Evaluation of unmarked deletion mutants as improved Brucella vaccine strains in the mouse and goat models

摘要

Historical data suggests that prolonged survival of Brucella vaccine organisms inthe target host enhances immune protection. Recent research has focused upon thedevelopment of rough vaccine strains to avoid interference with standard diagnostictests. Rough organisms are rapidly cleared from the host, however. In an effort todevelop improved vaccine strains, we have screened signature tagged mutagenesis banksto identify mutants with varying survival characteristics. We hypothesize that in orderfor a vaccine to be efficacious, it must survive in the host. In order to test this, weconstructed marked and unmarked deletion mutants of B. abortus and B. melitensis ingenes previously demonstrated by transposon mutagenesis to attenuate in vivo and invitro virulence. Survival and efficacy of these novel deletion mutants were thenevaluated in the mouse model. The asp24 mutants, which persist for extended periods invivo, appear superior as a vaccine candidate compared to approved vaccine strains S19and Rev1 in the mouse model against either homologous or heterologous challenges.Once enhanced protection against infection was demonstrated in the mouse, componentsof immune function that appeared to be most important were identified to correlate theimmune response with the observed protection. We demonstrated that the most persistent mutant, delta-asp24, affords the greatest protection in mice against virulentchallenge. In order to evaluate safety of the novel vaccine strains as well as protectionagainst infection and abortion, we tested selected B. melitensis unmarked deletionmutants in a natural host, the goat. The delta-asp24 mutant was shown to be safe in pregnantgoats while providing significant protection against infection and abortion.