Black phosphorus nanosheets activate tumor immunity of glioblastoma by modulating the expression of the immunosuppressive molecule PD-L1

The tumor microenvironment in glioblastoma (GBM) is characterized by a pronounced immunosuppressive state, which significantly hampers tumor treatment and contributes to treatment resistance. While our previous research established that black phosphorus nanosheets (BPNS) inhibited glioblastoma cell migration and invasion, the impact of BPNS on the anti-tumor-associated immune mechanism remains unexplored. This study firstly investigated whether BPNS could modulate the tumor microenvironment through immunotherapy and elucidated the underlying mechanisms. We used a subcutaneous mouse model of GBM, which evaded immune surveillance to evaluate BPNS effects on immune cells within the tumor microenvironment. Our results demonstrated that BPNS significantly enhanced the tumor-suppressive microenvironment, reactivating immune cells' cytotoxicity against tumor cells. Moreover, further analysis revealed that BPNS counteracted the immunosuppressive state by reducing the expression of the immunosuppressive molecule PD-L1 in tumor cells, leading to an anti-tumor effect. Mechanistically, BPNS reduced PD-L1 expression through two main pathways: by inducing autophagy via binding to the HSP90 protein, leading to PD-L1 degradation through the autophagy pathway, and by inhibiting the PI3K-AKT signaling pathway, which reduced PD-L1 mRNA levels. This study expands the understanding of BPNS biological activity and suggests new strategies for utilizing BPNS as an adjuvant in immunotherapy.