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The syntheses of two tumor-associated carbohydrate antigens, Tn and TF, have been achieved using glycal assembly and cassette methodologies. These synthetic antigens were subsequently clustered (c) and immunoconjugated to a carrier protein (KLH or BSA) or a synthetic lipopeptide (pam) for immunological study. Three Tn conjugates were used to vaccinate groups of mice, and all preparations proved to be immunogenic. The Tn(c) covalently linked to KLH (27−KLH) plus the adjuvant QS-21 was the optimal vaccine, inducing high median IgM and IgG titers against Tn(c) by ELISA. These antibodies were strongly reactive with the Tn(c) positive human colon cancer cell line LS-C but not the Tn(c) negative colon cancer cell line LS-B by FACS. The antibodies' reactivities with natural antigens were inhibited with synthetic Tn(c) but not with structurally unrelated compounds. On the basis of these results, vaccines containing 27−KLH and 30−pam plus QS-21 are being tested in patients with prostate cancer.

This review provides an account of our explorations into oligosaccharide and glycoconjugate construction for the creation and evaluation of vaccines based on carbohydrate-centered tumor antigens. Our starting point was the known tendency of transformed cells to express selective carbohydrate motifs in the form of glycoproteins or glycolipids. Anticancer vaccines derived from carbohydrate-based antigens could be effective targets for immune recognition and attack. Obtaining significant quantities of such structures from natural sources is, however, extremely difficult. With the total synthesis of tumor-associated carbohydrate antigens accomplished, we began to evaluate at the clinical level whether the human immune system can respond to such fully synthetic antigens in a focused and useful way. Toward this goal, we have merged the resources of chemistry and immunology in an attack on the problem. The synthesis and immunoconjugation of various tumor-associated carbohydrate antigens and the results of such constructs in mice vaccinations will be described. For fashioning an effective vaccine, conjugation to a suitable immunogenic carrier was necessary and conjugates of KLH (keyhole limpet cyanin) have consistently demonstrated the relevant immunogenicity. Preclinical and clinical studies with synthetic conjugate carbohydrate vaccines show induction of IgM- and IgG-antibody responses. Another approach to anticancer vaccines involves the use of clustered glycopeptides as targets for immune attack. Initial attention has been directed to mucin related O-linked glycopeptides. Synthetic trimeric clusters of glycoepitopes derived from the Tn-, TF- and Lewis(y)-antigens, appropriately bioconjugated, have been demonstrated to be immunogenic. The hope is that patients immunized in an adjuvant manner with synthetic carbohydrate vaccines would produce antibodies reactive with cancer cells and that the production of such antibodies would mitigate against tumor spread, thereby enabling a more favorable survival and "quality of life" prognosis.