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A major limitation of retrovirus gene therapy technology is the often low percentage of target cells transduced. This is in part due to the low diffusivity of retroviruses, as well as their short half-life (~5 h). An approach to overcome these limitations has been developed using the forces in an acoustic standing wave field. An air-backflush mode of operation obtained up to 8-fold increases in TF-1 cell transduction compared to static controls and this was sustained from 2 to 24 h. The transduction increased as a function of power input, but at elevated power levels the acoustic transducer generated excessive heat. A new design with improved heat dissipation allowed continuous acoustic treatment over 2 days with no decrease in cell viability. This acoustically increased transduction reduces the need for additives and avoids the complications of recovering anchored cells. While acoustic separators can be used for bioreactor volumes ranging from hundreds of mL to >100 L, it is also important to define operational settings that avoid negative thermal influences on the cells. Additional cell culture experiments with CHO cells were performed to determine the acceptable temperature variations. [ABSTRACT FROM AUTHOR]