The present invention provides methods for high level, regulated 
transgene transcription that is restricted to 
cell populations of specific types. The process is designed to work with any inducible expression regulation systems, adapting them to a tissue-specific 
expression pattern while simultaneously delivering maximal achievable expression levels. In particular, the invention utilizes 
hybrid promoters that contain the 
DNA elements for both 
cell type-specific and regulated transcription. By placing the 
gene of the transcriptional activation factor (TAF) under the control of this tissue-specific / 
drug-regulated (TSDR) 
promoter, this invention achieves high expression levels of TAF in specific target cells by first initiating TAF expression using 
cell-
type specific transcription elements, and subsequently amplifying 
transcriptional activity by establishing an autoregulatory 
positive feedback loop. In non-target cells, 
cell type-specific elements of the TSDR 
promoter will be inactive, the TAF expression will not be initiated, and auto-upregulation will not occur. For 
cell type-specific promoters with leaky low-
level activity in non-target cells, a variation of this 
system has been developed which combines autologous upregulation of TAF with the expression of cross-competing transcriptional silencers (TSi) to achieve a type of eukaryotic “genetic switch”—either shutting off 
transgene and TAF expression completely or promoting maximal expression levels, depending on the original 
activity level of the specific 
promoter in that particular cell.