Comparison of cis and trans tat gene expression in HIV LTR-based amplifier vectors

The long terminal repeat (LTR) of the human immunodeficiency virus (HIV) drives highly efficient gene expression in the presence of the transactivator, Tat. Thus, tat-containing vectors may be very useful tools in gene therapy. However information about the optimal way of delivering the tat gene is limited. In this study, we compared the effects of cis and trans expressions of the tat gene and its effects on HIV LTR-driven gene expression in different cell lines using non-viral vectors. The human interleukin-2 (IL-2) gene was used as a reporter gene under the control of the HIV2 LTR (pHIV2-IL-2). The tat gene, driven by a cytomegalovirus (CMV) promoter, was either co-transfected separately (pCMV-Tat) or inserted downstream of the IL-2 gene (pHIV2-IL-2-neo-C-Tat). Our results showed that HIV2 LTR-Tat-based vectors were much more potent than CMV promoter-based vectors in transient expression. The co-transfection of both plasmids was comparable to a single transfection of pHIV-IL-2-neo-C-Tat in both high and low transfection efficiency cells. In conclusion, the co-placement of HIV2 LTR and tat genes on a single plasmid allows for gene expression as efficiently as a two-plasmid system, suggesting that HIV2 LTR-Tat-based vectors may be attractive tools for gene therapy.