Single‐cell transcriptomics uncovers cellular architecture and developmental trajectories in hepatoblastoma

Background and Aims: Hepatoblastoma (HB) is the predominant type of childhood liver cancer. Treatment options for the clinically advanced HB remain limited. We aimed to dissect the cellular and molecular basis underlying HB oncogenesis and heterogeneity at the single‐cell level, which could facilitate a better understanding of HB at both the biological and clinical levels. Approach and Results: Single‐cell transcriptome profiling of tumor and paired distal liver tissue samples from five patients with HB was performed. Deconvolution analysis was used for integrating the single‐cell transcriptomic profiles with the bulk transcriptomes of our HB cohort of post–neoadjuvant chemotherapy tumor samples. A single‐cell transcriptomic landscape of early human liver parenchymal development was established for exploring the cellular root and hierarchy of HB oncogenesis. As a result, seven distinct tumor cell subpopulations were annotated, and an effective HB subtyping method was established based on their compositions. A HB tumor cell hierarchy was further revealed to not only fit with the classical cancer stem cell (CSC) model but also mirror the early human liver parenchymal development. Moreover, FACT inhibition, which could disrupt the oncogenic positive feedback loop between MYC and SSRP1 in HB, was identified as a promising epigenetic‐targeted therapeutic strategy against the CSC‐like HB1–Pro‐like1 subpopulation and its related high‐risk “Pro‐like1” subtype of HB. Conclusions: Our findings illustrate the cellular architecture and developmental trajectories of HB via integrative bulk and single‐cell transcriptome analyses, thus establishing a resourceful framework for the development of targeted diagnostics and therapeutics in the future.