Agarose gel electrophoresis of cellular DNA. HO-1 cells were cocultured with peptide-free autologous LCL (lane 1), DEK-CAN peptide-loaded autologous LCL (lane 2), or DEK-CAN peptide-loaded HLA-DR53–negative allogeneic LCL (lane 3) at an E:T ratio of 3:1 for 4 hours. The DNA was extracted from each sample and electrophoresed in 2% agarose gel. DNA extracted from B-LCL and alloantigen-specific CD8⁺ CTLs, which had been cocultured for 4 hours was also electrophoresed as the control for fragmented DNA (lane 4). Lane M shows 100-bp ladder markers.