Regulatory T Cells in Hepatocellular Carcinoma: Spatial Niches, Biomarkers, and Clinical Implications.

Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality worldwide, increasingly driven by metabolic dysfunction-associated steatotic liver disease alongside viral and alcohol-related cirrhosis. The tolerogenic immune environment of the liver enables tumor immune escape, with regulatory T cells (Tregs) playing a central role. This review synthesizes human-focused evidence (tissues, blood, clinical cohorts, and single-cell/spatial studies) through September 2025 to define how Tregs are recruited, maintained, and functionally deployed in HCC. Across datasets, intratumoral effector-like Tregs (eTregs) expressing ICOS, CTLA-4, CCR8, and CD39/CD73 accumulate within tumors and co-localize with exhausted cytotoxic PD-1hi CD8+ T cells and suppressive myeloid cells. Recruitment is driven mainly by CCL20-CCR6 and CCL22/CCL17-CCR4 signaling, while CCR8 marks highly suppressive tumor-resident Tregs. Their persistence is supported by TGF-β, IL-10, IL-35, adenosine signaling, IL-2 sequestration, and metabolic adaptation. Spatial biomarkers, including ICOS+/CCR8+ eTreg density and CD8:Treg ratios, associate with prognosis and emerging immunotherapy responses. Etiology further shapes immune architecture: HBV-related HCC often forms Treg-exhausted T-cell niches around viral antigens, whereas MASLD/MASH promotes stromal and metabolic barriers that may reduce PD-(L)1 efficacy. Current treatments (PD-(L)1 blockade with anti-VEGF or CTLA-4, and some TKIs) intersect with Treg biology, while emerging strategies targeting CCR8, CCR4, ICOS, or the adenosine pathway aim to selectively disrupt intratumoral eTreg networks. This review underscores that an etiology-aware, spatial-biomarker framework may guide the integration of selective Treg targeting with PD-(L)1-based therapies in HCC.