Formulation and immunogenicity of a potential multivalent type III secretion system-based protein vaccine

The virulence of many pathogenic Gram-negative bacteria is dependent upon their type III secretion (TTS) systems. Here, we discuss initial formulation studies of five TTS needle tip proteins IpaD (Shigella flexneri), BipD (Burkholderia pseudomallei), SipD (Salmonella spp.), LcrV (Yersinia spp.), and PcrV (Pseudomonas aeruginosa) as targets for subunit vaccines. Excipient screening and subsequent assays lead to the selection of 10% sucrose and 5% dextrose as an optimal stabilizer combination for all five proteins. All of the proteins adsorb to aluminum hydroxide adjuvant, although the mechanisms of adsorption may vary. The proteins are physically stable when adsorbed to the adjuvant for at least 3 months at room temperature and chemical stability is enhanced in the presence of excipients. The ability of the IpaD and SipD proteins to elicit strong humoral immune responses was also tested in a murine model in the presence and absence of their needle counterparts MxiH and PrgI (see previous paper in this issue). Both proteins produce high antibody titers regardless of dose. While the IpaD titer is boosted slightly in the presence of its needle protein, MxiH, SipD titers appear to be reduced when administered in the presence of its needle counterpart, PrgI.