Stimulation of protective immune responses against intracellular pathogens is difficult to achieve using non-replicating vaccines. BALB/c mice immunized by intramuscular injection with killed Francisella tularensis (live vaccine strain) adjuvanted with preformed immune stimulating complexes admixed with CpG, were protected when systemically challenged with a highly virulent strain of F. tularensis (Schu S4). Serum from immunized mice was used to probe a whole proteome microarray in order to identify immunodominant antigens. Eleven out of the top 12 immunodominant antigens have been previously described as immunoreactive in F. tularensis. However, 31 previously unreported immunoreactive antigens were revealed using this approach. Twenty four (50%) of the ORFs on the immunodominant hit list belonged to the category of surface or membrane associated proteins compared to only 22% of the entire proteome. There were eight hypothetical protein hits and eight hits from proteins associated with different aspects of metabolism. The chip also allowed us to readily determine the IgG subclass bias, towards individual or multiple antigens, in protected and unprotected animals. These data give insight into the protective immune response and have potentially important implications for the rational design of non-living vaccines for tularemia and other intracellular pathogens.

Genetic relationships among flaviviruses within the yellow fever (YF) virus genetic group were investigated by comparing nucleotide sequences of the 3 noncoding region (3NCR). Size heterogeneity was observed between members and even among strains of the same viral species. Size variation between YF strains was due to duplications and/or deletions of repeated nucleotide sequence elements (RYF). West African genotypes had three copies of the RYF (RYF1, RYF2, and RYF3); the Angola and the East and Central African genotypes had two copies (RYF1 and RYF3); and South American genotypes had only a single copy (RYF3). Nucleotide sequence analyses suggest a deletion within the 3NCR of South American genotypes, including RYF1 and RYF2. Based on studies with the French neurotropic vaccine strain, passage of a YF virus strain in cell culture can result in deletion of RYF1 and RYF2. Taken together, these observations suggest that South American genotypes of YF virus evolved from West African genotypes and that the South American genotypes lost RYF1 and RYF2, possibly in a single event. Repeated sequence elements were found within the 3NCR of other members of the YF virus genetic group, suggesting that it is probably characteristic for members of the YF virus genetic group. A core sequence of 15 nucleotides, containing two stem-loops, was found within the 3NCR of all members of the YF genetic group and may represent the progenitor repeat sequence. Secondary structure predictions of the 3NCR showed very similar structures for viruses that were closely related phylogenetically.

Burkholderia pseudomallei is the etiological agent of melioidosis, a serious human disease for which no vaccine is available. Immunization of susceptible BALB/c mice with the live attenuated mutant B. pseudomallei ilvI (referred to as "2D2") generated significant, although incomplete, immunity. Splenic B. pseudomallei-specific T cells, detected in immunized mice, proliferated and produced interferon-gamma in vitro in response to dead bacteria. Assessment of T cell antigen specificity indicated that subpopulations of B. pseudomallei-reactive T cells were responsive to BopE, a type III secretion system (TTSS) effector protein, and to a lesser extent to BipD, a TTSS translocator protein. Increased survival of severe combined immunodeficient mice adoptively transferred with T cells from immunized mice, compared with that of naive T cell recipients, demonstrated that immunization with 2D2 generated T cell-mediated immunity. CD4+ and CD8+ cell depletion studies demonstrated that CD4+ cells, but not CD8+ cells, mediated this protection in vivo. Thus, CD4+ T cells can mediate vaccine-induced immunity to experimental melioidosis.

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