Bicistronic retroviral vectors for combining myeloprotection with cell-surface marking

Abstract

We have developed a retroviral vector coexpressing the multidrug-resistance 1 (MDR1) cDNA for inducing cancer drug resistance and the truncated version of the low-affinity nerve growth factor receptor (ΔLNGFR) for cell-surface marking of transduced cells. The vector is based on the FMEV backbone which mediates high levels of gene expression in hematopoietic cells. To achieve optimal expression levels of both cDNAs, untranslated regions from MDR1 and ΔLNGFR were removed and three different connections were tested: retroviral splice signals, an internal ribosomal entry site (IRES) from encephalomy-ocarditis virus, and an internal promoter from the chicken β-actin gene. As determined by two-color flow cytometry, the best correlation of the expression of both cDNAs was obtained using the vector SF1mSδ which utilized retroviral splice signals for co-expression. Simultaneous expression of both cDNAs at the single cell level was also shown by confocal laser microscopy. Lymphoid and hematopoietic progenitor cells, including primary human CD34+ cells, transduced with SF1mSδ acquired dominant multidrug resistance. Transduced primary CD34+ cells could be enriched in vitro based on expression of ΔLNGFR, avoiding exposure to cytostatic agents. Thus, monitoring the selection of chemotherapy-resistant cells and analyzing their biological properties may be alleviated, both in vitro and in vivo.