ABSTRACT
<p><b>OBJECTIVE</b>To explore the myelo-protection effect of mdr1 transfected cord blood cells (CBMNCs) graft against high-dose homoharringtonine leukemia-bearing severe combined immunodeficient (SCID) mice model.</p><p><b>METHODS</b>Multidrug resistant (mdr1)gene was transferred into CBMNCs by a retrovirus vector, containing full-length cDNA of human mdr1 gene. CBMNCs and high-titer retrovirus supernatant were cocultured with cytokine combinations for 5 - 6 days. The SCID mouse models bearing human HL-60 cell leukemia were divided into three groups. Group A received tail vein injection of 2 x 10(6) mdr1 gene transduced CBMNCs at day 1 and 3, groups B and C 2 x 10(6) un-transduced CBMNCs and same volume of normal saline, respectively. The 3 groups of the mouse model were treated with weekly escalated doses of homoharringtonine. The peripheral white blood cell (WBC) counts, the human leukemia cells percentage in peripheral blood, the histological findings of main organs were assayed. The CD33 positive HL-60 cells in bone marrow were determined by flow cytometry. The function and expression of mdr1 gene were examined by PCR, immunochemistry (IC) and DNR extrusion test in vivo.</p><p><b>RESULTS</b>(1) mdr1 gene was transferred into CBMNCs successfully and the transfection frequency was 30%. (2) Leukemia SCID mice were xenotransplanted with mdr1-transfected BMMNCs by a programmed procedure and could be used as a valuable model for in vivo evaluating myelo-protection effects. (3) The transfected mice could tolerate homoharringtonine 5 approximately 6 folds higher than conventional dose and kept peripheral WBC count at a mean of 3 x 10(9)/L, with the peripheral human myeloid leukemia cells percentage decreasing to less than 5%. Histological examination showed that there was no leukemia infiltration in the main organs, the CD33 positive HL-60 cells in bone marrow were less than 5%. (4) The repopulation frequency of the transfected CBMNs in marrow were 9.13%. DNR extrusion test confirmed that the P-gp product maintained its biological function in the marrow.</p><p><b>CONCLUSION</b>mdr1 transferred-human CBMNC can xenotransplanted and repopulated in leukemia-bearing SCID mouse and are protected from chemotherapy-induced myelosuppression.</p>