Metastatic PD-L1+ melanoma cells, infiltration of M2-like macrophages and CD31+ endothelial cells, and high expression levels of 15-LOX/CYP450 4A enzymes in the brain tumor microenvironment of the tumor control mice were significantly attenuated in dLGG-treated mice; conversely, M1-like resident microglia and cytotoxic T cells were increased. The gene discussed is ALOX15; the disease is melanoma.