After engraftment into recipient mice, the E2A-PBX1 cell line expressing human T-BsAb targets leads to disseminated leukemia that involves the bone marrow and spleen with circulating leukemia cells. (A) After engraftment of E2A-PBX1 cells expressing huCD123 into recipient mice, huCD123⁺/mCD19⁺ leukemia cells can be detected in the blood, spleen, and bone marrow 7 days later. (B) Leukemia cells expressing human antigen can be distinguished from normal B-cell lineage subsets by a combination of surface markers (CD127, CD43, CD69, and CD44). (C) Detection of CD127⁺/CD43⁺/CD69⁺/CD44hi leukemia cells in the bone marrow and spleen.