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Mucins are attracting great interest as potential targets for immunotherapy in the development of vaccines for cancers expressing Mucin 1 (MUC1) (e.g., breast, pancreas, ovary, and others) as there is (1) a 10-fold increase in the amount in adenocarcinomas; (2) an alteration in expression where they become ubiquitous, and (3) due to altered glycosylation, new epitopes appear on the cell surface that are absent in normal tissues. These new epitopes can be carbohydrate; others are peptide in nature. The cloning of the cDNAs from mucins, particularly MUC1, has led to rapid advances being made, and it is clear that a highly immunogenic peptide exists within the variable number of tandem repeats (VNTR) found in all mucins. This peptide is immunogenic in mice, giving rise to strong antibody production, and most monoclonal antibodies made to breast cancer, which react with the protein core, react with the peptide APDTR. It is now also clear that humans with breast cancer have, in their draining lymph nodes, precursors of cytotoxic T cells that can be stimulated in vitro to react against breast cancer and indeed against the APDTR or a closely related peptide–shown from antibody-blocking studies. These CTLs are unique in that they are non-MHC restricted. The identification of suitable targets, coupled with the known immunogenicity of both the peptide and neo-carbohydrate epitopes, has led to the development of several different programs to immunize humans against breast cancer using either synthetic carbohydrates or peptides conjugated with adjuvants, and clinical trials are now in progress to evaluate their immunogenicity and anti-cancer effects.