A major issue for successful human gene therapy or genetic vaccination is a safe high-transgene expression level. Plasmid-based (non-viral) physical methods of gene transfer offered attracting approaches but their low efficiencies have limited their use in human pre-clinical trials. One of the limits appears to be the size of the plasmid that must be transferred across the cell membrane to the nucleus for its processing. In the present work to enhance gene transfer and expression, we evaluated a new generation of DNA vector; the minicircle, combined with the electropulsation technique. Minicircle is a doubled-stranded circular DNA with reduced size as it is devoid of bacterial sequences. We showed that electrotransferred minicircle encoding green fluorescent protein had higher in vitro transfection level compared with full-length plasmid. We demonstrated that minicircle great efficiency was not because of cellular toxicity decrease but was correlated to more efficient vector uptake by cells. Vector electrotransfection was operated in vivo and, using fluorescence imaging, minicircle electrotransfer was shown to enhance the efficiency and duration of tissue-targeted gene delivery and expression. By combining powerful expression and delivery systems, we have provided a valuable method for new approaches in gene therapy and genetic vaccination.

BK polyomavirus is ubiquitous, with a seropositivity rate of over 75% in the adult population. Primary infection is thought to occur in the respiratory tract, but asymptomatic BK virus latency is established in the urothelium. In immunocompromised host, the virus can reactivate but rarely compromises kidney function except in renal grafts, where it causes a tubulointerstitial inflammatory response similar to acute rejection. Restoring host immunity against the virus is the cornerstone of treatment. This review covers the virus-intrinsic features, the posttransplant microenvironment as well as the host immune factors that underlie the pathophysiology of polyomavirus-associated nephropathy. Current and promising therapeutic approaches to treat or prevent this complication are discussed in relation to the complex immunopathology of this condition.