Hepatocellular carcinoma (HCC) is the most common primary liver cancer and a leading cause of cancer mortality worldwide. Its pathogenesis reflects a combination of tumour-intrinsic heterogeneity and a profoundly immunosuppressive tumour microenvironment. Growing evidence shows that tumours recapitulate developmental programs to establish an oncofetal ecosystem, characterised by the re-expression of foetal antigens and foetal-like stromal and immune subsets. These features drive immune evasion and shape therapeutic response, contributing to immunotherapy outcomes in clinic. This review outlines mechanistic insights into oncofetal reprogramming across tumour, stromal, and immune compartments and evaluates therapeutic strategies that target these dependencies. We highlight emerging vaccine platforms, cellular therapies, and biologics targeting oncofetal antigens, with particular emphasis on mRNA–lipid nanoparticle vaccines and their potential to induce robust, durable antitumour immunity. We further discuss rational combinatorial strategies that integrate vaccines with immune checkpoint inhibitors. Finally, we discuss how overcoming liver tolerance and antigenic heterogeneity will be essential for effective oncofetal-directed therapies. Collectively, targeting the oncofetal ecosystem through coordinated vaccine, cellular, and immunotherapeutic strategies offers a path toward more durable responses and broader immunotherapy benefits in HCC.