Midkine restrains T-cell mediated anti-tumor immunity by suppressing macrophage M1 polarization in lung adenocarcinoma.

BACKGROUND: Lung adenocarcinoma (LUAD) is characterized by a highly immunosuppressive tumor microenvironment (TME), which limits the efficacy of current anti programmed cell death protein 1 (anti-PD-1) immunotherapy. Midkine (MDK), a heparin-binding growth factor, is frequently overexpressed in various malignancies; however, its specific role in regulating anti-tumor immunity in LUAD remains unclear. This study aimed to investigate the immunomodulatory role of MDK in LUAD, and to evaluate the therapeutic potential of MDK neutralization. METHODS: In this study, we analyzed single-cell sequencing datasets and validated MDK expression across multiple non-small cell lung cancer (NSCLC) cell lines. To explore the immunomodulatory functions of MDK, we established ex vivo co-culture models using human peripheral blood mononuclear cells (PBMCs) and LUAD cells. We assessed the impact of recombinant MDK and an MDK-neutralizing antibody (α-MDK) on T cell proliferation, differentiation, and cytotoxicity, as well as macrophage polarization, using flow cytometry, lactate dehydrogenase (LDH) release assays, and multiplex cytokine measurement. RESULTS: We confirmed that MDK is significantly upregulated in malignant LUAD cells compared to normal lung epithelial cells. Functional analysis revealed that MDK signaling suppresses T cell-mediated anti-tumor immunity by inhibiting the expansion of cytotoxic CD8+ T cells and restricting T helper type 1 cell (TH1) polarization. Furthermore, MDK impaired the polarization of macrophages towards the pro-inflammatory M1 phenotype, and dampened antigen-presenting cell function. Notably, blocking MDK signaling with a neutralizing antibody effectively reversed these immunosuppressive effects, restoring T cell cytotoxicity and enhancing the secretion of pro-inflammatory cytokines such as interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α). CONCLUSIONS: Our findings demonstrate that MDK acts as a key regulator in the LUAD TME by simultaneously restraining T cell activation and M1 macrophage polarization. These data suggest that targeting MDK offers a promising therapeutic strategy to overcome immune suppression and improve clinical outcomes in LUAD.