Response: Lentiviral vectors and transduction of human cancer B cells

We thank Dr Lévy et al for their comments on our recent manuscript¹  and commend them for their interesting data. They point out that, unlike us, they could not efficiently transduce chronic lymphocytic leukemia (CLL) cells using lentiviral vectors. Therefore, they engineered a new generation of lentiviral vectors carrying glycoproteins of the measles virus with which they reported an efficient gene transfer in T cells, B cells, and CLL cells.^2,3  In their experiment, 48 hours after lentiviral transduction the green fluorescence protein (GFP) was removed by washing. Therefore they speculate that our flow cytometric analysis detected sticking proteins rather than transduced cells. Evidently, their data are incomparable with ours. Lévy et al did not use our vector, our short hairpin RNA (shRNA) construct, or our transduction conditions. For example, we concentrated the viral supernatant at 770g and vigorous washing did not remove GFP from transduced CLL cells. Unfortunately, Lévy et al failed to appreciate the data presented in Figure 6 of our manuscript demonstrating significant changes in CLL cells transduced with STAT3 shRNA, but not with the empty retrovirus, such as down-regulation of the expression of STAT3 gene, STAT3-regulated genes, and STAT3 protein levels. Obviously, these changes could not be obtained with washable GFP-positive sticky proteins. Nevertheless, Lévy et al should be congratulated on generating an improved transduction system.