PD-L1 and VEGF dual blockade enhances anti-tumor effect on brain metastasis in hematogenous metastasis model.

Immunotherapy improves survival outcomes in cancer patients, but there is still an unmet clinical need in the treatment of brain metastases. Here, we used a mouse model to investigate the antitumor effect of programmed death-ligand 1 (PD-L1) and vascular endothelial growth factor (VEGF) dual blockade on metastatic brain tumors and evaluated immune responses during treatment. After establishing hematogenous brain metastasis by transplanting murine bladder carcinoma MBT2 cells stably expressing secNLuc reporter via the internal carotid artery of C3H/HeNCrl mice, we observed the formation of metastases not only in the brain parenchyma but also in the ventricles. The observed pathological areas showed that metastases in the ventricle were histologically larger than that in the brain parenchyma. Regarding the total tumor burden in the whole brain as revealed by Nluc activities, the combination of anti-PD-L1 antibody and anti-VEGF antibody showed a stronger anti-tumor effect than each single agent. Anti-PD-L1 antibody alone enhanced CD8⁺ T cell priming in regional lymph nodes, increased the proportion of activated CD8⁺ T cells in whole brain, and increased the density of CD8⁺ cells in the brain parenchyma. Furthermore, anti-VEGF antibody alone decreased microvessel density (MVD) in ventricular metastases, and the combination treatment increased intratumoral CD8⁺ cell density in the brain parenchyma and ventricular metastases. These results suggest that PD-L1 blockade enhanced cancer immunity not only in brain metastases lesions but also in the regional lymph nodes of the metastases, and that the addition of VEGF blockade increased the antitumor effect by increasing the infiltration of activated CD8⁺ T cell and decreasing MVD.