Purpose: Melanoma brain metastases (MBM) and leptomeningeal melanoma metastases (LMM) are two different manifestations of melanoma CNS metastasis. Here, we used single-cell RNA sequencing (scRNA-seq) to define the immune landscape of MBM, LMM, and melanoma skin metastases. Experimental Design: scRNA-seq was undertaken on 43 patient specimens, including 8 skin metastases, 14 MBM, and 19 serial LMM specimens. Detailed cell type curation was performed, the immune landscapes were mapped, and key results were validated by IHC and flow cytometry. Association analyses were undertaken to identify immune cell subsets correlated with overall survival. Results: The LMM microenvironment was characterized by an immune-suppressed T-cell landscape distinct from that of brain and skin metastases. An LMM patient with long-term survival demonstrated an immune repertoire distinct from that of poor survivors and more similar to normal cerebrospinal fluid (CSF). Upon response to PD-1 therapy, this extreme responder showed increased levels of T cells and dendritic cells in their CSF, whereas poor survivors showed little improvement in their T-cell responses. In MBM patients, therapy led to increased immune infiltrate, with similar T-cell transcriptional diversity noted between skin metastases and MBM. A correlation analysis across the entire immune landscape identified the presence of a rare population of dendritic cells (DC3) that was associated with increased overall survival and positively regulated the immune environment through modulation of activated T cells and MHC expression. Conclusions: Our study provides the first atlas of two distinct sites of melanoma CNS metastases and defines the immune cell landscape that underlies the biology of this devastating disease.

Despite functional heterogeneity, the high frequency of intratumoral neutrophils predicts poor clinical outcomes. The tumor microenvironment reprograms neutrophils into immunosuppressive subsets that hinder anticancer immunity, thereby contributing to tumor growth and resistance to immunotherapies. However, the mechanisms underlying neutrophil reprogramming remain elusive. In this study, we report that the immunosuppressive ability of brain tumor–infiltrating neutrophils was restricted to a highly glycolytic and long-lived subset expressing CD71, which acquired immunosuppressive properties in response to hypoxia. Mechanistically, hypoxia boosted glucose metabolism in CD71+ neutrophils, leading to high lactate production. Lactate caused histone lactylation, which subsequently regulated arginase-1 expression, required for T-cell suppression. Targeting histone lactylation with the antiepileptic drug isosafrole blocked CD71+ neutrophil immunosuppressive ability, delayed tumor progression, and sensitized brain tumors to immunotherapy. A distinctive gene signature characterizing immunosuppressive CD71+ neutrophils correlated with adverse clinical outcomes across diverse human malignancies. This study identifies histone lactylation as a potential therapeutic target to counteract neutrophil-induced immunosuppression within tumors. Significance: Neutrophils are critical contributors to the immunosuppressive microenvironment that restricts the effects of promising immunotherapies in glioblastoma. Our study identifies hypoxia-driven histone lactylation as a potential target to block immunosuppressive neutrophils and boost the effects of immunotherapy in glioblastoma and in other cancer settings beyond brain tumors.

Genome-wide analysis of glioblastoma (GBM) reveals pervasive aberrations in apoptotic signaling pathways that collectively contribute to therapeutic resistance. Inhibitors of apoptosis proteins (IAP) exert critical control on the terminal segment of apoptosis leading to apoptosis evasion. In this study, we uncover a unique role for BIRC3, as an IAP that is critical in GBM in response to therapy. Using the TCGA dataset of 524 unique samples, we identify BIRC3 is the only IAP whose differential expression is associated with long-term survival in GBM patients. Using patient tissue samples we further show that BIRC3 expression increases with recurrence. When extrapolated to a preclinical model of a human GBM cell line, we find an increase in BIRC3 expression in response to irradiation (RT) and temozolomide (TMZ) treatment. More importantly, we mechanistically implicate STAT3 and PI3K signaling pathways as drivers of RT-induced up-regulation of BIRC3 expression. Lastly, we demonstrate that both in-vivo and in-vitro BIRC3 up-regulation results in apoptosis evasion and therapeutic resistance in GBM. Collectively, our study identifies a novel translational and targetable role for BIRC3 expression as a predictor of aggressiveness and therapeutic resistance to TMZ and RT mediated by STAT3 and PI3K signaling in GBM.

Glioblastoma (GBM) is an aggressive brain tumor with a highly immunosuppressive microenvironment that promotes tumor progression and therapy resistance. Tumor-associated macrophages (TAMs), comprising up to 50% of the tumor mass, are recruited via chemokine axes such as CCL2/CCR2, CX3CL1/CX3CR1, and CXCL12/CXCR4 and adopt an M2-like immunosuppressive phenotype, facilitating immune escape and angiogenesis. Key signaling pathways, including CSF1R, STAT3, NF-κB, PI3K/Akt, and HIF-1α, regulate TAM function, making them promising therapeutic targets. Strategies such as TAM depletion, reprogramming, and immune checkpoint blockade (PD-1/PD-L1, and CD47-SIRPα) have shown potential in preclinical models. Emerging approaches, including CAR-macrophage (CAR-M) therapy, nanotechnology-based drug delivery, and exosome-mediated modulation, offer new avenues for intervention. However, clinical translation remains challenging due to GBM’s heterogeneity and adaptive resistance mechanisms. Future research should integrate multi-omics profiling and AI-driven drug discovery to refine TAM-targeted therapies and improve patient outcomes. This review provides a comprehensive analysis of TAM-mediated immune regulation in GBM and explores evolving therapeutic strategies aimed at overcoming its treatment barriers.

Glioblastoma (GBM) is a highly lethal cancer that is universally refractory to the standard multimodal therapies of surgical resection, radiation, and chemotherapy treatment. Temozolomide (TMZ) is currently the best chemotherapy agent for GBM, but the durability of response is epigenetically dependent and often short-lived secondary to tumor resistance. Therapies that can provide synergy to chemoradiation are desperately needed in GBM. There is accumulating evidence that adaptive resistance evolution in GBM is facilitated through treatment-induced epigenetic modifications. Epigenetic alterations of DNA methylation, histone modifications, and chromatin remodeling have all been implicated as mechanisms that enhance accessibility for transcriptional activation of genes that play critical roles in GBM resistance and lethality. Hence, understanding and targeting epigenetic modifications associated with GBM resistance is of utmost priority. In this review, we summarize the latest updates on the impact of epigenetic modifications on adaptive resistance evolution in GBM to therapy.