DNA vaccines are gaining popularity due to their inexpensive production and good stability even at room temperature. While it was possible to overcome the initially unsatisfyingly low antigen-specific antibody response in larger animals and humans by use of electroporation, which greatly increases the cellular uptake of the DNA, this method is comparatively laborious and painful for the vaccinee. Novel delivery methods are thus necessary. Being the DNA delivery specialists that viruses are, pseudoviruses (PsVs), which package the vaccine-plasmid inside their capsid, can mediate the delivery of the vaccine and ensure the efficient shuttling of the DNA vaccine into the cells. Different animal papilloma viruses were detected and analyzed for their ability to form PsV particles, package DNA in form of a reporter plasmid and transduce cells in vitro. While most of the tested non-human papilloma viruses bearly showed a transfer of DNA in vitro, two candidates – papillomaviruses that normally infect the puma (PcPV1) and the macaque (MfPV11) – transduced especially effectively. PcPV1 and MfPV11 PsVs were therefore studied further in in-vivo experiments. Both candidates mediated the transduction of a luciferase reporter plasmid after intramuscular application in mice, leading to the expression of firefly luciferase. This expression lasted several weeks after injecting PcPV1 PsVs. Further, in a vaccination including intramuscular and intranasal application, it was tested whether the papilloma PsV mediated the delivery of a DNA vaccine against the respiratory syncytial virus (RSV) in mice. Finally, the mice were infected with infectious RSV and the viral load was quantified. The application of PcPV1 and MfPV11 PsVs carrying a plasmid coding for RSV-F led to a significantly reduced viral load in the lungs of the vaccinated mice upon challenge. Human papilloma PsVs have successfully been used for gene delivery in the past, but have limitations due to vector immunity, which would occur in all individuals that have previously been exposed to these viruses. The project results show that non-human papilloma viruses have the potential of being promising gene delivery vectors and present a vaccine platform for intramuscular or mucosal application.
Dr. Thomas Grunwald