Enhanced immune responses and protection by vaccination with respiratory syncytial virus fusion protein formulated with CpG oligodeoxynucleotide and innate defense regulator peptide in polyphosphazene microparticles.

Although respiratory syncytial virus (RSV) is the leading cause of serious respiratory tract disease in children, to date no RSV vaccine is available. To produce an effective subunit vaccine, a truncated secreted version of the F protein (F) was expressed in mammalian cells, purified and shown to form trimers. The F protein was then formulated with a CpG oligodeoxynucleotide (ODN) and an innate defense regulator (IDR) peptide in polyphosphazene microparticles (F-MP). Mice immunized either intramuscularly (IM) or intranasally (IN) with F-MP developed significantly higher levels of virus-neutralizing antibodies in the sera and lungs, as well as higher numbers of IFN-γ secreting cells than mice immunized with the F protein alone. In contrast, the IM delivered F induced high production of IL-5 while the IN delivered F did not elicit a measurable immune response. After RSV challenge, essentially no virus and no evidence of immunopathology were detected in mice immunized with F-MP regardless of the route of delivery. While the mice immunized IM with F alone also showed reduced virus replication, they developed enhanced levels of pulmonary IgE, IL-4, IL-5, IL-13 and eotaxin, as well as eosinophilia after challenge. The level of protection induced by the F-MP formulation was equivalent after IM and IN delivery. The efficacy and safety of the F-MP formulation was confirmed in cotton rats, which also developed enhanced immune responses and were fully protected from RSV challenge after vaccination with F-MP. In conclusion, formulation of recombinant F with CpG ODN and IDR peptide in polyphosphazene microparticles should be considered for further evaluation as a safe and effective vaccine against RSV.