T-cell recognition of foreign HLA class I molecules displayed by DCs.

DCs from an HLA-A2–negative individual were cultivated on a monolayer of nonirradiated melanoma cells expressing the HLA-A2 allele (•). As a control, DCs were either untreated (○) or cocultured with an HLA-unrelated melanoma cell line (▵). After 20 hours, DCs were harvested, purified from the potential melanoma contamination by CD45RO microbead separation, and used as targets in a standard chromium release assay. Only DCs exposed to the HLA-A2 melanoma are recognized by anti–HLA-A2 cytotoxic T-cell effectors. Recognition of the HLA-A2–positive melanoma cells is shown (▪).