce.

METHODS

We retrospectively identified patients who received resection of the primary tumor and BM between 01/1990 and 10/2022. Density quantification of TAMs (CD68+, CD163+) and TILs (CD3+, CD8+, CD45RO+, FOXP3+) was performed by immunohistochemical staining of matched tumor tissue samples. Images were processed with QuPath software and heterogeneity of generated heatmaps was measured by Shannon Entropy. Time-to-BM (TTBM) was defined as the time from diagnosis of the primary tumor until the first diagnosis of BM.

RESULTS

In total, 104 patients (46.2% female; median age 57.3 years at BM diagnosis) were included: 78/104 (75%) non-small cell lung cancer, 18/104 (17%) breast cancer, 8/104 (8%) renal cell carcinomas. Densities of CD3+ (p < 0.001) and CD8+-TILs (p < 0.001) were higher in primary tumor samples, while CD68+ (p = 0.035) and CD163+-TAM densities (p < 0.001) were higher in the matched BM. Higher CD3+, CD8+-TILs and CD163+-TAMs densities in primary tumors were associated with shorter TTBM (p = 0.005, p = 0.015 and p = 0.006, respectively). Higher entropies of CD3+ (p < 0.001) and FOXP3+ (p = 0.011) TILs were observed in primary tumors compared to BM. Longer TTBM was associated with higher entropy of FOXP3+ TILs (p = 0.024) and lower entropy in CD163+ TAMs (p = 0.039). No significant associations of immune cell densities or entropies with OS after BM diagnosis were found.

DISCUSSION

By utilizing a unique cohort of matched primary tumor and BM tissue samples, we could demonstrate higher TIL densities in primary tumors and higher TAM densities in BM, respectively. Higher cell densities of CD3+, CD8+-TILs and CD163+-TAMs in primary tumors were associated with shorter TTBM, while a larger difference between CD3+ and CD8+ densities between primary tumor and BM was associated with longer TTBM. These findings highlight the potential of targeting TAMs as a therapeutic strategy to mitigate the development of brain metastases.

Intratumoral gene delivery of 4-1BBL boosts IL-12-triggered anti-glioblastoma immunity

The standard of care in high-grade gliomas has remained unchanged in the past 20 years. Efforts to replicate effective immunotherapies in non-cranial tumors have led to only modest therapeutical improvements in glioblastoma (GB). Here, we demonstrate that intratumoral administration of recombinant interleukin-12 (rIL-12) promotes local cytotoxic CD8 POS T cell accumulation and conversion into an effector-like state, resulting in a dose-dependent survival benefit in preclinical GB mouse models. This tumor-reactive CD8 T cell response is further supported by intratumoral rIL-12-sensing dendritic cells (DCs) and is accompanied by the co-stimulatory receptor 4-1BB expression on both cell types. Given that DCs and CD8 POS T cells are functionally suppressed in the tumor microenvironments of de novo and recurrent glioma patients, we tested whether anti-tumor response at the rIL-12-inflamed tumor site could be enhanced with 4-1BBL, the ligand of 4-1BB. 4-1BBL was delivered using an adeno-associated virus (AAV) vector targeting GFAP-expressing cells and resulted in prolonged survival of rIL-12 treated GB-bearing mice. This study establishes that tumor antigen-specific CD8 T cell activity can be directed using an AAV-vector-mediated gene therapy approach, effectively enhancing anti-GB immunity.

Gemistocytic tumor cells programmed for glial scarring characterize T cell confinement in IDH-mutant astrocytoma

Isocitrate dehydrogenase 1/2 mutant (IDHmt) astrocytoma is considered a T cell-deprived tumor, yet little is known regarding the phenotypes underlying T cell exclusion. Using bulk, single nucleus and spatial RNA and protein profiling, we demonstrate that a distinct spatial organization underlies T cell confinement to the perivascular space (T cell cuff) in IDHmt astrocytoma. T cell cuffs are uniquely characterized by a high abundance of gemistocytic tumor cells (GTC) in the surrounding stroma. Integrative analysis shows that GTC-high tumors are enriched for lymphocytes and tumor associated macrophages (TAM) and express immune cell migration and activation programs. Specifically, GTCs constitute a distinct sub-cluster of the astrocyte-like tumor cell state that co-localizes with immune reactive TAMs. Neighboring GTCs and TAMs express receptor-ligand pairs characteristic of reactive astrogliosis and glial scarring, such as SPP1/CD44 and IL-1β/IL1R1. Collectively, we reveal that T cell confinement in IDHmt astrocytomas associates with GTC-TAM networks that mimic glial scarring mechanisms.

