Sylvie Bay

A fully synthetic therapeutic vaccine candidate targeting carcinoma-associated Tn carbohydrate antigen induces tumor-specific antibodies in nonhuman primates.

We recently developed an efficient strategy based on a fully synthetic dendrimeric carbohydrate display (multiple antigenic glycopeptide; MAG) to induce anticarbohydrate antibody responses for therapeutic vaccination against cancer. Here, we show the superior efficacy of the MAG strategy over the traditional keyhole limpet hemocyanin glycoconjugate to elicit an anticarbohydrate IgG response against the tumor-associated Tn antigen. We highlight the influence of the aglyconic carrier elements of such a tumor antigen for their recognition by the immune system. Finally, we additionally developed the MAG system by introducing promiscuous HLA-restricted T-helper epitopes and performed its immunological evaluation in nonhuman primates. MAG:Tn vaccines induced in all of the animals strong tumor-specific anti-Tn antibodies that can mediate antibody-dependent cell cytotoxicity against human tumor. Therefore, the preclinical evaluation of the MAG:Tn vaccine demonstrates that it represents a safe and highly promising immunotherapeutic molecularly defined tool for targeting breast, colon, and prostate cancers that express the carbohydrate Tn antigen.

Anti-Tumor Immunity Provided by a Synthetic Multiple Antigenic Glycopeptide Displaying a Tri-Tn Glycotope

In many cancer cells the alteration of glycosylation processes leads to the expression of cryptic carbohydrate moieties, which make them good targets for immune intervention. Identification of cancer-associated glycotopes as well as progress in chemical synthesis have opened up the way for the development of fully synthetic immunogens that can induce anti-saccharide immune responses. Here, we synthesized a dendrimeric multiple antigenic glycopeptide (MAG) containing the Tn Ag O-linked to a CD4+ T cell epitope. This MAG is based on three consecutive Tn moieties (tri-Tn) corresponding to the glycotope recognized by an mAb (MLS 128) produced against the LS180 colon carcinoma cell line. The Abs induced by this MAG recognized murine and human tumor cell lines expressing the Tn Ag. Prophylactic vaccination using MAG provided protection of mice against tumor challenge. When used in active specific immunotherapy, the MAG carrying the tri-Tn glycotope was much more efficient than the mono-Tn analogue in promoting the survival of tumor-bearing mice. Furthermore, in active specific immunotherapy, a linear glycopeptide carrying two copies of the tri-Tn glycotope was shown to be poorly efficient compared with the dendrimeric MAG. Therefore, both the clustering of carbohydrate Ags and the way they are displayed seem to be important parameters for stimulating efficient anti-saccharide immune responses.

Analysis of the fine specificity of Tn-binding proteins using synthetic glycopeptide epitopes and a biosensor based on surface plasmon resonance spectroscopy

Using synthetic Tn (GalNAc‐O‐Ser/Thr) glycopeptide models and a biosensor based on surface plasmon resonance spectroscopy we have determined that isolectin B4 from Vicia villosa (VVLB4) binds to one Tn determinant whereas the anti‐Tn monoclonal antibodies 83D4 and MLS128 require at least two Tn residues for recognition. When an unglycosylated amino acid is introduced between the Tn residues, both antibodies do not bind. MLS128 affinity was higher on a glycopeptide with three consecutive Tn residues. These results indicate that Tn residues organized in clusters are essential for the binding of these antibodies and indicate a different Tn recognition pattern for VVLB4.

The Pta–AckA pathway controlling acetyl phosphate levels and the phosphorylation state of the DegU orphan response regulator both play a role in regulating Listeria monocytogenes motility and chemotaxis

DegU is considered to be an orphan response regulator in Listeria monocytogenes since the gene encoding the cognate histidine kinase DegS is absent from the genome. We have previously shown that DegU is involved in motility, chemotaxis and biofilm formation and contributes to L. monocytogenes virulence. Here, we have investigated the role of DegU phosphorylation in Listeria and shown that DegS of Bacillus subtilis can phosphorylate DegU of L. monocytogenes in vitro. We introduced the B. subtilis degS gene into L. monocytogenes, and showed that this leads to highly increased expression of motility and chemotaxis genes, in a DegU‐dependent fashion. We inactivated the predicted phosphorylation site of DegU by replacing aspartate residue 55 with asparagine and showed that this modified protein (DegUD55N) is no longer phosphorylated by DegS in vitro. We show that although the unphosphorylated form of DegU retains much of its activity in vivo, expression of motility and chemotaxis genes is lowered in the degUD55N mutant. We also show that the small‐molecular‐weight metabolite acetyl phosphate is an efficient phosphodonor for DegU in vitro and our evidence suggests this is also true in vivo. Indeed, a L. monocytogenesΔptaΔackA mutant that can no longer synthesize acetyl phosphate was found to be strongly affected in chemotaxis and motility gene expression and biofilm formation. Our findings suggest that phosphorylation by acetyl phosphate could play an important role in modulating DegU activity in vivo, linking its phosphorylation state to the metabolic status of L.  monocytogenes.

