Development of cancer vaccines from fully synthetic mucin-based glycopeptide antigens. A vision on mucins from the bioorganic chemistry perspective - Carbohydrate Chemistry: Chemical and Biological Approaches - page 557

focused on the preparation of carrier-free, fully synthetic vaccines. In
such cases, the MUC1 B-cell determinant has been combined with
immune stimulating components, i.e. T-cell epitope peptides and/or
lipopeptide ligands as built-in adjuvants, in order to override the
natural tolerance and induce a suciently strong immune response.
Moreover, the synthesis of additional MUC1-protein conjugate vaccines,
in which the MUC1 glycopeptide antigen has been coupled with dif-
ferent protein carriers, such as Tetanus toxoid (TTox), will also be
discussed.
3.5.1 Unimolecular multicomponent vaccines. Kunz et al. have
pioneered the synthesis and evaluation of vaccine constructs incorpor-
ating tumor-associated mucin glycopeptides, in particular MUC1. 11b
Early work explored two-component vaccines wherein MUC1 motifs
glycosylated with the STn antigen were covalently linked with different T-
cell peptide epitopes (from TTox or ovalbumin) in the absence of car-
rier. 50,51 TTox is of particular interest as a vaccine carrier protein because
vaccines based on TTox have already been used for immunization in
humans. Similarly, MUC1 tandem repeat glycopeptides mono-, di- and
triglycosylated with STn and Tn side chains, and connected to the same
ovalbumin T-cell peptide epitope (OVA 323-339 ) were synthesized and
evaluated (Fig. 9). 52
Preclinical studies in mice of these synthetic vaccines showed that
high titers of IgG specific antibodies could be induced. However,
although the antibody titers were considered to be sucient for break
the natural tolerance, the overall response rate was low in comparison
to that obtained with tumor associated MUC1 glycopeptides conjugated
to carrier proteins. One such example includes a monoglycosylated STn
MUC1 glycopeptide with the same structure as the one coupled to the
OVA 323-339 T-cell epitope peptide describe above, which was conjugated
to TTox carrier protein instead, using diethyl squarate as the coupling
reagent. 53 Immunological evaluation of this vaccine construct was
shown to induce a reliable and very strong immune response in mice
with generation of very specific antibodies against the tumor-associated
MUC1 glycopeptide antigen. Further investigations into the synthesis
and evaluation of the same MUC1 glycopeptide vaccine, but carrying the
TF antigen and its 6,6 0 -difluoro-TF analogue as a means to improve
biostability, showed that these constructs also elicited a robust immune
response in mice. 54 Importantly, IgG antibodies thus produced were
found to recognize the native TF antigens on the MCF-7 breast tumor
cells, revealing that the glycoform of MUC1 glycopeptide vaccines
can be varied without impairment of immunogenicity. More recently,
synthetic STn-glycosylated MUC1 glycopeptide-TTox vaccines con-
taining two immunodominant domains were shown to elicit a very
strong immune response. 55 Remarkably, the induced antisera not only
recognized MCF-7 and T-47D cancer cells lines but they also bound
to breast tumor tissues, providing evidence of the diagnostic value of
the antibodies produced by the synthetic MUC1 glycopeptide TTox
vaccines.