Linear PADRE T Helper Epitope and Carbohydrate B Cell Epitope Conjugates Induce Specific High Titer IgG Antibody Responses

Abstract

Linear carbohydrate-peptide constructs based on the 13 amino acid nonnatural pan DR epitope (PADRE) and carbohydrate B cell epitopes are demonstrated to be potent immunogens. These data support our belief that PADRE should be considered as an alternative to more complex carriers for use in prophylaxis and therapeutic vaccines. Two model carbohydrate-PADRE glycoconjugates were used to demonstrate that PADRE could effectively provide T cell help for carbohydrate-specific Ab responses. Conjugates of PADRE covalently linked to the human milk oligosaccharide, lacto-N-fucopentose II or a dodecasaccharide derived from Salmonella typhimurium O-Ag induced high titer IgG Ab responses in mice, which were comparable to glycoconjugates employing human serum albumin (HSA) as the carrier protein. Different adjuvants, in combination with PADRE conjugates, allowed for the modulation of the isotype profile with alum supporting an IgG1 profile; QS-21 an IgG2a, 2b profile, while an alum/QS-21 mixture generated a balanced IgG1/IgG2b isotype profile. As defined by binding to synthetic glycoconjugates, dodecasaccharide-specific Abs exhibited fine specificity similar to protective polyclonal Ab responses previously reported for dodecasaccharide-protein conjugates. The same Abs bound to intact S. typhimurium cells, suggesting that biologically relevant specificities were produced. The affinity of the dodecasaccharide-specific Abs was further shown to be comparable to that of a well-characterized, high affinity monoclonal anti-carbohydrate Ab recognizing the same epitope.

Synthetic bacterial lipopeptide analogs facilitate naive CD4+ T cell differentiation and enhance antigen-specific HLA-II-restricted responses

“…Finally, we investigated the effect of P 3 CSK 4 on CD4 + T cell responses to two HLA-DR-promiscuous, immunodominant epitopes derived from two common human pathogens: TT 947-967 and hepatitis B surface antigen (HBsAg) [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] [23,24]. A higher frequency of peptidespecific T cells in cultures conditioned by P 3 CSK 4 as compared to CSK 4 was demonstrated by LDA analysis (Fig.…”

“…TT, TT 947-967 and HBsAg [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] peptides, and rIL-2 were provided by Dr. A. Wack (Chiron Vaccines, Siena, Italy). GM-CSF was from R&D Systems (Abingdon, UK).…”

“…Freshly isolated PBL from healthy donors were stimulated in vitro with 3 lg/mL TT 947-967 or HBsAg [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] with BLpA. After 5 days, cell lines were restimulated in limiting dilutions (20 Â 10 3 -2.5 Â 10 3 cells/well) in the presence of autologous irradiated PBMC (2 Â 10 4 cells/well) pulsed with the specific antigenic peptide.…”

How much help does a vaccine-induced T-cell response need?

“…Similarly, in the experiments cited above by Bhardwaj and colleagues (9), the injection of ex vivo-generated mature dendritic cells obviated the need for helper antigen. A number of preclinical vaccine studies using peptides, proteins, or antigen-pulsed dendritic cells have employed nonspecific Th sequences to stimulate Th cells and to promote an augmented antibody or CTL response (12)(13)(14). Clinical studies with peptide vaccines have not confirmed that nonspecific helper peptides boost CTL immunity (15), but several recent studies indicate that nonspecific helper sequences pulsed onto dendritic cells generate strong Th activity (14,16).…”

Robust immune responses elicited by a fully synthetic three-component vaccine

“…In addition, foreign carrier proteins such as keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) and the linker that attach the saccharides to the carrier protein can elicit strong B-cell responses, which may lead to the suppression of antibody responses against the carbohydrate epitope 5,6 . It is clear that the successful development of carbohydrate-based cancer vaccines requires novel strategies for the more efficient presentation of tumor-associated carbohydrate epitopes to the immune system, resulting in a more efficient class switch to IgG antibodies [7][8][9][10][11][12][13][14][15][16][17] .…”