The crystal structure of a plant lectin in complex with the Tn antigen

The structure of the tetrameric Vicia villosa isolectin B4 (VVLB4) in complex with a cancer antigen, the Tn glycopeptide (GalNAc‐O‐Ser), was determined at 2.7 Å resolution. The N‐acetylgalactoside moiety of the ligand binds to the primary combining site of VVLB4 in a similar way as observed for other Gal/GalNAc‐specific plant lectins. The amino acid moiety of the Tn antigen is largely exposed to the solvent and makes few contacts with the protein. The structure of the complex provides a framework to understand the differences in the strength of VVLB4 binding to different sugars and emphasizes the role of a single protein residue, Tyr127, as a structural determinant of Tn‐binding specificity.

Carbohydrate Antigens: Synthesis Aspects and Immunological Applications in Cancer

Tumor Associated Carbohydrate Antigens (TACAs) constitute powerful tools as tumor markers and as targets for anticancer immunotherapy. In this review, methods of production of glycopeptide-based vaccines, as well as results of preclinical and clinical studies in cancer patients are discussed.

Glycosidic Tn-based vaccines targeting dermal dendritic cells favor germinal center B-cell development and potent antibody response in the absence of adjuvant

In vivo targeting of C-type lectin receptors is an effective strategy for increasing antigen uptake and presentation by dendritic cells (DCs). To induce efficient immune response, glycosylated tumor-associated Tn antigens were used to target DCs through binding to macrophage galactose-type lectin (MGL). The capacity of Tn-glycosylated antigens-and the multiple antigenic glycopeptide Tn3 therapeutic candidate vaccine-to target mouse and human MGL(+) DCs are demonstrated, especially regarding dermal DCs. In mice, MGL(+) CD103(-) dermal DCs efficiently captured and processed glycosylated Tn antigen in vivo, inducing a potent major histocompatibility complex (MHC) class II-restricted T-cell response. Intradermal immunization with Tn-glycopeptides induced high levels of Th2 cytokines-even in the presence of unmethylated cytosine-phosphate-guanosine-and was associated with increased expansion of the germinal center B-cell population. Therefore, MGL acts as an efficient endocytic antigen receptor on dermal DCs in vivo, able to prime Tn-specific T- and B-cell responses. Moreover, even in the absence of adjuvant, immunization with this glycosidic Tn-based vaccine induced high levels of anti-Tn antibody responses, recognizing human tumor cells. In vivo DC-targeting strategies, based on Tn-MGL interactions, constitute a promising strategy for enhancing antigen presentation and inducing potent antibody response.

Induction of a Melanoma‐Specific Antibody Response by a Monovalent, but not a Divalent, Synthetic GM2 Neoglycopeptide

Human tumor cell‐specific antibodies were induced in mice after immunization with a synthetic glycopeptide, which is based on the GM2 ganglioside carbohydrate moiety produced on a gram scale in bacteria. Such neoglycopeptides represent a promising cancer vaccine strategy for active immunotherapy targeting carbohydrates.

Production and functional characterization of two mouse/human chimeric antibodies with specificity for the tumor-associated Tn-antigen

In this work, we have constructed two functional mouse/human chimeric antibodies (IgMkappa and IgG1kappa isotypes) by inserting genomic DNA fragments encoding VH and Vkappa variable regions of the murine monoclonal antibody IgMK-83D4 into mammalian expression vectors containing human mu, gamma1, and kappa constant exons, and by transfecting them into the nonsecreting mouse myeloma X-63 cell line. In previous works, we have demonstrated that 83D4 murine mAb reacts with Tn determinant (GalNAcalpha-O-Ser/Thr) expressed in 90% of breast, ovary, and colon carcinomas. Both expressed chimeric antibodies were purified from the transfected cell line supernatant by affinity chromatography, and their reactivities against Tn antigen were confirmed by ELISA on asialo ovine submaxilar mucin and immunofluorescence studies on MCF-7 breast carcinoma cell line. We have demonstrated by gel filtration chromatography, that the principal secreted forms were monomers for IgG1kappa and pentamers for IgMkappa. The binding affinities of these chimeric antibodies against synthetic Tn glycopeptides, were evaluated by surface plasmon resonance showing an affinity constant similar to that of 83D4 native antibody for IgMkappa and a lower affinity constant for IgG1kappa chimeric antibody. On the other hand, the replacement of mouse C regions with human C regions confers both chimeric antibodies the ability to activate human complement. These mouse/human chimeric antibodies should be much less immunogenic and could play an important role in the lysis of tumor cell expressing Tn-antigen. Therefore, these anti-Tn chimeric antibodies could be considered as potential tools for human in vivo studies.

Enzymatic synthesis of β-galactosyldipeptides and of β-1,3-digalactosylserine derivatives using β-galactosidase

Abstract The transgalactosidation from lactose to dipeptides has been achieved using β-galactosidase from E. Coli as catalyst. Two series of dipeptides have been studied, each of them containing a serine residue. The best condensations occur when serine is at the N-terminal end of the dipeptide. Mild hydrolysis of the ester group of the labile glycosyl-dipeptide derivatives has been achieved using subtilisin. We also describe the condensation of lactose with β-galactosyl serine to give β-1,3-digalactosyl-serine derivatives.