Immunogenicity and Efficacy ofCryptococcus neoformansCapsular Polysaccharide Glucuronoxylomannan Peptide Mimotope-Protein Conjugates in Human Immunoglobulin Transgenic Mice

Abstract

Peptide mimotopes of capsular polysaccharides have been proposed as antigens for vaccines against encapsulated pathogens. In this study, we determined the antibody response to and efficacy of P13, a peptide mimetic of the Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM), in mice that produce human antibodies. P13 was conjugated to tetanus toxoid (TT) or diphtheria toxoid (DT) and administered subcutaneously in Alhydrogel with or without CpG to mice transgenic for human immunoglobulin loci (XenoMouse mice) and expressing either immunoglobulin G2 (IgG2) (G2 mice) or IgG4 (G4 mice). Mice were vaccinated and revaccinated two or three times. The serum antibody responses of the mice to GXM and P13 and antibody idiotype expression were analyzed by an enzyme-linked immunosorbent assay. The results showed that both P13-TT and P13-DT were antigenic, inducing a mimetic response to P13 in both G2 and G4 mice, and immunogenic, inducing a mimotope response including V H 3 (idiotype)-positive antibodies to GXM in G2 but not G4 mice. CpG led to higher titers of IgG to P13 and GXM in P13-TT-vaccinated G2 mice. C. neoformans challenge of P13-protein conjugate-vaccinated and control G2 mice induced anamnestic IgG-and V H 3-positive responses to GXM and was associated with a significantly decreased risk of death and a prolongation of survival in P13-DT-vaccinated mice compared to phosphate-buffered saline-treated or protein carrier-vaccinated mice. These findings reveal that P13 elicited a human antibody response with V H 3 expression in human immunoglobulin transgenic mice that has been observed for human antibodies to GXM and support the concept that peptide mimotope-based vaccines may hold promise for the treatment of C. neoformans infections.

A Peptide Mimotope of Type 8 Pneumococcal Capsular Polysaccharide Induces a Protective Immune Response in Mice

“…Our data showing that PUB1 inhibited the type 8 PS binding of human IgAs, but not other isotypes, suggest that PUB1 could be a surrogate for an epitope that elicits naturally occurring type 8 PS-reactive IgA. In view of evidence that isotype influences polysaccharide and peptide specificity (30,32,35), our data suggest that the specificity of type 8 PS-specific IgA could differ from that of IgM or IgG. Alternatively, our findings could reflect differences in affinity or avidity or unique characteristics of the primary or secondary reagents that were used.…”

“…be sufficient to predict the ability of certain mimetics to be successful immunogens against the antigen of interest (5,48). Similar to a cryptococcal capsular polysaccharide epitope mimotope selected by a human IgM (53) that induced a protective antibody response (16,29,30), PUB1 was selected by a human IgA, an antibody isotype that could be more representative of an innate or primary antibody response. The IgMselected GXM mimotope was recognized by naturally occurring antibodies (16,53).…”

A peptide inhibitor of HIV‐1 neutralizing antibody 2G12 is not a structural mimic of the natural carbohydrate epitope on gp120

“…For a peptide to succeed as an immunogen that can generate a specific anticarbohydrate antibody response, carbohydratepeptide cross-reactivity must translate into immunogenic mimicry (i.e., the ability of a crossreactive peptide to elicit that same antibody, or functionally similar ones). Immunogenic mimicry of carbohydrate epitopes by peptides has been previously reported (22)(23)(24)(25)(26)(49)(50)(51), which suggests that cross-reacting peptides may elicit antibodies functionally equivalent to those elicited by carbohydrate epitopes. In contrast, our preliminary immunization of rabbits with recombinant 2G12.1 phage produced a significant antipeptide response but no crossreactivity with gp120, indicating that 2G12.1 elicits an antibody response that is qualitatively different from 2G12 (see Supplemental Table 3 and Supplemental Fig.…”

Filamentous phage as an immunogenic carrier to elicit focused antibody responses against a synthetic peptide

“…To do this, vaccine-lead peptides are chemically-conjugated to strongly-immunogenic "carrier" proteins that provide T-cell epitopes (TCEs). These typically include: ovalbumin (OVA) [17][18][19], tetanus toxoid (TT, which is FDA-approved) [2,12,20], BSA [3,18,21], and keyhole limpet hemocyanin (KLH) [5,6,18]. However, these types of carrier protein themselves elicit strong Ab responses such that immundominant BCEs on the carrier may undermine the Ab response against the synthetic peptide, especially if that peptide is less immunogenic than carrier BCEs.…”