Single-cell profiles delineate immune cell remodeling and enhanced tumor-fibroblast interaction of hepatoblastoma after chemotherapy.

Hepatoblastoma (HB), the most common pediatric liver cancer, is typically treated with chemotherapy, yet its impact on the tumor microenvironment (TME) and mechanisms of chemoresistance remain unclear. We perform single-cell RNA sequencing (scRNA-seq) on 32 HB tumors pre- and post-chemotherapy, integrating data from spatial transcriptomics, bulk transcriptomics, multiplexed immunofluorescence, and patient-derived xenografts. Chemotherapy enriches CD69+CD8+ T cells and shifted myeloid cells toward immune-activating phenotypes. HB tumor cells exhibit both hepatic and mesenchymal features, with hepatic-like cells showing greater chemoresistance. A subset of AFP-high hepatic tumor cells expresses high fibroblast growth factor receptor 4 (FGFR4) and showed elevated proliferation. Post-treatment, mesenchymal-like tumor cells and MMP11+ cancer-associated fibroblasts enhance FGF-FGFR signaling. FGFR4 inhibition significantly suppressed tumor growth in xenografts. These findings provide a high-resolution landscape of the HB immune TME and highlight cancer-fibroblast interactions, especially via FGF signaling, as key contributors to chemoresistance.