Reprogramming tumor-associated macrophages in DMG/DIPG: emerging molecular and biophysical strategies

Diffuse Midline Glioma (DMG), often formerly called Diffuse Intrinsic Pontine Glioma (DIPG) when in the brainstem, DMG/DIPG is a lethal pediatric brain tumor defined by infiltrative growth, resistance to conventional therapies, and a profound immunosuppressive tumor microenvironment (TME). Tumor-associated macrophages (TAMs), including resident microglia and infiltrating monocyte-derived macrophages, are the predominant immune population in DMG/DIPG. These cells adopt an immunosuppressive, pro-tumor state, promoting immune evasion and limiting the efficacy of therapies such as chimeric antigen receptor (CAR) T cells. Reprogramming TAMs toward a pro-inflammatory, anti-tumor phenotype offers a promising strategy to remodel the DMG/DIPG microenvironment. This review is the first to provide a comprehensive, integrative perspective on TAM-directed strategies in DMG/DIPG, spanning molecular, epigenetic, and biophysical approaches. We summarize TAM-mediated tumor progression and therapy resistance, and discuss molecular reprogramming strategies, including colony-stimulating factor 1 receptor (CSF1R) inhibition, microRNA-based circuits, and epigenetic modulators such as histone deacetylase (HDAC) and bromodomain and extra-terminal domain (BET) inhibitors. Nanoparticle-mediated delivery systems allow selective TAM targeting and enhanced blood-brain barrier (BBB) penetration. Additional strategies, including oncolytic viruses and macrophage-specific checkpoint blockade (e.g., CD47/SIRPα axis inhibitors), simultaneously promote tumor clearance and immune activation. We also highlight emerging biophysical approaches to modulate TAM function in situ. Photodynamic therapy (PDT) induces immunogenic cell death and pro-inflammatory macrophage activity, while focused ultrasound (FUS) transiently disrupts the BBB to enhance drug delivery and immune infiltration. Photobiomodulation and low-level light therapy (LLLT) may influence macrophage metabolism and phenotype, though their application in DMG/DIPG remains largely unexplored. Finally, we discuss combinatorial strategies integrating TAM reprogramming with CAR T cell therapy or chemotherapy to overcome the immunologically "cold" nature of DMG/DIPG. By uniting mechanistic insights with translational opportunities, this review establishes TAM reprogramming as a critical, underexplored frontier in DMG/DIPG immunotherapy, offering the potential to render an otherwise intractable tumor immunologically targetable.