Progress in personalized immunotherapy for patients with brain metastasis

Brain metastasis leads to poor outcomes and CNS injury, significantly reducing quality of life and survival rates. Advances in understanding the tumor immune microenvironment have revealed the promise of immunotherapies, which, alongside surgery, chemotherapy, and radiation, offer improved survival for some patients. However, resistance to immunotherapy remains a critical challenge. This review explores the immune landscape of brain metastases, current therapies, clinical trials, and the need for personalized, biomarker-driven approaches to optimize outcomes.

The immune landscape in brain metastasis

The prognosis for patients with brain metastasis remains dismal despite intensive therapy including surgical resection, radiotherapy, chemo-, targeted, and immunotherapy. Thus, there is a high medical need for new therapeutic options. Recent advances employing high-throughput and spatially resolved single-cell analyses have provided unprecedented insights into the composition and phenotypes of the diverse immune cells in the metastatic brain, revealing a unique immune landscape starkly different from that of primary brain tumors or other metastatic sites. This review summarizes the current evidence on the composition and phenotypes of the most prominent immune cells in the brain metastatic niche, along with their dynamic interactions with metastatic tumor cells and each other. As the most abundant immune cell types in this niche, we explore in detail the phenotypic heterogeneity and functional plasticity of tumor-associated macrophages, including both resident microglia and monocyte-derived macrophages, as well as the T-cell compartment. We also review preclinical and clinical trials evaluating the therapeutic potential of targeting the immune microenvironment in brain metastasis. Given the substantial evidence highlighting a significant role of the immune microenvironmental niche in brain metastasis pathogenesis, a comprehensive understanding of the key molecular and cellular factors within this niche holds great promise for developing novel therapeutic approaches as well as innovative combinatory treatment strategies for brain metastasis.

Metastatic brain tumors: from development to cutting-edge treatment

Metastatic brain tumors, also called brain metastasis (BM), represent a challenging complication of advanced tumors. Tumors that commonly metastasize to the brain include lung cancer and breast cancer. In recent years, the prognosis for BM patients has improved, and significant advancements have been made in both clinical and preclinical research. This review focuses on BM originating from lung cancer and breast cancer. We briefly overview the history and epidemiology of BM, as well as the current diagnostic and treatment paradigms. Additionally, we summarize multiomics evidence on the mechanisms of tumor occurrence and development in the era of artificial intelligence and discuss the role of the tumor microenvironment. Preclinically, we introduce the establishment of BM models, detailed molecular mechanisms, and cutting-edge treatment methods. BM is primarily treated with a comprehensive approach, including local treatments such as surgery and radiotherapy. For lung cancer, targeted therapy and immunotherapy have shown efficacy, while in breast cancer, monoclonal antibodies, tyrosine kinase inhibitors, and antibody-drug conjugates are effective in BM. Multiomics approaches assist in clinical diagnosis and treatment, revealing the complex mechanisms of BM. Moreover, preclinical agents often need to cross the blood-brain barrier to achieve high intracranial concentrations, including small-molecule inhibitors, nanoparticles, and peptide drugs. Addressing BM is imperative.

Consortium for Intracranial Metastasis Academic Research (CIMARa): Global interdisciplinary collaborations to improve outcomes of patient with brain metastases

Brain metastases (BrM) arising from solid tumors is an ever-increasing and often devastating clinical challenge impacting hundreds of thousands of patients annually worldwide. As systemic anticancer therapies, and thus survival, improve, the risk for central nervous system (CNS) recurrence has increased. Historically, patients with BrM were excluded from clinical trials; however, there has been a shift toward increasing inclusion over the past decade. To most effectively design the next generation of clinical trials for patients with BrM, a multidisciplinary team spanning local and systemic therapies is imperative. CIMARa (Consortium for Intracranial Metastasis Academic Research), formalized in June 2021, is an inclusive group of multidisciplinary clinical investigators, research scientists, and advocates who share the collective goal of improving outcomes for patients with BrM. CIMARa aims to improve outcomes through the development, coordination, and awareness of multi-institutional clinical trials testing novel therapeutic agents for this unique patient population alongside the translation of preclinical research to the clinical setting.

