Intratumoral PPT1-positive macrophages determine immunosuppressive contexture and immunotherapy response in hepatocellular carcinoma

Background: Hepatocellular carcinoma (HCC) is a malignancy with limited treatment options and poor prognosis. Macrophages are enriched in the HCC microenvironment and have a significant impact on disease progression and therapy efficacy. We aim to identify critical macrophages subsets involved in HCC development.

Methods: Macrophage-specific marker genes were identified through single-cell RNA sequencing analyses. The clinical significance of macrophages with palmitoyl-protein thioesterase 1 (PPT1) positive was investigated in 169 patients with HCC from Zhongshan Hospital using immunohistochemistry and immunofluorescence. The immune microenvironment of HCC and the functional phenotype of PPT1⁺ macrophages were explored using cytometry by time-of-flight (CyTOF) and RNA sequencing.

Results: Single-cell RNA sequencing analyses revealed that PPT1 was predominantly expressed in macrophages in HCC. Intratumoral PPT1⁺ macrophages abundance was associated with inferior survival durations of patients and an independent risk factor of prognosis for HCC. High throughput analyses of immune infiltrates showed that PPT1⁺ macrophage-enriched HCCs were characterized by high infiltration of CD8⁺ T cells with increased programmed death-1 (PD-1) expression. PPT1⁺ macrophages exhibited higher Galectin-9, CD172a, and CCR2 levels but lower CD80 and CCR7 levels than PPT1^- macrophages. Pharmacological inhibition of PPT1 by DC661 suppressed mitogen-activated protein kinase (MAPK) pathway activity but activated nuclear factor kappa B (NF-κB) pathway in macrophages. In addition, DC661 enhanced the therapeutic efficacy of anti-PD-1 antibody in the HCC mouse model.

Conclusions: PPT1 is mainly expressed in macrophages in HCC and promotes immunosuppressive transformation of macrophages and tumor microenvironment. PPT1⁺ macrophage infiltration is associated with poor prognosis of patients with HCC. Targeting PPT1 may potentiate the efficacy of immunotherapy for HCC.

Immunotherapy; Liver Neoplasms; Macrophages; Tumor Biomarkers; Tumor Microenvironment.