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Abstract Respiratory syncytial virus (RSV) G glycoprotein has recently reemerged as a vaccine antigen due to its ability to elicit potent neutralizing antibodies and ameliorate disease in animal models. Here we designed three constructs to display the G central conserved domain (Gcc) focused on inducing broad and potent neutralizing antibodies. One construct displaying Gcc from both RSV subgroups trimerized via a C-terminal foldon (Gcc-Foldon) was highly immunogenic in mice and in MIMIC, a pre-immune human in vitro model. To explore an optimal RSV vaccine, we combined the Gcc-Foldon antigen with a stabilized pre-fusion-F nanoparticle (pre-F-NP) as a bivalent vaccine and detected no antigenic interference between the two antigens in the MIMIC model. In RSV-primed macaques, the bivalent vaccine elicited potent humoral responses. Furthermore, both Gcc-Foldon and the bivalent vaccine conferred effective protection against RSV challenge in mice. This two-component vaccine could potentially provide effective protection against RSV infection in humans and warrants further clinical evaluation.

Efforts to develop a broadly protective vaccine against the highly pathogenic avian influenza A (HPAI) H5N1 virus have focused on highly conserved influenza gene products. The viral nucleoprotein (NP) and ion channel matrix protein (M2) are highly conserved among different strains and various influenza A subtypes. Here, we investigate the relative efficacy of NP and M2 compared to HA in protecting against HPAI H5N1 virus. In mice, previous studies have shown that vaccination with NP and M2 in recombinant DNA and/or adenovirus vectors or with adjuvants confers protection against lethal challenge in the absence of HA. However, we find that the protective efficacy of NP and M2 diminishes as the virulence and dose of the challenge virus are increased. To explore this question in a model relevant to human disease, ferrets were immunized with DNA/rAd5 vaccines encoding NP, M2, HA, NP+M2 or HA+NP+M2. Only HA or HA+NP+M2 vaccination conferred protection against a stringent virus challenge. Therefore, while gene-based vaccination with NP and M2 may provide moderate levels of protection against low challenge doses, it is insufficient to confer protective immunity against high challenge doses of H5N1 in ferrets. These immunogens may require combinatorial vaccination with HA, which confers protection even against very high doses of lethal viral challenge.

Sustained outbreaks of highly pathogenic avian influenza (HPAI) H5N1 in avian species increase the risk of reassortment and adaptation to humans. The ability to contain its spread in chickens would reduce this threat and help maintain the capacity for egg-based vaccine production. While vaccines offer the potential to control avian disease, a major concern of current vaccines is their potency and inability to protect against evolving avian influenza viruses.The ability of DNA vaccines encoding hemagglutinin (HA) proteins from different HPAI H5N1 serotypes was evaluated for its ability to elicit neutralizing antibodies and to protect against homologous and heterologous HPAI H5N1 strain challenge in mice and chickens after DNA immunization by needle and syringe or with a pressure injection device. These vaccines elicited antibodies that neutralized multiple strains of HPAI H5N1 when given in combinations containing up to 10 HAs. The response was dose-dependent, and breadth was determined by the choice of the influenza virus HA in the vaccine. Monovalent and trivalent HA vaccines were tested first in mice and conferred protection against lethal H5N1 A/Vietnam/1203/2004 challenge 68 weeks after vaccination. In chickens, protection was observed against heterologous strains of HPAI H5N1 after vaccination with a trivalent H5 serotype DNA vaccine with doses as low as 5 microg DNA given twice either by intramuscular needle injection or with a needle-free device.DNA vaccines offer a generic approach to influenza virus immunization applicable to multiple animal species. In addition, the ability to substitute plasmids encoding different strains enables rapid adaptation of the vaccine to newly evolving field isolates.