Whereas reverse vaccinology approaches have yielded
promising results in terms of identifying vaccine targets
against bacterial pathogens, so far this approach has had
limited success for more complex eukaryotic organisms.
Among the reasons why anthelmintic vaccines have not
benefited from reverse vaccinology approaches include
the large genome of parasitic helminths and difficulties
in shaping moderate to high throughput approaches for
protein expression and preclinical testing in laboratory
animal models. To address the first component, we have
narrowed our antigen selection program for the human
hookworm vaccine to the parasite’s gut transcriptome.
The hookworm intestine expresses a wide range of proteins
or enzymes involved in blood-feeding and homeostasis
between the parasite and its host. The functional
antigens expressed in the hookworm gut have become
major targets for vaccine and drug development. In order
to discover additional hookworm vaccine antigens, the A.
ceylanicum intestinal transcriptome was generated and
analyzed. Ancylostoma ceylanicum was selected because
of its relative convenience for vaccine testing in a hamster
laboratory animal model. Analysis of the full transcriptome
of the adult male A. ceylanicum intestine reveals that
two categories of proteins were highly expressed in the
hookworm intestine, namely proteolytic enzymes involved
in blood digestion and transporter proteins involved in
the absorption of nutrient metabolites and the maintenance
of homeostasis between the parasite and its environment.
Glutathione S-transferases involved in the binding
and detoxification of oxidative heme derived from bloodfeeding
were also highly expressed in the intestine. In
addition, other proteins including a family of cysteinerich/
antigen 5/pathogenesis-related proteins (CAP);
C-type lectins; and heat shock proteins all also upregulated
in the hookworm intestine and possibly contribute
to the survival of worm in the host. Thus at least two classes
of potential hookworm antigens are related to adult
blood-feeding, whereas the function of the CAP proteins,
C-type lectins, and heat shock proteins in the hostparasite
relationship are still under investigation. More
hookworm-specific intestinal proteins involved in bloodfeeding
may further be identified by comparing other
available intestinal transcriptomes of nematodes such as
Ascaris suum (non-blood-feeding) [74], Trichuris suis
(tissue-feeding) and Haemonchus contortus (bloodfeeding)
[75]. In subsequent studies, the vaccine candidates
identified here will be ranked for downstream antigen
target selection based on criteria including abundance,
possible functions related to survival, uniqueness in the
parasite versus the vertebrate host, and ultimately solubility
and yield of expression.