Objective    To observe the distribution of bone marrow mononuclear cells (BM-MNCs) after the transfection of exogenous multi-drug resistance gene-1 (MDR1) and its protective effect on the haematogenesis in bone marrow cells in gene therapy.     Methods    Thirty-two BALB/c tumor-bearing mouse were randomly and equally divide into 4 groups

normal control (A)

blank control (B)

negative control (C) and transfection control(D). The animals of last 3 groups received a radiation of 1.5 Gy and then infusion of normal saline

untransfected and transfected BM-MNCs respectively. Normal control group underwent no treatment. After chemotherapy of overdose adriamycine

their peripheral blood (PB) cells were counted and the tumor volume was measured. The distribution and expression of exogenous human MDR1 and P-gp by were detected by RT-PCR and immunohistochemistry.     Results    No difference was observed on the red cell and platelet count after chemotherapy (P0.05). The white cell count of group D was decreased to (3.32±0.26) after 4 weeks’ chemotherapy

significantly lower than that of pre-chemotherapy (6.64±0.39) (P0.05). The white cell count was higher in group D than in group C after 3-week chemotherapy (P0.05)

and the tumor growth was slower in the group D (P0.05). The MDR1 and P-gp expression was detected in bone marrow and PB mononuclear cells. There was no MDR1 and P-gp expression in the heart

liver

lung

spleen and kidney. There was P-gp but not MDR1 expression in the tumor mass.     Conclusion    The transfection of MDR1 gene into tumor-bearing mice BM-MNCs may provide chemoprotection for BM haemopoiesis to some extent.