Systemic immune profiling uncovers divergent mechanisms and predictive biomarkers of response to combination immunotherapies in hepatocellular carcinoma

Background Combination immunotherapies such as atezolizumab plus bevacizumab (Atez/Bev) and durvalumab plus tremelimumab (Dur/Tre) improve outcomes in advanced hepatocellular carcinoma (HCC), yet systemic immune mechanisms underlying response remain incompletely defined. Methods We performed single-cell RNA sequencing with CITE-seq on peripheral blood mononuclear cells from 19 advanced HCC patients (Atez/Bev: 5 responders (R), 5 non-responders (NR); Dur/Tre: 4 R, 5 NR) before and during treatment, yielding 345 962 single-cell transcriptomes spanning 22 immune cell clusters. Analysis included transcriptional profiling, gene set enrichment analysis, T cell receptor (TCR) repertoire analysis, and CellChat-based intercellular communication modeling. Results Baseline comparisons revealed distinct systemic immune states by etiology: non-viral HCC exhibited CD8 + T cells with heightened cytotoxic and memory-associated signatures. Under Atez/Bev, CD14 + monocytes in responders were reprogrammed toward antigen-presenting and lymphocyte-supporting functions, while PRKCH + NK cells acquired a robust cytotoxic program reinforced by monocyte–NK interactions via ICAM–integrin and HLA-E–NKG2C axes. In contrast, Dur/Tre responders exhibited CD14 + monocyte programs enriched in inflammatory and interferon-driven antigen presentation, alongside transcriptional reprogramming of CD8 + central memory T cells into an effector-ready state with strong crosstalk to monocytes. TCR analysis revealed regimen-specific differences: clonotype expansion occurred irrespective of response under Atez/Bev, whereas Dur/Tre responders showed both clonotype expansion and higher pretreatment CD8 + T cell diversity, with expanded clones displaying cytotoxic and interferon-responsive profiles. Pretreatment immune composition, including naïve CD4 + T cells and PRKCH + NK cells for Atez/Bev and conventional dendritic cells for Dur/Tre, also predicted response. Conclusions Our findings reveal regimen-specific systemic immune mechanisms in advanced HCC: Atez/Bev amplifies monocyte–NK cytotoxic axes, whereas Dur/Tre enhances monocyte–T cell inflammatory networks and TCR repertoire diversity. These insights highlight distinct predictive biomarkers and support regimen-tailored immunotherapy in HCC.