Alternative strategies to the design of microbial vaccines are needed that take advantage of antigenic determinants that serve as good targets for an immune response, but are not themselves effective immunogens. For example, oligosaccharide (OS) determinants isolated intact from bacterial lipopolysaccharides (or lipooligosaccharides [LOSs]) are poor immunogens, usually resulting only in T-cell independent responses. We have approached the design of a potential vaccine candidate against Neisseria gonorrhoeae by """"""""converting"""""""" an OS epitope derived from gonococcal LOS into mimics: (i) an anti-idiotope antibody and (ii) short peptides, each mimicking the oligosaccharide [OS] epitope. This epitope, called 2C7, was defined by its reactivity with a monoclonal antibody (mAb), also named 2C7. 95% of gonococcal strains display the LOS-derived 2C7 epitope in their LOS, in vivo, in infected patients. In addition to 2C7 epitope, we plan to convert a second commonly expressed OS epitope, called 2-1-L8, to a peptide mimic(s). Humans develop antibodies against both of these epitopes after natural infection. Antibodies directed against the 2C7 and 2-1- L80S epitopes both show strong complement dependent bactericidal function. To enhance specific immune responses, using 2C7 and 2-1-L8 as representative vaccine candidates, and also to characterize the parameters necessary to construct successful peptide mimics of saccharide antigens, we propose to make peptide/adjuvant constructs, test their ability to stimulate effective immune responses directed against the nominal (OS) epitope, and characterize and optimize antigen presentation and T-cell signaling by these constructs.
In specific aim 1, we will conjugate peptide mimics of N. gonorrhoeae oligosaccharide (2C7 and 2-1-L8) to known adjuvants that will include: complement component C3d and alpha-2 macroglobulin, mannose and proteosomes, the latter comprised of gonococal porin (Por) proteins.
In specific aim 2, we will immunize mice intraperitoneally and intranasal with these peptide/adjuvant complex preparation and test immunogenicity by measuring IgM, IgG and IgA responses, against the nominal OS epitopes, elicited in serum and vaginal washes. We will also examine functional immune responses in vitro by bactericidal assay and protection in vivo, by assessing the prevention or shortening of gonococcal colonization in estradiol-treated mice.
In specific aim 3, we will study the role of different antigen presenting cells (APCs) and the T-cell signals that they produce in the immunopotentiation of adjuvants on the immune response to peptide mimics. These studies will serve to characterize the parameters required to drive the immune response of peptides, used as OS mimics, to a specific response against the nominal epitope and also define methods necessary both to produce a T cell mediated antibody response and to define the resulting characteristics against peptides used as saccharide mimics.
| Gulati, Sunita; Zheng, Bo; Reed, George W et al. (2013) Immunization against a saccharide epitope accelerates clearance of experimental gonococcal infection. PLoS Pathog 9:e1003559 |
| Ngampasutadol, Jutamas; Rice, Peter A; Walsh, Mary T et al. (2006) Characterization of a peptide vaccine candidate mimicking an oligosaccharide epitope of Neisseria gonorrhoeae and resultant immune responses and function. Vaccine 24:157-70 |
