Induction of high levels of resistance to schistosome infection in buffalo vaccinated with a prime/boost regimen using a new delivery method. (166.14)

Abstract

Abstract Schistosomiasis japonicum remains a serious zoonotoc disease of man and livestock, with water buffaloes accounting for about 75% of schistosome transmission to humans in China. A mathematical model of schistosome transmission suggests that a vaccine that induces 40% efficacy against infection, would significantly reduce transmission to humans. We tested the ability of SjC23, using four different vaccine delivery regimens, to induce the desired levels of efficacy in water buffalo. Comparing GLP-grade plasmid DNA Sj23-Hsp70 to our in-house produced DNA vaccine, we observed no differences in efficacy. Increasing the time between boosts from 1 to 3 months actually resulted in lower levels of efficacy, 37.2% and 31.5% compared with 41.2% and 45.8% adult worm burden and liver egg burdens respectively. Co-administration of an IL-12 plasmid DNA significantly enhanced SjC23 plasmid DNA vaccine efficacy. We then tested priming with SjC23 and SjCTPI plasmid DNAs, followed by a boost with recombinant SjC23 and rec SjCTPI, using our new vaccine delivery method. The prime/boost, new delivery method strategy yielded the highest levels of efficacy seen to date; 55% reduction in adult worms and 57% reduction in fecal egg hatching rates compared to levels in control vaccinated buffalo. Serological and immunological analyses are under way. We believe we can further enhance vaccine efficacy by priming with plasmid DNA vaccines delivered by electroporation.