Department of Chemical Pathology, Women's and Children's Hospital, North Adelaide South Australia, 5006.
Helper plasmids for production of HIV-1-derived vectors
Vectors derived from human immunodeficiency virus type 1 (HIV-1) appear an attractive option for many gene therapy applications. This is due to their ability to transduce noncycling cell populations and to integrate their genome into the host cell chromosome, resulting in the stable genetic modification of the transduced cell. These properties have permitted the direct in vivo transduction of several tissues, including the central nervous system, retina, and liver. However, the pathogenic nature of HIV-1 has raised considerable concerns about the safety of such vector systems. To help address these concerns, we have expressed each of the primary transcriptional units encoding trans functions relevant for vector production in individual plasmid constructs. The gag-pol gene sequence was codon-optimized for expression in mammalian cells resulting in high level Rev/Rev-response element (RRE)-independent expression. Codon optimization of gag-pol also reduces sequence homology with vectors containing gag gene sequences, which results in reduced transfer of biologically active gag-pol sequences to transduced cells. Furthermore, the vif reading frame overlapping the 3' end of the pol coding sequence is destroyed by codon optimization. We have also shown that the Gag and Gag-Pol polyproteins can be efficiently expressed from separate transcriptional units. This has enabled the removal of a cis-acting viral element, the gag-pol translational frameshift sequence, from the vector/packaging system and prevents detectable transfer of biologically active sequences equivalent to the gag-pol gene to transduced cells.
Hum Gene Ther. 12(17): 2081-93.
To facilitate the production of recombinant virus for gene therapy studies with increased safety, a series of constructs were made for the expression of HIV1 proteins and combined with a suitable vectors. The synthetic constructs for gag-pol(gagpolml), gag (gagml), and pol (polml) genes were made based on the optimal codon usage for mammalian gene expression. The variant of the synthetic gag-pol sequence, gagpolfusionml , in which the frameshift of the region of overlap between the reading frames encoding gag pol were replaced by codon- optimized sequence encoding gag-pol polyprotein. According to the experimental results, codon-optimized gag-pol gene sequence (pcDNA3gagpolml) showed expression and virus production efficiently, the expressions of codon optimized gag (pcDN3gagml), pol (pcDNA3polm), and pcDNA3gagpolfusionml on their own can not support the production of virus however. In contrast, the combination of the two plasmids pcDN3gagm and pcDNA3gagpolfusionml can replace the pcDNA3gagpolml codon-optimized construct.