Identification and validation of Birc5 as a novel activated cell cycle program biomarker associated with infiltration of immunosuppressive myeloid‐derived suppressor cells in hepatocellular carcinoma

BACKGROUND: Preclinical studies and clinical trials have demonstrated that tumor‐intrinsic activation of the cell cycle program impedes anticancer immunotherapy. Identification of cell cycle‐related biomarkers may provide novel therapeutic targets to augment the efficacy of immunotherapy in hepatocellular carcinoma (HCC). METHOD AND RESULTS: Based on the genes related to cell cycle program, two clusters (Cluster 1 and Cluster 2) were detected in HCC patients via non‐negative matrix factorization algorithm. Multivariable‐adjusted Cox regression analysis indicated that the cell cycle gene‐based classification was a significant prognostic factor for predicting the clinical outcome of HCC patients. Cluster 1 showed shorter overall survival time and progression‐free interval time was associated with activated cell cycle program, higher infiltration of myeloid‐derived suppressor cells (MDSCs) and less sensitivity to immunotherapy. A three‐gene prognostic model, including BIRC5, C8G, and SPP1, was constructed to characterize the cell cycle‐based classification of HCC, which had strong robustness and a stable predictive performance. Notably, Birc5 was positively correlated with CD11b expression (a MDSC marker) in HCC tissue. Concordant high expression of Birc5 and intratumor infiltration level of MDSCs were correlated with worse prognosis of HCC patients. In vitro, hepatocellular Birc5 overexpression promoted immunosuppressive CD11b(+)CD33(+)HLA‐DR(−)MDSC expansion from human peripheral blood mononuclear cells. Genetically modified animal model of liver cancer revealed that Birc5 depletion upregulated the genes related to lymphocyte‐mediated immunity, natural killer cell‐mediated immunity, interferon‐gamma production, T‐cell activation, and T‐cell‐mediated cytotoxicity. These results suggest an immunosuppressive function of Birc5 in HCC. CONCLUSION: Birc5 was a potential biomarker and inducer of intratumor infiltration of MDSCs, which led to T cell exclusion or dysfunction in tumor immune microenvironment, consequently resulting in reduced response to ICIs in HCC.