TLR9 and acute lymphoblastic leukemia: B-ALL patients (N = 49) in our hospital showed higher TLR9 expression in peripheral blood mononuclear cells (PBMCs) than healthy controls (N = 10) (median: 0.004 vs. 0.067, p < 0.001, Fig. 1A); thus, it is indicated that TLR9 is widely expressed in B-ALL cells.