We propose to conduct a Phase 1 trial of two live oral S. Paratyphi A vaccine candidates that are attenuated by a deletion in guaBA and in either clpX or clpP.
We have shown previously that introducing a deletion in the guaBA locus (which encodes two enzymes employed in the distal de novo purine biosynthesis pathway) is a promising strategy for attenuating pathogenic S.Typhi [Wang I&I 2001]. Creation of a deletion in either component of the clpXP complex has the potential to provide a second, independent attenuating mutation (to minimize the risk of reversion to a wild type genotype) as well as to enhance immunoprotective responses by inducing hyper-expression of the flagellar protein [Tomoyasu J Bact 2002]. ClpXP functions as an ATP-dependent protease that represses transcription of flagellar protein by intracellular Salmonella that have migrated from the Peyer’s Patches to mesenteric lymph nodes and systemic sites [Cummings Molec Micro 2006]. Rendering flagellar expression below the T cell activation threshold allows the organism to elude immune recognition and survive in intracellular extra-intestinal foci. Indeed, Salmonella deleted in clpP (encoding a protease that targets flagellin regulatory protein), clpX (encoding an ATPase which confers substrate specificity), or clpXP are attenuated in their ability to produce systemic infection [Yamamoto I&I 2001] [Matsui I&I 2003]. Nonetheless, the resultant clpXP mutants remain capable of protecting mice against wild type challenge [Matsui I&I 2003], presumably in part due to their ability to hyper-express flagellar protein, an immunoprotective antigen [Strindelius 2004] and a potent stimulant of a broad range of immune responses in mice and humans, both innate [Gewirtz 2001] and adaptive humoral [Sbrogio-Almeida 2001] and cell-mediated responses [Cookson 1997, Sztein 1994].
Myron Levine, Karen Kotloff