WT1-CTL emergence is associated with disease reduction and stabilization. WT1-CTL frequencies in the PB generally increase after DLI and fluctuate over the course of disease. WT1-CTL frequencies were quantified by intracellular IFN-γ assay in freshly isolated PBMCs. Absolute numbers of WT1-CTL were then computed and compared with the clinical marker of disease, M-spike gamma. (A) Representative FACS plots of intracellular IFN-γ production by CD8⁺ and CD4⁺ T cells against autologous nonpulsed and WT1 peptide-pulsed target PBMC (UPN1, time point indicated by “FACS” arrow in panel D). (B) UPN9; (C) UPN4; (D) UPN1; (E) UPN8; (F) UPN10.