Retroviral vectors for the transduction of the PML-RAR alpha fusion product of acute promyelocytic leukemia

We have designed several retroviral constructs to transduce the PML-RAR alpha fusion product of human acute promyelocytic leukemia. Our aim to generate high-titer stable vector-producing cell lines was hindered by a toxic effect of PML-RAR alpha expression on packaging cells. To circumvent this, we tested retroviral vectors expressing the transgene from several internal promoters including inducible and myelospecific promoters. To compare efficiency of these constructs in their ability to generate protein expression in the appropriate target cells and optimal viral titers, we used the BOSC23 transient packaging cell line. We found that the direct-oriented vector did not ensure tissue-specificity of PML-RAR alpha expression, while the reverse-oriented retroviral vector did. The latter construct, however, failed to generate high-titer recombinant virus. This study exemplifies the unpredictable behavior of retroviral constructs and the superiority of transient systems for transduction of a toxic product.