Antibody-blocking experiments and cold target inhibition assaysusing OFA-iLRP-specific CTLs. To investigate MHC-dependent cytotoxicity, anti body blocking experiments (A) were performed in a 4-hour ⁵¹Chromium release assay against the Karpas-422 target. Cold target inhibitions assays (B) were conducted in a 4-hour ⁵¹Chromium release assay using the Karpas-422 lymphoma cell line (HLA-A2⁺/OFA-iLRP^-). The specificity of the CTL lines was tested in the presence of unlabeled cold targets, ie, Karpas-422 cells, K562 blasts, and primary leukemic blasts from the patient with AML-1 (HLA-A2⁺/OFA-iLRP⁺). Cold targets were added at an inhibitor-to-target ratio of 20:1.