DNA vaccinations have been progressively used as a
more attractive vaccine approach because they are capable
of directly transfecting dendritic cells, and can
stimulate both humoral and cellular immunity [7]. However,
the generated specific antibody titres of DNA vaccination
are generally observed to be far less than those
induced by protein vaccination [8]. DNA vaccinations
with Fasciola antigens have shown effectiveness of such
vaccines in evoking immune responses [9-15]. In order
to increase the antibody responses of DNA vaccines encoding
antigen, a number of strategies have been
employed. The most popular strategies applied are
secretory and vaccine cytoplasmic vectors. For example,
secretory and cytoplasmic DNA encoding F. hepatica
glutathione S transferase, fatty acid binding protein and
cathepsin L5 was investigated in mouse trials, and the
encoded antigens evoked higher immune responses in
the secreted form [