Abstract
BACKGROUND: Hepatocellular carcinoma (HCC) remains a leading cause of cancer-related deaths worldwide, especially in advanced stages where limited treatment options result in poor prognosis. The immunosuppressive tumor immune microenvironment (TIME), characterized by low immune cell infiltration and exhaustion, limits immunotherapy efficacy. To address this, our study investigates the role of C-C motif chemokine ligand 3 (CCL3) in modulating the HCC TIME. METHODS: We analyzed CCL3 expression in human HCC samples from The Cancer Genome Atlas database, focusing on its correlation with inflammatory gene signatures and immune cell infiltration. High-dimensional single-cell RNA sequencing (scRNA-seq), flow cytometry, and multiplex immunofluorescence were used to investigate CCL3's effects on macrophage function and T cell activation. The biological impact of CCL3 on macrophages was assessed using co-culture systems, confocal imaging, metabolite detection, and inhibition assays. Preclinical HCC models and ex vivo tumor fragment assays further explored how CCL3 modulates immune responses and enhances immune checkpoint blockade efficacy. RESULTS: Our study shows that CCL3 is suppressed in the tumor microenvironment and positively correlates with immune infiltration and inflammatory responses. Targeted liver delivery of rAAV-Ccl3 reprograms the immune microenvironment in HCC, promoting immune cell recruitment and tertiary lymphoid structure formation, thus suppressing tumor growth via immune engagement. Through scRNA-seq, flow cytometry, and multiplex immunofluorescence, we found that CCL3 enhances macrophage antigen uptake and activates cytotoxic T cells. In vivo and in vitro experiments confirmed that CCL3 facilitates T cell infiltration and upregulates MHC II expression on macrophages, enhancing antigen presentation. The CCL3-CCR5 pathway also boosts macrophage metabolism, increasing lysosomal activity and antigen uptake, thereby strengthening adaptive immune responses and increasing sensitivity to immune checkpoint blockade therapies in preclinical models. CONCLUSIONS: This study highlights the pivotal role of CCL3 in reshaping the TIME and enhancing antitumor immunity in HCC. By promoting immune cell recruitment and enhancing antigen presentation, CCL3 demonstrates significant potential to improve the efficacy of immunotherapy, particularly in combination with immune checkpoint inhibitors. Targeting CCL3 may help to overcome the immunosuppressive TIME in HCC and improve patient outcomes.