PD-L1 and VEGF dual blockade enhances anti-tumor effect on brain metastasis in hematogenous metastasis model

Immunotherapy improves survival outcomes in cancer patients, but there is still an unmet clinical need in the treatment of brain metastases. Here, we used a mouse model to investigate the antitumor effect of programmed death-ligand 1 (PD-L1) and vascular endothelial growth factor (VEGF) dual blockade on metastatic brain tumors and evaluated immune responses during treatment. After establishing hematogenous brain metastasis by transplanting murine bladder carcinoma MBT2 cells stably expressing secNLuc reporter via the internal carotid artery of C3H/HeNCrl mice, we observed the formation of metastases not only in the brain parenchyma but also in the ventricles. The observed pathological areas showed that metastases in the ventricle were histologically larger than that in the brain parenchyma. Regarding the total tumor burden in the whole brain as revealed by Nluc activities, the combination of anti-PD-L1 antibody and anti-VEGF antibody showed a stronger anti-tumor effect than each single agent. Anti-PD-L1 antibody alone enhanced CD8+ T cell priming in regional lymph nodes, increased the proportion of activated CD8+ T cells in whole brain, and increased the density of CD8+ cells in the brain parenchyma. Furthermore, anti-VEGF antibody alone decreased microvessel density (MVD) in ventricular metastases, and the combination treatment increased intratumoral CD8+ cell density in the brain parenchyma and ventricular metastases. These results suggest that PD-L1 blockade enhanced cancer immunity not only in brain metastases lesions but also in the regional lymph nodes of the metastases, and that the addition of VEGF blockade increased the antitumor effect by increasing the infiltration of activated CD8+ T cell and decreasing MVD.

Revisiting the CXCL13/CXCR5 axis in the tumor microenvironment in the era of single-cell omics: Implications for immunotherapy

As one of the important members of the family of chemokines and their receptors, the CXCL13/CXCR5 axis is involved in follicle formation in normal lymphoid tissues and the establishment of somatic cavity immunity under physiological conditions, as well as being associated with a wide range of infectious, autoimmune, and tumoral diseases. Here in this review, we focus on its role in tumors. Traditional studies have found the axis to be both pro- and anti-tumorigenic, involving a variety of immune cells, including the tumor cells themselves and those in the tumor microenvironment (TME), and the prognostic significance of this axis is clinical context-dependent. With the development of techniques at the single-cell level, we were able to explain in detail the status of the CXCL13/CXCR5 axis in the TME based on real clinical samples and found that it involves a range of crucial intrinsic anti-tumor immune processes in the TME and is therefore important in tumor immunotherapy. We summarize the cellular subsets, physiological functions, and prognostic significance associated with this axis in the most promising immune checkpoint inhibitor (ICI) therapies of the day and summarize possible therapeutic ideas based on this axis. As with any TME study, the most important takeaway is that the complexity of the CXCL13/CXCR5 axis in TME suggests the importance of personalized therapy in tumor therapy.

Systems immunology insights into brain metastasis

Brain metastasis poses formidable clinical challenges due to its intricate interactions with the brain's unique immune environment, often resulting in poor prognoses. This review delves into systems immunology's role in uncovering the dynamic interplay between metastatic cancer cells and brain immunity. Leveraging spatial and single-cell technologies, along with advanced computational modeling, systems immunology offers unprecedented insights into mechanisms of immune evasion and tumor proliferation. Recent studies highlight potential immunotherapeutic targets, suggesting strategies to boost antitumor immunity and counteract cancer cell evasion in the brain. Despite substantial progress, challenges persist, particularly in accurately simulating human conditions. This review underscores the need for interdisciplinary collaboration to harness systems immunology's full potential, aiming to dramatically improve outcomes for patients with brain metastasis.

