Highly concentrated and purified lentivirus for delivery of the Tet-On 3G transactivator to target cells.  Any gene of interest under the control of a TRE3G promoter can be tightly controlled by the presence and absence of Dox in the culture medium. Tet-On 3G is a modified, improved Tet-On Advanced transcriptional activator protein (transactivator) which has been evolved to display far higher sensitivity to the inducer molecule dox. Tet-On 3G generates very high maximal expression and responds to lower Dox concentrations than its predecessors.