Targeting tumor-associated macrophages to overcome immune checkpoint inhibitor resistance in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) remains a critical global health concern, particularly in regions with high endemicity of hepatitis B, hepatitis C, and non-alcoholic fatty liver disease. Immunotherapy, particularly immune checkpoint inhibitors (ICIs), has emerged as a promising therapeutic strategy for advanced HCC. Despite encouraging results, primary and acquired resistance to ICIs continues to pose significant challenges in clinical practice. Recent research has identified tumor-associated macrophages (TAMs) as key contributors to immune evasion and ICI resistance in HCC, primarily through polarization to the M2 phenotype. M2-polarized TAMs secrete a range of immunosuppressive cytokines that inhibit T cell activation and promote tumor progression through processes such as angiogenesis and epithelial-mesenchymal transition. These mechanisms compromise the efficacy of ICIs and facilitate tumor expansion and metastasis. This review summarizes the role of TAM-related signaling pathways in driving immune evasion and ICI resistance in HCC, with particular emphasis on the contribution of TAM surface receptors and chemokines in immune suppression. Additionally, the review highlights emerging insights into TAM metabolic reprogramming and transcriptional regulation, which have been closely linked to ICI resistance. Furthermore, we explore promising therapeutic strategies targeting TAMs and their associated signaling pathways to enhance ICI efficacy in HCC. Integrating these novel approaches could potentially overcome TAM-driven immune evasion and ICI resistance, boosting the efficacy of immunotherapy and improving patient prognosis in HCC.