DNA Vaccination by Electroporation and Boosting with Recombinant Proteins Enhances the Efficacy of DNA Vaccines for Schistosomiasis Japonica

Schistosomiasis japonica is an endemic, zoonotic disease of major public health importance in China. Control programs combining chemotherapy and snail killing have not been able to block transmission of infection in lakes and marsh regions. Vaccination is needed as a complementary approach to the ongoing control programs. In the present study, we wanted to determine if the efficacies of DNA vaccines encoding the 23-kDa tetraspanin membrane protein (SjC23), triose phosphate isomerase (SjCTPI), and sixfold-repeated genes of the complementarity determining region 3 (CDR3) in the H chain of NP30 could be enhanced by boosting via electroporation in vivo and/or with cocktail protein vaccines. Mice vaccinated with cocktail DNA vaccines showed a significant worm reduction of 32.88% (P < 0.01) and egg reduction of 36.20% (P < 0.01). Vaccine efficacy was enhanced when animals were boosted with cocktail protein vaccines; adult worm and liver egg burdens were reduced 45.35% and 48.54%, respectively. Nearly identical results were obtained in mice boosted by electroporation in vivo, with adult worm and egg burdens reduced by 45.00% and 50.88%, respectively. The addition of a protein vaccine boost to this regimen further elevated efficacy to approximately 60% for adult worm burden and greater than 60% for liver egg reduction. The levels of interleukin-2, gamma interferon, and the ratios of immunoglobulin G2a (IgG2a)/IgG1 clearly showed that cocktail DNA vaccines induced CD4(+) Th1-type responses. Boosting via either electroporation or with recombinant proteins significantly increased associated immune responses over those seen in mice vaccinated solely with DNA vaccines. Thus, schistosome DNA vaccine efficacy was significantly enhanced via boosting by electroporation in vivo and/or cocktail protein vaccines.