SLAMF8 as a potential therapeutic target for modulating tumor-associated macrophages in colorectal cancer.

Abstract

2573 Background: Reprogramming or repolarizing tumor-associated macrophages (TAMs) has emerged as a novel strategy in tumor immunotherapy, leveraging their remarkable plasticity. Our previous studies have demonstrated that SLAMF8, predominantly expressed in macrophages, is a promising biomarker for predicting the efficacy of immune checkpoint inhibitor (ICI) therapy in colorectal cancer (CRC). This study aims to elucidate further the regulatory role of SLAMF8 in TAMs and its influence on the tumor immune microenvironment. Methods: In vitro, M2 macrophage and TAM models were established to investigate the regulatory role of SLAMF8 in macrophage immunophenotypic transition and its impact on CD8+ T cell function using qRT-PCR, flow cytometry, and co-culture assays. Additionally, pathway enrichment analysis of RNA-seq data and western blotting were conducted to elucidate the underlying molecular mechanisms. In vivo, SLAMF8-specific small interfering RNA (siSLAMF8) was utilized to inhibit SLAMF8 expression in subcutaneous colorectal cancer (CRC) tumor models. Subsequent observations included tumor growth monitoring and analysis of immune cell infiltration via flow cytometry. Furthermore, two subcutaneous tumor models, one sensitive and one resistant to PD-1 therapy, were constructed to explore potential synergistic effects between SLAMF8 inhibition and anti-PD-1 treatment. Results: In vitro studies reveal that SLAMF8 facilitates the polarization of macrophages toward the M2 phenotype, contributing to the immunosuppressive characteristics of TAMs and dysfunction of CD8+ T cells. Inhibiting SLAMF8 in vivo significantly delayed colorectal cancer (CRC) progression. Flow cytometry analysis confirmed that the infiltration of anti-tumor TAMs (CD86+ F4/80+) and cytotoxic CD8+ T cells (IFNγ+ GZMB+ CD8+ T cells) was augmented, while the infiltration of pro-tumor TAMs (CD206+ F4/80+) and exhausted CD8+ T cells (PD1+ LAG3+ CD8+ T cells) was reduced in tumors treated with SLAMF8-specific small interfering RNA (siSLAMF8). Additionally, targeting SLAMF8 enhances the efficacy of anti-PD-1 therapy. Mechanistically, Western blotting experiments confirmed that the phosphorylation levels of key molecules in the PI3K/AKT and JAK/STAT3 signaling pathways were significantly increased in SLAMF8-overexpressing macrophages. Conclusions: Inhibition of SLAMF8 delays tumor growth, enhances the sensitization to ICI therapy, and reverses the immunosuppressive microenvironment by modulating TAMs via the PI3K/AKT and JAK/STAT3 pathways in CRC. These findings reveal the potential of SLAMF8 as a therapeutic target for immunotherapy focused on TAMs.