Directing the Immune Response to Carbohydrate Antigens

Abstract

Peptide mimetics may substitute for carbohydrate antigens in vaccine design applications. At present, the structural and immunological aspects of antigenic mimicry, which translate into immunologic mimicry, as well as the functional correlates of each, are unknown. In contrast to screening peptide display libraries, we demonstrate the feasibility of a structure-assisted vaccine design approach to identify functional mimeotopes. By using concanavalin A (ConA), as a recognition template, peptide mimetics reactive with ConA were identified. Designed peptides were observed to compete with synthetic carbohydrate probes for ConA binding, as demonstrated by enzyme-linked immunosorbent assay and isothermal titration calorimetry (ITC) analysis. ITC measurements indicate that a multivalent form of one particular mimetic binds to ConA with similar affinity as does trimannoside. Splenocytes from mimeotope-immunized mice display a peptide-specific cellular response, confirming a T-cell-dependent nature for the mimetic. As ConA binds to the Envelope protein of the human immunodeficiency virus, type 1 (HIV-1), we observed that mimeotope-induced serum also binds to HIV-1-infected cells, as assessed by flow cytometry, and could neutralize T-cell line adapted HIV-1 isolates in vitro, albeit at low titers. These studies emphasize that mimicry is based more upon functional rather than structural determinants that regulate mimeotope-induced T-dependent antibody responses to polysaccharide and emphasize that rational approaches can be employed to develop further vaccine candidates.

Antigenic Properties of Peptide Mimotopes of HIV-1-associated Carbohydrate Antigens

“…Here we compare the avidity and affinity of a linear peptide with the sequence YRYRYGRYRSG-SYRYRYGRYRSGS (referred to as peptide 911) and a cyclic form (peptide D002) of the putative RYRY sequence tract having the sequence RGGLCYCRYRYCVCVGR, which forms disulfide bridges between the 1st and 4th and between the 2nd and 3rd cysteine residues. The multivalent peptide 911 and its monomeric form YRYRYGRYRSGS display a free energy of association comparable with those reported for core trimannoside-ConA and pentasaccharide-ConA interactions (15). These results suggest the feasibility of designing mimotopes to render effective humoral responses to HIV Env-associated mannosyl epitopes that would simplify current carbohydrate-based vaccine approaches.…”

“…We have argued that mimicking epitope clustering would be an important general feature in immunogen design (15). As multivalent binding depends on the spacing of binding sites and the recognition of ligands presented in particular orientations, we designed a peptide that contains repeats of the RYRY sequence, YRYRYGRYRSGSYRYRYGRYRSGS (referred to as peptide 911).…”

“…DC-SIGN, however, appears to have evolved its binding specificity in that it is found to bind to mannan, fucose, and all fucosylated lactosamines excluding sLe x and sLe a (14). We have used ConA previously as a template to define a peptide mimotope of Env-associated mannosyl residues (15). We have shown that peptide mimotopes of the neolactoseries (16 -18) and mannose glycans (15,18) can induce serum antibodies in mice that bind to the Env protein, neutralize Lab isolates, and block the adhesion of HIV-1-infected cells to human dendritic cells (DC) (19).…”

“…We have used ConA previously as a template to define a peptide mimotope of Env-associated mannosyl residues (15). We have shown that peptide mimotopes of the neolactoseries (16 -18) and mannose glycans (15,18) can induce serum antibodies in mice that bind to the Env protein, neutralize Lab isolates, and block the adhesion of HIV-1-infected cells to human dendritic cells (DC) (19). Here we compare the avidity and affinity of a linear peptide with the sequence YRYRYGRYRSG-SYRYRYGRYRSGS (referred to as peptide 911) and a cyclic form (peptide D002) of the putative RYRY sequence tract having the sequence RGGLCYCRYRYCVCVGR, which forms disulfide bridges between the 1st and 4th and between the 2nd and 3rd cysteine residues.…”

Mimotope vaccines

“…Very little is understood about the nature and degree of mimicry, and how these translate into the immunological responses observed. To exploit more rational approaches, recent studies have been designed to elucidate this mimicry and to establish objective methods for predicting immunogenicity [18,19]. The development of a peptide vaccine that mimics the immunogenic regions of meningococcal lipo-oligosaccharide (LOS) has included the determination of binding af®nities of peptide mimics to the antibody used for their identi®cation by real time kinetic measurements on a resonant mirror biosensor [11,18] and competition assays to determine the effectiveness of these mimics to compete with the nominal carbohydrate antibody in binding to the antibody.…”