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Report Summary

Biodistribution of DNA Plasmid Vaccines against HIV-1, Ebola, Severe Acute Respiratory Syndrome, or West Nile Virus Is Similar, without Integration, despite Differing Plasmid Backbones or Gene Inserts


Study Summary

Overall Study Design 
The Vaccine Research Center has developed a number of vaccine candidates for different diseasesinfectious agents 
HIV-1 Severe Acute Respiratory Syndrome virus West Nile virus and Ebola virus plus a plasmid cytokine 
adjuvant-IL-2Ig based on a DNA plasmid vaccine platform To support the clinical development of each of these vaccine 
candidates preclinical studies have been performed in mice or rabbits to determine where in the body these plasmid 
vaccines would biodistribute and how rapidly they would clear In the course of these studies it has been observed that 
regardless of the gene insert expressing the vaccine immunogen or cytokine adjuvant and regardless of the promoter used 
to drive expression of the gene insert in the plasmid backbone the plasmid vaccines do not biodistribute widely and remain 
essentially in the site of injection in the muscle and overlying subcutis Even though  1014 molecules are inoculated in the 
studies in rabbits by day 8 or 9  1 week postinoculation already all but on the order of 104106 molecules per 
microgram of DNA extracted from tissue have been cleared at the injection site Over the course of 2 months the plasmid 
clears from the site of injection with only a small percentage of animals generally 10-20 retaining a small number of 
copies generally around 100 copies in the muscle at the injection site This pattern of biodistribution confined to the 
injection site and clearance within 2 months is consistent regardless of differences in the promoter in the plasmid 
backbone or differences in the gene insert being expressed by the plasmid vaccine In addition integration has not been 
observed with plasmid vaccine candidates inoculated im by Biojector 2000 or by needle and syringe These data build on 
the repeated-dose toxicology studies performed see companion article Sheets et al 2006 to demonstrate the safety and 
suitability for investigational human use of DNA plasmid vaccine candidates for a variety of infectious disease prevention 
indication 
DNA vaccines are a novel product class with limited though ever increasing clinical experience beginning with clinical 
trials in the late 1990s Ulmer et al 1996 Thus their development represents a unique preclinical challenge The US 
FDA Food and Drug Administration has provided manufacturers with guidance on toxicology studies they deem necessary 
to support the safety of this novel product class to enter clinical trials CBER 1996 2005 Among these recommended 
studies are repeated-dose toxicology biodistribution and integration analyses DNA vaccines consist of a closed circular 
bacterial plasmids containing a bacterial origin of replication generally a selectable marker such as an antibiotic 
resistance gene and a gene insert expressing a vaccine immunogen or cytokine adjuvant under the control of a generally 
strong mammalian promoter often one from a human or animal virus and polyadenylation signals for good transcriptional 
expression in the vaccinee Frequently the gene insert has been codon optimized for efficient translation in the species to 
be vaccinated 
The Vaccine Research Center VRC is developing several vaccine candidates for human diseases based on a DNA 
vaccine platform These various candidate vaccines are intended for use in prevention of diseases from emergent viruses 
such as the HIVAIDS severe acute respiratory syndrome SARS virus or West Nile virus WNV as well as for 
counterterrorism measures such as vaccines against Ebola virus An immune response is generated by the in vivo 
expression of the viral proteins after inoculation with the plasmid vaccine candidates encoding them In addition one 
plasmid described herein expresses a cytokine adjuvant Therefore the authors have performed numerous similar 



 

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