TITLE:
Comparison of Five Expression Vectors for the Ha Gene in Constructing a DNA Vaccine for H6N2 Influenza Virus in Chickens
AUTHORS:
Songhua Shan, Trevor Ellis, John Edwards, Stan Fenwick, Ian Robertson
KEYWORDS:
DNA Vaccine, Multiple Expressing Vectors, H6N2 Avian Influenza a Virus, Chickens
JOURNAL NAME:
Advances in Microbiology,
Vol.6 No.4,
April
20,
2016
ABSTRACT: A number of eukaryotic expression vectors have been developed for use as DNA vaccines. They
showed varying abilities to initiate immune responses; however, there is little data to indicate
which of these vectors will be the most useful and practical for DNA vaccines in different species.
This report examines the use of five expression vectors with different promoters and Kozak sequence
to express the same hemagglutinin (HA) protein of an H6N2 avian influenza virus for DNA
vaccination in chickens. Although intramuscular vaccination with seven DNA constructs elicited
no or limited measurable H6 HA antibody responses in Hy-Line chickens, variable reduction in virus
shedding for either oropharyngeal or cloacal swabs post-virus challenge were observed. This
indicated that all DNA constructs generated some levels of protective immunity against homologous
virus challenge. Interestingly, lower dose (50 or 100 μg) of plasmid DNAs consistently induced
better immune response than higher dose (300 or 500 μg). In the transfection experiments there
appeared to be a hierarchy in the in vitro expression efficiency in the order of pCAG-optiHAk/
pCAG-HAk > pCI-HAk > VR-HA > pCI-HA > pCI-neo-HA > pVAX-HA. Since the level of in vitro expression
correlates with the level of immune response in vivo, in vitro expression levels of the DNA
constructs can be used as an indicator for pre-selection of plasmid vaccines prior to in vivo assessment.
Moreover, our results suggested that the Kozak sequence could be used as an effective
tool for DNA vaccine design.