Patient-based multilevel transcriptome exploration highlights relevant chemokines and chemokine receptor axes in glioblastoma

Chemokines and their receptors form a complex interaction network, crucial for precise leukocyte positioning and trafficking. In cancer, they promote malignant cell proliferation and survival but are also critical for immune cell infiltration in the tumor microenvironment. Glioblastoma (GBM) is the most common and lethal brain tumor, characterized by an immunosuppressive TME, with restricted immune cell infiltration. A better understanding of chemokine-receptor interactions is therefore essential for improving tumor immunogenicity. In this study, we assessed the expression of all human chemokines in adult-type diffuse gliomas, with particular focus on GBM, based on patient-derived samples. Publicly available bulk RNA sequencing datasets allowed us to identify the chemokines most abundantly expressed in GBM, with regard to disease severity and across different tumor subregions. To gain insight into the chemokines-receptor network at the single cell resolution, we explored GBmap, a curated resource integrating multiple scRNAseq datasets from different published studies. Our study constitutes the first patient-based handbook highlighting the relevant chemokine-receptor crosstalks, which are of significant interest in the perspective of a therapeutic modulation of the TME in GBM.

Distinct tumor architectures and microenvironments for the initiation of breast cancer metastasis in the brain

Brain metastasis, a serious complication of cancer, hinges on the initial survival, microenvironment adaptation, and outgrowth of disseminated cancer cells. To understand the early stages of brain colonization, we investigated two prevalent sources of cerebral relapse, triple-negative (TNBC) and HER2+ (HER2BC) breast cancers. Using mouse models and human tissue samples, we found that these tumor types colonize the brain, with a preference for distinctive tumor architectures, stromal interfaces, and autocrine programs. TNBC models tend to form perivascular sheaths with diffusive contact with astrocytes and microglia. In contrast, HER2BC models tend to form compact spheroids driven by autonomous tenascin C production, segregating stromal cells to the periphery. Single-cell transcriptomics of the tumor microenvironment revealed that these architectures evoke differential Alzheimer's disease-associated microglia (DAM) responses and engagement of the GAS6 receptor AXL. The spatial features of the two modes of brain colonization have relevance for leveraging the stroma to treat brain metastasis.

IMMUNE AND MOLECULAR CORRELATES OF RESPONSE TO IMMUNOTHERAPY REVEALED BY BRAIN-METASTATIC MELANOMA MODELS

Despite the promising results of immune checkpoint blockade (ICB) therapy, outcomes for patients with brain metastasis (BrM) remain poor. Identifying resistance mechanisms has been hindered by limited access to patient samples and relevant preclinical models. Here, we developed two mouse melanoma BrM models that recapitulate the disparate responses to ICB seen in patients. We demonstrate that these models capture the cellular and molecular complexity of human disease and reveal key factors shaping the tumor microenvironment and influencing ICB response. BR1-responsive tumor cells express inflammatory programs that polarize microglia into reactive states, eliciting robust T cell recruitment. In contrast, BR3-resistant melanoma cells are enriched in neurological programs and exploit tolerance mechanisms to maintain microglia homeostasis and limit T cell infiltration. In humans, BR1 and BR3 expression signatures correlate positively or negatively with T cell infiltration and BrM patient outcomes, respectively. Our study provides clinically relevant models and uncovers mechanistic insights into BrM ICB responses, offering potential biomarkers and therapeutic targets to improve therapy efficacy.

Cranioencephalic functional lymphoid units in glioblastoma

The ecosystem of brain tumors is considered immunosuppressed, but our current knowledge may be incomplete. Here we analyzed clinical cell and tissue specimens derived from patients presenting with glioblastoma or nonmalignant intracranial disease to report that the cranial bone (CB) marrow, in juxtaposition to treatment-naive glioblastoma tumors, harbors active lymphoid populations at the time of initial diagnosis. Clinical and anatomical imaging, single-cell molecular and immune cell profiling and quantification of tumor reactivity identified CD8+ T cell clonotypes in the CB that were also found in the tumor. These were characterized by acute and durable antitumor response rooted in the entire T cell developmental spectrum. In contrast to distal bone marrow, the CB niche proximal to the tumor showed increased frequencies of tumor-reactive CD8+ effector types expressing the lymphoid egress marker S1PR1. In line with this, cranial enhancement of CXCR4 radiolabel may serve as a surrogate marker indicating focal association with improved progression-free survival. The data of this study advocate preservation and further exploitation of these cranioencephalic units for the clinical care of glioblastoma.

