PLGA-dendron nanoparticles enhance immunogenicity but not lethal antibody production of a DNA vaccine against anthrax in mice

Dendriplexes, complexes of dendrons and condensed plasmids containing the gene for protective antigen (PA) of Bacillus anthracis, were encapsulated in poly-lactide-co-glycolide (PLGA) particles using the double emulsion method. The two dendrons employed are a dendron with three C18 chains (C18 dendron) and one with no attached hydrocarbon chains (the C0 dendron). Three types of particles were examined, namely PLGA-C18 dendriplexes, PLGA-C0 dendriplexes and the control PLGA-naked DNA system. These were characterised by standard biophysical methods such as photon correlation spectroscopy (PCS) and scanning electron microscopy to select the complexes for in vivo testing. Three intramuscular immunizations were carried out using 14 μg of DNA per dose at weekly intervals in BALB/c mice. Antibodies against rPA were measured using ELISA. Results indicate that the PLGA-C18 dendriplex particles produced superior levels of anti-PA IgG antibodies in comparison to animals immunized with the PLGA-C0 dendriplex particles. The level of antibody production was dependent on the number of immunizations, higher antibody levels being measured after two booster vaccinations. However toxin neutralizing antibodies were absent in all treatment groups, and it is likely that the mice lack protection against lethal toxin and anthrax infection. Further studies are needed to optimize the formulation of DNA vaccines and increase the level of anti-lethal toxin antibodies and enhance their functionality.