Increased resistance and selection in paclitaxel for peripheral blood progenitor cells following transduction with the MDR1 gene

Introduction: The technique of retrovirally mediated gene transfer allows t he introduction and stable expression of therapeutic genes in hematopoietic cells. Clinical applications include the marking of bone marrow and periph eral blood stem cell transplants, the correction of monogenetic disorders, and the inhibition of viral infections. A specific therapeutic option for t he treatment of cancer patients consists in the transfer of drug resistance genes rendering transplantable hematopoietic cells resistant to the cytoto xic drugs used in high-dose chemotherapy protocols. Methods: We have invest igated the effects of MDR1 gene transfer via a retroviral vector into prest imulated CD34-enriched primary hematopoietic cells from human peripheral bl ood. Results: Using a PCR to detect proviral sequences within the DNA of th e target cells we observed a transfer efficiency of 70% into clonogenic pro genitor cells with a markedly decreasing efficiency into more immature subp opulations. Clonogenic progenitors could be rendered resistant to paclitaxe l at a frequency of 14.8 +/- 2.6% when comparing MDR1 transduced cells to a mock control. Retrovirally transduced cells and mock control cells were se lected in vitro for seven days in paclitaxel and then further expanded. The numbers of nucleated cells and progenitor cells were compared and revealed a twofold selective advantage for progenitors derived from MDR1-transduced cells. The proliferative capacity did not differ between MDR1-transduced a nd mock cells. Conclusion: Increased paclitaxel resistance and a selective advantage for in vitro-expanded hematopoietic progenitors were detected. Th is observation may be helpful for the design of future gene therapy trials.