NaCl enhances CD8+ T cell effector functions in cancer immunotherapy

CD8+ T cells control tumors but inevitably become dysfunctional in the tumor microenvironment. Here, we show that sodium chloride (NaCl) counteracts T cell dysfunction to promote cancer regression. NaCl supplementation during CD8+ T cell culture induced effector differentiation, IFN-γ production and cytotoxicity while maintaining the gene networks responsible for stem-like plasticity. Accordingly, adoptive transfer of tumor-specific T cells resulted in superior anti-tumor immunity in a humanized mouse model. In mice, a high-salt diet reduced the growth of experimental tumors in a CD8+ T cell-dependent manner by inhibiting terminal differentiation and enhancing the effector potency of CD8+ T cells. Mechanistically, NaCl enhanced glutamine consumption, which was critical for transcriptional, epigenetic and functional reprogramming. In humans, CD8+ T cells undergoing antigen recognition in tumors and predicting favorable responses to checkpoint blockade immunotherapy resembled those induced by NaCl. Thus, NaCl metabolism is a regulator of CD8+ T cell effector function, with potential implications for cancer immunotherapy.

The Emerging Role of Immune Checkpoint Blockade for the Treatment of Lung Cancer Brain Metastases

Lung cancer has the highest incidence of brain metastases (BM) among solid organ cancers. Traditionally whole brain radiation therapy has been utilized for non-small-cell lung cancer (NSCLC) BM treatment, although stereotactic radiosurgery has emerged as the superior treatment modality for most patients. Highly penetrant central nervous system (CNS) tyrosine kinase inhibitors have also shown significant CNS activity in patients harboring select oncogenic drivers. There is emerging evidence that patients without oncogene-driven tumors derive benefit from the use of immune checkpoint inhibitors (ICIs). The CNS activity of ICIs have not been well studied given exclusion of patients with active BM from landmark trials, due to concerns of inadequate CNS penetration and activity. However, studies have challenged the idea of an immune-privileged CNS, given the presence of functional lymphatic drainage within the CNS and destruction of the blood brain barrier by BM. An emerging understanding of the interactions between tumor and CNS immune cells in the BM tumor microenvironment also support a role for immunotherapy in BM treatment. In addition, posthoc analyses of major trials have shown improved intracranial response and survival benefit of regimens with ICIs over chemotherapy (CT) alone for patients with BM. Two prospective phase 2 trials evaluating pembrolizumab monotherapy and atezolizumab plus CT in patients with untreated NSCLC BM also demonstrated significant intracranial responses. This review describes the interplay between CNS immune cells and tumor cells, discusses current evidence for ICI CNS activity from retrospective and prospective studies, and speculates on future directions of investigation.

Cytometry in the Short-Wave Infrared

Cytometry plays a crucial role in characterizing cell properties, but its restricted optical window (400-850 nm) limits the number of stained fluorophores that can be detected simultaneously and hampers the study and utilization of short-wave infrared (SWIR; 900-1700 nm) fluorophores in cells. Here we introduce two SWIR-based methods to address these limitations: SWIR flow cytometry and SWIR image cytometry. We develop a quantification protocol for deducing cellular fluorophore mass. Both systems achieve a limit of detection of ∼0.1 fg cell-1 within a 30 min experimental time frame, using individualized, high-purity (6,5) single-wall carbon nanotubes as a model fluorophore and macrophage-like RAW264.7 as a model cell line. This high-sensitivity feature reveals that low-dose (6,5) serves as an antioxidant, and cell morphology and oxidative stress dose-dependently correlate with (6,5) uptake. Our SWIR cytometry holds immediate applicability for existing SWIR fluorophores and offers a solution to the issue of spectral overlapping in conventional cytometry.

