Enhancing plasmid nuclear import and delivery system: room for improvement

The use of plasmid DNA vectors for gene transfer representsan important platform for clinical applications, notably withDNA vaccination wherein large-scale vaccine production is noteasily manageable with other forms of vaccine including recombinantprotein, whole tumor cells, or viral vectors. A varietyof clinical trials against cancer have provided evidence that DNAvaccines are well tolerated and have an excellent safety profile.Nevertheless there is still a gap between the experimental dataand their application in a clinical setting due to low level of antigenexpression.DNA vaccines allow incorporating multiple components toactivate and direct selected immune effector pathways and areprone to be delivered in many different manner. To achievemore efficient gene expression from plasmid vectors CMVpromoter driven, DNA nuclear targeting sequences (DTSs) areintroduced to increase the efficiency of nuclear plasmiduptake from cytoplasm. Electrogenetherapy is promising forthe treatment of muscle disorders, as well for the systemicsecretion of therapeutic proteins, DNA vaccination, immunotherapyand cancer therapy. The inclusion in a DNAvector backbone of a DTS localized in a non-coding regionof the SV40 virus sequence is established to increase in vivoexpression up to 20-fold using electroporation delivery inmuscle tissue.We have used this delivery technique in combination withplasmids containing a tandem repeat of two 72-bp DNA elementsfrom the SV40 enhancer in preclinical immunization protocols.To evaluate the increase in performance we analyzed overtime the IL-2 expression of anti-idiotypic DNA vaccines, developedagainst an aggressive murine B-cell lymphoma modeland co-expressing IL-2 as immunomodulating agent. The antiidiotypichumoral response was assayed as well.Our in vivo results show that the combination of electroporationand a plasmid vector carrying DTSs elements results in efficaciousDNA vaccines.