Current situation and future prospects of Echinococcus granulosus vaccine candidates: A systematic review

Cystic echinococcosis is a worldwide zoonotic disease, represents a threat for livestock and humans, manifests as a quiescent, subclinical and chronic hydatid cyst infection. The disease imposes high expenditures and economic losses in medical and veterinary. Prophylactic vaccination would be one of the effective preventive health care against echinococcosis. During the last decades, many studies have characterized the protective antigens of Echinococcus granulosus and their role in immunization of various animal host species. Herein, we aimed to systematically evaluate and represent the best antigens as possible vaccine candidates for cystic echinococcosis. Data were systematically searched from five databases including ProQuest, PubMed, Scopus, ScienceDirect and Web of Science, up to 1 February 2020. Two reviewers independently screened and assessed data extraction and quality assessment. A total of 47 articles were eligible for inclusion criteria in the current study. The most common antigens used for vaccination against E. granulosus were EG95 and antigen B. Freund's adjuvant and Quil A have been predominantly utilized. In addition, regarding the antigen delivery, animal models, measurement of immune responses and reduction in hydatid cyst have been discussed in the text. The data demonstrated that DNA vaccines with antigen B and recombinant protein vaccines based on EG95 antigen have the best results and elicited protective immune responses.

Construction and identification of the recombinant plasmid pET30a-EgA31-Eg95 of Echinococcus granulosus

To clone the Eg95 and EgA31 antigen genes into the prokaryotic expression plasmid pET30a-EgA31-Eg95, we expressed the recombinant protein EgA31-Eg95 and confirmed with western blot analysis. The total RNA was extracted from the protoscoleces of Echinococcus granulosus (E. granulosus) adult worms. The complementary DNA (cDNA) encoding the EgA31 antigen was amplified via quantitative real-time polymerase chain reaction (qPCR). The recombinant plasmid pET30a-EgA31 was used as a carrier and was connected with the Eg95 vector. The recombinant plasmid pET30a-EgA31-Eg95 was constructed and the fusion protein EgA31-Eg95 was detected using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The positive clone was the empty recombinant vector. The recombinant protein pET30a-EgA31-Eg95 was ~46 kDa, and the expressed product accounted for approximately 20% of the total soluble proteins. We successfully constructed the recombinant plasmid pET30a-EgA31-Eg95 and expressed the recombinant protein EgA31-Eg95. The results may be the foundation of research on its immunogenicity in the future.