Macrophage Polarization and Spatial Architecture Characterize the Tumor Immune Microenvironment and Prognosis in Hepatoblastoma.

Hepatoblastoma, the most common primary pediatric liver malignancy, exhibits resistance to contemporary treatments in a subset of patients. Understanding the tumor immune microenvironment is essential for the development of novel immuno-oncological therapies. Herein, the microenvironment of hepatoblastoma was characterized by mapping the spatial distribution of immune cells, identifying prognostic immune features, assessing chemotherapy-induced alterations, and exploring potential immunotherapeutic targets. Whole-slide multiplex immunofluorescence staining (n = 35) was performed on formalin-fixed, paraffin-embedded hepatoblastoma specimens from 25 patients. Immune cell densities were analyzed in precytotoxic and post-cytotoxic treatment samples. Spatial characteristics were assessed using nearest-neighbor distances and Gcross functions, and differential protein abundance patterns were identified using quantitative proteomics (n = 18). This study revealed a predominantly myeloid-rich microenvironment in hepatoblastoma. Macrophages shifted toward a proinflammatory state following cytotoxic treatment. Proinflammatory phosphorylated STAT1 (pSTAT1)+ macrophages were associated with improved patient survival when retained in proximity to tumor cells after chemotherapy. Down-regulation of extracellular matrix pathways was observed in these pSTAT1-rich samples. Common lymphatic endothelial and vascular endothelial receptor 1 (CLEVER-1), an immunosuppressive marker and potential therapeutic target, was abundantly expressed, particularly in stromal macrophages. This study highlights the significance of macrophage phenotypes in hepatoblastoma and their potential as a therapeutic target. Moreover, the findings underline the prognostic value of pSTAT1+ macrophages and CLEVER-1 as a promising immunotherapy target. Future research should explore combination strategies to exploit chemotherapy-induced shifts in macrophage polarization.