The EF1 pCDH vectors by SystemBio use a composite promoter; hEF1a-HTLV

http://discovery.ucl.ac.uk/20480/1/20480.pdf

"hEF1a-HTLV promoter is a composite promoter comprising the human Elongation Factor-1α (EF-1α) core promoter and the R segment and part of the U5 sequence (R-U5’) of the Human T-Cell Leukemia Virus (HTLV) Type 1 Long Terminal Repeat. The EF-1α promoter exhibits a strong activity and yields long lasting expression of a transgene in vivo. The R-U5’ has been coupled to the EF-1α core promoter to enhance stability of RNA"

Has anyone seen any decrease in gene expression over time when using this promoter? I've had issues with the CMV promoter, and unfortunately I cant use 5-aza in my experiments.