We overcome these technical hurdles and show here, for the first time, that following systemic administration (i.e., intraperitoneally), CpG-C was abundantly taken up by TLR9-expressing cells across the brain without affecting BBB integrity or infiltration of immune cells into the brain (Fig 4, S5 Fig), and dramatically reduced brain colonization by circulating tumor cells (Figs 1,2,6 and 7, S2 and S7 Figs). The gene discussed is TLR9; the disease is neoplasm.