Coexpression of the cytosine-deaminase and the hIL-4-gene for combined immuno-/chemotherapy

Background: Tumor cells engineered to produce interleukin-4 (IL-4) can medi ate antitumor cytotoxicity in a T-cell-independent manner and generate a sy stemic immune reponse against parent tumor cells. The bacterial cytosine de aminase (CD) has the potential to render cells sensitive to the nontoxic pr odrug 5-fluorocytosine (5-FC) by converting it into the toxic compound 5-fl uorouracil (5-FU). In an attempt to study the combined effect of immunother apy and chemotherapy we constructed plasmid rectors containing both genes a nd demonstrated expression in mammalian cells. Methods: We cloned the hIL-4- and mIL-4-cDNA in an expression plasmid conta ining the bacterial cytosine deaminase gene (CD). Following stable integrat ion of the genes into human and murine tumor cells gene expression was show n by enzyme linked immunosorbent assay and Western blot analysis. Results: CD expression of different clones resulted in the killing of up to 90% of cells after 11 days. CD-expressing cells were able to kill nonexpre ssing cells which confirms that the CD gene has a bystander effect. We show ed combined expression of CD and IL-4 in human and murine cell lines and de monstrated abrogation of IL-4 production in the presence of 5-FC. Conclusions: Vectors containing both a suicide gene and a cytokine gene may be useful for combined immuno-/chemotherapy. In addition, abrogation of cy tokine production can be achieved in the presence of 5-FC mediated by CD wh ich may be used as a safety mechanism to control gene expression.