Synthetic
carbohydrate cancer vaccines have been shown to stimulate antibody-based immune responses in both preclinical and clinical settings. The
antibodies have been observed to react in vitro with the corresponding natural
carbohydrate antigens expressed on the surface of
tumor cells, and are able to mediate
complement-dependent and/or antibody-dependent cell-mediated cytotoxicity. Furthermore, these
vaccines have proven to be safe when administered to
cancer patients. Until recently, only monovalent
antigen constructs had been prepared and evaluated. Advances in total synthesis have now enabled the preparation of
multivalent vaccine constructs, which contain several different
tumor-associated carbohydrate antigens. Such constructs could, in principle, serve as superior mimics of
cell surface antigens and, hence, as potent
cancer vaccines. Here we report preclinical ELISA-based evaluation of a TF-Le(y)-Tn bearing construct (compound 3) with native
mucin glycopeptide architecture and a
Globo-H-Le(y)-Tn
glycopeptide (compound 4) with a nonnative structure. Mice were immunized with one or the other of these constructs as free
glycopeptides or as keyhole lymphet
hemocyanin conjugates. Either
QS-21 or the related
GPI-0100 were coadministered as adjuvants. Both keyhole lymphet
hemocyanin conjugates induced
IgM and
IgG antibodies against each
carbohydrate antigen, however, the
mucin-based TF-Le(y)-Tn construct was shown to be less antigenic than the unnatural
Globo-H-Le(y)-Tn construct. The adjuvants, although related, proved significantly different, in that
GPI-0100 consistently induced higher titers of
antibodies than
QS-21. The presence of multiple
glycans in these constructs did not appear to suppress the response against any of the constituent
antigens. Compound 4, the more antigenic of the two constructs, was also examined by fluorescence activated cell sorter analysis. Significantly, from these studies it was shown that
antibodies stimulated in response to compound 4 reacted with
tumor cells known to selectively express the individual
antigens. The results demonstrate that single
vaccine constructs bearing several different
carbohydrate antigens have the potential to stimulate a multifaceted immune response.