Unveiling spatial complexity in solid tumor immune microenvironments through multiplexed imaging

Deciphering cellular components and the spatial interaction network of the tumor immune microenvironment (TIME) of solid tumors is pivotal for understanding biologically relevant cross-talks and, ultimately, advancing therapies. Multiplexed tissue imaging provides a powerful tool to elucidate spatial complexity in a holistic manner. We established and cross-validated a comprehensive immunophenotyping panel comprising over 121 markers for multiplexed tissue imaging using MACSima™ imaging cyclic staining (MICS) alongside an end-to-end analysis workflow. Applying this panel and workflow to primary cancer tissues, we characterized tumor heterogeneity, investigated potential therapeutical targets, conducted in-depth profiling of cell types and states, sub-phenotyped T cells within the TIME, and scrutinized cellular neighborhoods of diverse T cell subsets. Our findings highlight the advantage of spatial profiling, revealing immunosuppressive molecular signatures of tumor-associated myeloid cells interacting with neighboring exhausted, PD1high T cells in the TIME of hepatocellular carcinoma (HCC). This study establishes a robust framework for spatial exploration of TIMEs in solid tumors and underscores the potency of multiplexed tissue imaging and ultra-deep cell phenotyping in unraveling clinically relevant tumor components.

Single-cell RNA sequencing reveals distinct transcriptomic profiles and evolutionary patterns in lung cancer brain metastasis

Background

Lung cancer metastasis to the brain presents significant clinical challenges. Therefore, elucidating its underlying mechanisms and characterizing its transcriptomic landscape is essential for developing therapeutic interventions.

Methods

We analyzed two distinct single-cell RNA sequencing datasets of lung cancer metastasis to analyze the evolutionary trajectory of brain metastatic tumors. In addition, a systematic comparison of cell-cell interaction between tumor cells and lymphocytes was conducted within primary and brain metastatic tumors.

Results

The brain metastatic tumors showed greater transcriptomic changes (reflected by a higher pseudotime) than tumors in the lymph nodes and primary tumors. Furthermore, our investigation has not only revealed specific shared ligand-receptor pairs in both mLN and mBrain, exemplified by the interaction between SPP1 and CD99 in T cells, but has also unveiled a diverse array of ligand-receptor pairs exclusive to the mBrain. Notably, this includes distinctive pairs such as APP and IL1 observed specifically in myeloid cells.

Conclusion

The distinct microenvironment in the brain may influence the observed transcriptomic changes in tumors, emphasizing the significance of the specific environment in determining tumor behavior and therapeutic response.

Interrogation of endothelial and mural cells in brain metastasis reveals key immune-regulatory mechanisms

Brain metastasis (BrM) is a common malignancy, predominantly originating from lung, melanoma, and breast cancers. The vasculature is a key component of the BrM tumor microenvironment with critical roles in regulating metastatic seeding and progression. However, the heterogeneity of the major BrM vascular components, namely endothelial and mural cells, is still poorly understood. We perform single-cell and bulk RNA-sequencing of sorted vascular cell types and detect multiple subtypes enriched specifically in BrM compared to non-tumor brain, including previously unrecognized immune regulatory subtypes. We integrate the human data with mouse models, creating a platform to interrogate vascular targets for the treatment of BrM. We find that the CD276 immune checkpoint molecule is significantly upregulated in the BrM vasculature, and anti-CD276 blocking antibodies prolonged survival in preclinical trials. This study provides important insights into the complex interactions between the vasculature, immune cells, and cancer cells, with translational relevance for designing therapeutic interventions.

Exploring the Molecular Tumor Microenvironment and Translational Biomarkers in Brain Metastases of Non-Small-Cell Lung Cancer

Brain metastases represent a significant clinical challenge in the treatment of non-small-cell lung cancer (NSCLC), often leading to a severe decline in patient prognosis and survival. Recent advances in imaging and systemic treatments have increased the detection rates of brain metastases, yet clinical outcomes remain dismal due to the complexity of the metastatic tumor microenvironment (TME) and the lack of specific biomarkers for early detection and targeted therapy. The intricate interplay between NSCLC tumor cells and the surrounding TME in brain metastases is pivotal, influencing tumor progression, immune evasion, and response to therapy. This underscores the necessity for a deeper understanding of the molecular underpinnings of brain metastases, tumor microenvironment, and the identification of actionable biomarkers that can inform multimodal treatment approaches. The goal of this review is to synthesize current insights into the TME and elucidate molecular mechanisms in NSCLC brain metastases. Furthermore, we will explore the promising horizon of emerging biomarkers, both tissue- and liquid-based, that hold the potential to radically transform the treatment strategies and the enhancement of patient outcomes.

[Tumor-host cell interaction in the microenvironment: new target points for treatment?]

