The induction of CD8+ cytotoxic T lymphocytes (CTLs) is desirable for immunization against many diseases, and recombinant-synthetic peptide antigens are now favored agents to use. However, a major problem is how to induce CTLs, which requires a Ti-type response to such synthetic antigens. We (refs. 4 and 5; unpublished data). The unusual finding is that if the conjugation is done under oxidizing conditions, then cell-mediated immunity is selectively stimulated, compared with using reducing conditions for conjugation when antibody responses occur.A successful vaccine for cancer immunotherapy requires a suitable target antigen and production of cytotoxic T lymphocyte (CTL) responses (6). In adenocarcinomas, it appears that mucins, particularly MUC1, may provide a suitable target as there is a 10-fold increase in mucin expression on the cell surface, and altered glycosylation leads to exposure of normally hidden peptide sequences (e.g., APDTR). These changes in cancer generate a potential new target for immunotherapy that is apparently absent in normal mucin (7-10). The APDTR sequence [from the variable number of tandem repeats (VNTR) region] is immunogenic in mice, leading to antibody formation, whether the antigen is administered as MUC1+ cancer cells, purified mucin (HMFG), or as peptides (11,12). Such studies of immunogenicity in mice would be of little relevance to humans were it not for the findings that tumorspecific CTL precursors (CTLp) exist in the lymph nodes of patients with cancer of breast, ovary, or pancreas, or in multiple myeloma patients (13-16). The CTLp can be stimulated by antigen and interleukin 2 (IL-2) in vitro to become functional CD8+ CTLs, the target antigen being the APDTR sequence of MUC1 (13-16
MATERIALS AND METHODSChemical Studies. MUC1 FP containing 5 VNTR of human MUC1 and peptide (Cpl3-32) were produced as described (2). FP was conjugated to mannan in two ways. (i) Ox-M-FP: Mannan (Sigma), at 14 mg/ml in 0.1 M phosphate buffer (pH 6.0), was oxidized with sodium periodate (0.01 M) for 60 min at 40C. Ethanediol (10 ,ul) was added and incubated for a further 30 min at 4°C, and the mixture was passed through a Sephadex-G25 column equilibrated in bicarbonate buffer (pH 6.0-9.0). The oxidized mannan that eluted in the void volume (2 ml) was mixed with 900 gg of MUC1 FP, incubated overnight at room temperature, and used without further purification. (ii) Reduced (Red)-M-FP: The ox-M-FP mixture was treated with sodium borohydride (1 mg/ml) for 3 hr and used without further purification.Immunizations
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