Importance of a Prime–Boost DNA/Protein Vaccination to Protect Chickens Against Low-Pathogenic H7 Avian Influenza Infection

Abstract

Control of H5/H7 low-pathogenic avian influenza (LPAI) virus circulation is a major issue regarding animal and public health consequences. To improve vaccines and to prevent vaccinated poultry from becoming infected and from shedding wild viruses, we initiated studies targeting prevention of H7 infection through DNA vaccines encoding H7 and M1 viral proteins from an Italian H7N1 LPAI virus isolated from poultry in 1999. More recently, we expressed recombinant H7 and M1 proteins in the baculovirus system to assess whether they might enhance immunity when given as a boost after DNA vaccination. The protection afforded by three vaccine combinations-DNA/DNA, DNA/protein, protein/protein-given 3 wk apart were experimentally compared in 20 specific-pathogen-free chickens per group. Ten days after the boost, chickens were challenged with a homologous (Italian H7N1 LPAI) or heterologous (French H7N1 LPAI isolated from mallards in 2001) virus. Tracheal and cloacal shedding was measured by a matrix gene (M)-based real-time reverse transcription polymerase chain reaction assay and compared with that displayed by unvaccinated infected controls. After the homologous challenge, chickens of every vaccinated group displayed a significant decrease in cloacal shedding, whereas tracheal shedding was not significantly reduced in the protein/protein group. After the heterologous challenge, only the DNA/DNA group showed a nonsignificant decrease in tracheal shedding. According to these two trials, prime-boost DNA/protein vaccination appeared be more advantageous. Further development could be aimed at improving protein expression, shifting subtype (H5), and assessing the interest of proteins as a boost of recombinant vaccines.

Development of avian influenza virus H5 DNA vaccine and MDP-1 gene of Mycobacterium bovisas genetic adjuvant

“…Agarose gel electrophoresis following RT-PCR showed successful expression of H5 mRNA for groups immunized with H5 and H5 + MDP1 vaccines (Figure 2). This finding is consistent with the results of previous studies suggesting the successful delivery and presentation of the target gene to the immune system [14,23-25]. The extracted RNA was analyzed with PCR amplification only in which no band of the expected size was detected (data not shown), indicating that the amplified product from the RT-PCR experiments were from in vivo transcription of the target genes.…”

“…This result was consistent with a study performed by Le Gall-Recule' and co-workers (2002), who found that AIV H7 cloned into an eukaryotic expression plasmid, pCMV could lead to antibody response, using different administration methods [23]. However, in another study, direct intramuscular immunization using naked plasmid did not produce the same HI titer in all the treatment, probably due to the inaccurate gene delivery system [25].…”

Prime-Boost Immunization Using a DNA Vaccine Delivered by Attenuated Salmonella enterica Serovar Typhimurium and a Killed Vaccine Completely Protects Chickens from H5N1 Highly Pathogenic Avian Influenza Virus

“…Similarly, the authors (31) and others (32) have shown that Salmonella or Shigella HA DNA vaccination induced low levels of HI antibodies, an observation in agreement with this study. But when a killed vaccine boost was used, we found that a significant rise in HI antibody titers occurred among the Salmonella DNA vaccine-primed chickens, as this was also seen in previous studies (20,21,27). These results indicated that a strong B-cell memory response was generated after Salmonella HA DNA vaccination.…”

Vaccination with recombinant 4×M2e.HSP70c fusion protein as a universal vaccine candidate enhances both humoral and cell-mediated immune responses and decreases viral shedding against experimental challenge of H9N2 influenza in chickens

“…These time points represent the peak in oropharyngeal and cloacal shedding, respectively (Spackman et al, 2010;Le Gall-Reculé et al, 2007).…”