BACKGROUND

Primary brain tumors and metastases in the central nervous system (CNS) are characterized by their unique microenvironment, which interacts with neuronal structures and influences structural and adaptive immunity.

OBJECTIVE

How significant are various tumor-host interactions from a prognostic and therapeutic perspective?

MATERIAL AND METHOD

A literature search was carried out for relevant articles on the topic: microenvironment glioblastoma or metastasis through PubMed and Medline.

RESULTS

Modern high-throughput methods, such as spatial and single-cell resolution molecular characterization of tumors and their microenvironment enable a detailed mapping of changes and adaptation of individual cells within the microenvironment of tumors; however, treatment approaches based on altered tumor-host cell interactions, such as immune modeling, cell-based treatment methods or checkpoint inhibition have so far not shown any significant advantages for survival.

CONCLUSION

A deeper understanding of the complex immune landscape and the microenvironment of metastases of the CNS and intracerebral tumors is essential to optimize future treatment strategies.

T Cell Features in Glioblastoma May Guide Therapeutic Strategies to Overcome Microenvironment Immunosuppression

Glioblastoma (GBM) is the most aggressive and lethal primary brain tumor, bearing a survival estimate below 10% at five years, despite standard chemoradiation treatment. At recurrence, systemic treatment options are limited and the standard of care is not well defined, with inclusion in clinical trials being highly encouraged. So far, the use of immunotherapeutic strategies in GBM has not proved to significantly improve patients' prognosis in the treatment of newly diagnosed GBM, nor in the recurrent setting. Probably this has to do with the unique immune environment of the central nervous system, which harbors several immunosuppressive/pro-tumorigenic factors, both soluble (e.g., TGF-β, IL-10, STAT3, prostaglandin E2, and VEGF) and cellular (e.g., Tregs, M2 phenotype TAMs, and MDSC). Here we review the immune composition of the GBMs microenvironment, specifically focusing on the phenotype and function of the T cell compartment. Moreover, we give hints on the therapeutic strategies, such as immune checkpoint blockade, vaccinations, and adoptive cell therapy, that, interacting with tumor-infiltrating lymphocytes, might both target in different ways the tumor microenvironment and potentiate the activity of standard therapies. The path to be followed in advancing clinical research on immunotherapy for GBM treatment relies on a twofold strategy: testing combinatorial treatments, aiming to restore active immune anti-tumor responses, tackling immunosuppression, and additionally, designing more phase 0 and window opportunity trials with solid translational analyses to gain deeper insight into the on-treatment shaping of the GBM microenvironment.

Organ specific microenvironmental MR1 expression in cutaneous melanoma

The microenvironment is an important regulator of intertumoral trafficking and activity of immune cells. Understanding how the immune system can be tailored to maintain anti-tumor killing responses in metastatic disease remains an important goal. Thus, immune mediated eradication of metastasis requires the consideration of organ specific microenvironmental cues. Using a xenograft model of melanoma metastasis in adult zebrafish, we perturbed the dynamic balance between the infiltrating immune cells in the metastatic setting using a suite of different transgenic zebrafish. We employed intravital imaging coupled with metabolism imaging (FLIM) to visualize and map the organ specific metabolism with near simultaneity in multiple metastatic lesions. Of all the MHC complexes examined for brain and skeletal metastases, we determined that there is an organ specific expression of mhc1uba (human ortholog, MR1) for both the melanoma cells and the resident and infiltrating immune cells. Specifically, immune clusters did not express mhc1uba in brain metastatic lesions in immune competent fish. Finally, the differential immune response drove organ specific metabolism where tumor glycolysis was increased in brain metastases compared to skeletal and parental lines as measured using fluorescence lifetime imaging microscopy (FLIM). As MR1 belongs to the MHC class I molecules and is a target of immunotherapeutic drugs, we believe that our data presents an opportunity to understand the relationship between organ specific tumor metabolism and drug efficacy in the metastatic setting.

Drivers of heterogeneity in the glioblastoma immune microenvironment

Glioblastoma is the most common and aggressive primary brain tumor, characterized by a highly complex and heterogeneous tumor immune microenvironment (TIME). In this review, we discuss the impact of tumor-intrinsic and tumor-extrinsic drivers that contribute to heterogeneity in the adult glioblastoma TIME, focusing on four main factors: genetic drivers, sex, age, and standard of care therapy. We describe recent insights into how each of these factors affects key aspects ranging from TIME composition to therapy response, with an emphasis on the cross-talk between tumor and immune cells. Deciphering these local interactions is fundamental to understanding therapy resistance and identifying novel immunomodulatory strategies.

