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] CD48 TAMs were identified associating with accelerated tumour progression, immunotherapy resistance and poor clinical outcomes. These TAMs exhibited protumorous phenotypes, driving immunosuppression and promoting extracellular matrix remodelling. Genetic CD48 ablation attenuated HCC progression while promoting CD8 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.