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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.

The metastatic potential of some tumor cells is associated with the expression of the neolactoseries antigens sialyl-Lewis x (sLex) and sialyl-Lewis a (sLea) as they are ligands for selectins. We have recently shown that peptide mimetics of these antigens can potentiate IgG2a antibodies, which are associated with a Th1-type cellular response. As L-selectin is preferentially expressed on CD4+ Th1 and CD8+ T cell populations, specific induction of these phenotypes could augment a response to L-selectin ligand-expressing tumor cells. Here we demonstrate that immunization with a multiple antigen peptide (MAP) mimetic of sugar constituents of neolactoseries antigens induces a MHC-dependent peptide-specific cellular response that triggers IFN-gamma production upon peptide stimulation, correlating with IgG2a induction. Surprisingly, T lymphocytes from peptide-immunized animals were activated in vitro by sLex, also triggering IFN-gamma production in a MHC-dependent manner. Stimulation by peptide or carbohydrate resulted in loss of L-selectin on CD4+ T cells confirming a Th1 phenotype. We also observed an enhancement in cytotoxic T lymphocyte (CTL) activity in vitro against sLex-expressing Meth A cells using effector cells from Meth A-primed/peptide-boosted animals. CTL activity was inhibited by both anti-MHC class I and anti-L-selectin antibodies. These results further support a role for L-selectin in tumor rejection along with the engagement by the TCR for most likely processed tumor-associated glycopeptides, focusing on peptide mimetics as a means to induce carbohydrate reactive cellular responses.

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