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

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.

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.

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 (T_H1) 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).

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.