A zebrafish model to develop DNA-based vaccines - identification of cdh as a protective antigen against mycobacterial disease

Abstract Mycobacterium tuberculosis, the causative agent of human tuberculosis, is an intracellular pathogen killing nearly two million people annually. The current live vaccine is controversial and thus novel preventive approaches are needed. DNA vaccines represent an alternative for immunizing against tuberculosis. As a vertebrate model organism with a fully developed immune system, zebrafish (Danio rerio) presents itself as an attractive and ethical option for screening novel vaccine antigens. Here we show that antigens can be expressed in the adult zebrafish as DNA-based vaccines. Furthermore, introduction of DNA plasmids expressing a combination of three previously characterized mycobacterial antigens (Ag85B, ESAT-6, CFP-10) was protective against M. marinum challenge in adult zebrafish. Using a low-dose intra peritoneal infection with 19-28 bacteria, both the number of granulomas and the amount of affected organs were reduced. Likewise, using a lethal infection dose of 20,000 cfu, vaccination significantly reduced both mortality and bacterial counts. In addition, a putative diacylglycerol pyrophosphatase cdh was protective against lethal M. marinum infection with 25, 000 cfu decreasing mortality by more than 50% compared to controls. In summary, DNA-based vaccination protects adult zebrafish against experimental Mycobacterium marinum infection and cdh is a promising novel protective antigen in this model.