Cross-priming of MUC-1 specific CTLs. After the third stimulation of CD8+ T cells by DCs loaded with killed T47D, CD8+ T cells were stimulated with DCs loaded with MUC-1 peptide once and analyzed 5 days after last stimulation. The results of 51Cr release assay show the presence of MUC-1 specific CD8+ T cells. The percentage cytotoxicity is measured as a function of spontaneous and total release. (a) Lack of killing of target cells expressing MUC-1 peptide after 3 weeks of culture with DCs loaded with killed breast cancer cells. (b) Killing of target cells after brief re-stimulation of the same cultures with DCs loaded with MUC-1 peptide, indicating the presence of primed T cells. Results are representative of five experiments, and each value represents the mean from triplicate wells. CTL, cytotoxic T lymphocyte.