CD48 is a novel immune checkpoint on tumour‐associated macrophages in hepatocellular carcinoma

BACKGROUND: Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality with limited therapeutic options. Despite promising immunotherapy, response rates remain suboptimal. Tumour-associated macrophages (TAMs) constitute a pivotal component of the immunosuppressive HCC microenvironment, yet TAM heterogeneity and contributions to tumour progression and immunotherapy resistance remain poorly defined. OBJECTIVE: To identify and characterise critical TAM subsets in HCC and evaluate their potential as therapeutic targets. DESIGN: Integrated multiomics analysis of hepatocellular carcinoma (HCC) clinical specimens was performed and validated across independent cohorts. Single-cell RNA sequencing identified tumour-associated macrophage (TAM) subpopulations. Functional characterisation employed whole-body and macrophage-specific CD48 knockout mice, adoptive transfer experiments and co-culture systems. Mechanistic studies used immunoprecipitation-mass spectrometry, immunofluorescence colocalisation and pathway analysis. Therapeutic efficacy was evaluated using anti-CD48 monotherapy and combination with anti-programmed cell death protein 1 (PD1) in orthotopic HCC models. RESULTS: T-cell function. Adoptive transfer of CD48-deficient macrophages validated tumour-suppressive effects. Mechanistically, matrix metalloproteinase-14 (MMP14) was identified as a novel cis-interacting partner for CD48, functioning independently of the canonical CD48-CD244 axis. This interaction activated RAP1 GTPase, triggering Yes-associated protein (YAP) nuclear translocation and YAP-signal transducer and activator of transcription 3 (STAT3) complex formation to upregulate immunosuppressive genes. Anti-CD48 antibodies effectively inhibited tumour progression and demonstrated synergistic effects with anti-PD1 therapy. CONCLUSION: CD48 represents a novel immune checkpoint on TAMs critical for HCC progression and immunotherapy resistance. Targeting CD48 may overcome immunosuppression and increase therapeutic efficacy in HCC.