We previously reported that the glycosylated MUC1 tumor antigen circulating as soluble protein in patients' serum is not processed by dendritic cells and does not elicit MHC-Class II-restricted T helper responses in vitro. In contrast, a long synthetic peptide from the MUC1 tandem repeat region is presented by Class II molecules, resulting in the initiation of T helper cell responses. Here we addressed the ability of dendritic cells to present various glycosylated or not glycosylated forms of MUC1 by MHC Class I. We found that three different forms of MUC1, ranging from glycosylated and underglycosylated protein to unglycosylated synthetic peptide, were able to elicit MUC1-specific, Class-I-restricted CTL responses. The efficiency of processing and the resulting strength of CTL activity were inversely correlated with the degree of glycosylation of the antigen. Furthermore, the more efficiently processed 100mer peptide primed a broader repertoire of CTL than the glycosylated protein.
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