Redox Storm in the Tumor Microenvironment (ΤΜΕ): Multifaceted Redox Injury and Immunometabolic Reprogramming Induced by Immune Checkpoint Blockade in B16F10 Melanoma: An Ultrastructural Study of the Peritumoral Interface

Immune checkpoint blockade (ICB) has revolutionized melanoma treatment, yet the in vivo ultrastructural consequences within the tumor microenvironment (TME) remain poorly characterized. This study investigates the morphological alterations induced by ICB at the peritumoral interface through a “redox storm” paradigm. B16F10 melanoma-bearing mice were treated with anti-CTLA-4, anti-PD-1, or their combination, and evaluated by transmission electron microscopy (TEM) at Days 20, 30, and 40; quantitative morphometric analyses were performed for comparative purposes. This design enabled the assessment of ultrastructural changes from initial immune activation to late-stage remodeling, linking early cytotoxic events with subsequent stromal adaptations. TEM provided evidence of a sequential redox cascade characterized by lymphocyte reactivation, mitochondrial cristolysis, lipid droplet accumulation, foamy macrophage-like cells, efferocytosis-driven M2-like polarization, and metabolic plasticity in surviving tumor cells. Specifically, combination therapy was associated with marked cytolysis and extensive stromal remodeling, while anti-PD-1 appeared to promote prominent cholesterol crystal formation and lipotoxicity. Morphometric analyses supported these qualitative findings, indicating significant alterations in lipid droplet area and cell death area across treatment groups. This ultrastructural dissection provides morphological evidence for the “redox storm” and offers a framework to understand ICB efficacy, resistance, and dynamic TME remodeling, ultimately providing a basis for targeted combination strategies.