The
severity and longevity of the current Ebola outbreak highlight
the need for a fast-acting yet long-lasting vaccine for at-risk populations
(medical personnel and rural villagers) where repeated prime-boost
regimens are not feasible. While recombinant adenovirus (rAd)-based
vaccines have conferred full protection against multiple strains of
Ebola after a single immunization, their efficacy is impaired by pre-existing
immunity (PEI) to adenovirus. To address this important issue, a panel
of formulations was evaluated by an in vitro assay
for their ability to protect rAd from neutralization. An amphiphilic
polymer (F16, FW ∼39,000) significantly improved transgene
expression in the presence of anti-Ad neutralizing antibodies (NAB)
at concentrations of 5 times the 50% neutralizing dose (ND50). In vivo performance of rAd in F16 was compared
with unformulated virus, virus modified with poly(ethylene) glycol
(PEG), and virus incorporated into poly(lactic-co-glycolic) acid (PLGA) polymeric beads. Histochemical analysis of
lung tissue revealed that F16 promoted strong levels of transgene
expression in naive mice and those that were exposed to adenovirus
in the nasal cavity 28 days prior to immunization. Multiparameter
flow cytometry revealed that F16 induced significantly more polyfunctional
antigen-specific CD8+ T cells simultaneously producing
IFN-γ, IL-2, and TNF-α than other test formulations. These
effects were not compromised by PEI. Data from formulations that provided
partial protection from challenge consistently identified specific
immunological requirements necessary for protection. This approach
may be useful for development of formulations for other vaccine platforms
that also employ ubiquitous pathogens as carriers like the influenza
virus.