Figure 1

Experimental design and a CR-to-relapse treated leukemic model established in non-irradiated T-ALL mice. a Schematic representation of experimental strategy. Eight-week-old C57/BL6 J mice (CD45.2⁺), each injected with 10⁵ congenic T-ALL cells (CD45.1⁺), are used to develop T-ALL. When leukemic cells reach 1–5% of the mononuclear cell (MNC) in peripheral blood (PB) of these mice, chemotherapy (Ara-C and CTX) is given, and both leukemic cells and normal hematopoiesis are examined thereafter. b Leukemic infiltration in spleen, bone marrow and liver of the dying T-ALL mice in the late disease stage. Mice injected with T-ALL cells were sacrificed on the 21st day post injection for histopathological evaluation. Tissues were collected and fixed with 10% formalin overnight, stained with hematoxylin-eosin (H&E) and examined by an inverted microscopy. c Expression of T-ALL cell markers on flow cytometry for the leukemic cells as GFP⁺CD45.1⁺CD3⁺CD4⁺CD8⁺. d–e Peripheral blood cell counts of T-ALL mice showed a gradual appearance of lymphocytic leukocytosis and decreased hemoglobin and platelets (n = 3–4). Peripheral blood samples were tested by an automatic whole-blood analyzer (XT-2000T; SysmHGBex). f Leukemic burden in BM of T-ALL mice increased daily, and reached nearly 10% of MNC on the 12th day post injection (n = 4). g T-ALL mice showed a much shorter life-span compared to the normal control (median survival days post T-ALL cells injection: 29; n = 19; p = 0.0001). h–k When leukemic burden of the T-ALL mice reached about 1–5% in PB, mice received 1-day therapy composed of Ara-C (150 mg/kg) and CTX (100 mg/kg). h The treated leukemic mice (1-day treated leukemic group) showed prolonged survival time compared to the untreated leukemic group (median survival days post T-ALL cells injection: 39.5 vs. 29; n = 10; p = 0.002). i Leukemic burden in PB of the treated leukemic mice at different time points post therapy (n = 6–8). j Leukemic burden in BM of the treated leukemic mice at different time points post therapy (n = 3–4). Leukemic burden in PB and BM both decreased right after treatment, and regenerated since the 5th day post therapy. It was nearly undetectable on the 2nd to the 5th day post therapy. k Platelet count in PB of the treated leukemic mice post therapy (n = 6–9). It showed no significant difference when compared with the PBS injected control mice, though there was a decrease tread on the 12th day post therapy when leukemia relapsed. All data were presented as mean ± SEM.