Biodistribution, persistence and lack of integration of a multigene HIV vaccine delivered by needle-free intradermal injection and electroporation

Abstract

It is likely that gene-based vaccines will enter the human vaccine area soon. A few veterinary vaccines employing this concept have already been licensed, and a multitude of clinical trials against infectious diseases or different forms of cancer are ongoing. Highly important when developing novel vaccines are the safety aspects and also new adjuvants and delivery techniques needs to be carefully investigated so that they meet all short- and long-term safety requirements. One novel in vivo delivery method for plasmid vaccines is electroporation, which is the application of short pulses of electric current immediately after, and at the site of, an injection of a genetic vaccine. This method has been shown to significantly augment the transfection efficacy and the subsequent vaccine-specific immune responses. However, the dramatic increase in delivery efficacy offered by electroporation has raised concerns of potential increase in the risk of integration of plasmid DNA into the host genome. Here, we demonstrate the safety and lack of integration after immunization with a high dose of a multigene HIV-1 vaccine delivered intradermally using the needle free device Biojector 2000 together with electroporation using Derma Vax™ DNA Vaccine Skin Delivery System. We demonstrate that plasmids persist in the skin at the site of injection for at least four months after immunization. However, no association between plasmid DNA and genomic DNA could be detected as analyzed by qPCR following field inversion gel electrophoresis separating heavy and light DNA fractions. We will shortly initiate a phase I clinical trial in which healthy volunteers will be immunized with this multiplasmid HIV-1 vaccine using a combination of the delivery methods jet-injection and intradermal electroporation.

Fig. 1

Schematic overview of the antigen encoded by the seven different plasmids. V: variable loop; A, B, C – indicates that the protein, or indicated part of the protein, derives from HIV-1 of subtype A, B, or C, respectively.

Fig. 2

Presence of plasmid in skin at the injection site and underlying muscle. DNA was extracted and subjected to qPCR-analysis detecting the plasmid backbone. Results are shown as number of copies of plasmid/μg of extracted DNA at the indicated time points after immunization. Exact plasmid copy number for each time-point can be found in Table 2.

Fig. 3

ELISpot analysis of IFN-γ secretion by splenocytes from mice immunized with the 7 plasmid vaccine and stimulated with peptides from HIV-1 Gag or Env, respectively. The animals were sacrificed 2 weeks after the fourth immunization. Error bars show standard deviation. M: male, F: female, C: saline injected animals (both female and male mice).