The immune cell landscape of glioblastoma patients highlights a myeloid-enriched and immune suppressed microenvironment compared to metastatic brain tumors

Introduction

Brain metastases (BrM), which commonly arise in patients with melanoma, breast cancer and lung cancer, are associated with a poor clinical prognosis. In this context, the tumor microenvironment (TME) plays an important role since it either promotes or inhibits tumor progression. Our previous studies have characterized the immunosuppressive microenvironment of glioblastoma (GBM). The aim of this study is to compare the immune profiles of BrM and GBM in order to identify potential differences that may be exploited in their differential treatment.

Methods

Tumor and/or blood samples were taken from 20 BrM patients and 19 GBM patients. Multi-parametric flow cytometry was used to evaluate myeloid and lymphoid cells, as well as the expression of immune checkpoints in the TME and blood. In selected cases, the immunosuppressive ability of sorted myeloid cells was tested, and the ex vivo proliferation of myeloid, lymphoid and tumor cell populations was analyzed.

Results

High frequencies of myeloid cells dominated both the BrM and GBM landscapes, but a higher presence of tumor-associated macrophages was observed in GBM, while BrM were characterized by a significant presence of tumor-infiltrating lymphocytes. Exhaustion markers were highly expressed in all T cells from both primary and metastatic brain tumors. Ex vivo analysis of the cell cycle of a single sample of a BrM and of a GBM revealed subsets of proliferating tumor cells and blood-derived macrophages, but quiescent resident microglial cells and few proliferating lymphocytes. Macrophages sorted from a single lung BrM exhibited a strong immunosuppressive activity, as previously shown for primary GBM. Finally, a significant expansion of some myeloid cell subsets was observed in the blood of both GBM and BrM patients.

Discussion

Our results define the main characteristics of the immune profile of BrM and GBM, which are distinguished by different levels of immunosuppressive myeloid cells and lymphocytes devoid of effector function. Understanding the role of the different cells in establishing the metastatic setting is critical for improving the therapeutic efficacy of new targeted immunotherapy strategies.

The local microenvironment drives activation of neutrophils in human brain tumors

Neutrophils are abundant immune cells in the circulation and frequently infiltrate tumors in substantial numbers. However, their precise functions in different cancer types remain incompletely understood, including in the brain microenvironment. We therefore investigated neutrophils in tumor tissue of glioma and brain metastasis patients, with matched peripheral blood, and herein describe the first in-depth analysis of neutrophil phenotypes and functions in these tissues. Orthogonal profiling strategies in humans and mice revealed that brain tumor-associated neutrophils (TANs) differ significantly from blood neutrophils and have a prolonged lifespan and immune-suppressive and pro-angiogenic capacity. TANs exhibit a distinct inflammatory signature, driven by a combination of soluble inflammatory mediators including tumor necrosis factor alpha (TNF-ɑ) and Ceruloplasmin, which is more pronounced in TANs from brain metastasis versus glioma. Myeloid cells, including tumor-associated macrophages, emerge at the core of this network of pro-inflammatory mediators, supporting the concept of a critical myeloid niche regulating overall immune suppression in human brain tumors.

CRUSTY: a versatile web platform for the rapid analysis and visualization of high-dimensional flow cytometry data

Flow cytometry (FCM) can investigate dozens of parameters from millions of cells and hundreds of specimens in a short time and at a reasonable cost, but the amount of data that is generated is considerable. Computational approaches are useful to identify novel subpopulations and molecular biomarkers, but generally require deep expertize in bioinformatics and the use of different platforms. To overcome these limitations, we introduce CRUSTY, an interactive, user-friendly webtool incorporating the most popular algorithms for FCM data analysis, and capable of visualizing graphical and tabular results and automatically generating publication-quality figures within minutes. CRUSTY also hosts an interactive interface for the exploration of results in real time. Thus, CRUSTY enables a large number of users to mine complex datasets and reduce the time required for data exploration and interpretation. CRUSTY is accessible at https://crusty.humanitas.it/ .