Blockade of CLEVER-1 restrains immune evasion and enhances anti-PD-1 immunotherapy in gastric cancer.

Background: Gastric cancer (GC) remains a major global health burden. Despite the advancements in immunotherapy for patients with GC, the heterogeneity of GC limits response rates, especially in immune "cold" subtypes, including genomically stable and epithelial-mesenchymal transition GC. Common lymphatic endothelial and vascular endothelial receptor-1 (CLEVER-1), a newly recognized immune checkpoint molecule predominantly expressed on tumor-associated macrophages (TAMs), remains poorly understood in GC. This study aims to explore the clinical significance of CLEVER-1+TAM infiltration, elucidate its role in modulating the tumor immune landscape, and investigate the therapeutic potential of CLEVER-1 blockade in enhancing immunotherapy.

Methods: This study analyzed two independent GC cohorts and single-cell RNA sequencing data (GSE183904). CLEVER-1 expression in TAMs was assessed via multiplex immunofluorescence, flow cytometry, and RNA sequencing. The clinical relevance of CLEVER-1+TAM infiltration was evaluated in relation to tumor, node, metastases staging, molecular subtypes, prognosis, and immunochemotherapy response. Transcriptomic and pathway analyses characterized the immunophenotype of CLEVER-1+TAMs. Functional assays examined their suppression on CD8+T cells, while interventional experiments assessed the impact of CLEVER-1 blockade alone or with programmed cell death protein-1 (PD-1) inhibition.

Results: CLEVER-1 was predominantly expressed on TAMs in GC and was associated with worse clinical outcomes. Transcriptomic and phenotypic analyses revealed that CLEVER-1+TAMs display a dynamic immunophenotype and critically suppress T-cell function, fostering an immunosuppressive microenvironment. High CLEVER-1+TAM infiltration was linked to poor response or adaptive resistance to PD-1 blockade therapy. CLEVER-1 blockade reprogrammed TAMs toward a pro-inflammatory phenotype, resulting in enhanced CD8+T cell cytotoxicity and proliferation. Co-targeting CLEVER-1 and PD-1 synergistically enhanced antitumor responses.

Conclusions: High infiltration of CLEVER-1+TAMs indicates immune suppression and poor prognosis in GC. The combination of CLEVER-1 and PD-1 blockade emerges as a dual-pronged strategy to boost immune-mediated tumor control and prevent treatment relapse in GC.