TLR9 and acute lymphoblastic leukemia: Given the ability of TLR9 signaling to confer protection against B-ALL [27], we compared a panel of endosomal TLR agonists for their ability to target the bone marrow niche and achieve protection against outgrowth of adoptively transferred primary B-ALL cells in both syngeneic mouse models and primary patient-derived xenografts (PDX).